A positive displacement pump moves a fluid by repeatedly enclosing a fixed volume and moving it mechanically through the system. The pumping action is cyclic and can be driven by pistons, screws, gears, rollers, diaphragms or vanes.
Positive displacement pump or PDP is a type of pump in which a certain amount of fluid is captured inside the cavity, and then discharge the same. This displacement of fluid takes is done by plunger, piston, diaphragm etc. depending on the type of the pump. Some equipment have expanding cavity at the suction side and/or a decreasing cavity at the discharge side. The liquid is taken in the form of suction through the inlet side when the cavity expands, and discharges it when the cavity decreases.