Selection of safety valves
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1. When selecting a safety valve, the most important factor is its discharge capacity; that is, the discharge capacity of the safety valve used in a pressure vessel must be greater than its safe release volume. Only in this way can it ensure that gas is discharged promptly once the safety valve opens when the vessel is under overpressure, thereby preventing the pressure inside the vessel from continuing to rise. 2. Attention should be paid to its pressure range, as each safety valve has a specific operating pressure range. Spring-loaded safety valves designed for high pressure should not be used in low-pressure containers with excessive relief, nor should safety valves designed for low pressure be used in high-pressure containers with excessive loading; when selecting such valves, springs of the same rating appropriate for the container’s operating pressure should be used. 3. The process conditions of the container and the properties of the working medium must be taken into consideration; for general containers, spring-loaded safety valves are suitable, while for containers with low pressure and no vibration effects, lever-type safety valves can be used. If the medium in the container is a toxic, flammable gas or other gas that pollutes the atmosphere, a closed-type safety valve should be used. For high-pressure vessels and medium/low-pressure vessels with a large safety discharge volume, full-opening safety valves are the preferred choice. Since, for the same discharge capacity, the diameter of a full-opening valve is smaller than that of a slightly opening valve, this allows for a reduction in the size of the openings in the vessel. However, the reset pressure of full-opening safety valves is lower, usually somewhat lower than the normal operating pressure of the vessel; therefore, they are not suitable for vessels that require absolute pressure balance.
It seems to be a teacher specializing in pressure vessels, or else someone who has just learned about this topic and encountered this question. The basic requirements for safety valves are as follows: (1) They must operate sensitively and reliably; (2) At the discharge pressure, the valve disc should reach its fully open position and be able to release the specified amount of gas; (3) They must have good sealing properties； (4) Compact structure, easy to adjust. Requirements for the installation of safety valves: 1) Safety valves should be installed vertically, and they should be placed in the gas space above the liquid level of the pressure vessel, or connected to pipes that are attached to the gas space of the pressure vessel. 2) The cross-sectional area of the connecting pipes and fittings between the pressure vessel and the safety valves must not be smaller than the inlet area of the safety valves. 3) When several safety valves are installed at one connection port of the pressure vessel, the inlet area of that connection port must be at least equal to the total inlet area of those safety valves. 4) It is not advisable to install an intermediate stop valve between the pressure vessel and the safety valve. For pressure vessels containing flammable media, or those with extremely high, high, or moderate toxicity, or viscous media, a stop valve can be installed between the pressure vessel and the safety valve to facilitate the replacement and cleaning of the safety valve; however, the structure and diameter of such a stop valve should not interfere with the proper functioning of the safety valve. When the pressure vessel is in normal operation, the stop valve must remain fully open and sealed with a lead seal. 5) The installation location of the safety valve should facilitate inspection and maintenance.
Maintenance of safety valves: To keep safety valves in good condition at all times and ensure they remain sensitive and functional, it is necessary to carry out regular maintenance and inspections on them during the operation of pressure vessels. (1) It is necessary to keep the safety valve clean. Prevent the valve body spring from becoming clogged with oil residues, dirt, etc. or from rusting, and prevent the safety valve discharge pipe from being blocked by oil residues or other foreign objects. (2) Regularly check whether the lead seal of the safety valve is intact, and inspect whether the weight of the lever-type safety valve is loose, displaced, or has additional weights attached to it. (3) When signs of leakage are detected in the safety valve, it should be replaced or repaired promptly. It is prohibited to reduce valve leakage by applying additional load. (4) Safety valves must be inspected regularly, including grinding, cleaning, testing, and calibration adjustment. The regular inspection cycle for safety valves is one year