HVLP

Almost four decades ago, I apprenticed at a cabinetshop where a regular high-pressure system was used to apply lacquer and stain to kitchens. Despite numerous extraction and filtering devices, the entire building filled up with fumes from the overspray. I would get light-headed and short of breath at times from these volatile fumes, even while wearing a carbon filtered mask. If only we'd known! A couple of years after I left, that shop was destroyed by a fire that started in the spray booth. There was a 1/4" thick residue of overspray on the walls, and it lit up the downtown like a fireworks display. Thankfully, high-pressure spraying is essentially obsolete among woodworkers today.

In 1971 a new technology was patented by a European company called Sicmo. It sprayed the same finishes as the old guns, but used a whole lot less pressure to deliver the material. That meant there was a lot less overspray - finish sent into the air that never arrived at its destination. The new system came into its own during the '80s and especially the '90s, and its name describes exactly what it does... high volume, low pressure, or HVLP.  

FUJI's Q4 Pro™ Self-contained system.

Over the next few years, HVLP gained a lot of popularity while small unit manufacturers worked out the bugs and became more and more familiar with its advantages. Many of them concentrated on complete systems like the Fuji shown here, which included an air pump, freeing up small shop compressors for other tasks. Today, virtually everybody setting up a spray operation in a small or medium sized shop goes with this safer, healthier, more economical choice.

So, what exactly is HVLP?
Well, the first and probably most obvious attribute is that the pressure has to be low. Very low. Under 10 psi. According to the folks at FUJI, most "HVLP turbine motors produce over 100 CFM (cubic feet per minute) at just 3 to 8 psi." The guns that woodworkers used to run operated at more than five times that pressure. The lower pressure translates into lower speed as the material travels through the air to its target. And that means the pattern is much more controllable, and it won't bounce off the surface.
The lower pressure also means that more of the product (stain, lacquer, varnish etc) lands gently on your project - up to 85%. Cutting waste in half is a great idea for your bottom line, but more importantly, it's a wonderful boost to your health. And because of that gentle delivery, the final coat is just as beautiful as a high pressure finish, and many woodworking pros say it's actually better.

And how does it work?
To understand HVLP, you need to keep in mind that "high volume" refers to the amount of air, and not necessarily the amount of finish being pumped at low pressure. FUJI's tech people supplied this info online:
"If the area of the air holes (orifices) in a typical HVLP air cap are added together, the combined diameter will only be about 3/8". Although much is said about how high the CFM rating is on these motors, the fact remains that because the pressure is low, only around 12 - 20 CFM passes through the air cap  anyway - the rest of the air is surplus. In fact, using a Y-connector, 2 sprayguns can be attached to the turbine and no real loss of power will be noticed. At very low pressures, with this type of turbine motor, psi becomes much more important than CFM. The more pressure that is used, the more CFM passes through the air cap. It is therefore the pressure that forces more air through the same air cap. The result is better atomization with the higher pressure."

Another manufacturer, Turbinaire, explained it this way on their Web site:
" Conventional high pressure paint-spraying systems use pressure to atomize (break-up) the coating being applied. Conventional compressor-powered spray guns use high pressure compressed air at a very low volume (40-80 PSI @ 6-8 CFM) to atomize the paint. Airless (electric) sprayers pump the paint from the paint tank to the gun at such high pressure (up to 5000 PSI) that the paint virtually self-atomizes. Air-assisted airless sprayers are a combination of conventional compressor-powered and airless sprayers. All of these systems spray the paint at high pressure, causing the paint to literally bounce back from the surface and create large amounts of overspray (clouds, mist) and obvious paint wastage."
 

Turbinaire MiniPro™ Model 1225

The Turbinaire HVLP system shown here used "an electric turbine (110v or 220v) to deliver a high volume of air at low pressure to the gun's air cap. When the trigger is activated, the paint is released at the fluid tip and the high-volume low-pressure air atomizes the coating externally as it is being applied." The Turbinaire site also pointed out that conventional spray systems operate at 60-80 PSI @ 8 CFM, which results in a 30-50% transfer efficiency. According to the company, about 60% of the finish never makes it to the project. They pointed out that this is unhealthy for the operator and harmful to the environment. Turbinaire's HVLP systems operated at 4-6 PSI @ up to 130 CFM - a combination that delivers up to 90% of the product to its target.


To do further research, you can find manufacturers such as Apollo, Wagner, Fuji, Graco and SATA
in the 'Finishing Supplies & Equipment' section of our our Links Page.


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