Pump Reliability Solutions: PTFE Diaphragms
What are Diaphragm Pumps?
Diaphragm pumps are positive displacement pumps that use contracting and expanding cavities or displacement chambers to move fluids via a reciprocating or flexing diaphragm. Simple diaphragm pumps consist of a diaphragm, a displacement chamber, two valves, and a driving mechanism. Modern industrial diaphragm pumps can have multiple chambers and many diaphragms.
They are composed of an elastomeric or otherwise flexible material that is fixed in place between the displacement chamber holding the fluid and an attached flange, or secondary chamber, holding a driving fluid such as air or hydraulic oil. The displacement chamber has two check valves, which allow flow in from the intake and out from the exhaust port. The check valves are spring-loaded ball valves, or flapper valves, often made of the same material as the diaphragm.
Diaphragm pumps work by pushing fluid out of the displacement chamber as the diaphragm is flexed by a drive mechanism such as air pressure, hydraulic fluid, reciprocating piston or solenoid. The flexes of the diaphragm cause alternating pressure increases and decreases in the chamber, which moves media into and then out of the diaphragm pump.
Diaphragm pumps are increasingly being used due to their high reliability compared to alternative pump types because they contain few moving parts, no parts in sliding contact and no shafts or bearings requiring sealing from the media. Sealing or lubricating oils are not required, so oil vapors cannot leak into and contaminate the pumped media. Since they are oil-free, they typically are seal-less too, which minimizes cleaning and maintenance downtime.
Diaphragm pumps can handle gases, liquids, slurries or gas-liquid mixtures via a reciprocating diaphragm. The diaphragm material must be chemically resistant and, ideally, inert in regard to the media pumped. Diaphragm pumps can move thin to highly viscous media; even abrasive slurries can be moved because the diaphragm isolates media from pump internal mechanisms. Diaphragm pumps are an important process tool in industries handling paints, coatings, colorants, pigments, foods, beverages, adhesives, chemicals, pharmaceuticals, wastewater and biological materials (e.g., blood, plasma, cells).
Flexible Membrane Performance
Less Unplanned Maintenance
Understanding the stresses and performance requirements of the diaphragm can help in selecting the optimum material to increase pump effectiveness, reliability, and life. Diaphragm membranes must withstand millions to tens of millions of flex cycles. Long flex-life materials are desirable and provide predictable performance, which enables scheduled shutdowns for maintenance and membrane replacement. A diaphragm material with a short flex life will often cause unplanned shutdowns due to pump failure and can be extremely costly. Pump failure can cause a multitude of problems downstream in a production plant. A sudden loss of fluid flow can damage valuable capital equipment in paper mills, chemical process plants, power generation facilities, pharmaceutical factories, and semiconductor wafer fabrication sites as well as loss of a complete production batch. Replacing or repairing specialized production equipment can take days or weeks, resulting in lost production. The high durability and long life of VERSIV™ flexible barrier materials typically increases the mean time between required maintenance cycles and reduce unplanned shutdowns.
Reducing pulsations and providing smooth flow is important in some diaphragm pump applications, such as precision dispensing and metering of coatings, adhesives, lubricants, dyes or active pharmaceutical ingredients. Several pump OEMs recommend pulsation dampeners to control pulsing and surging. Reducing the intensity of pulsations and achieving a more continuous flow is possible with an increased number of smaller displacement diaphragm flex cycles per unit time.
The increased number of flex cycles demands a material with even higher flex-life performance properties compared to traditional diaphragm materials. Electric-operated diaphragm pumps use a small electric motor and cam to reciprocate a piston and flex the diaphragm. They can generate high cycling and reduced pulsation compared to pumps driven by pneumatic or hydraulic fluids. A high flex-life diaphragm barrier is particularly beneficial in these applications.
Easy cleaning and non-stick characteristics is another important consideration in production lines that run different chemicals, pigments, coatings, or drugs on the same line. Media must be purged or cleaned to prevent cross-contamination. Flex barriers with a low surface energy prevent media from chemically bonding or sticking and facilitate clean-in-place procedures. Flex barriers with high smoothness and crack and void-free surfaces are easy to maintain because they have fewer surface inhomogeneities (protuberances or cavities) for dirt or media to lodge or build up. Increasing material smoothness also reduces the coefficient of friction, which enhances pump flow and cleanliness. The diaphragm material must have excellent chemical resistance to solvent, acidic and alkaline media. Abrasion resistance is important in applications pumping slurries, pastes, grease or pigment-filled resins or paints.
Fewer Diaphragm Leaks
Permeability is another consideration for selecting a flex barrier for a pump diaphragm. Depending on the thickness and density, as well as the chemical nature of the flex film, vapors can permeate or pass through a pump diaphragm. If toxic or corrosive chemicals are dissolved in the media, they could pass into the hydraulic system or surrounding air, which would pose a hazard. Diaphragm pumps and diaphragm valves are considered “leakless” under EPA Leak Detection and Repair (LDAR) guidelines.
