Varieties of fluids and applications call for varieties of pumps. Pumps, for the most part, can be divided into two groups based on how they send or displace fluid through piping systems. Centrifugal pumps use rotational energy to transport fluids, while axial-flow pumps use impellers within the pipes to move fluids along a vertical or horizontal axis. But perhaps the most common pumping mechanism is the positive-displacement pump, which captures and releases fluid to send the fluid on its way. In this guide, we’ll take a closer look at how positive-displacement pumps work.


Most positive-displacement pumps operate through reciprocating action. In layman’s terms, reciprocation is a push and pull, or give and take—motion in one direction returned by motion in the opposite direction along that axis. The most common application of reciprocating action is in a piston, which moves up and down its shaft. The piston pump uses this principle to perfection by matching the piston with a seal, which separates the fluids inside the pump. Plunger pumps and diaphragm pumps also rely on this principle to impel fluid, though they use slightly different parts to accomplish the same task. The repetitive but reliable nature of reciprocating action means these positive-displacement pumps are best when accuracy matters.

Rotary Action

Not to be mistaken for centrifugal pumps, some positive-displacement pumps use rotary action to displace their fluids into systems. Rather than an impeller that moves along an axis in a linear fashion, rotary pumps use impellers that rotate, such as gears. By rotating within its casing, this gear creates suction, which traps fluid and then releases it. Gear pumps and vane pumps commonly find use in automotive applications, such as steering and transmission.

Difficulties with Pumps

Whether your positive-displacement pump is reciprocating or rotary, chances are that the hard work it performs will eventually lead to performing repairs on your pump. Moley Magnetics is about more than electromagnets—our pump repair services will work with you and your facility to get any pump back in working order and help you replace pumps that have done all they can do. By understanding how positive-displacement pumps work, you can get an idea of just which moving parts are susceptible to breakdown.