# Buying a fume hood



## DJPGold (Nov 5, 2022)

What fume hoods can be recommended for purchase rather than building one myself?
I only do small amounts of gold, 2oz at a time is the most I really plan on so I can’t figure out if a scrubber is necessary either. I would like to have one for safety sake, I’m not interested in reclaiming the acids etc. I live in a dense neighbour hood so even if the small amount of gasses could potentially be fine if vented higher up, it’s not something I want to take chances with. 
I assume that most of the fume hoods for sale would be subject to pretty heavy corrosion


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## orvi (Nov 6, 2022)

DJPGold said:


> What fume hoods can be recommended for purchase rather than building one myself?
> I only do small amounts of gold, 2oz at a time is the most I really plan on so I can’t figure out if a scrubber is necessary either. I would like to have one for safety sake, I’m not interested in reclaiming the acids etc. I live in a dense neighbour hood so even if the small amount of gasses could potentially be fine if vented higher up, it’s not something I want to take chances with.
> I assume that most of the fume hoods for sale would be subject to pretty heavy corrosion


Firstly, I do not have experience with manufactured hoods, but what I can tell you from the start, try to take one where is minimal ammount of any metal parts in the "active" part of the hood, exposed (no matter if painted or not). If possible, you want everything to be plastic, vent pipe to be plastic, everything from plastic. No screws with heads in the inside of the "active" part of hood - as they will quickly corrode away and whole thing could be dangerous to use, as it could fall apart due to material corrosion.

"Chimney" from the hood is a good thing, if you can araise it at least 3-4 meters above ground, higher the better. Dispersion of the fumes will be much better. And it has advantage you can actually make scrubber spraying column into that same "chimney" piping, and simultaneously saving space and resources. For most purposes, slightly alkaline water is more than enough to fight NOx gasses and HCL/chlorine from AR processing to acceptable concentrations.


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## eaglekeeper (Nov 6, 2022)

Like orvi, I have no experience with manufactured hoods either. Because of my work area I had to make mine in place to fit where I wanted it. If you find a fume hood but it has metal hardware, you can possibly purchase plastic/Teflon replacement hardware. Using marine grade 5200 sealant over fasteners/small hardware would slow the corrosion down, but Hcl fumes are pretty intrusive and will find it's way in....eventually. 

The fan motor/blades/lighting fixtures would probably be a constant issue depending on it's placement in the system. Seems like every year I have to replace my "sealed" light fixtures because of internal corrosion. So far my fan motor hasn't failed.....yet. I do have a spare motor/power supply just in case it fails during a reaction and it can be replaced in about 5 minutes.


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## orvi (Nov 6, 2022)

eaglekeeper said:


> Like orvi, I have no experience with manufactured hoods either. Because of my work area I had to make mine in place to fit where I wanted it. If you find a fume hood but it has metal hardware, you can possibly purchase plastic/Teflon replacement hardware. Using marine grade 5200 sealant over fasteners/small hardware would slow the corrosion down, but Hcl fumes are pretty intrusive and will find it's way in....eventually.
> 
> The fan motor/blades/lighting fixtures would probably be a constant issue depending on it's placement in the system. Seems like every year I have to replace my "sealed" light fixtures because of internal corrosion. So far my fan motor hasn't failed.....yet. I do have a spare motor/power supply just in case it fails during a reaction and it can be replaced in about 5 minutes.


When set up with the "chimney" thing, you can cleverly put the motor at the end of the pipe, after the scrubber part, to greatly prolong it´s life. Some aerosol separator mesh or something similar needs to be placed after the spray nozzles of the scrubbing part, not to dampen the fan tho.
Yeah, HCL find it´s way to practically anything. Altough putting some protection on the bolts certainly helps a lot. And if you cannot wash the chlorides off of it, it will corrode till no metal is left.
Actually speaking, metal is thing of issue. As far as you go with plastic, or even hard wood, you will be served much better. 

My opinion is, it does not need to look nice, it just need to work as it should and be durable enough to not fall apart. Few plastic sheets, I found some fiberglass resin ones... Plexiglass for the front "door". Even asphalt soaked roofing material is OK for the walls, but I will certainly use something more durable... But I seen it personally to be used and it worked as it should. Piping from foldable PVC sleeved air conditioning "tube" is perfectly OK for the exhaust - cheap, flexible, non-flammable, nice resistance to NOx and Cl2 gasses, easily replacable if needed. Chassis of the hood, I seen built from the plastic/sawdust composite "timbers" (which are relatively nice as they usually contain fire retardants) bolted with plastic screws. As long as it does not need to support any weight from the top, it is perfectly OK. One folk has this exhaust tube lead through old and unused chimney all the way to the top of the roof - nice adaptation from my point of view. 

