# Building a chemical fume hood with a plain steel blower



## 4metals

I was going through some old papers from my first refinery and came across some sketches I thought some may find useful. This was the first hood I ever made and, all things considered, it wasn't bad. There are a few options I would add today, having had the experience of refining a few ounces under my belt, and maybe we can get some discussion going about what others have experienced and would do to change this design.




Because the blower is basically causing the exhaust by powering an eductor, it only sees room air, not fume laden air so any blower will do. The duct from the blower should be PVC along its entire length but especially from where it enters the hood and goes up into the stack. All elbows should be the biggest sweeps you can find so the air bends around the corner not bangs into a 90 degree wall like it will with a more compact elbow. One alternative is to use 2, 45 degree elbows with a gap equal to the diameter of the duct between them if you can't find an affordable sweep. 

One benefit of the blower was the ability to choose where the input air came from. So in summer I used air from the shop to feed the blower but in winter I used outside air. This made heating the shop easier as the only air I had to re-heat was the air sucked out by the draw of the eductor effect. 

The window folded up so I could work in the hood and when down I could still stick my hands in and do things. Back then I was a relatively small operation and the hood was capable of handling my production which rarely exceeded I kilo of fine gold a day before I needed to upsize. I controlled the rate I generated NOx by controlling the nitric additions so I did not use a scrubber with this setup. When I got larger I did, and the hoods and scrubber feeds changed but that's another story. 

The bottom of the hood was sealed and came up about 4" all around to act as a catch for all spills. (If you say you never have spills then you are one of two things, either a bold faced liar or new at this!) 

One of the things I would add to this system would be a waste drainage port. Sounds complicated but it is simply a bulkhead fitting permanently glassed into the bottom to feed into a drum for waste. The translucent drum (so you can see how full it is easily!) is placed under the hood so the legs of the hood must be tall enough. Then a 2" threaded pipe is threaded into the drum bung which is centered beneath the bulkhead so that you can thread the fitting on by looking down through the bulkhead fitting inside the hood and thread in the pipe. The pipe should extend a few inches above the bulkhead and you can cap it with an easily removable cap. The bulkhead should extend above the base of the hood enough to maintain your spill catching capability. (no sense making a 4" deep reservoir and adding a 2" bulkhead) Offsetting the drain port so it is not in the premium front workspace is a good idea. 

Now when you need to pour waste into a drum it is no longer a funnel full of stinky acid poured while holding your breath, it is simply uncapping the pipe, inserting the funnel, and pouring inside the vented hood. 

When the time comes to empty the drum, the pipe can be removed from inside the hood and the drum slid out for transfer and processing. I quickly realized that if it settled long enough a little more gold always came down so I modified my setup to have an overflow to a second drum by adding a bulkhead overflow a few inches from the top of the drum under the hood and feeding a shorter drum alongside it. That gave me a long retention time for settling and a yearly draining of the tank to recover the settled values on the bottom. I always used Viton gaskets for the bulkhead fittings and never had a leak with spent aqua regia waste. 

I also added lights by cutting a round 10" hole in the top of the hood (one on each side of the exit duct) and glassing in a 10" pyrex glass pie plate. Then a "chicken brooding lamp" can be fitted with a bright bulb and placed on top of the hood, out of the fumes so it will not be eaten up, and you have plenty of light to work with. (The older i get the more I appreciate good light!) 

When I first joined the forum I posted about building a hood and I think this information can add on to that post to help out a few members looking to make a lab for themselves. 

Any other suggestions, or add ons to make this work better are welcome.


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## Palladium

Oh now you tell me! I love reading stories from you gentlemen. Having gotten to where i am now you have to learn those kind of things through trial and error. And boy is there a lot of error! The simplicity of the waste drainage with two settling takes is something that i have had to adapt into my system because of chlorides and fine gold. Chasing them around the system can be a real pita in time and effort. I've learned to use vacuum transfer in almost everything i do now. Makes my job and the safety issue so much easier. I've also had to abandon my once productive fume hood and lab in place of a new building and larger reaction vessels with fume scrubbers like you spoke of. Some days the old lab just seemed like a simpler time.


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## g_axelsson

I've seen a lot of different designs of eductor based fume hoods on the forum and I think that almost every one had the same basic design flaw, the eductor was placed close to the hood. In some cases the long piping added so much drag that the hood got a positive pressure and failed.
If the eductor is placed closer to the exhaust with only a straight pipe and no bends the extra air from the fan will create minimal drag in the system and create a vacuum. In this way the hood will always get a suction and even with a lot of bends of the pipes it will suck out the fumes. The lower air speed in the piping to the hood will also minimize the drag and increase the efficiency.

For comparison I think (i.e. don't know) that virtually every suction dredge have the eductor close to the surface and not at the end of the suction tube.

Göran


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## butcher

There are two types of suction dredge designs, one the eductor is at the nozzle under water, this design uses two hoses underwater, and the other design on the eductor is above water at the sluice box.


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## dannlee

A twelve-inch eductor flue here in Minnesota with our prairie winds & weird turbulence....

Would that be inviting stalling or back drafts as building shading pulled negative air pressure on the structure etc.?

Whats the best way to add protection layers from possible back drafts with that type system?

And how about with direct fan/impeller driven system? Thanks :roll:


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## g_axelsson

I can agree that my comparison to a dredge could be a bit lacking... but I checked the last episode of "Bering Sea gold" to look at their suction hoses and none of them had the eductor at the nozzle. :mrgreen: To transport solid objects there is a benefit of higher flow rate so that gives an edge to the eductor in the suction nose.

But I still stand by my statement that placing the eductor too close to the fume hood is bad. You create over pressure in the pipes, any leakage is pressed back into the room. Too much drag can create an overpressure killing the suction totally.

If the eductor is placed close to the exhaust it will create suction in the pipe and any leakage will only lower the suction in the hood, not push the fumes back into the room. Lower flow (no air from the eductor) in the pipes means lower drag and in the end result in more suction in the fume hood.

