Paint Booths & Safe Ventilation?

[Miatatom]

Well, I've finished the glove box/paint booth and thought I'd share what I've done. I was hoping to keep the cost around $100 but that was a pipe dream. It wound up being about $240. The size is 2' deep by 3' wide.

I mounted an air filter I had left over from 1:1 work in line with the air regulator. The on/off switch is located next to it. The hose connects through the bottom of the booth on the right side.

The air filter is from WM. I mounted it on the top.

The exhaust port in the bottom is a plumbing piece as are the flanges I used to mount the gloves to the front. I'm using the gloves that veterinarians use for birthing calves. Nice and thin, but one size fits all so they're loose on my hands. To get them to fit tight, I put a vinyl glove on over each one.

The exhaust is 3” all the way. I used 3” I. D./3” O.D. automotive fittings in order to be able to connect and disconnect things quickly.

The hose from the booth connects to a 3” O. D. section mounted in the wall.

Here's the exhaust fan/power supply and hoses all hooked up on the other side of the wall.

I mounted it on an old kitchen chair. The exhaust fan is a 100 CFM bilge pump which is safe for combustible fumes. My brother in law gave me the power supply. He works on computers for a living.

The hose goes from the pump to a device I fabricated. It fits under the garage door and will keep the critters out at the bottom (wifes requirement). Again I used some 3” O. D.

The whole thing can be connected and ready to paint in less than 5 minutes.

No nasty fumes and no respirator needed. I've used it once and there was no junk in the paint job. Now I've just got to learn to paint!

[1930fordpickup]

Wow .

[Cato]

Your place is immaculate Tom. Thanks for sharing many novel ideas.

[AzTom]

The one I have is. Any type fan that the motor is outside the exhaust fumes is good.

Here's mine waiting to be used again after moving. I have had this one about eight years.

[Ben]

The one I have is. Any type fan that the motor is outside the exhaust fumes is good.

Here's mine waiting to be used again after moving. I have had this one about eight years.

Do they make a wider one like that? I build semi truck and the chassis for the tractor or the trailer would need a little over two feet in width to be able set it "inside" the booth.

[AzTom]

Ben, you would have to Google them, I have not looked into current models. We have sunshine 350 days a year so I paint big things

outside.

[Miatatom]

Thanks for the feedback guys. I'll post some pics of the whole place in another thread soon. The room is 12' x 24' so I've got plenty of space.

[Skip]

Your bilge blower is the best non-commercially built spray booth idea that's come up on this forum, it's specifically designed to exhaust flammable vapors out of an enclosed area. As long as it pushes / pills enough air to do the job it's a great idea!

Thanks

[Miatatom]

Thank you very much for the compliment. I calculated the number of complete air changes per minute which would be 12 cu. ft. / 100 cfm which equals one air change every .12 minutes or one every 7.2 seconds. My first test paint job was using MM lacquer. Got some orange peel so I'll try to get just a little closer or slow down or whatever it takes. Trying again tomorrow. We'll see how it goes.

[ScaleDale]

Very interesting design. A closed system is the best defense against dust. Flow rate is important, and I'm impress with the application of math in dealing with this. When I built my open faced booth I watch a bunch of videos on-line and got a kick out of a dude from another model forum who had to rebuild his half way through because his fan was under powered.

Here's the link to the article I used for mine. I have 4 60 cfm computer fans in mine.

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

Dale

[Miatatom]

I had used computer fans in another experiment that failed. Not because of the fans though.

The reason for a complete closed system was the dust issue. Seemed like there was always some junk in my paint jobs and I was never satisfied with them. I used to work at a nuclear weapons plant and spent many hours working in glove boxes so I just proceeded with that design in mind.

I need to find some larger flanges for the front arm ports. The biggest plumbing flange I could find was 5". Makes for some limited movement. I'll find something that'll work. Maybe someone will have a suggestion. That's where I came up with the veterinarian gloves. Someone suggested them and they're ideal. Cheap, fairly durable and thin enough to allow for some feel when air brushing.

[LOBBS]

While I can appreciate the design and execution of the box, the 100 CFM bilge pump is greatly underpowered to properly clear the space even with its downdraft layout. The industry standard is 100 CFM for every square foot of area that the fan has to clear. For your 2' x 3' box you would need a minimum of a 600 CFM blower even before you began adding the exhaust ductwork. The sheer length of flexible 3" hose you're using would add a great deal of airflow resistance. Not trying to step on any toes, it's about safety.

