How Do Air Operated Double Diaphragm Pumps Work?

You’ve seen them about, and maybe you’ve asked yourself “what on earth is that”. Air Operated Double Diaphragm (AODD) pumps are a strange beast, featuring neither motor nor pump head. They seem to be made of too many pipes and they make a strange noise.

What is an AODD Pump?

Sometimes called a diaphragm vacuum pump, pneumatic diaphragm pump, membrane pump, or even just a diaphragm pump, an AODD pump is a type of positive displacement pump featuring two flexible membranes whose alternating flex provides the energy to capture and move pumped media.

How an AODD pump works

AODD pumps are relatively simple. They consist of two chambers with a flexible diaphragm between them. These chambers have valves (usually ball valves) at their left and right inflow and discharge sides. Both chambers are connected to the same inlet and outlet.

AODD pumps are powered by an external air compressor. This air compressor feeds into an air distribution system which fills one side of a flexible diaphragm, and then switches to release pressure into the other side, filling it.

This alternating inflation and deflation of the left and right air diaphragms creates an alternating pressure and vacuum in the side chambers of the pump.

As a chamber’s air diaphragm inflates, the pressure within that chamber seals the valve connected to the inlet, but opens the ball valve connected to the outlet. The positive pressure within the chamber expels the pumped medium past the discharge ball valve from the chamber. 

As a chamber’s air diaphragm deflates, the reverse happens: the pressure within that chamber seals the valve connected to the outlet, but opens the valve connected to the inlet. The negative pressure pulls more of the pumped medium into the chamber, past the inflow ball valve.

As this happens, the inflow and discharge from each chamber is alternatingly pulling the pumped medium from the inlet and discharging it through the outlet.

While this process occurs in rapid succession, providing a relatively steady flow, it does produce pulses which can be problematic for some systems. If this is the case you may need to include dampening down stream.

Also, since AODD pumps require a compressed air supply, pumping speed is often determined by the differential pressure of the air supply and the pumped fluid. This means that increasing your air supply pressure will increase the speed of the pump. However, as the pressure of the pumped fluid increases, this will slow the speed of the pump. If constant flow is required you may need to consider these factors and include pressure and flow controls.

Benefits of AODD pumps

Thanks to the nature of the pumping action, AODD pumps have a variety of advantages over other pumps:

• They can move high viscosity, and abrasive substances better than most pumps. We’ve talked to people at tradeshows using AODD pumps for substances as difficult as diatomaceous earth. 
• Since there is no electricity and minimal friction in an AODD pump, they are inherently explosion proof. 
• They rarely leak. There are no moving seals, only stationary seals between wetted parts. The only time you should see leaking is when either a gasket has failed, or the diaphragm cracks.
• They can be run dry without damaging the pump.
• They are self priming.

We sell a number of AODD pumps both on and off carts. Check them out in our AODD pump section!