A double diaphragm is a positive displacement pump that utilizes two flexible diaphragms that reciprocate back and forth, creating a temporary chamber, which both draws in and expels fluid through the pump. The diaphragms work as a separation wall between the air and the liquid.

The first stroke

The two diaphragms are connected by a shaft through the center section where the air valve is located. The purpose of the air valve is to direct the compressed air to the back of diaphragm number one causing it to move away from the center section. The number one diaphragm causes a press stroke moving liquid out of the pump. At the same time diaphragm number two is performing a suction stroke. The air behind diaphragm number two is being pushed out to the atmosphere causing atmospheric pressure to push the liquid to the suction side. The suction ball valve is pushed away off its seat allowing the fluid to flow past the ball valve into the liquid chamber.


The second stroke


When the pressurized diaphragm number one has reached the end of its stroke, the movement of the air is switched from diaphragm number one to the back of diaphragm number two by the air valve. The compressed air pushes diaphragm number two away from the center block resulting in diaphragm number one being pulled toward the center block. In pump chamber number two the discharge ball valve is pushed off its seat, whilst in pump chamber number one the opposite occurs. Upon completion of the stroke, the air valve leads the air again to the back of diaphragm number one and restarts the cycle.

A diaphragm pump is a positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic, or Teflon diaphragm and suitable valves on either side of the diaphragm to pump a fluid. 






    AODD pumps have good suction lift characteristics, are self-priming in most fluids, and can run dry. These pumps can handle low to medium viscosity fluids with ease (including those containing large suspended solids) and may be used to pump both corrosive and flammable liquids. There’s a saying: “in the processing industries that if a material can be poured into an AODD pump, these types of pumps can generally pump it”.

    Due to their simple design, AODD pumps are relatively inexpensive to both purchase and operate as they are coupled with both efficiency and accuracy. Stainless steel versions are well suited for certain food-grade sanitary processing applications, including filling, dispensing, and metering fluids, as well as water removal. 

    Common uses in the food & beverage processing and biopharmaceutical manufacturing industries include:

    • Additive injection
    • Sampling
    • Dosing
    • Coating
    • Raw material unloading
    • Filling
    • Shear-sensitive processes
    • Filter presses
    • Aseptic transfer of proteins and cells
    • Producing the required flow and pressure for spraying & cleaning tasks



    • Unlike most other pump designs, AODD pumps can run dry for extended periods of time without damage
    • Due to their air-powered design, AODD pumps are well suited for use in hazardous situations (e.g., in environments where flammable materials are present), as the working mechanisms of these types of pumps don’t produce a spark
    • The pump’s design separates process fluids from potentially sensitive pump parts. The isolation of the pumps internals provide increased time between repair
    • AODD pump diaphragms come in many materials to cover a wide range of temperature and chemical compatibility applications
    • They are manufactured from a wide variety of metal and non-metal materials
    • Many AODD pumps are designed for sanitary and food-grade processing

    As with any pump, if the application isn’t right it can be disadvantageous, we suggest you contact an application specialist to ensure you use the right pump for your unique application