Valves - Sealing surfaces - Packing material selection - Shanghai Wachi Valves

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This post was last edited by Sammy_Wang on 2016-11-23 08:52. Many valves can adapt to various operating conditions, but if the choice is not appropriate, the performance and service life of the valve will be significantly reduced. To choose the right valve appropriately, it is first necessary to understand the operating conditions suitable for the materials of its various components; selecting the valve based on its range of application will enable it to perform at its best. Sealing surface material: The sealing surface is the most critical working surface of a valve, and the quality of this surface determines the valve’s service life. Typically, the material of the sealing surface must take into account factors such as corrosion resistance, scratch resistance, erosion resistance, and oxidation resistance. Soft materials ● Rubber (including nitrile rubber, fluororubber, etc.) ● Plastics (polytetrafluoroethylene, nylon, etc.) Hard-sealing materials ● Copper alloys (used for low-pressure valves) ● Chromium stainless steel (used for medium and high-pressure valves) ● Stellite alloys (used for high-temperature and high-pressure valves as well as valves exposed to severe corrosion) ● Nickel-based alloys (used in environments with corrosive media) Packing materials In valves, packing is used to fill the space in the valve stem packing chamber, thereby preventing the medium from leaking through that space. Soft fillers: Plant-based fillers are inexpensive and are commonly used in low-pressure valves operating below 100°C. Mineral fillers can be used in valves operating at 450-500°C. The temperature of the medium for rubber O-ring seals is generally limited to below 60°C. The packing on high-temperature and high-pressure valves is also sometimes made by compressing pure asbestos along with flaky graphite powder. Rigid fillers are made from plant materials such as **, flax, cotton, jute, etc., or from minerals such as asbestos fibers; they can also be ropes woven from asbestos fibers with metal wires embedded in them and coated with graphite powder. There are also compressed, molded fillers, as well as flexible graphite filler materials that have been developed in recent years. Selection of operating temperature for common packing materials; Packing materials suitable for common media; Relationship between valve materials and temperature; Selection of materials for valve bodies, bonnets, and disc valves; Selection of materials for valve sealing surfaces and packing