Sciencemadness Discussion Board

Fume cupboard motor

Saber - 26-8-2009 at 02:55

Hey people, i am selling this on ebay;

http://cgi.ebay.co.uk/Fume-Extractor-Ventilator_W0QQitemZ230...

Its a motor which we used for our attic but i realised could be perfect for a DIY fume cupboard.

Happy bidding!

kclo4 - 26-8-2009 at 09:56

Its actually not great for a fumehood. You don't want the gases to go over the motor as they will damage it, and may ignite.

I think the motor and setup of a swamp cooler is really the most practical thing to use if you are making a fumehood from various junk. The motor is out of the way, and I think all you'd need to do is pretty much direct the pull with a piece of wood so the vacuum can be directed using an attached hose or something...

Saber - 26-8-2009 at 11:44

The motor is sealed in a airtight plastic case in the middle so it is only the plastic casing that contacts the gasses.
I am not sure as to whether it is sparkless but that can be solved with a bit of silicone gel here and there.

kclo4 - 26-8-2009 at 13:42

Oh really? Well that is interesting, seems like the plastic would cause it to over heat or something.
odds of ignition is probably very unlikely anyways..

Saber - 26-8-2009 at 14:10

yep it looks pretty airtight to me. no vents or anything... i guess they dont want dust getting into the motor?
yea, this thing is pretty dam powerful, the flammable gas wouldnt be able to make the right % with O2 before its out the house...

watson.fawkes - 27-8-2009 at 08:22

Quote: Originally posted by Saber  
yep it looks pretty airtight to me. no vents or anything... i guess they dont want dust getting into the motor?
yea, this thing is pretty dam powerful, the flammable gas wouldnt be able to make the right % with O2 before its out the house...
Dust-tight is a lower standard than fume-tight. The hazard is that fumes seep inside the motor body, ignite, crack the motor case, and thus expose the innards more intimately to the gas flow. It would be a second ignition from a damaged motor, a failure that wouldn't be quickly detected because it needn't cause the motor to stop turning, that would be the real problem.

Saber - 27-8-2009 at 08:25

Yes but if you consider the fumes are traverling at great (and trust me this thing is fast) speeds, they barly have enough time to do anything, contact time with the palstic will be seconds... thus dust-tight is fine!
By all means if anybody lives near and would like to pop over to take a look ect. be my guest.

watson.fawkes - 27-8-2009 at 08:51

Quote: Originally posted by Saber  
Yes but if you consider the fumes are traverling at great (and trust me this thing is fast) speeds, they barly have enough time to do anything, contact time with the palstic will be seconds... thus dust-tight is fine!
By all means if anybody lives near and would like to pop over to take a look ect. be my guest.
I should point out that if the atmosphere being exhausted has a constant percentage content of flammable solvent (say, or corrosive, or whatnot), that the flow rate matters absolutely nothing with respect to the question of what will seep into the motor.

There's a reason for the existence of explosion-proof motors, and a reason why they're expensive.

Saber - 27-8-2009 at 16:30

Yes i agree there is always a risk. That is why i would never use something like this as a fume extractor for things like acetylene with a wide explosion % but the exhausted air will never have a constant % so for things like ethanol you should be fine.

entropy51 - 27-8-2009 at 17:08

Quote: Originally posted by Saber  
Yes i agree there is always a risk. That is why i would never use something like this as a fume extractor for things like acetylene with a wide explosion % but the exhausted air will never have a constant % so for things like ethanol you should be fine.


Holy hotdogs, this thread is worse than the other one.

Why would you need a fume hood for ethanol?

It's a shame stupidity isn't painful.

Mr. Wizard - 27-8-2009 at 17:42

Perhaps some of our less experienced members should familiarize themselves with what LEL ( Lower Explosive Limits) and UEL (Upper Explosive Limits) mean. The explosive range of ethanol is 3.3 % to 19.0 % , more than twice that of gasoline's 1.4 to 7.6.% volume in air.

http://en.wikipedia.org/wiki/Lower_explosive_limit

I recommend finding out before you get the surprise of your life. At 20C it has 100 mm of vapor pressure, so it will be 100/760% by volume. So it will be at 13% by volume. It sounds like the perfect combination for an accident.
http://en.wikipedia.org/wiki/Ethanol_(data_page)

Explosive limits doesn't mean it will explode, just that a flame will propagate through the volume. Then the increase in volume will make it seam like an explosion.