And as you very wisely pointed out, you should be able to easily and quickly replace the fan on the hood in case the used one dies down. I seen by-pass made on the end of the exhaust tube, which was sealed from the fumes, with "emergency" fan mounted. If something goes wrong and motor dies, you can switch the other one on in matter of seconds to save your work and health


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## eaglekeeper (Nov 6, 2022)

Correct, May extraction fan (puller) is on the outside of my shop. All of my ducting is in negative pressure in operation, so if a duct develops a hole the fumes wouldn't get forced into the shop. 

Yep, my fume hood looks like a high school science project that got a "C-" for a grade......nothing fancy, it just gotta work.


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## DJPGold (Nov 6, 2022)

eaglekeeper said:


> Correct, May extraction fan (puller) is on the outside of my shop. All of my ducting is in negative pressure in operation, so if a duct develops a hole the fumes wouldn't get forced into the shop.
> 
> Yep, my fume hood looks like a high school science project that got a "C-" for a grade......nothing fancy, it just gotta work.


Thanks for the info guys. It would be nice if there is a thread for photos of peoples fume hoods to draw inspiration from


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## slsmp40 (Nov 6, 2022)

The motor is isolated in a good quality commercial hood so corroding the thing is almost impossible. I have only seen them fail if the installer covers the vents for the separate space the motor sits in. Then you get overheating and i dont believe any motor handles that really well. I put a pic of one removed from a end of life hood that was removed from service. 15years of continuous service and the blower is still just fine. In fact the only problem with the unit was the maintenance log ran out of space so they replaced the entire unit. The problem is as a hobbyist a first quality lab hood is “cost prohibitive”.


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## 4metals (Nov 6, 2022)

Save your money for a good blower and make one of these. That’s a standard huge powder funnel from US plastics with a 4” throat. If you are doing small lots the inside area of the 55 gallon drum (around 2.5 sq ft) should be fine.


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## DJPGold (Nov 7, 2022)

4metals said:


> Save your money for a good blower and make one of these. That’s a standard huge powder funnel from US plastics with a 4” throat. If you are doing small lots the inside area of the 55 gallon drum (around 2.5 sq ft) should be fine. View attachment 53044
> 
> View attachment 53045


That’s a good budget design for sure! 

Does anyone have advice on dry scrubbers? I feel like they would be an easier solution/setup for a cheap scrubbing system.


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## popslab (Nov 7, 2022)

4metals said:


> Save your money for a good blower and make one of these. That’s a standard huge powder funnel from US plastics with a 4” throat. If you are doing small lots the inside area of the 55 gallon drum (around 2.5 sq ft) should be fine. View attachment 53044
> 
> View attachment 53045


great idea what motor does it have?


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## Yggdrasil (Nov 7, 2022)

DJPGold said:


> That’s a good budget design for sure!
> 
> Does anyone have advice on dry scrubbers? I feel like they would be an easier solution/setup for a cheap scrubbing system.


Depending on what to scrub, I think that is not even possible.
NOx and some other gases will need to be scrubbed wet.
An impractical amount of AC may or may not work, but that will be expensive.
Then the question is, how much at how much time, it might or might not be neccessary to scrub, check local regulations.


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## goldorack (Nov 7, 2022)

I will be getting a manufactured one on alibaba from China. About 1200 USD


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## justinhcase (Nov 7, 2022)

Just watch the industrial auctions, very good fume hoods come up all the time for peanuts.
If you want a top-of-the-line unit for a fraction of the new price you just have to be patent.


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## 4metals (Nov 7, 2022)

popplaysgold said:


> great idea what motor does it have?


You need a blower for this hood. The opening is about 2’ x 2’ so a 400cfm blower is the minimal exhaust to clear the fumes effectively. Small jewelers buy wet location exhaust fans which will work, until they don’t. Corrosion from the fumes is your enemy. If you have fume scrubbing the fan will obviously last longer.


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## goldorack (Nov 7, 2022)

yes auctions are very cheap (like equipnet, i have no connection with them)and it might be the best option. I prefer new since I never know what was in there before. When I did my masters we as students used to be quite careless there.


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## 4metals (Nov 7, 2022)

Another auction site that has lab equipment is www.govdeals.com.


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## justinhcase (Nov 7, 2022)

goldorack said:


> yes auctions are very cheap (like equipnet, i have no connection with them)and it might be the best option. I prefer new since I never know what was in there before. When I did my masters we as students used to be quite careless there.


I can think of no applications that will test equipment more than a metal refiner.
It would almost be a shame to destroy brand new kit.
In fact, I do kind of make a point of using other people's cast-off, classic old bits of kit that are far superior to their modern equivalent.
Have you ever heard of a "Womble" in your neck of the woods?
"The _Wombles_ of Wimbledon Common are we. _Making_ good _use_ of the _things_ that we find. _Things_ that the _everyday_ folks _leave behind_."


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## DJPGold (Nov 7, 2022)

Yggdrasil said:


> Depending on what to scrub, I think that is not even possible.
> NOx and some other gases will need to be scrubbed wet.
> An impractical amount of AC may or may not work, but that will be expensive.
> Then the question is, how much at how much time, it might or might not be neccessary to scrub, check local regulations.


