Dang I'm just getting startered with this whole thing. Building my first hood myself. But are you in florida by any chance. I'll have to hire you to wire up my next hood. Unless I can lock down that large refiner to buy my castings for 98% of spot and buy one of those fancy deals like sreetips got.
A gallery of home built hoods and fume scrubbers _hood_
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Dang I'm just getting startered with this whole thing. Building my first hood myself. But are you in florida by any chance. I'll have to hire you to wire up my next hood. Unless I can lock down that large refiner to buy my castings for 98% of spot and buy one of those fancy deals like sreetips got.
Amazing idea I will work on incorporating that into my hood. I'm working on the scrubber atm. I am a wood working hobbyist so the hood build isn't that much trouble.
I think this is how he thinks about bathroom fans, without the main fan no venturi.
They will fail relatively fast but will be inexpensive.
https://goldrefiningforum.com/threa...s-and-fume-scrubbers-_hood_.34601/post-378283
Martijn
Well-known member
What 4 metals said. Powerful enough, that depends per case. The bigger the restiriction, the more power you'll need to keep an acceptable air flow from the hood going, but also the more air you'll suck out. It's a balance which you will need to try out to stay economical, or over dimension it to be on the safe side.
And keep the pipes after the venturi free of too many bends and restrictions. The vacuum created by the venturi depends on easy flow from venturi all the way to the exhaust.
another thing to mind is keep your exhaust far from your fresh air inlet, to avoid sucking the fumes back in your lab.
but you'll have to try it yourself.
Even the position where the restriction outlet is in the Y-piece is critical to get the best vacuum generated. A little flow restriction through the fumehood (e.g. a closed fume hood window, vent openings almost closed) actually makes a venturi operate better, but give lower airflow.
Aren't physics great?
So you'll want to have the right ratio pipe diameter vs restriction opening vs fan power /output.
Good luck making something that sucks... air well enough
And keep the pipes after the venturi free of too many bends and restrictions. The vacuum created by the venturi depends on easy flow from venturi all the way to the exhaust.
another thing to mind is keep your exhaust far from your fresh air inlet, to avoid sucking the fumes back in your lab.
but you'll have to try it yourself.
Even the position where the restriction outlet is in the Y-piece is critical to get the best vacuum generated. A little flow restriction through the fumehood (e.g. a closed fume hood window, vent openings almost closed) actually makes a venturi operate better, but give lower airflow.
Aren't physics great?
So you'll want to have the right ratio pipe diameter vs restriction opening vs fan power /output.
Good luck making something that sucks... air well enough
These are not powerful enough to make nice airflow (and also generate poor pressure drop - meaning adding few kinks on the ducting and prolonging it and you practically make it useless) and thus unsafe to use with common size fumehoods. Of course, some fan is better than no fan, that is for sure. But I will not "cheapskate" this, since reliable hood is one of the most necessary things refiner should have.
You do not necessarily need to use venturi setup for fumehood, but be prepared that conventional radial or axial fans with unprotected metal parts inside will eventually die. Much much quicker than if they will suck normal air. I will upgrade the setup then and use fume extractor tube as 4metals shown - and this will be with venturi for sure. For this, less powerful blower would suffice - thus making it cheaper on this side.
Another benefit of using the venturi setup is by mounting the air intake for the blower outside your lab you will exhaust less air from your workspace but the air exhausted from the inside of the hood (where it matters) will give good fume exhaust. This really matters if you live in an area with cold winters where you need to heat the refinery.
@Yggdrasil is probably the member here who can appreciate this the most, while living in the Philippines heating of the airspace in the refining room is probably never done, but while he resides in Norway, it matters. Then again, if he made tons of money refining, he may air condition his refinery in the Philippines and then it does matter.
@Yggdrasil is probably the member here who can appreciate this the most, while living in the Philippines heating of the airspace in the refining room is probably never done, but while he resides in Norway, it matters. Then again, if he made tons of money refining, he may air condition his refinery in the Philippines and then it does matter.
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Yeah, I can relate to this. We have rated hoods in our workplace, and it is hard to cool them down in the summer - as the AC unit try the best to cool the air in, which is in turn exhausted out...
Wasteful practice. We do have phase converters (or inverters? - basically the circuit that change the frequency of mains voltage - which in turn regulate the speed of the motor) paired with our fan motors, so we can adjust the power of the fans - not the best practice, but when I don´t work with toxic substances, I do not need the hood to be cranked to the max. One "lifehack" of our older colleagues was to use some harmless, but very smelly chemical as "flow indicator" - chemical you are able to smell below 1ppm levels or so. They usually opened some old bottle of mercaptane/thiophenol/dimethyl disulfide in the running hood, while executing the dangerous chemistry. If by any chance you will be able to smell it, crank the power to max and evacuate yourself
Sounds lowtech and pretty basic, but it works very well.
One basic thing I always try to instill in people I am trying to teach to refine is always have a clear path to run. When you need to evacuate quickly you don't want to be side stepping drums and buckets.If by any chance you will be able to smell it, crank the power to max and evacuate yourself
