Ask the Expert Question-and-Answer Archive

by Ron Joseph

August, 2002

Spray Gun Design And Modification

Q. We have a painter that claims removing the air piston and spring from the gun provides ergonomic relief. What has to be done to make this modification legal and is it a good idea to modify a gun? Thanks

A. The only parameter that determines whether or not an HVLP spray gun is legal is the air pressure measured at the cap of the gun. If the atomizing air pressure is less than 10 psig the gun is legal, no matter what modifications have been made. We are assuming, of-course that the paint facility falls into a regulation that places a restriction on the atomizing air pressure.

If the painter can truly remove the piston and spring and still get a quality finish, then that's fine; however have you confirmed that he is truly able to control his film thickness and the quality of his finish? Please tell me more about his modification, because if it really works it might be useful information for others who find that the spring is too tight and that the gun requires too much effort to trigger.