The effect of back pressure on the opening of safety valves
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This post was last edited by jacques0920 on 2015-10-27 08:23. For ordinary safety valves, how does an excessively high back pressure affect the valve’s operation in terms of triggering? Is it difficult to take off, or do jumps occur frequently? What’s the reason again?
For ordinary safety valves, the operating pressure = back pressure + spring setting force; thus, an excessive back pressure leads to an increased operating pressure
The design of the safety valve outlet pipe must take into account that the back pressure should not exceed a certain value of the safety valve’s set pressure. For standard spring-loaded safety valves, the back pressure shall not exceed 10% of the valve’s set pressure ； Balanced safety valves (including diaphragm type, piston type, or pilot-operated type), whose back pressure does not exceed 30%–50% of the safety valve’s set pressure. For specific values, refer to the backpressure impact curve data provided by the manufacturer. After piping, a calculation of the pressure drop should be performed to prevent it from exceeding the allowable range.
You mean static back pressure, what about dynamic back pressure?
Excessively high dynamic backpressure, I don’t think, will cause frequent tripping nor affect the tripping pressure. To take an extreme example: if the outlet is a very, very thin pipe and the dynamic backpressure is infinitely high, then the safety valve will likely trip before it can relieve the pressure, and the pressure built up will continue to increase, leading to higher overpressure.
It shouldn’t be easy to jump, right? Think about it – there’s something pushing against you from behind; how can you jump easily in that situation?