Types of valve gaskets and their application ranges

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【Seals】Types of gaskets and their applications: Gasket-based sealing structures are widely used in various machinery and equipment, especially in pressure vessels, pipes, valves, and similar components. The simplest type of gasket is the flat gasket; it is made entirely of the same material and is used for providing static sealing at the joints of mechanical equipment, such as in the sealing of gearboxes. The ideal gasket structure should have a plastic layer on the surface and an elastomer layer on the inner side; the plastic surface layer ensures a tight fit or even interlocking for sealing, while the inner layer allows for some separation of the sealing surfaces and maintains a certain level of compressive stress throughout the sealing process. Many composite gaskets have been developed based on this concept or with slight modifications, but the principle remains the same. For example, polytetrafluoroethylene (PTFE) has good plasticity, excellent chemical resistance, and a wide operating temperature range of -190 to 250°C; it is widely used in static seal gaskets. However, its poor resilience and tendency to flow under cold conditions limit its use alone. By employing a composite structure, these drawbacks can be overcome – on one hand, it protects the gasket from corrosion by fluid media or prevents contamination in food and pharmaceutical industries, and on the other hand, it addresses the issues of poor resilience and cold flow associated with the use of PTFE alone. Types, materials, and application ranges of non-metallic gaskets
Type of gasket | Material | Pressure (MPa) | Temperature (°C) | Applicable media
Polytetrafluoroethylene gasket | Polytetrafluoroethylene sheet | ≤3.0 | -108 to 250 | Concentrated acids, bases, solvents, oils
Rubber-asbestos gasket | High-pressure rubber-asbestos sheet | Medium-pressure rubber-asbestos sheet | Low-pressure rubber-asbestos sheet | ≤6.0 | ≤4.0 | ≤1.5 | ≤450 | ≤350 | ≤200 | Concentrated acids, bases, solvents, oils
Oil-resistant rubber-asbestos sheet | ≤4.0 | -180 to 250 | Air, compressed air, inert gases, steam, ammonia, shift gas, coke oven gas, pyrolysis gas, water, seawater, liquid ammonia, condensed water, ≤90% sulfuric acid (by mass), salts, nitroammonia solution, sulfur-ammonia solution, methylamine solution, caustic soda, Freon, hydrocyanic acid, Capron production media, polystyrene production media

Types, materials, and application ranges of composite gaskets
Type of gasket | Material | Pressure (MPa) | Temperature (°C) | Applicable media
Wound gasket | Metal strip: stainless steel; Non-metallic strips: asbestos strip, polytetrafluoroethylene strip, flexible graphite strip | ≤6.4 | ≈600 | Used in internal combustion engines
Metal-faced flat gasket | Wave-shaped gasket | Metal: mild steel, aluminum, stainless steel, alloy steel; Non-metallic: asbestos sheet, rubber-asbestos sheet, polytetrafluoroethylene sheet, ceramic fiber | ≤6.4 | ≈600 | Steam, hydrogen, compressed air, natural gas, pyrolysis gas, shift gas, oils, solvents, residue oil, wax oil, oil slurry, heavy oil, propylene, caustic soda, molten salt heat carriers, acids, alkali/salt solutions, liquefied gas, water

Types, materials, and application ranges of metal gaskets
Type of gasket | Material | Pressure (MPa) | Temperature (°C) | Applicable media
Metal flat gasket | Metal toothed gasket | Mild steel, stainless steel, alloy steel | ≥4.0 | ≈600 | Steam, hydrogen, compressed air, natural gas, pyrolysis gas, shift gas, oils, solvents, residue oil, wax oil, oil slurry, heavy oil, propylene, caustic soda, molten salt heat carriers, acids, alkali/salt solutions, liquefied gas, water
Metal octagonal gasket | Metal lens gasket | Metal elliptical gasket | 10 steel, 1Cr13, alloy steel, stainless steel, etc. | ≥6.4 | ≈600 | Steam, hydrogen, compressed air, natural gas, pyrolysis gas, shift gas, oils, solvents, residue oil, wax oil, oil slurry, heavy oil, propylene, caustic soda, molten salt heat carriers, acids, alkali/salt solutions, liquefied gas, water

Asbestos-rubber sealing products
China is rich in asbestos resources. Through mechanical or chemical treatment, asbestos can be made to become more loose. When fully loosened, asbestos fibers have high tensile strength, a large surface area, good adsorption properties, are non-flammable, and possess excellent heat resistance. The highest safe operating temperature is 500–550°C, a range that generally meets the needs of industrial applications. Additionally, asbestos is inexpensive. However, its drawback is that asbestos dust causes environmental pollution and is harmful to human health; therefore, attention must be paid to environmental protection. Asbestos rubber sealing products can be divided into the following 3 categories: ① Gasket types—plate-shaped and sheet-shaped sealing products used on pipe flanges and container flanges ； ②Washers – molded and sealed products used in pumps, valves, and tanks ； ③Ribbon seals – rope-like and felt-like sealing products used in pumps, valves, and tanks. Asbestos rubber sheets are sealing materials used for pipe flanges, high-pressure vessel flanges, and various contact surfaces, made by rolling together asbestos, rubber, and additives. Oil-resistant asbestos rubber sheets are sealing materials used for pipe flanges, high-pressure vessel flanges, and various contact surfaces, manufactured by rolling together asbestos, oil-resistant rubber, and additives as the main raw materials. Reinforced asbestos rubber sheet is composed of an asbestos rubber sheet and one or more layers of galvanized steel wire mesh (or stainless steel wire mesh). They are generally divided into oil-resistant reinforcement plates and high-pressure reinforcement plates. The number of layers of wire mesh is related to the thickness of the product; generally, for every 1 mm increase in product thickness, an additional layer of wire mesh should be added. The wire mesh should be placed at the corresponding midpoints or thirds points of the asbestos rubber to enhance tensile strength, thereby enabling the product to withstand high temperatures and pressures. Thin gaskets are advisable in situations with high temperature and pressure. Thin gaskets can serve the same purpose as metal gaskets; in other words, they can achieve direct sealing between surfaces. In such cases, the roughness and flatness of the sealing surfaces must be very high. The thickness of reinforced asbestos rubber sheets generally does not exceed 3 mm. With the development of industries such as petroleum, chemicals, aviation, and defense. With the emergence of high-temperature and high-pressure as well as ultra-high-temperature and high-pressure equipment, management systems, and machines that are fast, compact, and highly powerful, conventional asbestos rubber sheets can no longer meet the requirements. Such materials need to have the properties of resisting high temperatures and pressures, being resistant to oils, being non-flammable, having good elasticity, and being able to cope with large fluctuations in temperature and pressure. They should also possess a long service life and excellent sealing capabilities. Therefore, only reinforced asbestos rubber sheets and the following asbestos steel sheets, wound gaskets, etc., can meet these requirements.