A classification of pump type in which fluids are transported by its displacement from one place to another for flow through pipelines, conduits, ducts, and channels. Examples include reciprocating pumps, which involve the displacement of a fluid from a chamber by a piston or plunger, and rotary pumps, which involve rotating gears or lobes with the fluid being transported between the teeth. There are many variations such as the diaphragm pump, which involves a diaphragm flexed to and fro, and the Mono pump, which involves a rotating helical worm.