How valve Cv is calculated
A valve's flow coefficient Cv is the flow of water in US gallons per minute it passes with a 1 psi pressure drop. Kv is the metric equivalent in m³/h at 1 bar. Sizing compares the coefficient your duty requires with the valve's rated value.
- US units:
Cv = Q·√(SG/Δp)with Q in gpm and Δp in psi - SI units:
Kv = Q·√(SG/Δp)with Q in m³/h and Δp in bar - Conversion:
Cv = 1.156·Kv
Worked example: chilled-water coil valve
Passing 25 gpm of water with a 5 psi drop across the valve needs a Cv of about 11.2. A valve rated Cv 16 would use about 70% of its capacity, inside the 20–80% range where control is good.
Good to know
- An oversized valve controls poorly because it does all its work close to the seat.
- Pro checks valve authority and the cavitation index for water, and flags flashing when the outlet falls below vapor pressure.