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Positive Displacement Pumps

Positive displacement pumps allow a wide range of liquids, slurries and foams to be transported without product degradation. Types of positive-displacement pumps are reciprocating, metering, and rotary pumps. Positive displacement pumps can be further classified as either rotary type (i.e. rotary vane pump) or reciprocating type (i.e. diaphragm pump or piston/plunger pump). Both rotary type and reciprocating type pumps operate very similar with slight differences between the two:

In all rotary designs, the chamber is created progressively through rotation of the drive shaft. There may be one or more chambers opened per revolution of the drive shaft. The chambers are sealed off from suction by close clearance between the rotor and the housing, or by close clearance between intermeshing rotors. Rotation of the shaft moves the chamber along the bore or housing towards discharge. The chamber is displaced to discharge rotation. The release to discharge progresses with rotation as the volume is expelled so that the flow is typically pulsation free.
In all reciprocating designs, there are check valves on the suction and discharge. Fluid flows through the suction valve and into the chamber as the plunger, piston, or diaphragm recedes. At the end of the stroke, the chamber is at its maximum size. The suction valve closes, the plunger moves forward into the chamber, forcing the fluid out the discharge valve. The flow from each chamber is a pulse flow. If the pump has several chambers, they are timed to have sequential pulses to minimize the overall pulsation.

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