kv flow coefficient


Thread Starter

Daniel Yap

does any one know whats the equation to calculate flow rate of air if given a valve with a kv flow coefficient of 15 litres per min?

Hrvoje Zelenka


First, try to contact any control valve manufacturer ( fisher, valtec, masonelian etc), and ask for the Manual. Kv is used in Germany and Cv in USA, but it is same.

To calculate the flow you also need the Pressure upstream, difference pressure, density .


H. Zelenka

Nassir Abedi

Please search for the equation on AGA. On their site you'll find it.

Nassir Abedi
>>Nassir Abedi(Mr.)
>>K. N. Toosi University of Technology
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>>E-mail: [email protected] or [email protected]

Bruce Durdle

Kv gives the flow coefficient if flow is expressed in m3/hour and pressure drop in bar.
Like Cv, the values are based on water as the fluid.

This in itself is not going to help, but you will be able to calculate the Cv from this: Cv = 1.16 x Kv, according to the ISA Practical Guide on control valves. And from there you will have to look up tables etc for the particular valve to find its performance on air.

Hope this helps,


Bruce Durdle
[email protected]
Thanks to everyone for their help with the kv coefficient, I managed to get the equation off a SMC catalogue.
Dear Daniel,

is it possible to share this equation with me? I think I have exactly the same question. I have KV values for water but I need a formula to transpose these values for the use of air.

Maybe you can help me out ?

Best regards,

Victor Ashkenazy

On Air Conditioning applications, for Control purpose of water flow rate, 3Way Valves are installed at outlet or inlet of Cooling/Heating Coils.

At the outlet of the coil 3Way valve is of Mixing type and at the coil inlet the valve is of Diverting type.

Pressure Drop of valve, including PD of bypass leg, must be lower -on both types- than pressure drop of coil at full design rate.

Using the concept of Coefficient of Flow Cv, it's possible to assure proper perform of those valves.

For [Flow]=[gpm] and [PD]=[ftwg], the formula

Kv is like Cv, but in SI Units.

Cv (or Kv)is calculated with designed flow rate and PD of Coil.

Because PD of Valve must be lower than PD of Coil, there will be a Cv minimum for the valve selection, that will satisfy that condition. Minimum because how much PD of valve is lower, Cv value is greater.