fume hood design

What you're after is a squirrel cage fan/blower.

Quote: Originally posted by S.C. Wack

As I've pointed out before, the original fume cupboards were powered by flame. Then ordinary fans. This was suitable for a long time. If you're having explosions, you need to either stop pouring stuff on the floor of the box instead of in glassware, use coolant with your condenser and receiver when distilling ether or acetaldehyde, or get a bigger fan.

Quote: Originally posted by entropy51

My hood is not too different from that one, but my hood is larger, with double plastic doors opening from each side. I also have an L-shaped baffle or "airfoil" under the doors so that a nice laminar flow of air enters and sweeps across the floor of the hood on its way to the exhaust port. I've worked with halogens, phosgene, AlCl3, Grignards, H2S and lots more without trouble.

Quote: Originally posted by bob800

What type of blower are you using?

Quote: Originally posted by bob800

So something like this would work: <a href="http://www.kalyx.com/store/proddetail.cfm/ItemID/897933/CategoryID/12000/SubCatID/2745/file.htm">http://www.kalyx.com/store/proddetail.cfm/It emID/897933/CategoryID/12000/SubCatID/2745/file.htm</a>? I don't understand why these squirrel cage blowers are so much more expensive per cfm then something like this: <a href="http://www.horticulturesource.com/product_info.php?products_id=6386">http://www.horticulturesource.com/product_info.php?products_id=6386</ a>

Quote: Originally posted by thorazine

I was wondering if was a good ideia use parquet on the floor of the fumewood! It's chemical resistant and cheap..

Quote: Originally posted by bob800

Also, how necessary is it to place the motor at the end of the duct if it's separated from the air flow?

Quote: Originally posted by bob800

How much resistance does an average duct have? I measured my hypothetical duct to be roughly 45" inches total, with 1 turn.

Quote: Originally posted by peach

[EDIT] CAN WE PLEASE MERGE AND STICKY THE FUME HOOD QUESTIONS?

Quote: Originally posted by bob800

However, I still have a remaining question: How much space does a 24/40 ground glass distillation setup take? I don't have one (I currently use a retort for corrosives) but may buy one eventually.

Quote: Originally posted by bob800

Thanks for measuring your setup. OK, I've figured out almost everything, however I need some feedback: 1. Dimensions: You said your setup is 70 x 70 cm, so I'll make my hood 2.5 x 2.5 feet (76 cm). If I'm correct, 2.5 feet * 2.5 feet * 60 = 375 cfm, which is in range of my blower. I don't understand why the depth of the hood isn't taken into the calculations? Should it be? PLEASE CORRECT ME IF I'M WRONG

If I read correctly the nomogram for 5" and 600 cfm shows 8 INCHES FRICTION!!!. That's way too much... Could I adapt the pipe to say 8" and read the chart from there? Or would the adapter still add a lot of friction? Or is the motor wheel just not physically big enough?

[Edited on 3-8-2010 by bob800]

[Edited on 3-8-2010 by bob800]

Entropy is correct, it's the area you need to consider when working out the flow velocity.

What's wrong with using PVC? There's a ton of it at the hardware store, you can cut it with a hacksaw and the fittings simply push together to provide a seal. The seal also can't fall apart, as the washers point inwards, like wipers, which prevents the pipe from sliding back out. In fact, it's physically impossible to pull them apart without releasing the collet. That's a lie, I did manage to pull a connection apart at one point, using the bucket of an excavator that was being driven by ten HP+ of hydraulic pumping; I did so intentionally before anyone jokes about it

110mm foul drain pipe isn't very expensive, it has a large ID, it's very smooth and fairly resistant. If you use 110mm, taper the edges of the cuts with a file and lubricate them up with something slippery; washing up liquid, KY, Molykote, Krytox, vacuum grease, Teflon grease, Vasoline, anal lube....



The lubricant won't make them fall apart, but they will slide together a lot quicker. Awwwww....

If you're concerned about safety, use toughened glass. If you call around the custom glass places, they'll have it. Bathroom suppliers or people involved with things like glazing for schools are good bets. The bathroom places will use it to produce things like panes for showers, or curve it to make walk in showers. You can even buy the toughened panes as components for showers from numerous places. But you'll probably need someone with a diamond saw to cut it, as the scratch and snap method is unlikely to work.

If you use a sheet of polycarbonate, that's fairly expensive to start with. Not as expensive as the toughened glass is likely to be, but on the way. Then add on the complexity of making a dual layer screen and the potentially shit performance it may give; e.g. bubbles between the layers, delamination, build time, etc. And you're on the way to the toughened glass being a time, money & effort saver. Delamination is a good probability if it's being exposed to odd, concentrated solvents, acids, bases and other reactive thingymejiggies.

If you choose the polycarbonate way, you'd probably want the plastic on the outside, as the glass will be more resistant. Whereas the plastic may fog up when exposed to certain things.

