What is an HVLP spray gun?

I've heard that an HVLP (high volume/low pressure) spray-finishing system offers benefits over traditional spray guns, but I'd like a further explanation. Also, can I convert my existing gun, or do I have to junk it? And do I need to replace my compressor with a turbine?
—Dick Guinan, Omaha, Nebraska

HVLP systems use large amounts of air delivered at low pressures at the air cap (10 psi or less) to reduce bounceback and overspray, Jeff, so more finish ends up on your project instead of being wasted. That improves the air quality in your shop and cuts costs.

Forget converting an older conventional spray gun to HVLP operation. Replacement parts can be hard to find, and worse, conversions only marginally improve an older gun. That's because turning up the pressure high enough to pull the finish out of the old gun's cup increases the delivery pressure, so you're back where you started.

Your best alternative for a compressor-driven HVLP is probably a gravity-feed gun like the one in the photo, above. (It's a DeVilbiss model FLG-635-316, but it's hard to find. We found a DeVilbiss model FLG-CNG-115 here, with a retail price of about $215.) Optional plastic cup liners dramatically reduce cleanup time, and they let you spray with the gun upside down to coat hard-to-reach places.

HVLP guns require plenty of air, so you may have to buy a larger compressor. The manufacturer of the gun shown recommends a minimum of a 3-hp compressor with a 20-gallon tank. Although this is an added investment, you can use the compressor to power other tools. An HVLP turbine, on the other hand, has a single function. Most manufacturers of turbine-driven

HVLP sprayers market a complete system to ensure compatibility of the components. And even though the cup is under the gun like a conventional sprayer, some air is piped into the container to pressurize the contents. We found complete HVLP systems at prices ranging from $100 to $700.