Kvwaarden

Kvwaarden, or Kv values, are a standard flow coefficient used to describe the capacity of a valve to pass liquid. The Kv value is defined as the volumetric flow rate in cubic meters per hour (m3/h) of water at 20°C that will pass through the valve with a pressure drop of 1 bar across the valve. The relationship between flow, pressure drop and Kv is expressed by Q = Kv × √ΔP, where Q is the flow rate in m3/h and ΔP is the pressure drop in bar.

Kv values are specified under standardized test conditions, typically using water at about 20°C, with density near 1000 kg/m3 and viscosity around 1 mPa·s. In practice, actual flow through a valve depends on fluid properties, temperature, and system geometry. Kv values provide a convenient, comparable measure for valve selection and sizing, but engineers must apply corrections or consult manufacturer curves when dealing with liquids other than water or under different temperatures.

The Kv value is closely related to the US customary Cv value. The approximate conversion is Kv ≈ 0.865 × Cv (and conversely Cv ≈ 1.156 × Kv). This allows compatibility between metric and imperial sizing data published by manufacturers.

Manufacturers publish Kv values in product datasheets and performance certificates, often accompanied by characteristic flow curves for different valve positions and fluids. In practice, Kv values are used in valve sizing to estimate the required valve size for a desired flow at a given system pressure drop, while acknowledging that real-world factors (temperature, viscosity, density, and fluid type) can shift actual performance from the nominal Kv.