Pump, Valve and Heat Exchanger

Heat Exchangers For Solids

2012-01-04T06:06:00.000-08:00

This section describes equipment for heat transfer to or from solids by the indirect mode. Such equipment is so constructed that the solids load (burden) is separated from the heat-carrier medium by a wall; the two phases are never in direct contact. Heat transfer is by conduction based on diffusion laws.

Some of the devices covered here handle the solids burden in a static or laminar-flowing bed. Other devices can be considered as continuously agitated kettles in their heat-transfer aspect. For the latter, unit-area performance rates are higher.

Computational and graphical methods for predicting performance are given for both major heat-transfer aspects in Sec. 10. In solids heat processing with indirect equipment, the engineer should remember that the heat-transfer capability of the wall is many times that of the solids burden. Hence the solids properties and bed geometry govern the rate of heat transfer. This is more fully explained earlier in this section. Only limited resultant (not predictive) and “experience” data are given here.

EQUIPMENT FOR SOLIDIFICATION

A frequent operation in the chemical field is the removal of heat from a material in a molten state to effect its conversion to the solid state. When the operation is carried on batchwise, it is termed casting, but when done continuously, it is termed flaking. Because of rapid heat transfer and temperature variations, jacketed types are limited to an initial melt temperature of 232°C (450°F). Higher temperatures [to 316°C (600°F)] require extreme care in jacket design and cooling liquid flow pattern. Best performance and greatest capacity are obtained by (1) holding precooling to the minimum and (2) optimizing the cake thickness. The latter cannot always be done from the heat-transfer standpoint, as size specifications for the end product may dictate thickness.

Table Type
This is a simple flat metal sheet with slightly upturned edges and jacketed on the underside for coolant flow. For many years this was the mainstay of food processors. Table types are still widely used when production is in small batches, when considerable batch-to-batch variation occurs, for pilot investigation, and when the cost of continuous devices is unjustifiable. Slab thicknesses are usually in the range of 13 to 25 mm (a to 1 in). These units are homemade, with no standards available. Initial cost is low, but operating labor is high.

Agitated-Pan Type
A natural evolution from the table type is a circular flat surface with jacketing on the underside for coolant flow and the added feature of a stirring means to sweep over the heat transfer surface. This device is the agitated-pan type (Fig. 11-51). It is a batch-operation device. Because of its age and versatility it still serves a variety of heat-transfer operations for the chemical-process industries. While the most prevalent designation is agitated-pan dryer (in this mode, the burden is heated rather than cooled), considerable use is made of it for solidification applications. In this field, it is particularly suitable for processing burdens that change phase (1) slowly, by “thickening,” (2) over a wide temperature range, (3) to an amorphous solid form, or (4) to a soft semi gummy form (versus the usual hard crystalline structure).

The stirring produces the end product in the desired divided-solids form. Hence, it is frequently termed a “granulator” or a “crystallizer.” A variety of factory-made sizes in various materials of construction are available. Initial cost is modest, while operating cost is rather high (as is true of all batch devices), but the ability to process “gummy” burdens and/or simultaneously effect two unit operations often yields an economical application.

Vibratory Type
This construction (Fig. 11-52) takes advantage of the burden’s special needs and the characteristic of vibratory actuation. A flammable burden requires the use of an inert atmosphere over it and a suitable nonhazardous fluid in the jacket. The vibratory action permits construction of rigid self-cleaning chambers with simple flexible connections. When solidification has been completed and vibrators started, the intense vibratory motion of the whole deck structure (as a rigid unit) breaks free the friable cake [up to 76 mm (3 in) thick], shatters it into lumps, and conveys it up over the dam to discharge. Heat-transfer performance is good, with overall coefficient U of about 68 W/(m2 ×°C) [12 Btu/(h×ft2 ×°F)] and values of heat flux q in the order of 11,670 W/m2 [3700 Btu/(h×ft2)]. Application of timing cycle controls and a surge hopper for the discharge solids facilitates automatic operation of the caster and continuous operation of subsequent equipment.

Belt Types
The patented metal-belt type (Fig. 11-53a), termed the “water-bed” conveyor, features a thin wall, a well-agitated fluid side for a thin water film (there are no rigid welded jackets to fail), a stainless-steel or Swedish-iron conveyor belt “floated” on the water with the aid of guides, no removal knife, and cleanability. It is mostly used for cake thicknesses of 3.2 to 15.9 mm (f to v in) at speeds up to 15 m/min (50 ft/min), with 45.7-m (150-ft) pulley centers common.

For 25- to 32-mm (1- to 1d-in) cake, another belt on top to give two sided cooling is frequently used. Applications are in food operations for cooling to harden candies, cheeses, gelatins, margarines, gums, etc.; and in chemical operations for solidification of sulfur, greases, resins, soaps, waxes, chloride salts, and some insecticides. Heat transfer is good, with sulfur solidification showing values of q = 5800 W/m2
[1850 Btu/(h×ft2)] and U = 96 W/(m2 ×°C) [17 Btu/(h×ft2 ×°F)] for a 7.9-mm (b-in) cake.

The submerged metal belt (Fig. 11-53b) is a special version of the metal belt to meet the peculiar handling properties of pitch in its solidification process. Although adhesive to a dry metal wall, pitch will not stick to the submerged wetted belt or rubber edge strips. Submergence helps to offset the very poor thermal conductivity through two-sided heat transfer. A fairly recent application of the water-cooled metal belt to solidification
duty is shown in Fig. 11-54. The operation is termed pastillizing from the form of the solidified end product, termed “pastilles.” The novel feature is a one-step operation from the molten liquid to a fairly uniformly sized and shaped product without intermediate operations on the solid phase.

Chemicals Pump

2011-12-11T15:09:00.000-08:00

Chemical pump need special specification because the chemical can corrosive and easily make the pump broken and leakage. Some part of this pump need special material like stainless steel or tungsten carbide.

The example of chemical pump model such as chemical Wilfley’s Model A7 is a heavy-duty chemical processing pump. It is designed for the most difficult applications, pumping highly corrosive liquids and, in certain instances, liquids containing solids.

Liquid can be pumped as follows:

Ammonium Nitrate
Caustic
Corn processing – starch
Hydrochloric acid
Kaolin clay
Lead/zinc
Molten sulfur
Milk of lime
Nitric acid
Phosphoric acid
Salt
Scrubber/contaminated liquids
Spent acids
Sugar
Sulfuric acid
Titanium dioxide
Urea melt
Waste fuels

Process that use that chemical can use this pump, like as below:

Batching applications
Crystallizer recirculation/transfer
Evaporator recirculation/product transfer
Filter feed
Thickener under/over flow
Loading/unloading applications

Parallel Centrifugal Pump

2011-11-19T21:18:00.000-08:00

Parallel combine of two centrifugal pump in parallel will result a higher volumetric of pumping capacity. As shown on the drawing below, inlet and outlet of each pump are at identical points in the system. Each pump will produce same pump head, the head combination will same as single pump head, the total flow rate in the system will same with the sum of individual flow rates for each pump.

Actual condition of centrifugal pump that are combined in parallel will shown slight different with the theory. On the system characteristic curve is considered with the curve for pump in parallel, the operating point at the intersection of two curves represents a higher volumetric flow rate than for single pump and also will have greater system head loss. A greater system head loss occurs with the increase of fluid velocity resulting from the increased volumetric flow rate. Due to the greater system head loss, the volumetric flow rate is actually less than the flow rate achieved by using a separate two single pump.

Horse Power of Hydraulic Pump

2011-10-09T15:22:00.000-07:00

Hydraulic pumps are one of the important components that hydraulic machinery have. The various hydraulic fluids such as oil and water are supplied to the hydraulic machinery with the help of a hydraulic pump. Basically, a hydraulic pump is the main tool needed in order for hydraulic machinery to work.

The formula to calculate the horse power of hydraulic pump can use the formula as follows:
Horse power can be expressed as P_hp ,

P_hp = q x p/1714

P_hp = horsepower (HP)
q = required pump capacity (gpm)
p = required pressure (psi)

1 gpm (US) = 6.30888 x 10-5 m³/h = 0.06309 dm³ (liter)/s = 2.228x10-3 ft³/s = 0.1337 ft³/min = 0.8327 gpm (UK)
1 psi (lb/in²) = 144 psf (lbf/ft²) = 6,894.8 Pa (N/m²) = 6.895x10-3 N/mm² = 6.895x10-2 bar
1 hp = 745.7 W

As an example how to calculate the horsepower needed as follow:

Power required by a a pump with 20 gpm capacity and 1500 psi pressure can be calculated as
PHP = 20 (gpm) 1500 (psi) / 1714
= 17.5 HP

Small Pump Type

2011-09-18T09:27:00.000-07:00

Small pump type can use in the garden or use in fishpond. In the garden can connected to sprinkle that spray water and turn automatically around the garden plant. Small pump in fishpond to make a water circulate along time and can through the water filter first before water flow back to the fishpond. To select the right type of this pump should identify the needed of this pump first.

There are several major mistake on selecting pump, and this mistake make the price of pump become expensive because they should change the pump with the other type. The main point on selecting small pump you should know the design needed of your flow of pump. After you know what is your needed like the flow of your pump you then notice to the pump specification before you choose to buy.

Many of the shelf pump have misleading performance labels. Often pump package will be labelled with something similar to 20 GPM, 55 PSI or it may say 20 GPM, 127 feet of lift. What mean by 20 GPM or 55 PSI? This is critical to know it. There is a huge difference in performance between a pump that produces 20 GPM at 55 PSI, and a pump that produces 20 GPM or 55 PSI. You should ask this label exactly to the pump vendor and ask the guarantee of this labeling.

For buying pump for your garden, you may search pump with name of "high pressure pump," because very few pumps marketed under the name like "irrigation pump" that are suitable for a typical sprinkler irrigation system with multiple sprinkler.To choose this pump don't confused with displacement pumps that are used for moving very thick liquids, creating very precise flow volumes or creating very high pressures. Displacement pump force the water to move by displacement, this means pumps such as piston pumps, diaphragm pumps, roller tubes and rotary pumps.

Sludge and Dewatering Pump

2011-08-10T09:49:00.000-07:00

Sludge Pumps
Sludge pumps are designed for professional use in tough applications like mines, construction sites, funnel sites and other demanding industries.

Sludge Pump

Sludge pumps designed for:

Pumping water with solids handling capacity up to the size of 3.2” (80 mm)
Pumping water which contains abrasive particles
Pumping different types of mud and sludge
Pumping light slurry

The pumps are designed for continuous, unattended operation. The pump should be proven their reliability and dependable performance in demanding areas like building and construction, mining, tunneling, quarries, general industries, car washes and rental applications.

Small dewatering and sludge pumps.
These small dewatering and sludge pumps are small, easy to carry, yet still intended for professional use. They are frequently used in construction and rental applications, flood relief in basements and other applications that require lightweight pumps. The sludge pump solid has set a new standard for lightweight sludge pumps and is appreciated all over the world. It can pump solids in suspension up to the size of 1.5” (38 mm). If the area where the pump will be applied have corrosive environment you can use stainless type materials. Usually this type of pump use in mines, construction sites, landfill sites and other applications that deal with corrosive water. One application is in mines where the water becomes caustic and destroy conventional pumps in a matter of days. The pump may also be used in applications where saltwater is pumped, like ship yards, fish farms, construction works in harbors and offshore projects.

Dewatering Pump

Sulzer Pump and Armstrong Pump

2011-07-23T18:28:00.000-07:00

Pump Type:

The pump manufactures that many used in industry like Sulzer pump and Armstrong pump.

Glimpse story about Sulzer Pump:
Sulzer Pumps is one of the world's leading pump manufacturers, recognized for excellent product quality, performance reliability and technical innovation. We provide a full line of pumps, equipment and related technologies to the Oil and Gas, Hydrocarbon Processing, Power Generation and Pulp and Paper industries.
With our global network of 13 product orientated factories and service centers and sales offices in more than 150 countries, we are a truly global company, close to customers acting locally through our regional teams with local market understanding and expertise.

Glimpse Story about Armstrong Pump:
At Armstrong, we take pride in a family tradition of fluid flow innovation, superb workmanship, and acknowledged product reliability.

Since our founding in 1934 by Samuel Allan Armstrong, our company has pioneered an uncompromising range of products for customers in residential, commercial and industrial markets. From the very beginning, the Armstrong name has been a benchmark for quality in design, engineering and manufacturing.

In 1952, our company, under the direction of James A.C. Armstrong, began to institute bold initiatives across the the entire spectrum of our corporate activities that set our course for the next30 years. In the decades that followed, we developed new technologies, established international manufacturing operations and expanded into more diverse markets. Today, as we serve customers throughout the world, our original commitment to production of the highest quality is unchanged. We will not compromise the expectation of us, and we will never allow an inferior product to carry the Armstrong name. For Armstrong, identifying customer needs, offering superior technology, and building great customer experiences, are all part of a long-standing family tradition.

Armstrong Pump

Fundamental of Hydraulic Pump

2011-06-07T22:41:00.000-07:00

In hydraulic systems forces and motion are transferred by liquids. By means of the transferring liquid it is possible to convert the forces and to control the movements precisely.
Example of application
Machine tools: Table movement in grinding machine; copy turning; transporting 2nd clamping of workpieces on transfer line; feed motion of machining units.
Vehicles: Brakes, automatic gears, tilting of loading surface, steering gear magnifier.
Crane, excavator: lifting and lowering motion of cantilever, gripper and boom.
Presses: Movement of plunger of press, generation of large pressures.
Mining plant: Hydraulic tunnel supports.
Aeroplanes: Movement of landing gear and empennage (tail group)

Advantages: convertion of large forces (pressures).
Continuous regulation of speed (feeds), precise control and actuating accuracy, bridging of long distances between drive and work units, mobility through flexible hose connection, starting from rest position under load, smooth running.

Basic definitions Hydrostastics
Hydro = water = liquid (fluid)
Static = rest.
Hydrostatics = static of fluid
When the liquid in a closed system of container and pipelines is set under pressure by the application of a force at any point, the resultant pressure energy may be received as force at any other point of the system, since work equals force multiplied by distance. Thus in hydraulic systems few law of hydrodynamics also occur.

Hydrodynamics
Hydrodynamics = dynamic of fluid.
In an open system of a tank and pipelines/penstock the liquid attains a very high flow-speed due to large gradient (height difference). At the end of the pipeline the energy of the following fluid can be converted into mechanical work, rotary motion, for example of a hydraulic turbine.

Whether a system is hydrostatic or hydrodynamic depends on the type of energy transfer, hydrostatic = pressure energy, hydrodynamic =motion energy. Although few laws of hydrostatic also apply, hydrolic systems are basically hydrostatic in nature because the energy transfer is carried out fundamentally by means f pressure energy.

Propagation of Pressure
In a close system, if the liquid at a point is set under pressure the whole of the liquid comes under the same pressure at all other points. The force developed acts normal (in perpendicular direction) to the inner walls of the container. Pressure vessels have, for safety reasons. Outward or inward curved bottoms; spray cans, steam boiler, champagne bottle, oxygen cylinder, etc.

Hydrant Pump

2011-05-23T16:51:00.000-07:00

Many type hydrant pump can install on your plant depend of how big water should flow if they are needed. From small type to big type of hydrant also available. Hydrant pump can operate inline or submersed operation. To choose and operate hydrant pump find on the guideline bellow:

Verify the pump size fits the application without dramatically restricting the flow, consult your local dealer or manufacturer's guidelines for the proper size and model of pump.
Do not reduce the input diameter of the pump.
You must incorporate a pre-filter when operation for a water circulation, waterfalls, ponds and fountains
Replace the impeller if there are any signs of damage or excess wear
Failure to maintain a pump will cause permanent damage to the impeller and/or pump. Routine maintenance is of the utmost importance to keep your pump working well.

Choose the Right Valve

2011-03-24T16:40:00.000-07:00

There are many kind of valve in the market, ball valve, globe valve, gate valve, diaphragm valve or check valve. All those valve have special uses or better for certain uses and sometime can't use for other purposes like check valves, because check valve just can be used for one direction. Check valves usually use in the bottom of suction pipe on the pump to prevent water or liquid flow back or to prevent the liquid empty on the bottom so the pump can cavitation, however, check valve also use in the front of the water meter that supplied from water pump industry to prevent the meter goes back.

Ball Valves use in the first opening of the liquid (water or air) and this valve should be full opened or full closed. To regulate the flow need other kind of valves, we can use globe valve, gate valve or diaphragm valve. Use Gate valve if the flow of the liquid need not to accurate enough, but we should use globe valve if the flow should be accurate. Diaphragm valve use when the liquid contain many suspended solid, like water with too many mud flows or other kinds of chemical that contain of mud. Especially on the chemical control, diaphragm valve should use suitable material that pretend on the chemicals.

Pump Trouble Shouting

2011-02-19T19:19:00.000-08:00

Problem solving that focuses on the centrifugal pump, have accumulate on certain book that contains of many solutions of problem applicable to well for pumps in general.

General problem on centrifugal pump, actually include of these matters:

 Flow
 Mechanical seal
 Bearings
 Rotor
 Cavitations
 Liquid density
 Couplings
 Vibration isolation
 Fan
 Metal corrosion
 Impeller
 Balancing
 Alignment
 Effects on electric motors

If you have a centrifugal pump problem. You can get a from book of 'Centrifugal Pump trouble shouting.

Water Hammer On Centrifugal Pump

2011-02-07T08:15:00.000-08:00

Pumping problem that often facing is water hammer, and issue of wrong pump and pipe designer that sometime can’t be handle by new operators. Water hammer often happened on a big centrifugal pump when wrong operate.

How it can happen?
Water hammer practically cannot detect if the increasing pressure accelerated or retarded pump by pump condition and valve changes can be normalize automatically. Usually this pressure changes just small, the rate of changes also gradual. If the pressure changes may ten times bar, and the forces on pump support can many tones till exceeding the support limitation, the pipe can be rupture or damage. Other case of lower level water hammer can cause chronic deterioration, and leading to the gasket leaks over time.

Water hammer can happen if the valve open or closed to fast, this action can cause pressure changes too quickly. The big pressure changes can cause the force to the pipe or to the pipe support out of balance. The force like this can shift the pipe even move from the pipe support.

How to avoid water hammer?
Water hammer can be avoided by many kind depend on each situation’s and circumstance. The following may be some conclusion as your consideration to apply.

Eliminating of problem source like from vibrating pressure of relief valve, fast emergency shutdown valve closure, change of the automatic close time like on the butterfly valve and many others.
Reduce the pumping velocity, this can be modified on the pump like to install expansion pipe to reduce pressure.
Install surge tanks
Use surge alleviators that commonly just fit for positive displacement pump.
Use air inlet valves.
Create a by pass pipe that passing the valve when closed.

Bronze Valve

2011-01-17T03:20:00.000-08:00

Valve with bronze material can use in fluid that have a little contain of corrosive material like in the water treatment that use chlorine as antiseptic agent. On the fluid that have characteristic like this one don't recommend for using usual material because this material will easily corrode and broken the valve. Bronze material more resist to medium corrosive fluid but not strong enough if the fluid strong corrosive. For fluid that have strong corrosive like on acid or acid fluid better use stronger material like stainless steel or even plastic material, to prevent from corrosive broken.

Bronze material can be used for many kind of valve like Ball Valve, Gate Valve or Needle Valve, and also can be applied to many other kind of valve.

