How do you calculate CFMs
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Junior User
Joined: Sep 2004
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How do you calculate CFMs
I am getting ready to get another air compressor and it used so there is no tag that tells me the cfm ratings. I want to make sure that it will be able to run all the tools I want it to. I want to make sure it will have enough cfms to run sandblaster, plasma cutter, automotive paint gun, and all common air tools. It is a 5hp 80 gallon 2 stage with 150 max psi. Is there a formula to calculate cfms?
Senior User
Joined: May 2003
Posts: 481
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From: St. Petersburg, FL
Too many variables. Basically, for long term continuous usage, it doesn't matter what size tank you have, it's only good for surges in air consumption. Your cfm's depend on what the motor and air pump can output. Also, the cfm's will vary based on the prssure requirements. 8 CFM at 40 PSI and 8 CFM at 80 PSI are vastly different, so it also depends on the tools requirements.
Having said that, 5HP with an 80 gallon tank is pretty respectable and should be able to run most common garage tools no problem.
Having said that, 5HP with an 80 gallon tank is pretty respectable and should be able to run most common garage tools no problem.
Posting Guru
Joined: Sep 2004
Posts: 1,616
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From: Sapulpa OK
If it is an industrial unit it should make about 4.5 SCFM per horsepower @ 125 PSIG. If it is a retail unit from a box store there is no telling how much capacity it will make because they grossly over rate their motors. It might say 5 peak horsepower but will only produce 2 horsepower continuosly.
If you can identify it let me know and I will try to help you. A picture would really help.
Good luck with it
If you can identify it let me know and I will try to help you. A picture would really help.
Good luck with it
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Originally Posted by fixnair
If it is a retail unit from a box store there is no telling how much capacity it will make because they grossly over rate their motors. It might say 5 peak horsepower but will only produce 2 horsepower continuosly.
Posting Guru
Joined: Sep 2004
Posts: 1,616
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From: Sapulpa OK
torque1st, you are right there was a lawsuit which the mfr. lost and some money was paid out. Don't know who or how much though. They were also ordered to cease and desist using the term " Peak Horsepower ". I haven't heard much on this issue in the last year.
They have really confused the consumer though. Horsepower should refer to one thing only=746 watts when referring to electric motors.
They have really confused the consumer though. Horsepower should refer to one thing only=746 watts when referring to electric motors.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
I have not seen much of a change in the stores but then I have not been paying close attention. I still see those bogus 5HP compressors advertised. Along with the 2.5HP electric tools that run off 120V thru a tinsel cord, -yeah right.
Kind of like those 1000W stereos.
We used to run into problems shipping machines to Europe. Any machine that was rated in HP was rejected. They wanted all of their ratings in KW.
746W per HP only works on high HP motors. The efficiency is low on the small single phase motors.
Kind of like those 1000W stereos.
We used to run into problems shipping machines to Europe. Any machine that was rated in HP was rejected. They wanted all of their ratings in KW.
746W per HP only works on high HP motors. The efficiency is low on the small single phase motors.
Last edited by Torque1st; Sep 15, 2005 at 11:54 PM.
Fleet Owner
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From: Brentwood,CA
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Posting Guru
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From: MI
Originally Posted by Fourwheelinj1
It is a 5hp 80 gallon 2 stage with 150 max psi.
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