Göran


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## 4metals

I would try a chimney cowl, I have seen them made in metal but you would have to make one in plastic. They have some that use a fin to point the exhaust stack into a direction where the wind can enhance suction. 

Goran,

The way an eductor works is to cause a low pressure area below where the eductor tube lets out in the larger pipe. Then air in the hood is drawn up into the area of low pressure and blown out by the exhaust from the fan. They are not as efficient as a blower which has an impeller in the air path but they are not as costly either. If you listen to the concerns of members on the forum it is the cost of a corrosion resistant blower. This design is to satisfy that concern. There are always trade-off's in life, refining is no exception.


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## butcher

Part of most educators is a venturi in the piping, I do not see that in the simple drawing above, just after the point where the fan outlet pipe (fan orifice nozzle output), in the drawing above the exhaust pipe should increase in size to create a venturi effect.

https://www.google.com/#q=venturi
https://www.google.com/search?q=venturi+exhaust+fan&source=lnms&tbm=isch&sa=X&ei=EePnUsWfOpfDoATm9IGgCg&ved=0CAgQ_AUoAg&biw=1024&bih=618


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## 4metals

Yes a professionally made venturi does choke down in diameter where the force of the blower exits but this works on the same principle it just costs less to make. I used one of these for years even after I had better professionally made systems this hood was in use. The one thing that is important is to have make up air, this will not pull air out of a negatively pressurized building, that is why in winter when the place was sealed up, I used outside air to feed the fan.


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## Anonymous

I think that the design that 4metals has posted here is a good framework that anyone can build upon or adapt to their individual requirements.

Nothing is perfect, and certainly everyone has differing needs. Which is why I made the comments in my first sentence. He stood up and offered something for the benefit of the community, but if anybody has built a better working model and is prepared to post it with diagrams then I'm all ears.


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## kurtak

Here are some pics of the fume hood I just finished building - it's basically on the same design as 4metals drawing in his first post

The pic where I am hold the black shop vac pipe up at the elbow is showing about how far the 2" PVC pipe goes beyond the elbow inside the 4" pipe so that the air flow though the 2" pipe cause the air to draw though the hood & not just pass over the elbow (it doesn't actually go in quit that far) 

The blower fan is one from a propane hot water heater (for vent the CO2) I also have a 120 volt computer fan blowing on the main blower motor to help keep it running cool being as how it runs 24/7

The 4" intake on the blower goes though the wall to the out side of the lab so it doesn't suck the heat out of my lab (the fume hood pulls enough as is)

Kurt


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## Irons

I don't know about most folks here, but venting fumes into the atmosphere just seems like a bad thing to do. I think the Code Enforcement Officer would agree with me. A Scrubber would keep the Authorities in a much better mood.


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## bmgold2

Irons said:


> I don't know about most folks here, but venting fumes into the atmosphere just seems like a bad thing to do. I think the Code Enforcement Officer would agree with me. A Scrubber would keep the Authorities in a much better mood.



Good point about the scrubber but it doesn't seem any worse than just processing outside. Quantity of fumes and how close your neighbors or your nice vehicle is would make a difference. Better than a box fan in a window anyway.


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## kurtak

Irons

Actually you may be surprised at how much you can vent before they (EPA/DNR - fed/state) becomes concerned

This last year when I was working on a joint venture with a local scrap yard we had to look into it because we had to be legit with the town/state & fed regulations 

Based on our expected discharge (which would be fair greater then an hobby operation) we were hardly even on the radar - no scrubber needed (we had one anyway) they more or less just wanted us to have our permit in place & know what we were doing - the permit was dirt cheep - we fell under "very small" producer

Can't remember numbers will see if I can get them

Now that I am back home - I am working out of a lab set up out in the old barn (close to a foot ball field away from the house) my nearest neighbor is close to 1/2 mile away --- the "little" bit I do as a hobby is not an issue --- if I had neighbors living just on the other side of my yard fence on 3 or 4 sides I would consider it an issue

Kurt


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## butcher

Small scrubbers for a heated reaction can be simple to set up and use, they can be beneficial to your local environment (or property) as well as to all of our environment including neighbors, the collection of fumes many time can result in useful acids to reuse, with the price and trouble to get nitric acid, collecting these gases and reusing them can keep a little money in your pocket.

It is true on an industrial scale you are allowed to release a certain amount of environmental pollution as long as you do not release more in the time allowed, and as hobbies we are exempt from some rules that the industry standards have to follow because we are small scale. 

BUT

Just try to explain that to the officials who come knocking on your door. Wondering what those toxic and air polluting fume are coming from your shed, explain to them why they should not condemn your property or make it a Superfund clean up because there meters show you are emitting many of the fumes that they condemn properties for (like they do in illegal drug manufacturing processes), try to explain why you are storing toxic sludge on your property, and how you understand how to dispose of it properly...

Try explaining to someone who has no clue, but knows he has the authority to do something about what he perceives is a danger to others and the environment, and who has no clue as to what you are doing or the chemistry behind it, not understanding, he will not think you know what you are doing...

Scrubbing fumes make sense, as well as fume hoods.

I totally agree with Irons and his wisdom, and common sense here:

Venting fumes into the atmosphere is a bad thing to do. I think the Code Enforcement Officer would agree with me. A Scrubber would keep the Authorities in a much better mood.


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## kurtak

butcher said:


> Small scrubbers for a heated reaction can be simple to set up and use, they can be beneficial to your local environment (or property) as well as to all of our environment including neighbors, the collection of fumes many time can result in useful acids to reuse, with the price and trouble to get nitric acid, collecting these gases and reusing them can keep a little money in your pocket.



