PSI vs CFM ?
Posting Legend
Joined: Sep 2001
Posts: 30,255
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Unless you need the higher pressure for some tool or machine stick with 125 PSI. The two stage compressors are slightly more efficient ($$$) but you lose all of that and more when you regulate down to ~100 PSI for tools. Most tools are rated to operate at 70-90PSI.
Senior User
Joined: Jan 2005
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Torque1st is right, but 175 psi will deliver 90 psi through a regulator longer than 125 psi between cycles of the compressor. PSI and CFM are directly related.
Higher pressure works better on smaller tanks for this reason.
That said, there is very little reason to have 175psi, because as Torque1st said, most tools run on 70-90 psi, if you have a decent size tank.
I have a 30 gallon tank 120 psi unit in the garage and several 2-4 gallon 120 psi compressors on that we use on jobsites for nailers. When we occasionally have to run a higher cfm tool like a small air hammer or cut-off tool on the small compressors they have to run continuously and still can't keep up. If I run that same tool in the garage, it is ok but even the cut-off tool will tax the big unit if run for a while.
If you don't have to move it around, get the biggest tank possible and don't worry about going over 120 psi.
Good luck,
Ed
Higher pressure works better on smaller tanks for this reason.
That said, there is very little reason to have 175psi, because as Torque1st said, most tools run on 70-90 psi, if you have a decent size tank.
I have a 30 gallon tank 120 psi unit in the garage and several 2-4 gallon 120 psi compressors on that we use on jobsites for nailers. When we occasionally have to run a higher cfm tool like a small air hammer or cut-off tool on the small compressors they have to run continuously and still can't keep up. If I run that same tool in the garage, it is ok but even the cut-off tool will tax the big unit if run for a while.
If you don't have to move it around, get the biggest tank possible and don't worry about going over 120 psi.
Good luck,
Ed
Senior User
Joined: Nov 2004
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Manufactures use a higher pressure to make up for a lower CFM. most tools have a very short life if you try to run them on 175psi , infact I really would not want to be hanging on to an impact with that much pressure there is little doubt that the hammers will be exploding in a very short time.
Keep in mind that PSI & CFM are two totally different things. just like volts & amps. you can get 175 psi through a 1/8" line but try to 20 CFM. Greg
Keep in mind that PSI & CFM are two totally different things. just like volts & amps. you can get 175 psi through a 1/8" line but try to 20 CFM. Greg
Posting Guru
Joined: Sep 2004
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From: Sapulpa OK
Torque1st and Ed are right in theory but in the real world in order to get 100 PSI at the tool you must overcome many restrictions along the piping network. Often this amounts to 50 PSI pressure drop while the tool is running. The worst restrictions are quick couplers, rotary unions found on the axis of a hose reel and 50' of 1/4" hose on a hose reel.
I have used my 1/2" model 231 I/R and 3/8" Gardner Denver impact wrenches for 25 Years or more at 150PSI and have never had to repair either of them. I have a hypodermic needle pressure gauge to check the pressure at the tool and have found this to be true many times.
For a blast cabinet you do need to regulate down to a lower pressure for proper performance. 100 PSI should work well there.
The average homeowner could get by with 125 PSI but if you are going to do some serious work with impacts, air chisels, grinders and sanders 150 PSI will get so much more work done.
175 PSI is too high for most applications unless you have long piping runs or many restrictions.
I have used my 1/2" model 231 I/R and 3/8" Gardner Denver impact wrenches for 25 Years or more at 150PSI and have never had to repair either of them. I have a hypodermic needle pressure gauge to check the pressure at the tool and have found this to be true many times.
For a blast cabinet you do need to regulate down to a lower pressure for proper performance. 100 PSI should work well there.
The average homeowner could get by with 125 PSI but if you are going to do some serious work with impacts, air chisels, grinders and sanders 150 PSI will get so much more work done.
175 PSI is too high for most applications unless you have long piping runs or many restrictions.
Posting Legend
Joined: Sep 2001
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So the solution here is if you want to use a high volume tool. Run a short large ID hose and large couplers right to the tank or have large distribution lines. Fortunately that is not required for most tools. Many tools are specified to operate on 90 PSI air but are designed to work on 70+ PSI air. Some of the off brand tools that are not designed to NFPA standards may have difficulties tho.
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Originally Posted by fixnair
The worst restrictions are quick couplers, rotary unions found on the axis of a hose reel and 50' of 1/4" hose on a hose reel.
I can do without 1/4" hose but my 3/8" hose reels are hard to give up.
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I had a noticeable gain in power to my 1/2" impact when I ditched the 1/4" couplings and went to 3/8" couplings. My compressor tops out at 125psi and I did not notice much difference using the 1/2" impact between having the compressor set at 100 psi or 125 psi. If you have a hose reel make sure the swivel coupling does not have unnecessary restrictions. I have a HF unit that is really pretty good. However for some reason they had a rubber seal between the connector in the reel for the hose and the swivel fitting. When the fitting were tightened up this rubber seal would choke off a most of the air supply. I don't know why they had it in there as the system seals up OK without it. After I removed it the flow to the reel hose was OK.
Lead Driver
Joined: May 2003
Posts: 9,303
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From: Lyndonville, Vermont
my compessor is a 5 hp 20 cfm at 100 psi. Rated at 175 psi it operates at 100-150.
I don't like to go below 100 ever and I don't need to go over 150 so its great for me plus the compessor will live longer due to limiting the pressure to 150. I have a reg on it at the output also.
I don't like to go below 100 ever and I don't need to go over 150 so its great for me plus the compessor will live longer due to limiting the pressure to 150. I have a reg on it at the output also.
