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Thread: Idiot Stunt or Brilliant Hack - Using DC To Vent fumes

  1. #1

    Idiot Stunt or Brilliant Hack - Using DC To Vent fumes

    So is this a stupid idea, likely to get me killed, or a reasonable way to vent?

    Currently working with a HVLP gun in a two car garage. I've also got a 1 1/2 HP Grizzly cyclone dust collector. I've been putting a 4" collecting duct right next to the project I'm currently working on.

    Downsides:
    1) Probably coating the inside of the flex tube, maybe cyclone
    2) It's a bit awkward
    3) Explosion? I don't think the motor of the DC is exposed to the inner workings of the cyclone chamber.

    Pros:
    1) DC moves ~1000 CFM, and vents to the outside. Currently no other outside ventalation, building is well sealed.
    2) Duct is 20' of 4" flex tube, so I can put it very close to the project being sprayed.

    This doesn't seem much more dangerous than your typical DIY paint booth with cheap box fan. Thoughts?

  2. #2
    What are you spraying?
    --Certainty is the refuge of a small mind--

  3. #3
    Quote Originally Posted by Paul F Franklin View Post
    What are you spraying?
    Currently General Finish High Performance water based poly.

  4. #4
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    From a safety standpoint, if you're only spraying water borne, you can ventilate any way you want. If you are spraying solvent based products, NOPE. But a DC system isn't the most efficient way to vent a "space" because of the way it works. DC is about moving a volume of air at a particular velocity. (CFM) The fan in the DC is designed to do that over a duct system that is within a defined range and with a tool inlet that's the same or slightly smaller size than the duct. You could probably get away with ventilating a small portable spray booth with it, but it's not going to be very efficient otherwise. Fans designed for spray booths are not small things and they work differently than the fan in your DC...they have to move a whole lot more air, too.

    BTW, don't forget about makeup air.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  5. #5
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    In principle it should work but I would filter the exhaust and make up air. You could for example make a small spray booth (frame with plastic covering) in your garage and put a filter between the booth and the DC input. That would take care of the issue of coating the pipe and/or cyclone. If you're just spraying water based products explosion proof is not an issue.

    With 20' of 4" hose you probably won't get 1000cfm

    You should also ensure that the make up air for the garage is not stirring up any dust.

  6. #6
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    Well if you are crazy so am I. I've been using my DC fan to vent my temporary spray booth for well over 5 years. I use a 2HP Grizzly DC/cyclone which moves about 1200 cfm, though I'm sure it's less through the 20' of 5" flex hose I use. But it's still plenty of CFM to pull overspray away from what I'm spraying and exhaust it outside from my approximately 8' x 8' booth. I spray large cabinets and passage doors sometimes, too, but get no overspray on my work which proves to me there is adequate flow. I vent it out a nearby window and have another widow across the shop open for makeup air. You need makeup air. The DC will get it from somewhere so make it from somewhere you want it to come from like a window, not by pulling furnace exhaust back down your chimney.

    I spray shellac and WB products only. Shellac is a risk but one I've done enough calculations on with my set up to be satisfied I'm not going to blow myself up. I use no filters, and advise you against using any; they will just slag up. I have looked inside my DC fan several times and there is no build up or even any evidence of what I've been spraying. I do sometimes get a little build up on the first few inches of the exhaust hose in the back of my spray booth, but it's no big deal and doesn't reduce the airflow. I sometimes get a little white powder outdoors when spraying clear coats or colored powder when spraying paints, but it's not an eyesore by any means.

    Is it optimum? Of course not. Does it work? It does for me. Did it cost much? Zero.

    John

  7. #7
    Quote Originally Posted by Jim Becker View Post
    From a safety standpoint, if you're only spraying water borne, you can ventilate any way you want. If you are spraying solvent based products, NOPE. But a DC system isn't the most efficient way to vent a "space" because of the way it works.
    Yeah, that's about what I'm thinking, but you never know what you don't know until the shops on fire.

    I agree 100% that a DC is not designed for this, but I'm a weekend warrior, and anything else would likely require lots of time and money. Looking at explosion proof fans built for installing in attics, or eaves and they easily hit several hundred dollars. So far I'm spraying every couple of weeks, or a month or so.

    Quote Originally Posted by Jim Becker View Post
    BTW, don't forget about makeup air.
    Okay, what would you suggest here? Obviously it's coming from somewhere, I assume outdoors, which at the moment is rainy. Open the garage door a crack? The garage has no windows, and no doors, and a single 2 stall door on the front. Would it be a good idea to maybe install a sealable vent in the eaves?

    In principle it should work but I would filter the exhaust and make up air. You could for example make a small spray booth (frame with plastic covering) in your garage and put a filter between the booth and the DC input.
    I'm currently using one of the el cheapo converted tents I got on amazon for $40. In the past I've also done a Dexter style kill room, and gone to town. I'm liking the tent, since it should be easily to put up, take down, but it essentially means that the one side is open to the rest of the garage, and there's not a good way to control in/out. Even if there were, there's about room for a dresser or something, and not a person as well.