However, if vapors or volatile organic compounds (VOCs) pass through to the atmosphere outside the pump, then costly repair actions could be required. Leaks in a diaphragm occur if it ruptures prematurely due to poor flex life. A highly permeable diaphragm material could allow water vapor to pass through as well. Contamination from the environment into the pumped media is another possibility. Water or vapor in the surrounding pneumatic system or hydraulic fluid could transmit through the membrane and contaminate the process media. A flex barrier material with low permeability and low mean time between failures prevents the release of media into the environment or vice versa.
Compliance with Food and Drug Regulations
Another consideration is the flex barrier’s conformability to hygienic regulations and sanitary standards, which can be a significant factor for diaphragms in pharmaceutical, medical, dental, and electronic equipment. Diaphragms handling foods and beverages must comply with the U.S. Food and Drug Administration 21 CFR 177 standards. Diaphragms carrying drugs or active pharmaceutical ingredients must comply with United States Pharmacopeia Convention (USP) Class VI standards. Manufacturing a flex barrier or pump diaphragm material with a combination of high flex life, low permeability, low friction surface energy, and regulatory compliance is challenging.
VERSIV™ Flex Barriers
VERSIV™ flex barrier materials consist of different film and laminate constructions made from premium high molecular weight fluoropolymer resins. VERSIV™ excels in chemical process applications requiring high levels of movement and cyclin, a wide operating temperature range, chemical resistance, and stress-crack-resistant performance such as tank linings, pump diaphragms, valve diaphragms, and check valve flappers. The VERSIV™ materials meet and often exceed industry requirements for fluorocarbon resin sheets and film such as ASTM D-3368 and other specifications.
Saint-Gobain uses specialized surface treatments and a proprietary lamination process to impart high flex life, low permeability and high smoothness, and a low coefficient of friction in VERSIV™ flex barriers. The high-molecular-weight fluoropolymer, such as polytetrafluoroethylene (PTFE) and perfluoroalkoxy (PFA) copolymer resin, provides excellent stress crack resistance and extended flex life when appropriately processed. The low surface energy of fluoropolymers provides outstanding anti-stick characteristics and exceptional chemical resistance, even to highly aggressive chemical media.
VERSIV™ materials are suitable for both cryogenic and high-temperature applications, with an operating temperature range of -425° F to 500° F (-254° C to 260° C). Figure 3 demonstrates the improved flex life of the VERSIV™ material compared to a conventionally modified PTFE. The VERSIV™ products had approximately a 70% increased lifespan in Saint-Gobain’s internal high-frequency flex life tests to simulate diaphragm material flex life performance.
VERSIV™ flex barriers are and have practically universal resistance to chemicals and highly aggressive media such as aromatic or chlorinated hydrocarbons, acids, caustics, ketones, and acetates. Resins used to produce VERSIV™ Flex Barrier materials conform to the major regulations critical to success in pharmaceutical, food and beverage, sanitary, and medical applications such as FDA 21 CFR 177.1550, (EC) No. 1935/2004, (EU) No. 10/2011, (EC) No. 23/2006 (GMP), USP Class VI and 3-A Sanitary Standard The VERSIV™ materials conform to REACH ((EC) No. 1907/2006) and RoHS (2011/65/EU) regulations, so they do not contain any hazardous or banned compounds that would restrict the materials used in electronics products.
The permeability of polytetrafluoroethylene materials varies significantly and performance is dependent upon choosing the right material grade and flex barrier construction. The VERSIV™ flex barrier (LP01) has higher permeability compared to a conventionally modified PTFE material. However, an additional PFA barrier to the VERSIV™ flex membrane product can mitigate this and reduce permeability by 30%. Saint-Gobain engineers are continuing to develop VERSIV™ Flex Barriers with even better permeability and flexing properties as it is often the combination of these two properties that are important in achieving longer life in very aggressive conditions.
*Saint-Gobain Composite Solutions will work with customers to address their needs in regard to the regulations noted in this brief.
Benefits of Extended Life Flex Membrane Diaphragms
- Reduced Installation & Repair Costs
- Reduced Pump and Process Line Downtime
- Increased Quality & Reduced Waste of Pumped Media
- Reduced Mean Time Between Failure (MTBF)
- Easier Cleaning Between Media Change Overs
- Reduced Cost of Consumables (CoC) - Reduced Inventory/Fewer Spare Parts
Utilizing VERSIV™ flex barriers within a diaphragm pump design or upgrading existing pumps can minimize the total cost of ownership due to several factors. Since the VERSIV™ flex barrier material provides longer diaphragm life compared to other materials, the frequency of shutdowns for maintenance or diaphragm replacement is reduced. This lowers the cost of the consumables as well because fewer spare parts or replacement diaphragms need to be kept on hand.
The high smoothness and low friction of a VERSIV™ diaphragm surface enables easy cleaning between process runs of different paints, chemicals, foods, or pharmaceutical ingredients. The high cleanliness and improved durability increase the quality of the media handled due to the reduced contamination risk. Reduced downtime, less maintenance, higher cleanliness, and the robustness provided by VERSIV™ flex-barriers result in overall increases in productivity and process yields.
This article was produced by IEEE GlobalSpec. Visit the Saint-Gobain Composite Solutions' Engineering360 page on IEEE GlobalSpec.