fume hood venting system

samuel-a · May 19, 2011

I would like to get some input from you guys on this makeshift venting system that i'm planing to install.
It soppose to scrub only vapors and let gasses rise up to the outlet hole.

Any thoughts? pro's, con's...

Thanks, Sam

goldenchild · May 19, 2011

Samuel,

I too am wanting to build a fumehood whenever I get the room for it. What will you be using as the blower? I am having trouble finding a good blower. This website comes highly recommended by GSP but I'm not paying $1000+ for a blower.

http://www.usplastic.com/catalog/search.aspx?search=blower&page=1

element47 · May 19, 2011

That looks pretty clever. One thing I would recommend considering is to adapt to a larger diameter output pipe. That would reduce backpressure and enhance your venturi effect. Easy, just a 4 >5 or 4 >6 adapter.

I looked at the squirrel-cage blowers shown at the link you provided. I don't see any reason why those are so bloody expensive. For $1K+++ you could buy one heck of a lot of $40-$50 squirrel-cage blowers which would slowly but relentlessly become destroyed by acrid fumes. I see that your fumes aren't being drawn through the blower cage itself, which IMO is a neat idea.

http://www.surpluscenter.com/electric.asp

http://www.surpluscenter.com/sort.asp?catname=electric&keyword=EBSA

(just the first things that came up when I googled "surplus squirrel cage blower")

Your challenge would simply be to find or fabricate the mating flange from the blower output to your "sewer" pipe which can handle being taken apart and put together many times as the blowers die and get replaced. You'd have to make that adaptation anyway, even with the $1K blowers. If you look at many models of surplus blower, you'll find across several brands they have a small collection of different output flange sizes. <<The implication is that for any given size of adapter-flange you come up with, you would not likely be confined to only one brand, one model of blower. (Important if you are buying them surplus!) There are a dozen manufacturers of blowers that have a 3" output flange or 4" output flange, for example.

jimdoc · May 19, 2011

Problem is you don't want them to fail, because when they do it will be at the wrong time. It is better to set it up to last, and be safe.

Jim

element47 · May 19, 2011

Point well taken. Buy 2 fans!

Is the idea to have the glass marbles just wetted with water (or akaline solution) or to have a full charge of water in there as it would be in a normal sink-drainpipe installation? How do you propose to control how much liquid is in there?

samuel-a · May 19, 2011

Mario, the idea is not to use expensive chemical resistant Blower, because nothing of that nature will pass through it.

I still don't know the required CFM, but the marbles are not suppose to be immersed in water/basic solution (though possible), just to provide large surface area for fumes to condense on.

samuel-a · May 19, 2011

jimdoc said:
Problem is you don't want them to fail, because when they do it will be at the wrong time. It is better to set it up to last, and be safe.

Jim

Agreed, that's exactly what happend to me the last time...

glondor · May 19, 2011

One of my contacts repairs furnaces. He gave me a blower motor from a furnace. This is what i will use for my hood. Variable speed up to 1200 cfm. Something like this.

http://www.google.ca/imgres?imgurl=http://furnace-blower-motors.co.cc/images/41sTd40qzIL._SL160_.jpg&imgrefurl=http://furnace-blower-motors.co.cc/&usg=__mN1QBz3ENysGKzQgr4tA3uLyOOY=&h=150&w=160&sz=6&hl=en&start=50&zoom=1&tbnid=er3yCcH9OKNw6M:&tbnh=120&tbnw=123&ei=0bjVTZLeO4Hj0QHEjOnCBw&prev=/search%3Fq%3Dfurnace%2Bblower%2Bmotor%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D853%26bih%3D560%26tbm%3Disch0%2C1666&um=1&itbs=1&iact=hc&vpx=658&vpy=201&dur=5193&hovh=120&hovw=128&tx=103&ty=55&sqi=2&page=5&ndsp=13&ved=1t:429,r:4,s:50&biw=853&bih=560

4metals · May 19, 2011

Everybody is forgetting the simple fact of nature that you have to move a high CFM through the hood so you are not breathing the fumes. That requires a blower with 100 CFM for every square foot of hood opening. For that reason I use a hood for general exhaust and suck the nasty stuff through a scrubber of lower CFM delivered to a scrubber by a dedicated duct (hose) which is right in the reaction being scrubbed. This allows for a smaller scrubber.

