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Thursday, March 11, 2010

Pump for Chemical and Water Treatment Industries

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.

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