Failure and solution of safety valve on liquid nitrogen tank

Improper use of safety valves can cause many failures. If these faults are not eliminated in time, the function and service life of the safety valve will be affected. Common failures of safety valves are:

(1) Valve disc does not return to seat after discharge

This is mainly caused by the spring bent valve stem, incorrect installation position of the valve disc, or being stuck. Should be reassembled.

(2) Leak

Under the normal working pressure of the equipment, the leakage between the valve disc and the seat sealing surface exceeds the allowable level. The reasons are: there is dirt between the valve disc and the sealing surface of the valve seat. You can use a lift wrench to open the valve several times to flush away the dirt; the sealing surface is damaged. It should be repaired according to the degree of damage by grinding or grinding after turning; the valve stem is bent, tilted or the lever and fulcrum are deflected to make the valve core and valve disc misaligned. Should be reassembled or replaced; spring elasticity is reduced or lost. Measures such as replacing the spring and readjusting the opening pressure should be taken.

(3) Do not open when the specified pressure is reached

The reason for this is that the fixed pressure is not allowed. Should readjust the compression of the spring or the position of the weight; the valve disc and the valve seat are stuck. The safety valve should be manually deflated or drained periodically; the lever of the lever-type safety valve is stuck or the weight is moved. The weight should be readjusted and the lever moved freely.


 

(4) Pressure continues to rise after exhaust

This is mainly because the safety valve displacement of the selected safety valve is small. The safety relief of the equipment should be re-selected. The valve stem centerline is not correct or the spring is rusted, so that the valve flap cannot be opened to its proper height. Or replace the spring; the exhaust pipe is not cut enough, you should adopt an exhaust pipe that meets the safety discharge area.

(5) Flap or vibration

Mainly due to too much spring stiffness. Should use a spring with appropriate stiffness; improper adjustment of the adjustment ring, so that the seat back pressure is too high. The position of the adjusting ring should be readjusted; the resistance of the discharge pipe is too large, causing excessive discharge back pressure. The discharge pipe resistance should be reduced.

(6) Opening under the specified pressure

The main reason is that the constant pressure is inaccurate; the spring aging elasticity decreases. Tighten the adjusting screw or replace the spring properly.

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