Medical Regulator Instrument

2010-12-26T22:24:00.000-08:00

1. Medical regulator is used for oxygen breathing in hospital.
2. The function of each part mainly:

Oxygen flow range: 1 – 10 L/min
Pressure reducing range: 2.0 – 3.0 kg
Relief valve pressure range: (3.5 kg ± 0.5 kg)

3. Appliance introduction:

Before using, please fill pour clear water into moisture bottle about one third reaching water line site.
DF-2 blind nut straw into bolt head, make the pipe of flow meter square water line.
Put off regulator (9), put on oxygen tube switch, so you will see the data from needle position of pressure gauge (2). At least, straw flow on/off at anticlockwise according to patients need, adjust switch.
If patient need oxygen for a long time, can use nose pipe to help patient absorb oxygen.
Moisture bottle (20) circle at clockwise, adjust (17) oxygen hole to other site.

4. Attention point:

Before using the suction, you will check all parts bad or good and clean it by drying cloth.
Pressure gauge (2), regulator (3) no oil, otherwise explode.
Cleanwater in moisture bottle keeps clean.
There is adjustable nut (6) in the front of plunder shall be straw at clockwise.
Relief value (7) (15) keeps out of danger.
Oxygen dosage is decide by doctor
After using suction, put off the oxygen tube switch, make rest oxygen out, pressure gage to zero site, last put off flow switch if using again, first put on the oxygen tube switch, avoid exploding.

5. If you don’t understand, please contact your vendor.

Look Other Articles:

Hydraulic Balancing Devices

2010-09-07T00:06:00.001-07:00

If all the single suction impellers of a multistage pump face the same direction, the total theoretical hydraulic axial thrust acting toward the suction end of the pump will be the sum of the individual impeller thrusts. The thrust magnitude will be approximately equal to the product of the net pump pressure and the annular unbalanced area. Actually the axial thrust turns out to be about 70 to 80 percent of this theoretical value.

Some form of hydraulic balancing device must be used to balance this axial thrust and to reduce the pressure on the seal chamber adjacent to the last stage impeller. This hydraulic balancing device may be a balancing drum, a balancing disk, or a combinations of the two.

Balancing Drums
The balancing chamber is at the back of the last stage impeller is separated from the pump interior by a drum that is usually keyed to the shaft and rotates with it. The drum is separated by a small radial clearance from the stationary portion of the balancing device, called the balancing drum head, or balancing sleeve, which is fixed to the pump casing.

The balancing chamber is connected either to the pump suction or to the vessel from which the pump takes its suction. Thus the back pressure in the balancing chamber is only slightly higher than suction pressure, the difference between the top being equal to the friction losses between the chamber and the point of return. The leakage between the drum and the drum head is, of course, a function of the differential pressure across the drum and of the clearance area.

Balancing Disks
The disk is fixed to and rotates with the shaft. It is separated by a small axial clearance from the balancing disk head, or balancing sleeve, which is fixed to the casing. The leakage through this clearance flows into the balancing chamber and from there either to the pump suction or to the vessel from which the pump takes its suction. The back of the balancing disk is subject to the balancing chamber back pressure, whereas the disk face experience a range of pressure. These vary from discharge pressure at its smallest so that the difference between the total force acting on the disk face and that acting on its back will balance the impeller axial thrust.

If the axial thrust of the impeller should exceed the thrust acting on the disk during operation, the latter is moved toward the disk head, reducing the axial clearance between the disk and the disk head. The amount of leakage through the clearance is reduced so that the friction losses in the leakage return line are also reduced, lowering the back pressure in the balancing chamber. This lowering of pressure automatically increases the pressure difference acting on the disk and moves it away from the disk head, increasing the clearance. Now the pressure build up in the balancing chamber, and the disk is again moved toward the disk head until an equilibrium is reached.

Reduction of Cavitation Damage

2010-08-25T22:08:00.001-07:00

After the pump has been built and installed, there is little that can be done to reduce cavitation damage. As previously mentioned, sharpening the leading edges of the blades by filling may be beneficial Stepanoff has suggested cutting back part of the blades in the impeller eye together with sharpening the tips, for low specific speed pumps, as a means of reducing the inlet velocity c, and thus lowering parameter s. Although a small amount of prerotation or prewhirtl in the direction of impeller rotation may be desirable, excessive amount should be avoided. This may require straightening vanes ahead of the impeller and rearranging the suction piping to avoid changes in direction or other obstructions. The cavitation damage to the impeller was believed to have been at least partly due to bad flow conditions produced by two 90o elbows in the suction piping. The planes of the elbows were at 90o to each other, and the arrangement should be avoided.

Straitening vanes in the impeller inlet may increase the NPSH requirement at all flow rates. Three or four radial ribs equally spaced around the inlet and extending inward about one quarter of the inlet diameter are effective against excessive prerotation and may require less NPSH then full length vanes. This is very important with axial flow pumps, which are apt to have unfavourable cavitation characteristic at partial flow rates. Operation near the best efficiency point usually minimizes cavitation.

The admission of a small amount of air into the pump suction tends to reduce cavitation noise. This rarely is done, however because it is difficult to inject the right amount to mixing air with the liquid pumped.

If new impeller is required because of cavitation, the design should take into account the most recent advances describe in the literature has suggested:

The use of ample fillets where the vanes join the shrouds
Sharpened leading edges of vanes
reduction of b, in the immediate vicinity of the shrouds
raking the leading edges of the vanes forward out the eye. Increasing the number of vanes for propeller pumps lower s for a given submergence.

Typical Part of Centrifugal Pumps

2010-08-15T19:01:00.001-07:00

A centrifugal pump is a relatively simple pump. Design, types and numbers of parts vary depending on centrifugal pump brand, type and configuration.

Typical main pump parts:

Casing/back plate:

Contains impeller where fluid is transferred from inlet to outlet.
Includes inlet and outlet ports.
Typically flexible port orientation.
Typically fitted to an adapter.

Shaft:

Rotates impeller which is fixed to it.
Is fixed to the motor and rotates with it.

Impeller:

Transfers fluid from inlet to outlet with increased capacity and pressure is fixed on the shaft and rotates with it.
Typical types are open, semi-open or closed.

Shaft seal:

Seals between rotating shaft and stationary casing.
Typically a mechanical seal, external or internal.
Typically available as single, single flushed and double flushed seal.

Adapter:

Fixes pump casing to the motor.

Motor:

Rotates shaft (impeller) which is fixed to it.
Typically a 3-phase electrical motor.
Typically available for various electrical site supplies (voltage and frequency).
Typically available in various protection classes (flameproof etc.).

Other parts: Seals, motor cover, seal flushing, coupling/ base (base-mounted pump).

Typical materials:

Steel parts of 316L or 304 stainless steel.
Elastomers of NBR, EPDM, FPM, PTFE.

Self Priming Pump

2010-08-06T02:02:00.001-07:00

The basic requirement for a self priming centrifugal pump is that the pumped liquid must be able to entrain air in the form of bubbles so the air will be removed from the suction side of the pump. This air must be allowed to separate from the liquid after the mixture of the two has been discharged by the impeller, and the separated air must be allowed to escape or to be swept out through the pump discharge. Such a self priming pump therefore requires, on its discharge side, an air separator, which is a relatively large stilling chamber, or reservoir, either attached to or built into the pump casing. Alternatively, a small air bleed line can be installed from the discharge pipe between the pump and the discharge check valve back to the suction source.

There are two basic variation of the manner in which the liquid from the discharge reservoir makes the pump self priming.

recirculation from the reservoir back to the suction and
recirculation within the discharge and the impeller itself

Recirculation to Suction
In such a pump, a recalculating port is provided in the discharge reservoir, communicating with the suction side of the impeller. Before the first handles whatever liquid comes to it through the recalculating port plus a certain reservoir, where the two elements are separated, the air passing out of the pump discharge and the liquid returning to the suction of the impeller through the recirculation port. This operation continuous until all the air has been exhausted from the suction line.

Recirculation at Discharge
This form of priming is distinguished from the preceding method by the fact that the priming liquid is not returned to the suction of the pump but mixes with the air either in the impeller or at its periphery. The principal advantage of this method, therefore, is that it eliminates the complexity of internal valve mechanisms.

Regenerative Turbine Pumps
Because these pumps can handle relatively large amounts of gas, they are inherently self-priming as long as sufficient liquid remains in the pump to seal the clearance between the suction and discharge passages. This condition is usually met by building a trap in the pump suction.

Lobe Pumps

2010-07-20T08:31:00.000-07:00

The lobe pump receives the name from the rounded shape of the rotor radial surfaces that provide the rotor to be continuously in contact with each other as they rotate. Lobe pump can be either single or multiple lobe pumps and carry fluid between their rotor lobes much in the same way a gear pump does.

Unlike gear pumps, however neither the number of lobes nor their shape permit one rotor to drive the other, and so all true pumps require timing gear. The body surfaces, rotor surfaces, the contact between rotors, and the contact between rotor lobe end and the pump body define the OTI of a pump. The contact between the lobe ends and the body wall and the adjoining body wall and lobe surfaces define the OTI volume. The body walls, rotor surfaces, lobe to body wall contacts, and the lobe to lobe contacts define the OTO volume.

In the two rotor lobe pumps, the torque is shared by both rotors with the proportional amount of torque dependent on the position of the rotor to rotor contact point on the rotor contact locus. When the contact point is at the major locus radius (maximum lobe radius of one rotor in contact with the minimum lobe radius of an adjoining rotor), one rotor sees the full pumping torque, while the other rotor feels a balanced as many times in each complete revolution of a rotor as there are lobes on the rotor.

An internal lobe, or gorotor pump has a single rotor with a lobe like peripheral shape. It moves in a combination of rotations and gyrations about its centre of rotation in a body with internal, lobe shaped contours in such away that the rotor always touches the body or more locations to preserve the fluid seal between OTI and OTO volumes. The outer rotor surface, and the fluid seal points between two adjacent fluid seal points define the CTIO volume. The outer rotor surface, inner body surface, and the rotor to body fluid sealing define the OTO volume.

Most pumps of this type have one fewer rotor lobe than an internal body lobe cavity and the term progressing tooth gear pump is sometimes used. The full pumping torque is seen by the single rotor, but the torque is cyclic. It is a function of the position of the rotor and its sealing arrangement with the pump body, while the number of torque cycles per rotor revolution is equal to the number of lobes on the rotor.

Lobe pumps are capable of flows up to about 1,000 gpm (3.785 l/min) and pressures up to 125 lb/in2 (8.6 bar). They are commonly used to pump single sludge in waste water treatment plants and in stainless steel systems for handling foodstuffs in the food, baverage, dairy, and pharmaceutical industries.

Vane, Gear, and Lobe Pumps

2010-07-13T02:33:00.000-07:00

Pumping with a vane, gear or lobe pump begins with the rotating and stationary parts of pump defining a given volume or cavity of fluid enclosure. This enclosure is initially open to be pump inlet but sealed from the pump outlet expands as the pump rotates. As rotation continues, the volume progresses through the pump outlet.

Depending on the particular pump, there can be more than one cavity in existence at any one time. As this happens, fluid also fills the clearances between the pumping elements and fluid. Rotation continuous and the cavities progress, moving fluid along the way. Soon a point is reached when the seal between the capture fluid volume of captured fluid out of the pump. While this happening, other cavities are simultaneously opening at the inlet post to receive more fluid in a continual progression from suction to discharge parts.

With rotary pumps, a driver turns one shaft and rotor assembly, which in turn physically meshes with another to form the cavities that move the fluid. This is known as an untimed arrangement. For some applications, however, there would be problems with gears, lobes, or screw meshing this way. For instance, stainless steel gears will gall and seize if rubbed against each other. High wear rates will also occur if any dirt is trapped between the meshing lobes of a lobe pump, regardless of their material, or if a pump with meshing gear.

The circumvent of this, the timed pump was developed. It uses timing gears physically located outside the pumping chamber to transmit torque between the pump shaft and synchronize the pumping elements relative to each other. By preventing them from contacting each other, they eliminate many of the problems of dirty fluids, material compatibility, and dry running. Most lobe pump are built this way, and gear pump can be timed or untimed as well.

Screw Pump Type

2010-07-09T02:56:00.001-07:00

There are three major type of screw pump exist:

Single rotor
Multiple rotor timed
Multiple rotor untimed

The second and third types are available in two basic arrangements, single-end and double-end. The double-end construction is probably the best known version, as it has been by far the most widely used for many years because of its relative simplicity and compactness of design.

Double end screw pump
The double end arrangement is basically two operated, single-end pumps or pump elements of the same size with a common driving rotor that has an opposed, double helix design with one casing. The fluid enters a common inlet with a split flow going to the outboard ends of the two pumping elements and is discharged from the middle or center of the pump elements.

The double end screw pump selection is usually limited to low and medium pressure applications, with 400 lb/in2 (28 bar) being a good practical limit to be used for planning purposes. However, with special design features, applications up to 1400 lb/in2 (97 bar) can be handled.

Screw Pump Theory

2010-06-30T20:02:00.000-07:00

Screw pump are a special type of rotary positive displacement pump in which the flow through the pumping elements is truly axial. The liquid is carried between screw threads on one or more rotors and is displaced axially as the screws rotate and mesh. In all other rotary pumps, the liquid is forced to travel circumferentially, thus giving the advantages in many applications where liquid agitation or churning is objectionable.

The application of screw pumps cover a diversified range of markets including navy, marine and utilities fuel oil services; marine cargo; industrial oil burners; lubricating oil services; chemical process; petroleum and crude oil industries; power hydraulics for navy and machine tools; and many others. The screw pump can handle liquids in a range of viscosities, from molasses to gasoline, as well as synthetic liquids in a pressure range from 50 to 5000 lb/in2 (3.5 to 350 bar) and flows up to 8000 gal/min (1820 m3/h).

Because of the relatively low inertia of their rotating parts, screw pumps are capable of operating at higher speeds than other rotary or reciprocating pumps of comparable displacement. Some turbine attached lubricating oil pumps operate at 10,000 rpm and even higher. Screw pumps, like other rotary positive displacement pumps, are self priming and have is sufficient viscosity in the liquid being pumped.

Screw pumps are generally classified into single or multiple rotor types. The latter is further divided into timed and untimed categories.

The single screw or progressive cavity pump has a rotor thread that is eccentric to the axis of rotation and meshes with internal threads of the stator (rotor housing or body). Alternatively, the stator is made to wobble along the pump centreline.

Multiple screw pumps are available in a variety of configurations and designs. All employ one driven rotor in a mesh and one or more sealing rotor. Several manufactures have two basic configurations available: single end and double end construction, of which the latter is the better known.

As with every pump type, certain advantages and disadvantages can be found in a screw pump design. These should be recognized when selecting the best pump for a particular application. The advantage of a screw pump design are as follows:

A wide range of flows and pressures
A wide range of liquids and viscosity
High speed capability, allowing the freedom of driver selection
Low internal velocities
Self priming with good suction characteristics
A high tolerance for entrained air and other gases
Low velocities for minimum churning or foaming
Low mechanical vibration, pulsation-free flow, and quiet operation
A rugged, compact design that is easy to install and maintain
High tolerance to contamination in comparison with other rotary pumps

The disadvantage are as follows:

Relatively high cost because of close tolerance and running clearances
Performance characteristics sensitive to viscosities changes
High pressure capabilities requires long pumping elements

Centrifugal Pump with Journal Bearing

2010-06-28T02:52:00.001-07:00

A journal bearing is essentially for a viscose pump, and it devices load capacity by pumping the lubricant through a small clearance region. To generate pressure, the resistance to pumping must increase in the direction of the flow. The journal moves to form a converging tapered clearance in the direction of the rotation or flow.

The eccentricity e is the total displacement of the journal from the concentric position. The attitude angle γ, is the angle between the load direction and the line of centres. Note, that because of the necessity to form a converging wedge, the displacement of the journal is not along a line that is coincident with the load vector. A positive pressure is produced in the converging region of the clearance. Downstream from the minimum film thickness which occur along the line of centres, the film become divergent. The resistance decrease in the direction of pumping, and either negative pressure occur or the air in the lubricant gasifies or cavitates and a region of atmosphere pressure occurs in the bearing area. This phenomenon is known as fluid film bearing cavitation. It should be clearly distinguished from other form of cavitation that take place in pumps, such as in the impeller, for example. The fluid is travelling at a high velocity and the inertia forces on each fluid element dominate. Implosion occur in the impeller and can cause damage.

In a bearing the viscose forces dominate and each fluid particle moves at a constant velocity in proportion to the net shearing forces on it. Thus cavitation on the bearing is more of a change of a phase of the lubricant that occurs in a region of lower pressure that permits the release of entrained gases. Generally bearing cavitation does not causes damage.

Bearing Types

2010-06-18T01:01:00.000-07:00

The most common type of journal bearing in the plain cylindrical bushing. It can be split and have lubricating freed groove at the parting line. A ramification is to incorporate axial grooves to enable better cooling and to improve whirl stability. The principle advantages of cylindrical bearing are (1) simple construction ad (2) a high load capacity relative to other bearing configuration.

This type of bearing also has several disadvantages:

Whirl instability: this is prone to sub synchronous whirling at high speed and also at low loads. Whirling is an orbiting of the journal (shaft) centre in the bearings, a motion that is superimposed upon the normal journal rotation. The orbital frequency is approximately half the rotating speed of the shaft. The expression half-frequency whirl is commonly used. The reason for the occurrence of this whirl and more details concerning bearing dynamics are presented in the section on bearing dynamics.
Viscose Heat Generation: because of the generally larger and uninterrupted surface area of this bearing, it generates more viscose power loss than some other types.
Contamination: The cylindrical bearing is more susceptible to contamination problems than other because contaminants that are dragged in at the leading edge of the bearing cannot easily dislodge because of the absence of grooves or other escape paths.

The advantage of simplicity and load capacity make the plain journal a leading candidate for most applications, but performance should be carefully investigated for whirl instability and potential thermal problems. Cylindrical bearings are generally used for medium speed (500 in/s (200 mm/sec) surface speed) and medium to heavy load application (250 to 400 lb/in2 (17 to 28 bar) on a projected area.

Cylindrical Bearing with Axial Grooves

A typical configuration of this type of bearing is a plain cylindrical bearing with four equally spaced longitudinal groove extending most of the way through the bearing. Usually, a slight land area exist at either end of the groove to force the inlet flow to each groove into the bearing clearance region, rather than out the groove ends. This configuration is a little less simple than the plain cylinder bearing, and because the grooves consume some land area, this configuration has less load capacity than the plain bushing. Since oil is fed into each of the axial grooves, this bearing requires more inlet flow but also will run cooler than the plain bushing. The grooves act as convenient outlets for any contaminant in the lubricant, and thus the grooved bearing can tolerate more contamination than the plain cylindrical bearing.

Empirical and Lobe Bearings

Elliptical and lobe bearing have noncircular geometries. As elliptical bearing is simply a two lobe bearing with the major axis along the horizontal axis. Thus at the leading edge region, a converging clearance produces positive pressure, but downstream from the minimum film thickness, a divergent film thickness distribution can be found with resulting negative, or cavitations, pressure.

The canted lobe, generally develop positive pressure throughout the lobe because the bearing is constructed with a completely converging film thickness in each lobed region. This design has excellent whirl resistance (superior to that of the symmetric lobe bearing) and a reasonable good load capability. A 2:1 ratio between leading and trailing edge concentric clearance is generally a reasonable compromise with respect to performance.

Elliptical and lobe bearing are often used because they provide better resistance to whirl than cylindrical configurations. They do so because they have multiple load producing pads that assist in preventing large attitude angles and cross coupling. Elliptical and lobe bearing are generally used for high speed, low load applications where whirls might be a problem.

