Pump T8 2" WILDEN AIR OPERATED DIAPHRAGM

What is an Air-Operated Double-Diaphragm pump?

 is a type of . It consists of two pumping chambers that are alternately filled and discharged by the movement of flexible diaphragms. Compressed air is alternately fed to, and vented from, air chambers on the opposite sides of the diaphragms to create the pumping action.

AODD pumps are generally used for transfer applications and can handle a wide variety of feeds including sludges, slurries, abrasive and shear sensitive fluids. Although they are robust, reliable and easy to maintain they can be noisy, prone to icing, and are limited to low pressure applications.

How does an AODD pump work?

An AODD pump moves fluid by the alternate and repeated back-and-forth movement (strokes) of two flexible membranes or diaphragms mounted on a common shaft (Figure 1). Although diaphragm pumps can be driven directly, with the shaft connected directly to a motor, an AODD pump uses compressed air with a sophisticated distribution system directing the air alternately to two air chambers on the opposite sides of the diaphragms. Figure 1 shows a complete cycle of an AODD pump: 

1. The compressed air control system directs air to air chamber A. 

2. The shaft moves to the left, and the movement of the diaphragms increases the volume of pumping chamber B and, at the same time, reduces the volume of pumping chamber A (Figure 1a). Valves on either side of the pumping chambers ensure that fluid flow through the pump only occurs in one direction: from inlet to discharge. The effect is to draw fluid from the inlet into chamber B, and discharge it from chamber A. 

3. As the shaft completes the stroke, the air distribution system vents air chamber A and directs the compressed air to air chamber B. 

4. The shaft now moves to the right, reducing the volume of pumping chamber B and, at the same time, expanding the volume of pumping chamber A (Figure 1b). Fluid is now discharged from chamber B, and drawn into chamber A. 

5. As the shaft completes the stroke, the air distribution system vents air chamber B and the cycle repeats when compressed air is directed to air chamber A again. 

What are the main features and benefits of an AODD pump?

AODD pumps are essentially leak-free. There are only stationary seals between the wetted parts and the outside environment so leakage can only occur if one or both diaphragms fail. As part of a general maintenance programme, diaphragms should be replaced regularly, according to the manufacturer’s recommendations. Diaphragms suffer less wear in an AODD pump than those in a mechanically driven diaphragm pump because of the benefit of pressure balancing by the compressed air supply.

AODD pumps are capable of handling abrasive, highly viscous fluids, sludges or slurries. In addition, the gentle pumping action makes them ideal for shear-sensitive fluids. The four internal check valves generally use either a ball (or cone)/seat or flap design. Ball valves provide a better seal and are less prone to wear than flap designs. Since flap-type valves are hinged, long-term use eventually causes fatigue at the flexing point. Ball valves wear more evenly since the ball is free to rotate during operation and settle in a different position on the seat. Flap-type check valves have the advantage that they can more easily pass large solids entrained within the pumped fluid.

3. With no internal seals or moving components requiring lubrication and cooling, an AODD pump can be run dry indefinitely without damage. AODD pumps are self-priming and some are capable of a suction lift of up to 8m.

4. AODD pumps are suitable for use in hazardous areas because of the use of compressed air as the power source rather than electricity. For the same reason, an AODD pump can be safely submerged - as long as the air vent is above the liquid level.

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