Working principle and selection of pressure relief valve

Pressure relief valve working principle can be simply interpreted as inlet pressure + outlet pressure = spring force, by controlling the pressure reducing valve to control the exit door of the opening of the mouth of the river closure of the size of pressure, the opening is smaller, the liquid through the mouth of the river closure of the fluid resistance is smaller, the smaller the loss of pressure, outlet pressure, the greater the outlet pressure, the smaller conversely. Assumptions on the diaphragm spring force for F function under the relief valve diaphragm of outlet pressure for F1 inlet pressure P1 the effect size of the diaphragm is S1 = F1 P1 & times; S1 role in the relief valve under the valve core of inlet pressure is F2 export pressure P2 the role of the valve core area of S2 F2 = P2 & times; S2 when balance is: F = F1 + F2 = P1 & times; S1+P2× S2 when the pressure fluctuate at the entrance, assuming that the inlet pressure change greatly P2 + delta P and other conditions unchanged, the spring force F < F1 + F2, pressure drive diaphragm upwards movement under the diaphragm, the spring is compressed F, at the same time of the opening of the mouth of the river has shrunk, liquid resistance, export the pressure decreases, F2 smaller, until reaching a new equilibrium. When none of the decompression valve outlet water or reduced pressure downstream of the valve is closed, outlet pressure continues to increase, F2 continued, under the pressure of diaphragm drive diaphragm continuously upgrade movement until the pressure relief valve is closed, the pressure relief valve outlet pressure is greater than the set value, but because of inertia effect, upward movement of the diaphragm will not stop immediately, will continue to move up a little, the equivalent of the exit valve cavity, larger volume, the internal liquid pressure drop, until just equal to the relief valve set pressure value