I'm trying to figure the max amount of air flow I can get through a 1/4" air line. Upstream pressure is roughly 25 INWC and downstream is atmospheric. Air temp is 130F. I'm looking for a flow in cfm. I'd like to see a calc as I am experimenting.

This is easy, but I'm rusty.

If it's too easy, try this one...
I'm trying to set up a DP flowmeter for the above situation. Accuracy is not that important (20%). Does anyone have a formula for an orifice? Thanks.

 

I believe the formula would be:
Q=14.5PD^2
where:
Q=CFM
P=absolute pressure
D=orifice diameter in inches

 

So am I to understand, a 3" PVC pipe with 1/2" backpressure, will yield 14.5 x 0.5 x (3 x 3)or 65 cfm of air flow? and 1" back pressure would yield 130 cfm?

 

Responding to Blackbomb77's query:

Because the driving pressure slightly exceeds ambient, one can assume the air is incompressible. Thus, the flow rate is proportional to the area x sqrt(2 x DP / rho).

Applying Bernoulli's "common" equation, I converted area, pressure-drop, and density (corrected for temp) to appropriate units. The answer is 7.2 cfm.

If details are required, contact me.

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])