Define "HVLP"

[Edward Oleen]

It would be nice if someone could define for me exactly what HVLP means, aside from "High Pressure, Low Volume". I further know that they are talking about air. What I don't know is just how High the HIGH is, and how low the volume.

Conversely, there is LPHV - I think - which would be Low Pressure - High Volume.

I need to spray a large surface, and buying spray cans seems a bit expensive, especially when I've got a nice compressor available to me.

[Scott Hearn]

It's hard to quantify really. The air caps and fluid tips on HVLP guns vs regular guns look very similar. I think the internal passages in the guns are where the main differences are. The advantage with HVLP is that you lose less material to overspray. I used to paint cars with polyurethane enamel at 75PSI with suction fed conventional guns. I've sprayed basecoat/clearcoats at 35PSI HVLP. One thing to note is the CFM requirements of the gun you are looking at. Most portable 25 gallon 3.5hp compressors won't run a full size HVLP gun, but may get along fine with a small "detail" gun. To run full size guns you are looking at 60 gallon 5hp and up compressors.

For woodworking I don't really see a pressing need for HVLP unless you are in a production environment or have crazy local ordinances that mandate them. An old school gun works just fine and actually is a little easier for lacquer. Cheaper too. Hope this helps.

[Jim Dwight]

I operate with a compressor, you need a "conversion gun". I used to use a Wagner conversion gun, relatively inexpensive, but have graduated to a 3 stage fan HVLP, a Fuji Mini-Mite. A conversion gun is set up to lower the pressure at the gun to the ~10psi that you need for HVLP. So you send it the normal 90psi or so and it drops at a regulator on the gun and thereby generates the high volume. A good conversion gun would probably work about as well as one for a fan but the Wagner is not a great gun. I also was trying to drive it with a compressor that was too small which was undoubtedly one of the problems. But even when the tank was full, it did not spray as big or as nice a pattern as my Fuji. Biggest advantage of HVLP is less overspray - but there is still plenty.

If you have a big enough compressor, you can save money using it. I didn't so a fan based unit made sense to me. They have a 1 inch hose going to the gun to handle the low pressure air. The cheapest way to spray, however, would be to get a little Harbor Freight conventional gun. My son and his buddy have painted cars with a HF gun but have also upgraded more recently to a better gun. But to try it out, you can't beat the ~$10 price.

[Jim Andrew]

My experience with spray guns, is that the conventional guns throw a fine mist of spray, while the hvlp guns throw larger drops of finish, and put out less mist. When I would spray the woodwork in a house, after it was installed, with the conventional gun, there was a fog in the house which made it hard to see. With the hvlp, the fog was much less. The finish was smoother with the conventional gun.

[Jim Dwight]

My Fuji will put out a fine spray that allows you to lay down finish that doesn't need to be rubbed out. It's hard for me to believe any gun does much better, HVLP or conventional. I don't think the quality of the spray is a function of the gun. It is a function of the quality of the gun. But a gun that will do this is several hundred dollars. The complete Fuji setup I use is $500-600. Cheap for a "good" setup but not cheap by my hobbiest standards.

[Bradley Gray]

It would be nice if someone could define for me exactly what HVLP means, aside from "High Pressure, Low Volume".

You have it backwards - it stands for High Volume Low Pressure.

I switched from spraying solvent base to water base in 1990 and switched to a turbine system at the same time. I am on my 3rd turbine/HVLP gun system. The set I currently use was made by Graco. It runs at 6 to 8 psi with a 3/4" hose. There is very little overspray with these guns so you breath less and buy less. I mostly spray WB poly and waterbourne dye but have also used the system for latex paint with good result.

[Jim Seyfried]

I am on my 3rd turbine/HVLP gun system.

With all your experience do you have any recommendations for a first time buyer? I have been considering getting a spray system for a while. I would like to get one that I would not need (or want to) to upgrade for a long time.

[Curt Harms]

As far as definition of "HVLP", I believe it's a maximum of 10 p.s.i. at the air cap. Conversion guns have approximately a 3:1 pressure reduction so 25-30 p.s.i. at the inlet to get 8-10 p.s.i. at the air cap. I have a Porter-Cable PSH1 that seems to work well at 25 p.s.i. at the inlet. As Jim said, the Harbor Freight purple HVLP guns get pretty good reviews as a way to experiment with spraying without spending mega $$$. I don't know about the availability of different needle/air cap sets for the HF guns.

