The valve is a control component in the pipeline fluid delivery system. It is used to change the passage section and the flow direction of the medium. It has the functions of diversion, cutoff, regulation, throttling, check, diversion or overflow pressure relief. In addition to considering the corrosive properties, flow characteristics, and connection form of the medium, the temperature and pressure of the medium are important parameters when selecting valves. Select valves suitable for working conditions according to different pressure values and temperatures.

Using temperature of common valve materials
01. The operating temperature of gray cast iron valves is -15～250℃.
02. The operating temperature of forgeable cast iron valves is -15～250℃.
03. The operating temperature of ductile iron valves is -30～350℃.
04. The operating temperature of high nickel cast iron valves is 400℃.
05. The operating temperature of carbon steel valves is -29～450℃, and the recommended operating temperature in JB/T3595-93 standard is t<425℃.
06. The operating temperature of 1Cr5Mo and alloy steel valves is 550℃.
07. 12Cr 1MoVA, alloy steel valves use temperature of 570℃.
08. 1Cr18Ni9Ti, 1Cr18Ni12Mo2Ti stainless steel valves use temperature of -196～600℃.
09. Copper alloy valves use temperature of -273～250℃.
10. Plastic valve use temperature:
11. Nylon is 100℃.
12. Polychlorinated polyether is 100℃.
13. Polyvinyl chloride is 60℃.
14. Polytrifluoroethylene -60～120℃.
15. Polytetrafluoroethylene -180～150℃.
16. Rubber diaphragm valves have different use temperatures due to different types of rubber:
17. Natural rubber is 60℃.
18. Nitrile rubber and chloroprene rubber are 80℃.
19. Fluororubber is 200℃.
20. When rubber and plastic are used for valve lining, the temperature resistance of rubber and plastic shall prevail.
21. Ceramic valves are generally used in working conditions below 150°C due to their poor resistance to sudden temperature changes. Recently, a super-  performance ceramic valve has appeared that can withstand high temperatures below 1000°C.
22. Glass valves have poor resistance to sudden temperature changes and are generally used in working conditions below 90°C.
23. Enamel valves, whose temperature resistance is limited by the sealing ring material, have an operating temperature of no more than 150°C.

Valve use pressure
The valve use pressure is determined by the material used to make the valve.
01. The nominal pressure allowed for gray cast iron valves is 1MPa.
02. The nominal pressure allowed for forged cast iron valves is 2.5MPa.
03. The nominal pressure allowed for ductile iron valves is 4.0MPa.
04. The nominal pressure allowed for copper alloy valves is 2.5MPa.
05. The nominal pressure allowed for titanium alloy valves is 2.5MPa.
06. The nominal pressure allowed for carbon steel valves is 32MPa.
07. The nominal pressure allowed for alloy steel valves is 300MPa.
08. The nominal pressure allowed for stainless steel valves is 32MPa.
09. The nominal pressure allowed for plastic valves is 0.6MPa.
10. The nominal pressure allowed for ceramic, glass, and enamel valves is 0.6MPa.
11. The nominal pressure allowed for FRP valves is 1.6MPa.

Relationship between valve temperature and pressure
The valve operating temperature and pressure have a certain internal connection and influence each other. Among them, temperature is the dominant factor. Valves of a certain pressure are only suitable for a certain temperature range. Changes in valve temperature can affect the valve operating pressure.

For example: the nominal pressure of a carbon steel valve is 10MPa. When the medium working temperature is 20℃, its working pressure P20 is 10MPa; when the medium working temperature is 400℃, its working pressure P40 is 5.4MPa; when the medium working temperature is 450℃, its working pressure is P54, which is 4.5MPa.