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Author: Subject: Fume Hood Construction
Yttrium2
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[*] posted on 18-5-2021 at 08:34


bump
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macckone
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[*] posted on 29-6-2021 at 07:52


yttrium2,
You might be able to find a crate of the correct dimensions but most cabinets and book shelves max out at 18" deep and 36" wide, with height from 36 to 72 inches.

You can order crates a 48" x 48" x 28" is $210 + shipping, it has a pallet attached so inside dimensions are 22" and a little less than 48.
https://www.uline.com/Product/Detail/S-18994/Wood-Crates/Woo...
They don't sell a 60" with a depth less than 48".

2x2s and 1/8" hardboard are what I used for mine.
At home hardware stores they can cut a couple of sheets to the sizes you need.
The 2x2s require a lot more cuts and you really need a saw but even a hand saw will work.
The hardboard can also be cut with a dremel or router (including a flooring router), but that takes time and patience.

mine is 48" high, 48" wide and 24" deep, which is a pretty standard size.
5ft high is better but the sheets come in 4" x 8" so it was cheaper with less waste.
And the space I am using is better suited for a 48" height, because you have to install a fan etc and the ceiling is 8 ft.
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teodor
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[*] posted on 9-7-2021 at 02:51
my new fume hood


I've made some upgrade to my fume hood. I replaced flammable walls with aluminium ones. It is not perfect because aluminium is attacked by some corrosive vapors forming a layer of powder on its surface (I can observe it on my air outlet after few years of usage) but for organic vapors it works great providing 60 ft/min stream of air through its opening. The reason I've made it from aluminium and not from, let say, stainless steel is just because this material is much easy to operate with - e.g. I just can use a table saw to make all cuts.
Can anybody recommend me some paint to protect the aluminium parts from corrosive vapors (let say, bromine)?



fh1.jpg - 148kB fh2.jpg - 156kB
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Oxy
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[*] posted on 9-7-2021 at 06:22


Nice hood but the material is indeed, not optimal. Aluminium is not the easiest to paint but after some preparation you can cover it with chemical resistant epoxy paint. Not a cheap (at least that which I found) but should work.
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teodor
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[*] posted on 9-7-2021 at 08:14


Thanks Oxy. Yes, I checked some products by googling. What I think now it is that more economical is just buy some adhesive polymer film like people often use on their windows and cover what is possible to cover. And after I will make a proof of my design (by a real usage) I will be able to replace any damaged parts with steel parts improving also the design based on my usage experience. But I will keep my eye on chemical resistant epoxy paints for metals, I think we can have problems with any uncovered metal in a hood - after working with gaseous HCl some of my stainless steel rods are already highly corroded.
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[*] posted on 9-7-2021 at 10:15


Quote: Originally posted by teodor  
I think we can have problems with any uncovered metal in a hood - after working with gaseous HCl some of my stainless steel rods are already highly corroded.


That's true, my rods are also highly corroded. I am trying to absorb corrosive fumes but it seems that they don't need much of it.
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Bubbles
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[*] posted on 13-1-2022 at 19:06


I am making a fume hood in my soon-to-be basement lab. I will use an existing entrance to an old chimney canal, that was used for a range hood and can accommodate 125mm ducting. I found this fan for 125mm:
https://www.ventilatieshop.com/buisventilatoren/125mm/buisve...

But would I be able to generate more suction if I used a more powerful 160mm fan, and fit it to my 125mm duct? Or would the increased resistance negate the benefit of more fan power?
This is the larger fan:
https://www.ventilatieshop.com/buisventilator-cyclone-centri...

Btw the 125mm duct will have two 90 degree bends and two 45 degree bends over its 5m length. After that it attaches to the chimney canal (which I believe becomes square 20*20cm inside but not sure), and travels straight to the roof 4m higher.

Any advice is much appreciated ;)
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teodor
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[*] posted on 14-1-2022 at 04:17


Bubbles, I think the suction will be dependent on the overall resistance of the construction to the airflow and the power of your fan. You can probably ignore the data about flow, it is only when the fan is not attached to your system.
Make sure that your chimney canal has no other branches, so it could be exclusively used by your hood delivering vapors outside (but I am sure you already checked that).
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Bubbles
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[*] posted on 14-1-2022 at 05:34


Okay, my feeling says that the 680 m3/h fan will create more suction than the 370 m3/h fan, even if the system is 125mm and the 680 m3/h fan 160mm.
But since I don't understand the physics well, I'm not sure.
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teodor
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[*] posted on 14-1-2022 at 06:15


An 85W fan can potentially create more suction than a 52W fan. But look at that graph. Even 85W fan can create only 400Pa pressure, after this point, there is no suction. It is only 3 mmHg. So, if your system needs more it will not deliver it.

