Pressure drop while spraying with HVLP spray gun

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Robert Matthews

I am running a Craftsman Single Cylinder Oil Free 6hp 30 gal compressor (8.6 scfm at 40 psi 6.4 scfm at 90 psi.)

My gun is rated at 9 scfm at 35 psi, 12 cfm at 43 psi. I have used this set up for over a year with no problems.

In the middle of spraying the other day the pressure of my gun started to drop while i was spraying. I released the trigger.

When I pulled it again the pressure was there but only for a sec or two. Then it would drop to almost nothing and paint would barely come out of the gun.

Every time I released the trigger for a few seconds and then pulled it again the same would happen. I hooked another gun up and the same.

My blow nozzle does the same but not as drastically.

Why is this happening?

Robert, it seems that something is blocking the orderly flow of compressed air to your HVLP paint gun.

I suspect that your regulator is failing.

Typical air regulator - this one installed with the adjusting knob on the side
Typical air regulator – this one installed with the adjusting knob on the side. The regulator will work in any orientation.

That, or, the ability of the compressor to maintain flow has been compromised… something else is blocking the air, but I still think it’s the compressor regulator failing.

You may have a regulator problem, but since I don’t know what else you have in the discharge manifold of your compressor, that’s only a guess.

I would remove the regulator from the circuit and see if that made any difference to the flow to the gun. If you have another regulator, replace the existing one as a test, perhaps?

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I am having a similar issue. I have been spraying my guitars for 3 years with an LVLP, and California Air Tools 10020C (2.0 HP, 10 gallon), no problems. Just starting a spray, the pressure dropped too low to atomize properly. Released trigger, the pressure went up for just a second or two, and dropped back down. I went this way, and got through the spray, however rough. I contacted CAT and the tech said clean out the regulator, which I did, same results. I ordered and got a new regulator, which in this case is built into the manifold.… Read more »

Update: Pulled the tank check valve, found it to be working fine, cleaned it a bit, and re-installed. Did not fix the issue. So, I detached the hose going from the pressure switch to the regulator manifold, and found that the steel fitting that goes into the body, at the end of the hose, with two small holes, one on each side, were about 90% clogged with hardened dirt, like an adobe brick. I cleaned the ports out, re-attached the hose, and it fixed the issue, good to go.

I’d be looking at that tubing. I think you’re right about something flapping, but it won’t be the check valve or the pressure switch. It could be something the plumbing to the pressure switch, but not likely.

Good luck.
P.S. Please don’t order a check valve or a pressure switch. There is no reason to suspect either at this point.

Thanks Doug !

Sure. You’re welcome, any time.
Although you seem to have figured it out on your own – congrats!