If you're doing things involving highly corrosive or toxic gases, the fume hood should be there only to mop up the escapees, not the bulk of it. Using greased tapers, keck clips and wash bottles will take care of 99%+ of the fumes. I can easily generate large quantities of HCl(g) and not even be able to smell it with my nose against the glass.

Fume hoods encourage lazy and dangerous attitudes towards letting things escape and hoping they'll be picked up and absorbed or blown off. Get rid of the risk as it leaves the glass.

It's akin to HazMat suits. The only time you should need one of them is when you're cleaning up someone else's mess or an accident, not for everyday work (unless you work in a nuclear power station, germ warfare or nerve agent factory, and even then, it shouldn't be in the atmosphere in the first place).

[Edited on 3-8-2010 by peach]

Quote: Originally posted by entropy51

It apparently works because I am here to talk about it in spite of having done some risky work in that hood.

Not sure about that, I dread to think what's lurking in my balls to surprise me later in life. I should probably make better use of them now before they go supernova, then shrivel up and need chopping off.

If I were working with anything you mentioned, I'd have gotten rid of it before it ever left the glass. E.g. base washes, solvent scrubbers and so on... back to the wash heads, my best friends in the ethereal glassware domain.

This is like I was saying, I think students need teaching that kind of thing first. Letting them get straight to the fume hood encourages the 'I'll just run this lethal stuff in a beaker' mentality. Like the engineers who can CAD model a bridge but have never picked up a hammer.

Quote: Originally posted by bob800

If I read correctly the nomogram for 5" and 600 cfm shows 8 INCHES FRICTION!!!. That's way too much... Could I adapt the pipe to say 8" and read the chart from there? Or would the adapter still add a lot of friction? Or is the motor wheel just not physically big enough?

Quote: Originally posted by entropy51

I would recommend that you stick close to the design space (CFM, duct dimensions, face area) that Magpie has used in his hood because he is a chemical engineer and he uses his hood quite a bit.

Quote: Originally posted by watson.fawkes

That's 8" water loss per 100' of duct. If you have 50' of duct, that's only 4" of loss.

Quote: Originally posted by bob800

I agree except that Magpie's hood is much bigger than I need (and the motor is too expensive for me-$400 new). All I need is to be able to barely fit a distil. setup.

Quote: Originally posted by peach

What's wrong with using PVC? There's a ton of it at the hardware store, you can cut it with a hacksaw and the fittings simply push together to provide a seal

Quote: Originally posted by bob800

So if my duct is around 45 INCHES long, at 5" diameter at 549 cfm, then I'd only have ~ 0.3 inches of S.P.! Then my blower would be PLENTY strong enough! Am I correct?

Quote: Originally posted by watson.fawkes

Quote: Originally posted by bob800   So if my duct is around 45 INCHES long, at 5" diameter at 549 cfm, then I'd only have ~ 0.3 inches of S.P.! Then my blower would be PLENTY strong enough! Am I correct? It's true if that's 45 inches of straight duct without bends. Bends add to static pressure drop.

Quote: Originally posted by entropy51

If the window is visible to passers by, it might be better to use a thick sheet of clear Plexiglas (PMMA) over the window and attach the blower to that. That's what I've done and it's never attracted any attention from the curious folk who seem to be everywhere. Even better to also plant a shrub in front of the window. Even better if you have no neighbors, but a low profile is always good.

If you're the kind of odd ball person I find floating around a number of these forums, you could also run the work once it's gone 11 or 12 at night, when most people will be home and probably in bed. I'm quite often up at 4am messing around. Watching people walking up and down the road hitting things with a garden spade, for example.

If you blown enough corrosive or dirty shit out the exhaust, that bush in front of it may begin to take on a chemically toasted appearance. If the rest of the garden is vibrant green, the bush may make the exhaust stand out even better to passers by than the exit it's self, when they hear the fan noise and notice a bush near were it's coming from has gone brown.

You may wish to add a one way flap to the outlet (like a piece of rubber sheeting), such that a gust of wind isn't going to blow the fumes back through the hood.

Running it on wet or rainy days will also knock a lot of things out of the air. HCl(g) will fall out quickly, for example. You can easily implement a method to force a constant rainy day on the output by simply sticking a tiny fogger or misting nozzle towards the end of the outlet.

In the UK, we have a brand called Hozelok that sell a ton of cute little micro-irrigation things at the garden centres. They sell a number of nozzles for producing a cone or fan of mist for the plants. All you need do is get one of those and hook it up to a tap, then turn it on when something nasty starts coming off. The water usage rate will be significantly lower than it would for an aspirator in the sink. If you're using PVC, corrosion won't be an issue and you can simply drill a hole for the nozzle to poke in and silicon or epoxy it in place, or a few of them at various angles down the length to get a good scrub action on the go.

I think I actually have some of those nozzles in the garage. If I can find them, I'll post you one or two for free.

