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DJPGold

Well-known member
Joined
Jul 29, 2021
Messages
78
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
 
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
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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.
 
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.
 
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.
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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 :)
 
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.
 
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.
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Thanks for the info guys. It would be nice if there is a thread for photos of peoples fume hoods to draw inspiration from
 
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 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
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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.
 
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.
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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.
 
popplaysgold said:
great idea what motor does it have?
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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.
 
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.
 
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.
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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."
 
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.
Click to expand...
 

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

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