Clearing the Air Lines in an HVLP Spraygun

Tips on troubleshooting the airflow through an HLVP spraygun. March 3, 2010

I've just bought my first HVLP sprayer - a Graco 3800 with cup gun. I've been using airless and AAA systems, so maybe I'm just not used to these types of sprayers, but it seems to me that something is wrong. When I trigger the gun, I get nothing but air for the first 3 or 4 seconds, followed by an intermittent spray fan that chops out when I angle the gun up or down by more than 20 or 30 degrees. I checked the fluid level in the cup and it was at 3/4 full, so that isn't the problem. I'm spraying lacquer with it and using a #3 fluid set. The lacquer is reduced about 25% with thinner.

I'm probably doing something wrong, but as I've never used HVLP before, I wouldn't know what that might be. Any ideas? I'd try running some straight thinner through it to see what happened, but I'm all out and the store isn't open again till tomorrow.

Forum Responses
(Finishing Forum)
From Paul Snyder, forum technical advisor:
You have a small air hose that goes from the gun to the cup to pressurize it. If that air supply gets blocked, you'll lose pressure in the cup and won't be able to spray. Hook the gun to the air without the cup attached and make sure sir is coming through the fitting on the bottom side of the gun. If you have the "duckbill" check valve flap on the bottom of the cup lid that stops the fluid from going up the air hose, make sure it's not stuck closed. Make sure the hose is not clogged from tipping the gun too far. Pull the air hose off the gun and pull the trigger to allow air flow; make sure air coming out of the fitting in the gun body. If the fitting in the gun body, the air hose, or the fitting/check valve in the gun cup lid is blocked, you won't be able to spray for more than a few seconds at a time. Other possible sources of the problem include a loose fluid nozzle, loose needle packing, or leaking fluid cup lid.

From the original questioner:
Thank you Paul - I just figured it out. It was clogged. I'm used to airless and AAA, so not familiar with using a gun that has no fluid filter. I ran some old thinner I had in the shop through a strainer, shot it through the gun for a minute, and now it's spraying like a beaut! I finally know how you guys make that powder coat look with lacquer. I always get the glass finish look with the AAA. I think I'm going to have fun with this little machine!