# I need two simple formulas to figure flow rate and velocity of air through an orifice

1. Sep 23, 2011

### intuit

I have been searching for formulas to determine the flow rate and velocity of air through an orifice at a given pressure differential. I need to know the flow rate to determine the CFM requirements of the compressor. And I need to determine the velocity to be able to accurately size the orifice for the job intended. I have found different formulas. Some more elegant than others. I need simple formulas to get a usable numbers. The application can be fine-tuned by trial and error. The variables used should be as follows:

V = Velocity in feet/sec
C = Orifice Coefficient = .95
P = Pressure differential = 130psi (150psi being released into 30psi)
A = Orifice area in inches squared = The orifice sizes will be in the range of .055" to .157" Diameter.
T = Air temperature = 70 degrees F.

I don't need an elegant formula, but if other variables are needed, use:
W = Mass of Air = Assuming .075 lbs/ft
Atmospheric Pressure will not be a factor in this application