Pumps are a vital technology that help operators complete essential processing and transfer functions in many industrial applications across multiple markets. Without this technology, these applications would not function as optimally as they
do today.
When it comes to these industrial applications, making the right pump technology choice is paramount. While many different technologies exist, air-operated double-diaphragm (AODD) pumps tend to be a common choice for a diverse range of fluids, such as chemicals, food, oil, paint and adhesives, among others.
AODD pumps work well with these fluids because of their design characteristics. These pumps, which rely on compressed air to function, can self-prime, run dry, process fluids with solids up to 3 inches (76 millimeters [mm]) in diameter, achieve suction lift up to 30 feet (9 meters [m]), resist deadhead pumping conditions and even operate while submerged. AODD pumps also feature a sealless design, which keeps valuable fluids in the pump.
Even with all these perks, another careful consideration must be made to enjoy all the benefits of AODD pumps. Operators must also pick the right diaphragm from a verified supplier when selecting this pump technology for an application. This decision is critical to the safety and efficiency of the AODD pump and helps ensure—with the right diaphragm—the pump’s long-term integrity and functionality.
Preselection
Before selecting the proper diaphragm, operators should ensure they are making that selection from a verified supplier or one recommended by the pump manufacturer. Operators who neglect this preselection step run the risk of obtaining a diaphragm that is not up to the standards set by the manufacturer.
In some cases, operators could be purchasing a pirated diaphragm. In either case, these unverified parts can negatively impact the performance of the AODD pumps. Detrimental effects include performance downgrades in the pump’s operation, pump damage and the lack of a warranty and manufacturer support.
Diaphragm Materials
AODD pumps have been around since 1955, giving operators plenty of time to test and review the impact of different diaphragms on this technology. Three main material families are used to categorize AODD pump diaphragms—rubber, thermoplastic elastomer (TPE) and polytetrafluoroethylene (PTFE). Each material provides characteristics that make them well suited for varying applications.
Rubber: Rubber diaphragms are made from synthetic rubber with a nylon fabric mesh to assist with the diaphragm’s flexibility. There are four available rubber diaphragm materials, which are neoprene, Buna-N, ethylene propylene diene terpolymer (EPDM) and fluoropolymer elastomers. Each of these materials aids the AODD pump in different applications and conditions.
For example, neoprene is a general-purpose, low-cost diaphragm designed for nonaggressive chemical applications, such as water-based slurries and seawater. It is known for its longevity and abrasion resistance. Buna-N works best with petroleum and oil-based fluids, ranging from gasoline to turpentine. Also referred to as nitrile, this diaphragm provides moderate longevity and abrasion resistance. It also functions well in food and beverage applications.
EPDM is a low-cost alternative diaphragm for pumping dilute acids or caustics. Typically found in the food, pharmaceutical, manufacturing and paint and coating industries, EPDM diaphragms are known for having good longevity and moderate abrasion resistance. On the flip side, fluoropolymer elastomer diaphragms are designed to handle extremely hot temperatures and harsh chemicals. It features exceptional performance with aggressive fluids, such as aromatic and chlorinated hydrocarbons, and has moderate longevity and abrasion resistance.
Thermoplastic Elastomers (TPE): TPE diaphragms are made through injection molding, meaning they do not require a fabric reinforcement like their rubber counterparts. These diaphragms have material options like polyurethane, Santoprene, copolyester and nitrile.
Polyurethane functions as the general-purpose diaphragm, designed for nonaggressive chemical applications such as water and wastewater. Its longevity and abrasion resistance are exceptional. Santoprene serves as a more affordable version of PTFE. These diaphragms are best suited for handling acidic and caustic fluids, such as sodium hydroxide and hydrochloric acid. Because it has excellent longevity and abrasion resistance, this diaphragm is used in the chemical, pharmaceutical, wastewater and chemical industries. Copolyester provides good longevity and excellent abrasion resistance. These diaphragms are ideal for food processing applications and offer low compression set characteristics. Nitrile is commonly used in petroleum applications due to its enhanced oil resistance and low oil swell. It offers moderate longevity and good abrasion resistance.
PTFE: Due to its chemical makeup, PTFE can be used with a wide range of fluids, even highly aggressive variations, such as hydrocarbons, acids, caustics, ketones and acetates. Featuring longevity and moderate abrasion resistance, PTFE works best in food and beverage and pharmaceutical applications. PTFE, however, is non-elastic, so a backup diaphragm of a different material is required for flexibility and memory. Options for backup diaphragms are neoprene, copolyester and high-temperature Buna-N.
Several Considerations
Operator knowledge and experience with diaphragms serve as one option for diaphragm selection, but even the most experienced operator should still look at several factors before choosing their diaphragm. As discussed with the materials and their distinct properties and features, there is not a universal diaphragm for every application.
To determine the best diaphragm for a given application, there are seven primary factors to consider—abrasion resistance, chemical resistance, temperature ranges, sanitary standards, inlet condition, longevity and cost.
Abrasion resistance is the diaphragm’s ability to withstand wear and friction when encountering solids and particles in the processed fluid. Chemical resistance measures the compatibility of the diaphragm’s material with the processed fluid. Temperature ranges indicate the flexibility and performance of the diaphragm at varying temperatures, as well as its capabilities in extremely high and low temperatures.
Sanitary standards come into play primarily in diaphragms used in food and beverage applications. These standards help ensure the diaphragm complies with hygienic or sanitary standards. The inlet condition looks at a diaphragm’s capacity to move fluid from one place to another. Longevity, also known as flex life, is the expected life cycle of the diaphragm before replacement. Cost involves multiple factors, such as initial price, rated longevity of the application, downtime expenses and diaphragm replacement labor.
With material capabilities and performance factors identified, operators can make an informed decision about what diaphragm will work best with their AODD pumps in a given application, but there is also an expedited way to guide operators to the type of diaphragms that will best suit their respective applications.