The selection of safety valve: The nominal pressure of the safety valve is determined by the operating pressure. The operating temperature of the safety valve is determined by the operating temperature. The fixed pressure value of the safety valve determines the fixed pressure range of the spring or the lever, and then determined according to the medium Safety valve material and structure type, and then calculated according to safety valve relief valve throat diameter. The following general rules for the selection of safety valve. (L) General use of hot water boilers are not closed with micro-valve wrench safety valve. (2) steam boiler or steam pipe is generally not closed with a wrench full safety valve. (3) water and other liquid incompressible media commonly used closed micro-valve, or safety relief valve. (4) high-pressure water supply Generally closed full Kai-type safety valve, such as high-pressure water heaters, heat exchangers. (5) compressible gas and other gases generally use closed-type safety valve, such as gas tanks, gas pipelines. (6) E-class steam boilers generally use heavy-duty safety valve. (7) large-caliber, large displacement and high pressure systems generally use pulse safety valve, such as temperature and pressure reduction devices, power station boilers. (8) General purpose built-in safety valves for tank trucks, tank trucks and storage tanks for transporting liquefied gas. (9) The top of the tank with hydraulic safety valve, need to be used in conjunction with the breathing valve. (10) Downhole drainage or natural gas pipeline generally with pilot-operated safety valve. (11) liquefied petroleum gas station tank pump outlet liquid return pipe commonly used safety valve. (12) Negative pressure or negative pressure may occur during operation of the system is generally used vacuum negative pressure safety valve. (13) Bellows relief valves are generally used for container or piping systems with large back pressure fluctuations and toxic flammability.