How AODD pumps work: principle, components and selection.

Principles of AODD pump operation

Air-operated double-diaphragm (AODD) pumps are reciprocating, positive-displacement pumps. Each completed stroke displaces fluid from one of two liquid chambers. Compressed-air pressure and air volume together determine the available pumping duty.

The moving wetted components include two diaphragms joined by a common shaft, two inlet valve balls and two outlet valve balls. The diaphragms separate compressed air from the liquid. Air pressure drives the diaphragms, balancing their load, while the ball valves open and close against their seats to direct liquid flow. Adjusting the air supply allows the operator to match pressure and flow to the process.

When the air distribution system supplies the right air chamber behind its diaphragm, that diaphragm moves away from the center block toward the liquid chamber and pulls the opposite diaphragm inward. The opposite chamber is then on its suction stroke: atmospheric pressure pushes fluid through the inlet manifold, lifts the inlet ball from its seat and fills the liquid chamber.

At the end of the stroke, the air valve redirects compressed air behind the opposite diaphragm. That diaphragm moves outward while pulling the right diaphragm toward the center. The inlet ball on the discharging side closes; the outlet ball lifts from its seat and fluid exits through the discharge manifold. Alternating the air supply repeats the filling and discharge process on the two sides.

When the pump returns to its original starting position, each diaphragm has completed one suction stroke and one discharge stroke. This is one complete pumping cycle.