Squirrel Cage Fan as a Paint Booth Exhaust?

tlmartin84 · Sep 10, 2014

I have several large squirrel cage fans with motors. I have been debating enclosing one of these with a return and using it for my paint exhaust fan.

If filtered properly do you guys see any issue with this?

I know this is going to go down to safety/explosion proof fans, but if the motor is out of the exhaust (belt driven) and the bearings are sealed. I can't see any possible issues.

Paint possibly collecting on the blades? good filters should kill the solids, right?

MaxThroughput · Sep 10, 2014

I've been looking into setting up my body shop also. What you're looking for are called "Paint Arrestors" in the biz. They are 98% efficiency, paint collecting exhaust filters.

Kevin54 · Sep 10, 2014

When I painted my Silverado in my garage, I had two windows, one in the side, and one in the back. I had some plywood that was the same height if the squirrel cage blower exhaust side. I opened the garage door, slid the blower under the door, then sealed off the rest of the opening with the plywood. On the windows, I put filters in the openings. Also, I had to seal off the top of the garage door where the opening was. It worked fantastic. It pulled the overspray out and the fresh air in. The filters in the windows kept any bugs from coming inside.

egnorant · Sep 10, 2014

I have a plan for using a squirrel cage for input air. My thought is to have a slight overpressure of filtered air as my booth will be hanging plastic in a shop that is never clean enough for me.

Bruce

creativecars · Sep 10, 2014

The real problem is the chance for explosion. Paint fumes are explosive and using a fan with an exposed electric motor to draw paint fumes over it is not a great idea. Its is one thing to push the fresh air in, but to draw it out wit a box fan can be bad. If you are looking to do this as a business I would not even consider a box fan. You can look up explosion proof fans from many autobody suppliers.

Gerald O · Sep 10, 2014

I built a temporary paint booth from PVC pipe covered with poly sheeting and used a squirrel cage blower to vent it. The blower was mounted outside the enclosure and only used to force in fresh air. You don't want it to circulate the air, so do not use a return. A thin plywood box was made to adapt the blower outlet to an air filter holder. This fastened high up on one end of the enclosure to provide filtered fresh air and to pressurize the enclosure. At the other end of the enclosure, down low, I added exhaust openings to vent to outside the garage door. The exhaust openings were also fitted with furnace filters to keep paint particles from getting out. Poly flaps on the outside dropped down over the exhaust filters when the fan was turned off to prevent reverse flow. This arrangement was essentially explosion proof because no fumes of any sufficient concentration could reach the blower as all fumes were exhausted outside.

Falcon67 · Sep 10, 2014

Use them to pressure the space, not exhaust it. Unless the fan motor is total enclosed explosion proof, you are taking a chance on a fire or worse. When I paint, I use 20" box fans to blow air into the paint space and filters on the exit windows.

TheEquineFencer · Sep 10, 2014

My guess is they are brushless motors. Where's the spark? I've used stuff like this before and I know you're not supposed to "try this at home" or run with scissors.

tlmartin84 · Sep 10, 2014

It's not just the motors in explosion proof fans, it is also about sealed bearings etc.

If the motor is out of the exhaust draw and sealed, I can't see that being an issue.

Nowater · Sep 10, 2014

Let us know if it explodes.

tlmartin84 · Sep 10, 2014

LOL

Reporting here will be the first thing on my list.

A_Pmech · Sep 10, 2014

TheEquineFencer said:
My guess is they are brushless motors. Where's the spark? I've used stuff like this before and I know you're not supposed to "try this at home" or run with scissors.

Capacitor start induction motors don't have brushes. However, the start winding centrifugal switch makes a nice spark when it opens upon starting. There also exists the possibility of faulty connections in the motor connection space causing a spark.

creativecars · Sep 10, 2014

http://www.autobodytoolmart.com/16-explosion-proof-fan-p-12575.aspx

They are not cheap...

16" Explosion Proof Fan
Price: $687
•Single speed, direct drive, 115V/230V, 1/3hp, 1725rpm, 3100 cfm
•16" spark resistant polypropylene blade w/rugged cast aluminum hub
•Sturdy, all welded construction frame
•20" x 20" x 9"
•Corrosion resistant powder coated finish
•Rugged safety backguard
•Totally enclosed fan cooled explosion proof motor with built-in automatic reset overload protection
•Motor is UL listed for Class 1, Group D, and Class II, Groups E, F and G atmospheres

gipp · Sep 10, 2014

I did something very similar to Gerald O, used to fan to blow air into the enclosure. i used one filter for this inlet and two for the outlet. It worked great. All of the over spray was contained by the two outlet filters, the exterior of the both was clean and free of over spray.
I simply set the fan on the floor and aimed it toward the inlet, no ducting.

MP&C · Sep 10, 2014

The "smoke ejectors" that you see on fire trucks are explosion proof, have the aluminum fan blades, all the same requirements of a paint booth fan. These two were at a local auction and went for just over 100 each, they sell for about 2K each new. I'd keep your eyes peeled for similar, or check your local fire dept's for any they may have needing repair.

If you plan on making a booth for more than a one time use, you may as well do it right.

signcrafter · Sep 10, 2014

So if you use your garage as a "paint booth" it's better to blow air into the garage with a fan then to **** air out with a fan? I always thought you wanted to blow the air out of the garage with the fan and fresh air gets drawn in through filters by the negative pressure? But you guys are saying to blow air into the garage to create positive pressure to force the air out of the garage?

