One documented liquid path and operating state

Documented Valve-Path Flow Coefficient & Pressure-Drop Calculator

Derive an effective coefficient from a documented Q–Δp point, or predict Δp from a sourced coefficient, for one identified valve path and opening. ISO 4401 mounting-interface designation is recorded but never used as a flow-capacity selector.

Explicit coefficient conventionPath-specific Q–ΔpNo CETOP auto-sizing

Calculation / test identifier

Valve product / model

Flow path, spool/element state and opening

Product curve, test report or datasheet source / revision

Documented mounting-interface designation

Interface drawing / controlled source

Calculation mode

Flow unit

Volume flow Q

Differential-pressure unit

Measured/published path differential pressure Δp

Q–Δp test/curve conditions and reading source

Liquid specific gravity SG (dimensionless)

Density/SG source, reference water basis and temperature

Documented coefficient convention

Documented coefficient value

Coefficient source, convention, path/opening and test conditions

Viscosity, temperature, cavitation, Reynolds-regime, pressure-rating and system review

Applicability gate: incompressible single-phase liquid, steady fixed path/opening and a square-root turbulent-flow coefficient applicable to the entered state. The effective coefficient can change with spool position, path, Reynolds number, viscosity, temperature, cavitation/aeration and measurement method. Use the manufacturer’s actual Δp–Q curve whenever available.

Documented valve-path result

Path differential pressure Δp

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Normalized flow

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Standard metric Kv(bar)

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Hydraulic Kₗ

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US Cv

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Steady fluid-power drop QΔp

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Calculation mode

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Interface role

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Implemented liquid coefficient model

Q(m³/h) = Kv √(Δp(bar)/SG)
Kv = Q √(SG/Δp)
Δp(bar) = SG [Q/Kv]²
Kₗ(L/min/√bar) = Kv/0.06
Cv(US) = 1.15609922835 Kv
Pdrop(kW) = Q(L/min) Δp(bar) / 600

The subscripted conventions are deliberate. Parker’s hydraulic technical guide uses a coefficient in L/min at 1 bar; Spirax Sarco describes the standard bar-based metric Kv in m³/h and warns that multiple Kv/Cv conventions exist. Never paste an unlabelled coefficient into a different convention.

Published numerical example

Spirax Sarco Example 6.3.1 uses 10 m³/h water and Kv=16. The implemented equation predicts Δp=(10/16)²=0.390625 bar, matching the published approximately 0.4 bar.

ISO 4401 mounting-interface boundary

ISO 4401:2005, edition 3, is Published and was confirmed in 2022. It specifies dimensions and other data for interchangeable mounting surfaces of four-port directional control valves; it does not assign a universal flow range, internal port diameter, Kv, pressure rating or pressure-drop curve. Exact mounting dimensions remain NEEDS_LICENSED_SOURCE and are not reproduced here.

Pressure-drop characteristic boundary

ISO 4411:2019, edition 3, Published and confirmed in 2024, specifies steady-state methods for determining differential-pressure/flow characteristics for a given valve path. The exact test procedure is not reproduced. Product curves remain path, spool, opening, fluid and temperature specific. For example, Parker CM catalogue gives different product-specific maximum flows and Δp–Q curves for NG06 and NG10 interfaces and states the test viscosity; those values are not universal interface limits.

Why the former page was changed

The former page could dereference an undefined CETOP record and crash on load (`portDia`). It automatically chose a mounting-interface size from fabricated universal flow bands, published unsupported port/thread/bolt/face/Kv tables and computed velocity from invented port diameters. It also implied that ISO 4401 supplied the flow formula, defaulted Q/Δp/SG, accepted numeric prefixes and called QΔp a guaranteed cooler heat load.

No valve or cooler selection: verify exact product/interface drawing, path and spool state, pressure/flow curve, rated pressure and tank-port limits, leakage, hysteresis, dynamics, viscosity/temperature range, contamination requirement, cavitation/aeration, actuator load and system transients. QΔp is the steady fluid-power decrease across the entered path, not by itself a cooler duty or proof of suitability.