Yes & I agree - I do not use my hood as a place to do primary reaction (heavy fume production) with the hood as the means of evacuating the fumes --- the hood is for working when prepping to do reactions & working with the solutions after reaction & heavy fuming is done

I believe I posted about this being the purpose of the hood at least one time in the past (maybe more) here on the forum

Here is a pic of my scrubber used for heavy fuming reactions & it works with buckets as well as with the flasks 

I comments to Irons was simply to point out that when working with the scrap yard we had to be in compliance with the town/state & fed therefore we had to look into it & it is surprising the amount you can discharge 

Kurt


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## 4metals

I agree with Irons as well but in a lot of states the EPA guidelines uses a "de minimus" status to determine how much NOx you generate. If you use less than 10 pounds of nitric in a day you are under the bar and you can operate with direct exhaust, HOWEVER, commercially you have to apply to be granted the de minimus status. 

But this hood is intended to provide a reasonable exhaust ventilation to keep the air clean for the operator, I would still scrub the concentrated NOx fumes through a scrubber and run the air from the hood exhaust as a direct vent.


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## kurtak

4metals said:


> I agree with Irons as well but in a lot of states the EPA guidelines uses a "de minimus" status to determine how much NOx you generate. If you use less than 10 pounds of nitric in a day you are under the bar and you can operate with direct exhaust, HOWEVER, commercially you have to apply to be granted the de minimus status.
> 
> But this hood is intended to provide a reasonable exhaust ventilation to keep the air clean for the operator, I would still scrub the concentrated NOx fumes through a scrubber and run the air from the hood exhaust as a direct vent.



Correct - which is why I posted the pic of my scrubber used for dealing with the concentrated fumes - the fume hood is a work station - not a reaction vessel 

Kurt


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## Irons

> Correct - which is why I posted the pic of my scrubber used for dealing with the concentrated fumes - the fume hood is a work station - not a reaction vessel
> 
> Kurt


I agree, Kurt. A lot of folks use a Fume Hood as a location to do all of their work, when it should be primarily to catch the stray fumes when working with reagents and venting glassware while changing-out reaction flasks and such. The best of both worlds is a fume hood with an outlet to a scrubber.
I don't have any choice, my neighbors are just looking for an excuse to complain. The Code Enforcement officer has already paid me a few visits as a result, so I have to go the extra mile to keep him happy. Luckily, my property is zoned Industrial, so he's restricted on how much he can do.


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## kurtak

Maybe these pics explain it better then my words

Also please keep in mind that this is a work in progress - I am still working on re-setting up at home after backing out on the joint venture at the scrap yard - what I am showing is no where near completion - I work on it continually while at the same time working at making a living (the bills do need to be paid)

At the scrap yard both our reaction vessels & fume hoods were set up with scrubbers - we had to large commercial hoods with 12 inch discharge pipe (run through a scrubber)

Kurt


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## 4metals

This little scrubber handles everything passing the condensor of a 12 liter reaction flask just fine. It only has a 3 cfm flow rate from the eductor that powers it but in a sealed reaction that's plenty. The hood moves a lot of air, as Irons says to remove the whiffs of reagent while filling and emptying the equipment and make the environment for me in front of the hood better. It's all about me! :lol:


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## philddreamer

I used your design when I built mine. Works great!!! 8) 

The left colum holds 4 litters of distilled water/peroxide; the middle 5 litters distlled water/peroxide; the right 5 litters of distilled water/sodium hydroxide.

Thanks!
Phil


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## kurtak

Nice Phil - thats my plan in the very near future

4 metals - I saw that back when you first posted it - the one I pictured is my fast cheap build just so I can keep playing till I get one like Phil's built --- it's called don't shut the operation down while you are working on bigger & better - only about 2 hours to build the fast cheap version

Kurt


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## bmgold2

philddreamer said:


> I used your design when I built mine. Works great!!! 8)
> 
> The left colum holds 4 litters of distilled water/peroxide; the middle 5 litters distlled water/peroxide; the right 5 litters of distilled water/sodium hydroxide.
> 
> Thanks!
> Phil



Are the contents of the columns useful for anything once they have been used? Do they collect acid that can be reused (specifically the 2 distilled water/peroxide ones)? Do they catch any PM's that might escape?


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## sharkhook

Distiller water/peroxide and distilled water/sodium hydroxide, what would the right mixture to use for each of these?


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## philddreamer

> Are the contents of the columns useful for anything once they have been used? Do they collect acid that can be reused (specifically the 2 distilled water/peroxide ones)? Do they catch any PM's that might escape?
> 
> 
> 
> Yes.
> If you ONLY scrub nitric, when the time comes to change the solution, you can use the solution for processing silver. If you scrub nitric and AR fumes, like I've done, then I use the solution when I make more AR.
> The Lye I will use for neutralizing waste. I believe there are many more uses, our fellow experts will chime in with more ideas.
> 
> 
> 
> 
> Distiller water/peroxide and distilled water/sodium hydroxide, what would the right mixture to use for each of these?
> 
> 
> 
> 
> 
> Click to expand...
Click to expand...

I don't remember right now, but 4metals shared that information before; I'm sure he'll help us out.

I believe I used 3.75 liters of water and 8 oz of peroxide...

P.S.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=18481&p=186085&hilit=scrubber#p186182


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## kurtak

philddreamer said:


> Are the contents of the columns useful for anything once they have been used? Do they collect acid that can be reused (specifically the 2 distilled water/peroxide ones)? Do they catch any PM's that might escape?
> 
> 
> 
> Yes.
> If you ONLY scrub nitric, when the time comes to change the solution, you can use the solution for processing silver. If you scrub nitric and AR fumes, like I've done, then I use the solution when I make more AR.
> The Lye I will use for neutralizing waste. I believe there are many more uses, our fellow experts will chime in with more ideas.
> 
> 
> 
> 
> Distiller water/peroxide and distilled water/sodium hydroxide, what would the right mixture to use for each of these?
> 
> 
> 
> 
> 
> Click to expand...
> 
> 
> 
> Click to expand...
> 
> I don't remember right now, but 4metals shared that information before; I'm sure he'll help us out.
> 
> I believe I used 3.75 liters of water and 8 oz of peroxide...
> 
> P.S.
> http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=18481&p=186085&hilit=scrubber#p186182
Click to expand...


