There are so many different pumps and meters these days. Picking the best one depends on what you need it to do. In some instances a positive displacement pump is necessary but, what is it they do exactly. With a positive displacement pump, liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume is a constant given each cycle of operation. The positive displacement pumps can be divided in two main classes, reciprocating and rotary.
Positive displacement pumps shouldn’t operate against closed valves on the discharge side of the pump. There is no shut off head on them like on centrifugal pumps. If so, operating against closed discharge valves continues to produce flow until the pressure in the discharge line is increased until the line bursts or the pump is severely damaged – or both.
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