Calculation method & selection limits
Enter a required relieving flow already established for the governing overpressure case. Set pressure is the valve opening setpoint. Relieving inlet pressure is calculated as P₁(abs) = Pset(g) × (1 + overpressure / 100) + Patm. Backpressure must be the total outlet pressure during discharge. No particular code compliance or allowable accumulation is inferred from these inputs.
Area A = mass flow / (Kdr × capacity correction × theoretical mass flux). Liquids use G = √[2ρ(P₁ − P₂)]. Gas/steam use the compressible nozzle expression G = √{2kP₁ρ/(k−1) × [r^(2/k) − r^((k+1)/k)]}, with r limited to the critical ratio [2/(k+1)]^[k/(k−1)]. All engine pressures are absolute Pa. Steam k defaults to 1.135 saturated / 1.3 superheated; these are preliminary approximations. Air defaults to ideal dry air, R = 287.05 J/(kg·K), k = 1.4, Z = 1; edit Z or properties if needed.
Water and steam properties: IAPWS-IF97 at relieving inlet conditions. Thermal oil properties: selected temperature table; no pressure correction. Oil vapor pressure is required for flashing screening. Liquid results are withheld when outlet pressure is at/below vapor pressure. This test does not rule out local cavitation. Wet steam, flashing liquids and two-phase sizing are outside this tool's scope.
Catalogue candidates are calculated separately using each valve's published actual area and EN coefficient. Screening is limited to atmospheric discharge, at least 10% overpressure, set pressure at least 1.5 barg and the tabulated family bounds. Do not combine effective/API areas with actual-area coefficients. Pressure–temperature curves, corrosion, backpressure configurations, inlet loss, discharge piping and manufacturer approvals must be checked before ordering. ZETKAMA 240A is not screened for thermal oil in this dataset. A missing candidate means the loaded dataset does not establish a selection, not that the manufacturer has no suitable valve.
Spirax Sarco — sizing method · LESER catalogue · ZETKAMA catalogue 01/2026 · Steam Properties · Thermal Oil Properties