Alignment of Pumps and Drivers

2010-05-12T02:25:00.000-07:00

Outside of serious unbalance of pump components, there is no single contributor of poor mechanical performance more significant than poor alignment. Incorrect alignment between a pump and its driver can cause:

Extreme heat in couplings
Extreme wear in gear couplings and fatigue in dry element couplings
Cracked shafts and totally failed shafts, with failure due to reverse bending fatigue transverse to the shaft axis initiating at the change of section between the large end of the coupling hub taper and the shaft.
Preload on bearing (evident by an elliptical and flattened orbit resembling a deflated beach ball); pure asymmetry of vertical and horizontal vibration can be misleading because the bearing spring constants could vary greatly in the k_yy (vertical) and the k_xx (horizontal) axis.
Bearing failures plus thrust transmission through the coupling, which can be totally locked (axial vibration checks across the coupling; that is, at each adjacent machine, will generally confirm this condition).

Significant changes in the cold non-running alignment of a pump and driver can take place if the temperature rise in machine is different and if the piping imposes forces on the pump.

Therefore, alignment under actual operating conditions must be predicted or, if unknown confirmed by instrumentation. In other case, an allowance must be made in the initial cold alignment to component for changes in alignment from cold idle to hot running.

The face and rim method has a sensitivity advantage when the diameter of a coupling exceeds the indicator open of reverse indicator bracket tooling. This is rare, as the pump will generally have in spacer coupling and the reach of the reverse indicators can be increased by clamping onto the driver or the gear could not be rotated, as it seems unlikely that the pump could not be rotated. In order to compensate for the measuring surface’s out being circular or smooth, both shafts should be rotated together when using this method.

Suction and Discharge Recirculation

2010-04-29T00:31:00.000-07:00

Cause and Effect:
Recirculation occurs at reduced flows and is the reversal of a portion of the flow back through the impeller. Recirculation at the inlet of the impeller is known as suction recirculation. Recirculation at the outlet of the impeller is discharge recirculation. Suction and discharge recirculation can be very damaging to pump operation and could be avoided for the continuous of pumps of significant energy level or pressure rise per stage.

Diagnosis from Pump Operation
Suction recirculation will produce the previously mentioned loud cracking noise and around the suction of the pump. Recirculation is of greater intensity than the noise from low NPSH cavitations and is a random knocking sound. Discharge recirculation will produce the same characteristic sound as suction recirculation except that the highest is in the discharge volute or diffuser.

Diagnosis from Visual Examination
Suction and discharge recirculation product evaporation damage to the pressure side of the impeller vanes. Viewed from the suction of the impeller, the pressure side would be the invisible, or underside, of the vane. This is unlike cavitations damage from inadequate NPSH that occurs on the low pressure surface of the inlet vanes. Damage to the pressure side of the vane from discharge recirculation is shown in the drawing. Similarly the casing tongue or diffuser vanes may show cavitations damage on the impeller side from operation in discharge recirculation.

Instrumentation
The presence of suction or discharge recirculation can be determined by monitoring the pressure pulsation in the suction and in the discharge areas of the casing. Piezoelectric transducer installed as close to the impeller as possible in the suction and in the discharge of the pump can be used to detect pressure pulsation. The data may be analysed with a spectrum analyser couple to an XY plotter to produce a record of the pressure pulsation versus the frequency for selected flows.

Corrective Procedure:
Every impeller design has specific recirculation characteristics. This characteristics are inherent in the design and cannot be changed without modifying the design. An analysis of the symptoms associated with recirculation should consider the following as possible corrective procedures:

Increase the output capacity of the pump
Install a by pass between the discharge and the suction of the pump
Substitute an improve material for the impeller that is more resistant to cavitation damage
Modify the impeller design

Centrifugal Pump Performance

2010-04-19T01:30:00.000-07:00

Volume Flow Rate

Abbreviated to “flow rate” and known traditionally as “pump capacity” Q, this is the volume of liquid per unit time delivered by the pump. To US customary system unit, Q is expressed in US gallon per minute or USgpm, for which the abbreviation of gpm is used (1 US gallon = 231 in3). For very large pumps, the unit ft3/sec are used. The consistent SI unit m3/s are implied when an SI value of Q is, unless the numerically convenient liters per second (l/s) are specifically called out.

Datum for Pump Head

The total head has components of pressure, velocity, and elevation z. because pump head H more precisely ΔH is the difference of total heads evaluated at the discharge flange d and the suction flange s respectively, the elevation of the datum from which Z is measured cancel out. However, for purpose of identification, computing NPSH, and so on, the standard datum as shown is used.

The standard datum for horizontal shaft pumps is a horizontal plane through the centreline of the shaft. For vertical shaft pumps, the datum is a horizontal plane through the entrance eye of the first stage impeller. Because pump head is the difference between the discharge and suction heads, it is not necessary that the standard datum be used, and any convenient datum may be selected for computing the pump head.

Power

In USCS, the pump output is customary given as liquid horsepower (hp) or as water horsepower if water is the liquid pumped.

lhp = QH (sp.gr.)/ 3960

where Q is the gallon per minute, H in feet, and sp.gr. is specific grafity. If Q is in cubic feet per second, the equation becomes,

lhp = QH (sp.gr.)/8.82

In SI, the power P in watts (W) is given by

P = 9797 QH (sp.gr.)

Where Q in cubic meters per second and H is in meters. Where Q is in liters per second and H is in meters.

P = 9.797 QH (sp.gr.)

Efficiency

The pump efficiency, ή is the liquid horsepower divided by the power input to the pump shaft. The latter usually is called the brake horsepower (bhp). The efficiency may be expressed as a decimal or multiplied by 100 and expressed as percent. In this subsection, the efficiency will always be the decimal value unless otherwise noted. Some pump driver units are so constructed that the actual power input to the pump is difficult or impossible to obtain. Typically of these is the “canned” pump for volatile or dangerous liquids. In such case, only an overall efficiency can be obtained. If the driver is an electric motor, this is called the wire to liquid efficiency or, when water is the liquid pumped, the wire to water efficiency.

Principle of Oil Seals

2010-04-07T21:39:00.000-07:00

Oil Seals
One of the most frequently used types of seal is the Rotary Shaft Seal. This is generally used for sealing lubricating oil or grease in rotary shaft applications. In exceptional cases, it is also used to seal other fluids, gases and powdered or granular solids. For trouble-free operation and optimum service life of a seal, shafts must have a satisfactory surface finish, within recommended limits and have no machine lay. Both correct design and material choice are critical if bearings and gears are to be sealed to prevent the leakage of lubricating oils and greases and the ingress of penetrating dust and dirt.

Sealing
A good lubricating oil forms a strong tenacious film on gears, bearings and shafts and is not easily removed from the pressure bearing surfaces of these. However, where the shaft extends away from the equipment, this oil film must be retained. In Oil Seals, the pressure or radial load exerted by the sealing lip must be sufficient to retain the oil film, whilst not so high that excessive friction losses or wear can occur. Good Oil Seal design is therefore a balance between optimum running properties of the material, lip design and integral garter spring.

Working principle
During rotation of the shaft, a hydrodynamic film of lubricant is produced beneath the sealing lip, the thickness of which depends on shaft speed, oil temperature, oil viscosity and the pressure or radial load exerted by the sealing lip on the shaft. Due to capillary forces and the surface topography of the shaft, the fluid being sealed forms a meniscus under the sealing lip and is prevented from leaking. The fluid, the seal material, the film thickness, the sealing lip geometry and the surface topography of the shaft are governing factors in the realisation of these capillary forces. A used seal having a shiny wear flat with hardening and radial cracking is indicative that it had operated on a shaft which was too smooth and /or that the radial load exerted by the lip was too high. A used seal having a wide wear flat is indicative that it had operated on a shaft which was too rough, especially if there was no hardening or radial cracking and could also be associated with incorrect sealing lip geometry. inside outside.

Construction of the oil seal
The most commonly used type is type R. This type has a carbon steel insert and has rubber outside diameter. The rubber gives a good sealing capability, even when the housing is not fully in tolerance. The sealing lip with spring provides interference on the shaft for effective sealing. The outside diameter, with inner metal reinforcement case, allows press-fitting in the housing, with sufficient interference on the rubber to provide static sealing. The sealing element is produced from a high performance Nitrile rubber.

This in combination with a high quality galvanised steel garter spring gives the ERIKS Oil Seal an optimum life. In order to prevent leakages due to a hydrodynamic pumping effect is it necessary that the sealing lip contact area on the sleeve or shaft is without any traces of machine lay.

Metal components
Depending on the application, ERIKS Oil Seals are supplied with various types of metal.
The reinforcing case Carbon steel as standard but stainless steel or brass on demand.

TYPE GR
This type is fully covered with rubber on the inside of the reinforcing case. ERIKS GR Viton® Oil Seals are of this type and are fitted with a stainless steel garter spring. This type can also be supplied in Nitrile rubber on demand.

The garter spring
Galvanised steel as standard. Stainless steel, bronze or an elastomer can be supplied on demand.

Air Operated Diaphragm Pumps (AODPS)

2010-04-05T03:10:00.000-07:00

In general diaphragm pumps of all types are sealless pump, have no dynamic seals or packing, are self priming, and have an infinitely variable flow rate and pressure rate within the pressure and capacity ranges of the pump. Air-operated diaphragm pumps (AODPS) can also run dry indefinitely, and the discharge can be throttled to zero flow indefinitely.

The most common types of AODPs are the double diaphragm pumps (duplex pumps). These contain two diaphragm chambers and two desired flexible diaphragms. The diaphragm are connected to each other through a connecting rod and are clamped at the outer edges of the diaphragm. The shaft connected diaphragms move in the same linear direction simultaneously. Compressed air directed to the back side of the left diaphragm moves both right diaphragm. After complexion of a stroke, an air distribution valve directs compressed air from the supply to the back side of the right diaphragm and exhaust air to the atmosphere from the left chamber. This continuous reciprocating motion, along wit properly operating internal check valve, create an alternating intake and discharge of pumped liquid into and out of each chamber that result in a nearly continuous action from the combined chambers.

A discharge pump air motor contains an air distribution valve that shifts position at the end of each stroke of the pump. The air distribution valve alternatively directs supply air pressure to one chamber and exhaust the other. Air motor often use a two stage valve to control the reciprocating motion of the pump.

Priming on Centrifugal Pumps

2010-04-01T02:36:00.000-07:00

A centrifugal pump is primed when the passageways of the pump are filled with the liquid to be pumped. The liquid replaces the air, gas, or vapour in the passageways. This may be done manually or automatically.

When pump is first put into service, the passageways are filled with air. If the suction supply is above atmospheric pressure, this air will be trapped in the pump and compressed somewhat when the suction valve is opened. Priming is accompanied by venting the entrapped air out of the pump through a valve provided for this purpose.

At the rate capacity, a positive displacement pump will develop the necessary pressure to exhaust air from the chambers and from the suction piping. Centrifugal pumps can also pump air at their rated capacity, but only at pressure equivalent to the rated head of the pump. Because the specific weight of the air is approximately 1/800 that of water, a centrifugal pump can produce only 1/800 of its rate liquid pressure. For every 1 ft (1 m) water has to be raised to prime a pump, the pump must produce a discharge head of air of approximately 800 ft (m). it is therefore apparent that the head required for a conventional centrifugal pump to be self priming and to lift a large column of liquid (and in some cases to greater than the rating of the pump. Centrifugal pumps that operate with a suction lift can be primed by providing;

A foot valve in the suction line.
A single chamber priming tank in the suction line or a two chamber priming tank in the suction and discharge line.
A priming inductor at the inlet of the suction line or
Some form of vacuum producing device.

Foot Valves:

A foot valve is a form of check valve installed at the bottom, or foot of a suction line. When the pump stops and the ports of the foot valve close, the liquid cannot drain back to the suction well if the valve seat tightly. Foot valves were very commonly used in early installation of centrifugal pumps. Except for certain applications their use is now much less common.

Priming Chamber:

Single chamber primer is a tank with a bottom outlet that is level with the pump suction nozzle and directly connected to it. An inlet at the top of the tank connects with the suction line. The size of the tank must be such that the volume contained between the top of the outlet and the bottom of the inlet is approximately three times the volume of the suction pipe. When the pump is shut down, the liquid in the suction line may leak out, but the liquid in the tank below the suction inlet cannot run back to the supply. When the pump is started, it will pump this entrapped liquid out of the priming chamber, creating a vacuum in the tank. The atmosphere pressure on the supply will force the liquid up the suction line into the priming chamber.

Hydraulic Driven Diaphragm Pumps

2010-03-23T02:02:00.000-07:00

Hydraulically driven diaphragm pumps are used in applications for the transfer or injection of chemicals into process streams at pressures up to 7500 lb/in2 (approximately 500 bar). Because the diaphragm is pressure balanced, the stresses in the diaphragm are low. Therefore, these pumps tend to require minimal maintenance. The pump’s capacities can be adjusted to match the specific process requirement by adjusting the effective stroke length or stroking speed of the pump. Effective stroke lengths are adjusted by either a hydraulic lost motion, a mechanical lost motion, or by varying the eccentric’s offset. The repeatability of the injected flow is plus or minus 1% or better.

Applications range from 0.26 to 26,000 gallon per hour (1 to 100,000 litters per hours). At flow about 26 gallons per hour (100 litters per hour), most pump models employ capacity adjustments based on variable eccentric or variable speed technology to avoid significant pressure spikes due to the rapid acceleration and deceleration of the fluid in the pipes.

As with the mechanical diaphragm pumps, a wide range of chemical can be handled. Wetted materials include PVC, Polypropylene, PVDF, 316 SS, Alloy 20, Alloy C-22, Titanium, and Inconel. Diaphragm for pressure up to 4350 lb/in2 (300 bar) are typically 316 SS, Alloy C or PEEK. Optional features include fluid temperature control jackets, diaphragm rupture detection capabilities, and remote diaphragm head design. Typical applications include the injection of acids and based for pH control, corrosion inhibitors, methanol, coagulants, primary process blending, process slurries, and drag reducers. These type of liquid ends are used, the disc diaphragm.

The disc diaphragm pump is equipped with process side and suction side restraining plates to prevent over displacement of the diaphragm during system upsets. When diaphragm reaches the suction the suction side restraining plate, the hydraulic oil pressure drops, causing the refill valve to open and replenish the oil. When the diaphragm hits the process side restraining plate, the hydraulic pressure rises, causing the relief valve to open, venting some oil. The fluid volume between the restraining plate is typically 150% of the maximum displaced volume of the pump. Therefore, the diaphragm does not contact both restraining plates during the same stroke.

The tubular diaphragm configuration is a variation of the disc diaphragm design. A diaphragm shaped in the form of a tube is placed in a chamber in front of the disc diaphragm assembly. This design eliminates the process fluid flowing through the front restraining plate, reducing viscose losses and wear in case of slurries. The chamber must be fitted with a precise amount of hydraulic fluid to avoid over displacing the tube.

The high performance diaphragm configuration eliminates the use of a process side restraining plate providing the through flow performance of a tubular design while eliminating the possibility of over displacing the tube during start-up and maintenance. With a mechanically arming, pressure sensitive refill valve, the hydraulic fluid can only be replenished when the diaphragm is in the most rearward position. This eliminates the possibility of overfilling the hydraulic chamber and therefore over displacing the diaphragm during system upsets (blocking suction or discharge lines).

Most problem with hydraulic diaphragm pumps occur due to incorrect system design. Pressure above 9 lb/in2 (0.6 bar) should be maintained in the pump diaphragm head during the suction stroke to stop vapour buildups in the hydraulic or process side cavities and special hydraulic fluids. NPSH calculation should include viscose losses in the check valves and contour plates (if so equipped).

Pump for Chemical and Water Treatment Industries

2010-03-11T01:00:00.000-08:00

Another type of mechanically driven diaphragm pump is used for the injection or transfer of chemicals into process streams at pressures up to 250 lb/in2 (17 bar). These pumps are designed to enable typically capacities can be adjusted through a 20:1 range. Injection capability is generally plus or minus 3%.

A wide range of chemicals can be handled. Wetted materials include PTFE or PTFE with elastomeric backing. Ball type check valves are usually employed.

Applications for this type of pump include the injection of acids and bases for pH control, biocides, chlorination, coagulations, and fertilizers. There are two basic configurations for pumps in this class; electromagnetic pumps, (solenoid) and motor driven pumps.

Electromagnetic (electronic) pumps are used in a variety of low power applications with flows from 0,026 to 26 gallons per hours (0.1 to 100 liters per hour) at pressures up to 250 lb/in2 (17 bar). These metering pumps employ an electronic control circuit that pulses on electromagnet that, in turn, generates the linear motion of an armature shaft diaphragm assembly. Each electronic pulse results in one discharge stroke of the pump. At the end of the stroke, a set of springs returns the diaphragm assembly to its initial position, drawing more fluid into the pump chamber in preparation for the next stroke.

These pumps are inherently safe, as they can be run indefinitely in the stalled condition without damage to the pump or over pressuring most systems. An additional feature of certain electronic pumps is the regulation of pulse strength through electronic power control, which leads to smoother fluid injection. Capacity is usually controlled by adjusting the stroke rate, but the stroke length can also be adjusted. Combining these adjustments provides a wide range of outputs.

Advances in the electronic controls have led to the capacity to control output manually from 4-20 mA process signals, digital pulses from external sources (such as flow meters), or serial data communications signals from computers. Yearly maintenance is recommended for low-pressure applications, but as pressure rise, diaphragm and check valves will need for low pressure applications, but as pressure rise, diaphragm and check valve will need to be replaced more frequently.

Mechanically Driven Diaphragm Pumps

2010-03-09T00:17:00.000-08:00

Many industries are served by mechanically driven diaphragms pumps. They are used in construction, chemical, and water treatment applications.

Construction Industry

Mechanically driven diaphragm pumps are widely used in the construction industry for dewatering applications where pumps may ingest rocks or other debris. A popular make of this type of pump contains a spring on the plunger rod. If the operating pressure exceeds the maximum recommended pumping pressure, the spring compresses and does not more the diaphragm. The spring can compress and thus keep a rock from being pushed through the wall of the pumping chamber or cause the drive mechanism to fall.

In single diaphragm pumps, the pumped liquid can have a lot of inertia if the suction and diaphragm lines are relatively long. A simple accumulator on the suction (inlet) side of the pump enable the pump to draw liquid from the accumulator while it simultaneously draws liquid through the suction line.

During the discharge stroke, the accumulator can refill with liquid from the suction line. If the discharge line from the pump is relatively long, the inertia of the liquid can be great, as mentioned earlier, and can impose severe loads on the diaphragm and drive mechanism. The spring on the plunger and can absorb some of the drive energy early in the discharge stroke and “give it back” during the latter part of the discharge stroke, greatly reducing the inertia loading on the diaphragm and drive mechanism.

Mechanically driven diaphragm pumps in the construction industry operator by a reciprocating plunger, usually secured to plates on both sides of the diaphragm. The diaphragms are customarily fabric reinforced elastomers (usually synthetic rubbers) similar in many ways to the fabric reinforced materials used in pneumatic tires. The diaphragms are normally molded with a convoluted section between the central damaged area and the clamped periphery. This convoluted section permits longer strokes than would be possible otherwise.

