Safety valve selection

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The selection of safety valves involves the following two aspects:: One aspect is the workpiece conditions of the equipment or system being protected, such as working pressure, allowable overpressure limits, safe emissions necessary to prevent overpressure, characteristics of the working medium, operating temperature, etc. ； On the other hand, it is the operating characteristics and parameter indicators, discharge capacity, materials, etc. of the safety valve itself. 1. Principles of safety valve setting The basic principle of safety valve setting is that it is suitable for clean, particle-free, low-viscosity fluids. If a safety valve must be installed in situations where particles are present, a filtering device should be considered in front of the safety valve. When adding a filtering device, it must be ensured that it will not affect the performance of the safety valve. Where a safety relief device is required but is not suitable for installation of a safety valve, a bursting disc or a safety valve and bursting disc should be installed in series. 2. Any container that falls into one of the following situations must be equipped with a safety valve: ①The pressure material of the container comes from situations where there is no safety valve ； ②Vessels and pipelines whose design pressure is less than the pressure at the pressure source ； ③Outlet piping for positive displacement pumps and compressors ； ④Containers with overpressure due to accumulation of non-condensable gases ； ⑤If there is a shut-off valve or control valve on the outlet pipe of the heating furnace, a safety valve should be installed upstream of the valve. ； ⑥Overpressure parts caused by process accidents, automatic control accidents, power accidents and public engineering accidents ； ⑦The part where the liquid undergoes thermal expansion due to the closing of the valves at both ends. ； ⑧Steam outlet pipe of condensing turbine ； ⑨In some cases, due to leakage of the pump outlet check valve, a safety valve is installed on the pump inlet pipe. ； ⑩In situations where there is frequent overpressure and where the temperature fluctuates greatly. 3. The following situations are not suitable for installing safety valves: ①The system pressure may rise rapidly, such as in chemical explosions, etc. ； ②The discharge medium contains particles, is easy to precipitate, crystallize, polymerize and has a high viscosity. ； ③The discharge medium is highly corrosive and the price of using a safety valve is too high. ； ④The working pressure is very low or very high, and it is difficult to manufacture safety valves at this time. ； ⑤Requires larger relief area ； ⑥The system temperature is low and affects the safety valve operating performance ； 4. Safety valves and bursting discs should be used together in the following situations:: ①If the process medium is very valuable or highly toxic and no leakage is allowed during the working process, the safety valve and bursting disc should be used in series or only the bursting disc should be used. ； ②In order to increase the relief area under abnormal working conditions (such as fire, etc.), consideration must be given to using it in parallel with a bursting disc.