Piston pumps and plunger pumps use a mechanism (typically rotational) to create a reciprocating motion along an axis, which then builds pressure in a cylinder or working barrel to force gas or fluid through the pump. The pressure in the chamber actuates the valves at both the suction and discharge points.

Axial-piston pump varies displacement by changing angle of swashplate. The piston pump is a rotary unit which uses the principle of the reciprocating pump to produce fluid flow. Instead of using a single piston, these pumps have many piston-cylinder combinations.