A diaphragm pump (also known as a Membrane pump) is a positive displacement pump that runs on the combination of the reciprocating actions of a rubber, thermoplastic or teflon diaphragm and suitable valves on either aspect 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. … The two diaphragms that are connected by a shaft through the centre section where 
in fact the air valve is situated.
Though this will Air Diaphragm Pump depend upon the pump and application, a positive displacement pump, is normally a self-priming pump. … For instance, air operated diaphragm pumps self-prime by creating a pressure differential in the diaphragm chamber. This allures surroundings and pulls the liquid in to the suction port.