Control Valve Gas & Steam Cv Calculator

Size compressible gas and superheated steam control valves per IEC 60534-2-1 with expansion factor Y, sonic choked flow boundaries, and mass/volumetric capacity.

Compressible Gas Properties

Gas Media Preset:

Molecular Weight (M):

Specific Heat Ratio (k = Cp/Cv):

Inlet Temperature T1 (°F):

Compressibility Factor (Z):

Pressures & Flow Capacity

Inlet Pressure P1 (psig):

Outlet Pressure P2 (psig):

Volumetric Flow (SCFM):

Valve Style xT Factor:

Compressible Sizing Results

Required Gas Flow Coefficient

-- Cv

-- lb/hr mass flow equivalent

Expansion Factor (Y)

IEC Gas Expansion

Flow Regime

x / x_choked

Pressure Ratio x = ΔP / P1,abs: --

Choked Pressure Limit x_crit: --

Specific Heat Factor Fγ: --

Evaluating sonic flow boundaries and gas expansion per IEC 60534-2-1.

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Frequently Asked Questions

What is the critical pressure drop ratio xT in IEC 60534?

xT is the pressure drop ratio factor for a control valve under compressible flow without attached pipe fittings. When the applied pressure drop ratio x = ΔP / P1 exceeds Fγ·xT, sonic velocity (Mach 1.0) is reached at the vena contracta, causing mass flow choking.

Why does the gas expansion factor Y bottom out at 0.667?

The theoretical expansion factor Y accounts for the change in gas density between the valve inlet and the vena contracta. At the onset of critical sonic choking, the theoretical expansion factor approaches exactly 2/3 (0.667). Lowering downstream pressure further does not decrease Y or increase mass throughput.

Can a valve size be reduced if operating in choked flow?

In choked flow, the maximum mass throughput per square inch of vena contracta is locked by sonic velocity. Increasing throughput requires raising upstream pressure P1, increasing valve Cv, or heating the gas to adjust acoustic speed.