Air-operated double diaphragm (AODD) pumps are used worldwide to move a wide range of fluids—with suspended solids, non-suspended solids and line-size solids—from Point A to Point B, above and below ground. End users select them over 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 sealless, semi-positive displacement pump. The pumping principle provides 100 percent efficiency at zero flow (see Figure 1).
Figure 1. AODD head and horsepower versus flow rate
Advantages
AODD pumps are a good choice for moving abrasive and shear-sensitive materials and high viscosity fluids. They are self-priming, available with optional discharge porting and run dry without significant damage or heat build-up.
AODD pumps are air or natural gas operated 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 (see Figure 2).
Figure 2. The balanced operation of an AODD pump
AODD pumps are self-priming from a dry start and are frequently installed in flooded suction and suction lift installations. With caution given to the non-wetted materials of construction, AODD pumps can be submerged for maximum installation versatility (see Figure 3). They safely operate on deadheaded/standby demand without the costs associated with the need to relieve pressure. At all deadhead condition points, they consume zero energy (see Figure 4).
Figure 3. AODD pumps can operate in many different environments
Figure 4. AODD pump performance curve
Flexibility
Fragile materials are safe when pumped with an AODD unit. Low internal velocities handle abrasive slurries without pump damage 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 also offer pumps with optional discharge porting:
- Bottom porting for a high concentration of heavy solids
- Top porting for thin liquids or if the liquid contains entrained air
AODD pumps can be regulated to adjust the pump flow from zero to maximum rated capacity.
Extending Pump Life
When end users decide to invest in AODD pumps, extending the life of the pumps becomes a high priority. Many pumps have a functional life of 30 or more years, but pump life depends on the application, the pump system and how the pump is operated and maintained. Many options are available for 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. AODD parts and kits provide the flexibility to switch the internal components to different materials. This allows the pump to change applications—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. AODD kits can provide end users with everything they need to get their pumps back to work quickly and more efficiently.
When considering the benefits of replacing versus repairing a pump, kits and replacement parts are an attractive choice for maintenance personnel and budget conscious end users.