Safety valve selection principles: 1, steam boiler safety valve, the general choice of open all-spring-type safety valve; 2, liquid medium with safety valve, the general choice of micro-spring-type safety valve; 3, air or other gaseous medium with safety Valve, the general choice of fully enclosed spring-loaded safety valve; 4, liquefied petroleum gas tanker car or liquefied petroleum gas tanker truck safety valve, the general selection of Kai-type built-in safety valve; 5, oil well export safety valve, the general selection Pilot-operated safety valve; 6, high-pressure bypass safety valve for steam power generation equipment, the pilot-operated safety valve with dual function of safety and control is generally used. 7, If safety valve is required to be opened regularly, safety with lifting wrench valve. When the medium pressure reaches more than 75% of the cracking pressure, the lifting wrench can lift the valve flap slightly from the valve seat to check the opening of the safety valve. 8. If the medium temperature is high, Temperature, the general when the closed safety valve temperature exceeds 300 ℃ and open safety valve temperature exceeds 350 ℃, should be used with a safety valve with a radiator; 9, if the safety valve outlet back pressure is changing, the amount of change over 10% open pressure, bellows safety valve should be used; 10, if the medium is corrosive, bellows safety valve should be used to prevent important parts due to media corrosion failure. 11, safety valve installation and maintenance should pay attention to the following points Construction, installation points 1), installation location, height, direction of import and export must meet the design requirements, pay attention to the flow direction of the media should be consistent with the direction of the arrow marked body, the connection should be solid close. 2), the appearance of the valve must be installed before the inspection, the valve nameplate should be consistent with the current national standard "General Valve Flags" GB 12220 requirements. For the working pressure is greater than 1.0 MPa and the main pipe to play the role of cut-off valve, the installation should be carried out before the intensity and tightness test, qualified after the standard use. Strength test, the test pressure of 1.5 times the nominal pressure, the duration of not less than 5min, valve housing, packing should be no leakage as qualified. Tightness test, the test pressure of 1.1 times the nominal pressure; test duration in line with the requirements of GB 50243; All kinds of safety valves should be mounted vertically. 12, safety valve outlet should be no resistance, to avoid compression phenomenon. 13, safety valve should be specially tested before installation, and check its official seal. 14, the use of safety valves should be regularly checked.