Recent improvements, low maintenance costs can give diaphragm pumps an advantage.
by Erik Solfelt
June 20, 2018

Since its invention in 1955 as a mining pump, the air operated double diaphragm (AODD) pump has established a well-earned reputation as a technology that is ideally suited for utilitarian, auxiliary or basic liquid-handling and transfer applications. AODD pumps excel in these types of applications because they have design characteristics that allow them to offer simple, sealless operation and enable them to self-prime, run dry, achieve suction lift up to 30 feet (9 meters or 14.7 pounds per square inch absolute [psia]), resist deadhead pumping conditions, operate while submerged and pass solids up to 3 inches (76 millimeters [mm]) in diameter.

It did not take long for companies to see why these operational characteristics would be highly desirable in many process applications and why AODD pumps are true “process” pumps capable of performing efficiently, reliably and safely in a wide range of critical fluid handling applications.

AODD pumps also hit the operational sweet spot in many of the fluid handling tasks that are prevalent in the chemical processing industry.

There are four key areas in which AODD pumps often outperform other technologies in terms of efficient, reliable and cost-effective operation. Chemical processors who are looking to optimize their operations would be wise to consider the advantages that AODD pumps can provide in these areas.

The Importance of Air

As the name states, the operation of AODD pumps relies on compressed air, which can be found in most chemical-processing plants around the world. Leveraging this readily available air can make the AODD pump a plug-and-play device that requires no infrastructure upgrades to incorporate. Additionally, the use of air to power the pump is the key source of one of its most sought-after capabilities: the ability to deadhead without damaging the pump, system or fluid. This makes AODDs easy and flexible pumps to operate.

image 1 plastic pumpsImage 1. While plastic pumps are typically a go-to pumping technology in chemical processing, there can be instances where metal pumps are a better choice for the operator. (Images courtesy of Wilden)

Keeping air usage low is critical to maintaining a healthy environment and a healthy processing plant, and recent technological advances have taken significant steps toward realizing these goals. The advances have been focused around one shortcoming in AODD pump operation. At the end of every pump stroke, a small amount of air is consumed that does not contribute to the movement of the fluid. Imagine hitting the gas pedal in a vehicle that is on ice; the wheels spin, but the car does not move.

One redesigned air distribution system addresses this problem with an air control spool that reduces the amount of air allowed into the pump at the end of the stroke, which reduces the amount of wasted energy that had traditionally been lost to the atmosphere.

This allows the AODD pump to realize up to 60 percent savings in air consumption, improves the pump’s suction-lift capabilities and enables the pump to better handle high inlet pressures, all while delivering more yield per standard cubic feet per minute (scfm) of air consumed than AODDs that feature traditional air distribution technology.

Low Maintenance Costs Through Proper Diaphragm Selection

Diaphragm pumps have a unique benefit when compared to many rotating-pump technologies in that they do not require any seals. Elimination of the need for packing or mechanical seals means that maintenance costs tend to be inexpensive and infrequent. Combined with the ease of operation, AODDs are a “set-and-forget” type of pump, provided the right diaphragms are selected for the application. Diaphragm material choice, shape and pump design all play a role.

Along with the advances in air distribution design and operation, the improvements made in diaphragm construction and function over the years have been meaningful. Chief among them is that long-life diaphragms that have been engineered for use in chemical-processing activities require less maintenance, which lowers repair costs for the operator.

image 2 newly developed air control spoolImage 2. A newly developed air control spool eliminates costly air loss at the end of the pump stroke, resulting in up to 60 percent savings in air consumption when compared to competitive models.

One piston diaphragm pump has an outer piston that is completely encapsulated within the diaphragm’s thermoplastic elastomer (TPE) material, which provides several benefits.

First, the design removes the phenomenon known as outer piston abrasion, which is when the outer piston rubs against the diaphragm as it cycles and over time, like sandpaper, wears away the material. Removing the outer piston eliminates this failure mode, dramatically increasing diaphragm life. Secondly, it also removes a known leak point in traditional diaphragm designs around the outer piston, improving overall safety when handling dangerous chemicals. Finally, the design eliminates an area along the outer piston where pumped fluid can be trapped.

In the end, the downtime and maintenance that unplanned failures can incur are typically more expensive for the facility operator than the spare parts required to keep the AODD pump operating. The use of these newer designs allows the pump to run longer before requiring diaphragm maintenance and will translate directly to a healthier bottom line.

Versatility & Compatibility

By definition, chemical processing requires the completion of some of the most intricate and complex industrial operations in the world.

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