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  #1  
Old 09-12-2014, 09:04 AM
Dan of SC Dan of SC is offline
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Default spray gun/compressor problem

I have an inexpensive HVLP gun from Northern Tool brand name Vaper, that I use with an air compressor rated at 6.0 cfm. The regulator at the compressor is set at 90 psi, and the small regulator at the gun is set around 25-35 psi. It's been working fine, I finished four instruments with lacquer in about 1 year, but now I'm having trouble. When I start to spray, I pull the trigger, the spray is good but in 1-2 seconds the pressure at the gun starts to drop rapidly. If I'm spraying the body of a guitar, I make 2-3 passes, I have to stop and wait for the pressure at the gun to build back up, this happening before the compressor starts to run. anyone have a clue what's going on? Any help would be greatly appreciated. Danny Gray
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Old 09-12-2014, 09:26 AM
charles Tauber charles Tauber is offline
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When you say "the pressure at the gun", this is observed as a drop in reading of the pressure gauge at the gun or just that the gun doesn't have much output when you pull the trigger?
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Old 09-12-2014, 10:20 AM
LouieAtienza LouieAtienza is offline
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You may be running out of air because the compressor is pretty small. It could be a leak somewhere, or you have to drain the tank of water, or your air mix at the gun is too high... 35psi is pretty strong for HVLP. I would drop the pressure at the compressor first, then the gun. Also if you're using a cheap translucent hose that comes with most compressors, throw it out, and get a longer rubber hose.
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Old 09-12-2014, 10:30 AM
printer2 printer2 is offline
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You have a restriction somewhere (I am assuming you have a relatively high pressure in the tank as you said the compressor does not kick on). Your hose is acting as a reservoir holding a high pressure and when your gun asks for air it slowly drops down to your gun's set pressure. You then have to wait till your compressor squeezes enough air past your restriction.

Could be dirt or rust. Put an air nozzle at the end of your hose and see if you can hold a large blast out the nozzle over time or if it drops before the tank pressure drops. You need to troubleshoot replacing parts that may work with one's you know work. If the air nozzle works fine then it might be dirt in the regulator of the gun. It has chambers and passages in it and a restriction in one of them can also give you the same problem. I tore apart a few regulators, even got some back together again. Don't advise the average person doing it though unless you have a good mechanical mind.
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Old 09-12-2014, 12:03 PM
Howard Klepper Howard Klepper is offline
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Sounds to me that you you need a new pressure switch on the compressor. Inexpensive but functional ones are available on Ebay.
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  #6  
Old 09-12-2014, 12:12 PM
KevinLPederson KevinLPederson is offline
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A vacuum is being created in the cup that holds the clear. So it starts to siphon or gravity drop (top side cup) and as the nozzle starts to spray its drawing the clear out, creating a vacuum in the cup.

Loosen the lid on the cup first to see if that helps, if so, then you have a weep hole clogged with lacquer.

Check the simple things first (diagnostics), then you can trouble shoot other things.

At least you'll know where to go from there if this doesn't help.

Kevin.
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  #7  
Old 09-12-2014, 04:33 PM
printer2 printer2 is offline
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Quote:
Originally Posted by KevinLPederson View Post
A vacuum is being created in the cup that holds the clear. So it starts to siphon or gravity drop (top side cup) and as the nozzle starts to spray its drawing the clear out, creating a vacuum in the cup.

Loosen the lid on the cup first to see if that helps, if so, then you have a weep hole clogged with lacquer.

Check the simple things first (diagnostics), then you can trouble shoot other things.

At least you'll know where to go from there if this doesn't help.

Kevin.
See, I have not yet took my gun out of the package. Will store that in the back of my mind somewhere among the clutter.
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