Controlled engineering reference

Valve Flow Coefficient Reference Calculator

Calculate a required liquid Kv, liquid flow, or valve-only pressure drop using one explicitly bounded relation. The page does not size gas or steam and does not select a valve.

Newtonian liquid onlyMetric controlled inputsNo automatic safety marginExplicit calculation

Reference calculation

Use only for a single-phase, non-vaporizing, Newtonian incompressible liquid in a turbulent regime. The entered pressure drop must be across the valve alone. Do not use this reduced relation for gas, steam, flashing, cavitation, choked liquid flow, high-viscosity/non-turbulent flow, mixtures, slurries, or installations requiring piping/reducer corrections.

Required quantity

Input source record

I confirmed a single-phase, non-vaporizing, Newtonian liquid in turbulent flow and recorded density at the flowing conditions. I confirmed Δp is across the valve alone and that cavitation, flashing, choking, non-turbulent effects, reducers and attached fittings do not require correction. I understand this result is not final valve selection; manufacturer-specific Kvs at the required travel, characteristic, rangeability, noise, material and actuator limits remain to be checked.

What the result means

Kv is a flow-capacity coefficient, not a valve diameter and not a guaranteed operating point.
Kvr is commonly used for the application-required coefficient; Kvs is the coefficient at the valve’s rated travel. They are not interchangeable.
The page applies no universal 30% margin. Required travel and reserve depend on the selected valve, characteristic, control objective and process envelope.
The Cv output is Cv (US). It is not the slightly different Imperial-gallon coefficient.

Gas and steam are intentionally excluded. Compressible-flow sizing needs absolute pressure and additional thermodynamic and valve-specific factors; a liquid square-root relation or a fixed pressure-ratio shortcut is not a safe substitute.

Relations used

All values are numerical values in the stated units. Let r = ρ/(1000 kg/m³), with Q in m³/h and Δp in bar:

Kv = Q × √(r / Δp)

Q = Kv × √(Δp / r)

Δp = r × (Q / Kv)²

Cv (US) = 1.156099 × Kv

These three liquid equations are algebraic inverses. Their dimensional meaning depends on the displayed unit normalization; the code does not silently convert L/min, US gpm, gauge pressure or line pressure. The Cv relation is the published US-Cv/Kv conversion shown by Spirax Sarco, not an assertion that Cv is an ISO quantity.

Символ	Input/result unit	Required interpretation
Q	м³/год	Actual liquid volumetric flow for the stated flowing condition.
ρ	кг/м³	Liquid density at the flowing temperature and composition; not a stored material preset.
Δp	бар	Positive pressure loss across the valve only, within the non-choked, non-cavitating scope confirmed by the user.
Kv	м³/год	Numerical metric flow coefficient for the stated relation; compare with manufacturer data at the applicable travel.
Cv (US)	US gpm-based coefficient	Reference conversion only. Do not confuse with Cv based on an Imperial gallon.

The calculation uses finite IEEE 754 binary arithmetic and displays up to 12 significant digits. Appropriate process-data uncertainty and manufacturer tolerances still apply.

Standards boundary and evidence

IEC 60534-2-1:2011, Edition 2.0 – Industrial-process control valves, Part 2-1.

The official IEC record lists the publication and its 2015 corrigendum as valid, with a stability date of 2028. Its installed-condition equations cover compressible and incompressible flow and include corrections beyond this reduced page. The IEC scope says the incompressible equations are based on Newtonian incompressible-fluid hydrodynamics and are not intended for non-Newtonian fluids, mixtures, slurries or liquid-solid conveyance.

Official IEC publication record

ANSI/ISA-75.01.01-2012 (60534-2-1 MOD).

The official ISA product record identifies the US modified adoption for installed-condition control-valve flow sizing. The licensed standard text was not used to invent clause numbers or to claim that this reduced calculator implements every correction.

Official ISA publication record

Bürkert Fluidic Calculator – official manufacturer reference.

Publishes the liquid Kv, Q and Δp inverse relations with Q in m³/h, Δp in bar and ρ in kg/m³; distinguishes Kvs at maximum travel and warns that approximate results do not replace technical planning or individual system design.

Official Bürkert reference

Spirax Sarco, Control Valve Capacity.

Distinguishes required Kvr from rated Kvs and publishes Cv (US) = Kv × 1.156099 while warning that Imperial and US Cv values differ.

Official Spirax Sarco reference

ISA, Control Valve Primer, Chapter 5.

The official chapter shows that gas sizing introduces expansion factor Y, absolute inlet pressure, specific-heat factor Fk, pressure-drop ratio xT and compressibility Z; it also shows liquid critical-flow and piping-reducer factors. This supports excluding those cases from the reduced relation.

Official ISA chapter PDF

Sources checked 16 July 2026. Classification: manufacturer-documented reference calculation within a restricted subset of the broader IEC/ISA sizing problem; not a conformity certificate, final valve selection or complete implementation of IEC 60534-2-1.

Why common shortcuts were removed

Why is there no gas mode?

A compressible fluid changes density through the valve and can choke. Required inputs and coefficients depend on the applicable sizing procedure and valve construction. A formula that omits Y/xT or silently assumes Z = 1 can produce an unsupported result.

Why is there no recommended Kvs = 1.3 × Kv?

No single multiplier proves controllability, available travel, rangeability, installed characteristic, noise performance or actuator adequacy. Select a documented valve and evaluate its manufacturer curves over the process envelope.

Why are there no built-in fluid presets?

Density depends on temperature, pressure and composition. A convenient unlabeled preset can detach the calculation from the actual process condition, so this page requires a recorded input source.

Can the calculated Δp be subtracted from line pressure?

Only after the engineer has established the same pressure basis and the actual valve-only loss. This page does not transform gauge/absolute pressure, model piping loss, prove an available pressure budget or assess cavitation/flashing.

Related tools

Revision: 16 July 2026. Result status: restricted engineering reference; manufacturer and process review required.