1. Determination of various parameters of safety valve
① Determine the nominal pressure of the safety valve.
The nominal pressure is selected according to the valve material, working temperature and maximum working pressure.
② Determine the working pressure level of the safety valve.
The working pressure level is selected according to the design pressure and design temperature of the pressure vessel, the working pressure of the safety valve and the working pressure level of the spring have different meanings.
The working pressure of the safety valve refers to the static pressure that the safety valve bears before the valve runs normally. It is the same as the working pressure of the protected system or equipment.
The working pressure level of the spring refers to the working pressure range allowed for a certain spring. Within this pressure range, the opening pressure of the safety valve (that is, the setting pressure) can be adjusted by changing the preload compression of the spring.
Safety valves of the same nominal pressure can be divided into a variety of different working pressure levels according to the design requirements of the spring.
When selecting a safety valve, the working pressure level of the valve should be determined according to the required opening pressure value.
③ Determine the discharge pressure Pd of the safety valve
The discharge pressure of the safety valve is generally 1.1 times the set pressure (opening pressure), and the discharge pressure of the steam boiler safety valve is 1.03 times the set pressure.
④ Determine the diameter of the safety valve
Determined according to the required discharge volume, the discharge capacity of the safety valve ≥ the required discharge volume.
The amount of emissions necessary for the protected system refers to the amount that must be excluded in order to prevent overpressure when the system has abnormal overpressure. It is determined by the operating conditions, capacity of the system or equipment, and the factors that may cause overpressure.
⑤ Determination of material
The selection of the material of the safety valve should take into account various factors such as the working temperature, working pressure, performance of the medium, and the manufacturability and economy of the material.
2. Determination of the special structure of the safety valve
① For the safety valve for steam with a cracking pressure greater than 3MPa or for gas with a medium temperature exceeding 320°C, a safety valve with a radiator (fin) should be used.
②For safety valves that are subjected to additional back pressure, and the back pressure variation exceeds 10% of the set pressure, bellows safety valves should be used.
In addition, for safety valves using corrosive media, in order to prevent the spring and the guide mechanism from being corroded by the media, bellows safety valves should also be used.
③ For flammable, extremely toxic or highly hazardous media, closed safety valves must be used. If a lifting mechanism is required, closed safety valves with wrenches should be used.
④ For non-hazardous media such as air, hot water above 60 ℃ or steam, the safety valve with wrench should be used.
⑤ The liquefaction tank (tank) truck should use the built-in safety valve.
For working conditions with large discharge capacity, full-open type should be used;
For working conditions where the working pressure is stable and the discharge volume is small, the micro-lift should be used;
For high pressure and large discharge conditions, it is advisable to use indirect start type, such as pulse safety valve;
Two or more safety valves shall be provided for vessels with a length of more than 6m.
⑦The fixed container with low working pressure can adopt static weight type (pressure cooker) or lever heavy hammer type safety valve. Mobile equipment should use spring-loaded safety valves.
⑧ For the medium that is thick and easy to block, the series combined relief device of safety valve and rupture disc should be selected.
Contact: Mr. Lu
Add: 3188 Jia'an Road, Jiading District, Shanghai