What are the common non-metallic materials for valves?

Nitrile rubber Buna-N
The rated temperature range of nitrile rubber valve seat is - 18 ℃ ~ 100 ℃. Usually also called NBR, nitrile, or Hycar. It is an excellent general-purpose rubber material, suitable for water, gas, oil and grease, gasoline (except gasoline with additives), alcohol and ethylene glycol, liquefied petroleum gas, propane and butane, fuel oil and many other media. At the same time, it also has good wear resistance and deformation resistance.
The rated temperature range of food grade (FG) nitrile rubber valve seat is - 18 ℃ ~ 82 ℃. Its composition complies with CFR Part 21 177.2600 Festival. Its application scope is the same as that of conventional nitrile rubber, but it needs FDA certification.
Ethylene propylene rubber EPDM
The rated temperature range of ethylene propylene rubber valve seat is - 28 ℃ ~ 120 ℃. EPDM is the abbreviation of its composition, that is, the terpolymer of ethylene, propylene and diene, which is usually also called EPT, nordell, EPR. Excellent ozone resistance and weather resistance, good electrical insulation, good resistance to polar capacitors and inorganic media. Therefore, it can be widely used in HVAC industry, water, phosphate, alcohol, ethylene glycol, etc. Ethylene propylene rubber valve seat is not recommended to be used in hydrocarbon organic solvents and oils, chlorinated hydrocarbons, turpentine, or other petroleum grease.

The rated temperature range of food grade EPDM valve seat is - 28 ℃ ~ 120 ℃. Its composition complies with CFR Part 21 177.2600 Festival. Its application scope is the same as that of conventional nitrile rubber, but it needs FDA certification.
Polytetrafluoroethylene PTFE
The rated temperature range of PTFE valve seat is - 32 ℃ ~ 200 ℃. Excellent high temperature resistance and chemical corrosion resistance. Because polytetrafluoroethylene has high compactness and excellent impermeability, it can also prevent the corrosion of most chemical media.
Conductive polytetrafluoroethylene is an improved polytetrafluoroethylene product, which allows current to pass through the lining, thus canceling the insulation performance of polytetrafluoroethylene. Because of its conductivity, conductive polytetrafluoroethylene cannot be tested by electric spark.
Reinforced polytetrafluoroethylene rtfe
Rtfe is a modifier of PTFE material. Although the friction coefficient of pure PTFE is very low (0.02 ~ 0.04), it has great wear. Moreover, due to its easy creep, poor mechanical properties, low bearing capacity and poor dimensional stability, the use of pure PTFE as friction material has great limitations. Only modification can meet the special requirements of all walks of life for wear-resistant sealing materials through material composite. In terms of improving the wear resistance of PTFE, some wear-resistant substances such as glass fiber, carbon fiber, graphite, molybdenum disulfide, bronze powder and some organic compounds can be added to make them form network nodes in PTFE layered structure, so as to improve the stiffness, thermal conductivity, creep resistance and wear resistance.
Viton Viton
The rated temperature of fluororubber valve seat is - 18 ℃ ~ 150 ℃. Viton is a registered trademark of DuPont company and fluorel is a registered trademark of 3M company equivalent to fluororubber. This material has high temperature resistance and excellent chemical corrosion resistance. It is suitable for hydrocarbon products, low concentration and high concentration mineral acids, but it can not be used in steam medium and water (poor water resistance).
UHMWPE UHMWPE
The rated temperature range of UHMWPE valve seat is - 32 ℃ ~ 88 ℃. This material has better low temperature resistance than PTFE, but still has excellent chemical resistance. UHMWPE also has good wear resistance and corrosion resistance, and can be used in high wear occasions.
Silicon copper rubber
Silicone copper rubber is a polymer with organic groups whose main chain is composed of silicon oxygen atoms. The rated temperature range is - 100 ℃ ~ 300 ℃. It has good heat resistance and temperature resistance, excellent electrical insulation performance and great chemical inertia. It is suitable for organic acid and low concentration inorganic acid, dilute alkali and concentrated alkali. Disadvantages: low mechanical strength. Post vulcanization treatment is required.
Graphite
Graphite is a crystal of carbon. It is a non-metallic material with silver gray color, soft quality and metallic luster. Mohs hardness is 1 ~ 2, specific gravity is 2.2 ~ 2.3, and its bulk density is generally 1.5 ~ 1.8. It has the characteristics of high temperature resistance, strong oxidation resistance, high chemical resistance, high thermal conductivity, high corrosion resistance, etc. It has special oxidation resistance, self lubrication and plasticity at high temperature, and has good conductivity, heat conduction and adhesion. It can be used as filler or performance improver for rubber, plastics and various composite materials to improve the wear resistance, compression resistance or conductivity of materials. Graphite is usually used to make the sealing gasket, packing and seat of the valve.
The melting point of graphite is very high. It begins to soften when it reaches 3000 ℃ in vacuum. When it reaches 3600 ℃, the graphite begins to evaporate and sublimate. The strength of general materials gradually decreases at high temperature, while the strength of graphite is twice that at room temperature when it is heated to 2000 ℃. However, the oxidation resistance of graphite is poor, and the oxidation rate gradually increases with the increase of temperature.