What is advantage of spray system that comes with turbine vs. using air compressor?

[Jason Roehl]

You guessed it on transfer efficiency.

However, I believe much higher efficiencies are possible with better adjustment of the gun. For many finishes, there's no reason to go for the most atomization possible--higher atomization can result in more overspray (it's like throwing a wad of cotton vs. throwing a wad of chewed gum). Besides, the goal isn't to just put on the thinnest coat possible every time--the goal is to get as much finish on as necessary in as few coats as practical. Larger droplets can mean a heavier coat that self-levels more effectively while building a thicker film more quickly.

[Daniel Berlin]

Dan, can you explain transfer efficiency? I assume it means more finish makes it onto the surface vs. being wasted from over-spray?

I would be stunned if this compressor can't keep up with that gun, at least at the pace and volume I do :-)

If it's a campbell hausfeld VT6275, they *claim* it will do 10CFM@90PSI, which means even with the top of the line HVLP guns that use 14-15CFM@30-40PSI, and with a 60 gallon tank, you would need to hold down the trigger for about a minute straight to outrun the compressor.
That's a *really* long time in spray finishing to not let go of a trigger, so i think you'll be fine

[Daniel Berlin]

You guessed it on transfer efficiency.

However, I believe much higher efficiencies are possible with better adjustment of the gun. For many finishes, there's no reason to go for the most atomization possible--higher atomization can result in more overspray (it's like throwing a wad of cotton vs. throwing a wad of chewed gum). Besides, the goal isn't to just put on the thinnest coat possible every time--the goal is to get as much finish on as necessary in as few coats as practical. Larger droplets can mean a heavier coat that self-levels more effectively while building a thicker film more quickly.

As the study i pointed to way earlier in the thread shows, spray technique matters a lot more to transfer efficiency than fine tuning knob on the gun.

It's certainly possible to over atomize a coating (and a class of problems are caused by this), at the same time, heavier droplets are also more liable to do things like "run down the side of your piece"
The thickness of the film per coat has no relation to atomization, if we exclude overspray. What matters is the volume of fluid coming out the needle.
If I atomize 1ml of finish, whether i do it into droplets that are 5 microns or 10 microns, it's still 1ml of finish that will hit the piece, and it will generate the same film thickness when it coalesces and levels. Additionally, the speed at which it comes out of the needle is only related to fluid viscosity, so you would generate the coat in the same amount of time.
Of course, at some point the drops become so small that they dry out in air, which causes a very rough finish, etc

[Jason Roehl]

Over-atomization also leads to "bounce-back"--that is, the spray is less likely to make it to the piece--it's more likely to float off before it gets there. I can say that definitively after years of spraying experience of all common types. I've been around other experienced painters while they were spraying, and I guarantee that my techniques result in less overspray and better transfer efficiency. I can also guarantee that atomizing to the nth degree will result in much more fog in the air. 40% of that 1 mL is a lot less finish on the piece than 75% of that same 1 mL, which means it's slower for a given rate of finish coming out of the gun. I'm not talking about droplets that are large enough to run on their own, that's not atomization.

High atomization also requires much more air, which leads to other problems when trying to put on more than a super-thin coat--the airflow can push around the finish that's already on the piece, and more fog in the air means more dust that can settle on your piece.

[Patrick Harmon]

The main difference between turbine units and compressed air HVLP is the way air is fed to the gun. In a turbine unit the series of fans helps supply the high volume of air in a compressed air system the compressor supplies the air. Turbine units are more portable but are typically more expensive, there greatest benefit is portability as they cannot always be used with the variety of coatings that a compressor fed spray hvlp spray gun can. Here is a complete review of the turbine and compressor HVLp SPray Guns.

[Patrick Harmon]

The main benefits with turbine are they are portable making them useful for field work or smaller scale shop projects. Plus if you have already have a compressor the turbine unit will be higher cost. Compressor fed guns can be conventional to which will make them useful for high viscosity coatings like glue if you need to spray it. For more on the benefits and drawbacks of each system there is a good guide here.

[Marty Schlosser]

Jason,

I've never heard of a "combo system" before. Who makes the one you have, and do you happen to have a link to them?

Thanks, in advance.

Personally, I prefer combo HVLP systems--they come with a small internal compressor to pressurize the cup/tank, then use the turbine to atomize the material. I've never much cared for siphon-type spray guns, they're just too finicky, and you have to spray to clean them. A combo system can be cleaned with just the compressor running, which will force out a stream of fluid from the tip without atomizing it.

[Jason Roehl]

Just an example:

http://www.graco.com/us/en/products/...-sprayers.html

The top unit shows a turbine-only unit. Scroll down a bit, and you see an add-on compressor. Compressors allow for the use of a remote pot, which gives you more flexibility in spray angle with the gun.