pump

Any device for moving liquids and gases, or compressing gases.

Some pumps, such as the traditional lift pump used to raise water from wells, work by a reciprocating (up-and-down) action. Movement of a piston in a cylinder with a one-way valve creates a partial vacuum in the cylinder, thereby sucking water into it.

Gear pumps, used to pump oil in a car's lubrication system, have two meshing gears that rotate inside a housing, and the teeth move the oil. Rotary pumps contain a rotor with vanes projecting from it inside a casing, sweeping the liquid round as they move.