compressor/spray gun problem

[Dan of SC]

I have a cheap HVLP gun from Northern Tools, brand name Vaper I've been using with an air compressor rated at 6.0 cfm @ 90 psi. The regulator on the compressor is set around 90 psi, and the in-line regulator at the gun I set at around 35-40 psi. It's been working fairly well for spraying lacquer, clear is all I do, I've finished 5 instruments with it, but now it's acting up. When I pull the trigger, the initial spray is good, but the pressure of the spray drops rapidly, down to almost nothing in 4-5 seconds, making it impossible to get a good finish. I tried replacing the regulator at the gun, that was no help. Anyone have a clue what's going on here? Any help would be greatly appreciated. Danny Gray

[Bluetickhound]

What is your cleanup procedure? Any time I have had trouble with a spray gun or airbrush the problem.has almost always been gunk in the gun...

[Marty Jacobson]

Absolutely. There are little crusty shells of lacquer that build up over time. They might be invisible, but once you're running solvent-based stuff through it, those little bits partly break up and form a sludge, sometimes an outright logjam, at all the little choke points.
Tear the whole thing apart and soak the parts in solvent if necessary. Brass brush everything well while it's still wet. Don't forget to remove the packings and seals. Clean them well but don't let them get soaked in solvent. When you re-assemble it, be sure to lube up all the moving parts that don't come in contact with finish, including the back half of the needle itself and the threads on the flow adjustment screws. I went for years thinking that it was better to avoid contamination in the finish by not lubing my spray guns, and they were miserable to use. Once I took the time to figure out what was safe to lube, they have all worked much better and been easier to operate.

[palosfv3]

If your gun is clean as suggested by others check the air consumption data on the gun and the compressor . Many HVLP guns will easily use 7+ cfm . If your compressor only pumps out 6 cfm you do not have enough compressor to properly run the gun. The size of your air reserve tank is also important . Your spray gun problem description screams not enough air flow. This was a common complaint as HVLP made its way into production spraying . The spray gun data may list a minimum CFM and psi for the gun to work correctly.

[sunburst]

Cleaning the gun is definitely good advice, but the initial pressure followed by the loss of pressure points to possible restricted air flow further up stream. Air can pressurize the lines slowly, and when you pull the trigger the pressure is good until the air in the line is used up, then whatever is restricting the air flow doesn't let enough air through to keep the pressure up. If cleaning the gun doesn't do the trick (hopefully it will), go over the whole system down stream from the compressor to see where else there may be a restriction.
I use quick disconnects throughout my air system, so the first thing I would try would popping the air line off of the gun and see if the air pressure remains good to the gun indicating there is no restriction up stream.