I've attached an article that Klaus Raddatz released years ago about building your own booth and how to properly calculate which motor is required for the size of the box and the attached duct work.

http://www.mediafire.com/?6wffygg65u98eo6

[Miatatom]

The 100 cfm seems to be working fine. I've painted in it 5 or 6 times so far and the inside stays clear without any sort of foggy condition. In fact, I decided to install a false floor above the exhaust vent in the bottom of the booth. I'm using lacquer paint and I was having problems with the paint drying before it got to the model and felt like I actually had too much flow. Your guideline of 100cfm/sq. ft. would mean I'd need a 1200 cfm fan. Since the enclosure is only 12 cu. ft., that would be a complete air change every 0.6 seconds. That sounds like a lot.

[LOBBS]

I can only hope for your safety that the 100 CFM rating listed for your bilge pump is given at an extremely high static pressure and that it's airflow abilities within your system (possibly lower SP) are much higher. The flow rate for this application is not a cubic calculation or the "air changes" that you keep referring to. It is quite simply the square area (in your case 2' x 3' or 6 sq ft) by the desired face velocity or FPM. Because your booth is a downdraft booth you can safely maintain a minimum of 50 FPM which would require at least 300 cfm blower (6 sq ft x 50 FPM) at the static pressure of your total system. Again your bilge pump, given its original application, may be able to support 300 cfm at a relatively low static pressure.

The biggest issue that I see with your setup is that your pump is already questionable and you are using, quite frankly, the worst possible solution for your ducting with those long sections of flexible 3" duct. 3" ducting is already fairly restrictive and the flexible type is around 3 times worse than that. That combination would produce an extremely high static pressure and it is very likely that your pump is not even producing anything close to the advertised 100 cfm. It is all in the article that I posted and Klaus has been a very respected member of the modeling community for a long, long time. With a sealed system like you've built, it is possible that you could be filling a confined space with an excess of volatile solvents (an explosion hazard) and your best warning device (the ole nose) is taken out of the equation.

I've built three booths using Klaus' instructions and they have all served me well for years with no incidences. The only reason I've built as many as I have is to improve on the materials in which they were originally constructed in (spare wood->MDF->sheetmetal) or to tweak minor things that I wanted to add to the previous generation.

Please give the article that Klaus published years ago a read and do the best that you can to verify that you have sufficient "oomph" in your system to safely exhaust the fumes.

Edited June 17, 2013 by LOBBS

[americanclassicmodels]

Hey guys, Caleb here from ACM. I'm in the process of designing my plans for my paint booth. I'm now looking for a good quality exhaust fan, without breaking the bank. It seems that just about every place I've looked at, there prices for the one I need are ridiculous! So, I resorted to looking on Ebay (go figure), I've actually had good luck in the past with Ebay, so I thought, "why not?". Sure enough, I searched and 8" exhaust fan and one of the first things I found was this:

http://www.ebay.com/itm/4-6-8-10-Inch-Duct-Fan-Exhaust-Vent-Air-Cooled-Hydroponic-Inline-Blower-/271175363361?pt=LH_DefaultDomain_0&var=&hash=item3f234fab21

What do you guys think? Its actually for gardening I think, but at the end of the day its still exhaust fan, its also compatible with the same diameter carbon filter.

8" exhaust fan:

110v/60 Hz.

47.7 watts

current: 120 volts

400 CFM

I hope this can be some help to someone else who's trying to find a good fan for their paint booth. Always glad to help. This fan is only $38 dollars I think, so not too expensive, its also a simple plug in and go fan too!

Thanks for looking, and since I'm new to the forums, please add me as your friend!

[Bobdude]

You could ask the seller if the fan is explosion proof.

[americanclassicmodels]

That's a good idea. Since it is an enclosed motor, meaning there aren't any exposed wiring, you would think it would be explosion proof. But it wouldn't hurt to ask. Thanks for the tip!

[ScaleDale]

This isn't really designed to be directly mounted to the paint booth. It would go in a duct leading out to a window or something. I looked at something like this to vent my garage where my booth is. For a booth fan to be safe it needs to have a brushless motor so that it won't generate sparks. Mine uses four computer fans. There are "squirrel cage" blowers that are commonly used with home paint booths. I can't recall the name, but searching Amazon or Ebay for that term will show you what I mean.

Find the other recent paint booth thread and read the link I posted to the best article on the subject.

