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Old 04-07-2018, 05:00 PM   #1
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Default HVLP Spitting Issues

I know this might be common knowledge amongst you experienced HVLP users, but for those new to them, or not terribly familiar, here is a bit of info on what I encountered with mine recently.

I was using my FUJI 4 stage while spraying thinned down SW primer on some new “pre-primed” MDF doors. Things sprayed out beautifully on the first three doors I did. On fourth and fifth, intermittent spitting due to primer leaking out of the nozzle tip was taking place. But by the fifth, primer was trailing (not just dripping) out after any attempt to spray.

Now I’m pretty anal with my gear and break down my guns and clean them pretty well. Still, one of the most common causes of spitting is the needle packing nut being too tight causing the needle to stick and not seat into the nozzle fully. Another issue can be debris stuck to the inside of the packing nut or needle itself. Making sure those surfaces are clean, and perhaps even lightly lubricating the needle (Vaseline is acceptable) can eliminate those problems.Well, after checking and recleaning all of those areas, spitting was still occurring.

Next, I took the spring at the back of the needle and stretched it out with the idea that perhaps it had lost some of it’s tension. Still no improvement.

It finally seemed to me that the needle itself had to be the culprit - even though I have been told that isn’t typically an issue. Checked it over looking for the telltale signs of damage (think of a beaver chewing on a tree - except very faint) but nothing readily apparent there. Still, since I had another identical gun, except newer, so I decided to swap out the needle, nozzle, and tip from that into the faulty unit. Presto! Problem solved. Went back and laid out my old needle against a piece of white paper, added a bit of extra light, and broke out my magnifying glass to inspect the tip. Although no easily detectable damage was evident, there was a slight scalloping on one side of the needle, possibly causing it not to fully seat on the one side.

Anyway, ordered a new tip, nozzle, and needle to replace the damaged one and now all is well. Just thought I’d share the different steps I took to try and eliminate the problem and what finally worked. Perhaps it might help someone else dealing with this frustrating issue.
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Last edited by RH; 04-07-2018 at 05:06 PM..
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Old 04-07-2018, 09:37 PM   #2
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@RH - Thanks for that information...this problem probably goes undiagnosed most of the time. I bet my Graco #3 needle is showing some wear...did you look at the tip as well? I would think it would be prone to similar abrasive wear.
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Old 04-08-2018, 01:20 AM   #3
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The actual spray tip was fine as far as I could tell. Especially since there is no metal to metal abrasion going on. Rep told me that when the tigger is pulled and the needle retracts, it doesn’t always do so in a straight line. Conversely, when the trigger is released then the needle moves forward ever so slightly off center and so hits the inside of the nozzle which eventually can result in a slight uneven wear on one side of the needle. The other, and more common, needle damage occurs when the nozzle is removed with the needle in place. Repeatedly doing so can result in the slight “ beaver damage” appearance I mentioned in my initial post. So always remove the needle before removing the nozzle.
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Old 04-08-2018, 10:24 PM   #4
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@RH - good information, thanks - makes sense when you think about it...
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