Spraying Questions

[Ted Illi]

Can I assume I do not need a turbine to deliver air to a HVLP spray gun if I already have compressed air in my shop which is dried, cooled, regulated, and can deliver the CFM's required to run a HVLP gun?
Is it a misconception on my part to think HVLP is airless spraying? My present pressure gun runs at 30 to 45 psi, so if the paint is being atomized at say 35psi, it's hitting the surface being painted at that pressure, correct?
HVLP guns are High Volume Low Pressure, right?. So if the gun runs at say 15 to 30 working pressure (the LP side of the equation) the paint is atomized at say 20 psi and hits the paint surface at 20 psi correct?
Is the higher volume of air ( HV side of the equation) used to compensate for the LP? Do you have to spray slower? What is the effect of the higher volume of air on the paint and surface etc.?
How reduced is the over spray with HVLP?
Last question! A Sales Representative from Kremlin Airless system told me "HVLP is nothing new; It's been around for the past 20 years"! "HVLP at best yields 20% savings in material and reduced over spray. A good airless spay system, operates at 80% transfer efficiency and the added upfront cost of the system can quickly be recovered in paint savings, quality, and clean up costs". Agree?

[Howard Acheson]

Let me say that if you are new to spraying, I recommend you first purchase Charron's Spray Finishing at Amazon. It will explain the different systems and equipment. It will tell you how to set it up and adjust everything. Then it will tell you how to spray. You don't just fill up the cup and pull the trigger.

To answer a couple of your questions.

Yes, you can use your own compressor if you have what is called a conversion gun. A conversion gun is different than the gun used with a turbine air source. Also, if you are using you own compressor and a conversion gun you need to match your guns CFM requirements to your compressor CFM capability. CFM is a critical specification with HVLP spray guns. Many compressors do not produce enough air (CFM) for spray painting.

Yes, there is less overspray with HVLP but how much is determined by the material being sprayed, the item being sprayed and the experience of the sprayer.

Finally, practice and get experience by spraying scrap material and cardboard boxes. Practice on both the outside and inside of the boxes. You will have to learn to spray inside or you end up with a face-full of finish. Do not attempt to spray a real item until you have gained some experience.

[Ted Illi]

Thanks for the info.

I have a lot of experience using standard pressure spray equipment. I just have not used HVLP and want to get a opinions on how much reduction in over spray is really gained from conventional equipment. Based on the atomizing pressures in both system the reduction of over spray would seem minimal? I don't want to upgrade twice, and at the cost of paint airless seem may be the way to go?

[Howard Acheson]

I realized that I did not address one of your questions. You may already know the answer, but "airless" is different from "HVLP". Airless sort of flings the coating material out of the gun or pumps it directly from the nozzle. No air is added and it depends on velocity to atomize the material. Either HP or HVLP mix air with the material to atomize the material.

[Joe Chritz]

There is also something called air assisted airless. Spraying is a whole world in itself and the people who are really good are really really good. Its as much art as science.

I have had good luck purchasing a mid level top cup conversion gun and just practicing with some finish. (I use a DeVillbis finishline) After 20 or so gallons it gets much easier.

A lot of finishes are easy to spray. Target's USL is one of them. It appears to be self leveling so the biggest thing is to avoid runs and dust.

It does take a big compressor to run an HVLP regularly. A big compressor is generally shop only so the turbines are popular from portability standpoint. Plus if you have to drop 5 bills on a compressor a turbine starts to be a cost effective option.

I forgot a couple points.

The overspray varies but is considerably less then high pressure spraying.

Airless is a good system but it depends on what you are spraying and how much. I like the top cup guns because I rarely spray more than a small amount at one time. Top cup gives me less waste and faster clean up. HVLP doesn't like thick materials like latex paints. Transfer efficiency is only part of the equation when dealing with material use. There are hoses, pressure pots, etc that are used with some systems.

Joe

[Phil Phelps]

I have had conversion HVLP's for about fifteen years. These guns require a lot of pressure at the compressor, like about 70-80 psi, and then it's best you have an in-line regulator at the base of your gun for better control. There is about 12-14 psi at the tip, however.You do use a lot of material with a HVLP with a lot less overspray, but there is overspray, don't be fooled. I can actually use my gun like a big air brush if I must. These guns require a lot more cleaning than a siphon gun and it's very important you keep them clean. Like any thing new, there is a learning curve, but you'll enjoy the HVLP.

[Jason Roehl]

1. Yes, but you need what is known as a conversion HVLP gun that will accept pressurized air.

2. HVLP is High Velocity Low Pressure spraying. Airless is high pressure spraying, with NO air to atomize the material, atomization is achieved by forcing the material through a small orifice at high pressure (typically 800+ psi).

3. See #2. Technically, HVLP is considered 10 psi or less by definition. It's only at that pressure at the tip. Once it's in free air, it expands to ambient pressure by some curve known only to physicists.

4. It takes huge amounts of air to atomize material. The heavier/thicker the material, the more air.

5. Overspray depends on how accurate your settings are. I can spray with an airless and have very little overspray, or I can spray with an HVLP and have a ton of overspray. The difference is that HVLP overspray tends to be much smaller and hang in the air longer.

6. Not necessarily so. The biggest problem with airless for fine finishing is that due to the longer hoses, there is more material lost in cleanup (with good technique it can be kept to a minimum, but you still need at least a quart to prime). Not a problem if you're doing a LOT of spraying, but it's just not appropriate if you're only spraying a step stool.

[Ted Illi]

Thanks everyone for the info. Most my questions have been answered.

I would really like to go the airless but I can't justify the cost, versus material waste. I think if I were doing bigger runs airless would be the way to go. Right now I'm painting once every two weeks for maybe a day and a half.

So........... Since I already have adequate air in the shop, and I don't need the portability a turbine offers, for now I will go the gravity feed HVLP route.

Joe Chritz,
It's nice to hear your using a DeVillbis Finishline gun and like it, because I just ordered one on line. I got three nozzle sizes 1.3, 1.5, and 1.8. Since I don't spray any Latex ( I let my wife roll that stuff on the house walls) I think I have a good range of tips for the material I spray. What nozzle sizes do you have? I paid $140 which I hope was a good price? I let you know what I think of the gun in a couple of weeks!

Thanks again to all for the info.

[Joe Chritz]

Only one tip set and I think it is 1.5 but I would have to go look.

My spray option through that gun are pretty limited. Very rarely I will spray thinned seal coat but that is usually through my other gun that is older and more beat up.

The finishline gets USL and that is about it.

If you are playing with different types of finishes with widely varying viscosity you may want to research and use a viscosity cup.

Joe