These pumps are sometimes duplexed so that the reciprocating means acts alternatively on two diaphragms with one on a section stroke, while the other in on a discharge stroke and vice versa. A connector called a walking bean is pivoted between two diaphragms. As one diaphragm is pushed down on a discharge stroke, the other diaphragm is simultaneously pulled up on a suction stroke. The pumping chambers with inlet and outlet check valve are manifolded together to a common inlet and a common outlet. The principle advantage of the duplex diaphragm pump is its more constant flow (two pressure pulsa times per cycle).

Pertinent Characteristic of Pumps

2010-02-14T21:41:00.000-08:00

Pertinent Positive Displacement Pump Characteristics

The discharge pressure produced is a function of the system requirement only and is independent of pump capacity.
The flow rate pulses between maximum and minimum values for each revolution of the crankshaft.
The pulsating flow imposes an acceleration used that adds to the net positive inlet pressure required.
Being more energy efficient, the positive displacement pump is normally the lead pump and the centrifugal pump is the supplement when operated in parallel.

Pertinent Centrifugal Pump Characteristics

The dynamic head of (or pressure rise) produced is a function of pump capacity as well as of system requirements.
For satisfactory operation, the flow must be kept within a limited range of the best efficiency capacity.
When used as a suction booster, the centrifugal pump must be designed so it cannot introduced air into the gas intolerant reciprocating pump. (Gas in positive displacement pumps, like liquids in positive displacement compressors, may cause severe hydraulic and mechanical shock).
Centrifugal pumps do not generate acceleration heads that impose on not positive suction head required. However, if a centrifugal pump is connected in parallel to a common suction line with a reciprocating pump, some of the system acceleration head loss from the positive displacement pump may affect the centrifugal pump.

Only two cases need to be considered: centrifugal pumps feeding:

In series into reciprocating pump to increase suction NPSHA to the reciprocating pump
In parallel to augment the delivered capacity. It would be most unusual to encounter a positive displacement pump feeding into the suction of a centrifugal pump because of the high pressure that could be imposed on the centrifugal pump suction and because of the amplification of flow pulsations resulting from interaction of the characteristic of the two pumps, which could be deleterious to both pumps.

Pump Selection and Pump Performance

2010-02-07T23:45:00.000-08:00

There are three principal performance parameters relating to pump selection:

Flow (or Capacity)
Total Delivery Head
Suction Lift

1. CAPACITY

Required capacity, measured in flow/time is determined by one of two factors:

If there is storage capacity it is related to total daily demand. Daily demand must first be estimated and then the hourly requirement calculated by dividing the daily demand by the number of hours the pump is required to work.
If there is direct supply pump capacity should be related to peak hourly demand. This would be appropriate in irrigation or pressure systems.

Capacity is measured in various units including gallons per hour – gallons per minute, liters per second, liters per minute and cubic meters (1000 liters) per hour. All Davis & Shirtliff products are rated in cubic meters per hour (m3/hr)

2. TOTAL HEAD

There are three principal components to total head of importance when specifying a pump: static head, dynamic head (friction loss) and pressure head.

Total Head = Static Head + Dynamic Head + Pressure Head

2.1 Static Head (H)

DIAGRAM 1 - Static Head Conditions

Static head is the vertical linear distance between the level of the water being pumped and either the delivery outlet or the reservoir water level, whichever is higher (see A & B). Of great

importance to note is that it is not necessarily the distance between the pump itself and the delivery point. This has particular reference to submersible pumps where the level the pump is set in the water does not determine static head. It is determined by the pumping water level (see C).

2.2 Dynamic Head

The only important component of dynamic head is pipe friction, this being determined by water velocity in the delivery pipe. The higher the velocity the higher the friction loss and it is important to match the pump to the pipeline. Friction loss values for GI and PVC pipes are given in table 1.

Some important points to note when matching pumps and pipelines are:

· Friction losses are considerably lower in PVC pipes than GI ones. For long pipelines the use of PVC will therefore reduce pump size and energy consumed.

· Piping can be considerably more expensive than the pumping installation and a pipe size smaller matched to a pump size larger can reduce the investment cost. Running costs will be higher though.

· Total head reduces up the pipeline and lighter duty pipes can be used towards the system’s delivery point.

Total friction loss for a pipeline (HF) = F x L/100

Where:

F = Friction loss given for a particular flow in a specified pipe size (m per 100m pipe length).

L= Pipe length (m)

Pipe friction is not linear and increases logarithmically as velocity (or flow) increases. A typical friction loss curve is given below.

DIAGRAM 2 - Typical Friction Head Loss Curve

This diagram can be plotted using friction loss values given for a particular pipe specification at different flow rates.

2.3 Pressure Head

When delivering to an open outlet pressure at the delivery point is zero and so in most water supply installations this is not a factor in total head calculations. However, when pressure delivery is required eg. for fire installations or irrigation nozzles the required pressure at the nozzle must be included when calculating total head.

DIAGRAM 3 - Pressure Head Condition System Head Curves

In order to find the total head required on a pump, static head plus dynamic head plus friction head must be added. This can be done graphically as follows:

DIAGRAM 4 - System Head Curve

From the above graph pump 3 or pump 4 can be selected, depending upon required pump capacity.

3. SUCTION LIFT

Centrifugal pumps have the capability of creating a vacuum in a suction pipe which enable them to suck water from below their setting level. The maximum theoretical suction lift is 1 atmosphere (approx 10m), though the maximum practical lift is well below this.

Maximum suction lift is determined by the formula:

Hmax = A – NPSH –Hf –Hv –Hs

DIAGRAM 5 - Suction Lift Conditions

Considerations relating to the various parameters are as follows:

A – Atmospheric pressure. At sea level it is 10.3m reducing by approximate 3% per 300m. Suction lift is therefore reduced at higher altitudes.

NPSH – The suction characteristic of the pump which is shown on the pump manufacturer’s curve.

DIAGRAM 6 - Typical NPSH Curve

The higher the flow the higher the NPSH and therefore the lower the available suction lift.

Hf – Friction loss in the suction pipe. This is calculated in a similar way to friction loss under section 2.2. The value increases with increasing flow thereby reducing the available suction lift.

Hv – The water vapour pressure. This is an important factor for liquids above 30oC, though is not important at normal ambient temperatures.

Vapour pressure values are as follows;-

DIAGRAM 7 - Vapor Pressure Values

HS - A safety margin, usually 1 m being acceptable. Some general points about suction conditions are as follows:

· It is good practice to keep suction pipes as short as is practical.

· Suction pipes must be totally airtight. If there are any leaks the pump will be unable to create the vacuum condition for suction to occur.

· Suction pipes must be straight and laid to rise continuously to the pump. If there are any leaks in the pipe air pockets will form and the system will become air locked.

· Suction pipes must be generously sized, one size larger than the delivery pipe being standard practice. Also all suctions should be fitted with foot valves.

· Where the distance from the pump mounting point to the water level is greater than the available suction lift either a submersible or a jet pump should be used.

4. CENTRIFUGAL PUMP PERFORMANCE

4.1 Performance Parameters

When specifying centrifugal pumps it is important to understand the various parameters that effect pump performance and their relationship with one another.

Typically a pump curve will provide the following information.

DIAGRAM 8 - Typical Centrifugal Pump Performance Curve

Three plots are given against flow – Pressure (or Q-H curve), Efficiency (h) and Power absorbed.

Pressure: Otherwise known as the pump performance or Q – H curve and plots the pressure/flow profile of the pump.

· At zero flow the pump will provide its maximum pressure (closed head pressure).

· At zero head the pump will provide its maximum flow.

Efficiency (h): The efficiency curve is the plot of overall efficiency against flow. Points to note are:

· The pump’s optimal duty point is that at which peak efficiency occurs and is usually around the mid point of the curve. The optimal performance envelop is the flow range which is greater than 90% of the pump’s maximum efficiency and applications should be within this envelope.

· Efficiency drops considerably at high pressures and high flows and specifying a pump to operate in these sections of a curve must be avoided.

Power: The power curve is a plot of power consumed against flow. Points of note are:-

· Maximum power consumption of a pump occurs at high flows/low pressures. Usually power consumed at high pressures is lower.

· When coupling motors to pumps it is important to ensure that the power consumed at open delivery is less than the motor size or else motor failure may occur.

4.2 Pump Parameters

The following parameters affect pump performance:

· Speed

· Impeller Diameter

· Number of Impellers

Speed: Impeller speed effects power consumed and pump performance as follows:

Speed = f (Power3)

Doubling Speed increases power consumed by a factor of 23 = 8

Speed = f(Pressure2)

Doubling Speed increases pressure by a factor of 22 = 4

Impeller Diameter: Impeller diameter effects pump performance in a similar way to speed.

Diameter = f(Power3)

A 10% increase of impeller diameter increases power consumed by (1.13 – 1) x 100 = 33%

Diameter = f(Pressure2)

A 10% increase of impeller diameter increases pressure by (1.12 – 1) x 100 = 21%

Number of Impellers

· Adding impellers in series increases pressure though has no effect on flow. This is the effect of a multistage pump.

· Adding impellers in parallel increases flow though has no effect on pressure. This is the effect of two pumps connected in parallel.

DIAGRAM 9 - Impeller Configurations

4.3 Pump Shaft Horse Power

Pump Shaft Horse Power can be calculated from the formula:

HP = Q x H/275 x h

Where Q = flow in m3/hr

H = Head in m

h = Pump Efficiency

Combined Displacement and Centrifugal Pumps

2010-02-03T01:23:00.000-08:00

Flow Control in Combined Displacement - Centrifugal Pumps

Systems that involve both centrifugal and reciprocating positive displacement pumps deserve some special consideration. Centrifugal pumps are often used as suction boosters to overcome acceleration head requirements peculiar to reciprocating pumps but are rarely used to supplement flow. Some unique characteristics of each type of pump that affect the other type must be considered in the design, operation, and control or the interrelated system.

Comparison of several capacity control schemes for positive displacement pump

Control method	Degree of Modulation	First Cost	Operating Cost		Comments
Directing Acting Pumps
Steam throttle	Full zero to 100%	low		low	Steam pressure required to balance liquid piston force and overcome breakaway friction. Steam volume throttled to produce desired capacity
Power Pumps
Start-stop	Zero or 100%	low		low	Limited in frequency of starts because of temperature rise from inrush.
Multispeed motors	Steps dependent on motor winding	medium		low	Cost of motor controller switch gear motors must be assessed
Variable frequency	Full zero to 100%+	high		low	Limited by current handling capacity of solid state controller
Direct current	Full zero to 100%	High		Medium	Drive is torque speed sensitive, pump is torque pressure sensitive at all speeds. Check drive for required
Wound rotor motors	Full zero to 100%	High		low	Drive is torque speed sensitive. Pump is torque pressure sensitive at all speeds. Check drive for required torque at minimum and maximum speeds
Combustion engine	Variable for limited range	high		low	Torsional analysis required to avoid high torsional stresses.
Steam or Gas turbine	Variable for limited range	medium		medium	Drive is torque speed sensitive at all speeds. Check drive for required torque at minimum and maximum speeds.
Hydraulic torque converter	Full zero to 100%	high		high	Low full speed efficiency

Pump Cavitations

2010-01-25T05:47:00.000-08:00

The formation and subsequent collapse of vapor filled cavities in a liquid due to dynamic action are called cavitation. The cavities may be bubbles, vapor filled pocket or a combination of both. The local pressure must be at or below the vapor pressure of the liquid for cavitation to begin, and the cavities must encounter a region of pressure higher than the vapor pressure in order to collapse. Dissolved gasses often are liberated shortly before vaporization begins. This may be an indication of impending cavitation, but true cavitation requires vaporization of the liquid. Boiling accomplished by the addition of heat or the reduction of static pressure without dynamic action of the liquid is arbitrarily extruded from the definition of cavitation.

When a liquid flows over a surface having convex curvature, the pressure near the surface is however and the flow tends to separate from the surface. Separation and cavitation are completely different phenomena. Without cavitation, a separated region contain turbulent eddying liquid at pressures higher than the vapor pressure. When the pressure is low enough, the separated region may contain a vapor pocket that fills from the downsteam end, collapses, and forms again many times each second. This causes noise and, if severe enough, vibration. Vapor filled bubbles usually are present and collapse very rapidly in any region where the pressure is above the vapor pressure.

Bubble that collapse on a solid boundary may cause severe mechanical damage. Shutler and Mesler photographed bubbles that distorted into toroidal shaped rings during collapse and produced ring shaped indentation in a soft metal boundary. The bubbles rebounded following the initial collapse and caused pitting of the boundary. Pressure on the order of 104 atm have been estimated during collapse of a bubble. All known material can be damaged by exposure to bubble collapse for a sufficiently long time. This is properly called cavitation erosion, or pitting.

It has been postulated that high temperature and chemical action may be present at bubbles collapse, but any damaging effects due to them appear to be secondary to the mechanical action. It seems possible that erosion by foreign material in the liquid and cavitation pitting may augment each other. Cavitation pitting, as measure by weight of of the boundary material removed per unit time, frequently increase with time. Cast iron and steel boundaries are particularly vulnerable. Controlled experiment have shown that cavitation pitting in metal such as aluminum, steel and stainless steel depends strongly on the velocity of the fluid in the disturbed flow past the surface.

Variable Flow Control

2010-01-21T04:35:00.000-08:00

Rather than by speed control (changes in the number of displacements in a given period of time), flow may be varied by changing the volume displace par stroke. Variable stroke are generally limited to small mattering or “controlled volume” pumps. Although large capacity variable strokes pumps have been built, the complexity of the mechanism involved and the development of other effective and economical means of flow control have precluded their use.

Changing Delivery to the System
Another means of capacity control is not to vary the pump capacity but to alter the amount of pumpage delivered to the system. There are two popular means of during thin.

Suction valve uploading:
Suction valve unloaders cause the displacement to the ineffective during the stroke for which the unloaders are activated. They command either full or zero delivery while the pump is kept running. Thus, current inrush problem from frequent motor starts are avoided. Because discharge pressure is not developed when suction valve are unloaded, energy consumption is held to a minimum.

A pump valve is unloaded by mechanically preventing the valve plate from returning to its sent. If the suction valve is held away from its sent, liquid will ebb and flow through the valve from suction header to pump cylinder and from cylinder to header during the stroking of the plunger or piston.

The unloader mechanism does not move the valve. The valve is lifted off its seat by the pressure differential created by normal pump operation. In synchronically unloading the suction valve spring that had already been compressed and moves away from the valve while the spring are still compressed. This permit the valve to close when the plunger begin its discharge stroke.

For smooth transition between full to zero, the unloading and loading are accomplished in an immediate and identical pumping order of the plunger. It is the function of the synchronized suction valve unloader distributor to control unloading event in that proper and immediate sequence. Similarly can be drawn in the gasoline engine distributor in its function of ensuring the proper and immediate sequence of firing of the spark plug.

The distributor driven directly by the crankshaft on its position is positively indexed in the stroking of the plungers. It provided an electrical signal to a solenoid valve, which admit motive fluid pressure to the unloader chamber when the suction valve to the particular cylinder has been opened. Then in sequence, each of the remaining suction valve is retained so, in the first revolution of the pump after a control signals the distributor to initiate so, in the first revolution of the pump after a control signals the distributor to initiate unloading, all suction valves are unloaded and the pump capacity is reduced to zero. When the control against to signal for capacity, such suction valve is released, in sequence during a single revolution of the crank.

GBC Couplings

2010-01-07T18:41:00.001-08:00

Couplings are use to joint of pumping system and the pump driver. Pump with high load need a high power should use a good perform coupling. Pump system should align all together and should be test by maintenance people. Design of GBC coupling has been optimized in order the power capacities balanced to the appropriate shaft diameter.

Load on the coupling to move the part like pump impeller can reduce by a flexible element, the deflection of which is a prime design consideration. Transient peak load also can reduce by this element.

Misalignment incidentally on the parallel angular and axial displacement of the connected shafts can be accommodated. Taper Bushes are fitted to the complete standard coupling range, bored to size flanges also available.

Selection using this kind of coupling is may either of two ways:

Where the prime mover is an electric motor and demand power or demand torque unknown, select the coupling using data from couple tables.
Where the driven machine demand power (or torque) and operating duty are known, select the coupling using the following procedure.

• Service Factor
• Design Power
• Coupling Size
• Bore Size

Pump Impellers

2009-12-28T01:18:00.001-08:00

In a single suction impeller, the liquid enters the suction eye on one side only. A double suction impeller is, in effect, two single suction impellers arranged back to back in a single casing. The liquid enters the impeller simultaneously from both sides, while the two casing suction passageways are connected to a common suction passage and a single suction nozzle.

For the general service single stage, axially split casing design, a double suction impeller is favored because it is theoretically in an axial hydraulic balance and because the greater suction head. For small units, the single suction impeller is more practical for manufacturing reasons, as the waterways are not divided into two very narrow passages. It is also sometimes preferred for structural reasons. End suction pumps therefore use single suction impellers. Because an overhung impeller does not require the extension of a shaft into the impeller suction eye, single suction impellers are preferred for pumps handling suspended matter, such as sewage. In multistage pumps, single suction impellers are almost universally used because of the design and first cost complexity that double suction staging introduces.

Impeller are called radial vane or radial flow when the liquid pumped is made to discharge radially to the periphery. Impellers of thus type usually have a specific speed N, below 4200 rpm if single suction and below 6000 rpm if double suction.

Impellers can also be classified by the shape end form of their vanes:

The straight-vane impeller
The Francis-vane or screw-vane impeller
The Mixed flow impeller
The Propeller or axial flow impeller

The description of each type those impeller will discussed more detail.

Variable Displacement Flow Control

2009-12-22T01:51:00.000-08:00

Rather than by speed control (changes in the number of displacements in a given period of time), flow may be varied by changing the volume displaced per stroke. Variable stroke are generally limited to small metering or controlled volume pumps. Although large capacity variable stroke pumps have been built, the complexity of the mechanism involved and the development of other effective and economical means of flow control have precluded their use.

Flow Control in Individual Pump

2009-12-01T20:37:00.000-08:00

See Other Many Kinds of Pumps:
Centrifugal Pump
Vertical Pump
Sump Pump and Multistage Pump
Propeller Pump
Positive Displacement Pump
Reciprocating Pump
Diaphragm Pump
Piston Pump
Rotary Screw and Gear Pump
Jet Pump and Electromagnetic Pump

An inherent characteristic of positive displacement pumping of relatively incompressible liquids is that flow rate is proportional to displacement rate and independent of pressure levels. The capacity of a centrifugal pump operating at constant speed varies from a maximum flow at no developed pressure to zero flow at a definite limiting pressure known as shutoff head. The average capacity of positive displacement pumps at constant speed is within design limits of pressure, practically constant, even though flow rate pulsations do occur as individual displacement are forced into the discharge pipe.

Flow control of positive displacement pumps is accomplished by:

Changing the displacement rate
Changing the displacement volume
Changing the proportion of the displacement delivered into the piping system

Throttle Control in Direct-Acting Steam Pumps
Direct acting pumps are controlled by speed change, which is effected by throttling the flow of steam (or other motive gas) to the drive cylinder. The magnitude of excess force on the drive piston over that required for the driven, or pumping, piston to force pumpage into the piping system dictates the stroke rate and therefore the capacity of the pump. A sensor that detects the desired result of pumping (pressure, level, flow rate, and so on) may be used to modulate the steam throttle valve.

Speed Control in Power Driven Pumps
Speed modulation is the most common means of flow control for power driven pumps. The most rudimentary speed control is intermittent (start stop) operation. The average capacity over relatively long time periods depends upon the percentage of time the pump operates at 100% versus the percentage of time it operate at zero flow. Of course, consideration must be given to the frequency of starts because electric motors may overheat if there is insufficient time for cooling after the inrush of starting current.

