【2026 Actuators】The impact of diaphragm material on pneumatic actuators
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Common materials for bread-like sheets include nitrile NBR, ethylene propylene diene monomer EPDM, fluororubber FKM/Viton, chloroprene CR, and rubber reinforced with fabric; these materials directly determine the gas tightness, service life, temperature resistance, chemical resistance, and thrust stability.
1. Nitrile rubber NBR (the most commonly used type): Advantages include wear resistance, tolerance to compressor oils used in instruments, low cost, good elasticity; it works well even when the air supply contains a small amount of lubricating oil, and its thrust remains stable at normal temperatures (–20 to 80°C). Disadvantages: Not resistant to high temperatures, acids, alkalis, organic solvents, or water vapor; it ages rapidly, becomes hard, and cracks when exposed to high temperatures. Applicable to: normal-temperature, dry, and clean instrument air and water / regular medium control valves. Performance drawbacks: Cracking and air leakage occur after 1–2 years in high-temperature environments, along with valve position drift.
2. Ethylene propylene diene monomer EPDM (resistant to water, acids, alkalis, and water vapor). Advantages: resistant to water vapor, weak acids and alkalis, aging, and high temperatures (-40～120°C); the preferred choice when the gas source contains water; resistant to ozone and less prone to cracking. Disadvantages: It is not resistant to mineral oils; the presence of large amounts of lubricating oil in the gas source can cause swelling, bubbling, softening, and loss of functionality. Applicable to: steam valves, humid gas sources with moisture, and water treatment applications. Consequences of wrong selection: Oil in the air supply → swelling of the diaphragm, resulting in jamming and internal leakage.
3. Fluororubber FKM (for harsh conditions involving high temperature and corrosion): Advantages include oil resistance, resistance to acids and alkalis, resistance to solvents, high-temperature tolerance (-20～180°C), corrosion resistance, and the longest service life. Disadvantages: High hardness, slightly poor elasticity, high cost; it tends to harden and experience a decrease in sensitivity when cooled too much at low temperatures. Applicable to: heat transfer oil, high-temperature oils, and chemical corrosive media applications. Advantages: It can withstand harsh operating conditions for 3 to 5 years without damage, and the valve stroke remains stable over time.
4. Rubber diaphragm with fabric interlayer (fiber canvas inserted in the middle). Plain rubber versions without fabric are used; fabric interlayers are necessary for actuators that require high thrust. Advantages: high tensile strength and resistance to stretching; it does not deform or bulge under compression; actuators with large diameters and high air supply pressures remain unchanged in shape, and the thrust remains constant. Disadvantages: Flexibility is slightly lower than that of pure glue, and low-temperature flexibility deteriorates. No disadvantages of fabric interlayer: Under high pressure, the diaphragm stretches and deforms, resulting in insufficient valve travel and poor sealing.
5. Chloroprene rubber CR (rarely used; for outdoor equipment): resistant to ozone and sunlight, suitable for use in outdoor actuators; not resistant to oils, and tends to swell and get damaged in environments with oil or gas present.
4 typical failures caused by incorrect material selection: Swelling: EPDM is used for oil-based applications, while NBR is used for oil, water, and gas applications → the diaphragm expands, causing jamming, air leakage, and sluggish operation.
Hardening and cracking: When high-temperature steam is used, NBR undergoes short-term cracking and air leakage occurs, with continuous leakage from the exhaust port.
Tensile deformation: Pure adhesive without fabric reinforcement used for high pressure and high thrust → bulging of the diaphragm; insufficient stroke, inability to shut off completely.
Corrosion perforation: Chemical corrosive agents penetrate into the membrane head when ordinary rubber is used → rapid degradation and failure.
Quick selection: ·Normal-temperature dry air, organic oil-containing gas sources → NBR clad fabric ·Steam, moisture-containing humid gas sources → EPDM clad fabric ·High-temperature hot oil, chemical corrosion → FKM fluorocarbon rubber