Ask the Expert Question-and-Answer Archive

by Ron Joseph

December, 2003

HVLP Gun

Q. Is it possible to achieve a cfm flow (14cfm @ 50 psi) for short > durations using a compresser rated at 8.6 cfm @ 40 psi? Does the > cfm potential shift over the duration of time? I plan to paint small > projects (guitars) using an hvlp gun.

A. Thank you for your email. Unless I'm missing something, I can't see how a compressor that is capable of delivering presumably a maximum pressure of 40 psig can deliver a higher pressure of 50 psig. If you find that the compressor can deliver a higher pressure, then of course it might also be possible to also deliver a higher cfm, but that will depend on its ability to store the comressed air in a pressurized vessel. Do you have an accumulator that can store the compressed air?

Q. Thank you for your quick reply. I should have been more specific in my question. When I mentioned the compressor, I assumed the tank was a part of the unit. Anyway, the compressor is rated at 8.6 cfm @ 40 psi, the tank is 22 gal. and can handle an accumulation of about 120 psi. So with this in mind, is it possible to have a short duration of airflow and pressure which would meet the requirements of an hvlp gun that has a 13.9 cfm / 50 psi specification? As I had mentioned, the gun will be used for small projects (such as guitars).

A. If your compressor is able to deliver 50 psig then you may well be able deliver short spurts of compressed air as required, but no matter how large the accumulator, if your compressor has a maximum compression of 40 psig, I don't see how you will be able to get that pressure to the spray gun. A larger accumulator can't increase the pressure, only the volume of air.

HOWEVER: Why do you need 50 psig? You might have sufficient atomizing air at 40 psig, provided that you do not loose pressure in the plumbing from the compressor to the handle of the spray gun. At 40 psig you should be able to get a really nice finish on your guitars. Also, if you are use a different cap/orifice/needle combination on your HVLP gun, then 40 psig will be more than sufficient to do the work. Since you are not on a production line you don't need to have a high fluid pressure (or fluid delivery rate), and hence you don't need too much air to atomize the coating. I suggest that you look at your gun manufacturer's catalog to see what cap/orifice/needle combinations are available that will still deliver sufficient paint to the guitars, but will require less atomizing air to do the job.

I'm confident that you can solve this problem.