AODD id equipped with two diaphragm chambers (pumping chambers) connected by a rod. One side of the chamber is wetted end (liquid end) and the other side is the dry end (air end). The pump is driven by compressed air.

                During the first stroke, compressed air enters the backside of one of the diaphragm chamber (air end) and ecerts pressure on that side, forcing liquid into the check valve (liquid end), into the manifold and out into the discharge port.

                That is known as the discharge stroke. In that same stroke, the compressed air in the opposite diaphragm chamber will be squeezed and expelled into atmosphere, thus causing a suction stroke. With each stroke, one chamber will be sucking and the other chamber will be discharging. Thus the pump will be producing an almost consistent flow. Note the arrangement of the check balls. The bottom check balls of both liquid chambers are arranged to be closed during discharge and opened during suction.

                 However, the top check balls of both liquid chambers are arranged to be opened during discharge and closed during suction. The air distribution system is arranged to allow air into one chamber while discharging air at the other and vice versa on the nextstroke.