## Kv and Cv Loss Model

AFT Impulse allows the user to enter valve coefficient data in terms of Kv or Cv. Conversions are handled seamlessly in the background. Kv is the metric equivalent to Cv.

Manufacturer Testing in Standard Units

Cv (Coefficient of flow for Valves) is a single parameter which relates fluid density (given in units of specific gravity), pressure drop (in psi), and flow rate (in gallons per minute).

One can get a better understanding of the role of Cv by setting the pressure drop (dP) and SG to 1, in which case Cv is equal to flow in gallons per minute. Cv could be considered the flow capacity (in gpm) of a given fluid (i.e. a given SG) for a given pressure drop. Or, one may wish to calculate the pressure drop through a valve, with a given Cv at a given flow rate.

Manufacturer Testing in Metric Units

If the engineer is provided with valve data in metric units, they are also likely to be provided a value for Kv and not Cv.

The only difference is the units used for Q and dP. Kv uses flow units of m3/hr and pressure drop units of bar.

If one wishes to calculate pressure drop through a valve, with a given Kv, at a given flow rate, the same relationship applies.