Tool Review: HVLP Spray Systems
If you've never tried your hand at spray finishing, it's never been easier, cleaner, or safer, thanks to high-
volume, low-pressure (HVLP) sprayers. Why spray? You complete more work in less time; benefit from fast-drying finishes that are far less susceptible to nibs from settling dust, and consistently produce smooth results. And, as your spraying skills improve, you can use techniques like toning and shading (adding color between finish coats) that bring depth and sophistication to your finishes.
You could get those results using a conventional spray gun powered by an air compressor. But they operate at high pressure and create a hazardous fog of overspray. As much as 80 percent of the finish that leaves a conventional spray gun bounces back off your workpiece, and winds up on every exposed surface, including the shop floor, walls, shelves, and tools. HVLP sprayers, on the other hand, use a large volume of air at low pressure to break up, or atomize, the stream of finish leaving the nozzle into a fine mist. This method greatly reduces finish bounce-back, saving you both money and time cleaning up.
HVLP sprayers come in two forms: Conversion guns and turbine-powered sprayers. Like conventional spray guns, conversion guns atomize finish with air supplied by a compressor, and that air must be filtered of both water and oil to avoid contaminating the finish. Conversion guns require 5-25 CFM (cubic feet per minute) of air to work well. To put that demand into perspective, a 30-gallon compressor typically can power a lower CFM gun adequately, but it takes an 80-plus-gallon model to supply enough air for the hungriest guns. That makes conversion guns better suited for large-scale spraying operations.
Turbine systems, on the other hand, provide a complete, self-contained, portable package that includes the gun, air supply (the turbine unit), and hose. The air from the turbine is dry and clean so it doesn't require water or oil filters. For those reasons, and because they nicely simplify the spray-
finishing operation, we prefer the turbine systems to conversion guns.
These three parts of the system work in concert to produce a smooth, level film on your project. Naturally, the gun and turbine impact performance the most. A powerful turbine can't compensate for a poorly performing gun, nor can the best gun effectively atomize finish with an anemic turbine, but a restrictive or easily crushed hose can render the whole system ineffective. Let's examine each key component, one at a time.
- The spray gun: Finesse comes at a cost. To best atomize a finish, three spray-gun adjustments must be balanced: fluid flow (the amount of finish leaving the gun), airflow (the amount of air exiting the spray cap), and fan width (how broad or narrow a pattern the gun can spray). A knob on the gun controls fluid flow; to control airflow, most HVLP turbine systems costing more than $600 use a valve either in the air line or on the gun (we like the air control at the gun end of the hose, which saves walking back to the turbine). Fan width makes up the third part of the atomization equation, and most guns provide a method of narrowing the fan width: either turning a knob at the rear of the gun or loosening the air cap. (We like knob adjustments.)
- The turbine: HVLP's power plant. An HVLP turbine is a series of fans, called stages, that move a lot of air at low pressure, and more stages equal greater air output (rated in cubic feet per minute, or CFM), which means better atomization. However, a number of other factors, including motor speed and the size of the turbine blades, also affect the air volume and pressure, so you can't judge a turbine only by its number of stages.
- The hose: important but underrated. Routing air from the turbine to the gun, the hose is the final big piece of the HVLP puzzle, and a good hose has durability, flexibility, and low weight. A too-stiff hose tends to steer the gun during spraying; a more flexible hose may not return to its original shape, restricting airflow. A "whip" hose -- a short length of extra-pliable hose connected between the heavy main-supply hose and the gun -- provides flexibility where you need it and durability where the hose can get underfoot.
Top Tools: AccuSpray 23i-T, Turbinaire 1235GT
Top Value: Campbell Hausfeld HV2002
Learn the results of our testing of the ten HVLP gun-and-turbine pairs in the April/May 2006 issue of WOOD magazine.