HVLP, LVLP, and Air-Assisted Airless Guns

      A brief discussion of how different spray-gun types work, and the effect it has on finish results. April 30, 2006

I'm spraying water base pigmented lacquer using a 4 stage turbine HVLP Fuji Q4. I would like to achieve something smoother and I'm thinking of buying a low volume, low pressure gun. Can somebody tell me how they're different from HVLP gun in terms of performance? I have a small shop.

Forum Responses
(Finishing Forum)
From contributor J:
In my opinion, HVLP or LVLP are good for applying stains and toners, but are not very good for applying heavy body finishes. There is nothing as good as an air-assisted airless.

From contributor T:
LVLP stands for Low Volume (of Air) at Low Pressure. HVLP stands for High Volume (of air) at a low pressure. A common misconception is to think that the initials are dealing with fluid pressure, when in fact it is the air. For instance, a typical HVLP will use 18 cfm of air at 10psi. A LVLP will use 12 CFM at 10psi. When you release compressed air, it will expand outward in all directions, thus creating overspray. By using the least amount of air, you will minimize overspray.

However, more air will help break up your paint particle, thus creating better atomization. So by using less air like a LVLP, you may not get as much particle breakup and your speed will be reduced, but your overspray will be reduced.

My personal favorite for the coating you're describing would be an Airmix gun. It uses medium fluid pressures (like 300psi to 500psi) instead of 20psi or 30psi like HVLP. Then it uses about 10 or 12 psi of atomizing air with only 3 or 4 CFM to further break up the fan pattern. This type of system offers you the speed of an airless with the control of an HVLP, but has better transfer efficiency than both. They are a lot more money than an HVLP or a LVLP, but I think you would like the results far better, if it's in your budget.

From Paul Snyder, forum technical advisor:
You should be able to get an excellent finish with the Fuji. Either the viscosity is wrong for the setup you have or you have a spray technique problem. What do you mean when you say the finish is not smooth? What's the viscosity of the finish you're spraying? What size needle/nozzle are you using?

From contributor R:
I agree with Paul. You should have no problem with the HVLP. I have used HVLP and now LVLP for 5 years to shoot water base with no problems, once I got the fluid pressure, needle/nozzle set up right. Call the tech department at the finish manufacturer you use and explain the system you are using. They will be able to tell you what size needle/nozzle you need and an idea of pressure settings. Also, are you using a pressure pot or a cup gun? As an example, I use an Accuspray LVLP gun with a pressure pot, a fluid setting of between 8-10psi, air at 22-24psi and a 1.1mm tip. I spray water based lacquers and stains and get smooth finishes consistently, except when I am rushing and forget something. Call tech and do some experimenting.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor S:
I'd like to clarify a few points contributor T made. Specifically, it's the psi more than the cfm that creates atomization. This is why you are having difficulty breaking up the higher viscosity materials with your turbine HVLP; just not enough pressure. Some LVLP guns (the Iwata LPH50, for example) operate on as little as 1.8 cfm, yet still produce a highly atomized finish with properly reduced materials. Even some of the more production models operate on less than 10 cfm but at a psi nearing 30.

One more comment to eliminate confusion is that the AirMix gun recommended is an air-assisted airless gun, not an HV or LVLP. An airless tip combined with an air cap produces a very nice finish at higher production rates. There are some decent portable models made by Graco and Titan, but be sure to specify you want the AAF or AAM tips. Do not use RACX system tips, they do not produce as nice a finish and do not allow for fan width adjustment.

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