I later bought an Earlex HVLP turbine setup because I wanted portability. When I first turned it on I expected I'd have paint specks everywhere because it put out a LOT of air compared to the P-C conversion gun. I was wrong, there is virtually no overspray. The Earlex gun does have one shortcoming - it has no fan width control. You control with size of the fan by how far you hold the gun from the work.

[Steve Baumgartner]

You won't get an absolute answer because there is no hard-and-fast boundary between High Volume Low Pressure (HVLP) and High Pressure Low Volume (HPLV).
As very rough rules of thumb, HVLP usually involves pressures of less than 10psi and volumes of 100 CFM or more (though small, low-end units may operate at lower values of both). Traditional high-pressure guns typically need between 20-50psi and 3-5CFM. Conversion guns let high-pressure/low volume air expand to get low-pressure/high volume. The product of pressure and volume stays about constant as air expands, which means it can be difficult for a small compressor to supply the amount of air equivalent to a sizable turbine when used with a conversion gun.

[Bradley Gray]

The technology has improved over the years. The Graco i am using now is superior to the first two and is now about 9 years old whereas the first two lasted about 7 years each. There may be something better out there now. The Graco came with a nice tool kit built into the top of the turbine along with 3 needle/nozzle sets for different finishes. I keep water base poly in the gun - I only clean it when it fouls - so it is ready to go in minutes. When I wear out this turbine I will check with these folks http://www.cjspray.com/ as they are knowledgeable and stock parts for what they sell. I hope this helps.

[Peter Quinn]

My HVLP conversion gun (Asturo), takes 29psi inlet and needs about 9cfm at that pressure, so it may be driven by a medium sized compressor, I've heard it will run on a large pancake but requires intermittent stopping to let the compressor catch up. They also make LVLP (low volume low pressure) guns that run a bit slower but quite effectively with smaller portable compressors.

[Chris Padilla]

I plunked down 1 large about 12 years ago for an Apollo 1000 HVLP, 4-stage turbine gun. I've sprayed lacquer, latex, dyes, waterborne and anything else you can think of and it just keeps chugging along. Now it sounds like a 747 taking off (wear ear protection for sure) and I'm just a hobbyist but I feel like it has been a good investment...nothing has gone wrong with it. I'd buy another Apollo in a heartbeat...but they are near the top-end of the game. I remember at the time of my search that it came down to Apollo or Fuji. They might have been the only game in town at the time for the higher end stuff.

[Jim Dwight]

..... The product of pressure and volume stays about constant as air expands, which means it can be difficult for a small compressor to supply the amount of air equivalent to a sizable turbine when used with a conversion gun.

Probably trivia for this forum but the ideal gas law is PV=nRT. In other words, the product of Pressure and Volume is equivalent to the product of the amount of material, times a constant, times the temperature. It is often summarized as Steve did. If pressure is reduced to one third the previous level, the volume is 3X the previous level (if the amount of material is the same and the temperature didn't change).

[Tom M King]

I expect you know what an air compressor is, and how the air feels coming out of the hose. With an HVLP turbine, it's more like a vacuum cleaner running in reverse. There are all manner of guns that use a different small part of the range from the high pressure compressed air, to the high volume low pressure of the vacuum cleaner air mover. Conversion guns are in between the two extremes.

Then there's airless, and then again there's air assisted airless. If you spend enough money on any of them, you can get flawless results easily.

[John TenEyck]

What material do you want to spray? If it's something like shellac, lacquer, or another low viscosity product, the HF purple gun will spray beautifully with a compressor that can output about 6 CFM at 40 psi. All the other data is interesting but irrelevant. You can get a great finish for the princely sum of $29 ($9 if you buy the one on sale w/o the mini regulator, and 20% less than that if you have a coupon). Those purple guns have a 1.4 mm orifice so they can't spray anything very well above 25 seconds through a #4 Ford cup (boring but important data). If you need to spray something with a higher viscosity then you can thin it or get a gun with a larger orifice, or buy a gun with multiple needles and air caps. That's the better option if you want to have one gun that can handle a wide range of products. If that's the case, call Jeff Jewitt at Homestead Finishing. He sells several products at fair prices and can recommend a good setup based on your needs and compressor capability. Me? I have 3 cheap guns that cost about $100 total and have no complaints with the finish quality they lay down. I also have one of the HF purple guns, that I bought as a lark just to see how well it can spray. For shellac it's awesome at about 20 psi inlet pressure, and I'm sure for lacquer, too, I just won't spray it in my basement shop.

If you have a good sized compressor I see no advantage of buying a turbine unit unless portability is important. A conversion gun will cost far less and have an easier time putting down a high end finish.

John