David Rozee is the managing director of UK-based company Tri-Ark Pumps Limited, which supplies industrial pumps and spares worldwide for all popular pump brands. These include Sandpiper pumps and the Blagdon and Graco ranges. For more information, visit tri-ark.com.
Air-operated double-diaphragm pumps (AODD) have been through many innovations in technology and design since their introduction to the market more than six decades ago. They are now a key player in the pump selection process.
AODD pumps offer a sealless, positive displacement alternative to centrifugal pumps. They are used for a number of applications across a wide range of industries including oil and gas, food processing, chemicals, paints, electronics and pharmaceuticals.
By considering these four advantages of AODD pumps, end users can decide if this type of pump is the right choice for their application.\
1. Simple Construction
A key selling point of AODD pumps is that they are easy to use. The simple design combined with the ability to pump most materials makes them a popular option.
AODD pumps do not have any close-fit, sliding or rotating parts and, as a result, require minimal assembly. Many refer to these pumps as "plug-and-play" items because, once they are connected to a compressed air line, they are ready to use immediately. Once in place, the pumps can effectively run with little maintenance.
The AODD pumps are able to run dry without damaging costly internal wear parts or destroying an expensive motor. Also, the pumps do not use oil or other lubricants, which means they do not stall or get clogged because of lack of lubrication.
A useful feature is that they can be deadheaded without damage to the pump. Also, if a system is programmed to shut down the pump when certain pressures have been reached (a filter press application, for example), it can do this safely without incurring huge repair bills for broken pumps.
Another advantage of an AODD pump is that they are lightweight and portable, making them ideal for use in multiple locations. They are also easy to dismantle, repair, clean and maintain compared with other types of pumps with a more complex construction that have multiple electrical components and parts. This simplicity ensures the production line continues to run smoothly, provided that regular pump maintenance is scheduled.
Various levels of customization are available for diaphragm pumps, and the size and material of construction depend on the intended purpose. This means AODD pumps can be used for mediums as diverse as water, harsh chemicals, effluent, animal entrails and naphtha. They can efficiently handle anything from water to 90 percent solids. The ability to customize the pump also ensures costs are kept to a minimum because users are not forced to purchase a pump that is too large for the application.
The type and composition of the pumped fluid will influence the material of the pump, and the desired flow rate and potential pressure conditions will determine the size of the pump. For example, a small metal pump used to pump water would be unsuitable for pumping acids because it would dissolve. In this case, a plastic construction would be better.
In some industries, diaphragm pumps must be certified and comply with national and international safety guidelines and standards. For example, selecting appropriate construction materials is crucial in the food and beverage industry where pumps are used for hygienic applications for products such as beer, wine, milk, vegetables and other foods.
3. Safe Design
AODD pumps do not require electricity or any fuel other than compressed air. This intrinsically safe design means that no harmful fumes are exhausted, eliminating the risk to the workers and product. Furthermore, they are fully sealed units, meaning they can be partially or completely submerged in a liquid. This minimal risk of contamination provides an added benefit to the food and beverage industry.
Diaphragm pumps are driven by air, eradicating the risk of a short circuit or liquid penetrating through the wiring to cause a spark or produce flashing. In addition to this built-in safety advantage, these diaphragm pumps are available ATEX (ATmosphères EXplosibles) certified for use in applications where it is unsafe or not possible to use electricity.
4. Flexibility & Discharge
AODD pump sizes range from 0.25 to 4 inches, with flow rates ranging between 19 and 1,100 liters per minute.
Today, manufacturers offer a range of flexible sizes, enabling users to buy a pump that will give them a balanced system.
AODD pumps are capable of pumping as slow as 1 gallon per minute. Of course, a 3-inch pump will carry a higher capital investment, but the returns can be exponential when it comes to productivity gains from using a larger pump.
Another benefit of AODD pumps is that standard units are 1-to-1 ratio pumps. When a discharge pressure of more than 125 pounds per square inch (psi) is required, users can opt for a 2-to-1—or even a 3-to-1—ratio pump unit which can exceed pressures of 300 psi.