Valve sealing issues

Soft seals are easy to manufacture, can achieve high sealing levels readily, but are prone to wear. Rigid seals can withstand high temperatures.

I read a paper that analyzed the materials used for valve sealing surfaces; it should be helpful. Sealing surface materials can be divided into two categories: metallic and non-metallic. The applicable conditions for common materials are as follows: (1) Rubber. It is generally used for the sealing surfaces of valves such as globe valves, diaphragm valves, butterfly valves, and check valves in low-pressure applications. (2) Plastic. Plastics used for sealing surfaces include nylon and polytetrafluoroethylene, which feature good corrosion resistance and a low coefficient of friction. (3) Babbitt alloy. Also known as bearing alloy, it possesses excellent corrosion resistance and good running-in properties. Suitable for the sealing surfaces of ammonia stop valves operating at low pressure and temperatures ranging from -70 to 150°C. (4) Copper alloys. It has good wear resistance and a certain degree of heat resistance. Suitable for water and steam at low pressure and temperatures not exceeding 200°C. (5) Chromium-nickel stainless steel. It has good corrosion resistance, erosion resistance, and heat resistance. Suitable for media such as vapor nitric acid. (6) Chromium stainless steel. It has good corrosion resistance and is typically used in valves for media such as oils and steam at high pressures and temperatures not exceeding 450°C. (7) High-chromium surfacing steel. It possesses good corrosion resistance and work hardening properties, making it suitable for use with high-pressure, high-temperature fluids such as oils and steam. (8) Nitrided steel. It has good corrosion resistance and scratch resistance, and is commonly used in gate valves for thermal power plants. (9) Cemented carbide. It possesses excellent comprehensive properties such as corrosion resistance, erosion resistance, and scratch resistance, along with a long service life, making it an ideal sealing material. Commonly used tungsten-cobalt alloys and drill-based alloy surfacing electrodes can be employed to create sealing surfaces capable of withstanding ultra-high pressure and temperature, and they are suitable for media such as oils, gas, and hydrogen. (10) Spray-welded alloy. There are titanium-based alloys, nickel-based alloys, and zirconium-based alloy materials, which possess excellent corrosion resistance and wear resistance. To ensure the safety and reliability of the valve sealing surface, the selection of the sealing surface material must be determined based on the specific operating conditions. If the medium is highly corrosive, when selecting materials, corrosion resistance should be given priority over other properties. For the sealing surfaces of gate valves, materials with good wear resistance should be chosen. The sealing surfaces of safety valves, throttle valves, and control valves are most susceptible to erosion by the medium, so materials with excellent corrosion resistance should be used. In cases where the sealing ring is integrated with the valve body, materials with high hardness should be considered for the sealing surfaces. For ordinary valves operating under low temperatures and pressures, rubbers and plastics with good sealing properties should be preferred for the sealing surfaces. When selecting materials for the sealing surfaces, it is important to ensure that the hardness of the valve seat sealing surface is slightly higher than that of the valve disc sealing surface.