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Old 10-07-2019, 12:22 AM   #1
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Default Hvlp spitting

Hello everyone

I have searched for my problem but could not quite find a topic for it.

when spraying really thin material (wood dye or water thin material) I get spitting on my first press of the trigger. I get a spit when the air start pushing out before the needle even let material flow. in other word it happen when you presse the trigger enough for air to flow but not enough for material to begin flowing.

After a lot a troubleshooting I found that my material seems to be leaking from the air diffuser part of the gun(got a fuji t75 gravity). When I press the trigger small droplets of material are coming from the holes of that diffuser. eventually they bead up to a big droplet wich spit on the first second of pressing the trigger but then it sprays fine.

I seems to have solved the problem by tightening the nozzle even harder but...

I am afraid I might be overtightening the nozzle.keep in mind it is far from being as tight a when it came from the factory. I had to use a ratched and white knucles to unscrew it.

for now I correct the problem by a quick press of the trigger away from my wood piece. I also don't have that problem with thicker material.

so here are my 2 questions:

Am I supposed to tighten the nozzle really hard?

Is it possible that cleaning the gun parts with acetone/lacquer thinner has damaged the plastic sealer/o-ring? (logic would say no since they are used to prevent leaks of the same solvent and most of my finishes are lacquer or acetone based) I usually clean them by dipping them for a few second in solvent then drying them.


thanks for your help?
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Old 10-07-2019, 12:12 PM   #2
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You don’t say how old your sprayer is. You may need a new “needle” tip. Eventually, they will fail and not seat properly.
Also, make sure the needle is sliding freely; after cleaning, apply a slight bit of mineral oil to the shaft to make sure it can move properly.
You should not have to tighten down the nozzle that hard.
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Old 10-07-2019, 01:02 PM   #3
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I don't have a Fuji gun and cup. Does it have a check valve setup to pressurize the cup? If so it may be back flowing into the air chamber area around the fluid tip. I use the 3m pps system and never worry about the check valve.


I use a bottle of spray gun lube instead of vasoline or mineral oil. Always afraid of contamination with waterborne finishes. Don't need fisheyes.


Use this on my gm3600 guns as well and the slide pins on my Titan g10xl's.

https://www.amazon.com/DeVilbiss-SSL.../dp/B000I1EEXA

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Old 10-07-2019, 01:08 PM   #4
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Yeah , that sounds like a worn or bent needle. Wear item, time to replace.
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Old 10-07-2019, 02:09 PM   #5
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thanks for your answer.

My gun is about 3 to 4 month old but I am a hobbyist so I would estimate that it has been in use for maybe 24h (total hours of use during those 4 month).

I have already ruled the needle out since the leak seems to be comming from the nozzle thread and not from the needle.
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Old 10-07-2019, 02:12 PM   #6
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sayn

it is a gravity fed gun and it does have a tube with a check valve.

My tube is starting to get a bit dirty and ordered some new ones.

could that me as simple as that.

I will put a clean one as soon as my package get home
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Old 10-07-2019, 02:45 PM   #7
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Quote:
Originally Posted by bigpopo123 View Post
sayn

it is a gravity fed gun and it does have a tube with a check valve.

My tube is starting to get a bit dirty and ordered some new ones.

could that me as simple as that.

I will put a clean one as soon as my package get home
It very well could be check valve , then. You probably can disassemble check valve and soak everything in lacquer thinner and clean. Should suffice until your new valves come. I thought you were a little more experienced and already would have checked the check valve...always the first thing to check! Good luck!
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Old 10-07-2019, 04:04 PM   #8
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Thanks lightning boy I am new to hvlp so I did not think that this valves my have been the cause.

will wash tonight and report back.

hopefully will solve my problem

hope I did not make a fool of myself 😉
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Old 10-07-2019, 08:04 PM   #9
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update everyone soaked everything(of the tube) in lacquer thinner and it seamed to have solvent the problem.

I will still change for a new tube and valve but the proof of concept was made

great many thanks to everyone
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