Sciencemadness Discussion Board - Fume Hood Construction

Fume Hood Construction

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Yttrium2 - 18-5-2021 at 08:34

bump

macckone - 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.

my new fume hood

teodor - 9-7-2021 at 02:51

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)?

Oxy - 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.

teodor - 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.

Oxy - 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.

Bubbles - 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

teodor - 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).

Bubbles - 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.

teodor - 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]

Bubbles - 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.

metalresearcher - 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.

Bubbles - 15-1-2022 at 21:09

Quote: Originally posted by metalresearcher

Quote: Originally posted by Bubbles

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.

Gammatron - 31-8-2022 at 16:29

Here is my hood. Built from 3/4 MDF. I put shelves and a mini fridge at the bottom for chemical storage and the exhaust fan on the top is mounted in the window with vinyl duct.

Help me finish my fume hood

Chemist1357 - 24-11-2022 at 22:50

I’ve almost finished my fume hood. The only thing i’m stuck on is building a sash that’s tight and able to slide up and down.

It is 930mm wide and 933 high.
It looks and seem simple but yea this has me stuck on what to do from here.

Any advice?

AFEFD242-5A15-4A59-A176-7A5882C262D5.png - 3.8MB

Rainwater - 25-11-2022 at 05:21

It sounds like you're wanting a "linear rail". Thingy bob that slidez up and amd down you can mount the glass to
https://www.amazon.com/OrangeA-Linear-SBR20-1000mm-4SBR20UU-...

Mateo_swe - 25-11-2022 at 06:44

That linear rail looks nice.
There are another type also but they are a bit more expensive i think.
This type (i just picked the first i found, search for better price and other models):

MGN12 Precise Linear Guide Rail & 2 Sliding Rail Block Set

Also, i would use a plastic plexiglass screen instead of glass.

Bubbles - 14-8-2023 at 09:15

With my design I'm also stuck at the sash.
Those linear rails look nice, how would I stop it in place though? So stop the plexiglass lower window from falling down when in the up position.

I've also looked at vertical sliding windows but didn't find anything suitable in the Netherlands.

charley1957 - 15-8-2023 at 05:35

When I built my fume hood I used an old glass storm door with a moveable sash. I built the fume hood to the width of the storm door and bolted the door to the front of the box. The sash of the storm door is now the sash of the fume hood. I raises and lowers and has stops at different heights. It was a pretty painless build.

mr_bovinejony - 26-2-2024 at 11:38

For a constant flow bypass is it important to install some kind of metal sheet with a grill? I've read it controls airflow better but the hood built by magpie looks like it's just an open space when the sash is closed. I have no idea how to build a grill thing so if it's not necessary I'll copy his build and leave it open

Mateo_swe - 7-6-2024 at 01:58

For stopping the vertical part one can use couterweights and some pullys so it balances out.
Not the most elegant solution but i guess it will work and its easy to move it up/down.
Or one can make it so there is some friction and that is hoilding it in place, or put a locking mecanism and move it manually.
But then a bit of musclepower is needed to raise/lower it.

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