Troubleshooting Air-Assisted Airless Performance

      A finisher isn't sure whether he's shopping for a new gun or trying to fix the one he has. Either way, he gets some advice in this thread. October 19, 2013

My Cat AAA has been collecting finish on the pump rod since Iíve owned it and rebuilding it hasn't seemed to improve things. I'm exploring other options to replace it and would appreciate any advice. Are there any drawbacks to going with a higher ratio pump? We mostly spray cv but plan on spraying some 2k poly when we get a new spray booth. Iím not planning on spraying any wb in the near future. Does anyone have any experience with Graco or Binks pumps? Are the parts expensive? I'm looking at a couple of used units without any guns. I understand that any gun will generally work with any pump, so which gun is the best? My Bobcat gun has been problematic at best (although I like its size). Is there any problem with buying used (aside from the normal risks)?

Forum Responses
(Finishing Forum)
From contributor J:
I have used a Graco and it did not even come close to a Kremlin. I wouldn't pay much for a used Graco, maybe 25% of new?

From contributor H:
Here is what may be your problem with 14-1. They have a set of packings that is designed for cv's. One time I switched and I had no problem. It is a packing stack rather than the biscuit shaped that you are probably using. Once I switched I had no problems at all. I think all the AA guns are real close. You can re-build almost any of them for about 300 dollars or less. The only reason I would get a higher pressure pump would be if I am using about 70 percent or more of the pumpís capacity. For example a 10-1 if I needed 700psi all the time or if higher I would upgrade. Even with all the thick water based products a 20-1 is about all you need and that gives you a lot of room to spare.

From the original questioner:
About the packings - I seem to be getting bubbling (micro and other) in all of my cv finishes. Magnamax sprays perfectly and dries the same. Most of my cv's spray fine but bubbles develop within 10-20 seconds and dry without melting back into the finish. The only way to counteract this is to get lucky or spray a really heavy coat (5-7 mils, beyond the manufacturer's recommendations). I've experimented with just about every combination of thinner and retarder and cannot get the results I get with lacquer. Iíve even sprayed the same finish from my cup gun to confirm the equipment and not the finish. Do you think different packings will get rid of these problems?

From contributor S:
If you get the bubbles with different equipment your viscosity is too thick or even a possibility that too much airflow is skinning the top before gasses escape.

From the original questioner:
Contributor S - I had another conversation with Cat yesterday and removed the micro-screen (at the tip) as it was revealed that they haven't tested it with the finish I was spraying and it could be shearing the finish with bubbles resulting. I did and the cv laid did very well with no issues to report.

I switched to the mirco-screens a while back because I was getting a lot of clogged tips and seemed to be constantly shooting small streams (partially clogged tip), all of which ruined that particular coat. The micro-screens did away with all of that but might have introduced a new wrinkle in to my finishing troubles. I'm set to test this with stealth (terrible bubbles) later in the week.

From contributor S:
I've sprayed a lot of finish through one of those cat pumps with a Cougar gun. They are good little pumps. What tip number or orifice size are you running? If youíre running a siphon screen and the inline filter on your gun you shouldnít get any junk coming through the lines and clogging your tips. This could very well be part of the equation but I'm still thinking it's orifice size, viscosity, or airflow related.

From the original questioner:
I usually run a 411 tip and occasionally run a 513 if I want to leave a little more per pass. Iím using their hopper with a screen for from a paint straining funnel (created my own since the hopper didn't come with one). The only other filter (aside from the micro-screen) is at the base of the gun. Fluid is typically 27-30 with the trigger pulled and air varies but is usually 10-15 with the trigger pulled. The lines are pretty new (eight months old) but Iíve had problems with clogged tips from the beginning. My whole set up is almost three years old and I probably average 1-5 gallons a week.

From contributor M:
Your pump pressure seems a little low. At 30lbs and a 14:1 ration youíre only getting 420lbs of fluid pressure. Try upping your fluid pressure to about 40lbs (560lbs of fluid).