:lol: :lol: :lol: :lol: - Phil - I am laughing because I just got done going back & reading the your thread about your new shed build - then I saw you had posted here again so checked in here to see what you had to say & see you provided a link to that thread - that was a good thread back then & was well worth going back to again

I have a question - what kind/size vac pump are you running on that size scrubber 

I ask because I have 2 vac pumps one is 2.5 CFM the other is 3 CFM & not sure that enough to run a larger scrubber

When I was working with the scrap yard we had a scrubber set up pretty much like yours only about twice the size but we also had a large vac pump - don't remember the CFM on that pump but it would collapse a plastic 55 gallon drum in a heart beat

Kurt


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## 4metals

The one benefit of using the glass erlenmeyer flasks, other than the fact that they were free, is I am able to see when the red fume is passing off the top into the next vessel. Then I just add either more peroxide or more caustic. 

I found that the full 4 liter volume of each flask worked well with each of the first 2 flasks having 100 ml of 35% hydrogen peroxide and 3900 ml of distilled water. And the last flask has 1 liter of 50% liquid caustic and 3 liters of water. This scrubs an entire karat scrap reaction of 50 ounces without further additions. I re-use the dilute nitric from the first 2 vessels as make-up water for nitric digestions and the liquid from the last vessel I use to neutralize acid waste. 

For quite a while I was buying 1 to 1 1/2 kilos a week of scrap gold and melting it and processing lots up to 50 ounces in size in a 12 liter flask. This small setup worked well and I never experienced NOx fumes in my lab or outside near the vent from the scrubber. I had a small setup and rarely ran more than 1 reaction a week and generated no more than 10 liters of waste a week, which was small enough to treat properly and evaporate the waste water.


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## kurtak

The big scrubber we made at the scrap yard was used for leaching CATs - it was made of 8" PVC pipe 5' long

The reason for the big scrubber was we were using 15 gallon plastic drums with the snap ring type lids on top as our reaction vessels - to keep the plastic drums from collapsing under vacuum we cut round spreader/stiffener's out of industrial plastic cat walk grating (used in corrosive environments) --- on top of each layer of CAT combs we would set a spreader/stiffener --- the 15 gallon reaction vessels (3 of them) sat in a cattle watering tank (plastic) with 2 cattle watering tank heater elements for a hot water bath 

Being a closed vacuum system we would re-dose the reaction vessels with CL (bleach) in the same way (using vacuum)

To check on whether the scrubber was becoming acidic we used a piece of litmus paper inserted through a removable plug hole on top of each scrubber tube

And yes the scrubber was set up so we could drain off some NaHO & then add more under vacuum when needed - so the vacuum was used for both adjusting chemistry in the reaction vessels & the scrubber

The reason that venture came to an end was between the competitive CAT market & the huge volume of waste to deal with it just wasn't worth it --- but hey we gave it a go & it was a heck of a learning experience for putting together a new set up here at home back on the hobby level --- lots of improvements are "under way" as I work on setting up again here at home

Kurt


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## rewalston

I found the thread with which Pawnbroker Bob was talking about his "AB TRAIN" would this work with PVC as Kurt used? I'm looking for something that I can use on buckets when running reactions from AP and HCl/Cl. And what would I need to change if anything?


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## philddreamer

> I ask because I have 2 vac pumps one is 2.5 CFM the other is 3 CFM & not sure that enough to run a larger scrubber


Kurt, mine is a 2, I believe. Now, I don't run mine in a "closed vacuum. The cover on the reaction vessel is loose, but there's enough suction to draw the fumes thru the scrubber.

The vacuum pump is a THOMAS K48ZZEPB3533.

Phil


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## kurtak

Rusty

the "AB TRAIN" that Pawnbroker Bob talked about in that thread is pretty much the same thing 4metals, Phil & I are showing here --- 4metals (like Bob) is using flasks - Phil & I are using PVC (or CPVC) 

The key to using buckets (plastic) as your reaction vessel with a scrubber that works on vacuum is keeping the buckets from collapsing when the vacuum is applied

so you have to have some kind of spreader/stiffener inside the bucket so the bucket holds its shape & does not collapse when under vacuum (as explained in my post about leaching CATS in 15 gal drums)

I have not done this with 5 gal buckets yet but intend to (now that I am back home working on a smaller scale) so I can't take & show any pics (yet)

Here is the plan (in part) cut the stiffener/spreader out of the bottom of a milk crate & using plastic threaded rod with plastic nuts & washers ether make legs so it stands about half way up from the bottom of the bucket - or hang it from the lid (plastic rod/nuts/washers) so it hangs half way down into the bucket when the lid is put on

then plumb the bucket so it can be hooked up to the scrubber

Kurt


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## kurtak

Thanks Phil

I saw that pic& was wondering how well that worked - I have thought about doing the same but didn't think my small pumps would be big enough to work on an open vac at the reactor & still pull the fumes through the scrubber 

Now I am going to have to give it a try :mrgreen: 

Kurt


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## philddreamer

Rusty could do something similar on the top, of the bucket cover. As long as there's a bit of outside air sucked in, there will be no chance of collapse, IMHO.


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## Mgnaing

I start refine 9000 grams of platinum scraps which contain 4050 gram of platinum and others are aqua regia insoluble groups metals. I have no fume hood right now. I have seen too many fume hood building in this forum , but i am confuse how to build . I also want to build fume scrubber, and i can get sodium hydroxide and hydrogen peroxide easily cheap, how much amount of these substance to be use.Can I use plastic tanks to make this fume scrubber ? how large tank is needed. Can anyone give me advice how to build fume hood and fume scrubber of size needed and which is the best way ,.. with regards, 
mgnaing


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## goldsilverpro

Aqua regia will dissolve the stainless container. If not today, maybe tomorrow. Soon.


