Setting up your gun

rex

New member
This has been asked lately so it's time for a how to,anyone feel free to add on.

Your most important isuue is air supply.Not only do you need a compressor to keep a constant psi but volume is just as important,especially with HVLPs.The days of 1/4" airline and fittings are pretty much gone,you need the volume that 3/8 line and fittings supply to atomize these hi-solid voc compliant clears properly.You can work around it but it's work and aggrevation you don't need and can cause problems like solvent popping and dieback from hosing it on thicker to achieve flow-and we're not getting into temp reducers or mixing.Also,at-the-gun regulators can throw a kink in your airflow by necking down your 3/8 line to 1/4 negating the extra money spent on the larger hose and fittings.If you run a regulator like I prefer to do buy a good one with large holes and run it wide open,adjusting the pressure at the wall regulator.This way you have full volume working for you but if you need to back down for any tight areas like some of these #@*&$^ bumpers you're not feathering the trigger with full pressure blowing puddles in the clear as you try to layer it up wet.If you don't want a regulator you can do the waterhose trick in these instances,fold it in half and squeeze.I don't do it because it breaks down the inner core prematurely.Speaking of that,getting odd sized black chunks in your paint and the hose is a few years old?That's a good posibility.

To set up your gun takes a few minutes but saves a ton of grief.HVLPs benefit from the use of an aircap guage to dial in the inlet pressure so you have the recommended aircap presure-usually 10psi.The prob is they're expensive so the following setup works,you just need to play more with inlet pressure.Also,don't be surprised if you excede the inlet pressure to achieve results,I've seen HVLPs take 5 or more psi inlet pressure than advertised as max to acheive that 10psi cap pressure with an aircap guage.So,the first thing to do is get a large sheet of paper,chunk of sheetmetal,anything to throw patterns on and lots of them.Now mix up 6 or so ounces of the material the gun is used for.What you're going to do is throw a pattern check on the surface (and verticle so hang the paper etc. on the wall) ,with the pattern adjustment and fluid adjustment wide open ,with a full pull of the trigger and complete release all in one motion,no run the air and then pull the fluid through-off,full trigger,off.Don't look at your pattern,look at the size of the droplets on the edge of the pattern.What you're trying to adjust is the droplet size to be the smallest possible.Initially all you want to do is play with your inlet pressure and fluid flow while basically maintaining your pattern.Once you get a small droplet and your inlet pressure is within range for the product specs and the fluid is a respectable setting you can adjust your pattern knob in a little to even out an hourglass pattern.If you really have to run in your pattern knob alot you're probably choked in too far on the fluid so come out some,don't sacrifice a wet,nice pattern for the ultimete small droplets.HVLPs are going to take a little longer for this process without an aircap guage because you'll be experimenting in unknown ranges and adjustments.For example,a Sata Jet90 might be running 10psi over max inlet with the fluid choked down to 40% and be good.

Test #2 is your wetness.Turn your aircap 1/4 turn for a horizontal pattern and with the same trigger stroke blow a pattern for 1 second with full trigger pull and release.Now watch the drips.You should get basically an even paint slide the length of the pattern.If it's faintly heavier in the middle it will fly but go back and tweak it to try to get it even from end to end.An older gun wont always adjust out but a new one should be dripping evenly end to end.

The reason you want small paint drops is coverage and flow.Think of it as trying to cover your floor with oranges or bowling balls.The oranges will cover with less coats,be thinner,and lay flatter than the bowling ballsNow,if you take this from the sealer and add in basecoat and clear you can see why at the end it'll work out nicer,using the bowling balls you're piling it on and exagerating orange peel (no pun intended) from start to finish way in excess of the smaller orange droplets.Hope this helps and feel free to add in everything I missed.
 
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tiller2nv

Guest
Thanks for the post Rex, Im going to try and get my new walcom sorted tomorrow. Ive been having some problems but this looks like it might help! Thanks again!
 

rex

New member
Thanx Scott,I figured you at least could add something in,I can't believe I didn't forget something /ubbthreads/images/graemlins/haha.gif
 
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MasterxAce

Guest
i believe for ever 50ft of 3/8" hose you lose 10 psi... or is it 5? bah cant remember... anyone? i think its 10
 
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flatscrewd

Guest
Hmmmmm. Interesting , you say air cap presure , now let me see if I get this right. That would be the air presure that is backing up in the gun, the air that is unable to escape. So the gauge that is on the gun along with the air control knob reads this "boost" presure. I say boost because I can relate this to forced induction motors. Boost presure is the amount of air the motor cant consume.
 

rex

New member
No,what an aircap guage reads is the airpressure coming out of the cap to atomise the paint coming out of the fluid tip hole.With conventional guns it's roughly the same as inlet pressure,but HVLP's step down the pressure internally.You might have 30psi going in but only 10psi or so coming out.I still don't own one other than a DeVilbiss SRI touchup gun,I think the DeVilbiss Plus is one of the better guns around.If I do buy another gun it will be an Iwata LPH 400 to replce my base gun.It's LVLP instead of HVLP and this thing is awesome.It will throw a true 12" perfectly even pattern and attomizes paint better than anything I've tried.With the large tip it might spay clear but the 1.2 or 1.3 tip can't handle high solid clears,it pulverizes it so much you have to get real close and move extremely slow to get a wet coat.Kind of rambling,I'll stop now.
 

flamethrower

New member
Hey Rex, man you type good left handed! Glad to hear you're recovering. Hey, I got a question on the airline thing.
I have a 7.5 Horsepower two stage 80 gal compressor. I feed it into 3/4" copper pipe and then after a large 3/4" pipe condenser (built by me) I run it into a DeVilbiss 500(I think) air filter/drier. It's one of the big suckers with two coalescing filters and a large desicant canister. My question is that the holes at the input and output of the coalescing filters are small compared to my overall system. I think the holes are about 1/4"-3/8". Does this mid-line bottleneck have an effect on my volume or does the larger system make up for it? Also, the air fittings I use on my guns are standard sized but the holes are also small. Does this effect it? I haven't noticed any problems yet, but was just curious about the bottlenecks in the air line.
Thanks for your help.
/ubbthreads/images/graemlins/cheers.gif
 

rex

New member
What's up man?You would't believe how long it takes me to type and work that shift key but at least I'm not writing,I can barely read it and a kindergardner writes cleaner.As long as your setup is working out for you I wouldn't worry much.You have a big compessor so I kind of wonder how badly it does affect it.In a shop there's alot of people using air but if only a gun is running you're not draining the tank.Since you still have a ton of pressure in reserve I would think it wouldn't hurt you as much as using a small compressor that's working to maintain pressure.Then there's that deal where a neckdown in the system increases pressure thru the restriction.I'm no engineer or physicist by any means so I reeally don't know how it does work for sure but I think the compressor size could make a big difference on how big a problem will be.You have a nice setup so I wouldn't wory.I would suspect the DeVilbiss setup will take the 3/8 fittings but I know the true fittings,line and couplers get expensive.Take care man and talk to you later. /ubbthreads/images/graemlins/cheers.gif
 
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