Air Operated Diaphragm Pumps - the how, what, and why
The Air Operated Diaphragm (AOD) Pump is a positive displacement pump powered by compressed air. AOD pumps offer a sanitary, energy-efficient way to transfer product. They are ideal for viscous products, products that require no or low shear, or products that contain solids or are nearly solid (it is a gentle beast). It is popular in the brewing industry as a product transfer pump; although there is often some confusion as to how they work and why a brewer would want one.
How do air operated diaphragm pumps work?
The key element that makes AOD pumps unique is that they use compressed air from a separate air compressor; instead of using an electric motor.
The pump consists of four check valves/balls, two diaphragms, a rod assembly in the centre of the pump, and two air valves. The two diaphragms move in and out of the fluid sections; one diaphragm will be in suction while the other is in discharge. While in suction mode, the diaphragm creates a low-pressure zone as it moves out of the fluid section, pulling liquid into the pump. The diaphragm then moves back into the fluid section forcing the product up to the balls/check valves and then the outlet, this is discharge mode. The rod assembly moves the air pressure between the diaphragms to shift them from side to side; exactly how this is done is different from model to model. The check valves have balls in them that are moved up and down by the pressure that the diaphragms forms, this opens and closes the valves. The combination of the diaphragm and the balls create a pressure vacuum that moves the product through the pump.
What to use diaphragm pumps for?
What can you use an AOD pump for in your brewery?
- Transfer and consolidation of finished beer
- Yeast Transfer
- Waste yeast from the fermenter vessels
- Bulk chemical transfer for tank cleaning
- Transfer of beer to and from barrels
Basically, you can use the AOD for anything that transfers your product at lower temperatures. It can even move your yeast or waste product. They can be completely sanitary, so it's okay to put your beer through them. They’re also great for carbonated drinks because the low speeds do not transfer kinetic energy to the product.
Why the AOD?
AOD pumps can transfer pressurized product (such as carbonated beverages) at low pressure and low speeds. This is extremely handy when the product is fizzy or frothy. It is also quite gentle for your more precious products. The self-priming pneumatic motor creates an oil-free design that does not require any lubrication. The risk of cavitation is removed and it can be deadheaded with no damage.
A couple interesting features of the AOD pump include:
- Very specific control of flow
- Can run at low speeds
- Can run dry
- Can transfer mostly solid products or products containing solids
- Low shear effects (Solids stay solid!)