Troubleshooting HVLP Performance

      A finisher gets help and advice making his new HVLP gun deliver the finish quality he wants. June 30, 2007

I have recently started spraying with an Accuspray 19 HVLP gun, using a 2 quart pressure pot. Prior to this I used a Turbinaire for almost 10 years. I am having trouble getting a good spray finish while spraying tinted General Enduro satin finish, which I am buying from Homestead finishing. It is very hard for me to get it adjusted to leave a nice even wet coat that looks good off the gun. It usually either has orange peel or looks like it has overspray on top of the finish.

I am using about 45 psi at the gun while the trigger is pulled, and about 5psi at the pot for the pot pressure. I have tried many different settings at both ends, and I still cannot match the finish I was getting with my Turbinaire with the attached one quart can. How can I get a better and more consistent finish? I realize there is probably a learning curve switching gun styles, but I didn't think it would be this hard.

I should mention that the Enduro is a water based varnish, which is tinted to an off white paint color. I should also mention that I was spraying Ben Moore alkyd Impervo last week with the same gun, and although it wasn't as tough to dial in as the water base, it was still a lot tougher for me than it would have been if I had been using my old Turbinaire.

Forum Responses
(Finishing Forum)
From contributor K:
I use the Accuspray Model 10 conversion gun and the Max pressure at the gun is 10. Try lowering your pressure and get the gun much closer. Enduro has to lay out for a while before it settles in. I tend to seal with SealCoat just to be sure before using waterbased finishes.

I don't know what tech support is like for Enduro since General Finishes bought it, but you might try their website. Also contact Homestead as they have good support. Christy at Accuspray is very helpful.

From the original questioner:
That is interesting that you are at only 10 psi at the gun. Jeff at Homestead told me to get as much air through the gun as possible, at around 45 psi. He said that I could go even higher, but I found that any higher and the overspray is unbearable. I will try the lower pressure even though he said at lower pressure the finish may not atomize.

From contributor A:
The conversion guns need more pressure so I don't think 45 lbs is too much. You could even try 60lbs. I would try setting the fluid pressure at 8-9 lbs. I recently did a job with Enduro clear and had major crawling/orange peel issues with the second topcoat (which I've experienced before). I spoke to General Finishes and they said that old formula Enduro was not that great at flowing out. They have changed the formula and sent me a gallon for free. It worked great. Maybe you have old product?

Regarding the gun, I used Accuspray guns and pressure pots with WB and never got great results. I bought a Kremlin for the Enduro job I recently did and it was flawless!

From contributor R
Contact the Accuspray folks and find out what the air pressure should be with trigger pulled. I have a Sata/pressure pot and know of no other gun that needs as much pressure: it uses 36psi with trigger pulled. My other Sata guns use only 29psi with trigger pulled.

Also find out what the cfm requirements are. I found I had to go to larger hoses and larger disconnects to achieve the necessary cfm. It's the cfm that's going to atomize the finish, not the pressure.

I switched from an Apollo turbine to conversion hvlp about 6 years ago. I'm glad I did for a variety of reasons, but the two systems do spray differently. I found that I need to go lighter with the conversion guns. I never had trouble with orange peel using the turbine but I do with the conversions - hence the need to spray lighter coats. I also use Enduro finishes.

Oh, my pressure pot is set at between 5psi and 10psi - I try to keep it close to 7psi.

From contributor K:
I have a lot of respect for Jeff - he knows more than I ever will. Perhaps the Model 19 gun is different from the Model 10. I bought mine from Compliant Spray, the former makers of Enduro, and that is what I was told and in fact it says so on the gun: Max 10psi.

From contributor J
Max 10 psi is for the fluid, not the pressure to atomize it. What size needle are you using compared to your turbine? Are you storing the finishes in the same temperature as before? They become very viscous in cold temp, and do not flow out worth a darn.

From the original questioner:
I bought my Accuspray from Jeff Jewitt at Homestead Finishing, and he is telling me that I should have 45 psi at the gun or more, and that the pot should be about 8 psi. I just bought the Enduro last month from Jeff, and he tinted it to an off white for me, so I am assuming it is the new formula? Needle and nozzle size was selected by Jeff as well for these types of finishes. I don't remember right now what size they are.

It seems that the finish either comes out without being atomized, which I was told would happen if the pot pressure is too high, or it comes out too thin, where it looks like it is only dusting the surface. The interesting thing, though, is how much different this product sprays with the turbine set up compared to the conversion gun.

Contributor A, what is different about the Kremlin system that made the spraying better? I am unfamiliar with this sprayer.

From contributor X:
45 PSI? I use a Binks mach 1 and never go past 25 psi at 9-11CFM at the gun regulator unless I want to obliterate the coatings. The pressure burst when you pull the trigger must be some kinda scary.

