The concept of various pressures of safety valves and the regulation of opening pressure

The nominal pressure of the safety valve represents the maximum allowable pressure of the safety valve at room temperature. The safety valve used in high temperature equipment should not consider the reduction of the allowable stress of the material at high temperature. The safety valve is designed and manufactured according to the nominal pressure standard.
Cracking pressure: also called set pressure, it is the medium pressure when the safety valve disc starts to rise under operating conditions.

Discharge pressure: the pressure on the inlet side when the disc reaches the specified opening height.

Re-seat pressure: After the safety valve is discharged, the disc re-presses the valve seat and the inlet pressure when the medium stops discharging. The return pressure is an important parameter that characterizes the quality of the safety valve. Generally, it is required to be at least 80% of the working pressure, and the upper limit is not to produce frequent flapping.

Opening and closing pressure difference: the difference between opening pressure and return pressure.

Regulations on the opening pressure of safety valves

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 is working pressure +0.02MPa and working pressure +0.04MPa;

(2) When the rated steam pressure is greater than 1.27MPa but less than 3.82MPa, the opening pressure is 1.04 times the working pressure and 1.06 times the working pressure respectively;

(3) When the rated steam pressure is greater than 3.82MPa, the opening pressure is 1.05 times the working pressure and 1.08 times the working pressure respectively.

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