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1. Determination of various parameters for safety valves ① Determine the nominal pressure of the safety valve. The nominal pressure is selected based on the valve material, operating temperature, and maximum operating pressure. ②Determine the operating pressure rating of the safety valve. The operating pressure class is determined based on the design pressure and design temperature of the pressure vessel; the operating pressure of a safety valve has a different meaning from the pressure class of its spring. The operating pressure of a safety valve refers to the static pressure acting on the valve before it operates normally, and it is identical to the operating pressure of the system or equipment being protected. The operating pressure range of a spring refers to the range of working pressures for which that particular spring can be used; within this range, the opening pressure of the safety valve (i.e., the set pressure) can be adjusted by changing the amount of pre-compression of the spring. Safety valves with the same nominal pressure can be divided into various operating pressure classes depending on the requirements of their spring design. When selecting a safety valve, the operating pressure class of the valve should be determined based on the required opening pressure value. ③Determine the discharge pressure Pd of the safety valve. The discharge pressure of a safety valve is generally 1.1 times the set pressure (opening pressure), while for steam boiler safety valves, it is 1.03 times the set pressure. ④The diameter of the safety valve is determined based on the required discharge volume, with the discharge capacity of the safety valve being ≥ the required discharge volume. The discharge volume necessary for the protected system refers to the amount that must be released in order to prevent overpressure when the system experiences abnormal pressure levels; it is determined by factors such as the operating conditions and capacity of the system or equipment, as well as those that may cause overpressure. ⑤Material selection: When choosing the material for a safety valve, various factors must be taken into account, including the operating temperature and pressure of the medium, the properties of the medium itself, as well as the processability and cost-effectiveness of the material. 2. Determination of the special structure of safety valves ① For safety valves used with steam at a discharge pressure greater than 3 MPa, or for safety valves used with gases at a temperature exceeding 320°C, safety valves equipped with radiators (fins) should be selected. ②For safety valves subjected to additional back pressure, and when the change in this back pressure exceeds 10% of the set pressure, diaphragm safety valves should be used. Furthermore, for safety valves used with corrosive media, in order to prevent the springs and guiding mechanisms from being corroded by the medium, diaphragm safety valves should also be selected. ③For flammable media with extremely or highly hazardous toxicity, closed safety valves must be used; if a valve equipped with a lifting mechanism is required, a closed safety valve with a wrench should be employed. ④For non-hazardous media such as air, hot water above 60°C, or steam, safety valves equipped with wrenches should be used. ⑤Liquefied gas tankers should be equipped with built-in safety valves. ⑥ For conditions with high discharge rates, a fully open type should be selected ； For operating conditions with stable working pressure and low discharge volume, a slightly open type is advisable ； For high-pressure conditions with large discharge volumes, a non-direct-acting type, such as a pulse safety valve, is recommended ； For containers with a length exceeding 6m, two or more safety valves should be installed. ⑦For fixed containers with low operating pressure, gravity-type (pressure cookers) or lever-weight type safety valves can be used. Mobile devices should be equipped with spring-loaded safety valves. ⑧For media that are thick and prone to clogging, a discharge device consisting of a safety valve in series with a burst disc is recommended.