You should be using a 1.4-1.8mm needle and set your fluid pressure to 5 psi. Start the gun off at 10-15 psi at the gun regulator (if you don't have one, get one) and open the needle about 1 full turn. Increase the air pressure till you have a nice fan. Test on a piece of cardboard so you can see the fan properly.

From contributor A:
Regarding the Kremlin: it's just great all around. No problem spraying thicker material, really efficient and atomizes beautifully. All the benefits of an airless and the subtleness of a HVLP. Also you don't have to mess around with pots! The finish comes out better because you're not passing a ton of air over the surface. I could keep going but I'm going to sound like a Kremlin commercial.

From contributor E:
Technically, HVLP does not really atomize. It sprays out small droplets of various sizes and needs the help of the coating to lay out and smooth itself. It will require a slower than normal drying product. Not all products are made to be sprayed out with HVLP. Stains, in my opinion, are about the only sure thing that HVLP will work on. When you start to get into clears that have some viscosity, your droplets will be bigger and you will need more dry time and the help from the coatings formulation. You have to understand what the different kinds of equipment can do and know the limitations of each.

From contributor G:
Wow, I think the responses in this thread have gone just about any and every different way.

Best plan of attack:
a) Make sure your gun (tip, needle, air cap, hoses, etc.) is set up to be able to run the coating correctly. Do this by getting your viscosity correct to tip/needle. Once you have flow, go to next step.

b) Can air cap easily atomize coating? With HVLP gun you need to confirm CFM needs to atomize. If you are running a 20cfm+ aircap - make sure you have 20cfm going to gun. (remember cfm losses here).

c) You are using HVLP gun, that means you should be using 3/8" hose, otherwise cfm losses.

If you can't figure this out on your own, work with a good equipment rep, go over issues and narrow it down.

Let's work with facts and not myths:
- Max 10psi stamped on gun - manufacturers do that do keep compliancy in reference to HVLP ratings. Most mark air caps with max ratings that will keep you in compliancy and/or max equipment performance ratings. Hence, if it is stamped 33psi and your pressures go over that pressure, you are starting to overcome the aircap design and overpowering the atomization zone (blowing it by the zone), therefore the cap is not working within its design. Solution = go to larger cfm aircap.

- Most turbines heat coating. True and not true; different for all manufacturers - they weren't designed to heat coatings but the equipment does get pretty damn hot on most I used in the past. This helps lower viscosity. You will notice that most turbines are using very small tip/needle combos as turbines aren't built for long term production work. Are you using the same tip/needle size? Did you go much larger?

On a side note: contributor J, you maybe slightly uninformed about what an HVLP gun does and how it is supposed to work. The theory behind the technology is to throw more material at lower forward velocities (slow it down to stick more). HVLP does mean High Volume Low Pressures. This is done by CFM, whereas conventional uses higher air pressures. I can get an HVLP gun to dry-spray just the same as a conventional gun, but you must be set up correctly. All production shops in the US are running HVLP air atomization spray (Binks-Dev) and pressure atomization spray (Kremlin). They have to spray high quality and high speed. There are guns out there now with new HVLP technology that are pretty damn amazing (DeVilbiss Compact, Sata, etc).

From the original questioner:
Well, I spent the rest of yesterday messing with the Accuspray, and thought I had it figured out. I turned the gun air down to 25-30 psi, and set the pot at about 5 psi, and I did see an improvement. However, there were a few doors I sprayed that the orange peel was too much, so I tried re-spraying those at the end of the day, and I had even more orange peel on the re-spray, with all the same settings.

I took out my old Turbinaire, set it up with a n/n size that was as close as I could find to my Accuspray, and sprayed the same finish on a few test pieces, and they looked great. So my Turbinaire is still giving me a far superior finish over the Accuspray. Thanks for all the input, but I don't think I am much closer to solving this yet. Jeff at Homestead is helping me out on this, and I hope we can solve it soon.

From contributor E:
I have preferences to what equipment will work best with each and every product. You may be looking for a 1 gun setup that will spray everything from stains to high solids products, or you may be a high production line that can afford various types of guns and pumps.

But let's face it, HVLP is not the most forgiving spray technology ever invented, coming from a coatings supplier. It does not atomize as well as conventional, airless or air assisted airless. I have had to change many formulas of products to get customers to be able to use HVLP. I always am looking for the practical use and what its limitations are. HVLP has more limitations than other systems, in my opinion. And this comes from an ex-coatings supplier.

From contributor S
I have the Accuspray 19c gun with a 2.5 gallon pot. I have the pressure pot set at 10psi and the regulator on the pot for the air supply to the gun set at 35-40 psi, trigger pulled on gun, 25ft hose. I use a 1.2 with great results. I primarily spray Target coatings Ultra spray lacquer and super clear poly. Is your air supply consistent?

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