Learn more about Positive Displacement Pumps and their types
What Positive Displacement Pumps do? With each pumping part revolution, positive displacement pumps displace a known amount of liquid. This is accomplished by trapping liquid between the pumping parts and a fixed case. Gears, lobes, rotary pistons, vanes, and screws are some of the pumping elements used. Positive displacement pumps, unlike centrifugal pumps, provide the same flow at any given speed regardless of discharge pressure. Because these pumps do not have a shut-off head like centrifugal pumps, they must not be run against a closed valve on the discharge side of the pump. A positive displacement pump running against a closed discharge valve will continue to produce flow until the pressure in the discharge line increases to the point where the discharge line breaks or the pump is badly damaged or both. As a result, a relief or safety valve on the pump's discharge side is absolutely essential. Internal or exterior relief valves are available. Internal relief or s...