Diaphragm & Positive Displacement Pumps

A positive displacement pump makes a fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe. ... Liquid flows into the pumpas the cavity on the suction side expands and the liquid flows out of the discharge as the cavity decreases.

A diaphragm pump (also known as a Membrane pump) is a positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable valves on either side of the diaphragm