Fan/Blower recommendation for standard hood?

[Harold_V]

Unless the air moved by a squirrel cage fan is extremely well filtered, there will be buildup on the wheel that eventually creates problems with air restriction as well as balance. They are not the best choice for the purpose, although they do work.

Harold

 

[jeneje]

I see you vented your fumes outside over your roof. Acids and roofing materials do not mix well with each other. In the not so near future I would consider building a scrubber to run the fumes through before exiting them outside above my roof.
Ken

edited; To explain this a little better, shingles are made from asphalt, asphalt contains up to 6% sulfur. The sulfur will mix with the acids causing decomposition of the asphalt, in return causing failure to the roof.

The reason I mention this, is, you commented on not being there over two or three years. The cost to replace a roof is very expensive, running between $165.00 to as much as $450.00 per 100 square feet of roof area. It is by far cheaper to construct a scrubber, verse replacing a new roof, depending on the size of your home.

 

[tedpgh]

Good job getting a setup together and making good use of your hood.

Be advised though the narrow diameter and ribbing of the tubing you use is likely restricting your airflow (A LOT).

Your setup may suffice, but if you find it's not pulling well enough then you'll want to use something smooth and wider.

-Ted

 

[MGH]

Hi again all. Thank you to everyone for their interest and taking the time to comment. I don’t want to be one of those people who gets super defensive with any amount of criticism – I hope this won’t read that way – but I do want to clarify a couple things in case there has been any misunderstanding.

One side of the fan is open (motor end side), the fan will pull air from side of least resistance easier, than trying to pull air from the hood through all of that corrugated pipe, You will most likely need to enclose this open side more, the motor itself is sitting in the path of corrosive fumes, the motors shaft and bushings may not hold up well to these fumes...

Be advised though the narrow diameter and ribbing of the tubing you use is likely restricting your airflow (A LOT).

You guys are absolutely right. I had already encountered the restriction due to the corrugated drain pipe, and placed some additional restriction on the motor side (just didn’t post a picture in my earlier post). There is still fresh air flow that gets in through this restriction on the motor side and passes across the motor, while providing enough restriction to force air through the hood. I’m not sure how much of the motor or bushing are in the path of the corrosive fumes. This fan has a kind of plate down the middle of the wheel portion which would seem to provide some separation between incoming air from the hood side and the motor. I used the drain pipe rather than smooth pipe both because of cost, and the difficulty of working around the wood framing of the roof. It was, of course, a compromise.

I see you vented your fumes outside over your roof. Acids and roofing materials do not mix well with each other. In the not so near future I would consider building a scrubber to run the fumes through before exiting them outside above my roof.

Of course a scrubber will be a priority. And of course I cannot assume that there is no contact between the fumes and shingles, but the exhaust exits several feet above the roof line, is pointed at an upward angle, and the flow is probably somewhere around 2000 – 3000 cfm – hopefully carrying the fumes up and away from the roof. The point about shingle damage is well taken, but this is a calculated risk as I think there must be minimal fume-to-shingle contact, and because the roof on this detached garage is already about 20 years old anyway, and I wouldn’t be surprised if I have to replace it before selling the house regardless of any refining activities.

Unless the air moved by a squirrel cage fan is extremely well filtered, there will be buildup on the wheel that eventually creates problems with air restriction as well as balance. They are not the best choice for the purpose, although they do work.

I have no rebuttal here. This point is also well taken. The blower and wheel assembly inside are reasonably accessible for inspection and cleaning. I will be sure to keep an eye on particulate buildup (and corrosion).

So my future needs are still: low flow alarm, scrubber, and better ducting and blower all-around. And again, not wanting to sound defensive or dismissive, but I think I accomplished my intermediate goal of setting up a functional hood which provides personal safety and a convenient/secure place to do some refining, all with minimal investment (the total spend was $577 for hood, blower, ducting, paint, polypropylene sheet, conduit, wiring, etc.). My first refining in the setup was about 800 grams of gold filled jewelry, base metals digested in two 400 gram batches. There were of course plenty of NOx fumes, but at no time could I detect any hint of their odour, neither while standing in front of the hood, or outside, downwind of the exhaust (I’ll post a picture in the gallery section). I know this doesn’t mean that the fumes simply ceased to exist, but I think the hood is serving its purpose for small refining activities.

Thanks as always to the GRF and to the individuals who shared their experience and knowledge in this thread in particular. This place is great!

 

[Harold_V]

Unless the air moved by a squirrel cage fan is extremely well filtered, there will be buildup on the wheel that eventually creates problems with air restriction as well as balance. They are not the best choice for the purpose, although they do work.

I have no rebuttal here. This point is also well taken. The blower and wheel assembly inside are reasonably accessible for inspection and cleaning. I will be sure to keep an eye on particulate buildup (and corrosion).

What's important for you to take away from my comment is the fact that any deposits you see will have value. Do not discard anything that is removed from the venting system of a fume hood, as, in spite of your most careful attempts, you're going to lose traces. That's why I had a filter system in my hood.

Understand that I refined commercially, and that my hood ran pretty much non-stop. It got cleaned out about every two years, with a yield of about eight ounces of gold from the recovered material. The yield seemed to be quite reliable, as the hood was cleaned out several times while I was in operation.

So my future needs are still: low flow alarm, scrubber, and better ducting and blower all-around. And again, not wanting to sound defensive or dismissive, but I think I accomplished my intermediate goal of setting up a functional hood which provides personal safety and a convenient/secure place to do some refining,

Unless you happened to be born with a genius level IQ, and already know all there is to know about refining, there is much you stand to learn by paying attention to comments offered by those of us who have been there, done that. It took three generations of hood design before I had addressed the pertinent issues. Part of the reason for that is that it is not always obvious to the novice what problems must be addressed. Filtering a hood is one of them, and it's more than obvious to me that precious few understand the importance.

Harold

 

[rickbb]

As Harold pointed out, it's a continuous process to tweak it and get it right. Don't stop now just because your getting some good results.

I've used commercial fume hoods in several jobs for 20+ years. When I started my hobby in recovery and refining of e-scrap and built my own hood, I had to re-work my hood 3 times to get it where it needed to be. And I still need to get a better scrubber working even for my small volumes.

 

[Plasticman]

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