    With 20' of 4" hose you probably won't get 1000cfm
    Probably not, and there there's the fan curve, ducting, manufacturer lies, blah blah blah. Honestly, I'm using that one since it's easy to do. I've got a short run that's 5' of 6", but it's up against a wall, rather than in the middle of the room.

    Also the sealing of the garage might play into that a bit as well, by making it hard for the make up air to get in to the garage. I've done my best to make it air tight, but obviously something's leaking.

    I have looked inside my DC fan several times and there is no build up or even any evidence of what I've been spraying. I do sometimes get a little build up on the first few inches of the exhaust hose in the back of my spray booth, but it's no big deal and doesn't reduce the airflow.
    Thanks, this was my other area of concern. Glad to know I'm not being too stupid. I'd hate to ruin at $1K DC.

  8. #8
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    Just curious to those using their DC to pull air from spray area; Are you not worried about dust being pulled along with the air across your project? I tried this in the past and had a terrible time with dust nibs getting on my projects. I stopped doing so until after I sprayed and put a barrier around my project, then started the DC again.
    SWE

  9. #9
    Quote Originally Posted by Steve Eure View Post
    Just curious to those using their DC to pull air from spray area; Are you not worried about dust being pulled along with the air across your project? I tried this in the past and had a terrible time with dust nibs getting on my projects. I stopped doing so until after I sprayed and put a barrier around my project, then started the DC again.
    So far I haven't noticed a problem. OTOH, this is pretty far from the project, and I've been working on open pored red oak.

  10. #10
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    How big is your spray area? NFPA states something like 100 linear feet of airflow per minute as a reference to get you to the right order of magnitude, you might get 600 real cfm off of your dust collector hose so that's maybe 2x3 evenly distributed. The evenly distributed is worth noting.

    I often use my miter saw station for hvlp spraying water-based coatings, though I use a different fan when spraying, probably closer to 400 real cfm and ~2x4. It isn't great, but it's certainly better than nothing. You should have some sort of baffle to evenly distribute flow or it doesn't work at all except right into the vent, where it works really well. I use old furnace air filters once or twice til they get too clogged. They also keep a lot of paint out of your tubes and equipment.

    -Steve

  11. #11
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    I would worry about coating the impeller with the sticky spray and dust. This would reduce efficiency of the DC.

  12. #12
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    Quote Originally Posted by Larry Frank View Post
    I would worry about coating the impeller with the sticky spray and dust. This would reduce efficiency of the DC.
    As I reported above, it hasn't happened with mine, over more than 5 years of use and spraying over 100 gallons of various products. Shellac and WB products dry to fine, stick free particles long before they get to the DC impeller.

    John

  13. #13
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    Quote Originally Posted by Steve Eure View Post
    Just curious to those using their DC to pull air from spray area; Are you not worried about dust being pulled along with the air across your project? I tried this in the past and had a terrible time with dust nibs getting on my projects. I stopped doing so until after I sprayed and put a barrier around my project, then started the DC again.

    That's a concern with any spray booth. The type of exhaust fan you use has no bearing on it. But to answer your question, no, I haven't had any problems with dust nibs. In fact, the problem is probably lower with my system over a legit spray booth because the CFM/sq. foot of frontal area is lower in mine, so the velocity is lower which means the air can't support dust particles as well.

    John

  14. #14
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    Quote Originally Posted by Steven Cooper2 View Post
    How big is your spray area? NFPA states something like 100 linear feet of airflow per minute as a reference to get you to the right order of magnitude, you might get 600 real cfm off of your dust collector hose so that's maybe 2x3 evenly distributed. The evenly distributed is worth noting.

    I often use my miter saw station for hvlp spraying water-based coatings, though I use a different fan when spraying, probably closer to 400 real cfm and ~2x4. It isn't great, but it's certainly better than nothing. You should have some sort of baffle to evenly distribute flow or it doesn't work at all except right into the vent, where it works really well. I use old furnace air filters once or twice til they get too clogged. They also keep a lot of paint out of your tubes and equipment.

    -Steve

    Yes, commercial spray booths are designing for something like 100 fpm across the open frontal area of the booth. That gets you to fans that can pull thousands of cfm for a spray booth like mine with a 7 x 7' frontal area. My DC only pulls maybe 1000 cfm, yet it works. How can that be? Well, clearly you don't need 100 fpm if you aren't worried about preventing explosive conditions. I also spray in a way that guides the overspray towards the exhaust, never away from it. I know this all sounds too good to be true, but it works and that's all that matters to me.

    IMG_5496.JPG

    IMG_5497.JPG

    John

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