This design seems to suck the entire contents of the hood (albeit with a poor fan system) through a small volume of packing and expecting it to either react (with caustic?) or condense. Scrubbing works because of the retention time of the fume in the media, if the flow is slow enough for this in this system, the CFM will be so low you will not have any exhaust out of the work area. And if the CFM is high enough top provide decent exhaust, the retention time for the scrubbing to work is not there.

The all plastic blowers would be my first choice as in the link goldenchild posted. You need good exhaust if you want to pursue refining seriously. I've spent years working reactions in hoods, and not a pound of pins in hydrochloric and peroxide either, I'm talking aggressive reactions. I'm here to talk about it, and very healthy by the way, because I spent the time and energy to get proper exhaust. Harold had a good alternative using a good blower with an aluminum impeller coated with an epoxy, as far as I can tell he's pretty healthy too. There are some times when it just doesn't pay to reinvent the wheel. Remember 100 CFM per foot of hood opening, for your health!

samuel-a · May 20, 2011

Hi 4metals.

Thank you very much for your insight !

i still haven't determined which blower i shall use and as Jim suggested, I'll save it for last.

At the moment i only have an improvised venting system that simply blowing air up a chimney, it works... but... any other solution will be better at the moment.
I now understand that i need to balance the CFM to scrubbing/condensation ratio that you implied to.

Thanks for the tip.

Sam

jimdoc · May 20, 2011

Actually I meant to set it up so that it lasts (not have spare parts for when it fails - set it up to not fail)

Jim

samuel-a · May 20, 2011

:mrgreen:
I read your post too fast...

anyway, point taken.

Oz · May 21, 2011

Ok, someone above mentioned 2 blowers of the cheap variety (or should I say doomed to fail variety). I am assuming they meant both blowers would run simultaneously so that when one failed at least the other still worked, and they still had fume control for their system but at diminished capacity. I love the idea of redundancy in critical systems, but let’s take this a step further.

One of my most harrowing situations in refining happened late one night when I was doing a sterling silver digestion as well as a heavy chlorine gas reaction simultaneously. Then the power went out!

I was left standing in the dark with no fume control or lighting. At a minimum I needed to immediately evacuate the area, but many other acidic solutions were in my near proximity in glass vessels and 5 gallon buckets that I may hit on my way out trying to maneuver in complete darkness. That was not at all a pleasant gamble in trying to leave the area without harm. I then had to get a flashlight so I could go back in and stop the reactions while holding my breath each trip in.

At a minimum I would suggest members have battery back-up emergency lighting with several flashlights in strategic locations for focused lighting in their refining areas. For members that do have proper fume control, they should feed the power to the blowers through Uninterruptible Power Supplies (like they have for computer systems) that have the amp hour capacity to give you at least 30 minutes of run time at full utility. Those 30 minutes should give you enough time to slow down or stop your reactions with ice or base chemicals as needed. It would also be desirable to have a low volume 6 hour fume evacuation system in place powered by battery that keeps your quieted reactions from causing harm to your equipment in the lab until mains power is restored.

It is just good old Murphy’s Law in practice, if it can go wrong, it will at some point. 4metals may be able to tell you how the big boys handle such situations. I’m just a small guy sharing what happened to me and what can happen to you as well.

goldenchild · May 21, 2011

Oz said:
4metals may be able to tell you how the big boys handle such situations. I’m just a small guy sharing what happened to me and what can happen to you as well.

