Spray Booths

Gip, thanks for posting the face velocity criteria. I went through all this about five years ago when I built my last spraybooth, but I couldn't find my reference. So I fell back to a more conservative position. When keeping nasty stuff out of the lungs, more cfm is better than too little. (And since everything but the electrical connections for my booth is scrounged, cost was not an object. Not counting labor, the whole thing cost about $20.)

I have found that a booth that does change room air faster than a 100cfm face velocity is nice to have—sometimes I'm working with things I don't want to breathe on the other side of the room from the booth, and its nice to have them just whisked away. My current booth has a face velocity of 180cfm.

Triarius wrote:

Bud, The fan must be capable of changing the air in your workroom once every two minutes. You determine this by comparing the volume of your work room with the cubic feet per minute (CFM) rating of the fan. For example, a 12 foot by 12 foot by 8 foot room has a volume of 1,152 cubic feet. Dividing by two gives 576 cubic feet. You need a fan with a minimum CFM rating of 576—you probably want a 600 CFM fan.

You've just described a scenario for general dilution ventilation (normal for HVAC applications).  This is great if there is no spray booth.  Actually, air changes should occur once every 15 minutes as a minimum; of course, two minutes is even better since it exceeds the minimum--but now cost becomes a significant factor.  Spray booths, on the other hand, are a type of local exhaust ventilation and utilize different criteria.  A face velocity of about 100 fpm is needed to keep vapors out of the breathing zone of the individual, and to adequately capture and entrain vapor concentrations so that they can be safely exhausted to the outside.  For example, a  2' X 2' face area on a spray booth would need approximately 400 cfm of airflow to adequately remove any vapors (2ft. x 2ft. x 100fpm).  Depending on setup, including exhaust duct diameter, length and number and type of bends, a "fudge factor" of about 25% should be added to account for any resistance and associated static pressure loss (e.g.,duct transport velocity).  Remember that a standard laminar flow booth requires more airflow because it has to overcome the weight of the vapor (All flammable organic vapors are heavier than air).  Conversely, downdraft booths are more efficient because they take advantage of gravity to a achieve the same effect.  That's why they only need about 50fpm face velocity as opposed to the 100fpm listed above.

Hope this helps.

Gip Winecoff

 

Triarius wrote:

MikeV wrote: Is this what you are looking for? http://modelpaint.tripod.com/booth2.htm if it isn't, it should be! Nice catch, Mike!

I have had that one saved for a long time Ross as I wanted to build my own once.
I ended up getting the new Badger spray booth and love it!

Thanks Ross and Jesse,  it all help :) you know........

 

Bud

I bought this one from Ebay: http://cgi.ebay.com/NEW-Paasche-Hobby-Shop-Paint-Spray-Booth_W0QQitemZ8278036531QQcategoryZ28111QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Inexpensive, collapes for storage, works great, all metal so you can't break it.

Jesse

MikeV wrote:

Is this what you are looking for? http://modelpaint.tripod.com/booth2.htm

if it isn't, it should be! Nice catch, Mike!

Is this what you are looking for?

http://modelpaint.tripod.com/booth2.htm

Thanks all

Bud

I built my own, there's a couple of photos here. I went against both point 1 and 2 above; I use a bathroom extractor fan, figured it's got to be used in steamy environments so should be good for me. In either case, it was quite cheap so if it breaks I'll get a new one. I also don't use anything particularly flammable either. As long as I spray pretty much underneath it, it sucks everything out pretty quickly.

Bud,

I may have written that article for FSM, although the subject has been revisited since mine: “A Spray Booth for All Seasons—and All Pocket Books,” FineScale Modeler, Kalmbach Publications, 1989. It is apparently no longer available. However:

Compact Spray Booth by Paul Boyer

Special Bonus Pull-Out Section: Make your own spray booth by Bob Beary

Several others have built their own and posted pictures to the forum—just search on "spray booth" or maybe "paint hood."

The three most important things to remember:

1. The booth must be vented to the outside of your house through its own ductwork.
2. The fan motor must be located outside of the air flow.
3. The fan must be capable of changing the air in your workroom once every two minutes. You determine this by comparing the volume of your work room with the cubic feet per minute (CFM) rating of the fan. For example, a 12 foot by 12 foot by 8 foot room has a volume of 1,152 cubic feet. Dividing by two gives 576 cubic feet. You need a fan with a minimum CFM rating of 576—you probably want a 600 CFM fan.