Too much compressor cfm for paint gun

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PostPosted: Wed Feb 03, 2021 9:15 pm
Ultra noob question - My compressor puts out 11.5 scfm @ 40 psi. Can I use a spray gun that only requires 7.1 scfm @ 40 psi and still get good paint coverage without damaging the gun? Everything I've researched online cautions about not having enough compressor cfm to match the gun requirements but not vice-versa. [size=85][/size]

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PostPosted: Wed Feb 03, 2021 11:05 pm
I don't think I've ever seen any air tool "overpowered" by cfm. Most air tool and especially guns are understated as far as their consumption on cfm. Now, if we were talking over pressurized that is another matter. That can take out seals in air tools......
Even that 11.5 at 40psi is kind of misleading....what is your cfm output at 90 psi?
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PostPosted: Wed Feb 03, 2021 11:36 pm
Darrelk

My compressor is a Campbell Hausfeld VT6195, 60 gallon, 3.7 hp. The specs say it develops 10.2 scfm at 90 psi, 11.5 at 40 psi. I guess to restate my question - How do I "throttle down" my compressor cfm to match the gun cfm for best performance? Or do I even need to worry about this? Will the gun automatically adjust and spray at the ideal 7.1 cfm? Will I damage my gun if I hit it with 11.5 cfm straight from the compressor? As I said, I'm a noob and I'm just trying to make sure I have compatible equipment to get started.

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PostPosted: Thu Feb 04, 2021 12:45 am
I think that you're confusing pressure (psi) and volume (cfm or scfm)

There will be a regulator on the compressor outlet and it's usual to have this set around 90psi. This is good for air tools but way too much for most spray guns, so most people put another regulator on the wall of their booth and this one regulates the pressure down to (maybe) 30psi or what the gun needs or operator wants.

"scfm" was designed to allow comparisons based on a set of standard value, i.e. temperature and pressure, but no-one seems to be able to agree on what those standard values are, or should be, so it's a pretty useless measurement, especially when quoted as "11.5 scfm @ 40 psi" (unless you added the 's'). "cfm" is just cubic feet per minute and is a measure of the volume of air used or delivered. For delivery it's usually qualified by the pressure, for example 13cfm @ 30psi. For usage it's usually quoted just as cfm, so your gun uses 7.1cfm.

As above, pressure can damage seals in spray guns, which is why there is usually a regulator nearer to the gun to reduce pressure to that needed by the gun. Usage by any given gun, is determined by the size of internal passages and the type of aircap that it's fitted with. Thus a HVLP gun will use more air (high volume), but at lower pressure.

If your gun uses 7.1cfm and the compressor can deliver 11.5cfm then that gun should work fine with that compressor. However, be aware that most other spray guns have a higher volume requirement and, if you wanted to change guns you would either be limited in your choice or have to change to a bigger compressor. Using air tools with that compressor would be almost out of the question.
Chris



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PostPosted: Thu Feb 04, 2021 8:38 am
Thank you for clearing that up. I understand that I have to lower my pressure going into my gun to the recommended operating pressure. I
was over-thinking it, and confusing myself, when it came to cfm air delivery. I guess as long as I have at least the minimum available cfm that my gun needs, I'll be alright. Having extra available air delivery volume won't hurt anything as long as I don't exceed the pressure rating for the equipment. Your thoughtful explanations are much appreciated!

Andy

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PostPosted: Thu Feb 04, 2021 9:13 am
I'm glad Chris gave you that detailed explanation of that cfm/pressure relationship....saved me a bunch of typing..... :)
We have this kind of semi-stupid thing in the world of air tools/compressors.....Air compressor production/cfm is usually overstated while air tool/gun usage cfm is understated. Almost all air tools are bigger air hogs than you think.... cfm is king....our wood shop unit puts out just about 30 cfm.
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PostPosted: Thu Feb 04, 2021 9:32 am
DarrelK wrote:...our wood shop unit puts out just about 30 cfm.


I'm jealous 8)
JC

(It's not custom painting-it's custom sanding)

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PostPosted: Thu Feb 04, 2021 1:28 pm
I get a little "giddy" every time I hear it run...... :happy:
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