The Stovebolt Site Forums The Shop Area The Tool Chest Venting spray booth

Hey bolters, soliciting ideas on venting a spray booth. I'm planning on putting up something in the garage, temporary only. I think I'd like to exhaust it maybe 20' from the garage using collapsible ducting. I think I could get by with 8x12x8' high. I will be using a HVLP gun. Any ideas on a fan and duct size?

You’ll want to put inlet filters in as well as have an exhaust fan. A propeller fan may not move enough air. Look for a tubular housing fan that’s probably at least 18 inch diameter and 1/2 horsepower. I don’t know the exact airflow you should shoot for. Homer52 built a paint booth recently. Maybe he can weigh in.

Make sure what ever you use the electric fan motor is outside the exhaust air flow (belt drive) as the air will be combustible and the motor could spark a dangerous flash fire/explosion.

Mike B

Good point on the explosion proof fan. The motor should definitely be explosion proof, and there are three different classes of spark resistant fan construction. Class A is everything is made of non-sparking material (usually aluminum or possibly plastic) and constructed so no rotating part can touch a non-rotating part. Class B requires that the wheel be non-ferrous and constructed to minimize contact with not-rotating ferrous metals (usually an aluminum rub ring is installed.) Class C is constructed to minimize contact between rotating and non-rotating ferrous materials (again an aluminum rub ring is typically installed.) These ratings assume that something goes wrong like the wheel comes loose from the shaft. For short term service, Class C is least expensive and probably fine for what you're doing.

I used 2 electric radiator fans wired up to a 12v power supply outside the booth. Fan motors are sealed to the elements, not sure how well they are sealed to vapor but so far they have been working great and move quite a bit of air.

Ditto on the belt drive fan. I ran a high school auto body shop for several years with an elderly DeVilbiss booth that had a huge fan and flowed way too much air. We had to leave the entry door at the front of the booth propped partway open to bypass some of the air, as it would pull dust through the filters in the doors- - - -12 of them, 2 feet square each. I'd recommend building a temporary booth from PVC pipe and very heavy duty plastic drop cloths, and vent it with 3 foot diameter shop fan, with a bunch of furnace filters straining the dust out of the incoming air. Another sneaky trick is to spray a mist of water on the shop floor near the inlet filters to trap as much dust as possible before it gets to the filters.
Jerry

What would you think about something like this: Axial fan

Dennis

That style might work, but I think that one is way light on capacity. It can only deliver ~1100 CFM at about 1/8 inches w.c. and if you put much ductwork on it, it may deliver way less than that. It's a propeller fan in a round casing, better than a flat panel fan but not by much.

The OSHA requirement for airflow thru a paint booth is 100 FPM, so a 1100 CFM would only be enough for an 11 square foot booth cross section. That might be a little tight to do any painting at little over 3 ft x 3 ft cross section dimensions. LOL.

I have a fresh air mask system so probably don't need all the OSHA specs.

Another part I've been noodling. Venting. I want to route this away from the garage maybe 20'. I'm curious if anyone else has done this and how it was done. Also, do I need to be concerned about static electricity setting things off?

Dennis

I think you need to worry more about spark producing equipment (open brush type motors, ferrous metal blades contacting ferrous metal housings, etc.) than static electricity. Normally humidity has to be real low to produce static sparks. Your fan equipment should be rated spark proof and the motor should be fully enclosed (TEFC - Totally Enclosed Fan Cooled) at a minimum. As far as discharging the vent, vertically would be the best. Get it up where the breeze will dissipate it.

If you put the fan on the fresh air intake side of the booth it's in the clean air and not subject to the combustibles of the exhaust air.

Mike B

Mike, what I'm trying to do though is get the fumes/overspray out of the booth. I will have filters for the incoming air. Seems like I will need to filter the air prior to the exhaust fan so I don't send all that overspray down the line. Not sure how much of that would be trapped though.

Dennis

Mike was suggesting you push the vapors out. Instead of pulling them out.

Knowing what your products like will help, too. The epoxy I use likes to be vented. So I'll do that while spraying. In fact, I've gotten to where I don't use a fan for epoxy and let the natural breeze do the work for me. I crack the tent flaps at both ends just a little bit. It seems to give the best results.

The single stage I use likes the vapors and off gassing to hang around a bit. So I don't vent for 1/2 an hour or more.

I use a half respirator with organic vapor cartridges while spraying (in a tent like Mark does). Works fine for epoxy and enamels (don't smell a thing), but the stain sprayed on my bed wood does make my eyes sting after just a bit. Keeping the tent open helps with that.

I wouldn't worry about overspray getting exhausted. It'll eventually coat the inside of the exhaust system with tiny dots of epoxy. Maybe after 20 years use it'll be uniformly coated.