This is determined by the working environment in which the device is used. There are many types of safety valves, which can be divided into spring type and lever type according to the structure. In the case of large-capacity requirements, there is a pulse-type safety valve, also known as a pilot-operated safety valve. According to the amount of emissions, it is divided into full-open and micro-open. According to the structure and the loading mechanism, it is divided into three types: weight lever type, spring type and pulse type. According to the medium discharge method, it is divided into three types: fully enclosed, semi-closed and open. According to the valve opening size, it is divided into two types: spring micro-opening high-pressure safety valve and spring full-open safety valve. How to choose the safety valve is not only to understand the classification of the above safety valve, but also to understand the medium used by the safety valve, whether it is corrosive, temperature, pressure (working pressure and opening pressure), whether the interface is a thread or a flange. Shanghai Wuyue Safety Valve Factory, as a professional safety valve manufacturer in the industry, further analyzes the problem of how to select safety valves.
General rules for safety valve selection
1) According to the calculation, the "nominal diameter" of the safety valve must be such that the discharge capacity of the safety valve ≥ the safe discharge amount of the pressure vessel.
2) Determine the pressure level of the safety valve based on the design pressure and design temperature of the pressure vessel.
3) Steam boilers or steam pipes are generally closed with a full-opening safety valve with a wrench. For safety valves with a pressure greater than 3 MPa for steam or a gas with a medium temperature above 320 °C, a heat sink (fin) should be used.
4) Hot water boilers generally use a non-closed wrench with a micro-opening safety valve.
5) For air, non-hazardous media such as hot water or steam above 60 °C, a safety valve with a wrench should be used.
6) Liquid incompressible media such as water generally use a closed micro-opening safety valve or a safety relief valve.
7) High-pressure feed water generally uses closed full-open safety valves, such as high-pressure feed water heaters, heat exchangers, etc.
8) Compressible media such as gas generally use closed full-open safety valves, such as gas storage tanks, gas pipes, and the like.
9) Large-diameter, large-displacement and high-pressure systems generally use pulse-type safety valves, such as temperature and pressure reducing devices, power station boilers, etc.
10) Closed safety valves must be used for flammable, highly toxic or highly hazardous media. If a lifting mechanism is required, a closed-type safety valve with a wrench should be used.
11) When the safety valve is likely to withstand a change in pressure or a toxic and flammable container or piping system with a back pressure of more than 10%, a safety valve with a bellows should be used.
12) Vacuum negative pressure relief valves are generally used for systems that may generate negative pressure during negative pressure or operation.
13) The system with low freezing point of medium generally adopts insulated jacketed safety valve.
14) Built-in safety valves should be used for train tankers, car tankers, storage tanks, etc. that transport liquefied gas.
15) The top of the tank is generally equipped with a hydraulic safety valve that needs to be used with a breathing valve.
16) Pilot-type safety valves are generally used for downhole drainage or natural gas pipelines.
17) A safety return valve is generally used on the liquid phase return pipe of the liquefied petroleum gas station tank pump outlet.
18) Select the appropriate safety valve material according to the characteristics of the medium. For example, the ammonia-containing medium cannot use copper or copper-containing safety valves; acetylene cannot use safety valves with 70% copper or copper.
19) For the working condition with large discharge volume, the full-open type should be selected; for the working pressure to be stable, the leakage capacity should be small, and the non-direct starting type should be selected for the high pressure and large discharge capacity. For example, pulse safety valves. Two or more safety valves should be provided for containers longer than 6 m.
20) Class E steam boilers or stationary vessels with low working pressure Pw can be used in static weight (pressure cooker) or lever heavy duty safety valves. Mobile equipment should use a spring-loaded safety valve.
21) For the medium is thick and easy to block, the series combination venting device of safety valve and rupture disc should be used.
22) The spring working pressure level selected according to the nominal pressure of the safety valve. The relationship between the nominal pressure of the safety valve and the working pressure of the spring.
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