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## kurtak

goldsilverpro said:


> Aqua regia will dissolve the stainless container. If not today, maybe tomorrow. Soon.



and contaminate you solution in the process & cement your values back out

Kurt


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## butcher

That electric heater sitting in the tank of acid looks to be a very dangerous situation.

I suggest you spend some time studying the forum, you will then be able to answer all of your questions, and find better and safer ways to process your materials.


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## Mgnaing

This is not stainless steel , this vessel is titanium vessel and the heater is made of titanium . stainless steel cannot resist on hydrochloric acid corrosion , below of titanium vessel is stainless steel vessel for assist not to crush the titanium vessel above by rough cement ......


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## Mgnaing

butcher said:


> That electric heater sitting in the tank of acid looks to be a very dangerous situation.
> 
> I suggest you spend some time studying the forum, you will then be able to answer all of your questions, and find better and safer ways to process your materials.



Thanks to butcher anymore , the electric heater is made of titanium and it can use continuously for a long time without cut off electricity . for about two or three days continuously . This titanium vessel is the first titanium vessel i order from titanium company worth $ 1500 . i first test with 20 L of hydrochloric acid + 5 L of nitric acid yesterday , but a huge fume become and too pungent and foul smell around my house. So i need advise friends from the forum to help me building a fume hood and fume scrubber . with thanks 
mgnaing


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## butcher

Thank you for clarifying the metal you are using, it is hard to tell the metal you are using from just seeing the pictures.

GFCI protection for electrical would be a must.

Reading 4 Metals, and many of the other member posts on fume hoods and scrubbers, should help you in building one suitable for your processing needs.

Do not process anything in your living area these fumes will kill.


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## Clneal2003

4metals said:


> Now when you need to pour waste into a drum it is no longer a funnel full of stinky acid poured while holding your breath, it is simply uncapping the pipe, inserting the funnel, and pouring inside the vented hood.



Amen! I'm totally going to use your model here as my first hood if you don't mind. Did the fumes just blow out a duct on top of your shed? I'm still really small time but am constantly looking for ways to simplify this...

Right now I march back and forth from the house grabbing jug after jug of solutions and jars. Constantly putting stuff up and pulling stuff outside depending on the weather. 

Oh yeah... What material did you use for the interior?


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## saadat68

Can someone say to me is there a hole on top of the bottle ? If no, So I think vacuum pump break it. right? :shock:


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## 4metals

The flask is vented from a hole in the stopper on top of the flask.


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## autumnwillow

4metals there's a hole in that setup?

Mine doesn't have any. If he is going to use 2L nitric acid thats going to leak for sure.

Saadat make your own thread and post pictures there, we'll help you from there.
If you make a closed system like this you can work indoors. And you will use half of the acid that you normally use as a closed system is more efficient. It can also scrub 99% of the fumes while you can recycle all of the wastes generated by the scrubber.


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## saadat68

autumnwillow said:


> 4metals there's a hole in that setup?
> 
> Mine doesn't have any. If he is going to use 2L nitric acid thats going to leak for sure.
> 
> Saadat make your own thread and post pictures there, we'll help you from there.
> If you make a closed system like this you can work indoors. And you will use half of the acid that you normally use as a closed system is more efficient. It can also scrub 99% of the fumes while you can recycle all of the wastes generated by the scrubber.


Thanks you 4metals and autmnwillow 
but if your flask doesn't have any hole, why pump doesn't break your flask ?


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## autumnwillow

saadat68 said:


> Thanks you 4metals and autmnwillow
> but if your flask doesn't have any hole, why pump doesn't break your flask ?



The vacuum is strong enough to break plastics containers, not borosilicate glass for lab use.


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## 4metals

If you suck air out of the flask and do not replace the air (from the hole in the stopper on top) you will have a flask under vacuum. A reaction that is happening in the flask under vacuum is more inclined to boil over, in addition an erlenmeyer flask is not the most desirable vessel for a digestion because as the solution rises with the reaction, the surface area inside the vessel decreases, the higher it rises the smaller it gets and the faster it rises. The word volcano comes to mind!

The hole in the top stopper allows air in and allows air plus fume to be scrubbed to be pulled through the the scrubbing device. Without a hole there is no flow.


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## FrugalRefiner

I like to use a thistle tube in the hole. It makes acid additions to the flask very easy.

Dave


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## saadat68

Thanks guys I think I am ready to start for make a scrubber. I understood what I want now. But I must buy a stopper and drill it ? How big is the hole ? is 1.5 mm diameter enough ?



FrugalRefiner said:


> I like to use a thistle tube in the hole. It makes acid additions to the flask very easy.
> 
> Dave



Isn't it very small ? how you pour acid from this tube? :shock:
Edited: No I think it have good size
https://www.alibaba.com/product-detail/Glass-Thistle-funnel-long-stem-funnel_60098651164.html?spm=a2700.7724838.0.0.la4DLA


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## Shark

FrugalRefiner said:


> I like to use a thistle tube in the hole. It makes acid additions to the flask very easy.
> 
> Dave



Thanks Dave, I had been wondering what that tube was called.


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## autumnwillow

4metals said:


> If you suck air out of the flask and do not replace the air (from the hole in the stopper on top) you will have a flask under vacuum. A reaction that is happening in the flask under vacuum is more inclined to boil over, in addition an erlenmeyer flask is not the most desirable vessel for a digestion because as the solution rises with the reaction, the surface area inside the vessel decreases, the higher it rises the smaller it gets and the faster it rises. The word volcano comes to mind!
> 
> The hole in the top stopper allows air in and allows air plus fume to be scrubbed to be pulled through the the scrubbing device. Without a hole there is no flow.



I agree and disagree here. I would agree if the reaction isn't that violent but I would disagree if the reaction is otherwise. As I have experienced, the rubber stopper actually bouncing out and giving off fumes. In order to prevent it, I had to increase the vacuum pressure. Now if this would happen where I had a hole in that rubber stopper, it would end up spewing gasses or liquid boil overs. I would rather have that gasses/boil overs pass through my condenser and scrubber system rather than spewing elsewhere.

