HVLP high volume low pressure spray guns attract a lot of attention due to their lower paint over spray figures. The basic principle of HVLP spray guns is that instead of a paint stream exiting the spray gun being atomised with high air pressures the stream of paint leaving the spray guns fluid nozzle is atomised with a much larger volume of compressed air at much lower pressures that typical conventional air spray guns.
HVLP high volume low pressure spray guns were required by law in certain areas where regulators attempted to reduce emissions with maximum air pressure restricted HVLP spray guns that could not spray above ten pounds per square inch at the air cap.
One huge draw back with HVLP high volume low pressure spray guns is the high volume of compressed air they require. Many smaller spray painting operations or DIY spray painters may not have air compressors large enough to support many HVLP spray guns due to the large volumes of compressed air required.
Many high end air spray gun manufacturers now offer compliant air spray guns. Compliant air spray guns have at least equal, or typically better transfer efficiency that EPA rules require. Another benefit of considering a compliant spray gun over a HVLP high volume low pressure spray gun is the compliant spray guns typically consume much less compressed air which lowers operating costs and allows most compliant air spray guns to be used on smaller air compressors than the air compressor size required by HVLP.
Which ever type of spray gun used there will always be some amount of paint over spray.
A great way to ensure an air spray gun is set near to where it will be achieving its best transfer efficiency is to always set the spray gun up with the lowest possible inlet pressure to achieve good paint atomisation and spray pattern fan width. Additional atomising air pressure will cause unnecessary paint over spray and reduce transfer efficiency.