Try this link.

http://www.asashop.org/autoinc/march2003/collision.cfm

http://dodconf.swri.org/2003Papers/Thelen.pdf

 

Thanks for the great link. The second one was exactly what I was looking for but couldnt find. As it says, even in a booth with pressurised intake the exhaust is tuned to negative. They elude to the laws of physics,, it just couldnt work any other way. Excellent link. I am going to save that one.

 

The old crossflow booths, had a large area of filters for an intake and an exhaust fan blowing the overspray out of the booth. I believe the modern downdraft booths have an intake fan up high, and grates in the floor for exhaust and put positive pressure on the booth to keep dust from blowing out of areas in the booth, and with the exhaust in the floor the overspray and any dirt that does get in gets sucked down to the floor. I may be wrong, but this is how I believe it is. At least thats how I am trying to set up my garage, I have a window in one wall where I am making a large intake fan for with an electric motor powering it and blowing in through a filter, with the motor outside so no paint fumes will get in it, and going to put a few house fans in the opening when the garage door is opened a way, down low with filters blowing out. The house fans are suppose to not have brushes so there isn't much of an explosion hazard except with the switch. Hopefully this will give me a semi downdraft setup, and the only dirt will be what the intake filter doesn't stop. Hope it works, I am tired of trying to paint with a bunch of overspray floating around, house fans don't move much air. The also sell attic fans under $100 if you watch for sales that move a bit of air. New exhaust fans of any size go for a few hundred bucks, and don't have that to spend right now, so gotta try something else. I'll see if I ever get it done. Guess it will be best to experiment with the flow and see what works best.

 

Look at the second link that Huntsman provided. We are getting some terminology mixed up. The exhaust fans do not blow anything out of the booth,, they draw it out. There has to end up with negative pressure on the exhaust side of the booth. Earlier the example was given comparing it to a control room. The only function of control room is to keep dust out, not to remove fumes. I think in a small home fabbed booth it may be difficult to tune wih pressureized intake,, give it a try though. You still are going to need more suction than intake. Thats why they elude in the link that all this changes when the exhaust filters get plugged and that they plug easier than the intakes. I agree with taking the air in from above, its certainly going to be cleaner and warmer. A little review here,, comparing to a central air system in a home. If you notice the duct work is sealed. Its under pressure, it would blow air out all the cracks. A furnace system works on slight positive pressure, but that is somewhat minimized by sucking the room air back thru the cold air returns. This is somewhat the goal with paint booths although the pressures are not exactly equelized as they would be in heating system as you want to remove the fume air. There isnt really a pressureized paint booth,,, if it was it would blow paint all around if the [ressure in was greater than the pressure out. The suck on it is what directs the air flow. These booths should really more appropriately be called pressure assisted air intake booths. I think it would be well worh studying the link Huntsman provided and giving some time to think about the principals of air movement. This is good food for thought here,, lots of guys want to do small booths and need to isolate the heating equipment in the same building. When I take time to tune mine you cant smell any paint while spraying in the rest of the building. For at least one wall some plastic is good,, makes it easy to gauge the exhaust. I think I put some booh pics in my gallery,, if not I will post a couple. The wall construction is very useful especially for small garage as it can be rolled up when not needed.

 

I have some material on booths in my old books from techschool that I haven't looked at for a long time that I will review. I will mess around with the fan setup till it seems to be working good enough. If needed I can put enough fans on the exhaust end by stacking them or putting them side to side. Any kind of air movement would be better then a fan blowing out the door. Getting a air change or two in there would be nice and if I don't have to try to see what I am painting through overspray. I don't know exactly how they are pressurized, but know in the good booths I've been in when you opened the door with the fans on you could feel there was some pressure. I know all about the plastic sheeting, been using that for years and how to attach it to a piece of wood so it can be rolled right up, but I only have a one and a half stall garage that i can empty out when I paint, so will just attach plastic to the walls and ceiling and seal on the floor.

 

Uh oh, better get Maaco!

 

Boy, This one got deep. I think we all ahve a bsic idea on the principles of your basic garage paint booth. We have also discussed engineering and physics. I've been a bodyman/painter for 15 years. Painted in some awesome paintrooms..But as far as producton paintrooms, there are lots of variables. I own a Garmat downdraft. I like to keep slightly positive pressure at the door.Don't have a problem with overspray blowing out. You will find this is probably the most common setting in body shops, Hence why people think they are positive pressure.But it requires constant adjustment . I can control my pressure at the control panel, pending size of vehicle(escort=no pressure , F250 DRW= lots o pressure) filter quality (new or time to change) even varies by wind speed outside (intake on roof ) . etc. You may want to slow pressures down to accomodate dry times or flash times. And last but not least then theres OSHA who says the enter/exit personnel door must close on its own(booth running or not)and it cannot take more than .3 pounds of pressure to open at any time , or some off the wall figure.Now that my friends is where engineering and physics jump in and make the good ol' paintroom a pain in the ..... Just wanted to chime in
Been reading this site for a long time just joined in . Be safe isocyanates KILL...... If you can smell the paint at all you're getting it!!!! Mask up from the time you open the can 'til done.....Of course they can also get in through your eyes...Or you could just paint with you eyes closed...LOL

 

When there is enough overspray you might as well paint with your eyes closed. Thats why I want to get an air supplied respirator. Shops I worked for a couple had homemade booths and none of them cared enough to invest in an air supplied respirator for thier employees, so I've gotten enough exposure over the years. That along with them not paying well at all. That is why I don't waste my time trying to get a job in a shop anymore.