## Kv and Cv Loss Model

AFT Fathom allows the user to enter valve coefficient data in terms of *K _{v}* or

*C*. Conversions are handled seamlessly in the background.

_{v}*K*is the metric equivalent to

_{v}*C*.

_{v}Manufacturer Testing in Standard Units

*C _{v}* (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 *C _{v}* by setting the pressure drop (

*dP*) and SG to 1, in which case

*C*is equal to flow in gallons per minute.

_{v}*C*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

_{v}*C*at a given flow rate.

_{v}

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 *K _{v}* and not

*C*.

_{v}

The only difference is the units used for *Q* and *dP*. *K _{v}* uses flow units of m

^{3}/hr and pressure drop units of bar.

If one wishes to calculate pressure drop through a valve, with a given *K _{v}*, at a given flow rate, the same relationship applies.