I also do not think that you need to refresh the air inside the reaction vessel as the reactions usually produce gasses as their byproduct. If I were to put a hole, I would have to increase the vacuum pressure which could probably lead to fumes not being scrubbed well as retention time is a key in scrubbing NOx fumes. And everytime I increase the vacuum pressure I end up with an acidic smell at the vacuum exhaust.

Correct me if I am wrong though.

Saadat,
You can use the smallest glass funnel instead.

And here's your shopping list:
Vacuum pump 3cfm (doesn't have to be a chemical type one, a normal one will last as long as you have setup the scrubbing system well)
Bleeder valve for vacuum pump.
Condenser system.
Teflon hose (for the connection between reaction vessel and the condenser, common hoses will deteriorate fast due to heat and chemical attack)
Common hoses - for connecting one scrubber unit to another
Pipes and fittings
Filtering flasks or PVC drums as scrubber units. (Filtering flasks are expensive but they are really an eye candy, PVC drums are cheap)
Bio balls as media for scrubber unit.


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## Barren Realms 007

autumnwillow said:


> 4metals said:
> 
> 
> 
> If you suck air out of the flask and do not replace the air (from the hole in the stopper on top) you will have a flask under vacuum. A reaction that is happening in the flask under vacuum is more inclined to boil over, in addition an erlenmeyer flask is not the most desirable vessel for a digestion because as the solution rises with the reaction, the surface area inside the vessel decreases, the higher it rises the smaller it gets and the faster it rises. The word volcano comes to mind!
> 
> The hole in the top stopper allows air in and allows air plus fume to be scrubbed to be pulled through the the scrubbing device. Without a hole there is no flow.
> 
> 
> 
> 
> I agree and disagree here. I would agree if the reaction isn't that violent but I would disagree if the reaction is otherwise. As I have experienced, the rubber stopper actually bouncing out and giving off fumes. In order to prevent it, I had to increase the vacuum pressure. Now if this would happen where I had a hole in that rubber stopper, it would end up spewing gasses or liquid boil overs. I would rather have that gasses/boil overs pass through my condenser and scrubber system rather than spewing elsewhere.
> 
> I also do not think that you need to refresh the air inside the reaction vessel as the reactions usually produce gasses as their byproduct. If I were to put a hole, I would have to increase the vacuum pressure which could probably lead to fumes not being scrubbed well as retention time is a key in scrubbing NOx fumes. And everytime I increase the vacuum pressure I end up with an acidic smell at the vacuum exhaust.
> 
> Correct me if I am wrong though.
> 
> Saadat,
> You can use the smallest glass funnel instead.
> 
> And here's your shopping list:
> Vacuum pump 3cfm (doesn't have to be a chemical type one, a normal one will last as long as you have setup the scrubbing system well)
> Bleeder valve for vacuum pump.
> Condenser system.
> Teflon hose (for the connection between reaction vessel and the condenser, common hoses will deteriorate fast due to heat and chemical attack)
> Common hoses - for connecting one scrubber unit to another
> Pipes and fittings
> Filtering flasks or PVC drums as scrubber units. (Filtering flasks are expensive but they are really an eye candy, PVC drums are cheap)
> Bio balls as media for scrubber unit.
Click to expand...


As 4metals said you need a hole in the top of your rubber stopper to allow air in. If you feel you are in need of more vacuum capacity put you a tank between your vacuum pump and you columns. Then you can have a valve you can regulate how much vacuum you pull.


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## 4metals

If you do not have a vent your reaction you will have a run away boil over because liquids boil at lower and lower temperatures the higher the vacuum pressure. An absolute vacuum is about 29.9 inches of mercury, at that vacuum water vaporizes quickly. But even a slight vacuum has effect on boiling points of liquid. In Denver Colorado, the mile high city, water boils at 203oF (95oC) because there is less atmospheric pressure bearing down on the water boiling in that city. 

Your vacuum source is capable of the same result, only much more extreme as better vacuum pumps and venturi's are capable of getting a very strong vacuum. 

If you don't allow atmospheric air in you may be able to shatter the glass, but I doubt that because those vacuum flasks are designed to withstand a strong vacuum, but you will greatly enhance your chances of a boil over. Aqua regia likes a little bit of pressure and it actually reacts better. Vacuum not so much!


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## saadat68

autumnwillow said:


> 4metals said:
> 
> 
> 
> If you suck air out of the flask and do not replace the air (from the hole in the stopper on top) you will have a flask under vacuum. A reaction that is happening in the flask under vacuum is more inclined to boil over, in addition an erlenmeyer flask is not the most desirable vessel for a digestion because as the solution rises with the reaction, the surface area inside the vessel decreases, the higher it rises the smaller it gets and the faster it rises. The word volcano comes to mind!
> 
> The hole in the top stopper allows air in and allows air plus fume to be scrubbed to be pulled through the the scrubbing device. Without a hole there is no flow.
> 
> 
> 
> 
> I agree and disagree here. I would agree if the reaction isn't that violent but I would disagree if the reaction is otherwise. As I have experienced, the rubber stopper actually bouncing out and giving off fumes. In order to prevent it, I had to increase the vacuum pressure. Now if this would happen where I had a hole in that rubber stopper, it would end up spewing gasses or liquid boil overs. I would rather have that gasses/boil overs pass through my condenser and scrubber system rather than spewing elsewhere.
> 
> I also do not think that you need to refresh the air inside the reaction vessel as the reactions usually produce gasses as their byproduct. If I were to put a hole, I would have to increase the vacuum pressure which could probably lead to fumes not being scrubbed well as retention time is a key in scrubbing NOx fumes. And everytime I increase the vacuum pressure I end up with an acidic smell at the vacuum exhaust.
> 
> Correct me if I am wrong though.
> 
> Saadat,
> You can use the smallest glass funnel instead.
> 
> And here's your shopping list:
> Vacuum pump 3cfm (doesn't have to be a chemical type one, a normal one will last as long as you have setup the scrubbing system well)
> Bleeder valve for vacuum pump.
> Condenser system.
> Teflon hose (for the connection between reaction vessel and the condenser, common hoses will deteriorate fast due to heat and chemical attack)
> Common hoses - for connecting one scrubber unit to another
> Pipes and fittings
> Filtering flasks or PVC drums as scrubber units. (Filtering flasks are expensive but they are really an eye candy, PVC drums are cheap)
> Bio balls as media for scrubber unit.
Click to expand...

