# Flow Coefficient

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

Flow coefficient, abbreviated as $$C_v$$, can be described as the volume (in US gallons) of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.  This gives us a method to compare flow capabilities of different valves.  The flow coefficient allows us to determine what size valve is required for a given application.

Flow Coefficient is primarily used when sizing control valves.  However, it can be used to characterize other types of valves such as ball valves and butterfly valves.

## Formulas that use Flow Coefficient

 $$\large{ C_v = Q \; \sqrt {\frac{SG}{\Delta p} } }$$ $$\large{ C_v = Q \; \left( {\frac{SG}{\Delta p} } \right) ^{\frac{1}{2} } }$$ (by volume) $$\large{ C_v = \frac {W}{500 \; \left( SG \; \Delta p \right) ^{\frac{1}{2}} } }$$ (by weight)

### Where:

$$\large{ C_v }$$ = flow coefficient

$$\large{ Q }$$ = flow rate capacity

$$\large{ W }$$ = flow weight

$$\large{ \Delta p }$$ = pressure differential

$$\large{ SG }$$ = specific gravity of fluid (water at 60°F = 1.0000)