Xiamen Dervos Valves Industry Co., Ltd

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How to select the safety valve
- Mar 07, 2018 -

How is the safety valve selected?                   

General rules for safety valve selection. 

1) According to the calculation, the "nominal diameter" of the relief valve must be made to ensure that the discharge capacity of the relief valve is greater than that of the pressure vessel. 

2) Determine the pressure level of the safety valve according to the design pressure and design temperature of the pressure vessel. 

3) Steam boilers or steam pipelines are generally operated with full open with wrench safety valves. 

For opening pressure more than 3 mpa steam or medium temperature over 320 with the gas,  the safety valve should be chosen with the radiator (fin) form. 

4) Hot water boilers are generally operated with a non-enclosed wrench. 

5) For not harmful medium such as air, more than 60 hot water or steam etc, the safety valve with wrench should be adopted. 

6) Water and other liquid incompressible media are normally sealed with a small open type safety valve or a safe discharge valve. 

7) The high pressure water is usually sealed with full open safety valve, such as high pressure feed water heater, heat exchanger, etc. 

8) The compressible medium, such as gas, is generally closed with a closed full open safety valve, such as gas storage tank and gas pipeline. 

9) Large diameter, large displacement and high pressure system are generally used with impulse relief valve, such as reducing temperature and pressure relief device, power station boiler, etc. 

10) A closed safety valve shall be used for inflammable, toxic or highly hazardous media, and a closed safety relief valve shall be adopted if a lifting mechanism is required. 

11) When the relief valve is likely to be subject to the back pressure change and the change amount is more than 10% to open the pressure or the toxic and flammable container or piping system, the relief valve with the bellows should be selected. 

12) Vacuum negative pressure relief valve is generally used in negative pressure or operation process. 

13) The system with lower medium freezing point is generally chosen with the heat preservation jacket type safety valve. 

14) A built-in safety valve shall be used for the transport of liquefied gas in the tank car, car tank, storage tank and so on. 

15) The top of the tank usually uses hydraulic safety valve, which needs to be used in conjunction with the breathing valve. 

16) A pilot safety valve is generally used for underground drainage or natural gas pipelines. 

17) The liquid phase reflux pipe of the liquefied petroleum gas station tank pump generally uses safe return valve. 

18) Select the appropriate safety valve material according to the media characteristics. If medium includes ammonia, copper or copper containing safety valve cannot be chosen. Acetylene cannot choose a safety valve with 70% copper or copper. 

19) In the case of large discharge volume, the whole formula safety valve should be adopted.

In the case of stable working pressure and low discharge volume, it is appropriate to choose low lift safety valve.

For high pressure and discharge conditions, the non-direct starting type safety valve should be selected, such as the impulse safety valve. Two or more safety valves should be set for the container length exceeding 6m. 

20) Type E steam boilers or stationary vessels with low working pressure can choose a static heavy (pressure cooker) or lever and weight safety valve.

The mobile device shall adopt a spring safety valve. 

21) In the case of thick and easily blocked media, it is appropriate to choose a series combination of relief valve and bursting disc. 

22) The working pressure level of spring is selected according to the nominal pressure of relief valve. The nominal pressure of safety valve is related to the spring working pressure.