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## VK3NHL (Nov 8, 2022)

DJPGold said:


> What fume hoods can be recommended for purchase rather than building one myself?
> I only do small amounts of gold, 2oz at a time is the most I really plan on so I can’t figure out if a scrubber is necessary either. I would like to have one for safety sake, I’m not interested in reclaiming the acids etc. I live in a dense neighbour hood so even if the small amount of gasses could potentially be fine if vented higher up, it’s not something I want to take chances with.
> I assume that most of the fume hoods for sale would be subject to pretty heavy corrosion


Ask Sreetips, aka Kadriver which one NOT to buy…
Good luck.


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## kingwilly (Nov 8, 2022)

4metals said:


> Save your money for a good blower and make one of these. That’s a standard huge powder funnel from US plastics with a 4” throat. If you are doing small lots the inside area of the 55 gallon drum (around 2.5 sq ft) should be fine. View attachment 53044
> 
> View attachment 53045


Can you provide more pics and info on this please, I would like to try to build one.


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## Yggdrasil (Nov 8, 2022)

AC will load relatively quick and then you will need to replace it, it will become costly.
Limestone, I don’t know how effective that is.
Maybe or maybe not.

Wet scrubbing will always work as long as it is wet, it will loose effectivity as it saturates but is cheap to replace.


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## Ohiogoldfever (Nov 8, 2022)

Lowes sells 4x8 sheets of white PVC 1/2” thick. Last I checked it was about $65.00 Just in case working in the drum isn’t enough space for you.


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## kreinhardt (Nov 8, 2022)

Ohiogoldfever said:


> Lowes sells 4x8 sheets of white PVC 1/2” thick. Last I checked it was about $65.00 Just in case working in the drum isn’t enough space for you.


Can you show a link for this? I've never seen 1/2" pvc that cheap. I'm in the process of designing and building a hood out of pvc sheet and the cheapest I've seen for 1/2" 4 x 8 is well over $500.


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## orvi (Nov 8, 2022)

kreinhardt said:


> Can you show a link for this? I've never seen 1/2" pvc that cheap. I'm in the process of designing and building a hood out of pvc sheet and the cheapest I've seen for 1/2" 4 x 8 is well over $500.


Effectively speaking, you does not need it to be that thick. Few mm is enough in my opinion, if you make chassis more strong. I used 3mm thick fiberglass resin sheets, and it was very good investment. 

Lexan (polycarbonate "glass") is also easy to find (used for transparent roofing, sometimes you can buy smaller "sheets" for very cheap, as they are hard to sell) and relatively durable, even to the corrosive fumes. Costs like 8-10euros/m2 here, brand new, 4mm hollow profile - enough strength for the wall cover. On places of significant contact (precipitation of the hot acidic mist is the worst) it can go to somewhat white and translucent, but overall it serves for a long long time before it needs to be replaced.


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## DJPGold (Nov 8, 2022)

Yggdrasil said:


> AC will load relatively quick and then you will need to replace it, it will become costly.
> Limestone, I don’t know how effective that is.
> Maybe or maybe not.
> 
> Wet scrubbing will always work as long as it is wet, it will loose effectivity as it saturates but is cheap to replace.


I’d like to do wet scrubbing, but can’t find the relevant information for a hobbyist refiner. Ideally I would have the same setup as the fella who built a new shed recently and made 3 compartments from PVC. But I don’t want one that big if I can avoid it. Like would three 1-2L vessels work? Do I HAVE to have three seperate vessels etc? I don’t want to re use the acid, I just want to make it safe in a constricted area. Obviously I could have a 6ft pvc vent tube above the shed but that’s still close to neighbours so if there’s an easy and small DIY scrubber solution then I’m all ears


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## Ohiogoldfever (Nov 8, 2022)

Wholly Christ it’s doubled sense I last looked. I guess no body’s shocked my that.


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## Yggdrasil (Nov 9, 2022)

DJPGold said:


> I’d like to do wet scrubbing, but can’t find the relevant information for a hobbyist refiner. Ideally I would have the same setup as the fella who built a new shed recently and made 3 compartments from PVC. But I don’t want one that big if I can avoid it. Like would three 1-2L vessels work? Do I HAVE to have three seperate vessels etc? I don’t want to re use the acid, I just want to make it safe in a constricted area. Obviously I could have a 6ft pvc vent tube above the shed but that’s still close to neighbours so if there’s an easy and small DIY scrubber solution then I’m all ears


For Nitric digestions one can use a vacuum system pulling from an upside down funnel through 3 bottles.
First with water (maybe a little Hydrogen Peroxide to increase efficiency) , second with NaOH solution and the last as a catch basin.
Preferably with an e-ductor as vacuum source.
There are pictures and schematic you will find when searching the forum.


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