[Quickstep]

I'm trying to get into spraying finishes and could use some guidance on getting the gun set up.

I think I mostly need to learn about determining how much pressure to use and adjusting the fluid control.


I've got a Devilbiss Plus HVLP conversion gun.
I'm shooting KTM Waterterborne lacquer that goes 12 seconds in a ford cup
I'm using a 1.4 tip per KTM's recommendation, but also have 1.2 1.3 1.6 and 1.8

The manufacturer recommends 25-30 Psi inlet pressure

I really don't know where to set the fluid control and shooting at 25 PSI seems high.

I'm hoping there's some science behind this.

If anyone is willing to exchange a few posts about setting up the gun, I'd appreciate it a lot.

 

[Rick Mosher]

Is this a gravity fed cup gun? It does make a difference as far as the settings go. On any HVLP gun CFM are much more important than air pressure. You need an air line with a larger ID than for a conventional gun. Also a small compressor won't keep up with an HVLP gun.

There should be 2 controls on your gun, one controls the fluid and the other controls the size of the fan. I prefer to spray with my fluid all the way open and I feather by hand, meaning I control the fluid by how far I pull the trigger. The fan should be pretty much as wide as it gets also unless you are spraying stain or shading.

To control fluid in an HVLP viscosity is the most important thing. If you get that right everything falls into place pretty well. With WB coatings adding water is usually the kiss of death. There is usually about as much water in there already as is possible. If you have trouble spraying right out of the can go to the next bigger size fluid nozzle until it works right. Also you don't spray as wet of a coat with WB coatings. Get some scrap and experiment until the finish looks good. (Don't watch the WB dry, it does really weird stuff as its drying, just check it after it has fully dried.)

 

[WillemJM]

With WB and the viscosity you mention, I would try the 1.2 tip for better atomization. If you get by with that without a sandy finish it will be the best, otherwise try the 1.3. With a 1.4 you may find it difficult to get a flowing wet coat without sags.

25 to 35 psi sounds right, important though that this is not set at the compressor. The pressure needs to be set so that you get your 30psi right at the gun air inlet, with trigger fully pulled at the spreader and volume setting you have on the gun.

 

[Quickstep]

Thanks, guys.

Yes, it is a gravity gun. I've read about guys opening the fluid all the way and feathering by touch, but I don't think I'm nearly that good. That's why I'm mostly looking for guidance on where to set that fluid control. I'm spraying a banjo resonator, so if I open the fan control all the way, I'll do the whole thing in one pass. That's good, I guess, but not what I imagined.

So, if I'm not opening the fluid control all the way, how many turns should I open it to start out? Remember..... I don't know what I'm doing!

 

[Rick Mosher]

Start with one turn and spray a sample. If that is not enough keep adding one turn at a time until it works.