A diaphragm pump (also called 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 part of the diaphragm
A double diaphragm is a positive displacement pump which utilises two flexible diaphragms that reciprocate backwards and forwards, creating a temporary chamber, which both draws in and expels fluid through the pump. … Both diaphragms that are connected by a shaft through the centre section where the air valve is situated.
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-primary by creating a pressure differential in the diaphragm chamber. This draws in surroundings and pulls the fluid in to the suction port.
