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| Static pressure spray booth http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=11699 |
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| Author: | Louis Freilicher [ Tue Apr 17, 2007 2:47 pm ] |
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I'm looking for a fan to build a spray booth around and with the prices of explosion proof fans I was thinking about trying to build a static pressure booth instead. The fan would be located outside the booth (inside the shop) and blow instead of suck. There would need to be a vent to the outside, close to floor, to allow fumes to be pushed out. With the fan motor separated from explosive vapor I could use any old fan that can move enough air to clear the air in a timely fashion. My planned booth will be pretty small, aprox. 5" x 7" x 7” with acrylic or Poly-something roof and window(s) to keep the lighting separate as well. Anyone run a set up like this? What am I missing? Thanks for sharing! Louis |
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| Author: | Bruce Dickey [ Tue Apr 17, 2007 10:05 pm ] |
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That ought to work. |
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| Author: | crazymanmichael [ Tue Apr 17, 2007 11:35 pm ] |
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i think if you research it you will find that it would take a much larger fan to push the required amount of air to develop a pressure high enough to give effective exhaust air streams, with the attendant higher noise levels, space requirements, filtering, etc.. explosion proof fans are only necessary if you are going to be using nitro, or a similarly inflammable finish. if you are going to be using a waterbourne there is no explosive issue. have you been checking ebay. when my old fan motor went belly up last year, i found a nos explosive proof fan on ebay for less than half the retail cost. unfortunatley not long after i was also able to pick up a nos replacement explosive proof motor for a ridiculous $9.99. with s&h less than $20. there are bargains to be had out there. if you can look long enough. |
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| Author: | Bruce Dickey [ Wed Apr 18, 2007 12:18 am ] |
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[QUOTE=crazymanmichael] i think if you research it you will find that it would take a much larger fan to push the required amount of air to develop a pressure high enough to give effective exhaust air streams [/QUOTE] I'm no engineer, but this doesn't make sense to me. If a fan sucks 2600 Cubic Feet of Air a Minute through a 2 foot by 2 foot hole, wouldn't the same fan push 2600 Cubic Feet of Air a Minute out a similar opening? I think the original idea would work fine. |
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| Author: | crazymanmichael [ Wed Apr 18, 2007 1:03 am ] |
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close, but not quite, if they are connected by a short tube of the same dimensions. when separated by a plenum , no. turbulence and friction and laminar flo issues affect the flow markedly. |
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| Author: | crazymanmichael [ Wed Apr 18, 2007 1:06 am ] |
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do wish we still had our edit button!!!! think about dust collection, and the role of friction, changes of direction, and the size and smoothness of duct walls in the design and sizing of dust colletion systems. the issues are mush the same. |
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| Author: | Barry Daniels [ Wed Apr 18, 2007 1:50 am ] |
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Moving air by blowing just doesn't work as well as sucking it. You don't need an explosion proof motor. A totally enclosed fan cooled (TEFC) motor is adequate. Explosion proof electrical conduit and fittings are very expensive. I got my fan from Graingers which has good pricing as well as replacement parts. Much recommended. |
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| Author: | Louis Freilicher [ Wed Apr 18, 2007 11:10 am ] |
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Thanks for the info and tips. I do spray nitro and I want to get the set up right the first time. I've missed two fans on eBay recently, out bid by a few bucks at the last minute. Persistence... I'll also look into separate motor and fan possibilities. Louis |
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| Author: | Bruce Dickey [ Wed Apr 18, 2007 2:14 pm ] |
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I bought an explosion proof fan/motor on Ebay for $75 used. Missed a new one for that much as well, couldn't get the shipping price in time to bid. Nitro go boom. Better safe than sorry. |
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| Author: | Kevin Gallagher [ Thu Apr 19, 2007 1:30 am ] |
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If you're spraying nitro lacquer you must have an explosion proof fan...even if you're only spraying one guitar at a time. I've seen the aftermath of a vapor explosion in a finishing booth and it's not pretty...and always injures someone in some way. A fan that is designed to remove a particular amount of air from a room as an exhaust unit will not remove the same same amount of air from the same room as a draft unit. With the exhaust application having a focused port of exit, a real draft is creatd across the spray booth between the fan and air allowance or entry ports. This draft is what gives us such a predictable overspray and VOC removal process. I never want to even get a whiff of my finish since that means it has made its way into me. Solvents can cause some very serious physical and medical problems that can affect your life in dramtic ways....or kill you in the long run. My Grandfather died from cncer that was suspected to have been caused by carless spraying of lacquers and in dicriminate use of solvents for cleaning of parts and even washing his hands to remove glues and finish materials from them. When the same fans are mounted to feed air into the room with the intention of it exiting through a predetermined port, the draft will be much less focused and powerful so there may be VOC and overspray buildup in the booth inspite of the intended ventilation efficiency. Bottom line....you need to pull the air out to actually get it out in the most timely manner. Pulling it also allows you more effectively determine your position in the booth in relation to your work and you gear. Those static situations create exactly what the term implies...static areas or areas unaffected by the draft where things can hang and not be removed very quickly. I have an explosion proof fan and lighting in my booth that cost me very little on eBay about ten years ago. When I step into my booth, I'm covered...including heavy pigmented gloves and an outside air supply unit that a friend of mine is in the patent process for. The UV cured stuff that i use is the most noxious and sickening smelling finish I've even been around, not to mention that MEK is the solvent media in it. It's nasty smelling and very hazardous. Regards, Kevin Gallagher/Omega Guitars |
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| Author: | Kevin Gallagher [ Thu Apr 19, 2007 1:35 am ] |
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Louis, I forgot to mention your lighting idea. My old booth in my old shop had a clear ceiling that was gasket sealed and allowed me to have regular lighting fixtures outside of the booth that worked well to light it. That can save you a good number of dollars and still give you good results. I also have friend who has been in the auto finishing business for decades. He has several lighting units that are simple lighting fixtures mounted on walls an enclosed by acrylic or plexiglass boxes that are sealed and airtight. He uses them as reflective reference units when he's spraying critical vertical panels and things. Regards, Kevin Gallagher/Omega Guitars |
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| Author: | Louis Freilicher [ Thu Apr 19, 2007 3:41 am ] |
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Thanks for the info Kevin. I was in the process of over engineering my booth without fully understanding the principles at work. I'm still a few weeks out from my spring shop overhaul so I will keep my eyes and ears open for the right fan. I am toying with the idea of incorporating a drying room or cupboard with a separate smaller exhaust to vent out gassing fumes once the spraying is done. Do you think that a medium or large bathroom type exhaust unit be OK for this application? Louis |
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| Author: | WaddyThomson [ Thu Apr 19, 2007 3:54 am ] |
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Make sure you check around at industrial auctions, etc. I know my son, who runs a cabinet shop, bought 2 complete spray booths (portable, commercial types, big enough for finishing cabs) for a total of about $500. |
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| Author: | Barry Daniels [ Thu Apr 19, 2007 3:56 am ] |
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Explosion proof (NEMA 7) in engineering terms means that all electical components are housed in enclosures that can contain an actual explosion. The wiring has to be in metal conduit with putty seals at specific intervals to prevent an explosion from travelling along the conduit. This is what's required in refineries and other hazardous environments. I think it is overkill for a home shop as it's VERY expensive. What I was suggesting was SEALED units such as the Totally Enclosed Fan Cooled (TEFC) motors to drive the fan. The fan should be spark proof which usually requires it to be of cast aluminum material. When most people speak of explosion proof exhaust booths, they are actually talking about sealed motors and/or lights so the term explosion proof is probably being misused in this context. |
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