building a spray booth fan

[Jeremy Patrick]

Hello folks,
Have a question aimed at building a fan setup for a garage spray booth. Have seen a decent number of posts and search results that show the cost of explosion proof fan units isn't exactly on the low cost side.
But... I do have a couple of electric motors on the shelf, one might even be explosion proof if I remember the plate info right. I think that one is 1725 rpm. Other one is 3450 which seems a bit overkill for a small booth.
Although some of the comments I've seen mention using a regular non EP motor/fan, my pyro interests aren't wanting to test the poof possibility, even if remote...

Was thinking even if the motor isn't rated as such, the concept for having the motor separated so it's not in the direct airflow of the flammable aerosol is the goal right?
Based on that, I was figuring that a fairly simple box could be constructed to hold both the motor (in a separate space) with a slot to allow the belt through to the actual fan blade assembly.

If this idea is going along the right line, then the needed items would be the receiving belt wheel for the motor and a belt driven blade assembly. The latter is something I'm not quite sure where to get, or where to search to get.
If anyone has a minute to comment and or suggest on this,

Thanks!

[Adam Herman]

if you can use a squirrel cage type, many older hvac fans are belt driven, I see them quite often at our local salvage building supply place. otherwise you are probably looking at finding something on craigslist. I would check out any of your local salvage places first though. I see that the large metal fans for shops and such are generally belt driven as well.

also: http://www.homedepot.com/p/Cool-Atti...2SPD/203931021

[David Kumm]

The motor can be isolated and drive the impeller by belt. Just make sure you get it big enough to supply the proper cfm- I think about 100 cfm per sq ft but verify. My table top 3-5' bank of filters is srun with a 12" fan and .75 or 1 hp motor. Dave

[Chris Padilla]

What are you spraying? Sometimes a three-fold of cardboard, a cutout with a filter and cheap box fan behind the filter might be good enough.

[Jeremy Patrick]

Items would range from room trim pieces, small hatch door, more or less smaller items. Stain, lacquer, paint depending on what is needed.

Aside from the fan I know I'm limited for what I can do given the colder temps approaching. Garage is an outbuilding and the only source of heat is propane. Have heard people warm the place up, turn off the heater, spray, then after a bit turn the heater back on. Will see what I can manage to do as winter approaches.

Anyways, I might have a squirrel cage fan that is already ready to rock. As long as the CFM is equal or a bit more than 100, in theory it should be fine? Don't remember off hand but it's not a small unit. I suppose something too big is going to send me the other direction and alter the way I'm spraying?

What is the general advantage of having a cage fan vs an aluminum prop/belt type setup (aside from part cost to build it?)

[Adam Herman]

centrifugal (squirrel cage type) fans can create a higher pressure difference between the in and out. radial can create more flow. radial is generally more power efficient per cfm than centrifugal. I am not sure it will make a big difference in this application.

[Charles Lent]

Consider the possibility of drawing clean air in with the fan(s) instead of drawing it out. I used a large fan (old attic whole house fan) in a rear window of a 1 car garage, with pleated filters on the window side of it to keep from drawing in pollen, leaves, etc. and sealed the window around the fan with cardboard and duct tape. Then I just opened the garage door a foot and put about five 12 X 20 fiberglass furnace filters between the concrete and the bottom of the door and sealed around them with more cardboard and duct tape. I clamped the door to keep it from moving with a pair of vice grips in the track. Then I sealed around the edges and top of the door with more cardboard and duct tape. I then wet the floor before spraying to keep the dust down and sprayed a little more during the day to keep it wet. This is a lot of trouble to do all of this if you will frequently need it for a spray booth, but for just one or two times it will do a pretty fair job. I was quite satisfied with my paint job, and I didn't need an explosion proof fan. Keeping a positive pressure in the garage kept small leaks from scattering dust in the air too.

Charley

[Jeremy Patrick]

Am I seeing the concept right though in that the fan is being used to generate just enough cross-airflow to draw away vapors and particulate from the spray area?

My garage isn't huge (1.5 car from the 50's, so nothing close to modern sizes) but from you wrote Charles I wondering if it would be worth it to make a back corner of the garage (with a close window) a semi dedicated area to work with. I'm not going all out full time with tons of items to spray, but if I can work with the temps in the winter I'd like to tackle a couple dozen items.

Trying to think out ideas for best using the cage type fan (since I have it), mounting, airflow etc.

[Wayne Lomman]

Charles is on the right track if you don't have explosion proof motors. Set it up to push the air in. You will need to have the area more or less sealed so that the spray mist laden air goes out where it should. The key is to have air flow. If you position your air intake the right way, you can run a heater to warm the air on the way in. Also install a flap so that when you shut down, air/ fumes don't drift backwards. Cheers

[Mark Kornell]

Jeremy,

I did exactly what you are considering. I purchased a barn exhaust fan/motor unit and decoupled the motor from the fan. Left the fan in its cage but moved the motor out of the airflow. Used pulleys to drive the fan - and you can always choose pulley sizes to get a specific fan rpm from a motor.

The motor got isolated in its own box with only small slots to allow for a belt to pass through.

I also built a frame in front (in side) of the fan to hold air filters. Figured I should try to take some particulate out of the air stream before exhausting it.

It seems to work very well. There is fairly strong airflow in the spray booth. And little evidence that particulate is free to escape.

Sorry, on vacation right now and can't provide pics.

[John TenEyck]

As mentioned, if you push the air into the room then you have no worries about explosion. Also, the filters in front of that fan won't get clogged up with overspray. Simple is good. Or you could go to waterborne finishes and do anything you want, safely.

For those who think it's fine to use a non-explosion proof setup with solvent finishes, you may want to reconsider that because if you do have an accident your insurance company may deny coverage.

John

[Wayne Cannon]

Just be certain that the slot for your belt is on the intake (suction) side of your fan so fresh air enters the slot rather than fumes exiting the slot.