# Real World Fluids Question



## I M A PE (Apr 18, 2014)

This is a pretty basic question for an expert in pneumatics or fluid power but I'm not sure of the answer. Standard Cubic Feet Per Minute (SCFM)... how does that relate to CFM?


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## Jonhnny123 (Apr 21, 2014)

Basically, SCFM means you don't need to take into account outside factors such as temperature or pressure. The majority of the time, SCFM = CFM.

SCFM means the CFM at standard conditions: room temperature (60-70 deg), atmospheric pressure (14.7 psi), normal relative humidity (30% maybe?), etc.


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## Ramnares P.E. (Apr 21, 2014)

I would agree with this ^. You do have to be careful with SCFM and ACFM of course.


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## I M A PE (Apr 22, 2014)

The trouble I'm having is sizing a pneumatic valve. I know the ACFM, it's simple arithmetic and it's right around 34 ACFM. The system operates at a max pressure of about 120 psig. I absolutely no idea what the compressed air temperature is typically and I'm sure it's highly variable. Could be ambient, could be much warmer so I don't know what to do but neglect it. Ambient T would give the highest (worst case) SCFM anyway, right? Same thing with relative humidity. I have no idea at all how to account for that in a typical pressurized air system.

So is the conversion from ACFM to SCFM 34 ACFM * (120+14.7)/14.7 = 310 SCFM?


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## kalvinjk (Apr 25, 2014)

Typically, I would bring the valve company in to determine what's the best application of valve.


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## Lumber Jim (May 12, 2014)

submit your pressure range to the valve manufacturer. (min operating and Max) they can help you to determine the correct sizing for the actuation and likely have something standard for the 120 psi max that you have listed above. as mentioned above, the valve manufacturer can help determine the application and will likely ask some pertinent questions that could affect performance that you may not have thought of....


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