As they frequently pop open at their pre-set pressure, spring-loaded relief valves are also referred to as POP Action” Safety Valves. The force needed to overcome the spring tension and open the valve is first produced by the pressure differential across the valve disc. Most huddling chambers have an area that is 15% to 30% greater than the valve seat, which causes the pop action (as the disc holder is bigger than the valve disc). There is a step shift in the upward stresses on the spring and the valve “pops” open once the pressure beneath the seat is sufficient to lift the valve disc off the nozzle.
