The Stovebolt Site Forums The Shop Area Paint and Body Shop HVLP question

The instructions always tell you that you need a certain PSI "at the gun" to maintain the correct PSI at the tip. What they fail to tell you is this with the trigger depressed or not.

I can adjust the pressure at the gauge on my gun to the suggested 45 PSI but when I pull the trigger the pressure at the gauge drops. Should I adjust the gauge to read 45 PSI with the trigger depressed?

The most obvious answer is to set the pressure with the trigger depressed but I want to be sure.

Woody,I spray lacquer,I am a woodworker, and my gun sprays @28.5 psi. I pull the trigger half way and get just air no finish and then I adjust my pressure to 28.5.
Also I am very interested in your thread about enamel. I just sprayed Tractor Supply tractor paint on my snow blower.
Looks good but then I am not getting fussy about this unit.

Hey woody, that should be 45lbs at the gun. Then the pressure is regulated internally to bring it down to the low pressure that the tip operates at. The HVLP guns have an expansion chamber in them where the pressure at the tip is dropped and the volume is increased. Some manufactures give the pressure at the tip, now that’s impossible for the average Joe to monitor, and I see no value in that. Might want to review Bernoulli’s principle again.
With a single stage regulator on you compressor your gonna read high until you start air flowing then it will drop to the regulated pressure. I’m sure you have noticed that on you air tools. So in other words yes, pull the trigger and adjust the gauge to the recommended pressure to the gun.

When your ready to spray, before you start the fluid from your gun just pull the trigger for a few seconds and bleed off the higher pressure then the pressure at the tip will be correct for you to add the fluid.

A good two-stage regulator will give you a steady pressure on the gauge at considerably more cost.

A more critical part of the HVLP setup is the tip size. One of the drawbacks to the cheaper guns is that you can’t find different sized tips for them so your stuck with the tip that they supplied with the gun. This means it might be to big for ideal paint spraying and to small for high fill primers.

Denny Graham
Sandwich, IL

Good explanation Denny. Thank you.

There's an excellent overview of HVLP use in Tech Tips under the painting section.

I know but it doesn't answer my question, nor does it identify any of the parts it refers to in the text on the gun pictured there. Interesting reading but begs more questions for the novice than it answers.

Check out the forums at autobodystore.com. They really go into a lot of detail on equipment and technique. Len, the proprietor, is especially helpful.