A positive displacement (PD) pump is an Air-Operated Double Diaphragm pump (AODD). The pump has two pumping chambers that are filled and expelled with fluids alternately by the movement of diaphragms. To provide the pumping motion, compressed air is alternately fed into and vented from air chambers on opposing sides of the diaphragms.

Double Diaphragm Pumps are commonly used in transfer applications and can handle a broad range of feeds such as sludges, slurries, abrasive, and shear-sensitive fluids. They are sturdy, dependable, and simple to maintain, but they are loud, prone to icing, and confined to low-pressure applications.

How does a Double Diaphragm Pump Work?

Air-operated double-diaphragm (AODD) pumps are employed in a wide range of facilities and industries. These pumps are popular and adaptable, with applications ranging from petrochemical to food and beverage. Their one-of-a-kind shape is suitable for transporting highly abrasive or viscous materials. But how do they function?

A double diaphragm pump is a type of positive displacement pump that is powered by compressed air. This pump uses dual diaphragms mounted to a connected shaft which moves back and forth constantly to pump fluids into and out of the chamber. A connected shaft passes the compressed air from one chamber to the other. The pump operates on an air displacement principle, which acts as a separating divider between the air and the fluid.

First Stroke:

The two diaphragms are joined by a shaft that runs through the middle part, which houses the air valve. The compressed air is directed to the rear of the first diaphragm by the air valve, which moves it away from the centre part.

The first diaphragm produces a pressure stroke that drains fluid from the pump. The suction stroke is performed by the second diaphragm at the same time. The air behind the second diaphragm is allowed to escape into the atmosphere, and atmospheric pressure drives the fluid to the suction side. The suction ball valve is pushed away from its seat, enabling fluid to pass through it and into the liquid chamber.

Second Stroke:

When the first pressured diaphragm reaches the end of its stroke, air flows through the air valve from the first diaphragm to the rear of the second diaphragm. The pressured air pushes the second diaphragm away from the central block, while the first diaphragm pulls towards it.

The output ball valve in the second chamber of the pump is forced out of its seat, whereas the converse is true in the first chamber. When the second stroke is finished, the air valve pumps air behind the first diaphragm, and the cycle begins again.

Things to Consider While Buying a Double Diaphragm Pump

Identify your Requirements

The first thing you need to know is what liquid you need to push using a double diaphragm pump. The type, content, and character of the fluid must be considered the most important factor to prevent corrosion of the wetted parts and wear and tear on the pumping equipment. Solid content, pH level, viscosity, density, specific gravity, and abrasion factor are all distinguishing characteristics.

Here are some types of fluids that you can push with a double diaphragm pump

  • Abrasive Fluids
  • Corrosive Fluids
  • Flammable Fluids
  • Shear Sensitive Fluids
  • Toxic Fluids

Flow Rate

The flow rate of AODD is proportional to its draining time. When calculating pump size, the flow rate is taken into account first. Use a larger pump with larger port sizes, such as suction and discharge connections, for higher flow rates, and vice versa. In general, the faster the draining time, the higher the flow rate. It is common practice to go up one port size when sizing a double diaphragm pump for the best efficiency and longevity.

Pressure Conditions

Analyzing the necessity for proper pressure conditions inside the AODD chambers aids in the selection of the suitable pump size. The pressure at the pump’s inlet is referred to as the suction pressure. Double Diaphragm Pumps are self-priming, making them suitable for both flooded suction and suction lift circumstances.

Because increased pressure provides a larger flow rate, it must also be managed. Excessive pressure might impair the suction valves’ capacity to lift. This might result in downtime. The height at which the fluid is pushed is determined by discharge pressure, also known as delivery pressure. It is calculated separately from the frictional loss.

Flow Viscosity

Viscosity is the flow’s resistance. Unlike some other types of pumps, AODD pumps are noted for being gentle on the fluids they pump. Their sealless design reduces maintenance while reducing shearing or deterioration of the goods they pump.

It is vital to understand the liquid’s viscosity. 1.5′′ is preferred for liquids with more than 5000 cps, for example. Most of the Double Diaphragm Pump Manufacturers in India provide a viscosity correction factor for different viscosities based on pump size for convenience. The flow rate for high-viscosity fluids must be reduced by applying a viscosity adjustment factor to the standard curves.


Temperature restrictions apply to pump materials. Temperature, in addition to chemical compatibility and pump materials, is an important element in the pump’s lifetime. To ensure that the pump material is most suited for a certain application, we must first determine the operating temperature as well as the ambient conditions.

Temperature ratings for rubbers and thermoplastics vary. Fluorocarbons, for example, can withstand temperatures as high as 177 °C. Teflon may be beneficial under cold conditions, such as those utilized in CBD production. The temperature limit of the neoprene diaphragm, on the other hand, is less than 100 degrees Celsius.

Final Words

Nirmala pumps and Equipment is one of the top Double Diaphragm Pump Suppliers in India, providing a variety of solutions to specific market application demands. We keep a competitive advantage in the industry because we are committed to providing 100% client satisfaction. Our expert team creates long-lasting relationships with our clients and gains their continuous business by always doing what is right.