Using an Air Operated Double Diaphragm Pump (AODD) is beneficial in many ways. This article will explain these benefits, particularly highlighting the superb effectiveness of the AODD pumps in specific applications while identifying the centrifugal pump's shortcomings. AODD pumps can handle the types of applications that centrifugal pumps do not support due to their design, such as fluids containing abrasives, solid-laden liquids, and viscous fluids.
AODD pumps can also handle applications fatal to most centrifugal pumps, such as dry-running, self-priming, and seal-less. Further, AODDs support deadheading the discharge or starving the suction with no damage to the pump. AODD pumps' mobility and portability also give them the upper hand when compared to centrifugal pumps.
AODD pumps have numerous applications. Some of the most common include:
Clay slurry
Ceramic transfer
Wastewater removal
Washdown under-grade
Sump or pit transfer
Asphalt slurry
More specifically, let us look deeper at some of the more regular applications seen in the market as additional examples:
Ceramic: loading and unloading transfer; product transfer applications for bulk storage, day and aging tanks; plant slip transfer to molds, lines, and recirculation of tanker; railcar unloading—just to name a few.
API Oil and Gas: upstream market for cellar sump and mud transfer applications; flap valve design allows passage of larger solids, ideal for abrasive slurries, suspended or non-suspended solids, and line-size solids.
Automotive: facility wastewater management; sumps and pits for filtering. waste and particulate-filled fluid removal.
Common Sources of Damage to Centrifugal Pumps
Fluids Containing Abrasives
In a centrifugal pump, any abrasive fluid will damage the mechanical seals, sleeves, and shaft. These damages require expensive pump repairs. It is necessary to use costly and specialized seal flush plans for even the slightest abrasives in centrifugal pumps. Conversely, AODDs can handle these abrasive fluids because they are designed with large openings, flow paths, and are fitted with diaphragm and check valve materials specifically designed to handle such liquids.
Solid Laden Liquids
Solids in any centrifugal pump will be catastrophic. Damage to the impeller and other internal rotating parts will occur along with the possibility of burning up the motor. That damage is avoided with AODDs because of their design to pass solids. 3/8"-size solids pass through the pump due to ball valve technology. Likewise, 3"-line size solids travel through the pump thanks to flap valve technology. Shear-sensitive products like live fish and eggs utilize flap valve pumps to transfer without harm to the products.
Viscous Fluids
Centrifugal pumps are generally limited to viscosities of 2900 SSU, whereas AODDs can handle well over 100,000 SSU, making them an ideal option for moving these viscous materials. AODDs are very effective for wastewater, sludges, and slurries with changing viscosities. Thicker consistent fluids such as glues and pastes can be moved effectively through these pumps also.
Difficult Tasks for a Centrifugal Pump Are No Problem for the AODD
No centrifugal pump can run dry for very long. Most of the time, in less than a minute of a dry-run condition, a centrifugal pump will typically seize up, completely ruining the mechanical seal. This will also cause the motor to overload or burn up. AODDs can run completely dry without seizing, meaning you will not lose a pump and motor.
It is important to understand that operating a centrifugal pump dry leads to tremendous heat generation inside the pump, which leads to impeller damage and eventual failure. Compared to centrifugal pumps, AODDs are self-priming, seal-less, and considered leak-free. They are very effective at emptying sumps or lifting liquids from underground; they do not require any special items or features to achieve this. A centrifugal pump would require a special priming chamber and could only work in a self-priming application if it had no other use.
Closing a discharge valve on a centrifugal pump will cause failure to both the pump and motor and possibly could cause detrimental damage to many upstream system components. AODDs can withstand a closed discharge or deadheading with absolutely no damage to any internal item or its source of power: the air compressor. Additionally, a deadheaded AODD will not use any energy, meaning the pump will not experience wear, nor will organizations need to spend money on compressed air.
Almost every centrifugal pump has a specific design for certain application parameters that define the motor horsepower, impeller diameters, seals, and flush plans. Also, centrifugal pumps include a permanent base-mounted location for the unit with hard piped suction and discharge connections. It is required to use expensive variable speed drives for changes in application flows and pressures. These dedicated systems often require expensive conversions to be utilized for anything other than its original, intended purpose. Mobility Is an Added Advantage to the AODD
Mobility Is an Added Advantage to the AODD
Here is a picture of an AODD on a pump cart that includes a strainer, valving, and gauges. This AODD was used for loading latex material from various tanks and the manufacturer’s site to the trucks to transport to the next process.
AODDs offer flexibility over centrifugal pumps due to their ease of portability and multiple different use cases. They can be cart-mounted and portable to work in numerous areas of any plant or outdoor job site and can be used to pump various fluids. This flexibility allows the AODD to act as a backup pump for units in repair, units in use, or as a utility clean-up pump on-demand. AODDs can also function as a sump pump for dewatering. These pumps offer variable flow rates by controlling air line pressure and can utilize control valves, float switches, and even batch controllers to be part of an automized system.
It is true that AODDs are not very energy efficient and can be noisy. They do vibrate and create pulses in the discharge that can be harmful to many downstream components. Although, the flow smooth out with pulsation dampeners. Despite these potential issues, AODD pumps are robust, reliable, easy to maintain, and relatively low cost when compared to centrifugal pumps. AODDs tend to be durable workhorse devices and work for various transfer applications in a wide variety of industries.
Estabrook Corporation is a leading regional sales and service organization that distributes high-quality pumps, valves, seals, controls, and repair for a total system solution approach. As a pump specialist in Ohio, Pennsylvania, and New York, we can help you properly size and select your air-operated double diaphragm pump. We have a full set of inventory and can support installation, start-up services, parts, and repair to keep your industrial processes up and running!
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