Plastic AODD Pumps Provide Reliability for Chemical Applications

The manufacture, transfer, handling and use of dangerous chemicals such as acids, caustics and solvents—which can be corrosive, toxic and hazardous to life and the environment—can pose significant challenges for steel pumps. Specific types of steel pumps may cover only a narrow chemical-resistance band, which, in some cases, can limit the applications they can handle—particularly those involving dangerous chemicals. One alternative for successful chemical-manufacturing and handling operations is the plastic pump. Within this subset, end users can choose from many types of pump technologies: for example, lobe, gear, vane, centrifugal and progressive cavity. Some of these technologies, however, can have potential shortcomings that may make them impractical for chemical-related applications. Some of these challenges include the inability to run dry or self-prime, use of leak-prone mechanical seals, shear-producing operation, inability to deadhead, limited viscosity ranges and elevated maintenance costs.

Plastic air-operated double-diaphragm (AODD) pumps may be an ideal alternative for handling dangerous, caustic chemicals. These pumps are capable of running dry and self-priming, produce a shear-sensitive flow, have no mechanical seals, can deadhead, are powered by air and can be easily maintained.

Benefits of Solid-Body Pumps

While plastic AODD pumps can be ideal for operations that manufacture or transfer dangerous chemicals, one question remains: Should the pump be constructed of injection-molded plastic or from a solid block of plastic? A reliable and proven choice for these applications is the plastic solid-body AODD pump, specifically one that is machined from a solid block of polyethylene (PE) or polytetrafluoroethylene (PTFE). The materials are also available in PE-conductive and PTFE-conductive formulations for use in potentially explosive atmospheres. End users seem to prefer solid-body plastic AODD pumps over their injection-molded cousins. One reason is that solid-body pumps are inherently thick-walled, providing stability during the pumping process. Injection-molded pumps can have small cavities or crevices in the body where liquids can accumulate and leak paths can form. Because injection-molded pumps are lightweight, any motion during the pumping process is transferred to surrounding system components and piping, which can lead to equipment damage. Pumps that are machined from a solid block of PE or PTFE, on the other hand, can provide more weight, wall thicknesses, chemical compatibility and sealless design along with the ability to withstand potentially explosive atmospheres. Pumps that are constructed of polyethylene offer excellent abrasion-resistance. One line of plastic solid-body AODD pumps has been shown to last seven times longer than pumps made with polypropylene—while still having similar chemical-resistance characteristics—and are said to be 1.6 times more durable than stainless-steel pumps. Solid PE may also deliver better sealing, higher static weight, smoother operation and better torque retention than other popular materials of construction. Similarly, PTFE has a nearly universal chemical resistance. The machining of a solid block of PE or PTFE is relatively economical because of advanced modern computer numerical controlled (CNC) technology, enabling far tighter tolerances to be achieved than those possible with many injection-molded parts, which require tightening straps and seals to compensate for mechanical variations from surrounding parts. The occurring loads in a solid-body AODD pump are absorbed by the component itself with no necessary external reinforcements. This allows the external unit to be designed without any metal at all, which reduces the risk of corrosion. An AODD pump with a solid-block design is more capable of withstanding external shocks, such as those created by improper handling. A solid-body pump is also capable of absorbing the loads created by the connecting pipes. Solid-body AODD pumps constructed of PE/PTFE-conductive plastic are intrinsically safe and meet the operational requirements of the European ATEX 94/9/EG directive, as well as the U.S. Food & Drug Administration for hygienic-manufacturing operations that take place in potentially explosive atmospheres.

From The Field

Anytime substances comprised of dangerous chemicals are manufactured or handled, an inherent risk is involved. This risk stems from the fact that the release of these chemicals can lead to severe health consequences for all forms of life and environmental damage. A number of high-profile companies that require full containment of the dangerous chemicals that play an important part in their manufacturing processes have successfully incorporated solid-body AODD pumps in their operations. Many of the solvents that a Switzerland-based pharmaceutical company uses in its production process are produced at its German research and diagnostics facility and are classified as hazardous or dangerous chemicals. They must be handled according to the ATEX requirements of European Union directive 94/9/EG regarding the use and disposal of potentially explosive liquids. "Safety and efficiency are the two most important aspects here at our site," the facility's assistant tank manager said. "I think that (these solid-body AODD) pumps are very safe and reliable, and they are one thing that I never have to worry about." A company in the Netherlands specializes in creating and supplying complete systems used in surface-treating steel, particularly pretreatment applications in the hot-dip galvanizing process. The hot-dip galvanizing process uses a flux fluid that is highly abrasive and corrosive, necessitating the use of plastic pumps. "We knew that to manufacture our products we would need plastic pumps that would have to deal with very corrosive fluids like hydrochloric acid," the director and co-owner of the company said. "Steel, carbon steel and stainless steel aren't compatible with these very aggressive fluids, so you need plastics like PE. The heart of our units is formed by (these types of) pumps. We have to rely on them."

Conclusion

Achieving the full containment of hazardous, flammable or explosive chemicals is a daily challenge and concern for plant operators who manufacture, handle or use them. Notable shortcomings in chemical compatibility, corrosion resistance and operational capabilities have limited the use of steel pumps and other pump technologies. As plastic AODD pumps, especially those constructed of PE or PTFE, grow in use in dangerous chemical applications, plastic solid-body AODD pump can be an ideal choice. Solid-body AODD pumps possess the weight, wall thickness, tolerances and machining needed to deliver leak-free operation when handling dangerous chemicals.