Dale

[americanclassicmodels]

Thanks for the heads up. Mind I ask, how do you have yours set up? The computer fan is probably what i'll go with, because I already have a bunch of them I can get. Whats your booth look like? I'm trying to get some ideas together. Any help would be appreciated.

[ScaleDale]

Here are the pics I took while I was building my booth. The fans are 60 cfm brushless 120 volt from Radio Shack that were around $30 each. The wiring isn't super neat but it's all soldered and sealed up tight so I'm not worried about sparks. It uses a 16X20 furnace filter that is good for around three or five projects before I change it. It isnt vented because it's in the garage on my other workbench for building wood stuff. I put a high velocity fan in the window to vent the paint fumes when I paint and the combination seems to work well enough for me. I'd like to vent it to the outside but that won't work now. It's adapted from the one in that link I posted in the other thread. I was about to go looney from watching YouTube videos of people talking about spray booths when I found it. Solid info.

Dale

Pics:

[Miatatom]

Thanks for the feedback, Kyle. I took the time to really study the article in the link you suggested. I've already moved the lights. My booth is all wood with a glass window. Since the biggest safety concern is explosions, eliminating all sources of sparks should remove that hazard. Is there something I'm not taking into account with that reasoning?

As for the flexible ducting, I can see that it's very restrictive but I've got to have a system that can be taken apart and stored. I'm going to study that situation more and may be able to come up with something.

[americanclassicmodels]

Thanks for the pics man! This really helps out alot!

[LOBBS]

Absolutely no fault to that logic. As I said before, I think it's a brilliant design. Safety is the top priority and if you can eliminate the ignition risks and ensure that your system can keep the box cleared of fumes you are golden.

[Aaronw]

While I can appreciate the design and execution of the box, the 100 CFM bilge pump is greatly underpowered to properly clear the space even with its downdraft layout. The industry standard is 100 CFM for every square foot of area that the fan has to clear. For your 2' x 3' box you would need a minimum of a 600 CFM blower even before you began adding the exhaust ductwork. The sheer length of flexible 3" hose you're using would add a great deal of airflow resistance. Not trying to step on any toes, it's about safety.

I've attached an article that Klaus Raddatz released years ago about building your own booth and how to properly calculate which motor is required for the size of the box and the attached duct work.

http://www.mediafire.com/?6wffygg65u98eo6

You've miss read what the sq ft relates to. It is not the size of the working area, it is the size of the opening. It may seem a trivial difference but has to do with the velocity of the air not simply movement, both are moving 100 cfm but the larger opening allows for slower moving air and areas of little movement.

If a closed 2x3 ft working area only has a 14" x 20" opening (fairly standard size filter) then you are looking at 1.9 sq ft, not 6. 1.9 x 50 (downdraft) would put the 100 cfm fan at the appropriate size.

I would be concerned that the 3" ducting is inadequate though and could be restricting the blower from seeing its full potential. I picked up a section of 6" metal flex duct at Home Depot, it is cheap, easy to use and provides for very little friction loss.

Here is an easy to use online airflow calculator. If you use it you will see that the 3" duct has 4x the restriction of a 4" duct and 30x the restriction of a 6" duct.

http://www.engineeringtoolbox.com/duct-friction-pressure-loss-d_444.html

[Aaronw]

Thanks for the feedback, Kyle. I took the time to really study the article in the link you suggested. I've already moved the lights. My booth is all wood with a glass window. Since the biggest safety concern is explosions, eliminating all sources of sparks should remove that hazard. Is there something I'm not taking into account with that reasoning?

As for the flexible ducting, I can see that it's very restrictive but I've got to have a system that can be taken apart and stored. I'm going to study that situation more and may be able to come up with something.

Everybody gets hung up on looking for ignition sources. The #1 priority should be on avoiding a flammable atmosphere in the first place (keeping the vapors to lean to burn). This is really why most people get away with a homemade booth using a bathroom fan or other "inappropriate" vent fan. They have adequate ventilation so never reach the lower explosive limits of the paint vapors. The only paint booth fire that I have seen posted with details, involved an individual using a shop vac for the blower. The cannister makes for an excellent bomb by collecting the vapors until they reach a level that will support combustion.

I advocate using an appropriate fan, but as long as the fan selected provides adequate ventilation there is minimal danger from using the wrong fan. Obviously the right fan and adequate ventilation is a better choice.