Solid and Split Casings

2009-11-23T23:51:00.000-08:00

Solid casing implies a design in which the discharge water ways leading to the discharge nozzle are all contain in one casting or fabricated piece. The casing must have one side open so that the impeller can be introduced into it. Because the sidewall surrounding the impeller are actually part of the casing, a solid casing, strictly speaking cannot be used, and design normally called solid casing are really radially Splits.

A split casing is made of two or more parts fastened together. The term horizontally split had regularly been used to describe pumps with casing divided by a horizontal plane through the shaft centerline or axis. The term axially split is now preferred, because both the suction and discharge nozzle are usually in the same half of the casing, the other half may be removed for inspection of the interior without disturbing the bearing or the piping. Like its counterpart horizontally split, the term vertically split is poor terminology. It refers to a casing split in a plane perpendicular to the axis of rotation. The term radially split are now preferred.

More about pump part:

Radial Thrust

2009-11-16T19:42:00.000-08:00

In a single volute pump casing design, uniform or near uniform pressures act on the impeller when the pump operates at design capacity (which coincides with the best efficiency). At other capacities, the pressures around the impeller are not uniform and there is a resultant radial reaction. A detailed discussion of the radial thrust and of its magnitude is presented in the other article. The unbalanced radial thrust increases as capacity decreases from threat at the design flow.

For any percentage of capacity, this radial reaction is a function of total had and of the width and diameter of the impeller. Thus, a high head pump with a large impeller diameter will have a much greater radial reaction force at partial capacities than a low head pump with a small impeller diameter. will have a much greater radial reaction force at partial capacities than a low head pump with a small impeller diameter. A zero radial reaction is not often realized the minimum reaction occurs at design capacity.

Although the same tendency for unbalance exists in the diffuser type pump, the reaction is limited to a small arc repeated all around the impeller. As a result, the individual reactions cancel each other out as long as flow is constantly removed from around the periphery of the diffuser discharge. If flow is not removed uniformly around the periphery, a pressure imbalance may occur around the diffuser discharge that will be transmitted back through the diffuser to the impeller, resulting in a radial reaction on the shaft and bearing system.

In centrifugal pump design, shaft diameter as well as bearing size can be affected by the allowable deflection as determinated by the shaft span, impeller weight, radial reaction forces, and torque to be transmitted.

Because of the increasing application of pumps that must operate at reduced capacities, it has become desirable to design standard units to accommodate such conditions. One solution is to use heavier shafts and bearings. Except for low liquid pumps in which only a small additional load in involved, this solutions is not economical. The only practical answer is a casing design that developed a much smaller radial reaction force at partial capacities. One of these is the double volute casing design, also called the twin volute or dual volute design.

Pump Casing and Diffusers

2009-11-04T17:53:00.000-08:00

The Volute Casing Pump:
This pump derives its name from the spiral shaped casing surrounding the impeller. This section collects the liquid discharged by the impeller and converts velocity energy to pressure energy.

A centrifugal pump volute increases in area from its initial point until it encompasses the full 360^o around the impeller and then flares out to the final discharge opening. The wall dividing the initial section and the discharge nozzel portion of the casing is called the tongue of the volute or the cutwater. The diffusion vanes and concentric casing of a diffuser pump fulfill the same function as the volute casing in energy convension.

A diffuser is seldom applied to a single stage, radial flow pump, except in special instances where volute passages become so small that machined or precission cast volute or diffuser like pieces are utilized for precise flow control. Conventional diffusers are often applied to multistage pump designs in conjunction with guide vanes to direct the flow efficiently from one impeller (stage) to another in a nimimum radial and axial space. Diffuser vanes are used as the primary construction method for vertical turbine and single stage, low head propeller pump.

Radial Thrust:
In a single volute pump casing design, uniform or near uniform pressures act on the impeller when the pump operate at design capacity (which coinsides with the best efficiency). At other capacity. the pressure arround the impeller are not uniform and there is a resultant radial reaction.

For any percentage of capacity, this radial reaction is a function of total head and of the width and diameter of the impeller. Thus a high head pump with a large impeller diameter will have a much greater radial reaction force at partial capacities than a low head pump with a small impeller diameter. A zero radial reaction is not often realized; the minimum reaction occurs at design capacity.

Although the same tendency for imbalance exist in the diffuser type pump, the reaction is limited to a small are repeated all around the impeller. As a result, the individual reactions cancel each out as long as flow is constantly removed from around the periphery of the diffuser discharge. If flow is not removed uniformly arround its periphery, a pressure imbalance may occur around the diffuser discharge that will be transmitted back through the diffuser to the impeller, resulting in a radial reaction on the shaft and bearing of pumping system.

Gland Plate Construction

2009-10-05T22:48:00.000-07:00

An essential component of any installation is the gland plate. The purpose of this part is to hold either the mating ring assembly or the seal head assembly, depending on whether the seal head is rotating with the shaft or stationary to the pump casing. It is also a pressure containing component of the installation. The aligment of one of the sealing surfaces, particularly the mating ring used with a rotating seal assembly and a gland plate bushing, is dependent on the lift of the gland plate to the pump. To ensure the proper installation, the API specification requires a register fit with the inside or outside diameter of the seal chamber. The static seal on the face of the seal chamber must be completely confined. Three basic gland plate are:

A plain gland plate is used where seal cooling is provided internally through the pump stuffing box and where the liquid to be sealed is not considered hazardous to the plant environment and will not crystalline or carbonize at the atmospheric side of the seal.
A flush gland plate is used where internal cooling is not available. Here coolant (liquid sealed or liquid from an external source) is directed to the seal faces where the seal heat is generated.
A flush and quench gland plate is required on those application that need direct cooling as well as a quench fluid at the atmospheric side of the seal. The purpose of the quench fluid, which may be a liquid, gas or steam, is to prevent the build up of any carbonized or crystalized material along the shaft. When properly applied, a seal quench can increase the life of a seal installation by eliminating the loss of seal flexibility due to hangup. The gland plate can also be used for flush, vent, and drain where seal leakage needs to be controlled. Flammable vapor leaking from the seal can be vented to a flare and burned off, while nonflammable liquid leakage can be directed to a seal sump.

Environmental Limitations

2009-09-29T21:09:00.000-07:00

Every pumping application results in either positive or negative pressure as the throat of the pump stuffing box. A possitive pressure will force the liquid pumped through the packing to the atmosphere side of the pump. Higher pressure will result in greater leakage from the pump. This results in excessive tighening of the gland, which causes accelerated wear of the shaft or shaft sleeve and packing. For pressure at the stuffing box greater than 76 lb/in² (5.1 bar), some mean of the throttling the pressure should be considered. A combination of hard and soft rings die formed to the exact stuffing box bore and sleeve dimension can be used. Harder rings at the inboard end of the box and at the lantern ring and gland break down the pressure and prevent the extrusion of the packing.

I the packing itself cannot be used to break down the pressure then a throttle bushing must be used. This is a typical arrangement for a vertical turbine where the stuffing box is the discharge pressure of the pump. Here the throttle bushing to used to bring the liquid to almost suction pressure, and most of the leakage through the bushing is bled back to the suction. When the suction pressure in the stuffing box. This prevents air leakage into the pump and excessive flow and wear at the bushing.

When a pump to fitted with a bypass line from the discharge, a valve can also be used to reduce the pressure at the stuffing box. This is another method for reducing pressure for the benefit of the installation.

Materials of Construction

2009-09-07T22:24:00.001-07:00

All component parts of a seal are selected based on their corrosion resistance to the liquid being sealed. The National Association of Corrosion Engineers (NACE) Corrosion Handbook provides corrosion rates for many materials of construction for mechanical seal used with a variety of liquids and gases. When the corrosion rate is greater than two mils (0.05 mm) per year, double seals that keep the hardware items of the seal in a neutral liquid should be selected to reduce corrosion. In the design, only the inside diameter of the mating ring, the primary ring, and the secondary seal are exposed to the corrosive liquid and should be constructed of corrosion resistant materials, such as ceramic, carbon, and Teflon.

The operating temperature is a primary consideration in the design of the secondary and static seals in the assembly. These parts must retain their flexibility throughout the life of the seal, as flexibility is necessary to retain the liquid at the secondary seal as well a to enable a degree of freedom for the primary ring to follow the mating ring.

An additional consideration in the selection of the primary and mating ring materials in sliding contact in their PV limitation. This value is an indication of how well the material combination will resist adhesive wear, which is the dominant wear in mechanical seal. Limiting PV values for various face combinations.

Common Material of construction for mechanical seals

Components	Material of Construction
Secondary Seals: O-rings	Nitrils, Ethylene Propylene, Chloroprene, Fluoroelastomer
Bellows	Nitrile, Ethylene Propylene, Chloroprene, Pluoroelastomer
Wedge or U Cups	Fluorocarbon
Metal Bellows	Stainless steel, Nickel base Alloy
Primary Ring	Carbon, Metal-filled Carbon, Tungsten Carbide, Siliconized Carbon, Bronze
Hardware (retainer, disc, snap rings, set screws, springs)	Stainless Steel, Nickel-base Alloy
Mating Ring	Ceramic, Cast Iron, Tungsten Carbide, Silicone Carbide

Classification of Seals By Arrangement

2009-08-04T20:45:00.000-07:00

Sealing arrangement can be classified into two groups:

1. Singgle seal installations

Internally mounted
Externally mounted

2. Multiple seal installations

Double seals
Tandem seals

Single seals are used in most applications. This is the simples seal arrangement with the least number of parts. An installation can be reffered to as inside mounted or outside mounted, depending on wether the seal is mounted inside or outside the seal chamber. The most common installation is an inside mounted seal. Here the liquid under pressure acts with the spring lead to keep the seal faces in contact.

Outside seals are considered to be used for low pressure applications since both seal faces, the primary ring and mating ring, are put in tension. This limit the pressure capability of the seal. An external seal installation is used to minimize corrosion that might occur if the metal parts of the seal were directly exposed to the liquid being sealed.

Multiple seals are used in applications requiring:

A neutral liquid for lubrication
Improved corrosion resistance
A buffered area for plant safety

Double seal consist of two single seal back to back, with the primary rings facing in opposite dirrection in the real chamber. The neutral liquid, at a pressure higher than that of the liquid being pumped, lubricates the seal faces. The inboard seal keeps the liquid being pumped from entering the seal chamber. Both inboard and outboard seals prevent the loss of neutral lubricating liquid.

Centrifugal Pump Mechanical Seals

2009-07-27T21:41:00.000-07:00

Centrifugal Pump Mechanical Seals, mechanical seal have been used for many years to seal any number of liquids at various speeds, pressures, and temperatures. Today plant operators are benefiting from improved seal technologies driven by the US clean air act of 1980, and the American Petroleum Institute (API) Standard 682. These new seal technologies are based on advanced commence testing at simulated refinery conditions required by the API. The results to date indicate not only an improvement in emissions control, but also a major increase in equipment reliability.

Classes of seal technology
Emerging seal technologies are providing clear choices for sealing. Various plant services require the application of these new technologies for emissions control, safety, and reliability. Sealing systems are now available that are based on the preferred method of lubrication to be used.

These classes of seals are as follows:
1. Contacting liquid lubricated scale:

Normally a single seal arrangement is cooled and lubricated to the liquid being sealed. This is the most cost effective seal installation available to the industry.
Dual seal are arrange to contain a pressurized or non pressurized barrier or buffed liquid. Normally this arrangement will be used on application where the liquid being seal is not a good lubricating fluid for a seal and for emissions containment. These arrangements require a lubrication system for the circulation of barrier or buffer liquids.

2. Non contacting gas lubricated seals:

Dual non-contacting gas-lubricated seals are pressurized with an inert gas such as nitrogen.
Dual non-contacting, gas-lubricated seals are used in a tandem arrangement and pressurized by the process liquid being sealed, which is allowed to flash to a gas at the seal.

A tandem seal arrangement is used on those liquid that represent a danger to the plant environment. For non-hazardous liquids, a single seal can be used.

Gland Packing

2009-07-15T00:21:00.000-07:00

For packing to operate properly, the finish on the shaft sleeve must be at least 16 µin (o.4 µm) centerline average (CLA) and the finish in the bore should be 63 µin (1.65 µm) CLA. The sleeve must be harder than the packing and chemically resistant to the liquid being sealed. If the sleeve has a coated material for a hard wear surface, the sleeve must also have good thermal shock resistance.

Lantern Ring (Seal Cages)
When an application requires that a lubricant be introduced to the packing, a lantern ring is used to distribute to flow. This ring is used or near the center of the packing installation. For ease of assembly, most lantern rings are axially split. The construction material range from metal to TFE (tetra fluoroethylene). TFE lantern rings are usually filler with glass or with glass and molybdenum disulfide. They are inherently self lubricating and will not score the shaft. A throat brushing at the bottom of the stuffing box can be used to provide a closer clearance with the shaft to prevent packing extrusion.

Staffing Box Gland Plates
All mechanical packing are mechanically loaded in the axial direction by the stuffing box gland. In cases where leakage of the process liquid is dangerous or can vaporize and create a hazard to operating personnel, a smothering gland is used to introduce a neutral liquid at lower temperature. A sufficient quantity of quenching liquid should be used to eliminate the danger from the liquid being pumped. The neutral circulated in the gland mixed with the leakage and carries it to a safe place to disposal. Close clearances to the gland control the leakages of the combined liquid to the atmosphere. This quenches can also be used to protect the packing from any wear through abrasion, because the leakage cannot vaporize and leave behind abrasive crystal.

Gland are usually made of bronze, but case iron or steel can be used for all iron pumps. When iron or steel glands are used, they are normally bushed with a non sparking material like bronze.

The size and Number of Packing Ring

2009-07-10T06:23:00.000-07:00

The number of packing rings may vary depending on the objective of the sealing system or the requirements of the rotating equipment. The most common packing arrangement for rotating equipment is illustrated in figure. Three rings of packing are used to seal the process liquid from the packing lubricant. Two rings between the lantern and gland are used to restrict the leakage of the lubricant to the atmosphere. The size of packing depends on the size of equipment, typically for rotating shafts, the standard square size packings shown in the table may be considered.

For packing to operate properly the finish on the shaft sleeve must be at least 16 μin (0.4 μm) conterline average (CLA) and the finish in the bore should be 63 μin (1.65 μm) CLA. The sleeve must be harder that the packing and chemically resistant to the liquid being sealed. If the sleeve has a coated material for a hard wear surface, the sleeve must also have good thermal shock resistance.

Fibers

Metal

Mineral

Animal

Vegetable

Synthetic

Lead

Metal

Graphite

Wool

Hair

Leather

Flax

Ramie

Jute

Cotton

Paper

Nylon

Rayon

TFE

Carbon

Aramid

Polyamide

Copper

Brass

P-Broze

The Design of Packing Rings

2009-06-30T02:49:00.000-07:00

Packing is used in the stuffing box of a centrifugal pump to control the leakage of the pumped liquid out, or the leakage of air in, where the shaft passes through the casing. The basic form of a seal can be applied in light-to medium duty services and to those liquids that prove to difficult to mechanic seals.

Packing may be referred to as compression, automatic or floating. Each term describes the type of operation in which the packing will be used.

Automatic and floating packing require no gland adjustment in controlling leakage. Automatic packing are confine to a given space and are activated by the operating pressure. Automatic packing rings are designed in the form of V-rings, U-cups and O-rings. Floating packing include piston rings and segmental rings that may be energize by a spring. These type of packing are commonly used in reciprocating application.

Compression packing is most commonly used on rotating equipment. The seal is formed by the packing being squeeze between the inboard end of the stuffing box and the gland. A static seal is formed at the end of the packing ring and at the inside diameter of the stuffing box. The dynamic seal is formed between the packing and shaft or shaft sleeve. Under a load, the packing deforms down against the shaft, controlling leakage. Some leakage along the shaft is necessary too cool and lubricate the packing. The amount of leakage will depend on the materials of the construction for the packing, the operating condition of the application, and the condition of the equipments.

Packing must be able to withstand equipment variables. The design of the packing ring and the materials of construction must be resilient to follow shaft run out and misalignment, as well as to compensate for thermal growth of the equipment without an appreciable increase in leakage.

Sealless Pumps

2009-06-03T02:40:00.001-07:00

Completely leakproff pumps are available for pumping corrosive, volatile, radioactive and otherwise hazardous liquids. Canned motor pumps are an assembly of a standard centrifugal pump and a squired cage induction motor in a hermetically sealed unit. Modifying a recalculating flow system in a canned motor pumped can allow it to be used in applications at up to 1000 oF (638 oC).

Magnetic drive pumps are an assembly of a rotor, an impeller, product lubricated bearings and a magnetic carrier inside an isolation shell or diaphragm. This rotor is driven by magnets outside outside the shell or diaphragm. No mechanical connection exist between the driven magnet and driving magnets. No seal exist and thus we have the term “sealless.”

Straight Radial Vane High Speed Pumps

For handling volatile liquids at low flow rates and high heads, the straight radial vane impeller in a diffuser casing offer several advantages. Volatile low specific gravity, poor lubricity liquids require larger running clearances, which is not possible with conventional high head multistage centrifugal or positive displacement pumps. High head pumping of this liquids can be handled by operating this completely open impeller at very high speeds through an integral gear increaser and with very large impeller to casing clearance, typically 0.030 to 0.070 in (0.76 to 1.8 mm). Test of one manufacturer’s design have shown this clearance can increase t 0/125 in (3.2 mm) with virtually no change in performance, and consequently there is no need to provide adjustment for impeller axial clearance.

Submersible Motor Driven Wet Pit Pump

2009-05-25T21:23:00.000-07:00

The installation of conventional vertical wet-pit pumps with the motor located above the liquid level may require a considerable length of drive shafting, particularly in the case of deep settings. The addition of this shafting, of the many line bearings, and possibly of an external lubrication system many represent a major portion of the total installed cost of the pumping unit. Furthermore, shaft alignment become more critical, and shaft elongation and power loses increase rapidly as the setting is increased, especially for deep well pump

A great variety of submersible motors have been developed to deviate these shortcoming. Submersible wet-pit pumps eliminate the need of extended shafting, shaft couplings, a mechanical seal or stuffing box, a subsurface motor stand, and to some cases, an expensive pump house. Both vertical turbine and volute type wet-pit pumps may be so driven.

There is of course, no shafting above the pump and the pump and motor unit is supported by the discharge pipe only. No external lubrication is required. The motor is completely enclosed and oil filled and is provided with a thrust bearing to carry the pump down thrust. A mechanical seal is provided at the motor shaft extension, which is connected to the pump shaft with a right coupling. Only a discharge elbow and the electric cable connection are seen above the surface support plate. On occasion, this type of pump is used horizontally as booster pump in a pipeline, and in such cases the elbow at the discharge is eliminated.

Vertical wet-pit volute type sump pumps can be obtained with close coupled submersible motors for drainage sewage, process, and slurry service. The pumps are supported by guide rails that make it possible to lower and raise the pumps by means of a chain hoist. During this operation, the discharge pipe is connected and disconnected without dewatering the tank. Other arrangements use foot supported pumps with rigid discharge piping.

Motor used for this type of construction are usually hermetically sealed, employing a double mechanically sealed oil chamber with a moisture sensing probe to detect any influx of conductive liquid past the outer seal. Controls to start and stop the pump motors can be either an air compressor bubbler system or level sensing switches that tilt when floated.

