What is a double diaphragm pump and how does it work?

An Air-Operated Double Diaphragm Pump(AODD Pumps) in action. Positive displacement pumps are diaphragm pumps. Pumping a fluid is accomplished by combining the reciprocal action of two flexible diaphragms, two ball check valves, and two outlet valves. The diaphragms separate the two pump chambers, which are separated into air and fluid areas.