What is HVLP Spraying?

HVLP stands for “high volume, low pressure.” Any spray system for paints and varnishes uses air pressure to propel the finish. An HVLP spray gun uses a high volume of air, but at a low pressure — which allows the gun to turn paint, stain, varnish, or lacquer into a very fine mist.

The resulting finish can be exceptionally smooth and even. Picture the best possible finish on a car or fine piece of furniture. This is much easier to achieve with HVLP than with other spraying systems.

Advantages of HVLP spraying

• Less cleanup - Minimizes overspray and bounceback.

• More precise spraying and less waste. — Finish lands where you want it. Most compressor spray guns transfer only about a third of the finish onto the surface being sprayed. HVLP turbines transfer rate is as high as 85 percent!

• Better for the environment — Minimizes volative organic compounds (VOC) put into the air.

• Versatile — can spray all finishes.

• Portable — Turbines weigh much less than most air compressors.

The basics of an HVLP Spray system

An HVLP system has four parts:

• a turbine that generates air (high volume, low pressure),

• a pressurized container for the finish to be sprayed, connected with a small tube to…

• a spray gun that injects the finish into the air stream, converting the liquid coating into a mist (called “atomizing” the finish)…

• and an air-supply hose that connects the gun to the turbine.

The spray gun is the key to mixing the fluid finish with air in exactly the right way, to “atomize” the finish — breaking it into air-borne particles tiny enough to blend perfectly into a smooth finish on the object being sprayed.

The hose is long enough (25 feet or more) to keep the turbine exhaust away from the area being sprayed, and so finish doesn’t get into the turbine.

Want to see all this in action? Rob Johnstone at Woodworker’s Journal has a nice video in his article, “How to Use an HVLP Sprayer,” showing a current Fuji system and spray gun. You’ll see how easy this is. (You can find lots more tips here at my Fuji Spray News & Tips blog.)

HVLP spray systems are easy to use

If you can use a paintbrush, you can spray with HVLP. HVLP spray guns are easier to use than most spray guns. It takes very little practice in order to spray with professional results, thanks to the lower velocity.

You make sure the fluid you want to spray is thin enough, and choose the spray nozzle best for it. Then the spray gun lets you adjust the rate and pattern of the spray to get the finish you want. Practice on a test piece to see how fast to move your arm.

HVLP systems are quite portable

A complete HVLP system weighs considerably less than most portable air compressors — about 22 to 32 pounds. The turbine also has a handle on top. Thus you can easily take an HVLP system outdoors to spray a fence (or house) — or spray kitchen cabinet frames, then spray the doors and drawer fronts in a garage or workshop.

HVLP turbines use fans to generate the air pressure.

HVLP systems are categorized by the number of fans they use — more fans mean higher air pressure. This is measured in pounds per square inch (PSI). Systems with more fans speed coverage and make it easier to spray heavier coatings such as latex paint.

• DIY or entry-level systems: A 2-stage HVLP turbine uses two fans, generating up to 6 PSI.

• Budget “sweet spot:” A 3-stage turbine uses three fans, generating up to 6.5 PSI.

• Pro level, & better if you spray a lot of latex: A 4-stage turbine uses four fans, generating up to 9.0 PSI.

• Fastest, most powerful: A 5-stage turbine uses five fans, generating up to 9.5 PSI. (This is the limit for what’s considered “low pressure” spraying.

HVLP spray guns inject finish into the stream of air from the turbine…,

The coating is thinned to the optimal viscosity for spraying.

Viscosity of coatings is important. Although I supply a guide, there is often some trial and error involved in arriving at the best viscosity. If a product is thinned too much, there are runs. Too thick, and 'orange peel' or rough finish is the result.

When thinning, it is essential to use a reducer that is compatible with the product you are using. To be sure, buy a thinner made by the same coatings company. Always verify that it is the right product. It is wise to experiment on a practice piece to ensure that the finish is perfect. You may also request information from the coatings manufacturer. Don't forget to mention you are spraying with HVLP turbine equipment.

Waterborn lacquers (acrylics, urethanes and varathanes etc.) can be applied successfully with HVLP. Most of these products require no thinning whatsoever. Many of these newer coatings contain a high-solids content of 30%-60% or more, so the turbine must be powerful enough (at least the 3-stage). Several thin wet coats are preferable to one or two thick coats. Scuff sanding between coats is recommended.

Tips on spraying with HVLP

When spraying with HVLP, keep the gun at a constant 6" - 8" away from the project. Release the trigger at the end of each stroke. Then, depress the trigger and overlap the previous pass by about 1/3. Continue in this fashion for consistent coverage.

The Air Control Valve

Whenever possible, to reduce over spray to an absolute minimum you may use the Air Control Valve to reduce the volume/pressure of air passing through the spray gun. Turn the valve until the air is at the point where it is just barely atomizing the paint and yet the finish quality is still ideal. If the valve is turned too low, orange peel may result.

There is a compromise here with setting the amount of paint sprayed and the size of the pattern. The Air Control Valve setting should be the last in the chain. In other words, decide on the viscosity and size of pattern first - then, you may find that you can reduce the air without affecting the quality of the finish.

More tips about HVLP Spraying:

• My News and Tips section.

• Customer Feedback often includes tips, as my customers say how they did their project.

• My Cabinet Refinishing section includes lots of tips.

• Woodworker Marty Schlosser has written a blog post for Fuji Spray about the advantages of hvlp systems.

• And of course,