# 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

2. Sep 23, 2011

### RocketSci5KN

Re: I need two simple formulas to figure flow rate and velocity of air through an ori

Check this website - they have formula's for what you want. Contact them
if you have any other questions. http://okcc.com/

3. Sep 27, 2011

### intuit

Re: I need two simple formulas to figure flow rate and velocity of air through an ori

Thank you Rocket. There is some very useful information on that website. However, their formulas are only useful with the charts that they have for their own products. I'm still searching for a formula from which I can create a spreadsheet calculator where I can enter in the pressure and the orifice area. I know that flow and velocity through the orifice (before expansion)are functions of differential pressure, orifice coefficient, and orifice area. But I have no idea what the relationships of all the factors are.

4. Sep 28, 2011

### Gannet

Re: I need two simple formulas to figure flow rate and velocity of air through an ori

try this online calculator. It requires java

http://www.flowmeterdirectory.com/flowmeter_orifice_calc.html" [Broken]

Last edited by a moderator: May 5, 2017