A diaphragm pump (also referred to as a Membrane pump) is a positive displacement pump that uses a mixture of the Air Diaphragm Pump reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable valves on either side of the diaphragm

A double diaphragm is a positive displacement pump which utilises two flexible diaphragms that reciprocate back and forth, creating a short-term chamber, which both draws in and expels liquid through the pump. … Both diaphragms that are connected by a shaft through the centre section where in fact the air valve is located.

Though it depends upon the pump and application, a positive displacement pump, is normally a self-priming pump. … For example, air operated diaphragm pumps self-prime by creating a pressure differential in the diaphragm chamber. This draws in surroundings and pulls the fluid in to the suction port.