# Flow Coefficient

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

## Flow Coefficient

Flow coefficient 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.

### Flow Coefficient Formula

$$\large{ C_v = Q \sqrt {\frac{SG} {\Delta p} } }$$

Where:

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

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

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

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