Spraybooth...Too much airflow?

buildit wrote:

"I'm thinking about trying to go with a downdraft design, but that's still under consideration.  I have a feeling that the fan I have may be a bit much..."

Keep in mind that downdraft booths don't need the same amount of airflow as a laminar flow booth does, because the downdraft relies on gravity and heavier-than-air solvent vapors to assist in the work effort (Interestingly, every solvent vapor we use in this hobby is heavier than air, with the exception of water vapor).  Downdrafts usually only need something on the order of about 50fpm face velocity for vapor capture as compared to 100fpm for a laminar flow booth. 

There are, however, some additional design considerations.  In order to even out the airflow, you should consider using some sort of evenly perforated surface covered with a filter to place your model on for spraying. Holes should be large enough to allow adequate airflow.  Holes too small plus a filter will provide quite a bit of resistance to your fan, and impede exhaust efforts.  In addition, adding a small plenum below your surface will provide more even distribution of the airflow within your booth, as it equalizes airflow pressures, and provides for adequate vapor capture equally across the perforated surface.

Hope this helps some.

Gip Winecoff 

Thanks for the input!  Looks like I've definitely got some figuring to do.  I'm thinking about trying to go with a downdraft design, but that's still under consideration.  I have a feeling that the fan I have may be a bit much, but I'll do some more studying then make the call.

Thanks again!

I'm building a booth with the same exact dimensions as you are (24x18x18), but I'm using 2 240 CFM bilge blowers invidually powered.  It'll give me the ability to turn off one blower if two are too much for what I'm doing.

I was originally planning on a 1" deep plenum between the diffusion plate and the back of the booth, but I like the idea of a 2" with an opening escape hatch to cut down on pull-through.

I hope I figure out all the design issues before I sit down to build the thing

-Fred

   What he said....

Gip

Yes, in fact it might be worse to have too much airflow as opposed to not enough. Too much and the paint might not even get to the surface before being whisked away by the air current. Or it might cause the paint to dry too quickly resulting in orange peel or rough surfaces.

Check out this LINK for an article on fan selection.