The choice of safety valve should be considered from the following aspects: 1, the structure of the form, depending on the process conditions of the equipment and the working medium, characteristics. General boilers, pressure vessels and more use of spring-loaded safety valve. If the equipment is toxic, flammable and explosive, should be selected closed safety valve. 2, boilers, high pressure vessels, large amount of safe discharge and wall thickness of the corrosion margin is not large, low pressure vessels should use full Kai safety valve. 3, the pressure range, each safety valve has a certain working pressure range. Selection should be based on the maximum allowable working pressure of the device selection of suitable safety valve. 4, the emission must be greater than the safe discharge of equipment, so as to ensure overpressure, the safety valve opens part of the media in time to prevent the pressure continues to rise. For boilers, the total displacement of the safety valve must be greater than the maximum continuous evaporation. For pressure vessels, safety valve displacement must be greater than or equal to the pressure vessel safety relief.