Valve Flow Coefficient (Kv, metric)

Kv is the European twin of Cv: cubic metres per hour of water at 1 bar of pressure drop instead of gallons per minute at 1 psi. A Kv 18 valve passes 18 m³/h — 300 L/min — at 1 bar. The two coefficients differ only by unit conversion, Cv = 1.156 Kv, so a valve stamped Kv 10 is a Cv 11.6 valve; European balancing-valve charts and North American control-valve catalogues describe exactly the same hardware in these two dialects.

The practical warning is that manufacturers publish both, and mixing them silently under-sizes a valve by about 15%. Check the datasheet units before you trust a number, and beware a third variant, Av, defined in SI base units (m² of equivalent orifice) with Av = 2.4 × 10⁻⁵ Kv. On balancing valves the published Kv is also a function of handwheel position, so the catalogue table has a Kv per turn — always read at the setting you will actually commission.