High Volume Low Pressure or HVLP for short is the industry standard for compliant spray guns that have low pressure at the air cap (not exceeding 0.7 bar) and have a minimum of 65% transfer efficiency. That said, most HVLP spray guns achieve more.
HV (High Volume)
This means that the spray gun has a higher volume of air flowing through the spray gun. This compensates for the lower pressure being used at the air cap.
LP (Low Pressure) This means that the spray gun will not go above 0.7 Bar pressure at the air cap.
While the painter may adjust the spray gun to 2.0 Bar at the regulator, by the time the air gets to the air cap this pressure will drop. This is because of the size of the drillings at the air cap. All the drillings need to be the correct size to ensure that enough air passes creating no more than 0.7 bar at the air cap. Smaller the drillings the higher the pressure.
A way of measuring the pressure at the air cap is by using a specially designed air cap with regulators attached.
Check out the picture above.
A spray gun that is HVLP will generally have reduced over spray and a higher transfer efficiency because of the high volume low pressure technology.
There are other types of spray guns that are compliant and still achieve over 65% Transfer efficiency but are not HVLP. We'll look into that on another post.
https://www.sata.com/index.php?id=hvlppistolen&L=11 (SATA HVLP spray guns)