HVLP Gun

[alexh1]

Hi,

I have had a original Accuspray turbine gun for years and the repair parts are no longer available so I have been looking at switching to a compressor based gun, it seems like they may have a bit more control especially for thicker finishes which have been a bit of a problem for me especially lately as with the Campbell post cat as I posted recently. 

So because of my difficulties, I was looking at the 3M HGP gun which is somewhat unique because it is a gravity gun that pressurizes the cup. However the problem with this unit is that it uses the older gen 1 tips and cup and I suspect they will discontinue those soon. I could easily buy a lifetime supply since I'm just an occasional user but the more I thought about it the pressurized cup should not be necessary. 

I say this because from what I can tell, a compressor based gun has more flexibility because you can adjust the pressure if you need better atomization (never used one so correct me if I'm wrong). So in that case I could go with the newer gun 3M 2.0 gun which does not have the pressurized cup. I'm not planning on spraying very thick coatings like gelcoat which is what the pressurized gun is designed for.

Also, I always spray solvent based products so the easy cleaning and mixing is attractive and I'm just and occasional user so the disposable aspect is not a big factor. My compressor is not quite up to snuff but it's a 30 gal and I never spray continuously for more than a few minutes so it should be OK.

Homestead sells Qualspray with bottom pressurized cups but I'm more accustomed to the gravity and again the easy cleanup of the 3M is attractive.

Is my thinking accurate?
Thanks

[jteneyck]

I have the Qualspray AM-6008 SmartPak, which you may have looked at.  I opted for the 3M PPS cup instead of the stock metal cup.  Both are pressurized, but with the PPS system you can spray at any angle, including upside down, w/o loss of finish flow.  That's a huge benefit and you get that benefit with any PPS, or similar bag system, whether pressurized or not.  That said, the pressurized cup system is a major advantage over an unpressurized cup.  It allows you to push higher viscosity finishes to the orifice w/o thinning than would be possible with a gravity feed cup. Your turbine unit has a non adjustable pressurized cup.  Going to a gravity feed conversion gun will necessitate using larger needle/nozzle sets to get a similar fluid flow compared to your turbine unit, or you will have to thin the finish more to reduce the viscosity if you want to use the same size N/N.  With the WB finishes I use thinning is generally a bad thing as it leads to a higher likelihood of sags and runs.  On the other end, you can turn the pressure way down when you want to reduce bounce in corners or mist on a dye etc.  

Compressor driven conversion guns do allow you to adjust the air pressure, something not possible with a fixed pressure turbine unit.  That said, 90% of the time I set it at 28 psi which gives 10 psi at the nozzle.  That's not much higher than 4 stage turbines.  I turn the air pressure down to around 20 psi when spraying SealCoat shellac, something similar to your solvent based products, and up to 35 psi when I use some really high viscosity products.  But for most every product with a viscosity of 30 - 150 seconds #4 Ford cup I set it at 28 psi.  With the lower viscosity products I'll install a 1.0 mm N/N set, 1.3 for the mid range products, and 1.5 for anything over about 100 seconds.  

With a variable pressure cup like on the Qualspray unit you can adjust the cup pressure from 2 up to about 8 psi.  For most products I set it at 5 psi, but for Sealcoat shellac I turn it down to 3 or 4 and for high viscosity products I turn it up to 6 - 7.  These pressure difference don't sound like a lot but they result in a large change in finish flow and expand the range of viscosity you can spray with each N/N set you have.  For the products I spray this feature is a greater advantage than being able to adjust the spray pressure.  

If you only spray low viscosity products you may find a gravity feed gun to meet all your needs.  But I recommend you still get the unpressurized PPS system. It will allow you to spray at any angle and clean up is much easier than with a conventional cup.  In most cases, you can avoid filtering your product before adding it to the PPS bag because the lid has a built in filter.  You can even leave finish in the bag/filter cap for days/weeks, switch to somethng else, then come back to the prior finish still in the bag. 

If you want a really, really good gravity feed gun look at the Iwata LPH400.  

Good luck with whatever you decide on.  

John

[jteneyck]

I forgot to mention a major benefit of conversion spray guns is the air stays cool.  Turbine guns often heat the air so much that it causes the finish to dry before it hits the work leaving a gritty feel.  That doesn't happen with a conversion gun.  The air is always cool.  On the other hand, you do need to clean the air of water and oil from compressed air and it can be a real bear depending upon where you live, what kind of compressor you have, and what products you want to spray.  I have a 60 gal oil lube compressor.  I live near Niagara Falls where it gets pretty humid in the Summer.  But with the WB and shellac products I spray I haven't had to add any special drying or filtering equipment to clean the air to the level needed for those products.  I have a stock filter regulator at the tank, another at my spray station and a cheap in-line filter at the gun inlet.  For other products and other locations, however, it can get pretty involved and expensive to clean the air to the level required.  Since you are spraying solvent based products you may need a more sophisticated setup. 

