Valve Kv and Cv calculator
Kv is the water flow in m³/h through a fully open valve at a 1 bar pressure drop. Know any two of flow, pressure drop and Kv, and you get the third.
Result
- Suggested Kvs (25% margin)
- 16 m³/h
- Pressure drop with this Kvs
- 0.25 bar
Kv = Q · √(ρ/ρ₀ / Δp)
Cv = 1.156 · Kv
Formulas for liquids without cavitation or choked flow. For gases, steam and large pressure drops use IEC 60534 sizing.
What is Kv?
Kv is the flow of water (in m³/h) at 5–30 °C through a valve at a 1 bar pressure drop. Kvs is the Kv of the fully open valve, as given in the catalogue. For another liquid and pressure drop: Q = Kv · √(Δp / SG), where SG is the specific gravity (water = 1).
In the US, Cv is used: the flow in US gallons per minute at a 1 psi drop. Cv = 1.156 · Kv.
Sizing a control valve
Work out the Kv needed at maximum flow and choose a valve with a Kvs about 1.2–1.3 times larger, so it isn’t fully open at maximum flow. An oversized valve works at small openings and controls poorly.
Common questions
What pressure drop should a control valve have?
Aim for a valve authority of at least 0.3–0.5, meaning the valve takes 30–50% of the drop in the controlled branch.
Can I use this for steam or gas?
No. Gases and steam use different formulas that account for compressibility and choked flow.