A diaphragm pump (also known as a Membrane pump) is 
a positive displacement pump that runs on the mixture of the reciprocating actions of a rubber, thermoplastic or teflon diaphragm and suitable valves on either part of the diaphragm
A double diaphragm is a positive displacement pump which utilises two flexible diaphragms that reciprocate back and forth, creating a temporary 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 Air Diaphragm Pump depends upon the pump and application, a positive displacement pump, is generally a self-priming pump. … For instance, air operated diaphragm pumps self-prime by creating a pressure differential in the diaphragm chamber. This allures air and pulls the liquid in to the suction port.