The gun, the air supply and the operator technique all affect the finish, and the equipment must match the product being sprayed.
HVLP (high volume, low pressure) guns atomise paint at lower pressure with higher transfer efficiency, which reduces overspray and is required by regulation in many areas. Conventional guns atomise better with some high-solid products but produce more overspray. Compliant and reduced-pressure guns sit between the two.
Needle and nozzle size must match the product viscosity. A 1.2-1.3 mm setup sprays basecoat and clearcoat; 1.4-1.6 mm suits primer and single-stage; 1.8-2.0 mm is for high-build primer and heavy products. Using too small a setup on a thick product gives a spitting, uneven pattern.
Air supply quality determines the finish more than the gun does. Moisture and oil in the air line cause fisheyes and poor adhesion, which is why filters, dryers and water traps are part of the spray setup rather than accessories. Air pressure must be set at the gun inlet with the trigger pulled, not at the compressor.
Technique — distance, speed, overlap, trigger control — accounts for more finish quality than the equipment. A good gun used badly produces worse results than a modest gun used well.
