A piston diaphragm pump includes a support plate, disposed on the side of the piston work chamber, for the diaphragm, which is held in a freely movable manner counter to the pressure of a plurality of springs engaging its circumference. A control push rod under the pressure of another spring, counter...http://www.google.de/patents/US4465438?utm_source=gb-gplus-sharePatent US4465438 - Piston diaphragm pump
