Re: HVLP question

Posted by Rod (NH) on February 13, 2004 at 13:18:57 from (12.148.160.138):

In Reply to: HVLP question posted by Dave on February 13, 2004 at 10:44:53:

Hi Dave,

Well, I'am not an avid fan of HVLP (being a dinosaur in that area) but I will add a couple of comments. It is NOT normal to need that high an air pressure for any style gun. Your gun should have the design pressure indicated directly on the handle or in the documentation that came with it. The HVLP design is based on an environmental legal requirement for maximum pressure "at the air cap" of 10 psig. Depending on the details of the internal design of the gun, this can translate to anywhere between, say 15 psig to 50 psig "at the gun air inlet". Whatever that pressure is should be specifically indicated by the gun manufacturer. For example, my DeVilbiss HVLP spot gun has "29 psi max inlet" indicated right on the gun handle. It is very important to realize what "at the gun inlet" means. It is NOT the same as what is shown on a regulator that may be 50 feet or more away on the wall or at the compressor. Such a gage reading will always be significantly higher that "at the gun inlet". I recommend you tee in a pressure gage directly to your gun inlet. I have such gages permanently attached to my three guns. While holding the trigger wide open, adjust your regulator to obtain the needed pressure "at the gun inlet". The actual reading back at your regulator is not particularly relevant. It's the pressure "at the gun" that is important.

Non-HVLP equipment is usually adjusted to between 40 and 60 psig at the gun by this method but HVLP is so dependent on the actual gun internal passage design that the maximum value can be different between manufacturers. It also should be noted that for HVLP it is a legal requirement that may apply in your area. Technically, you can increase the pressure to perhaps get a little better atomization but you could be breaking some local law by doing so. A good gun design should not require increasing pressure beyond stated requirements.

If you are unable to achieve an acceptable finish using the above method I believe you need to look at some area other than air pressure for the cause.

Rod

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