HVLP, or High-Volume/Low Pressure, uses a high volume of air (typically between 15-26 CFM) delivered at low pressure (10 PSI or less at the air cap) to atomize paint into a soft, low-velocity pattern of particles
HVLP - High Volume/Low Pressure
HVLP systems allow larger amounts of material to be delivered at lower pressure. These systems deliver air generated by a turbine to the spray gun via a flexible hose. The spray gun takes the high volume of air and reduces it to 4-10 psi (pounds per square inch) at 46-62 cfm (cubic feet per minute) allowing an even flow of the material with very little over-spray. The spray pattern of the HVLP gun can be set by adjusting the air cap in or out, thereby providing the amount and/or the fineness of the spray.
A turbine is similar to a vacuum cleaner motor. Turbines are rated by stages, or the number of fans they have. There are typically two to four stages. The fans operate at about 20,000 rpm. Turbines are normally smaller than compressors and weigh considerably less.
HVLP guns have larger passageways than compressor guns and airbrush guns. This is needed to accommodate the high volume of material passing through the fan under lower pressure.
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. However, many guns are designed to work with air compressor under a slightly different principle, and these are also called HVL guns.
An HVLP spray gun roughly resembles 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 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 HVLP guns, spray guns using air compressors did not have a way to regulate the air pressure coming through the gun. Material shot from the gun 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 disturbed surface that is not smooth and even.
The HVLP spray gun was developed to replace the conventional gun. A regulator controls 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. This 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 HVLP spray gun system is great, it isn’t particularly cheap and many people already own an air compressor. Therefore, several HVLP spray guns are sold a la carte to be connected to an air compressor. Before buying a gun 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). If a certain model requires 6-9 CFM @ 40 pounds per square inch (psi), your 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. You can find a decent HVLP spray gun for under $100 US Dollars (USD), but it might require a CFM flow that only a five or six horsepower air compressor can achieve. If you spent another hundred dollars you can find guns with 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.