From contributor Y:
I have a Cat AAA/Bobcat pump and a Graco Merkur sitting side by side. If I could I would put another Merkur in its place. Nothing wrong with the Cat but it is so much noisier and the unit just isn't as nice as the Merkur. Previously I had an Asturo pump that I had a similar problem with on the pump rod. In that case it ended up being that when I originally purchased the unit, which was possibly the first k20 unit to arrive in the country. It had one of the seal springs wrapped around the pump and I kept going through seals way too quick. Eventually I came to the conclusion the wire spring had scratched the pump rod causing the seals to fail. I replaced that and the seal problem went away.

From the original questioner:
Contributor Y - did you have any bubbling (micro or other) problems with the Asturo before it was fixed? I primarily spray MLC Envirovar cv and stealth for pigmented jobs. The bubbling still exists in the Envirovar since I removed the micro-mesh in the tip but to a much lesser extent. Yesterday I increased the air and might have eliminated it (keeping my fingers crossed - I just sprayed some small samples).

The stealth however is a completely different story. I get bubbles immediately with the Stealth with a 513 tip running 35-38 fluid and 15 air. These are good size and all over the panel (approximately 1/8" apart so basically everywhere). If I spray a real heavy coat (5-6 mils) most go away, but the finish lays down after a few minutes and the end result is semi-perfect or perfect enough for most home owners. The stealth just doesn't have all of the bubbles in it when I apply it with a cup gun and seems to lay out a little better. Does this relate to your Asturo experience? The bubbles are very frustrating and seem to be caused by the cat pump and setup.

From contributor G:
I have a Kremlin 10:14 and have the same problem with micro-bubbles. I have been told that the new EOS pump solves this problem but don't want to spend the money just now as the 10:14 has very few miles on it. I spoke with a rep from MLC and he recommended 30 lbs on the fluid side and 15-18 on the air side. It does result in more over-spray but my first trial with Klearvar resulted in no micro-bubbles. I need to do more testing but you might try those settings to see if they help.

From the original questioner:
Contributor G - we might be speaking with the same MLC rep as Iíve heard the 30lbs on the fluid side and have been working from that with the Envirovar. I might have solved the bubbles in Envirovar with setting the air at 15-18 like you said. Most over-spray but I can live with that. As for the Stealth, the bubbles leave an okay finish but I'm still looking for answers. Does a higher ratio pump cause micro-bubbles like starter pumps do? The Graco I originally asked about is a 23:1.

From contributor G:
The way I understand it it's not just the ratio but the way the pump operates? At least that is what I was told in regards to the EOS pump. When I cycle the material through while priming the pump I find I get froth on the top of the container even though I am aiming the stream at the side of the container at a high angle with low pressure. I would like to see a Kremlin rep spray Resistant or some of the other materials prone to micro bubbles with the EOS. As I said at this point I just want to get some more mileage out of the pump I have. It does sound like we are talking to the same rep or at least getting the same advice.

From contributor Y:
Personally I never sprayed Stealth with my Asturo. I did spray Magnamax, Resistant, Krystal, as well as Aqualente. The micro-bubbles are a product of the AAA and the way the pump operates. Going to a Kremlin won't solve it except possibly with the new one as mentioned. I think the Merkur might be better based on just seat of the pants experience but I only have been using that pump for WB finishes and the CAT for solvent. I usually have my fluids set at 40-50 and the air at 15-20 depending on the thickness of the coating I am pushing through it. Primers may take as much as 55-60 fluid to pump.

I think the pumps are universally pretty good. I know the CAT is darn loud compared to the Asturo pump we used to have. I also know that the Merkur is whisper quiet and as a unit I like the pump and the gun better than the pumps and guns on the other two units. Kremlin has great pumps and guns too. I was set to buy an EOS but the rep blew me off so I went to my local paint store and he recommended the Graco (since he sold them). It was priced at $1,600 which was considerably less than an EOS so I took him up on the 15 day test drive and liked it so much it will stay here for as long as we are spraying.

From the original questioner:
Contributor Y - interesting that you stated that AAA's cause micro-bubbles. Iíve read just about everything in the Knowledge Base and have never come across a statement like this. I know cat makes a 1/2" suction tube and inlet to counteract the bubbling in WB products and I have this, but their hopper only works with the 3/8" tubing and inlet so that's what I have on there now. I haven't sprayed WB through it so no experience there, but I thought solvent products we unaffected. Based on your statement above - are you getting micro-bubbles in all of your finish work? How are you combating it? Like I said initially, our finish work is 95% perfect but the 5% of defects is driving me crazy.

