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Old 05-24-2009, 06:29 PM
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Getting more preasure to my paint gun

Hi,

Sorry if this is the wrong section; I'm not sure if this is a tool question or a body section (since it's a tool, but a body specific tool I'm asking about).

K, so I sprayed my epoxy, high build, and sealer, and now i got to the base coat. I've been having run problems all along, but have chalked it up to inexperience.

Now my base looks bad - I have orange peel AND runs. I've read that orange peel control is fluid adjustment, and run control is pressure adjustment over at the SPI site (more pressure = less runs if I read correctly).

If I dial back the fluid to get rid of my runs, I get orange peel. If I get rid of the peel it runs.

I can only get 15 PSI at the gun during a full trigger pull. It starts plenty high, like 90 PSI on my at-the-gun regulator, but drops like mad with the trigger open, and settles around 15. The compressor tank is at 120.

I have, starting at the tank, a ball valve to shut off the air, a regulator with gauge, a desiccant dryer, and then a female coupler. The 3/8" hose has a male coupler. At the other end of the hose is a high-flow female. The gun has a high flow male, a regulator/pressure gauge, one of those pumpkin 'last chance' water/oil filters, and then the gun itself.

Does anything stand out? Where would you start looking to get more preasure at your gun?

And I'm clearing over this - when I sanded my black primer, it turned grey, but got nice and black and glossy when I put some W&G remover on it. Will the base be the same - go grey when I sand, but blacken up when I get the clear on?


Thanks for any advice!

Oh, it's a 3.5 HP 60 gallon compressor, and a Shapre Finex FX300 HVLP in case that helps.

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Old 05-24-2009, 07:15 PM
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15 psi before or after the last chance filter?

You mean compressor tank will maintain indefinitly 120 psi when the gun is at 15 psi?

some trash in the line can cause high dP.

I guess you gun is about 11 cfm at 30 psi wide open and your compressor will provde the same?

Why don't you plug your hose straight from the compressor to the gun to test for pressure drop problems.

I don't bother with the last chance filters...how do you know when dessicant is saturated in those...you must cahnge frequently if you have wet air. Spray concrete floor with an air gun attached and see how much water is coming out.

Maybe your other dessicant filter is saturated?

If your compressor is working to hard it will produce so much water that small desicant filters don't have a chance.


To minimize orange peel all conditions must be right...ambient temp and humidity must match paint specs. The gun nozzle size must be in the ball park of paint data sheet. For example, if you are spraying thick primer through a small 1.3 nozzle the you can't get the widest wide spray pattern to lay down slick. Do you have any old paint or maybe buy some cheap general purpose enamel and thinner and practice spraying different viscosities till you get your system tuned in. If your nozzle is smaller than paint spec then reduce your fan width to compensate. If nozzle is too big you can choke down the fluid needle to an extent...too much causes performance problems.

The first gun setting I would try is: fan wide open, pressure set to gun/paint spec, roughly correct nozzle size, fluid needle wide open, gun distance per instructions. I would spray 2' wide patterns on scrap sheet metal to get a feel for how fast you have to move the gun.

Last edited by 001mustang; 05-24-2009 at 07:49 PM.
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Old 05-25-2009, 05:28 AM
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Do you have a reulator at the gun? You must remember that for every foot of hose you have you will lose 2 lbs of pressure per foot. So if you have a 50ft hose you can lose 10 lbs of pressure at the gun. I have a regulator at my gun so when I pull the trigger I can regulate exactly what pressure is coming out. That way you can keep the pressure at the outlet on the wall at 120 and regulate down to the 40-45 lbs or whatever the pressure needs to be for what you are shooting.
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Old 05-25-2009, 06:08 PM
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Look for HVLP-specific airline fittings too. They have twice the bore diameter and will NOT be a restriction.

Russ
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