Fluoroelastomer Specialists
Air Operated Double Diaphragm (AODD) pumps are an interesting seal-less, displacement alternative to centrifugal pumps. They are extraordinarily good ‘all-rounders’, finding applications in a wide range of industries, including construction, mining, electronics, chemicals and food processing.
The pumps are self-priming so they can run dry without any damage and because they are powered entirely from compressed air, they are ideal for use in remote or hazardous locations, not to mention explosive environments. They require low amounts of maintenance and offer low cost of ownership, completing an attractive package.
Pumping waste fluids
The pumping of waste fluids is an important requirement in a host of different industries and liquid waste can frequently contain varying amounts of solids, from sludge, slurries and solids in municipal and industrial waste applications, to slurries laden with rocks, pebbles and other particulates in the mining industry.
Air Operated Double Diaphragm pumps triumph over other pump designs, such as those with close-fitting or rotating mechanisms where abrasive slurries can cause serious wear to functioning parts.
As a result this can cause significant restoration costs and in many cases suspend productivity. Due to the size and make-up of AODD pumps, these issues rarely occur.
Of course AODD pumps are not restricted to pumping waste containing solids; they are equally well suited to pumping other types of waste, including aggressive chemicals and even viscous fluids since the flow rate is directly proportional to the speed of the pump.
For this type of application, AODD pumps differ from other pump types in that they automatically reduce the pumping rate as the level of viscosity increases. They also cleverly stop pumping when the liquid can no longer move in order to stop the potential of damaging itself. Other pumps struggle with viscous materials and can lose friction within the pump itself as well as between the walls of the pipe and the liquid.
The AODD pumping principle
In order to better understand the many benefits offered by AODD pumps, it is worth examining the way that these pumps work. Fig. 1. shows how the two diaphragms in the pump (A and B) are moved from left to right and back again by directing compressed air alternately to them via a central air valve.
The movement of diaphragm A towards the centre of the pump generates a partial vacuum in the chamber, causing ball valve 1 to close while ball valve 2 opens as air pressure forces liquid from the inlet (‘I’) into the chamber.
At the same time, diaphragm B compresses the volume in its chamber, which closes valve 3 and forces fluid past valve 4 and out through the outlet port (‘O’). When the air valve reverses the movement of the diaphragms, fluid is pumped via the left hand side of the pump. The diaphragms are clamped to the walls of the pumping chamber so there are no sliding seals in the pump. The diagram shows the flow of liquid from the bottom to the top, however alternative designs allow liquid to flow from the top to the bottom of the pump or even through the centre of the pump, which can lead to smoother flows.
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