From contributor Y:
Maybe we should define what the term micr- bubbles is as it may mean different things to different people. From your posts it seems that you spray the coating and in one way or the other you are getting some dissolved gas in the coating that doesn't flash off before the finish skins over. Is this correct? If so, is this happening on some woods more than others? Have you had the same results on MDF? Have you tried shooting your finish on a plate of glass to isolate whether this is a problem in the coating vs. the object you are spraying? That is where I would start if I were you.

First get a few pieces of glass and set up the AAA as well as a cup gun with the same product pulled from the same container as the AAA at the same time. Then spray each piece of glass, one with the AAA and one with the cup gun. If you have micro-bubbles in the AAA glass but none in the glass you know the source and you can get your coatings rep and the AAA manufacturer involved. The term you may look for in regards to the AAA I am referring to is MicroShear. I have never had a problem with this but have heard others have. Maybe I am lucky. If you have no bubbles in either then do the same test with two pieces of wood and see if you get problems with the AAA that are not there with the cup gun.

If that happens then I would look in adding a reducing or retarding product to the finish and see if the extra open time allows the bubbles to flash off. Whether it is air trapped under the coating or air that is evacuating the pores as you cover them with the liquid coating, they just need to be given time to go their own way.

So, in an effort to not get too long winded let's start there and let me know more precisely what you are running into and what the results are and we can dig deeper into it as more information is available.

By the way, I am no professionally trained chemist or engineer so I am not sure I have the technical skill set to diagnose all problems through a computer monitor. I can only help to the extent that I have gone through a similar experience in real life situations. Temp, humidity, air movement and other things can have an effect on how things apply and cure on any given product.

From the original questioner:
Thanks for your detailed reply Contributor Y. I increased my air and fluid today to spray some Clawlock2 and had great results. I haven't sprayed much of this stuff but it came out of the gun great and laid down without any bubbles/etc. The dried product is as good as it gets for primer. Air - 15, fluid - 40-45, and tip 513. For Stealth I've already experimented with my AAA verses a cup gun and with the cup gun I didn't get any instant bubbling. I don't really remember any appearing as it dried. I have some more to spray tomorrow and/or Tuesday and will see what type of results I get when increasing the fluid and air some more. Last time I'd left my fluid alone (per the advice of the MLC rep) and only tinkered with thinning and air). I still had bubbles appear instantly, but like before most did not mess up the final feel of the finish. I'm semi-suspecting an issue with my pump.

From contributor Y:
Before you conclude it is the pump also look into your technique. How close is the gun to the wood, and how many wet mils are you applying? Is it happening on all coats or just the first coat? Try moving the gun two inches farther than you are now and speed up the passes for a thinner coat.

From the original questioner:
An update: I've found a little bit of success by upping the air pressure to 20lbs plus for stealth (fluid now set around 40). Upping the air also helped with Envirovar. This seemed to get rid of the immediately appearing bubbles and has led to a nicer finished surface. The only drawback of course is now my transfer efficiency is lower and Iím getting over-spray on par with my HVLP cup gun. I spoke with the Kremlin rep for our area last week and he suggested a new gun. He thought the Cat pumps are okay but doesn't think much of the gun.

From contributor D:
To the original questioner: How did the Kremlin gun compare, and was there a quality difference? I am looking to buy an AAA. The quietness of the Merkur sounds good but so does the Kremlin? I need a demo and don't want to settle for less quality. Is there a consensus?

From the original questioner:
I like the Kremlin Excite gun just a little better than the Bobcat gun. The finish just seems to lay down a little bit better and for that I now have an Excite gun on a Cat pump. However, all of that could be changing as I just picked up a Graco 20:1 pump, Kremlin 10:14, and two Kremlin 17a2's earlier in the week at an auction. They all need a thorough cleaning and the Graco and 10:14 will need fluid re-builds. I'm excited to be able to try out some new equipment.

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