Small portable pumps are available with flexible discharge hoses and built-in water level motor control switches activated by trapped air pressure. Motor for this pumps are usually oil filled and have a single mechanical shaft seal but are also available in a hermetically sealed design. The submersible motors are cooled by the liquid in which they are immersed and therefore should be run dewatered, although some motors can operate for short periods (10 to 15 minutes) this way.

In pump-motor combination, the motor is cooled by the pumped liquid as it moves through a passage around the sides of the motor. This design also uses a pressurized oil-sealed chamber to assure positive sealing.

Shaft Elongation in Vertical Pumps

2009-05-20T03:07:00.000-07:00

The elongation of a vertical pump shaft is caused by three separate phenomena:

The tensile stress caused by the weight of the rotor.
Tensile stress caused by axial thrust
The thermal expansion of the thrust

In most cases the tensile stress created by the axial thrust is several times greater than that created by the weight. In typical example of a 16,000 gpm pump designed for a 175-ft head and 5o ft long, the elongation caused by the weight of a 1600 lb (726 kg) impeller will be of the other of 0.0033 in. The elongation caused by the axial thrust will be approximately 0.0315 in.

The elongation caused by thermal expansion has to be considered from two angles. Firs, if the shaft and the stationary parts are built of materials that have essentially the same coefficient of expansion, both will expand equally and no significantly the same range of temperature in which they were assembled, no significant relative expansion will take place, even if dissimilar coefficients expansion are involved. Whatever the case, the pump manufacturer take these factors into consideration by providing the necessary vertical and play between the stationary and rotating pump components.

Load of foundations of Vertical Pumps

It the motor support is integral with the pump discharge column, and if the hydraulic thrust is carried by the motor thrust bearing, this thrust is not additive to the deadweight of the pump and of its motor plus the weight of the water contained in the pump, insofar as the load on the foundations is concerned. This is because the pump and motor mounted in this fashion form a self contained entity and all internal forces and stresses are balanced within the entity. If the pump and motor is supported separately, however, and joined by rigid coupling that transmits the pump hydraulic thrust to the motor thrust bearing, the foundation will carry the following heads when the pump is running.

Axial Thrust in Vertical Pumps

2009-05-13T02:40:00.000-07:00

Axial Thrust in Vertical Pump With Single Suction Impeller . The subject of axial thrust in horizontal pumps has already discussed in my article before. When pumps are installed in a vertical position, additional factors need be taken into account when determining the amount and direction of the thrust to be absorbed in the thrust bearings.

The first and most significant of these factors is the weight of the rotating parts, which is a constant downward force for any given pump, completely independent of the pump operating capacity or total head. Since in most cases the single suction impellers of vertical pumps are mounted with the suction eye facing downward, the normal hydraulic axial thrust is exerted downward and the weight of the rotating parts is additive to this axial thrust.

The second factor involves the dynamic force (or change in momentum) caused by the change in the direction of flow, from vertical to either horizontal or partly horizontal, as the pumped liquid flows through the impeller. This force acts upward and balances a small for water having a specific weight (force) of 62.34 lb/ft2.

The Application of Vertical Wet-Pit Pump

2009-04-29T02:44:00.000-07:00

Like all pumps, the vertical wet-pit pump has advantages and disadvantages. One disadvantage is that installation does not require a separate dry pit to collect the pumped liquid. If the impeller (first-stage impeller in multistage pumps) is submerged, no priming problem exists and the pump can be automatically controlled without fear of its ever running dry. Moreover, the available NSPH is greater (except in closed tanks) and often permit in higher rotative speed for the same service conditions. A second advantage is that the motor or driver can be located at any desired height above fixed level.

It has the following mechanical disadvantages:

the possibility of freezing whom idle
similar installation
the inconvenient of lifting out and dismantling of inspection and repair, no matter how small
the pump bearing have a relative short life unless the water and bearing design are ideal.

In the summary the vertical wet-pit pump is the best pump available for some applications. Its not ideal be the most economical for certain installations, a poor for some, and the least desirable for still others,

Volute Pump

2009-04-27T01:29:00.000-07:00

A variety of wet pit pumps are available. The liquid pumped, be it clean water, sewage, abrasive liquids or slurries, dictates whether a semi open or an enclosed impeller will be used, whether the shafting will be open or closed to the liquid pumped, and whether the bearings will be submerged or located above the liquid.

A single volute pump with a single suction enclosed nonclog impeller, no pump-out vanes or wearing ring joints on the back side of the impeller, and enclosed shafting. The pump is design to be suspended from an upper floor by means of a drop pipe and for pumping sewage or other solid laden liquids. To seal against leakage along the shaft at the point where it passes through the casing, a seal chamber or a stuffing box is provided.

In most application these volute pumps have been replaced with vertical wet-pit pump with the stuffing box/seal chamber in the discharge head. This pump is suitable for pumping heavy concentration of solid material (such as sludge or slurries) or in certain food processing application, but other type of impeller can be substituted. Pumped liquid leakage from casing is relieved back to the suction through holes in the support pipe. The seal chamber or stuffing box at the driver floor elevation is used only when gas tight construction is desired. The lower and any intermediate sleeve bearing are grease-lubricated as shown, but gravity feel oil lubrication is also available in other design. The upper anti friction thrust bearing is grease-lubricated. A solid shafts motor and flexible shaft are used.

An interesting design of the wet-pit pump uses a single stage, double suction impeller in a twin volute casing. Because the axial thrust is billings are externally lubricated, either with oil or with water. The lower bearing its lubricated from an external pipe connection.

Propeller Pump

2009-04-24T00:40:00.001-07:00

Originally, the term of vertical propeller pump was applied to vertical wet pit diffuser or turbine pumps with a propeller or axial flow impellers, usually for installation in an open sump with a relatively short setting. Operating head exceeding the capacity of a single stage axial flow impeller might call for a pump of two or more stages or single stage pump with a lower specific speed and a mixed flow impeller. High enough operating heads might demand a pump with mixed flow impellers and two or more stages. For lack of a more suitable name, such high head design have usually been classified as propeller pump also.

Although vertical turbine pump and vertical modified propeller pump are basically the same mechanically and could even be of the same specific speed hydraulically, a basic turbine pump design is suitable for a large number of stage. A modified propeller pump, design, however, is basically intended for a maximum of two or three stages.

Most wet pit drainage, low head irrigation, and storm water installation employ conventional propeller or modified propeller pumps. These pumps have also been used for condenser circulating services, but a specialized design dominates this field. As large power plants are usually located in heavily populated areas, they frequently have to use badly contaminated water (both fresh and salt) as a cooling medium. Such water quickly shortens the life of fabricated steel. Cast iron, bronze, or an even more corrosion resistant cast metal must therefore be used for the column pipe assembly. This requirement means a very heavy pump if large capacities are involved. To avoid the necessity of lifting this large mass for maintenance of the rotating parts, some design are built so that the impeller, diffuser and shaft assembly can be removed from the top without disturbing the column pipe assembly. These design are commonly designated as pullout design.

Like vertical turbine pumps, propeller and modified propeller pumps have been made with both open, and enclosed line shafting except for condenser circulating services, enclosed shafting, using oil as a lubricant but with a grease lubricated tail bearing below the impeller, seems to be favored. Some pumps handling condenser circulating water use enclosed shafting but with water (often from another source) as the lubricant, thus eliminating any possibility of oil getting into circulating water and coating the condenser tubes.

Couplings Jaw

2009-04-22T02:54:00.000-07:00

The Wrap N Snap (WNS) coupling eliminates the need for dismantling connected equipment while replacing or inspecting the elements because of it’s wrap around rubber connecting element. This eliminates excessive downtime on machinery which dramatically improves productivity.

With modular hub design and a spacer option, and a range of prebored hubs, the wrap N Snap (WNS) coupling is perfect for quick installation, maintenance, and is unsurpassed for quality, and flexibility.

WNS Coupling Features:

The WNS coupling allows inspection and replacing within minutes. Modular hub design allow the same hubs to be used for different models. Hubs are fully machined which guarantees a smooth contact surface, ease of alignment and excellent balance. Hubs come prebored and keyed to standard IEC motor shaft sizes. Spacer couplings are available for pump applications. Water, dust, oil and greases do not affect performance.

Selection

Service Factor
Determine appropriate Service Factor from the table.
Design Power
Multiply running power of driven machinery by the service factor. This gives Design Power which is used as a basis for coupling selection.
Coupling Size
Refer to respective table for your required coupling type and read from the appropriate speed column until a power equal to a greater than the Design Power is found.
Bore Size
Refer respective coupling dimensional table to check that the required bores can be accommodated.

Vertical Turbine Pumps

2009-04-20T02:35:00.001-07:00

Vertical turbine pumps were originally developed for pumping water from wells and have been called deep-well-pumps, turbine well pumps, and bore hole pumps. As their application to other fields has increased, the name vertical turbine pumps has been generally adopted by manufacturers. This is not too specific is designation because the term turbine pump has been applied in the past to any pump employing a diffuser. There is now a tendency to designate pumps using diffusion vanes as diffuser pumps to distinguish them from volute pumps. As that designation becomes more universal, applying the term vertical turbine pumps to the construction formerly called turbine well pumps will become more specific.

The larger fields of application for the vertical turbine pump are pumping from well for irrigation and other agricultural purposes, for municipal water supply, and for industrial water supplies, as well as for processing, circulating, refrigerating, and air conditioning. This type of pump has also utilized for brine pumping, mine dewatering, oil field repressuring and other purposes.

Vertical turbine pumps should be designed with a shaft that can be readily raised or lowered from the top to permit proper positioning of the impeller in the bowl. An adequate thrust bearing is also necessary to support the vertical shafting, the impeller, and the hydraulic thrust developed when the pump is in service. As the driving mechanism must also have a thrust bearing to support its vertical shaft, it is usually provided with one large enough to carry the pump parts as well. For this two reasons, the hollow-shaft motor are sometimes made with their own thrust bearings to allow for a belt drive or for drive through a flexible coupling by a solid shaft motor, gear, or turbine. Dual driven pumps usually employ and angle gear with a vertical motor mounted on its top.

Bases and Support for Vertical Pump

2009-04-12T19:22:00.000-07:00

Vertical shaft pumps like horizontal shaft units, must be firmly supported. Depending upon the installation, the unit can be supported at one or several elevations. Vertical unit are seldom supported from walls, but even that type of support to sometimes encountered.

Occasionally, a nominal horizontal shaft pump design is arranged with a vertical shaft and a wall used as the supporting foundation. Regular horizontal shaft units can be used for this purpose without modification, except that the blade-plate is attached to a wall. Careful attention must be given to the arrangement to the pump bearings to prevent the escape of the lubricant. Installation of double suction, single-stage pumps with the shaft in the vertical position are relatively rare, except in some marine or navy applications. Hence, manufacturers have few standard pumps of the kind arrangement so that a portion of the casing forms the support (to be mounted pumps on soleplantes).

Vertical Single Suction Pump

2009-04-08T01:30:00.000-07:00

Vertical single suction pumps with bottom suction are commonly used for larger sewage, water supply or condenser circulating applications. Such pumps are provided with wing feet that are bolted to soleplates grouted in concrete pedestal or piers. Sometimes the wing feet may be grouted right in the pedestal. This must be suitably arranged to provide proper access to any handholes in the pump and to allow clearance for the elbow suction nozzle if these are used.

If a vertical pump is applied to a condensate service or some other service for which the eye of the impeller must be vented to prevent vapor binding, a pump with a bottom single inlet impeller is not desirable because it does not permit effective venting. Neither does vertical pump employing a double suction impeller. The most suitable design for such applications incorporate a top single inlet impeller.

If the driver of a vertical pump can be located immediately above the pump, it is often supported on the pump itself. The shaft of the pump and driver may be connected by flexible coupling, which required that each have its own thrust bearing. If the pump shaft is rigidly coupled to the driver shaft or an extension of the driver shaft, a common thrust bearing is used, normally in the driver.

Although the driving motors are frequently mounted on top of the pump casing, one important reason for the use of the vertical shaft design is the possibility of locating the motors at an elevation sufficiently above the pump to prevent the accidental flooding of the motors. The pump and its driver may be separated by an appreciable length of shafting, which may required already bearing between the two units.

Bearings for vertical dry-pit pumps and for intermediate guide bearings are usually antifriction grease lubricated types to simply the problem of retaining a lubricant in a housing with a shaft projecting vertically through it. Larger units, for which antifriction bearing are not available or desirable, use self-oiling Babbitt steady bearings with spiral oil grooves. The pump is connected by rigid coupling to its motor which is provided with a line and a thrust bearing.

Vertical Pump

2009-04-07T01:45:00.001-07:00

Vertical shaft pump fall into two classifications: dry-pit and wet-pit. Dry pit pumps are surrounded by air, the wet-pit types are either fully or partially submerged in the liquid handled.

Vertical Dry-pit Pumps

Dry pit pumps with external bearings include most small, medium, and large vertical pumps, most medium and drainage and irrigation pumps for medium and high heads, many large condenser circulating and water supply pumps, and many marine pumps. Sometimes the vertical pumps is preferred (especially for marine pumps) because it saves floor space. At other time it is desirable to mount a pump at a low elevation because of suction conditions, and it is also preferable or necessary to have the pump driver at a high elevation. The vertical pump is normally used for large capacity applications because it is more economical than the horizontal type, all factor considered.

Many vertical dry-pit pumps are basically designs with minor modifications (usually in the bearings) to adapt them for vertical shaft drive. This is not true of small and medium sized sewage pumps, however. In this units, purely vertical design in the most popular. Most of these sewage pumps have elbow suction nozzle because of their suction supply is usually taken from a wet well adjacent to the pit in which the pump is installed. The suction elbow usually contains a handhole with a removable cover to provide easy access to the impeller.

The dismantle one of these pumps, the stuffing box head must be unbolted from the casing after the intermediate shaft or the motor and motor stand have been removed. The motor assembly is drawn out upward, complete with the stuffing box head, the bearing housing and the like. This rotor assembly then be completely dismantled at a convention location.

Motor For Hazardous Areas

2009-04-02T21:38:00.000-07:00

Motor used within a hazardous location require a higher level of protection against the risk of harmful occurrences. PPA motors are available in the three most common high protection configurations. Exe, ExnA (formally Exn) and ExtD (formally DIP), all supplied with a protection rating of IP66. Most PPA hazardous area motor versions are available in frame sized 80 to 400. Combination of protection such as Exe and ExtD, or ExnA and ExtD, are also available.

International and Australian Standards

AS/NZS2381.1 specifies general requirement for the selection of electrical equipment and its installation and maintenance, to ensure safe use in areas where handled, stored or otherwise used, and which are therefore potentially hazardous.

The term flammable material includes gases, vapors, liquids, mist, solids and dusts, but does not include those materials which are specifically manufactured as explosives or materials which are inherently explosive.

The requirements of the listed standards apply only to the use of electrical equipment under normal or near normal atmospheric conditions. The requirements specified for hazardous location electrical equipment are supplementary to and not alternative to any requirements which would apply to equipment and installations in non hazardous areas.

Related Geometry Performance of Pump

2009-03-11T02:11:00.001-07:00

Size Effect

For sufficient high NSPH (or sufficient low suction specific speed); and low viscosity for high Reynolds Number), real pump also posses a strong size effect on efficiency. This is because in normal manufacturing processes, the clearance and preventing internal leakage do not scale up in proportion to the size, nor do the surface roughness height. Thus a larger pump tends to be more efficient. Strictly speaking, however, the geometry of the larger pump is not the same as that of the smaller pump, and this forces one to modify.

Viscosity Effect

Centrifugal pump geometries have not generally been optimized versus Reynolds number-often because the effect on hydraulic shape is not very great except for the highest viscosity of the pumpage, and a given application can sometime experience a substantial range of viscosity. Studies of conventional centrifugal pump over a range of Reynolds number have been combined in monographic chart in the hydraulic Institute Standards, which yield correction factor to the head, efficiency and flow rate of the BEP of a low viscosity pump in order to obtain the BEP of that pump when operating in higher viscosity.

NSPH Effect

In many excess, the available NSPH is low enough, or the suction specific speed, at which the pump stage must operate is high enough for significant two phase activity to exist within the impeller. This is to expected in centrifugal impeller of water pump if the available speed is greater than about 3 to 4.

Heat Exchanger Design

2009-02-11T20:10:00.000-08:00

Design methods for several important classes of process heat-transfer equipment are presented in the following article. Mechanical descriptions and specifications of equipment are given in this section and should be read in conjunction with the use of this material. It is impossible to present here a comprehensive treatment of heat-exchanger selection, design, and application. The best general references in this field are Hewitt, Shires, and Bott, Process Heat Transfer, CRC Press, Boca Raton, FL, 1994; and Schlünder (ed.), Heat Exchanger Design Handbook, Begell House, New York, 1983.

Approach to Heat-Exchanger Design The proper use of basic heat-transfer knowledge in the design of practical heat-transfer equipment is an art. Designers must be constantly aware of the differences between the idealized conditions for and under which the basic knowledge was obtained and the real conditions of the mechanical expression of their design and its environment. The result must satisfy process and operational requirements (such as availability, flexibility, and maintainability) and do so economically. An important part of any design process is to consider and offset the consequences of error in the basic knowledge, in its subsequent incorporation into a design method, in the translation of design into equipment, or in the operation of the equipment and the process. Heat-exchanger design is not a highly accurate art under the best of conditions.

The design of a process heat exchanger usually proceeds through the following steps:

Process conditions (stream compositions, flow rates, temperatures, pressures) must be specified.
Required physical properties over the temperature and pressure ranges of interest must be obtained.
The type of heat exchanger to be employed is chosen.
A preliminary estimate of the size of the exchanger is made, using a heat-transfer coefficient appropriate to the fluids, the process, and the equipment.
A first design is chosen, complete in all details necessary to carry out the design calculations.
The design chosen in step 5 is evaluated, or rated, as to its ability to meet the process, specifications with respect to both heat transfer and pressure drop.
On the basis of the result of step 6, a new configuration is chosen if necessary and step 6 is repeated. If the first design was inadequate to meet the required heat load, it is usually necessary to increase the size of the exchanger while still remaining within specified or feasible limits of pressure drop, tube length, shell diameter, etc. This will sometimes mean going to multiple-exchanger configurations. If the first design more than meets heat-load requirements or does not use all the allowable pressure drop, a less expensive exchanger can usually be designed to fulfill process requirements.
The final design should meet process requirements (within reasonable expectations of error) at lowest cost. The lowest cost should include operation and maintenance costs and credit for ability to meet long-term process changes, as well as installed (capital) cost.

Exchangers should not be selected entirely on a lowest-first-cost basis, which frequently results in future penalties.

Pressure Reducing Valve

2009-01-29T19:29:00.001-08:00

This valve is use for reduce pressure like from high pressure compressor or high pressure steam from boiler.

Fully machined forged valve
Allows controlled start-up and shut-down of different loops in the power plant with a minimum of heat losses
Resistant against thermal stress and requires no additional preheating above the demand for superheated steam in the inlet
Cage plug for flow control that results in a protected seat area and high range ability – 50:1 or more Pressure reducing pipes in outlet to create a multistep pressure reduction providing for minimum noise and vibrations
Special seal bonnet to guarantee tightness and easy maintenance
Bolted bonnet also used for low pressure class

Applications

The BTG valve type VLR has been designed as a pressure reducing valve for high pressure and/or low pressure systems where a steam conditioning valve is not applicable.

