When the pressure directed by the Air Valve is applied to the right side, diaphragm is pushed outward compressing the fluid. Compressed fluid lifting the upper ball forces the upper discharge valve to open, releasing liquid into the discharge manifold. The lower ball in the suction valve is pushed down, closing the suction valve.

At the same time, when the right discharge chamber is pumping fluid out of the pump, a connecting rod pulls the left diaphragm inward. Negative pressure is created inside the left chamber. This negative pressure sucks upper ball down closing the left upper discharge valve. The same force is lifting the lower ball in the suction valve, opening the suction valve. Liquid drawn through the suction manifold is filling the left chamber.

As soon as diaphragm center disc in the left chamber hits the Pilot Valve the small air channel opens, allowing air pressure to enter Air Valve compartment and change Air Valve position. Change of Air Valve position causes a change in air pressure feed direction. Now the right side of the pump, that was on the discharge cycle start the suction cycle. And the left side passes from the suction cycle to the discharge cycle. Thus, the pumping action is reversed.