Air Operated Double Diaphragm Pumps

An Air Operated Double Diaphragm (AODD) pump is a type of positive displacement pump that uses compressed air as its power source rather than an electric motor. It is a “workhorse” in industry, known for its ability to handle tough, abrasive, and highly viscous fluids that other pumps might fail on.

How It Works

The pump consists of two chambers, each containing a flexible diaphragm. A central shaft connects these diaphragms.
Suction Stroke: Compressed air is directed into the back of Diaphragm A, pushing it forward to discharge liquid. Simultaneously, the connecting shaft pulls Diaphragm B inward, creating a vacuum that draws liquid into the second chamber.
Discharge Stroke: An air valve automatically shifts the air flow to the back of Diaphragm B. This reverses the movement, discharging the liquid from Chamber B and drawing new liquid into Chamber A.
Check Valves: Ball or flap valves at the inlet and outlet of each chamber ensure that fluid only moves in one direction (from suction to discharge).

Key Features & Benefits

Run-Dry Capability: Unlike centrifugal pumps, AODD pumps can run without fluid (dry) for extended periods without damaging internal components.
Self-Priming: They can create enough suction to draw fluid from a tank or pit located below the pump level without needing to be manually primed.
Intrinsically Safe: Because they run on air rather than electricity, they produce no sparks, making them ideal for hazardous or explosive environments.
Handles Solids & Viscous Fluids: They can easily pump “dirty” liquids containing solids, slurries, or thick materials like honey, sludge, or glue.
Shear Sensitive: The gentle pumping action does not “churn” the fluid, which is critical for delicate liquids like food products or certain chemicals.
Variable Flow: You can control the pump’s speed and output simply by adjusting the air pressure or volume entering the pump.

Common Applications

Chemical Industry: Transferring acids, solvents, and corrosive chemicals.
Wastewater Treatment: Moving sludge, lime slurry, and dewatering.
Food & Beverage: Handling ingredients like chocolate, syrups, and sauces (using FDA-compliant materials).
Paint & Ink: Circulating and dispensing highly flammable solvents and pigments.
Mining: Dewatering underground sites and moving abrasive mineral slurries.
Oil & Gas: Transferring crude oil and chemical injection.

Materials of Construction

To handle different fluids, AODD pumps are available in various materials:
Pump Bodies: Aluminium (lightweight), Stainless Steel (corrosion-resistant), Polypropylene (chemical-resistant/low cost), and PVDF (high-purity/aggressive acids).
Diaphragms (Elastomers): PTFE (Teflon) for maximum chemical resistance, Santoprene for long life and durability, and Buna-N or Viton for oil and fuel applications.
Limitations to Consider
Pulsation: The reciprocating nature creates a pulsing flow (often mitigated with “pulsation dampeners”).
Noise: The venting of compressed air can be loud.
Icing: In cold or humid environments, the expanding air can cause ice to form on the exhaust valve, potentially stalling the pump.