AODD pumps can offer a good ‘all-round’ pumping solution – finding applications in the food processing areas. The pumps are self-priming so can run dry without any damage & because they are powered entirely from compressed air, they are suited to use in remote, hazardous or explosive environments. They require little maintenance & offer low cost of ownership.
Pumping waste fluids is an important requirement across the food industry. However, Air Operated Double Diaphragm Pump win out in such applications when compared to other pump designs, where abrasive or corrosive media can cause serious wear to functioning parts which can result in significant restoration costs & in many cases can reduce productivity due to pump downtime. The size & make-up of AODD pumps means that such issues rarely occur.
AODD pumps are not restricted simply to pumping waste containing solids; they are equally well suited to pumping other types of waste, including aggressive chemicals & even viscous fluids because the flow rate is directly proportional to the speed of the diaphragm pump. For this type of application, AODD pumps differ from other types of pump in that they automatically reduce the pumping rate as the level of viscosity goes high. They also stop pumping when the liquid cannot move longer, in order to stop any damage to the pump itself. Many other pumps struggle with viscous materials & can lose friction within the pump as well as between the walls of the pipe & the liquid.
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Pumping principle
To better understand the benefits of AODD pumps, it is worth examining the way that the pumps work. Figure 1 shows how the two diaphragms in the pump (A & B) are moved from left to right & 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 into the chamber. At the same time, diaphragm B compresses the volume in its chamber, which closes valve 3 & forces fluid past valve 4 & out through the outlet port (‘O’). The diaphragms are clamped to the walls of the pumping chamber so there are no sliding seals in the diaphragm pump. The pump 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 middle of the pump, which can lead to smoother flows.
AODD pumps contain fewer moving parts than many other pump types & are simple to set up. The diaphragm is a dynamic seal that converts the pneumatic pressure on one side to a fluid pressure on the other (the medium to be pumped) side of the pump. Discharge flow rates are adjusted by controlling the air inlet, so no complex control systems are required.
AODD pump is also inherently dry self-priming. They are capable of drawing up liquid even when installed above the source liquid level. This feature allows them to act as scavengers. By attaching a hose to the inlet, the pump can function as a type of vacuum cleaner to clear out & completely empty drums, barrels & other containers.
Unlike most centrifugal & displacement pumps that fail if they run dry, AODD pumps have the ability to run faster without damage when operating dry. Air shut-off valves can be added to decrease the amount of compressed air wasted whilst running dry.
Key factors to take into account while checking the suitability of a diaphragm pump for an application include the materials that needs to be pumped, the temperature at which the double diaphragm pump will need to be operated, the potential effect on the equipment & the flex life of the diaphragm itself.
Advantages
Air diaphragm pumps are a very effective type of transfer pump. These pumps can handle liquids which have high, medium or low viscosities. They are also designed to pump liquids that contain a considerable amount of solids. Air operated double diaphragm pumps can be constructed out of materials that can handle pumping even the most acidic chemicals.
Disadvantages
Most air diaphragm pumps require around 20 standard cubic-feet per minute & 100 psi of air intake to operate efficiently. Also, AODD pumps tend not to pump very accurately at their bottom end. A functioning air diaphragm pump pulsates, & a dampener must be fitted onto the pump to reduce pulsing.
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