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A high volume low-pressure (HVLP) spray gun is used for applying lacquers, varnishes, stains, and paints of all kinds. The “true” HVLP gun is connected to a turbine motor that drives a high volume of warm air under low pressure into the gun, giving the gun its name. Many guns are designed to work with air compressor under a slightly different principle, however, although they are known by the same name.
Most HVLP spray guns roughly resemble a pistol-grip garden hose nozzle, which allows water to flow when the trigger is squeezed, turning off the flow when released. Instead of water, the spray gun shoots air mixed with paint or another material. The idea behind a spray gun is that the escaping air atomizes the material, spreading it into tiny droplets that can be applied on to a surface in thin, even layers.
Prior to these devices, spray guns using air compressors did not have a way to regulate the air pressure coming through the gun. Material shot out with such force that it produced problems including large amounts of overspray and blowback. Overspray not only wastes material, but it requires more prep work to protect surrounding areas from paint. Blowback occurs when paint hits the surface so hard that it bounces off, leaving a surface that is not smooth and even.
The HVLP spray gun was developed to replace the conventional gun. A regulator controls the air pressure, allowing the material to be atomized but leave the gun at a slower rate, reducing overspray and blowback. A turbine HVLP system comes with an electric turbine motor that generates warm, filtered air for the gun, which eliminates the possibility of accidentally introducing oils or moisture sometimes generated by air compressors. The heated air also helps to “flash” the material being sprayed — the industry term for dry time. Since most materials need more than one coat, reducing flash time between coats is a plus.
While the turbine system is great, it isn’t particularly cheap and many people already own an air compressor. Therefore, several spray guns are sold a la carte to be connected to an air compressor. Before buying a gun, consumers should be sure to check the specifications; each gun will be rated for the amount of air necessary to drive it. This measurement is usually given in cubic feet of air per minute (CFM), so if a certain model requires 6-9 CFM @ 40 pounds per square inch (psi), the air compressor needs to be able to generate that specification to properly drive the gun.
The general rule with non-turbine HVLP guns is that the less expensive the gun is, the more air it probably takes to drive it. Shoppers can find a decent HVLP spray gun for under $100 US Dollars (USD), but it might require a CFM flow that only a 5 or 6 horsepower air compressor can achieve. More expensive guns often have lower CFM requirements. To please people with small air compressors that can only generate 3 CFM @ 40psi, there are “LVLP” spray guns, or low volume low-pressure guns.
Regardless of the type of HVLP spray gun, all come with one or more spray nozzles designed to deliver different materials. Enamels, lacquers, urethanes, varnishes, and stains each have their own levels of viscosity and are best shot with a certain size nozzle. The manufacturer of the material to be sprayed commonly specifies a recommendation for nozzle size, and the gun’s literature might also specify which materials it is designed to shoot. People who don’t own a spray gun but have a paint job in mind should choose the paint first and then look for the recommended gun.
HVLP guns come in different sizes. Small ones can be used for touch up jobs or for applying graphics to motorcycles or vehicles, while standard sizes are used for painting entire vehicles, for example. The gun is fed material from a mounted filler cup, which might be mounted on the top of the gun, known as a gravity feed, or on the bottom. Gravity feed guns are generally preferable for auto painting because they don’t leave unused material in the cup.
Individuals who will be taking on a major job like painting a house may want to look for larger industrial style guns, which can draw up material through a feeder hose from gallon-sized (1 gallon = 3.78 liters) containers. Sometimes, these systems are available to rent from home improvement centers, but they can also be purchased.
HVLP spray guns are available from most automotive and paint centers. They are also available online along with tutorial videos to help new painters pick up tips on how to get professional results.