Main safety valve refusal and solution

The phenomenon of the main safety valve not moving after the impulse safety valve is activated is usually referred to as the refusal of the main safety valve to move. The refusal of the main safety valve to operate is a significant hazard to the running boiler, which is a major equipment hazard and seriously affects the safe operation of the equipment. Once the pressure of the medium in the operating pressure vessel and pipeline exceeds the rated value, the main safety valve will not operate, making the equipment prone to damage and major accidents due to overpressure operation.The main safety valve product names of China Safety Valve Network include:A28X Air Compressor Safety Valve,AD Safety Valve Muffler,Bellows Spring Fall Lift Safety Valve,Built-in Safety Valve,Butterfly Spring Type Safety Valve,Copper Safety Valve,Duplex Safety Valve,Double Lever Safety Valve

Before analyzing the reasons for the refusal of the main safety valve to operate, first analyze the operating principle of the main safety valve. As shown in Figure 1, when the pressure inside the pressure vessel rises to the full pressure of the impulse safety valve, the impulse safety valve will actuate, and the medium will rush from the container to the piston chamber of the main safety valve through the pipeline. There will be a slight expansion and pressure reduction in the piston chamber. If the pressure inside the piston chamber is P1 and the piston throttling area is Shs at this time, the f1 acting on the piston is:

f1=P1×Shs……………………(1) 

If the pressure of the medium inside the pressure vessel at this time is P2 and the area of the valve core is Sfx, then the upward force f2 of the medium on the valve core at this time is:

f2=P2×Shx………….. (2) 

Usually, the piston diameter of a safety valve is larger than the valve core diameter, so in equations (1) and (2), Shs>Sfx, P1 ≈ P2

If the tension force exerted by the spring on the valve core through the valve stem is set to f3 and the friction force between the moving parts and the fixed parts (mainly the friction force between the piston and the piston chamber) is set to fm, then the prerequisite for the action of the main safety valve is that only when the force f1 acting on the piston is slightly greater than the sum of the force f2 acting on the valve core to make it upward and the tension force f3 exerted by the spring on the valve core through the valve stem and the friction force between the moving parts and the fixed parts (mainly the friction force between the piston and the piston chamber) fm, that is, when f1>f2+f3+fm, the main safety valve can be activated.

Through practice, the refusal of the main safety valve to move is mainly related to the following factors:

The moving parts of the safety valve are stuck. This may be due to improper assembly, mixing of dirt and impurities, or corrosion of parts; Poor surface finish, surface damage, grooves, hard spots and other defects in the piston chamber. This increases the friction force fm between the moving parts and the fixed parts, and under other constant conditions, f1<f2+f3+fm, so the main safety door refuses to move.

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