A diaphragm pump (also referred to 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

A dual diaphragm is a positive displacement pump which utilises two flexible Air Diaphragm Pump diaphragms that reciprocate back and forth, creating a temporary chamber, which both draws in and expels fluid through the pump. … Both diaphragms that are linked by a shaft through the center section where the air valve is situated.

Though this will depend upon the pump and application, a positive displacement pump, is normally a self-priming pump. … For instance, air operated diaphragm pumps self-primary by creating a pressure differential in the diaphragm chamber. This draws in atmosphere and pulls the liquid into the suction port.