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Old 07-26-2011, 07:07 AM
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HVLP pressure drop at gun?

I have a HVLP Devilbiss Tekna with 7E7 tip and the pressure drop at the gun is about 45 psi down to 16 psi when the trigger is pulled. The manufacturer setting is 16-22 psi with the trigger pulled or I assumed that means with trigger pulled.

"AIR SUPPLY SETUP"
13.4 cfm @ 40 PSI compressor
25 feet of 1" pipe
DEVHAR 602 FILTER (3/8" oulet)
3/8" AIR REGULATOR
1/2" AIR HOSE
"NO" quick connect fittings in the line


I am just wondering if this much pressure drop is close to what everyone is getting or acceptable range?

Thanks

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Old 07-26-2011, 01:37 PM
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That seems a bit much to me.
The longer your air hose and the type of fittings all play a part.
I use the larger air fittings and get about a 5 psi drop on a 25' hose.
with the regular 1/4" fittings it was more like 15 psi.
If you have no quick disconnects, I don't see why yours is that low.
something is restricting flow, and it's not the hose of that size.
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Old 07-26-2011, 01:53 PM
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And that pressure drop is at the gun or at the regulator?
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Old 07-27-2011, 06:44 AM
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I attached the gun directly to the regulator and the end of the 1/2" hose for comparison and only got 1-2 psi difference on trigger pull. To get 18 psi at trigger pull I am running static or line pressure at 39 psi. Oh well seemed to paint OK. I figure with that much difference in pressure I'm probably increasing the velocity of the air at the tip which I think would cause more over spray.
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Old 08-23-2011, 02:13 PM
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I think the pressure drop is because the tank outlet is only 3/8" even though the compressor rating 13 cfm @ 40 psi. Although all the piping is 1" and supply hose is 1/2". I can change the tank outlet to a bigger outlet if need be. I bet most hvlp users tank outlets are at least 1/2" or larger.
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Old 08-24-2011, 08:28 AM
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How long is the air hose? Are you using pvc pipe. 25ft seems a lot of one inch pipe. i use about fifteen 15 galvanized 1/4" pipe with 25 feet of hose and i still get a little pressure drop with a 5hp 80 gal compressor. Oh and yes you are always supposed to adjust your pressure at the regulator while pulling the trigger.
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Old 08-24-2011, 09:04 AM
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The 1/2" air hose is 50 feet. I checked the pressure drop at the regulator and at the end of the 1/2" hose and it was only 2-3 psi.
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Old 08-24-2011, 01:53 PM
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Your deadhead pressure will always be higher than with the orifice open. If you adjust your regulator to 100PSI with the trigger closed, you'll see another big drop. Adjust your regulator with the trigger on the gun pulled.
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Old 08-24-2011, 02:02 PM
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I know static pressure is going to be higher. The original question being how much pressure drop are most hvlp paint guns getting between air flow and static at the gun or trigger pulled and not pulled? I'm getting about 20 psi drop. I have to set the gun @ 39 psi static pressure to get +- 18 psi @ flow with the trigger pulled. I would assume the more pressure drop the worse performance from the paint gun.

Last edited by bigriver; 08-24-2011 at 02:10 PM.
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Old 08-24-2011, 02:23 PM
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I understand what you're saying but have never tried adjusting the pressure for my gun that way, I always adjust it with the trigger pulled...just not to the point of spraying paint while adjusting it.
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Old 08-24-2011, 02:29 PM
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I adjust it with the trigger pulled also. But when I release the trigger the pressure goes from 18 psi @ flow to 39 psi static. Do you have pressure gauge at the gun? If so what pressure difference do you get?
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Old 08-24-2011, 02:46 PM
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I don't have a gauge at the gun and my 3000RP digital doesn't read the pressure until the air flows. Sorry, I'm no help on this one.
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Old 08-24-2011, 02:54 PM
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From what I could find most hvlp setups don't experience that much pressure drop at the gun. Needless the to say the gun performed very well with the sealer and base coat. Clear coat was a different story.
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