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A brief introduction to O-rings commonly used in valves

Release time:

Jul 06,2024

Rubber O-rings have good resistance to abrasion, ozone, oil, corrosion and temperature, as well as good elasticity and flexibility. Under various working conditions, they can effectively prevent gas or liquid leakage and reduce vibration and noise, and are widely used in the stem sealing of valves.

   Rubber O-rings have good resistance to abrasion, ozone, oil, corrosion and temperature, as well as good elasticity and flexibility. Under various working conditions, they can effectively prevent gas or liquid leakage and reduce vibration and noise, and are widely used in the stem sealing of valves.

   Stem O-ring sealing principle: the use of O-rings to form a seal between the stem and the valve body. O-ring is an annular rubber seal with compression deformation and elastic recovery characteristics. A groove is machined on the valve stem and the O-ring is installed in the groove. When the stem is connected to the valve body, the O-ring is compressed. Due to the elasticity of the O-ring, it generates an inward springing force, making a seal between the O-ring, the stem and the valve body.

   When the valve is closed, the gap between the valve stem and the valve body will be subjected to the pressure of the internal medium, and the elasticity of the O-ring will be further strengthened, thus enhancing the sealing effect. Even under high pressure, the O-ring can effectively seal.

   According to the different working conditions and media used in the valve, the choice of O-ring is also different, valve O-ring commonly used materials are FKM, CR 、NBR、 EPDM、 FFKM.

    一、FKM:  FKM is a well-known high-performance rubber with particularly good resistance to high temperatures, ozone, weather, oxidation, mineral oils, fuel oils, hydraulic fluids, aromatics and many organic solvents and chemicals.

Applicable temperature range: Static Seal: -26°C ~ 232°C, up to 275°C for short periods of time. Although it can still be used for a short period of time at a temperature of 275℃, its service life will be shortened when the temperature exceeds 250℃.    Dynamic seal: -15°C ~ 200°C

    FKM is commonly used in the automotive, chemical, aerospace and many other industries due to its excellent resistance to high temperatures, oils, solvents, flames, chemicals and weather.

     二、CR:CR is a copolymer of chlorine and butadiene.CR has good ozone, weather, chemical and ageing resistance. It also has good mechanical properties, flame retardancy and good low temperature elasticity.

     Temperature range: -40℃ ~ 100℃, short time up to 125℃. CR is used in thousands of different environments, including automotive, wire and cable sheathing.

     三、NBR: The amount of acrylonitrile in the NBR molecule is variable (18% - 50%) and affects the properties of the finished material. The higher the content of acrylonitrile, the better the resistance to lubricants and fuel oils, but its low-temperature elasticity and compression set rate deteriorate. The lower the acrylonitrile content, the better the low-temperature resistance, but at the same time sacrifices the oil resistance at high temperatures. Given these relative relationships, the compromise is a rubber with a medium acrylonitrile content. Compared to other elastomers, NBR has good mechanical properties and high friction resistance. NBR is not very weather and ozone resistant. Special formulations are available to improve this, or NBR/PVC blends can be used to provide excellent weathering, ozone, and fuel resistance.  Temperature range: -40 ~ 100°C

     四、EPDM: EPDM is a terpolymer made of ethylene and propylene, plus a trace amount of third monomer. EPDM has excellent ozone resistance, heat resistance and weather resistance, good elasticity at low temperatures, good chemical resistance, and also has excellent insulating properties. Temperature range: -55 ~ 125°C (TR10-46.1°C), up to 150°C with organic peroxide vulcanisation. EPDM has a wide range of applications in the automotive industry, where the use of EPDM as a sealing component in phosphate-ester-based hydraulic fluids and glycol-based brake fluid systems is a good choice.

    五、FFKM： FFKM, which has a higher fluorine content than FKM, has a fluorine content of 74-76%. Because of the higher fluorine content than FKM, FFKM has the best temperature and chemical resistance among all elastomers.  Temperature range: -25 ~ 250°C

    FFKM is used in the semiconductor industry, petrochemical industry, automotive industry, nuclear energy industry, aerospace equipment, etc. In the more difficult environments, FFKM's excellent sealing and endurance capabilities can give full play to its performance advantages.

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