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Safety -- Make sure you are safe! |
2011-07-11, 7:05pm
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Senior Member
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Join Date: Jun 25, 2009
Location: Southeast MI
Posts: 570
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Fan too strong?
Ok, here goes. I have a fume cabinet 26 x 33 front opening, with back and sides enclosed. Fan sits directly on top of cabinet and has one speed. I have approx 5 feet of ducting (metal, accordian type-eight inch, husband installed and no I couldn't talk him into smooth ducting) with one 90 degree angle to vent out basement window. I'm using NG with one 5 L oxycon. Purchased an inline duct fan with 760 cfms. My makeup air comes from a large window to my left approx 15-20 feet away and I can feel the air coming from behind me when I torch. Problem is my flame wavers alot and I'm constantly chasing it. If I ducted my MU air under my bench to my workspace, would that stop my flame from jumping? It would be difficult if not impossible to raise the fan off of the frame as it was built from a metal shelving unit. I've got a call into my electrician to see if he can install a variable speed switch on the fan, but not sure if this can be done. Maybe it's too powerful or did I get the math wrong? Anyone with ideas?
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Kat
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2011-07-12, 1:17am
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Join Date: Apr 11, 2006
Location: Switzerland
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If I understood your setup correctly, I'd say the problem is the air coming from the side. Ideally it should indeed be coming from somewhere below the table you work on but then again if the incoming flow is too much it may not help a lot.
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Anne
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2011-07-12, 6:08am
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Bringing the air up just in front of your torch would cut down on the turbulence created as the air flows around you and will likely stabilize your flame. You can may be also creating a low pressure area just in front of you that can pull fumes back towards you and increases the turbulence in the flame. The MU air coming up in front of the torch will solve this problem, too.
Robert
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Robert Simmons
(Former) Director for Bead Donations
Beads of Courage, Inc.
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2011-07-12, 6:56am
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Gentleman of Leisure
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Join Date: Jun 10, 2005
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Your math is pretty good for fan size/air flow....
You problem is controlling the turbulence....
Dale
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2011-07-12, 7:15am
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Senior Member
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Join Date: Jan 23, 2006
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Rheostat
I got one at Md. Hydroponics that you plug your fan into
it has a control switch on it with variable speeds.
about 25 bucks.
I'm sure there are other places to get these.
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2011-07-12, 9:50am
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Thank you Ann, Robert and Dale. Sure appreciate it!
Yellowbird: I went to Maryland Hydroponics but did not see this. Did a google search and am not coming up with much. Do you have any other link for this? Do I match my wattage for the fan to the wattage for the rheostat?
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Kat
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2011-07-12, 10:25am
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Ah, never mind. Found some on ebay. Thanks!
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Kat
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2011-07-13, 10:11am
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Curmudgeon Engineering
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Join Date: Feb 15, 2006
Location: Near Seattle, WA
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You might also try to balance the exhaust with the makeup air by adjusting the window opening. Just be careful to not have less air than needed to makeup.
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