Q: I have a 2 hp 6 gallon air compressor with a maximum of 135 psi that produces 2.6 SCFM @ 90 psi. Would this be sufficient with a small touch up air spray gun with an average air consumption of 2.8 CFM @ 30 PSI; 4.0 CFM @ 50 PSI?
A: Going strictly by the numbers, I’d say yes, but of course, life does not always go by the numbers. That compressor should have no problem feeding a gun that draws 2.8 CFM at 30 psi, provided you in fact set it at 30 psi. That is a fairly low pressure, but a reasonable one that should be adequate for a touch up gun spraying thin material. Naturally, spraying thicker material may require more pressure and more air volume, which may tax the compressor somewhat. By the way, it is not just the gun 
itself, but rather the tip and air cap combination that controls the amount of air needed and the size of the fan produced. Often, guns are offered with several tip and air cap options which provide both smaller and larger fan widths, and have correspondingly smaller and larger CFM requirements. Sacrificing a larger fan width for a smaller one is one good way to maximize the available output of the compressor you already own without having to buy a larger one, and the difference in spraying time is minimal.
Monday, July 06, 2009
Q: So, will a compressor that produces 2.6 SCFM @ 90 psi work alright if set at 40 psi for waterbased lacquer?
A: As I said, it should work according to the numbers, but the numbers mean very little. Compressor manufacturers routinely overstate their unit’s abilities, and gun manufacturers routinely understate their gun’s requirements. Thus, it could work just fine, could be brinksmanship all around, or could leave you frustrated.
For the most part, waterbased material tends to be low viscosity. Thus, it likes a relatively small fluid aperture (1 mm), which means lower CFM draw. However, it also tends to like slightly higher pressures, which often mean higher CFM draw. Because you want to spray it very sparsely so that the surface is just barely wet, the odds are in your favor, but whenever you are walking the line, it is a bit of a crap shoot.
From the sounds of it, you already own both the compressor and the gun, so try it and see how it works. If not, I’ll give you one bit of sage advice: The odds of all this working with a standard touch up gun are vastly better than with an HVLP conversion gun of any size. HVLP guns are, relatively speaking, air hogs. If you have a choice, in this case you are better off with a standard compressed air touch up gun.
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