Very good post 
Thanks a lot
I have some questions
#I don't want use Condenser lab. no problem?
#Can I use another hose or pipe instead of teflon hose ? I don't think I can find them here!
#Which type of bleeder valve I must use


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## 4metals

> #I don't want use Condenser lab. no problem?



A condenser will do 2 things for you, it will condense nitric fumes and extend the life of your acid, so you need less nitric. And second it cools off the fume making it easier to scrub effectively. That's why I like to use them. 



> #Can I use another hose or pipe instead of teflon hose ?



You can use PVC or even vinyl hose. The hose will get soft and go limp before it fails so just keep checking it. Teflon is the best but the best is also costly. 



> #Which type of bleeder valve I must use



I would just insert a short length of tubing or a thistle tube as Dave suggested. You do not want to shut it off so why add a valve.


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## saadat68

4metals said:


> #I don't want use Condenser lab. no problem?
> 
> 
> 
> 
> A condenser will do 2 things for you, it will condense nitric fumes and extend the life of your acid, so you need less nitric. And second it cools off the fume making it easier to scrub effectively. That's why I like to use them.
> 
> 
> 
> 
> #Can I use another hose or pipe instead of teflon hose ?
> 
> Click to expand...
> 
> 
> You can use PVC or even vinyl hose. The hose will get soft and go limp before it fails so just keep checking it. Teflon is the best but the best is also costly.
> 
> 
> 
> 
> #Which type of bleeder valve I must use
> 
> Click to expand...
> 
> 
> I would just insert a short length of tubing or a thistle tube as Dave suggested. You do not want to shut it off so why add a valve.
Click to expand...

Thanks 4metals again
Yes I read in another topic bleeder valve is not necessary. and about condenser it is good idea. I don't like it!!! prefer don't use but maybe use it


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## FrugalRefiner

4metals said:


> #Which type of bleeder valve I must use
> 
> 
> 
> 
> I would just insert a short length of tubing or a thistle tube as Dave suggested. You do not want to shut it off so why add a valve.
Click to expand...

Autumnwillow mentioned a "Bleeder valve for vacuum pump". I believe he's probably using this valve to control the amount of vacuul applied to the reaction vessel and scrubber system. Based on this assumption, I further assuming that he uses this valve after the scrubber system, between the scrubber and the vacuum pump. By putting a valve here, he can limit the vacuum placed on the system before it. In that way, he doesn't have a problem with extreme vacuum building up in the reaction vessel or scrubber that could break the flask or collapse a scrubber.

With some tweaking, you can combine both systems. The bleeder can slow the passage of fumes through the scrubber, increasing its efficiency, but there is the risk that without close monitoring, the bleeder could be opened too much, allowing fumes to escape through the thistle tube.

Dave


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## saadat68

FrugalRefiner said:


> 4metals said:
> 
> 
> 
> 
> 
> 
> #Which type of bleeder valve I must use
> 
> 
> 
> 
> I would just insert a short length of tubing or a thistle tube as Dave suggested. You do not want to shut it off so why add a valve.
> 
> Click to expand...
> 
> Autumnwillow mentioned a "Bleeder valve for vacuum pump". I believe he's probably using this valve to control the amount of vacuul applied to the reaction vessel and scrubber system. Based on this assumption, I further assuming that he uses this valve after the scrubber system, between the scrubber and the vacuum pump. By putting a valve here, he can limit the vacuum placed on the system before it. In that way, he doesn't have a problem with extreme vacuum building up in the reaction vessel or scrubber that could break the flask or collapse a scrubber.
> 
> With some tweaking, you can combine both systems. The bleeder can slow the passage of fumes through the scrubber, increasing its efficiency, but there is the risk that without close monitoring, the bleeder could be opened too much, allowing fumes to escape through the thistle tube.
> 
> Dave
Click to expand...

I prefer don't use it
Thanks 
Why this forum doesn't have thanks button? :?


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## autumnwillow

Mind you that I had no condenser before, and the hoses and pvc were deteriorating, condensations occuring everywhere. Even the scrubber liquids were overflowing due to condensations. I re-designed and used a teflon and condenser and I no longer had any clean ups to do.

I also did not have any bleeder valve before to control the vacuum. I ended up having to put very little acid in order to avoid too much fumes from being generated. And this took too much time.

As soon as I modified my lab everything was running so fast that the small money that I've spent is well worth for what it is capable now.

A bleeder valve is easy to build. Its just a valve that connects to your vacuum pump.

Vacuum pump -> hose -> T fitting (1 for scrubber, 1 for a gate valve)


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## 4metals

Whose hood is that with the scrubber cylinders in the red milk crate? Is this the system you are talking about or is this someone else's system? 

I'm confused[emoji848]


Sent from my iPhone using Tapatalk


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## saadat68

Hi
4Metal
Can you check blow picture? The picture of first post is very small and I can't read all of numbers
Thanks


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## 4metals

The blower is 500 CFM and the pipe coming out of the blower is 6"

The duct leaving the hood is 12". In the setup I used this hood it went straight up 20 feet through the roof. 

The opening is 30" x 30" 

The door covering the opening is 30" x 18" Leaving an opening of 12" x 30" when closed. 

