Banging the drum for AODD systems

Air-operated double-diaphragm (AODD) pumps have a variety of characteristics that able them to excel in diverse applications. 

These include: simple startup; self-priming capability,; resistance to dry running and smooth running with solids; gentle displacement pumping; continuous adjustability via controllable air volumes. 

They are also self-adjusting when the medium changes, contain no drives or rotating parts in the pumped medium, have no shaft seals and are overload-proof without regulation or monitoring via mean supply response time (MSRT) devices. Additionally they are easy to use in ATEX areas, with current-less drive via compressed air.

The first two characteristics explain AODD pumps’ flexibility. Since there is no need to align the pump when changing locations, installation can be performed by simply standing the pump upright and connecting the fluid lines and air supply, plus there is no need to prime an AODD pump. 

Once in operation, it is easy and simple to control, does not require any control electronics and/or expensive frequency converters, which might cause the motor temperature to rise during slow running without a forced cooling fan (critical for ATEX). 

Instead, the air volume and the pump flow rate is simply regulated with a needle valve. In addition, if, for example, the density or viscosity changes due to the temperature, the pump will automatically run slower or faster without damage to the pump or without the loss of liquid, as is the case with internal pump slip or a magnetic coupling that can tear during operation. And if the liquid fails to flow, for example, because the tank is empty, it simply continues to run dry. 

Another important design characteristic of the AODD pump is gentle displacement pumping. This characteristic stems from the fact that these pumps allow solids of considerable size to pass through them, resulting in very gentle pumping and low shear. And because AODD pumps do not contain any drive parts or other rotating parts within the fluid, there is no need to worry about damaging the shaft seal. Operational risks and the need to maintain mechanical seals (including the use of additives for flushing, etc.) are also eliminated. 

As they are overload-proof, the pump can only build up as much pressure as you give it via the drive air pressure, which can be the maximum permissible pressure of your filter. If outlet pressure reaches the drive air pressure, the pump simply stops, with no danger of the pump or the line bursting if the pressure line is blocked. 

There is not a risk of sparks from an electric drive, also self-heating is not an issue, and static charges can be dissipated via the pump’s conductive materials (as well as plastic). This also makes AODD pumps ideally suited for use in hazardous areas (ATEX) and mobile applications. Light and compact, these pumps are also simple to install in hazardous areas and can even operate with stored air in the case of an emergency.

Another key characteristic of an AODD pump is its enormous range of pump materials and their possible combinations. Depending on the mechanical/chemical properties or the temperature of the medium, the pump can almost always adapt to the application. Solid-block design construction also provides additional design advantages for safety, including high stability and rigidity, static weight and smooth and highly chemical-resistant surfaces.

Peter Schu?ten is the product management director for Almatec