We have a Kremlin 20:15 pump that we have been using regularly for about 2 years, spraying PU. Just recently, when spraying any flatish panel or say a fielded door, the underside is getting a buildup of overspray. I have replaced all the gaskets at the fluid tip, etc. and thoroughly stripped and cleaned the pump, but still the problem is there. I have not altered the viscosity of the product.
In theory it has to be a turbulence problem or something to actually coat the underside of the panel when, say, spraying a door edge and face and some have had quite a heavy coat of overspray! It is very frustrating. I even sprayed a simple frame yesterday and found the underside coated in dry spray.
From contributor J:
Check the possibility of ventilation problems, if you are spraying in a spray booth. Also, make sure your atomizing air isn't set too high. This could be putting unnecessary material into your spray area.
I have replaced the filters and given the booth a birthday today. So again I can see if that helps. I am also going to spray a similar item out in our open ended booth to see if I get the same results, as this will take another element out of the equation.
If you are using too high atomization and are spraying on any type of board, whether the panels are raised above the board or not, you will most likely get bounce. If this is the case, try suspending the doors from a rack system or horses to eliminate this from happening.
I also cleaned up an area of bare metal on the booth to provide a good earth, as I don't think where I was earthing from before was any good (but something I hadn't really thought about).
So far the results seem positive, as I did a quick test panel with no problems at all. Many thanks for all your responses.