Ask the Expert Question-and-Answer Archive

by Ron Joseph

April, 2004

Transfer Efficiency Values for Paint Spray Guns

Q. I am trying to find a table of Transfer efficiencies for different types of spray paint techniques. I found a range of 90 to 95% in AP-42, Section 4.2, but could use a well documented number.

A. The EPA has published tables of transfer efficiencies in some of the documents published in the early 1990s. I seem to remember that conventional spray guns had a transfer efficiency of 40%, airless and air-assisted airless had transfer efficiencies of 40%, electrostatic spray guns where rated at 65%, and the dip operations above 90%.

At the time the EPA published these values HVLP spray guns were not yet available and I would assume that based on current regulations the EPA would give them a rating of 65%.

I have performed numerous transfer efficiency tests on spray guns over the past twenty years and have found that transfer efficiencies very extensively depending on the size of the object being painted, the distance between the spray gun and the object, the viscosity of the coating and more than anything the painters' techniques.

If you intend to use the transfer efficiency table values in EPA calculations then I suggest that you try to get hold of the CTG documents that were published in 1977 and 1978, respectively. Unfortunately, they were published long before the Internet came into being and you will need to purchase copies from the Government Printing Office.