Cross section showing inside air operated double diaphragm pump.

Ease of maintenance and operation make these pumps a good solution for many applications

Air-operated double diaphragm (AODD) pumps are used worldwide to move a wide range of fluids, suspended solids, non-suspended solids and line-size solids from Point A to Point B, both above and below ground. End users select AODD pumps versus other pump types such as positive displacement when challenged with difficult pumping situations.

Although an AODD pump is a displacement type, it is actually a hybrid. While its pressure–versus capacity characteristics resemble those of a centrifugal pump, it is best defined as a seal less, semi-positive displacement pump. The pumping principle provides 100 percent efficiency at zero flow (Figure 1).

Advantages of AODD Pumps
AODD pumps are a good choice for pumping abrasive, shear-sensitive and high viscosity materials and fluids. They are self-priming, available with optional discharge porting and run dry without significant damage or heat build-up.

AODD pumps can be powered by either compressed air or natural gas and differ from other positive displacement pumps, because of air pressure acting on the entire surface of the diaphragm, the diaphragm is in a balanced condition while pumping. This process extends the diaphragm life over that of mechanically operated diaphragm pumps. Because compressed air is limited, the maximum pressure developed by the pump is also safely limited. As a result, AODD pumps are appropriate for on-demand intermittent requirements (Figure 2).

These pumps are self-priming from a dry start and are frequently installed in either flooded suction installations or suction lift installations. With caution given to the non-wetted materials of construction, AODD pumps can be submerged for maximum installation versatility (Figure 3).

AODD pumps safely operate on deadheaded/standby demand without the added costs associated with the need to relieve pressure. More important, at all deadhead condition points the AODD pump consumes zero energy (Figure 4).

AODD Pump Flexibility
Fragile materials are safe when pumped through an AODD unit. Low internal velocities handle abrasive slurries without damage to the pump or loss of volumetric efficiencies. The gentle pumping action does not shear fragile materials. High viscosity fluids, heavy and pourable, are capably handled.

Many manufacturers’ offer pumps with optional discharge porting:

  • Bottom porting is an option for a high concentration of heavy solids
  • Top porting should be selected for thin liquids or if entrained air could be a problem

AODD pumps can be regulated to adjust the pump flow from zero to maximum rated capacity.

Extending the Life of AODD Pumps
When the decision to invest in AODD pumps has been made, extending the life of the pumps becomes a high priority. Many pumps have a functional life of 30 or more years, but pump life is entirely dependent on the application, the pump system and how the pump is operated and maintained. Numerous options are available for when maintaining and extending the life of an AODD pump.

Most AODD pump manufacturers offer genuine replacement parts. Some manufacturers sell several different convenient kits that are developed for specific pump models, making maintenance simple. Kits are available to support different levels of service from minimal repairs to full refurbishment of the pump. AODD parts and kits provide the flexibility to swap out the internal components of the pumps to different materials. This allows the pump to change application paint to ceramics for example and provide varying levels of performance such as ball to weighted ball.

From the air valve o-ring to outer diaphragm chamber, AODD pump manufacturers can provide the parts needed to keep pumps running smoothly. Genuine AODD parts are manufactured to precise specifications and are built for durability, reliability and productivity. Today’s applications demand that pumps provide maximum efficiency, minimum operating costs and the longest life possible, without compromising production. AODD kits can provide pump users with everything they need to get their pumps back working quickly and more efficiently.

When thinking of the benefits of replacing versus repairing a pump, kits and replacement parts are an attractive choice for maintenance personnel and budget conscious pump users.

AODD pumps allow for simple maintenance and repair, ensuring the life of the pump investment.

For more information pump users should contact their preferred manufacturer or local distributor.

Mathew Harris is the Regional Manager for IDEX Corporation a global leader in fluid handling equipment and applied solutions. He can be contacted on

Image: Cross section showing inside air operated double diaphragm pump. Image credit: Surasak_Photo/

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