With 2 mmHg difference, the flow is degraded to 400 m3/h.

The pressure difference will build up because you need to push the air through your chimney pipes and also the hood itself starts to create "negative" pressure when you lower the sash.

So, an actual flow which you will get probably could be determined only with a flow meter. I am not aware of how to calculate it based on your pipe diameters.

I only know that you need a fan that can create the highest pressure.


[Edited on 14-1-2022 by teodor]
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[*] posted on 14-1-2022 at 09:17


These centrifugal fans are advertised as high pressure fans.
I haven't found any better ones.
The 125mm ducting is all I can manage to vent to the roof. Otherwise I have to vent straight out to the street..
I hope I can still operate a small fume hood within my current situation, as I don't see an alternative.
I have a softbox, a box with a 700 m3/h fan suspended in it. It has a 160mm baffle (6'').
I will fit it to the 125mm chimney and see if it delivers.
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metalresearcher
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[*] posted on 14-1-2022 at 10:18


Quote: Originally posted by Bubbles  
I am making a fume hood in my soon-to-be basement lab. I will use an existing entrance to an old chimney canal, that was used for a range hood and can accommodate 125mm ducting. I found this fan for 125mm:
https://www.ventilatieshop.com/buisventilatoren/125mm/buisve...

But would I be able to generate more suction if I used a more powerful 160mm fan, and fit it to my 125mm duct? Or would the increased resistance negate the benefit of more fan power?
This is the larger fan:
https://www.ventilatieshop.com/buisventilator-cyclone-centri...

Btw the 125mm duct will have two 90 degree bends and two 45 degree bends over its 5m length. After that it attaches to the chimney canal (which I believe becomes square 20*20cm inside but not sure), and travels straight to the roof 4m higher.

Any advice is much appreciated ;)


These bends will definitely degrade the venting, but with 125mm pipe it won't be a problem. Depends on how high the chimney is beyond the 5 meters you mention. As it is probably a masonry chimney, check that there are no leaks in it or (toxic fumes ?) will leak into your house. A stainless steel inner pipe of 125mm as used for wood stoves might be an option, but count on $500-$1000 for a e.g. 10m chimney.

I have a similar 100mm fan (64 W) but the tube is only 3 meters above the top of the fumehood and it works fine.
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[*] posted on 15-1-2022 at 21:09


Quote: Originally posted by metalresearcher  
Quote: Originally posted by Bubbles  
I am making a fume hood in my soon-to-be basement lab. I will use an existing entrance to an old chimney canal, that was used for a range hood and can accommodate 125mm ducting. I found this fan for 125mm:
https://www.ventilatieshop.com/buisventilatoren/125mm/buisve...

But would I be able to generate more suction if I used a more powerful 160mm fan, and fit it to my 125mm duct? Or would the increased resistance negate the benefit of more fan power?
This is the larger fan:
https://www.ventilatieshop.com/buisventilator-cyclone-centri...

Btw the 125mm duct will have two 90 degree bends and two 45 degree bends over its 5m length. After that it attaches to the chimney canal (which I believe becomes square 20*20cm inside but not sure), and travels straight to the roof 4m higher.

Any advice is much appreciated ;)


These bends will definitely degrade the venting, but with 125mm pipe it won't be a problem. Depends on how high the chimney is beyond the 5 meters you mention. As it is probably a masonry chimney, check that there are no leaks in it or (toxic fumes ?) will leak into your house. A stainless steel inner pipe of 125mm as used for wood stoves might be an option, but count on $500-$1000 for a e.g. 10m chimney.

I have a similar 100mm fan (64 W) but the tube is only 3 meters above the top of the fumehood and it works fine.


Okay that's good to hear :)
I found a fan that can handle a lot more pressure, the Vents KSA 150-2e.
Fan curve: http://old.ventilation-system.com/images/cat/87_255_cat_file...
Tasty curvature, worth the extra expense (€230 instead of €90).

The fan blades are made of galvanized steel, which doesn't like HCl too much. But it should be able to handle the pressure drop of a carbon filter.
I hope with the filter, it will last.

For the bottom of the hood I plan to use trespa (HPL), the sides plywood with epoxy paint.
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