I am just getting aquainted with a 3 stage GRACO turbine HVLP spray unit. Once you get the hang of them - they are GREAT! The air from the turbine is heated so the gun handle gets quite warm. The atomization of the paint is unbelievable. I am practicing by painting an old Jetta for starters. Here is what I have found so far:
1) The HVLP lays down a coat that is smooth as glass - no problem. HOWEVER - get any speck of dust in the air and you will see it in the finish. A dustfree spray area is a MUST.
2) The HVLP laydown is so smooth - ANY imperfection in the body work will be magnified. Sanding with 400 grit paper, washing with paint prep and finishing with a tack rag MUST BE DONE. To that end - more attention to prep body work, priming and sanding must be done to get the proper finish.
So far the HVLP Turbine unit is much easier to use than the old spray guns and there is very little paint in the air from spraying. My automotive paint supplier used to sell me 1 gallon of paint to paint a Jetta with the old style regular guns. Two quarts of paint will do the same Jetta with the HVLP without even trying to be cheap with the laydown. 70%-90% of the paint goes on the car as opposed to 30%-40% with the regular air spray gun.
So far I am very impressed with the HVLP gun.
I have read about the HVLP conversion guns that allow you to hook up to a compressor instead of a turbine unit. My only thoughts on that are:
1) make sure you have the volume of air at the right pressure going to the gun from the compressor or you will get orange peeling.
2) make sure you have an oil and water trap on your air line to remove these contaminants before they hit the gun.
3) I like what the heated air of the turbine does to the paint atomization and laydown - I don't know if cold compressor air will give the same effect.
These are my thoughts on HVLP spraying for DIYers. Hope they are helpful