I asked this very question in another post and was told that these situations were avoided through diligent testing and maintenance of the equipment. I'd still like to know what the procedure would be if a system did fail. Maybe some places don't have one until it happens?

qst42know · May 21, 2011

Oz said:
Ok, someone above mentioned 2 blowers of the cheap variety (or should I say doomed to fail variety). I am assuming they meant both blowers would run simultaneously so that when one failed at least the other still worked, and they still had fume control for their system but at diminished capacity. I love the idea of redundancy in critical systems, but let’s take this a step further.

One of my most harrowing situations in refining happened late one night when I was doing a sterling silver digestion as well as a heavy chlorine gas reaction simultaneously. Then the power went out!

I was left standing in the dark with no fume control or lighting. At a minimum I needed to immediately evacuate the area, but many other acidic solutions were in my near proximity in glass vessels and 5 gallon buckets that I may hit on my way out trying to maneuver in complete darkness. That was not at all a pleasant gamble in trying to leave the area without harm. I then had to get a flashlight so I could go back in and stop the reactions while holding my breath each trip in.

At a minimum I would suggest members have battery back-up emergency lighting with several flashlights in strategic locations for focused lighting in their refining areas. For members that do have proper fume control, they should feed the power to the blowers through Uninterruptible Power Supplies (like they have for computer systems) that have the amp hour capacity to give you at least 30 minutes of run time at full utility. Those 30 minutes should give you enough time to slow down or stop your reactions with ice or base chemicals as needed. It would also be desirable to have a low volume 6 hour fume evacuation system in place powered by battery that keeps your quieted reactions from causing harm to your equipment in the lab until mains power is restored.

It is just good old Murphy’s Law in practice, if it can go wrong, it will at some point. 4metals may be able to tell you how the big boys handle such situations. I’m just a small guy sharing what happened to me and what can happen to you as well.

Have you considered a condenser for your silver reactions? You would get more use of your nitric supply and unless you are on well water it is unlikely both your water and electric would go out at the same time. At least the wet condensible portion of your reaction would be captive.

jaythenutz · May 29, 2011

HELLO im jay and just wanted to let anybody know that if your in the S.F. bay area my buddy's has got 10 or more of those squirrel cage fan things of all different sizes. Contact me ASAP and i will have him set a couple a side. If your interested hurry before he scraps them. /// Jay

goldenchild · Jun 16, 2011

I want to touch on this fan thing again. Would a fan like this be appropriate?
What is 2.5" S.P.?

http://www.mkplastics.com/products/...ewall-centrifugal-fiberglass-exhaust-fan.html

Edit
It means static preasure but... what is that?

samuel-a · Jun 16, 2011

goldenchild said:
It means static preasure but... what is that?

I can't explain it any better:

Joeforbes · Jul 2, 2011

I use a squirrel cage fan like this one -

http://t2.gstatic.com/images?q=tbn:ANd9GcRA_SLO0f5mTnKG85t833BxodzLcfsjF3nsR3zBGX3APNpbae1Lrw&t=1

Electric motor on the outside connected to the fan with pulleys so that nothing ever passes over the motor. The scrubber will get most of the acid fumes, but not all of them. This one has been holding strong for three months now, but it is starting to show slight signs of acid ware. I expect it will last several months still though, as the ware is very minimal and slow going.

Old furnaces used them pretty often. They move a ton of air.

Harold_V · Jul 3, 2011

Joeforbes said:
I use a squirrel cage fan like this one -

Old furnaces used them pretty often. They move a ton of air.

Yes---filtered air, which is key to not ending up with a huge amount of vibration. Any moisture on the fan tends to trap particles, eventually leading to a fully loaded fan, which then sheds portions, leaving it well out of balance. I used a squirrel cage blower for my first fume hood.

Never again.

Do note that I also incinerated with my hood---so I had particularly bad problems with the fan loading.

Harold

fume hood venting system

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