Please... no hot motors, no motors with brushes, no motors with starting switches or anything electrical in a fume hood. These rules have been learned by hard experience, no sense in relearning them the hard way.

S.C. Wack - 27-8-2009 at 18:10

As I've pointed out before, the original fume cupboards were powered by flame. Then ordinary fans. This was suitable for a long time.

If you're having explosions, you need to either stop pouring stuff on the floor of the box instead of in glassware, use coolant with your condenser and receiver when distilling ether or acetaldehyde, or get a bigger fan.

kclo4 - 27-8-2009 at 20:16
Quote:

Please... no hot motors, no motors with brushes, no motors with starting switches or anything electrical in a fume hood. These rules have been learned by hard experience, no sense in relearning them the hard way.


Why does my fumehood have wall outlets in it then? :D

Must not be made for flammables?

watson.fawkes - 28-8-2009 at 06:07

Quote: Originally posted by kclo4  
Why does my fumehood have wall outlets in it then? :D

Must not be made for flammables?
That's right, it's not made for inflammables.

Look I have no problem with people using inline fans in a fume hood as such. What I have a problem with is people claiming that such fans are without danger. If you use an inline fan, or have spark sources (e.g. outlets) in your hood, then you really don't want to put inflammables up the flue. And I don't mean "intend to put"; I mean "actually put", which means planning for the eventuality of an accident, such as, oh, glass breakage during a solvent distillation.

If anybody wants to disregard the risks and do it anyway, whatever; I'm not your mother. But do not go claiming that doing is Just Fine and thereby mislead others. The line between your nose and my fist is that between putting yourself at risk and encouraging others to do so, even if implicitly.

S.C. Wack - 28-8-2009 at 18:36

Quote: Originally posted by watson.fawkes  
The line between your nose and my fist is that between putting yourself at risk and encouraging others to do so, even if implicitly.


An idealist assaulting pragmatists that they've never met, because they reject idealism? Shocking.

not_important - 28-8-2009 at 22:30

Quote:
Why does my fumehood have wall outlets in it then?


That's interesting, the fumes hoods I'm familiar with would have locking outlets if those were interior to the hood, conventional wall outlets exterior. The locking outlets aren't likely to be accidentally disconnected, so no sparks from that; you could of course plug something in while flammable vapours were present, but you also could bring a lit road flare into the hood too - can't completely guard against stupidity.

And outlets in the hood avoid having power cords for heating mantles and mag stirrers draped over the front, where they are more likely to be accidentally snagged. I'm remembering that those items intended for use in the hoods had the locking plugs on them, and were certified as being non-sparking. There were no locking-outlet to standard-plug adapters in stock so it was hard to cheat and you'd likely get chewed out if caught with cords dangling out the front of the hood.

Contrabasso - 6-9-2009 at 04:03

OK I'll let this forum debate the venturi principal!

Take a cheap air moving fan and direct it into the input of a venturi made from plumbing pipe, use the venturi suction leg to draw air and fumes from the fume cbd vent the fumes in a safe way!

This way the fumes, corrosives or flammables do not pass through the fan and motor.

Scale it to your needs!

Magpie - 6-9-2009 at 08:49

Here's my previous contribution on the venturi idea:
Quote:

Before I gave up and bought a blower I did try to build an air driven jet suction device based on the venturi principle as used in an aspirator. This was suggested in Ammen's book on refinining of precious metals. But he only gave a crude sketch, no details. In the 3rd picture of mine (above) you will see a number of PVC pipe pieces by the cabinets. Those are from my experimentation in this area using my old household electric furnace blower as motive air. I did manage to create some vacuum (0.5"H2O) but the system was not nearly sufficient to move the large volume of air needed for a fume hood (my blower draws 400-500 cfm @ 0.75"H2O pressure drop). Commercial jets are available that are commonly used at construction sites for their portability and ease of setup. The only utility needed is a source of high pressure air (~90-120psi, IIRC). They move a lot of air. They are also, I understand, quite noisy.