Size a safety relief valve for liquid service per API 520 / GB/T 12243. Calculates required orifice area and verified capacity with back-pressure, overpressure and viscosity corrections. Formula: Ac = 0.1964·Wr / (Kdr·Kb·Kp·Kv·√(ρ·(1.25·Ps−Pb))).
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The 0.1964 coefficient derives the required orifice area from mass flow, density and the 1.25·Ps−Pb pressure differential.
The 1.25·Ps factor assumes 25% accumulation per API 520 liquid-service allowance.
Kdr = 0.4 is the derated discharge coefficient for liquid service (lower than gas 0.8).
Kb corrects for superimposed and built-up back pressure; 1.0 for conventional valves at near-atmospheric back pressure.
Kv reduces capacity for viscous liquids per API 520; 1.0 for water-like fluids.
ρ (kg/m³) at the relieving temperature sets the mass flow through the orifice.
Input required relief capacity Wr and set pressure Ps (gauge).
Enter density ρ at relieving temp and back pressure Pb (gauge).
Set Kdr (0.4), Kb, Kp, Kc and Kv for the valve and fluid.
Read required area Ac, diameter do and verified capacity W.
Enter your parameters and get instant sizing and pass/fail results.
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