A diaphragm pump (also known as a 
Membrane pump) is a positive displacement pump that runs on the 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 diaphragms that Air Diaphragm Pump reciprocate back and forth, creating a short-term chamber, which both draws in and expels liquid through the pump. … Both diaphragms that are linked by a shaft through the center section where the air valve is located.
Though this will depend 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 allures surroundings and pulls the fluid in to the suction port.