Setting HVLP Spray Gun Pressure

[zepher11]

I have updated my $9.99 HF HVLP gun that I have used for the past 15 years with great results to a lower end DeVilbiss paint gun.

I have always used a regulator and adjusted the air pressure to about 30lbs, That is static pressure...with the trigger not pulled. It was an HF inline at gun regulator.

Well, the DeVilbiss gun came with a new at gun air regulator. When I went to set the pressure, It was always at 90lbs, which is what my regulator at the compressor is set at. When I pulled the trigger it would drop down to say 5lbs, or 15lbs, or wherever I adjusted it when the trigger was pulled. Yet the gauge would always go back to 90lbs when I released the trigger. Even if I screw it all the way down and no air came out when the trigger is pulled, the gauge would go back to 90lbs.

Hmmm...got me to thinking. I went back to my old gun which was set at about 30lbs and pulled the trigger...dropped the air pressure down below 10lbs. I have always painted like that. However, I have recalled turning the pressure up while painting before.

Now I'm thinking that I should pull the trigger on the gun and set the air pressure at 25lbs to 30lbs while spraying. So, long story short, should one set the air pressure at say 25lbs to 30lbs while the trigger is pulled and spraying, or between these settings before pulling the trigger? There is a very noticeable difference in pressure in the two circumstances.

Almost embarrassed to ask, but couldn't find an answer searching. Any insight is appreciated from those that paint and/or know what they are doing on how to set the air pressure on an HVLP gun or what the air pressure general should be. The instructions say not to exceed 30lbs air pressure.

 

[dnschmidt]

That is not a regulator it's a cheater valve. It works but you always adjust air pressure with the trigger pulled and in this case you should adjust it to 29 PSIG with the trigger pulled as that's a common starting point. You can go up or down from there but normally that will get you in the ballpark. A true diaphragm regulator maintains a constant pressure but not a simple valve which is all your using.

 

[zepher11]

That is not a regulator it's a cheater valve. It works but you always adjust air pressure with the trigger pulled and in this case you should adjust it to 29 PSIG with the trigger pulled as that's a common starting point. You can go up or down from there but normally that will get you in the ballpark. A true diaphragm regulator maintains a constant pressure but not a simple valve which is all your using.

Thank you. I didn't realize before it was to be set with the trigger pulled. Yeah, they aren't high dollar cheater valves/regulators. I ended up setting it at 18lbs and I adjusted the volume and patter and seemed to be good to go.

However, when I went to paint my fenders the first pass was good and then the second pass had very little splatter of paint on the fender. Couldn't figure it out for a bit until I realized the little hole in the plastic lid was already plugged with paint. These DeVilbiss lids are a lot cheaper than the HF lids which are pretty nice. Never had the HF one plug up before in 15 years. I'll have to watch that...at least I know now to keep a nail with me while I paint.

Anyway, I went out early to paint, but by the time I sprayed it was likely 100 degrees. The rear fenders turned out pretty decent. The front fenders, which was my third attempt due to the tiger stripping I was getting, still had minor tiger stripping. I ended up with three coats trying to blend it. Anyway, I'm calling it good as I'm done sanding these things. They will be what they are:

 

[plout99]

Like dnschmidt posted set the pressure with the trigger pulled, go by what the tech sheet for your paint says most hvlp guns should not be over 35 psi max. I used to set regulator at the compressor at 100 psi then use the regulator on the gun to drop the pressure. Watched a video from Sata the spray gun company they were setting the compressor regulator around 40 psi then fine tuning with the regulator on the gun. I started doing that and ended up with a little better atomization. You can also buy an air cap gauge that will give you the exact pressure the paint is coming out the gun so it can be tuned better.

 

[RV8guy]

I set my spray gun (Devilbiss TEKNA) to around 23psi with the needle adjustment turned 2.5 turns out. I never get a bad finish out of that gun.

 

[zepher11]

Like dnschmidt posted set the pressure with the trigger pulled, go by what the tech sheet for your paint says most hvlp guns should not be over 35 psi max. I used to set regulator at the compressor at 100 psi then use the regulator on the gun to drop the pressure. Watched a video from Sata the spray gun company they were setting the compressor regulator around 40 psi then fine tuning with the regulator on the gun. I started doing that and ended up with a little better atomization. You can also buy an air cap gauge that will give you the exact pressure the paint is coming out the gun so it can be tuned better.

I set my spray gun (Devilbiss TEKNA) to around 23psi with the needle adjustment turned 2.5 turns out. I never get a bad finish out of that gun.

The instructions just say not to exceed 30psi. I finally found another source for Xylene which I haven't been able to get for about two years now. I may need to thin the paint a little more. I think if I get a little practice with these new guns, I will get the hang of it. I have to prime and paint the entire body here within the next week, so I hope I get it down by then...

Appreciate the feed back!

 

[zepher11]

That is not a regulator it's a cheater valve. It works but you always adjust air pressure with the trigger pulled and in this case you should adjust it to 29 PSIG with the trigger pulled as that's a common starting point. You can go up or down from there but normally that will get you in the ballpark. A true diaphragm regulator maintains a constant pressure but not a simple valve which is all your using.

Thank you again. I set my primer gun at 29psi and shot my whole command car body last evening. Wow! Other than the cloud of overspray I haven't had for years, the primer went on extremely nice and coverage was excellent. Not one run in the primer at all either inside or on the outside of the body. What a bonehead I have been...

 

[ZRX61]

Pretty sure my Devilbiss HVLP guns run at about 10psi.

 

[gungatim]

These are the instructions I use with the HF gun and they have worked well for me.

about half way down: Setting up and spraying with the Harbor Freight HVLP gun #38308 and the 43430

http://purplesagetradingpost.com/sumner/techinfo/HVLPspraygun.html

 

[zepher11]

Pretty sure my Devilbiss HVLP guns run at about 10psi.

For the primer gun 29psi worked great. May have been able to dial it down a bit, but the result was better than I have had in a long time.

I'll have to practice with the finish gun and see what psi it likes before I shoot the OD.

 

[zepher11]

These are the instructions I use with the HF gun and they have worked well for me.

about half way down: Setting up and spraying with the Harbor Freight HVLP gun #38308 and the 43430

http://purplesagetradingpost.com/sumner/techinfo/HVLPspraygun.html

Thank you for the instructions! Very informative.

 

[ZRX61]

For the primer gun 29psi worked great. May have been able to dial it down a bit, but the result was better than I have had in a long time.

I'll have to practice with the finish gun and see what psi it likes before I shoot the OD.

I set mine by pulling the trigger to only feed the air without pulling it far enough to start feeding paint.

But I do run my primer cannon at higher psi.

 

[zepher11]

I set mine by pulling the trigger to only feed the air without pulling it far enough to start feeding paint.

But I do run my primer cannon at higher psi.

I have mixed a lot of primer and OD the past month, and I have noticed that the OD is a lot thinner than the red oxide primer I use. Highly likely that the finish gun may need to be set lower. I'll play with it quite a bit before I shoot the body of my cc to make sure I'm good to go.