Valve sealing is a universal technology essential across all industrial sectors. Sealing technology is essential not only for industries like construction, petrochemicals, shipbuilding, machinery manufacturing, energy, transportation, and environmental protection, but also for cutting-edge industries like aviation and aerospace. Valve sealing has a wide range of applications, encompassing any device involved in fluid storage, transportation, and energy conversion.

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The Importance of Valve Sealing Technology
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The Development of Valve Sealing Materials
With the advancement of science and technology, the operating conditions of valve sealing structures have become increasingly demanding. Due to the significant increase in temperature, pressure, and corrosiveness of valve sealing fluids, traditional sealing materials such as felt, hemp, asbestos, and putty no longer meet valve operating requirements and are gradually being replaced by rubber and other synthetic materials. Rubber and other synthetic materials are generally high-molecular polymers, with functional groups (such as chlorine, fluorine, cyano, vinyl, isocyanate, hydroxyl, carboxyl, and alkoxy) on the macromolecular chains, forming active crosslinking points. Under the influence of catalysts, vulcanizing agents, or high temperatures and high-energy radiation, macromolecules transform from linear or branched structures into spatial networks. This process is called vulcanization. After vulcanization, the macromolecules of rubber or other synthetic materials lose their original fluidity and become elastomers with high elastic deformation. Commonly used rubber and synthetic materials for valve seals include natural rubber, styrene-butadiene rubber, chloroprene rubber, nitrile butadiene rubber, ethylene-propylene rubber, butyl rubber, polyurethane rubber, acrylic rubber, fluororubber, and silicone rubber.
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Performance Indicators for Determining the Quality of Valve Sealing Materials
1. Tensile Properties of Valve Sealing Materials Tensile properties are the primary properties to consider for sealing materials, including tensile strength, tensile stress, elongation at break, and permanent set at break. Tensile strength is the maximum stress at which a specimen is stretched to fracture. Tensile stress (modulus of tensile strength) is the stress reached at a specified elongation. Elongation is the deformation caused by a specimen subjected to a specified tensile force, expressed as the ratio of the incremental elongation to the original length. Elongation at break is the elongation at break. Permanent set at break is the residual deformation between the markings after the specimen is tensilely fractured.
2. Valve Sealing Material Hardness

The hardness of valve sealing materials indicates the sealing material's ability to resist external pressure and is one of the basic properties of sealing materials. The hardness of a material is related to other properties to a certain extent. Higher hardness indicates greater strength, lower elongation, better wear resistance, and poorer low-temperature resistance.
3. Compression Properties of Valve Sealing Materials

Valve rubber seals are typically in a compressed state. Due to the viscoelasticity of the rubber material, the pressure decreases over time during compression, manifesting as compression stress relaxation. When the pressure is removed, they cannot return to their original shape, manifesting as compression set. This phenomenon is more pronounced in high temperatures and oil-based media. This property is directly related to the durability of the sealing product's sealing ability. 4. Low-Temperature Performance of Valve Sealing Materials: This indicator measures the low-temperature characteristics of rubber seals. Two methods are described below: Low-Temperature Retraction Temperature: The sealing material is stretched to a certain length, then fixed and rapidly cooled to below freezing. After reaching equilibrium, the specimen is released and the temperature is increased at a constant rate. The temperatures at which the specimen retracts by 10%, 30%, 50%, and 70% are recorded as TR10, TR30, TR50, and TR70, respectively. Material standards use TR10 as an indicator, which is related to the brittle temperature of rubber. Low-Temperature Flexibility: After freezing the specimen at a specified low temperature for a specified time, the specimen is bent back and forth at a specified angle to assess the sealing performance of the seal under repeated dynamic loads at low temperatures.
5. Oil or Media Resistance of Valve Sealing Materials: In addition to contact with petroleum-based, diester, and silicate oils, valve sealing materials are sometimes exposed to corrosive media such as acids and alkalis in the chemical industry. In addition to being corroded by these media, exposure to high temperatures can also lead to expansion, reduced strength, and decreased hardness. Plasticizers and soluble substances in the sealing material are also extracted, resulting in a reduction in mass and volume, which can cause leakage. Generally, changes in mass, volume, strength, elongation, and hardness are measured after immersion in the medium for a certain period of time at a certain temperature to assess the oil or medium resistance of the sealing material.
6. Aging Resistance of Valve Sealing Materials
Valve sealing materials can deteriorate in performance when exposed to oxygen, ozone, heat, light, moisture, and mechanical stress, a phenomenon known as sealing material aging. Aging resistance (also known as weathering resistance) can be measured by changes in strength, elongation, and hardness after aging. The smaller the rate of change, the better the aging resistance.
Note: Weathering resistance refers to a series of aging phenomena that occur in plastic products due to exposure to external conditions such as sunlight, temperature fluctuations, wind and rain, including fading, discoloration, cracking, chalking, and decreased strength. Ultraviolet radiation is a key factor in plastic aging. 04
Common Materials for Rubber Seals in Valves
Nitrile-butadiene rubber (NBR) is a copolymer synthesized by emulsion polymerization of butadiene and acrylonitrile monomers. Its main properties include aging resistance, heat resistance, and wear resistance. It is widely used in oil-resistant rubber products with an operating temperature range of -50 to 100°C.
Silicone rubber (Si or VMQ) is a linear polymer with silane-oxygen bonds (-Si-O-Si) as the main chain and organic groups as side groups. The development of cutting-edge industries such as aviation and aerospace has created an urgent need for rubber sealing materials with both high and low temperature resistance. Silicone rubber has excellent heat resistance and high-temperature stability, and can be used at 150°C for long periods of time, or even at 350°C for short periods. Silicone rubber also has good resistance to polar solvents and food oils and is an excellent flame retardant. Fluorocarbon rubber (FKM or Viton), also known as fluoroelastomer, is a polymer containing fluorine atoms on carbon atoms in the main and side chains. It exhibits excellent resistance to heat, ozone, and various hydraulic fluids. It can operate at temperatures between -40 and 250°C, but is not suitable for use in certain phosphate ester solutions. Ethylene propylene diene monomer (EPDM) is a terpolymer of ethylene, propylene, and a small amount of non-conjugated dienes. EPDM rubber exhibits excellent properties such as ozone resistance, corrosion resistance, and heat resistance. Its operating temperature range is -60 to 120°C, and its natural color is beige. Polyurethane elastomer (PU) is a polymer made from polyisocyanates, polyether polyols, polyester polyols, and/or small molecule polyols, polyamines, or water, along with chain extenders or crosslinkers. It exhibits high elasticity, strength, wear resistance, and oil resistance, and is widely used across various industrial sectors. Polytetrafluoroethylene (PTFE), known as the "King of Plastics," possesses excellent chemical stability, corrosion resistance, and high lubricity. Its operating temperature range is -20 to 250°C.