⚠️ Safety / Relief Valve Sizing (API 520)
Compute the required orifice area for gas/vapor, steam, or liquid overpressure relief per API 520, and select the standard orifice designation per API 526.
📝 Configuration
📊 Results
Configure inputs and click Size.
📘 Methodology
API 520 Gas/Vapor
A = W·√(TZ/(Mk)) / (C·Kd·P1·Kb). The coefficient C depends on the isentropic exponent k. Kd is the discharge coefficient (0.975 for gas). Kb corrects for backpressure.
API 520 Steam & Liquid
Steam: A = W/(51.5·Kd·P1·Kn·Ksh). Liquid: A = Q·√(ρ/ΔP)/(38·Kd·Kw·Kv). Each service type uses specific correction factors per the standard.
API 526 Orifice Designations
Standard orifice letters D through T define discrete valve sizes from 71 mm² to 16,774 mm². The selected orifice must equal or exceed the calculated required area.