The Kv/Cv-value of the valve depends on the pressure ratio p1/p2 and must – for each valve – be calculated in the BTG computer program, where all throttling points in the valve are taken into consideration. Certified dimensional drawing will be supplied by CCI.

Main applications – high pressure system

Pressure control/turbine bypass.
Controlled pressure build-up in the boiler.
Protection against exceeding the design pressure. Note!

However without the safety function for which the valve VLR-O should be used.
Main applications – low pressure system

Controlled pressure build-up in the reheater.
Pressure control/bypass of the intermediate and low pressure part of the turbine. This will assist in avoiding release of the safety valves and consequently helps to prevent large condensate losses.
Protection of the condenser in case of disturbances.
Turbine extraction control

Main duties – process industry

Controlled pressure in steam pipes to the process – in parallel with the back pressure turbine.
Provides the process with steam flow during start-up of the turbine.
Fast take-over of the whole steam flow from boiler to process when the turbine stops/trips.

Centrifugal Pump With Magnetic Bearing

2009-01-28T00:10:00.000-08:00

Magnetic bearing maintain the rotor of a pump in suspension through the force of attraction of a magnetic circuit. Thus although they bear up to weight and hydraulic loads of the impellers and the shaft, they are not really bearings in the traditional sense of the rotating and stationary surfaces bearing on one another. The supporting magnet circuit for each bearing includes stationary magnets in a stator surrounding the shaft, a laminated rotor that on the shaft, and the shaft itself. The stator consists of electromagnet in the traditional heteropolar design, and if a homopolar design is employed, permanent magnets can be added. Sensors monitor the position of the shaft and signal a controller to adjust the magnetic loads to keep the shaft to within about 0.001 in (26 μm) of the desired position.

Magnetic bearings are found in small, high speed turbomachinery such as high speed, multistage, axial flow turbomelecular vacuum pumps. They were introduced into large turbomachinery in the nearly 1980s, mainly in gas compressors and truboexpanders. Their use and acceptance has grown slowly but steady since then. Pump applications of a signings can provide a technically sound bearing with maintenance and operating advantages, including zero wear. However, due to the technical complexity of magnetic bearing systems, the economics of scale associated with production quantities are required to make these systems affordable.

Two representative magnetic bearing equipped pumps are summarize in the table below. One is a multistage boiler feedwater pump and the other a single stage double suction hydrocarbon process pump. The multistage pump was retrofitted with magnetic bearings, together with another identical pump that still contains the oil lubricated bearing, both installed in an electric generating station. The magnetic bearing pump is not encumbered with the usual complexity of a bearing lubrication system.

Parameter	Multistage Pump	Single Stage Pump
Power, hp (MW)	610 (0.46)	800 (0.6)
Rated speed, rpm	3580	1780
Shaft weight, lb (kN)	800 (3.6)	Thrust end: 930 (4.1) Drive end: 1415 (6.3)
Thrust bearing design load, lb (kN)	4000 (17.8)	4000 (17.8)
Number of Stages	8	1

Pump Therminology

2009-01-26T18:32:00.001-08:00

Displacement
Discharge of a fluid from a vessel by partially or completely displacing its internal volume with a second fluid or by

mechanical means is the principle upon which a great many fluid transport devices operate. Included in this group are reciprocating piston and diaphragm machines, rotary-vane and gear types, fluid piston compressors, acid eggs, and air lifts.

The large variety of displacement-type fluid-transport devices makes it difficult to list characteristics common to each. However, for most types it is correct to state that (1) they are adaptable to high pressure operation, (2) the flow rate through the pump is variable (auxiliary damping systems may be employed to reduce the magnitude of pressure pulsation and flow variation), (3) mechanical considerations limit maximum throughputs, and (4) the devices are capable of efficient performance at extremely low-volume throughput rates.

Centrifugal Force
Centrifugal force is applied by means of the centrifugal pump or compressor. Though the physical appearance of the many types of centrifugal pumps and compressors varies greatly, the basic function of each is the same, i.e., to produce kinetic energy by the action of centrifugal force and then to convert this energy into pressure by efficiently reducing the velocity of the flowing fluid.

In general, centrifugal fluid-transport devices have these characteristics: discharge is relatively free of pulsation; mechanical design lends itself to high throughputs, capacity limitations are rarely a problem; the devices are capable of efficient performance over a wide range of pressures and capacities even at constant-speed operation; discharge pressure is a function of fluid density; and these are relatively small high-speed devices and less costly.

A device which combines the use of centrifugal force with mechanical impulse to produce an increase in pressure is the axial-flow compressor or pump. In this device the fluid travels roughly parallel to the shaft through a series of alternately rotating and stationary radial blades having airfoil cross sections. The fluid is accelerated in the axial direction by mechanical impulses from the rotating blades; concurrently, a positive-pressure gradient in the radial direction is established in each stage by centrifugal force. The net pressure rise per stage results from both effects.

Electromagnetic Force
When the fluid is an electrical conductor, as is the case with molten metals, it is possible to impress an electromagnetic field around the fluid conduit in such a way that a driving force that will cause flow is created. Such pumps have been developed for the handling of heat-transfer liquids, especially for nuclear reactors.

Transfer of Momentum
Deceleration of one fluid (motivating fluid) in order to transfer its momentum to a second fluid (pumped fluid) is a principle commonly used in the handling of corrosive materials, in pumping from inaccessible depths, or for evacuation. Jets and eductors are in this category.

Absence of moving parts and simplicity of construction have frequently justified the use of jets and eductors. However, they are relatively inefficient devices. When air or steam is the motivating fluid, operating costs may be several times the cost of alternative types of fluid-transport equipment. In addition, environmental considerations in today’s chemical plants often inhibit their use.

Mechanical Impulse
The principle of mechanical impulse when applied to fluids is usually combined with one of the other means of imparting motion. As mentioned earlier, this is the case in axial-flow compressors and pumps. The turbine or regenerative-type pump is another device which functions partially by mechanical impulse.

Measurement of Performance
The amount of useful work that any fluid-transport device performs is the product of (1) the mass rate of fluid flow through it and (2) the total pressure differential measured immediately before and after the device, usually expressed in the height of column of fluid equivalent under adiabatic conditions. The first of these quantities is normally referred to as capacity, and the second is known as head.

Capacity
This quantity is expressed in the following units. In SI units capacity is expressed in cubic meters per hour (m3/h) for both liquids and gases. In U.S. customary units it is expressed in U.S. gallons per minute (gal/min) for liquids and in cubic feet per minute

(ft3/min) for gases. Since all these are volume units, the density or specific gravity must be used for conversion to mass rate of flow. When gases are being handled, capacity must be related to a pressure and a temperature, usually the conditions prevailing at the machine inlet. It is important to note that all heads and other terms in the following equations are expressed in height of column of liquid.

Typical parts in a centrifugal pump

2008-12-22T20:22:00.000-08:00

A centrifugal pump is a relatively simple pump. Design, types and numbers of parts vary depending on centrifugal pump brand, type and configuration.

Typical main pump parts:

Casing/backplate:

Contains impeller where fluid is transferred from inlet to outlet.
Includes inlet and outlet ports.
Typically flexible port orientation.
Typically fitted to an adapter

Shaft:

Rotates impeller which is fixed to it.
Is fixed to the motor and rotates with it.

Impeller:

Transfers fluid from inlet to outlet with increased capacity and pressure
Is fixed on the shaft and rotates with it.
Typical types are open, semi-open or closed.

Shaft seal:

Seals between rotating shaft and stationary casing.
Typically a mechanical seal, external or internal.
Typically available as single, single flushed and double flushed seal.

Adapter:

Fixes pump casing to the motor.

Motor:

Rotates shaft (impeller) which is fixed to it.
Typically a 3-phase electrical motor.
Typically available for various electrical site supplies (voltage and frequency).
Typically available in various protection classes (flameproof etc.).

Other parts:

Seals, motor cover, seal flushing, coupling/base (base-mounted pump).

Typical materials:

Steel parts of 316L or 304 stainless steel.
Elastomers of NBR, EPDM, FPM, PTFE.

The Principle of a centrifugal pump

2008-12-15T19:39:00.001-08:00

The centrifugal pump transfers fluid at a certain capacity from one point to another in a process. The pump builds up fluid pressure to overcome losses in the process. Capacity and pressure are created by the rotating impeller inside the pump casing.

General principle:

· Fluid enters the pump casing and impeller center and is forced into a circular movement by the impeller vanes and the centrifugal force. The fluid thus leaves the casing with increased pressure and velocity.

· Typically suitable for low viscous, non-particulate and non-aerated fluids such as beer, CIP, cream, juice, milk, soft drinks, water etc.

Single-stage principle:

The fluid inlet, the built-up of velocity and pressure and the fluid outlet all happens in one stage (one casing and one impeller).

Multi-stage principle:

· Fluid enters the pump casing and impeller center, and fluid pressure and velocity are built up in the first stage (casing and impeller) similar to the single-stage pump.

· Fluid with increased pressure and velocity is directed to the second stage (casing and impeller), where the fluid pressure and velocity is further increased.

· The result is a pressure increase (boost) in each stage, where the total pressure increase depends on the number of stages in the pump.

· Typically available with 2-4 stages.

Priming of a centrifugal pump:

· The pump casing should always be filled with fluid before starting the pump to ensure correct operation.

· The pump can operate with a positive inlet pressure (flooded inlet) or with a negative inlet pressure (suction lift).

· For suction lift, fluid can remain in the pump casing by using a non-return valve in the suction line.

Basic of Centrifugal Pump

2008-12-08T19:39:00.000-08:00

A centrifugal pump is typically the most common sanitary pump type used in sanitary processes. Benefots include a relatively low purchase cost, wide selection, simple design and easy maintenance.

The various aspects of centrifugal pumps are very important to consider when dealing with flow technology and flow equipment. Understanding the aspects of centrifugal pumps makes it easier to select correct pumps, optimize processes and minimize costs.

Process with centrifugal pump (principle)

On the process itself centrifugal pump can arrange in many type, the example of centrifugal pump arrangement on the process system can see on the picture bellow:

Centrifugal Pump Type

Centrifugal pump design can see the parts assembly as follows:

Centrifugal Pump Design

Examples of centrifugal pumps

A centrifugal pump is used in processes with non-viscous and nonparticulate fluids, e.g. beer, CIP, cream, milk, soft drink and purified water.
There are typically many types of centrifugal pumps available for various types of applications.
The main parts of a centrifugal pump are motor, shaft, adapter, shaft seal, impeller, casing and seals.
A centrifugal pump is typically selected from a pump curve or a pump selection program.

Pump performance curve

2008-12-04T00:33:00.000-08:00

The head and flow rate determine the performance of a pump, which is graphically shown in Figure 5 as the performance curve or pump characteristic curve. The figure shows a typical curve of a centrifugal pump where the head gradually decreases with increasing flow.

As the resistance of a system increases, the head will also increase. This in turn causes the flow rate to decrease and will eventually reach zero. A zero flow rate is only acceptable for a short period without causing to the pump to burn out.

Electrical Energy Equipment: Pumps and Pumping Systems

Figure 5. Performance Curve of a Pump

Pump operating point
The rate of flow at a certain head is called the duty point. The pump performance curve is
made up of many duty points. The pump operating point is determined by the intersection of the system curve and the pump curve as shown in Figure 6.

Figure 6. Pump Operating Point (US DOE, 2001)

Pump suction performance (NPSH)
Cavitation or vaporization is the formation of bubbles inside the pump. This may occur when at the fluid’s local static pressure becomes lower than the liquid’s vapor pressure (at the actual temperature). A possible cause is when the fluid accelerates in a control valve or around a pump impeller.

Vaporization itself does not cause any damage. However, when the velocity is decreased and pressure increased, the vapor will evaporate and collapse.

This has three undesirable effects:

Erosion of vane surfaces, especially when pumping water-based liquids
Increase of noise and vibration, resulting in shorter seal and bearing life
Partially choking of the impeller passages, which reduces the pump performance and can lead to loss of total head in extreme cases.

The Net Positive Suction Head Available (NPSHA) indicates how much the pump suction exceeds the liquid vapor pressure, and is a characteristic of the system design. The NPSH Required (NPSHR) is the pump suction needed to avoid cavitation, and is a characteristic of the pump design.

Pumping System Characteristics

2008-12-02T18:31:00.001-08:00

Resistance of the system:
Head Pressure is needed to pump the liquid through the system at a certain rate. This pressure has to be high enough to overcome the resistance of the system, which is also called “head”. The total head is the sum of static head and friction head:

1. Static head

Static head is the difference in height between the source and destination of the pumped
liquid (see Figure 2a). Static head is independent of flow (see Figure 2b). The static head at a certain pressure depends on the weight of the liquid and can be calculated with this equation:

Head (in feet) = (Pressure (psi) X 2.31)/Specific gravity

Static head consists of:

Static suction head (hS): resulting from lifting the liquid relative to the pump center line. The hS is positive if the liquid level is above pump centerline, and negative if the liquid level is below pump centerline (also called “suction lift)
Static discharge head (hd): the vertical distance between the pump centerline and the surface of the liquid in the destination tank.

2. Friction head (hf)

This is the loss needed to overcome that is caused by the resistance to flow in the pipe and fittings. It is dependent on size, condition and type of pipe, number and type of pipe fittings, flow rate, and nature of the liquid. The friction head is proportional to the square of the flow rate as shown in figure 3. A closed loop circulating system only exhibits friction head (i.e. not static head).

Electrical Energy Equipment: Pumps and Pumping Systems

In most cases the total head of a system is a combination of static head and friction head as shown in Figures 4a and 4b.

Pumping Systems

2008-12-01T20:02:00.000-08:00

Pumping systems account for nearly 20% of the world’s electrical energy demand and range from 25-50% of the energy usage in certain industrial plant operations (US DOE, 2004).

Pumps have two main purposes:

Transfer of liquid from one place to another place (e.g. water from an underground aquifer into a water storage tank)
Circulate liquid around a system (e.g. cooling water or lubricants through machines and equipment)

The main components of a pumping system are:

Pumps (different types of pumps are explained in previous section)
Prime movers: electric motors, diesel engines or air system
Piping, used to carry the fluid
Valves, used to control the flow in the system
Other fittings, controls and instrumentation
End-use equipment, which have different requirements (e.g. pressure, flow) and therefore determine the pumping system components and configuration.

Examples include heat exchangers, tanks and hydraulic machines. Electrical Energy Equipment: Pumps and Pumping Systems.

The pump and the prime mover are typically the most energy inefficient components.

Overall Heat Exchanger Coeficient

2008-11-27T14:42:00.000-08:00

The basic design equation for a heat exchanger is

dA = dQ/U DT (11-1)

where dA is the element of surface area required to transfer an amount of heat dQ at a point in the exchanger where the overall heat transfer coefficient is U and where the overall bulk temperature difference between the two streams is DT. The overall heat-transfer coefficient is related to the individual film heat-transfer coefficients and fouling and wall resistances by Eq. (11-2). Basing Uo on the outside surface area Ao results in

Uo = 1/ (1/ho + Rdo + xAo/KwAwm + (1/hi + Rdi)Ao/A ) (11-2)

Equation (11-1) can be formally integrated to give the outside area required to transfer the total heat load QT:

To integrate Eq. (11-3), Uo and DT must be known as functions of Q. For some problems, Uo varies strongly and nonlinearly throughout the exchanger. In these cases, it is necessary to evaluate Uo and DT at several intermediate values and numerically or graphically integrate. For many practical cases, it is possible to calculate a constant mean overall coefficient Uom from Eq. (11-2) and define a corresponding mean value of DTm, such that

Ao = QT /Uμm dTm (11-4)

Care must be taken that Uo does not vary too strongly, that the proper equations and conditions are chosen for calculating the individual coefficients, and that the mean temperature difference is the correct one for the specified exchanger configuration.

Mean Temperature Difference The temperature difference between the two fluids in the heat exchanger will, in general, vary from point to point. The mean temperature difference (DTm or MTD) can be calculated from the terminal temperatures of the two streams if the following assumptions are valid:

All elements of a given fluid stream have the same thermal history in passing through the exchanger.*
The exchanger operates at steady state.
The specific heat is constant for each stream (or if either stream undergoes an isothermal phase transition).
The overall heat-transfer coefficient is constant.
Heat losses are negligible.

Heat Exchanger Type

2008-11-17T01:42:00.000-08:00

TEMA-style shell-and-tube-type exchangers constitute the bulk of the unfired heat-transfer equipment in chemical-process plants, although increasing emphasis has been developing in other designs. These exchangers are illustrated in Fig. below, and their features are summarized in list.

TEMA Numbering and Type Designation Recommended practice for the designation of TEMA-style shell-and-tube heat exchangers by numbers and letters has been established by the Tubular Exchanger Manufacturers Association (TEMA). This information from the sixth edition of the TEMA Standards is reproduced in the following paragraphs.

It is recommended that heat-exchanger size and type be designated by numbers and letters.

1. Size: Sizes of shells (and tube bundles) shall be designated by numbers describing shell (and tube-bundle) diameters and tube lengths as follows:

2. Diameter: The nominal diameter shall be the inside diameter of the shell in inches, rounded off to the nearest integer. For kettle reboilers the nominal diameter shall be the port diameter followed by the shell diameter, each rounded off to the nearest integer.

3. Length: The nominal length shall be the tube length in inches. Tube length for straight tubes shall be taken as the actual overall length. For U tubes the length shall be taken as the straight length from end of tube to bend tangent.

4. Type: Type designation shall be by letters describing stationary head, shell (omitted for bundles only), and rear head, in that order, as indicated in Figure.

Typical Examples

(A) Split-ring floating-heat exchanger with removable channel and cover, single-pass shell, 591-mm (23d-in) inside diameter with tubes 4.9 m (16 ft) long. SIZE 23–192 TYPE AES.

(B) U-tube exchanger with bonnet-type stationary head, split-flow shell, 483-mm (19-in) inside diameter with tubes 21-m (7-ft) straight length. SIZE 19–84 TYPE GBU.

(C) Pull-through floating-heat-kettle-type reboiler having stationary head integral with tube sheet, 584-mm (23-in) port diameter and 940-mm (37-in) inside shell diameter with tubes 4.9-m (16-ft) long. SIZE 23/37–192 TYPE CKT.

(D) Fixed-tube sheet exchanger with removable channel and cover, bonnettype rear head, two-pass shell, 841-mm (33s-in) diameter with tubes 2.4 m (8-ft) long. SIZE 33–96 TYPE AFM.

(E) Fixed-tube sheet exchanger having stationary and rear heads integral with tube sheets, single-pass shell, 432-mm (17-in) inside diameter with tubes 4.9-m (16-ft) long. SIZE 17–192 TYPE CEN. Functional Definitions Heat-transfer equipment can be designated by type (e.g., fixed tube sheet, outside packed head, etc.) or by function (chiller, condenser, cooler, etc.). Almost any type of unit can be used to perform any or all of the listed functions. Many of these terms have been defined by Donahue [Pet. Process., 103 (March, 1956)].

Equipment Function:

Chiller: Cools a fluid to a temperature below that obtainable if water only were used as a coolant. It uses a refrigerant such as ammonia or Freon.

Condenser: Condenses a vapor or mixture of vapors, either alone or in the presence of a noncondensable gas. Partial condenser Condenses vapors at a point high enough to provide a temperature difference sufficient to preheat a cold stream of process fluid. This saves heat and eliminates the need for providing a separate preheated (using flame or steam). Final condenser condenses the vapors to a final storage temperature of approximately 37.8°C (100°F). It uses water cooling, which means that the transferred heat is lost to the process.

