Control Valve Sizing (Cv)

Quick pick (TL;DR)

For liquids: Cv = Q · √(SG / ΔP) (Q in m³/h, ΔP in bar).
Calculate the required Cv at maximum flow, then pick a valve whose rated Cv gives 60–80% travel there (and >10% at minimum flow).
Check cavitation/flashing (service sigma vs valve) and choose the body: globe for fine control, segmented ball/butterfly for high capacity.
Pair with equal-percentage trim on most pressure-varying loops.

Step 1 — Calculate required Cv

Water, 65 m³/h, ΔP 2 bar

Liquid Cv formula Cv = Q · √(SG / ΔP) Given Q_max = 65 m³/h , SG = 1.0 , ΔP = 2 bar Step 1 — Required Cv Cv = 65 · √(1.0 / 2.0) Cv = 65 · 0.707 = 46 Step 2 — Select rated Cv target travel 70% → rated Cv = 46 / 0.70 rated Cv ≈ 66 → pick valve Cv 70 Step 3 — Min-flow check at 30 m³/h: Cv = 30·0.707 = 21 21 / 70 = 30% travel → controllable Answer → globe valve, rated Cv 70, equal-%

Sizing exactly to Cv leaves no control margin — target ~70% travel at max, >10% at min.

Control valve Cv calculator (liquid)

Liquid Cv & cavitation check

Liquid sizing + cavitation check. Gas/steam use compressible equations (datasheet).

Max flow (m³/h)

Normal flow (m³/h)

Inlet P1 (bar a)

Outlet P2 (bar a)

Specific gravity

Vapour pressure (bar a)

FL (recovery)

Target travel (%)

Screening tool — verify with vendor sizing software.

Reference — typical globe valve rated Cv

Body size	Full-bore Cv (≈)	Reduced trim
1"	12	to ~2
1.5"	28	~5–28
2"	48	~10–48
3"	110	~25–110
4"	195	~50–195
6"	450	~110–450
8"	750	~195–750

Indicative — reduced trim gives intermediate Cv; confirm with the maker.

Decision flow

1. Cv = Q·√(SG/ΔP) at max flow

2. Rated Cv = required ÷ 0.7–0.8

Min flowTravel > 10%

CavitationΔP > FL²(P1−Pv) → special trim

BodyGlobe / ball / butterfly

Gas & steam use the IEC 60534 compressible equations, not the liquid formula.

Step 2 — Cavitation & body type

Check cavitation; use anti-cavitation trim if marginal.
Globe control; ball capacity; butterfly cheap/high-flow.
Confirm actuator thrust vs full ΔP.

Step 3 — Don't forget

Gas/steam use compressible Cv equations.
Reducers → apply Fp factor.
Match characteristic to the loop.

Common mistakes

Required Cv = rated Cv.
Ignoring cavitation.
Oversizing → low-flow hunting.

Requisition & datasheet

Fluid, flows, P1/P2, ΔP, SG.
Required & rated Cv, body, trim.

Frequently asked questions

What should I know about Control Valve Sizing (Cv)?

For liquids: Cv = Q · √(SG / ΔP) (Q in m³/h, ΔP in bar). Calculate the required Cv at maximum flow, then pick a valve whose rated Cv gives 60–80% travel there (and >10% at minimum flow). Check cavitation/flashing (service sigma vs valve) and choose the body: globe for fine control, segmented ball/butterfly for high capacity. Pair with equal-percentage trim on most pressure-varying loops.

Which standards or codes apply?

IEC 60534-2-1 (sizing equations), ISA 75.01, IEC 60534-8 (cavitation/noise), IEC 60534-2-3 (test).

Standards — IEC 60534-2-1; ISA 75.01; IEC 60534-8.