Control Valve CV Calculator (MKS Units) - IEC 60534 / ISA 75.01
Control Valve CV Calculator — MKS Units
Sizing (Liquid / Gas & Vapour, incl. choked flow) · Existing Valve Rating · Opening vs Flow Curve · Field Data Fit | Basis: IEC 60534-2-1 / ISA 75.01.01
Inputs
kg/hr
kg/cm2
kg/cm2
DegC
kg/m3
kg/cm2
kg/cm2
Pv/Pc only matter for liquids near flashing/cavitation. For light hydrocarbon liquids use appropriate Pv, Pc at T1. Defaults shown are indicative for water – override for actual fluid.
Results
Optional: Flashing Across the Valve (liquid inlet → vapour forms at/after vena contracta, e.g. JT / hot condensate letdown)
The required Cv above already accounts for choked/flashing flow via FL and FF (dP is capped at the choked limit). Use this box only to estimate how much vapour forms downstream – useful for outlet piping, knock-out drum sizing, noise/erosion risk and trim selection. Leave blank to skip.
For a valve where the inlet stream is already a liquid/vapour mixture (e.g. flashing feed from upstream equipment, wet steam, two-phase blowdown). Uses the homogeneous no-slip volumetric method (mass-weighted mixture density from actual inlet volumes) – a standard simplified engineering approach (Baumann-type). This is approximate: it assumes no slip between phases and does not capture true flashing critical (choked) two-phase flow as rigorously as vendor two-phase sizing software. For high dP ratio, high quality, or erosion-critical service, verify with vendor software (e.g. Fisher FlowSizer, Masoneilan MASSIZE) and consider anti-cavitation / multi-stage trim.
kg/hr
kg/hr
kg/m3
kg/m3
kg/cm2
kg/cm2
kg/cm2
kg/cm2
Results
Existing / Selected Valve Rating – Predict Flow at Given Conditions
%
kg/cm2
kg/cm2
kg/m3
Results
Valve Opening (%) vs Flow – Constant ΔP
kg/cm2
kg/cm2
kg/m3
Assumes upstream/downstream pressure (and hence ΔP) stays constant as the valve travels – i.e. system resistance elsewhere is negligible. Flow is scaled directly from Cv(h)/Cv(max).
Opening % vs Flow
Evaluate Flow from Existing Field Data — Curve Fit & Interpolation
Enter known (opening %, flow) data points from an existing valve. The tool fits the data to determine the rated Cv and characteristic parameters, then predicts flow at any opening. Useful for diagnosing installed characteristics, verifying as-built performance, or predicting flow at untested openings. Supports Equal Percentage and Quick Opening (and Linear).
kg/cm2
kg/cm2
kg/m3
Enter at least 2 data points. For Equal %, at least 3 points spanning a wide range (e.g. 20–80%) give a more reliable R estimate. For Quick Opening, low-opening points improve the fit.