Cooler: Cools liquids or gases by means of water. Exchanger Performs a double function: (1) heats a cold fluid by (2) using a hot fluid which it cools. None of the transferred heat is lost.

Heater: Imparts sensible heat to a liquid or a gas by means of condensing steam or Dowtherm.

Reboiler: Connected to the bottom of a fractionating tower, it provides the reboil heat necessary for distillation. The heating medium may be either steam or a hot-process fluid.

Thermosiphon: Natural circulation of the boiling medium is reboiler obtained by maintaining sufficient liquid head to provide for circulation. Forced-circulation A pump is used to force liquid through the reboiler.

Steam generator: Generates steam for use elsewhere in the plant by using the available high-level heat in tar or a heavy oil.

Superheater: Heats a vapor above the saturation temperature.

Vaporizer: A heater which vaporizes part of the liquid. Waste-heat boiler Produces steam; similar to steam generator, except that the heating medium is a hot gas or liquid produced in a chemical reaction.

Lift Check Valve and Titling Disk Check Valve

2008-11-10T00:51:00.001-08:00

Lift Check Valves

These valves are made in three styles. Vertical lift check valves are for installation in vertical lines, where the flow is normally upward; globe check valves are for use in horizontal lines; angle check valves are for installation where a vertical line with upward flow turns horizontal. Globe and angle

Tilting-Disk Check Valves

These valves may be installed in a horizontal line or in lines in which the flow is vertically upward. The pivot point is located so that the distribution of pressure in the fluid handled speeds the closing but arrests slamming. Compared with swing check valves of the same size, pressure drop is less at low velocities but greater at high velocities.

Closure at the instant of reversal of flow is most nearly attained in these valves. This timing of closure is not the whole solution to noise and shock at check valves. For example, if cessation of pressure at the inlet of a valve produces flashing of the decelerating stream downstream from the valve or if stoppage of flow is caused by a sudden closure of a valve some distance downstream from the check valve and the stoppage is followed by returning water hammer, slower closure may be necessary. For these applications, tilting-disk check valves are equipped with external dashpots. They are also available with low-cost insert bodies.

Valve Trim various alloys are available for valve parts such as seats, disks, and stems which must retain smooth finish for successful operation. The problem in seat materials is fivefold:

Resistance to corrosion by the fluid handled and to oxidation at high temperatures,
Resistance to erosion by suspended solids in the fluid,
Prevention of galling (seizure at point of contact) by differences in material or hardness or both,
Maintenance of high strength at high temperature, and
Avoidance of distortion.

All valve trim materials have coefficients of thermal expansion which exceed those of cast or forged carbon steel by 24 to 45 percent and tend to cause distortion of seats and disks. To some extent leakage from this cause is prevented by closing the valve more tightly. Inserting a ring of high-temperature elastomeric or plastic, either in or alongside the trim metal in the seat or disk, prevents leakage from this cause.

Butterfly and Check Valve

2008-11-03T06:00:00.000-08:00

Butterfly Valves

These valves occupy less space in the line than any other valves. Relatively tight sealing without excessive operating torque and seat wear is accomplished by a variety of methods, such as resilient seats, piston rings on the disk, and inclining the stem to limit contact between the portions of disk closest to the stem and the body seat to a few degrees of curvature.

Fluid-pressure distribution tends to close the valve. For this reason, the smaller manually operated valves have a latching device on the handle, and the larger manually operated valves use worm gearing on the stem. This hydraulic unbalance is proportional to the pressure drop and, with line velocities exceeding 7.6 m/s (25 ft/s), is the principal component in the torque required to operate the valves. Compared with other valves for low-pressure drops, these valves can be operated by smaller hydraulic cylinders. In this service butterfly valves with insert bodies for bolting between existing flanges with bolts that pass by the body are the lowest-first-cost valve in pipe sizes 10 in and larger. Pressure drop is quite high compared with that of gate valves.

Swing Check Valves

These valves are used to prevent reversal of flow. Normal design is for use only in horizontal lines, where the force of gravity on the disk is at a maximum at the start of closing and at a minimum at the end of closing. Unlike most other valves, check valves are more likely to leak at low pressure than at high pressure, since fluid pressure alone forces the disk to conform to the seat. For this reason elastomers are often mounted on the disk. Swing check valves are available with low cost insert bodies. Other kind of check valve are lift check valve.

Angle Valve, Diaphragm Valve

2008-10-28T22:19:00.000-07:00

Angle Valves

These valves are similar to globe valves; the same bonnet, stem, and disk are used for both (Fig. Top). They combine an elbow fitting and a globe valve into one component with a substantial saving in pressure drop. Flanged angle valves are easier to remove and replace than flanged globe valves.

Diaphragm Valves

These valves are limited to pressures of approximately 50 lbf/in2 (Fig. Middle). The fabric-reinforced diaphragms may be made from natural rubber, from a synthetic rubber, or from natural or synthetic rubbers faced with Teflon* fluorocarbon resin.

The simple shape of the body makes lining it economical. Elastomers have shorter lives as diaphragms than as linings because of flexing but still provide satisfactory service. Plastic bodies, which have low moduli of elasticity compared with metals, are practical in diaphragm valves since alignment and distortion are minor problems.

These valves are excellent for fluids containing suspended solids and can be installed in any position. Models in which the dam is very low, reducing pressure drop to a negligible quantity and permitting complete drainage in horizontal lines, are available. However, drainage can be obtained with any model simply by installing it with the stem horizontal. The only maintenance required is replacement of the diaphragm, which can be done very quickly without removing the valve from the line.

Plug Cocks

These valves (Fig. Bottom) are limited to temperatures below 260°C (500°F) since differential expansion between the plug and the body results in seizure. The size and shape of the port divide these valves into different types. In order of increasing cost they are short venturi, reduced rectangular port; long venturi, reduced rectangular port; full rectangular port; and full round port.

In lever-sealed plug cocks, tapered plugs are used. The plugs are raised by turning one lever, rotated by another lever, and reseated by the first lever. Lubricated plug cocks may use straight or tapered plugs. The tapered plugs may be raised slightly, to reduce turning

effort, by injection of the lubricant, which also acts as a seal. Plastic is used in nonlubricated plug cocks as a body liner, a plug coating, or port seals in the body or on the plug.

In plug cocks other than lever-sealed plug cocks, the contact area between plug and body is large, and gearing is usually used in sizes 6 in and larger to minimize operating effort. There are several leversealed plug cocks incorporating mechanisms which convert the rotary motion of a handwheel into sequenced motion of the two levers.

For lubricated plug cocks, the lubricant must have limited viscosity change over the range of operating temperature, must have low solubility in the fluid handled, and must be applied regularly. There must be no chemical reaction between the lubricant and the fluid which would harden or soften the lubricant or contaminate the fluid. For these reasons, lubricated plug cocks are most often used when there are a large number handling the same or closely related fluids at approximately the same temperature. Lever-sealed plug cocks are used for throttling service. Because of the large contact area between plug and body, if a plug cock is operable, there is little likelihood of leakage when closed, and the handle position is a clearly visible indication of the valve position.

CONTROL VALVES

2008-10-25T23:12:00.001-07:00

A control valve consists of a valve, an actuator, and possibly one or more valve-control devices. The valves discussed in this section are applicable to throttling control (i.e., where flow through the valve is regulated to any desired amount between maximum and minimum limits). Other valves such as check, isolation, and relief valves are addressed in the next subsection. As defined, control valves are automatic control devices that modify the fluid flow rate as specified by the controller.

Valves are categorized according to their design style. These styles can be grouped into type of stem motion—linear or rotary. The valve stem is the rod, shaft, or spindle that connects the actuator with the closure member (i.e., a movable part of the valve that is positioned in the flow path to modify the rate of flow). Motion of either type is known as travel. The major categories are described briefly below.

Globe Control Valve

The most common linear stem-motion control valve is the globe valve. The name comes from the globular shaped cavities around the port. In general, a port is any fluid passageway, but often the reference is to the passage that is blocked off by the closure member when the valve is closed. In globe valves, the closure member is called a plug. The plug in the valve shown in Fig 1 is guided by a large-diameter port and moves within the port to provide the flow control orifice of the valve. A very popular alternate construction is a cage-guided plug as illustrated in Fig.2. In many such designs, openings in the cage provide the flow control orifices. The valve seat is the zone of contact between the moving closure member and the stationary valve body, which shuts off the flow when the valve is closed. Often the seat in the body is on a replaceable part known as a seat ring. This stationary seat can also be designed as an integral part of the cage. Plugs may also be port-guided by wings or a skirt that fits snugly into the seat-ring bore.

One distinct advantage of cage guiding is the use of balanced plugs in single-port designs. The unbalanced plug depicted in Fig. 1 is subjected to a static pressure force equal to the port area times the valve pressure differential (plus the stem area times the downstream pressure) when the valve is closed. In the balanced design (Fig. 2), note that both the top and bottom of the plug are subjected to the same downstream pressure when the valve is closed. Leakage via the plug-to-cage clearance is prevented by a plug seal. Both plug types are subjected to hydrostatic force due to internal pressure acting on the stem area and to dynamic flow forces when the valve is flowing.

The plug, cage, seat ring, and associated seals are known as the trim. A key feature of globe valves is that they allow maintenance of the trim via a removable bonnet without removing the valve body from the line. Bonnets are typically bolted on but may be threaded in smaller sizes.

Ball Valve

2008-10-19T21:27:00.000-07:00

These valves are limited to temperatures that have little effect on their plastic seats. Since the sealing element is a ball, its alignment with the axis of the stem is not essential to tight shutoff. In free-ball valves the ball is free to move axially.

Pressure differential across the valve forces the ball in the closed position against the downstream seat and the latter against the body. In fixed-ball valves, the ball rotates on stem extensions, with the bearings sealed with O rings. Plastic seats may be compressed or spring loaded against the ball and the body by the assembly of the valves, or they may be forced against the ball by pressure across the valve acting against O rings which seal between the seat and the body.

Ball valves in which the ball and seats are inserted from above are known as top-entry ball valves. Replacement of seats is easiest in this type. The others are known as split-body valves. Some of these incorporate bolted assembly which permits their use as joints for assembly of the piping. Replacement of seats in this type is easiest when the body consists of three pieces with the ball and the seats contained in the middle piece.

For the larger sizes in high-pressure service, the fixed-ball type with O-ring seat seals requires less operating effort. However, these require two different plastic materials with resistance to the fluid and its temperature. Like plug cocks, ball valves may be either restricted port or full-port, but the ports are always rounded and pressure drop is low.

Globe Valves

2008-10-16T00:29:00.001-07:00

These valve are designed as either inside screw rising-stem or outside-screw rising-stem. Small valves generally are of the inside-screw type, while in larger sizes the outside-screw type is preferred. In most designs the disks are free to rotate on the stems; this prevents galling between the disk and the seat.

In the larger sizes, with conical seats, this swivel may permit enough misalignment to prevent proper sealing between the disk and the seat. When the valve is close to an elbow on the upstream side, the swivel also permits uneven distribution of the fluid to spin the disk on the stem. Guides above the disk, below the disk, or both are used to prevent misalignment and spinning.

Misalignment can also be prevented by the use of spherical seats and designing the disk so that the pressure point of the stem on the disk is at the center of the sphere. In some designs, spinning and misalignment are prevented by rigidly attaching the disk to the stem, preventing rotation of the stem by lugs which ride along the yoke, and using a yoke bushing as in outside screw-and-yoke gate valves. Large globe valves should be installed with stems vertical. Globe valves are preferably installed with the higher-pressure side connected to the top of the disk. Exceptions occur (1) when blocked flow caused by separation of the disk from the stem would damage equipment or (2) when the valve is installed in seldom-used vertical drain lines in which accumulation of rust, scale, or sludge might prevent opening the valve.

Pressure drop through globe valves is much greater than that for gate valves. In Y-type globe valves, the stem and seat are at about 45° to the pipe instead of 90°. This reduces pressure drop but impairs alignment of seat and disk.

Globe valves in horizontal lines prevent complete drainage. Seat-wiper valves in which the disk may be rotated by a separate stem inside and concentric with the main stem are used to clear the seats of solid deposits.

Gate Valves

2008-10-12T19:52:00.001-07:00

These valves are designed in two types. The wedge-shaped-gate, inclined-seat type is most commonly used. The wedge gate is usually solid but may be flexible (partly cut into halves by a plane at right angles to the pipe) or split (completely cleft by such a plane). Flexible and split wedges minimize galling of the sealing surfaces by distorting more easily to match angularly misaligned seats. In the double-disk parallel-seat type, an inclined-plane device mounted between the disks converts stem force to axial force, pressing the disks against the seats after the disks have been positioned for closing. This gate assembly distorts automatically to match both angular misalignment of the seats and longitudinal shrinkage of the valve body on cooling.

When shearing high-velocity flow of dense fluids, the gate assemblies shake violently, and for this service solid-wedge or flexible wedge valves are preferred. When valve operation is manual, small bypass valves installed in parallel with the main valve may be used to eliminate the shake problem and to minimize manual effort in opening and closing the valves. Double-disk parallel-seat valves should be installed with the stem essentially vertical. All wedge gate valves are equipped with tongue-and-groove guides to keep the gate sealing surfaces from clattering on the seats and marring them during opening and closing. Depending on the velocity and density of the fluid stream being sheared, these guiding surfaces may be as cast, machined, or hard-surfaced and ground.

Gate valves may have non-rising stems, inside-screw rising stems, or outside-screw rising stems, listed in order of decreasing exposure of the stem threads to the fluid handled. Rising-stem valves require more space, but the position of the stem visually indicates the position of the gate. Indication is clearest on the outside-screw rising-stem valves, and on these the stem threads and thrust collars may be lubricated, reducing operating effort. The stem connection to the gate assembly prevents the stem from rotating. Next is Globe Valve.

Valve

2008-10-03T09:16:00.001-07:00

In addition to the throttling control valve, other types of process valves are used to manipulate the process. Valves for On/Off Applications Valves are often required for service that is primarily nonthrottling in nature. Valves in this category, depending on the service requirements, may be of the same design as the types used for throttling control or, as in the case of gate valves, different in design. Valves in this category usually have tight shutoff when they are closed and low pressure drops when they are wide open. The on/off valve can be operated manually, such as by handwheel or lever; or automatically, with pneumatic or electric actuators.

Batch Batch process operation is an application requiring on/off valve service. Here the valve is opened and closed to provide reactant, catalyst, or product to and from the batch reactor. Like the throttling control valve, the valve used in this service must be designed to open and close thousands of times. For this reason, valves used in this application are often the same valves used in continuous throttling applications.

Ball valves are especially useful in batch operations. The ball valve has a straight-through flow passage that reduces pressure drop in the wide-open state and provides tight shutoff capability when closed. In addition, the segmented ball valve provides for shearing action between the ball and the ball seat that promotes closure in slurry service.

Isolation A means for pressure-isolating control valves, pumps, and other piping hardware for installation and maintenance is another common application for an on/off valve. In this application, the valve is required to have tight shutoff so that leakage is stopped when the piping system is under repair. As the need to cycle the valve in this application is far less than that of a throttling control valve, the wear characteristics of the valve are less important. Also, because there are many required in a plant, the isolation valve needs to be reliable, simple in design and simple in operation.

The gate valve, is the most widely used valve in this application. The gate valve is composed of a gate-like disc that moves perpendicular to the flow stream. The disc is moved up and down by a threaded screw that is rotated to effect disc movement. Because the disc is large and at right angles to the process pressure, large seat loading for tight shutoff is possible. Wear produced by high seat loading during the movement of the disk prohibits the use of the gate valve for throttling applications.

Vibration Monitoring

2008-09-21T16:44:00.000-07:00

One of the major factors that causes pump failure is vibration, which usually causes seal damage and oil leakage. Vibration in pumps is caused by numerous factors such as cavitations, impeller unbalance, loose bearings, and pipe pulsations. Typically, large-amplitude vibration occurs when the frequency of vibration coincides with that of the natural frequency of the pump system. This results in a catastrophic operating condition that should be avoided. If the natural frequency is close to the upper end of the operating speed range, then the pump system should be stiffened to reduce vibration. On the other hand, if the natural frequency is close to the lower end of the operating range, the unit should be made more flexible. During startup, the pump system may go through its system natural frequency, and vibration can occur. Continuous operation at this operating point should be avoided.

ASME recommends periodic monitoring of all pumps. Pump vibration level should fall within the prescribed limits. The reference vibration level is measured during acceptance testing. This level is specified by the manufacturer. During periodic maintenance, the vibration level should not exceed alert level. If the measured level exceeds the alert level then preventive maintenance should be performed, by diagnosing the cause of vibration and reducing the vibration level prior to continue to operations.

Collection and analysis of vibration signatures is a complex procedure. By looking at a vibration spectrum, one can identify which components of the pump system are responsible for a particular frequency component. Comparison of vibration signatures at periodic intervals reveals if a particular component is deteriorating. The following example illustrates evaluation of the frequency composition of an electric motor gear pump system.

Figure of Frequency range of typical machinery faults.

Jet Pumps and Electromagnetic Pumps

2008-09-15T20:16:00.000-07:00

JET PUMPS

Jet pumps are a class of liquid-handling device that makes use of the momentum of one fluid to move another. Ejectors and injectors are the two types of jet pumps of interest to chemical engineers.

The ejector, also called the siphon, exhauster, or eductor, is designed for use in operations in which the head pumped against is low and is less than the head of the fluid used for pumping.

The injector is a special type of jet pump, operated by steam and used for boiler feed and similar services, in which the fluid being pumped is discharged into a space under the same pressure as that of the steam being used to operate the injector. As drawing shows a simple design for a jet pump of the ejector type. The pumping fluid enters through the nozzle at the left and passes through the venturi nozzle at the center and out of the discharge opening at the right. As it passes into the venturi nozzle, it develops a suction that causes some of the fluid in the suction chamber to be entrained with the stream and delivered through this discharge. The efficiency of an ejector or jet pump is low, being only a few percent. The head developed by the ejector is also low except in special types. The device has the disadvantage of diluting the fluid pumped by mixing it with the pumping fluid. In steam injectors for boiler feed and similar services in which the heat of the steam is recovered, efficiency is close to 100 percent. The simple ejector or siphon is widely used, in spite of its low efficiency, for transferring liquids from one tank to another, for lifting acids, alkalis, or solid-containing liquids of an abrasive nature, and for emptying sumps.

ELECTROMAGNETIC PUMPS

The necessity of circulating liquid-metal heat-transfer media in nuclear-reactor systems has led to development of electromagnetic pumps. All electromagnetic pumps utilize the motor principle: a conductor in a magnetic field, carrying a current which flows at right angles to the direction of the field, has a force exerted on it, the force being mutually perpendicular to both the field and the current. In all electromagnetic pumps, the fluid is the conductor. This force, suitably directed in the fluid, manifests itself as a pressure if the fluid is suitably contained. The field and current can be produced in a number of different ways and the force utilized variously.

Both alternating- and direct-current units are available. While dc pumps as above drawing are simpler, their high-current requirement is a definite limitation; ac pumps can readily obtain high currents by making use of transformers. Multipole induction ac pumps have been built in helical and linear configurations. Helical units are effective for relatively high heads and low flows, while linear induction pumps are best suited to large flows at moderate heads.

Electromagnetic pumps are available for flow rates up to 2.271 103 m3/h (10,000 gal/min), and pressures up to 2 MPa (300 lbf/in2) are practical. Performance characteristics resemble those of centrifugal pumps.