Setting Pressure of Safety Valves

Safety valves are important safety accessories for boilers, pressure vessels and other pressure equipment. Their operational reliability and performance are directly related to equipment and personal safety and are closely related to energy conservation and environmental protection. If the pressure setting of the safety valve is too high, the safety valve cannot be opened in time when there is a danger, and it is easy to cause accidents. If the pressure setting is too low, leakages of safety valves will occur, which waste energy and pollute the environment. Sometimes, the sealing surface of safety valves is damaged due to frequent popping.
 
The setting pressure of the safety valve is also called the opening pressure, which is an important parameter related to that whether the safety valve can be opened in time when the equipment is overpressured. The annual inspection of safety valves mainly check whether the inside of the safety valve is damaged and the sealing surface is damaged; reset the setting pressure of the safety valve to keep the safety valve in the best open state. How to calculate the setting pressure of safety valves after knowing the importance of pressure setting of safety valves? The calculation method of steam boilers and pressure vessels will be introduced below.
 
Setting values of safety valves of steam boilers

 
The following should be noted:
1. There must be one safety valve on the boiler adjusted according to the lower setting pressure in the table.
2. The working pressure in the table refers to the working pressure of the installation location of the safety valve.
3. The setting pressure of the gas economizer and reheater should be 1.1 times the working pressure of the installation site.
 
Setting pressure of safety valves of pressure vessels 
When only one safety valve is installed, its opening pressure should not be greater than the design pressure, and the sealing test pressure should be greater than the maximum working pressure of the vessel, that is, maximum working pressure being less than opening pressure and opening pressure being less than or equal to designed maximum working pressure. The opening pressure is generally 1.05 to 1.1 times the maximum working pressure of the safety valve. The setting parameter of safety valve is serious. Choosing the appropriate setting pressure parameters will directly affect the safety of the equipment. The above calculation methods are provided here to ensure that we work in a safe environment.
 
The nominal pressure of the safety valve represents the maximum allowable pressure of the safety valve at room temperatures. The reduction of the allowable stress of the material at high temperatures should not be considered for safety valves for high-temperature equipment. The safety valve is designed and manufactured according to the nominal pressure standard.
 
Opening pressure: it is also called set pressure, which is the medium pressure when the safety valve's disc starts to rise under operating conditions.
Discharge pressure: it is the pressure on the inlet side when the disc reaches the specified opening height.
Reseating pressure: it is the inlet pressure after the safety valve is discharged, and the disc presses the valve seat again when the medium stops discharging. The reseating pressure is an important parameter that characterizes the quality of the safety valve. It is generally required to be at least 80% of the working pressure, and the upper limit is not to produce frequent popping of the valve disc.
Opening and closing pressure difference: it is the difference between opening pressure and return pressure.
 
The opening pressure of the safety valve of the boiler drum and superheater is specified as follows:
(1) When the rated steam pressure is less than 1.27MPa, the opening pressure are working pressure +0.02MPa and +0.04MPa.
(2) When the rated steam pressure is greater than 1.27MPa but less than 3.82MPa, the opening pressure are 1.04 times and 1.06 times the working pressure of safety valves.
(3) When the rated steam pressure is greater than 3.82MPa, the opening pressure are 1.05 times and 1.08 times the working pressure of safety valves.

The opening pressure of the safety valve of the economizer is 1.5 times the working pressure of the economizer. The opening pressure of the safety valve of the pressure vessel shall not exceed the design pressure of the pressure vessel.