Question about Compressor CFM

[Jersey Mike]

Im looking at upgrading my compressor. Im looking into two different models.
IR 60 gallon single stage compressor 11cfm @90 psi

IR 80 gallon two stage compressor 14.3 cfm @90 psi

Are the extra 3 cfm really going to make that big of a difference. It will be used for general auto work as well as spraying. There is a $400 price difference between the two and at this time of year $400 is alot to me. But if it will make a big difference I might spring for it.What do you guys think?

[harman]

I have a ir 60 gallon with 15.8 cfm I think that is at 90psi. It is a 2 stage model ts5 I think. It was just over a thousand 3 years ago not sure if price changed much. I will say the higher cfm might be worth it if you plan on doing any sandblasting. I can run a 20 gallon sandblaster reasonably good with this unit. I guess it depends on what you are going to use the compressor for.

[Len]

There are three big differences in those two compressors...

1. The CFM of the larger model is 30% greater than the smaller model. This allows the compressor to keep up better with the work being done.

2. The tank size is 30% larger than the smaller compressor and this makes a big difference because the compressor won't come on and off nearly as much.

3. The two stage compressor doesn't need to work nearly as hard as the single stage to produce the same amount of air.

The smaller compressor is about the smallest I'd recommend for a one man shop but the larger unit is a better tool.

[88GT]

I have (I think) 2 of the 60s you mention. I would rather have the one larger compressor. The small one will keep up with most tasks and should work fine for "occasional" use. However, no one ever complains about having too much air.

[Jersey Mike]

Thanks guys. All valid points. I never thought of it as Len described. Percentage wise it does look like a big difference. Even though its a 3 cfm difference. Im also assuming that the two stage should last longer because its doing 1/2 the amount of the single stage. Correct?

[easymoney]

i like a 2 stage better because they are capable of higher pressure. up to 175 psi on a lot of models. that higher pressure is good if you are going to run an impact wrench. most other tools do not need to be ran at near that pressure tho. the 2 stage is generally the best if you can affod it.

[88GT]

I forgot about my DAD 500 that has a max pressure of 150. I knew I convinced myself I did the right thing on accident LOL
Take into account the pressure a 2 stage produces. It would actually be too much for my set up. Plus I have underground pvc pipe connecting my 2, but its only about 6" underground.

[Phil V]

I would never recommend ANY bodyshop to run their 2 stage air compressor at 175 psi shut off. There are NO air tools used in a bodyshop that are designed to run on more than 100 psi of air. I have a top of the line oil pressure fed Quincy 2 stage 80 gallon air compressor and Allied Compressors that I bought it from suggested to me when I bought it in 1984 that I drop the shut off pressure down to 150 psi and the kick on pressure at 125 psi. They explained to me that the extra 25 psi from 150 to 175 psi required that compressor to work a lot harder at those higher pressures which are hard on any compressor and the disadvantages far outweigh the advantage of the higher air pressure at around 175 psi. My compressor has been kicking on at 125 and off at 150 psi now just about every day for the last 26 years without a single problem (other than a new electric motor around 6 or 7 years ago). I'll say it one more time -- there are NO tools in a body shop designed to run on more than 100 psi. Running air tools on higher psi will cause premature failure of the air tool.

[JCCLARK]

Well said. Phil is right.
A compressor puts out a lot more CFM when pumping it into
a 150 PSI tank than it does pumping against a 175 PSI tank.
the extra 25 PSI is only a reserve and gets you very little.
I noticed my new Eaton changed their set points down to 150 shut-off
(like Phil said) They use to be 175.

Once your compressor kicks on from useing it, tank size doesn't matter.
The only thing that matters then is if the pump can replace the cfm faster than you use it, and it will run longer to refill the bigger tank.
Neither one of those compressors are rated high enough to run air sanders.
Mine pull 15 CFM at 90 PSI, that's typical.
Sure, you can make it work, but those compressors will run continuously
when useing a tool like that and that'll cause a lot of heat and moisture
problems. Not to mention the overworking of the compressor.
A lot of motors on cheaper compressors are not rated for
continuous duty.

[Jersey Mike]

Thanks for the info Phil and Clark. Its all stuff that I wasn't aware of. Thats why I ask:)

[88GT]

The SS3L3 like I have (and Im sure the others too) are 100% duty cycle if you use synthetic oil ;)

[dixie1776]

i never thought of that extra 25 doing damage till you mentioned it, good point though.... after i cut down the pressure on mine tomarrow maybe i'll add a couple more years to its service life as it'll take a lot of pressure off of the rings, head, valves, etc.
my compressor doesn't run that often cause i have the 80 with the compressor and an extra 80 for volume and somewhere for water to drain back to from the pitch of my air lines as to keep it out of my compressor tank.

[JCCLARK]

The SS3L3 like I have (and Im sure the others too) are 100% duty cycle if you use synthetic oil ;)

It's the motor I was referring to.;)