- #1

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## Main Question or Discussion Point

I just want the formula that shows how to find for CFM. I have the pipe diameter and the PSI that are available. I'm just using air, nothing special.

- Thread starter shellback
- Start date

- #1

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I just want the formula that shows how to find for CFM. I have the pipe diameter and the PSI that are available. I'm just using air, nothing special.

- #2

stewartcs

Science Advisor

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Can you be more specific with what you want to know? I presume you mean how to determine the flow rate of air in cubic feet per minute through a pipe when knowing only the pipe diameter and back pressure?I just want the formula that shows how to find for CFM. I have the pipe diameter and the PSI that are available. I'm just using air, nothing special.

CS

- #3

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Yes, that's exactly right. I know there's a way to do it. I just haven't been able to work that out.Can you be more specific with what you want to know? I presume you mean how to determine the flow rate of air in cubic feet per minute through a pipe when knowing only the pipe diameter and back pressure?

CS

- #4

russ_watters

Mentor

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The pressure is the static pressure in the pipe? That isn't enough to determine the airflow. You need a differential pressure across an orifice, pressure drop in a venturi or velocity pressure from a pitot tube.

Once you get some form of velocity pressure (and if you give us more details about your setup, we can tell you how to measure/estimate it), you can use a form of Bernoulli's equation to find the velocity:

V=4005*sqrt(Vp)

where

V= velocity in fpm

Vp= velocity pressure in inches of water gauge.

Once you get some form of velocity pressure (and if you give us more details about your setup, we can tell you how to measure/estimate it), you can use a form of Bernoulli's equation to find the velocity:

V=4005*sqrt(Vp)

where

V= velocity in fpm

Vp= velocity pressure in inches of water gauge.

Last edited:

- #5

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We're going to have a compressor maintaining a constant pressure of +100psi regulated to 100psi and a 3/8" ID for the pipe at its' most narrow.The pressure is the static pressure in the pipe? That isn't enough to determine the airflow. You need a differential pressure across an orifice, pressure drop in a venturi or velocity pressure from a pitot tube.

- #6

russ_watters

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