How AODD Pumps Work
Here's a hint: it's similar to an internal combustion engine.

Air-operated double diaphragm (AODD) pumps are modern, highly-versatile pump systems. The unique design uses the reciprocating action of two flexible diaphragms and suitable inlet and discharge check valves on either side of the diaphragm to pump fluid. Because of this, AODD pumps can transfer different types of liquids and solids including very abrasive or viscous products. AODD pumps have applications that include fluid transfer, filter press, dewatering, spray and cleaning, dispensing, and filling and metering in industries such as mining, pharmaceuticals, foods, and chemicals.

AODD Pump Operation

An AODD pump uses the positive displacement principle to move liquids by trapping a fixed amount of fluid and forcing it into a discharge pipe. As a result, the AODD produces the same flow at a given speed regardless of the discharge pressure. Looking inside the pump, the diaphragms connect to a shaft located in the center section. The reciprocating or stroking action of the AODD pump moves the diaphragms within two chambers. Each chamber consists of an “air side” and a “liquid side.”

During operation, the diaphragms form a separation wall between the air and the liquid. An air valve located in the center section of the diaphragm pump directs the compressed air to the back of diaphragm number one and causes the diaphragm to move away from the center section. The movement of the diaphragm becomes a press stroke that moves liquid out of the pump. When the pressurized diaphragm number one has reached the end of the press stroke, the movement of the air switches from diaphragm number one to the back of diaphragm number two through the air valve. With this action, the inlet check valve moves from its seat and allows the fluid to flow into the liquid chamber.

The compressed air pushes diaphragm number two away from the center block and begins to develop the suction stroke. As this action occurs, diaphragm number one pulls toward the center block and forces the air side of the chamber to exhaust air through the valve. Upon completion of the stroke, the air valve leads the air again to the back of diaphragm number one and restarts the cycle.

AODD Pump Features

A wide range of AODD designs can meet specific needs. Because of the combination of portability, the capability to move solids, self-priming capability, and a design that has no seals or gaskets and few moving parts, the pumps offer reliability, longevity, and easy maintenance. Depending on pump sizes that range from ¼” to 3” and because of the capability to vary air inlet pressure and control discharge valves, AODD pumps offer variable flow rates that range from 5 to 260 GPM.

When selecting an air-operated, double diaphragm pump, consider the following items:

  • application and type of fluids
  • potential need to pump solids and the manufacturer’s particle size limit
  • amount of pressure needed for the application
  • manufacturer’s specifications

A positive displacement pump has an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume remains constant with each cycle of operation.