How you can Ruin the Benefit of HVLP Spray Guns
HVLP is a term that means High Volume Low Pressure and refers to how the gun atomizes material. As opposed to a conventional spray gun that uses high volume high pressure of air, HVLP saves on the pressure of air that is used. The benefit to this is that it reduces overspray which means you reduce paint waste by about 50%. The end result is that HVLP helps save money. However, this savings only occurs if you follow the rules of the HVLP gun.
All HVLP guns have a maximum air pressure at the horn of the air cap that is considered to be in HVLP spray compliance; this number is typically at most 10 PSI. While the pressure is low, the volume of air is still high, the drop in pressure occurs inside the gun. However, if you supply the gun with an excess amount of air you can actually create too much pressure at the horns of the air cap resulting in a gun that is no longer HVLP and no longer more efficient than a conventional spray gun. This is where the most important question comes in. How do you prevent your HVLP gun from starting to spray like a conventional gun? This is where you have to find out the highest air pressure that can be supplied to the gun. This number is usually published on the air cap as well as the literature that came with your spray gun and varies based on air caps. As long as you supply your gun with less than the highest approved amount of air at the air inlet you will maintain the benefits of less paint waste and improved efficiency that is applicable with HVLP. For example, if your cap says 24 psi is your maximum air pressure than you should not be feeding that spray gun with more than 24 psi of air at anytime. What if I cannot atomize my coating effectively enough with my air cap on my HVLP gun? The answer is if the cap is not supplying enough air to atomize your coating you have to change the air cap to a larger cap that will atomize your coating. Most spray guns come with a variety of air caps that are specified for different materials. To best size an air cap it is helpful to know the viscosity of your material and the flow rate from the gun.