Gerald O · Sep 10, 2014

signcrafter said:
So if you use your garage as a "paint booth" it's better to blow air into the garage with a fan then to **** air out with a fan? I always thought you wanted to blow the air out of the garage with the fan and fresh air gets drawn in through filters by the negative pressure? But you guys are saying to blow air into the garage to create positive pressure to force the air out of the garage?

No, talking about using fan to blow into a paint booth, not the garage itself. Don't use your garage for painting without some kind of separation/enclosure--unless you don't care about making your garage and everything in it look like ****.

R6 Racer · Sep 10, 2014

The motor is not in the path of the paint fumes. There will be no "ignition" issues unless you somehow push the fumes up & around the motor.
I use 2 of them in a tent when i'm grinding. I cut 2 holes in the tent in the back corners & have the blowers in the tent with them blowing out. By doing this I have negative pressure in the tent & no dust escapes except whats pulled out by the blower fans & that goes threw furnace filters.
It keeps the dust down to a minimum (hardly any outside the tent) & also keeps the air a lot cleaner. I do still where a respirator tho. It really ***** the tent walls in when I turn them on. I leave the door cracked open behind me that way I always have a breeze blowing through whatever i'm working on.

I dont know weather you want a negative or a positive pressure environment for painting. I think you would want the opposite of what I do & positively pressure your area by forcing in clean filtered air in with your blowers. That would stop you from pulling in contaminants threw any tiny air holes that go into your paint area.

Bottom line, I don't know for sure, but but since it's a belt drive type it makes sense to me that it won't explode. I'm gonna sit back & watch any other answers that come in.
Good luck & let us know what you do do.

tlmartin84 · Sep 10, 2014

Something else...........

These came off of GAS and OIL furnaces. One would think that the risk would have to be minimal.

If I plumbed a draw through unit, the fan will set on the backside of a wall adjacent to the booth. So with the exception of the belt, pulley and shaft, electrical spark will be a non issue in this setup.

My electrical concern is plumbing the lights, not quite sure how to do them. I plan to recess them with plexi over them, all switches will be on the outside of the of the adjacent wall. I guess there is still a possibilty of vapor being trapped between the walls. Again one would think that if the panels were sealed properly there would be very little infiltration as the fan is sucking it out as quick as you are spraying it.

sberry · Sep 10, 2014

signcrafter said:
So if you use your garage as a "paint booth" it's better to blow air into the garage with a fan then to **** air out with a fan? I always thought you wanted to blow the air out of the garage with the fan and fresh air gets drawn in through filters by the negative pressure? But you guys are saying to blow air into the garage to create positive pressure to force the air out of the garage?

You got it, **** out, not blow in.

sberry · Sep 10, 2014

READ THIS. http://finishingacademy.com/training/aero/aero_mod3/aero_mod3_intro.html

creativecars · Sep 10, 2014

It is best to move the air, but with no pressure. In order for one fan or set of fans to move enough air to keep the painting area clear it has to work hard. It is more efficient to have some filtered air pushing in and fan/s pulling air out.

sberry · Sep 11, 2014

Paint Booth Pressure Levels

Much thought has been given to paint booth pressures. Usually this discussion centers on whether the booth is under a negative or positive pressure. Some discussions insist that the booth be held at a positive pressure relative to the outside so that dirt and debris cannot enter the painting chamber and soil the object being painted. This is a serious consideration in booth design and is generally solved by having very good seals on the doors and completely caulking the panels. Others insist the booth be at a negative pressure relative to the outside. This prevents emissions and VOCs from entering the room adjacent to the spraying chamber. Once again, having very good seals on the doors and caulking the panels solve this problem.

I copied this.

Falcon67 · Sep 11, 2014

FWIW - I've done a little of DIY car painting, both siphon gun and HVLP. Fans pushing into the space with furnace filters taped to the back side. The siphon made one hell of a mess, lots of paint on everything and it even got some in tool boxes wrapped in plastic. It even traveled around the building and back into the fans. I keep that gun handy as a reminder to never use it.

The HVLP shooting was typically done in a open shed with a wet floor and same pusher fans. Virtually zero mess, and ended up with a nice finish. No plastic, etc and the painted items would be placed about 10' in from a 16' x 7' opening that faced a gravel driveway.

Only pic I have handy from one of those open shed HVLP shoots:

6768rogues · Sep 11, 2014

When you turn it on, be sure to tell your buddies, "Hold my beer and watch this!"

pepi · Sep 11, 2014

Squirrel Cage Fan as a Paint Booth Exhaust YES and works very well.

My booth uses negative pressure, also keep the air flow at grown level. Eliminating any trash and overspray landing in the paint, the duct is 12 in.

The pictures will give you some ideas, the top of the room was covered with the same plastic as the sides, floor has a drop cloth.

sberry · Sep 11, 2014

Fans pushing into the space with furnace filters taped to the back side. The siphon made one hell of a mess, lots of paint on everything and it even got some in tool boxes wrapped in plastic. It even traveled around the building and back into the fans. I keep that gun handy as a reminder to never use it.

Here we get back to basics. I use a siphon gun but,,,,, again,,,,,,,,, fans pushing in are for a clean room not for evacuating paint or fumes. Pushing in pressurizes and blows paint everywhere, a negative or a draw moves it toward the pull.
Look at the curtains in the above pic,,,, a pull on the room.

Squirrel Cage Fan as a Paint Booth Exhaust?

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