Pump Type Follows:

Tuesday, July 20, 2010

Lobe Pumps

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.

Tuesday, July 13, 2010

Vane, Gear, and Lobe Pumps

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.

Friday, July 9, 2010

Screw Pump Type

There are three major type of screw pump exist:
  1. Single rotor
  2. Multiple rotor timed
  3. 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.