# 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


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## 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


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## 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.


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## 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


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## 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?


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## 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.


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## 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...


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## 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


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## 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!


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## 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


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## 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


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## samuel-a (May 20, 2011)

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

anyway, point taken.


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## 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.


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## 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?


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## 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!
> 
> ...



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.


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## 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


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## 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?


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## samuel-a (Jun 16, 2011)

goldenchild said:


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



I can't explain it any better:


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## 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.


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## 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


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## samuel-a (Jul 3, 2011)

This is the "new" :mrgreen: design of the vent.
Since the suction (veturi effect) on the last design was created far from the pipe opening (hood side), i bearly got any suction and at the moment i do not have 200-500 CFM blower at my disposal.
Instead, i improvised a contraption to hold togather 3 48V fans (CFM unknown) that blow inside the pipe. Air flow is reduced with an old soft drink bottle that had a great funnel like shape, i cut the bottom from it and fitted inside the "T' connection as illustrated in my picture.

With the PSU i can feed either 5V or 12V to the fans, 5V is when i'm gone or there no reactions going on and doors are closed.
12V is good enough to work a reaction with one door open and still don't smell anything.
I guess if i could feed them the full 48V each it will suck everything without a problem... the only major disadvantage to this arrangement is th noise...




I understand this is not ideal setup, but at least the fans are away from any corrosive fume/gasses and i do not expect them to fail.
Hope this might halp somone else


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## texan (Jul 5, 2011)

Looks like the draft would work better if the exhaust from the hood itself was of a smaller diameter than the blower arrangement. Wouldn't this create a lower pressure that would suck fumes from the hood more effeciently.

Texan


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## cjfeath (Jul 13, 2011)

I have a safety question on fume hoods. 

Is it safe to tie your venting into your exhaust for your furnace and water heater? Is there any sort of combustion or circulation concerns with doing this?


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## glondor (Jul 13, 2011)

Think about the chemicals you will be venting and ask yourself what is the worst that can happen.....Nox fumes in the furnace? Acid in the water heater? Forced air whole house poisoning? Don't do it. Dedicated proper vent please.


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## Barren Realms 007 (Jul 13, 2011)

cjfeath said:


> I have a safety question on fume hoods.
> 
> Is it safe to tie your venting into your exhaust for your furnace and water heater? Is there any sort of combustion or circulation concerns with doing this?



With most heaters having forced air for the vent it is no longer a good idea to have the vents tied together. And it is a VERY BAD idea to try and use the same vent to exhaust refininning fumes.


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## Harold_V (Jul 14, 2011)

cjfeath said:


> Is it safe to tie your venting into your exhaust for your furnace and water heater?


Absolutely not! Not under any condition, nor for any reason. Carbon monoxide poisoning is a real possibility, to say nothing of the corrosive tendencies of fumes from the hood. 

Harold


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## eeTHr (Jul 14, 2011)

If two fans are used in parallel, when one fails, air from the working one will flow backwards out the failed one, unless you have a means to block it off.


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## Barren Realms 007 (Jul 14, 2011)

I also forgot to mention that the interior pipe of the vent is aluminum and will not stand up to the fumes.


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## cjfeath (Jul 14, 2011)

Did not think so, but thought I would ask. Limited Space and was trying to find a spot for lab. Thanks for the replies all.


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## ericrm (Mar 27, 2013)

samuel-a said:


> This is the "new" :mrgreen: design of the vent.
> Since the suction (veturi effect) on the last design was created far from the pipe opening (hood side), i bearly got any suction and at the moment i do not have 200-500 CFM blower at my disposal.
> Instead, i improvised a contraption to hold togather 3 48V fans (CFM unknown) that blow inside the pipe. Air flow is reduced with an old soft drink bottle that had a great funnel like shape, i cut the bottom from it and fitted inside the "T' connection as illustrated in my picture.
> 
> ...



i the picture of samuel i have put in red a section of it setup , do someone know how to calculate the proportion of that thing so i can choose the desired size of the opening in the fume hood?

edit i aslo wondering ,in the use of one of those system could you... could you create a vaccum (unvolontary) in the room that would be stronger than the vacuum in the fume hood?


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## samuel-a (Mar 29, 2013)

Eric

I suppose it could be theoretically pre calculated... but i have no idea.
An air flow meter is needed to get actual readings from the intake. From that, considering the pipe diameter you could calculate the actual suction cfm your system is producing.


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## kjavanb123 (Mar 19, 2017)

Hi,

I am trying to build a fume hood venturi system following the post by 4metals, I used a 100-liter bucket, cut the partion of it to place a door, and used a large funnle to place on top which is attached to a T connection, to serve as fume hood,



Attach to blower is a paper cup that I cut the bottom of it, and also glue to it a piece of paper rolled up to be used as venturi pipe, 



Now when I test this system, I tried to simulate fumes by lighting toilet paper and leave them in a pot, placed about 25 cm under the T connection inside the fume hood, it sucks all the fumes out but as soon as I attach the gray pipe to a vertical pipe which is the same height as fume hood and is submerged to 100-liter barrel filled with water, I get positive pressure at T connection hole.

The pipe submerged in water has 8 holes drilled on it.

Should I increase the lentgh of gray pipe attached to T connection before attaching it to the scrubb pipe?

Regards
Kj


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## 4metals (Mar 19, 2017)

The use of a venturi style exhaust is only to suck air out of the hood, not to power suction through a scrubber. If you use the venturi setup you made to exhaust just the hood you should be OK as the burning of paper to generate smoke to test it confirmed. The power for the scrubber is an entirely different and second system you need to add.


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