Pressure Pot Settings

Less expensive pressure pots sometimes need a little creative tweaking when it comes to getting the pressure into a practical range. July 3, 2008

Question
Iím going to try and make this short and sweet. Iím using a Devilbiss CVI pressure gun with 1.0 and 1.4mm tips with an imported pressure pot. Iím spraying pigmented lacquer 29sec Ford #4

The first time I used my pressure gun I ended up with horrible, well not great, results. I ended up with orange peel and sagging from applying it too thick. It seemed no matter what I did, I couldnít get the finish to atomize correctly. It seemed that too much material would flow due to the pressure in the pot, and the aircap couldnít keep up. The pressure pot has a gauge that reads to 120psi. I had it set around 5 psi (manual said 25psi, but it came out like a fire hose) and was having difficulty fine tuning the pressure in the pot.
My thought is that the regulator will not allow me to set the tank pressure low enough to get the proper flow.

What sort of pressure should the pot be set to? Do I need a better pot, better regulator? Maybe I just need some good setup info?

Forum Responses
(Finishing Forum)
From contributor C:
Does the gun stop spraying when you release the trigger? Iím just trying to determine if it's the gun or the pot thatís the cause.



From the original questioner:
Yes, the gun stops spraying. $300 gun, $60 10L pot, my guess is itís the pot, or more appropriately, the regulator as it doesnít seem to allow precise control at low pressure. I wanted to ask for help here before I went and shelled out cash for a good pot in case I was just doing something wrong.


From contributor C:
Normally when Iím using a pot it's set between 5 to 10 lbs for 22 second zahn for 29 sec ford. You may have to set it a bit higher. That said I would do this first to determine for sure if it's the pressure regulator. Have the pressure totally off (no pressure in the pot) and in 1/4 turn increments of the handle spray and see what the results are. If after a full turn youíre getting flood coats and no atomization itís most likely the regulator is messed up. Atomization should be at 40 lbs and fan at 6-8" at 10" away from surface.


From contributor J:
I have sprayed with a low cost 2 1/2 gal pot for years. I spray MLC resistant thinned 7-8 oz of std thinner per qt. Contributor C is right on for the pressure settings. I set the pot at 9 -10 psi for pigmented CV, and 5 or so for clear. When the gun is triggered with no air, you should shoot an arc that lands on the floor 3' in front of you. Experience will tell you what this should look like.

My regulator is located on the wall with a short length of hose going to the pot. This keeps the vapors from making the regulator sticky. My regulator has a tendency to creep up in pressure, I think because of a low quality regulator.
You really need a regulator (and gages) designed for regulating small pressures. Plus or minus 2psi doesn't cut it. Fluid hose length will affect the pressure required as well. My hose is a 3/8 x 25'. Iím not sure, but your tip size sound a little small. You may try a 1.7 or 1.9.



From contributor J:
Another thought. 29 sec for # 4 sounds a little thick. You may try thinning a little more. I believe MLC recommends 22-25 sec.


From contributor W:
We used to use the 2qt pot setup from harbor freight and just throw away the cheap gun. They have recently switched the design of the pressure pot which basically makes it unusable as you describe. I just bought a great 2qt pot for $80 from Finish Systems.

From contributor S:
29 sec. in a ford #4 with a 1.0 or a 1.4 tip is way too thick. You would have to really crank up pot pressure to get it out of the gun and the finish results would be less than desirable. I would rather be around 18-20 sec. with a 1.4 tip setup and 5lbs on pot and 35-40 on the air/gun side.