John

[Willyou]

If your compressor "is not quite up to snuff" cfm wise, you might look into a LVLP model that requires a lessor amount of cfm. I have a couple of the Sprayit brand guns sold by Home Depot, California Air, and maybe others. I don't know how the quality compares to more expensive guns but I have used it to finish a few furniture projects and I'm pleased with it. Specs say they operate at 4 to 6 cfm. My guns are side feed. They also have top feed models that work at even lower cfm. All of them appear to be same or similar to Iwata models.

[jteneyck]

If your compressor "is not quite up to snuff" cfm wise, you might look into a LVLP model that requires a lessor amount of cfm. I have a couple of the Sprayit brand guns sold by Home Depot, California Air, and maybe others. I don't know how the quality compares to more expensive guns but I have used it to finish a few furniture projects and I'm pleased with it. Specs say they operate at 4 to 6 cfm. My guns are side feed. They also have top feed models that work at even lower cfm. All of them appear to be same or similar to Iwata models.

Good point.  The Iwata LPH-400 takes a lot of air IIRC, but the Qualspray AM-6008 comes in both an HVLP and LVLP version.  The LVLP can run on less than 6 cfm I think.  

This focuses the discussion back on the compressor, which should not be the prime consideration as to what gun to buy.  The more correct approach is to first decide what products you want to spray.  From that list you choose what gun(s) best meet that need, and then you match the rest of the system to supply the amount of air required to it.  We all have to make compromises sometimes and that's OK as long as you can still meet the original objective.  

John

[alexh1]

Thanks all, I read some more from professional users and I realized the pressurized cup is big advantage. With my current gravity gun (non pressurized) the thickest I can get to go through it is about 40 secs on a Ford with 2.1 tip and even then only with very slow drying mineral oil based finishes (basically oil based paints) that flow out regardless of the poor atomization. And that's with a 4 stage turbine. The Fuji turbine system gets stellar reviews likely mostly because it has pressurized cups but I prefer not to invest in another turbine system.

John mentioned 100 secs or even higher - that's not even remotely possible with my setup.

I think the other advantage of pressured material is speed of application. In general you would not think that's important for a serious hobbyist but it can be when the material is very fast drying and from what I have been experiencing (especially in a low VOC state) sometimes there's no way around this when spraying large surfaces - it's basically impossible to maintain a wet edge if application rate is slow. Some pros complained that the 3M non pressurized gun is slow compared to other non pressurized HVLP guns so that's off my list.

And just for others that may read this, my non-pressurized gravity gun (and other non pressurized guns) do a fine job with the majority of finishes. I have shot a few gallons of oil based paint, lots of nitro lacquer and some precat finish. It's just certain "difficult" finishes that may require pressure and even then often my difficulties are because many finishes in my state are 275 VOC and sometimes the distributor can't get the appropriate reducers.

Again thanks for all of the detailed responses, definitely will consider the guns mentioned as I'm really tired of struggling with some finishes.

[Cabinet Monkey]

The better 5 stage turbines from Apollo, Fuji, Graco are variable speed and are capable of spraying just about anything you can throw at them. Titan has a six stage.  Their guns are all solid but Apollo’s 7700 is the cream of the crop for many.  You can mix and match gun/turbines if you like.  

3M’s PPS system can be use with just about any set up.  Pressurized cup is def. the way to go unless all you shoot is clearcoat. The legacy 1.0 system should be supported for a long time with liners, so little worry there.  Biggest advantage is cleaning and reduced use of the amount of solvent required. 

Curious why you “prefer” not to invest in another turbine , but you are willing to invest in an all new compressor , lines, driers, ect……?

If you’re concerned about speed of application , you’d best start looking at “big” compressors and their cost.  Even a lvlp gun that uses 6cfm isn’t going to run on a compressor from the box stores. Some of the guns will devour 10+ cfm.  Do a quick search of compressors with that capability and let us know what you find/think.

[CEPenworks]

I run the LVLP gravity fed Qualspray with a 2HP craftsman hotdog compressor. I got a larger 2.something nozzle and spray things over 100 sec. It doesn't sound like you are doing large things where you are going to have the trigger pulled for minutes. I have never run out of air with my setup.

[fixtureman]

I know you don't want to hear this but we use the cheap Harbor freight gun.  It is one of their Gems.

[jteneyck]

I know you don't want to hear this but we use the cheap Harbor freight gun.  It is one of their Gems.

The cheap HF purple gun works great for spraying low viscosity products, both waterborne and solvent.  They are so cheap that you can justify replacing them when the seals fail in a couple of years of regular use.  And here's more reason to try one - you can convert any gun to a pressure cup cup.  Just buy the correct adapter and mount a pressurized 3M PPS cup on it and a regulator to pressurize it.  Suddenly, that cheap HF gun has amazing versatility.  

John