How to Determine Air Compressor CFM Output

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So I bought a CL air compressor last night. It's a 14 gallon, 3/4 hp motor, belt drive, old school unit. It takes about 3 minutes to pump up to 100 psi. It's so old that there's no manual for it and the company (Sanborn) has long been bought out by Coleman. Coleman doesn't even make air compressors anymore, so they have no tech support for this unit. When I was looking, one of the criteria was >4.5cfm @ 90psi so it would run my 1/2" impact gun. This one runs the gun, but I'm still curious as to what its output is. This thing is so quiet compared to the old direct drive relic that I had before. Lousy cell pic for reference:
 
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your gun only needs that intermittently, so if that tank goes to 125 or 150psi you should be quite well set.
 
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I guess you could run it next to a known rated one and blow up two air mattresses in a race. Realistically it's probably sized to take all 15 amps from a standard socket. That 3/4 horse is a strong beast, might be equal to 5 sears horses. wink
 

threeputtpar

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The placard is completely faded away, not even a model number. I believe it's a 44A75 Sanborn, but even Google knows nothing about that model. I think I can make out that the max psi is 110, but I'm not sure. The motor says 14.5 amps and my garage is all 15 amp plugs but it fires up quite nicely where I plan on using it. I guess it'll get a good test this weekend when I put new brakes on the back of a friend's car. I was just curious as to what these old ones were rated at compared to comparable sized new units. I bet this old one would blow away new compressors. Oh, and it's oil lubed. ND30 the best recommendation? I think it takes <10 ounces.
 
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14.5 amps for 3/4hp? Is the motor 1725rpm? Nowdays it's possible for a 14 amp compressor to do 4.5cfm, but that's pushing it. Thankfully I doubt you can do a 100% duty cycle with your impact wrench. I use a pancake for mine and don't have any issues. Unless you sandblast or paint I don't see the need for large capacity, but then I'm shadetree and not a pro.
 
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Does it takes 3 minutes to reach 100 psi from zero??? This guide is a very fast and good approximation to calculate the cfm, if you want a better approximation, then the next step will be to use the Ideal Gas Law but you will need to measure the temperature of the gas also. From the data you posted your compressor delivers 4.24 CFM
 

JC1

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Oshawa, Ontario Canada
Originally Posted By: threeputtpar
So I bought a CL air compressor last night. It's a 14 gallon, 3/4 hp motor, belt drive, old school unit. It takes about 3 minutes to pump up to 100 psi. It's so old that there's no manual for it and the company (Sanborn) has long been bought out by Coleman. Coleman doesn't even make air compressors anymore, so they have no tech support for this unit. When I was looking, one of the criteria was >4.5cfm @ 90psi so it would run my 1/2" impact gun. This one runs the gun, but I'm still curious as to what its output is. This thing is so quiet compared to the old direct drive relic that I had before.
Did you get the drain opened to see if there is any rusty water in the bottom of the tank? Looks like it will serve you well. Enjoy. Regards, JC.
 
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Originally Posted By: Darwin1138
Does it takes 3 minutes to reach 100 psi from zero??? This guide is a very fast and good approximation to calculate the cfm, if you want a better approximation, then the next step will be to use the Ideal Gas Law but you will need to measure the temperature of the gas also. From the data you posted your compressor delivers 4.24 CFM
Had to run the math on my compressor 4min30sec to go zero to 175psi 80 gallon tank calculated to 28.2cfm tag on tank says 27.2cfm @90psi very easy to do thanks.
 

threeputtpar

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Darwin1138, nice find on that. For whatever reason, Google didn't find that in my searches. I worked your math and got the same answer. I suppose I should record the time it takes to reach 90psi instead of 100psi and use that as that's the capacity I'm looking for.
 
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