i am thinking about buying another spray gun. i have an old binks that i have used for years and am thinking its time for a devilbiss gravity feed hvlp gun. i had always used my binks on my smaller (maybe 5-6 cfm max) compressor with a 20 gall tank with no problems. i now have a 30gallon compressor that is rated for 10.5 cfm at 40psi. the gun requires 14cfm at 23psi. so now for my question, do you think the cfm will be high enough if i pressurize the tank to 100 psi and reg. it down to 23 at the gun?

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have no worries.....President Obama swears "If you like your gun, you can keep it

For how long? For a period of time you'll be using the "precompressed" air and won't have any supply problems. Eventually though, you'll run your tank down low, and then, as your numbers show, your compressor doesn't have enough capacity to run the gun on it's own. I suppose your compressor might have a higher CFM rating at 23psi than it does at 40, but it's likely not large enough to make a difference. Even if it did, you'd be running your compressor at 100%, and that's rough on equipment.

How long will you be painting? The stored air in the tank may last you through a small job, or if you're pausing often, the compressor can make up the difference.

MV

once in a great while would i be spraying for long periods of time. (i may end up spraying a buddys truck at some point). For the most part it would be small projects. I just dont want to not be able to use it at 100% once in a while

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have no worries.....President Obama swears "If you like your gun, you can keep it

Without getting into the reason, I've had two tanks, from "frapped" compressors, ganged together with a working compressor...set the trip-off point at 120psi and had more than enough "head-room" for the project I needed the extra air for...

The question that needs answering though is: Does the compressor, alone, keep up with the useage at the time?

If it doesn't, then you'll want to see if you can acquire more "storage" of extra compressed air...gauge the work, then pause long enough to allow the compressor a chance to bring your air-supply back up to a manageable level of psi..

My $0.02 worth...keep the change...

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M. G. Burg
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“I didn’t really say everything I said.”
. . . . . . . . . . . . . . . . . . ~ Yogi Berra ~

I think you will run low on air at some point. However, if you stop sraying for a minute and let the compressor catch up, you should be fine. Also remember that the cup capacity limits how long you can spray, too.
I have used a Harbor Freight gravity flow HVLP gun on my smallish compressor with quite satisfactory results for several years painting 3 or 4 complete cars.
Having said that, air supply is important. Anything you can do to improve the air will help.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

You will not keep up if you run the compressor at 100psi. It will only provide 10.5 at 40psi, and it will necessarily provide less at a higher pressure (since the air in the compressor cylinder must be precompressed further before it can even enter the tank). But this means, of course, that your compressor will run full-time until the pressure in the tank lowers enough that the compressor input equals the load (if possible).

So the only question is, can your compressor deliver 14cfm at 23psi?

Note that "cfm" for an air compressor refers to STP cubic feet of air. That is, it's not really 14cfm of air at 23psi. It's 14cfm of atmosphere compressed another 23psi.

It's my understanding that the CFM to PSI is a ratio and it should be relatively linear except for any pumping losses. If you convert 10.5 CFM @ 40 PSI to the required 14 CFM for the gun, the compressor should be able to sustain 30 PSI which will satisfy the gun at 100% duty cycle.

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-Evan


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Pumping losses are the big thing here, but that causes more loss at higher pressure, making it even more likely that he will be able to provide sufficient airflow at 23psi.