The bend upward from the blower inside the hood should not be a 90 degree elbow but a sweep. Sweeps get expensive so a pair of 45 degree elbows will suffice. There is too much flow lost in a standard 90 degree fitting, a long sweep is best, 4-22 1/2º fittings is next, 2-45º fittings next and last is a standard 90º fitting. The more air flows through the 6" pipe, the more air is sucked along with it up the 12" pipe. So if you are buying a blower opt for the highest CFM flow.


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## saadat68

Thanks for your nice and cheap design


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## saadat68

Hi
20 inch for deep is OK ?


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## saadat68

I have an idea :idea: 
add blower under the hood. It can increase efficiency
Isn't better?


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## saadat68

4metals 
Sorry 
Can you help me ? I am confusing
As you said more CFM is better I want to add one 1000 CFM exhaust fan to my hood. Exhaust fan is cheaper than blower and it costs 35$  

I can not find 12" pipe. which is better ?

Add 2 pipe (4.33") over the hood and 2 pipe (2.48") from blower
Add 1 pipe (4.33")over the hood and 1 pipe (3.54") from blower

I can find these pipes here:

4.99"
4.33"
3.54"
2.48"


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## Barren Realms 007

saadat68 said:


> 4metals
> Sorry
> Can you help me ? I am confusing
> As you said more CFM is better I want to add one 1000 CFM exhaust fan to my hood. Exhaust fan is cheaper than blower and it costs 35$
> 
> I can not find 12" pipe. which is better ?
> 
> Add 2 pipe (4.33") over the hood and 2 pipe (2.48") from blower
> Add 1 pipe (4.33")over the hood and 1 pipe (3.54") from blower
> 
> I can find these pipes here:
> 
> 4.33"
> 3.54"
> 2.48"




Check in your country for a plumbing supply company they should have the pipe size you are wanting.


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## saadat68

Thanks for your reply 
I searched in web. companies produce larger pipes here but I can not find in shops. Large pipes use in big projects. Largest size that I can buy is 4.92"
I think I must use 2 or 3 pipes instead of one


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## saadat68

OK
This is my design. Add 2 pipes 4.9" over the hood and add 2 pipes 3.54" from 700 CFM exhaust fan
20" deep and 23" * 12" opening 
Tomorrow go to carpentry. Hope it works
I will post picture after finishing


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## butcher

creating a venturi, with different pipe sizes, will improve performance.

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=venturi+effect


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## saadat68

Today I get my hood from carpenter
Now I must coat it with epoxy paint and add pipes and an exhaust fan for blowing air


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## saadat68

I buy this fan for 11$. It is 640 CFM
Can I use it instead of blower ?


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## Palladium

Though that fan may move air at a certain cfm rate it does so with really creating any resistance to the air or creating any vacuum. It blows 640 cfm with restrictions. Once you channel that air through pipes and turns it's going to lose it's pull or vacuum. You need a squirrel cage blower or centrifugal fan. Find you a scrap yard and get a blower from an old heating system if nothing else. I buy them for $20-50 depending on size. They are cheap and need replacing about every 2-3 years, but are cheap and easy to replace. 

https://www.google.com/search?q=squirrel+cage+fan&num=30&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjmo5Pi8dHRAhVC4CYKHV4OCeAQ_AUICSgC&biw=1252&bih=582




.


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## saadat68

Finish! (90% completion )
Today I test my hood with fire some paper in the face of opening of the hood and I think it works 8) It sucks smokes 

Thanks all specially 4metals


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## saadat68

4metals said:


> image.jpg
> 
> This little scrubber handles everything passing the condensor of a 12 liter reaction flask just fine. It only has a 3 cfm flow rate from the eductor that powers it but in a sealed reaction that's plenty. The hood moves a lot of air, as Irons says to remove the whiffs of reagent while filling and emptying the equipment and make the environment for me in front of the hood better. It's all about me! :lol:


Hi
One year ago I made a scrubber like this with 3 of 5 liter erlenmeyer 
But after 3 days I saw 2 of them were broken. They contain sodium hydroxide and I think it breaks my flasks 
( I must say my erlens made from glass and not pyrex or etc )
Do you know what was my problem ?
Thanks


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## 4metals

https://nvlpubs.nist.gov/nistpubs/jres/27/jresv27n2p143_A1b.pdf

I used the caustic sparingly only enough to maintain a slight alkalinity and never had any issues using Pyrex vacuum flasks.


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## saadat68

http://goldrefiningforum.com/~goldrefi/phpBB3/download/file.php?id=24799&t=1

I think white pipes is PVC
Can we use PP or PE pipes and connections instead of them ? ( I want learn to my countryman to how build scrubber but there is no pvc pipe like picture in my country )
Also we can use pvc hose but in some sections it is very better to use pipe
Thanks


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## francisco rodriguez

Hola a todos, empezando a fabricar el limpiador de gases, estaria correcto.?
Lo mas barato del mundo.
Gracias por sus criticas .


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## francisco rodriguez

Haber si soy capaz de enviar mas foto.?


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## FrugalRefiner

Francisco, you'll get more relies if you post in English. It's much easier for you to translate your post one time than for every member to translate it when they try to read it.

Dave


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## francisco rodriguez

Lo siento Dave, con el ingles lo tengo complicado y por lo que veo con las publicaciones, tambien..
Gracias de todas maneras, sigo estudiando.


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## Shark

francisco rodriguez said:


> Lo siento Dave, con el ingles lo tengo complicado y por lo que veo con las publicaciones, tambien..
> Gracias de todas maneras, sigo estudiando.



Si bien no es perfecto esto puede ayudar.

https://translate.google.com/?hl=en&tab=TT


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## francisco rodriguez

thank you very much shark, it seems that yes, that helps


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## francisco rodriguez

With regard to the filling of the boat, will it work to clean the nox.? Of course, I'm making two more, with a capacity of five liters each for the H2O2, with similar filling. (This has eight liter capacity, for NaOH.)
 
Paco (Hipocoristico of the name Francisco.) :mrgreen:


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