This is a method used in some commercial fume hoods. To deviate a little for a history lesson, in 'ye olde days' they didn't even use a fan. They'd have a flame at the back of the hood to draw the fumes out by convection. This also happens if the exit is high up, it's called the chimney effect and it's partly why chemical plants and power stations use chimneys, the air rushing over the top creates a venturi like effect and sucks gas up automatically. The helical swirls you see on some are vortex breakers, so the airflow around the top doesn't place too much bending load on the stack. U-Boats used this trick in water when they realized in WW2 that raising the periscope effectively draws a long white line of foam, created by turbulence, towards the exact location of the sub, for a plane overhead to line up with and then bomb. Hoffman also commented that he was using flame aspirated hoods in his lab when he produced LSD, when discussing how basic their equipment was back then despite dealing with something so powerful. For biologists in particular, the flame has the additional benefit of killing anything organic trying to escape. State of the art aerospace design also makes use of vortex properties. Those little fins you see sticking vertically out of the wings on an airliner are vortex catchers. By stabilizing the vortex under the wing, it creates high lift efficiency. If they're allowed to burst under the wing, the pressure difference drops. And the randomized popping creates turbulence. The same effect is now being proposed for wind turbines, to increase their efficiency. And, yet again, it's also seen in nature. The bumps on the fins of big whales have evolved to be there as they allow the fin to cut through the water better by controlling the vortexes flowing over it, and so, the turbulence.

The activated filters are also standard for modern commercial hoods, the recirculating hoods are largely just a carbon filter. Which worries me somewhat given the variability of things that'll go through them, as anyone who's looked at respirators will know one cartridge will not safely absorb every fume. E.g. ammonia and monoxide will pass through carbon filters okay.

I don't know about the precise velocities and such that you'll achieve with the filter in place, but you can buy huge ones and you can always modify the fan selection. If commercial hoods use them, you'll be able to do it, it's just a matter of cost. Anything another human has designed or built, you can understand or replicate given enough effort.

Another option would be to use a HEPA filter with an activated carbon back, which will also allow a lot of gas through. You could even fit the filter behind the baffles, such that most of the nasty shit is absorbed within the hood before it gets to the duct. Big, high flow rate, low pressure drop HEPA filters will probably work out even cheaper than the hydroponics scrubbers, as they are manufactured in vast quantities, globally and are very basic in terms of construction, but also effective enough for use in silicon wafer labs, hospitals and biological laboratories. I've never taken apart a commercial recirculating hood. But I wouldn't be surprised to find a HEPA filter in a number of them.

You're looking for active carbon HEPAs, and the flat kind for the lowest price. You only need the filter element (which are available as consumables for replacement when the originals run off their ratings or start to clog, after about a year to three of heavy use). To drop the back pressure and improve the flow rates even more, you could then pull off the micronic filter stage and just have the activated carbon. Taking care not to pull off whatever is being used to keep it in place, or you'll look like a cartoon character that's just had a bomb go off in their face when you turn it on (the carbon is incredibly fine dust and black, so there'll be something inside containing it).

All the premade filters aside, you could even produce your own, spend even less and likely have it work even better than a commercial option. I expect it'd take less than an hour to put together, probably just a few minutes, as the parts are designed to fit together in seconds with no tools.

To do so, I'd;

1.) Buy a bag of activated carbon powder.
2.) Try to find out what it's rough particle size is
3.) Find something with a mesh rating that's slightly smaller than that (like woven cloth or wire mesh); some places sell wire mesh so finely woven it will filter micronic moisture droplets out of the air, and they often sell it in various metals (like stainless) and in little 1 foot swatches.
4.) Get some PVC sewer pipe and fittings.
5.) Cut a length of it and stick a swatch of material over it, then press the fitting on
6.) Pour in the carbon
7.) Repeat stage 5 for the other end.

That requires zero input from someone who needs the capital to set up a factory and machines, pay peoples wages and make money on it. It's also balls easy. If you make the carbon section a bit bigger than the charge you add, the particles will also get some opportunity to move around, decreasing the build up of concentrated layers. It'll also mean the filter has less opportunity to pack and produce back pressure.

In terms of the mesh, the wire will distort the least (messing with the pore rating) as you jam it in place. But more active metals may also rot open, so a plastic may be better if you're not getting stainless. The pore size should be a little below the dust particle size, but not a lot more. You just want to trap the dust, making it any smaller will make it more expensive and produce more back pressure, making the fan more expensive too.

The American Society for Testing and Materials (ASTM) counts activated carbon as powered (PAC) when the mesh goes above 80, or below about 0.17mm for us newbs who can't visualize mesh numbers. This is the same stuff used in the expensive commercial filters.

The stainless mesh is expensive. A 100 micron (0.1) teflon coated mesh is about £20 per square foot. 100 mesh copper (won't react with HCl(g)) is about £10. Aluminium is around £10. Bronze is £6.25. Brass is about £5. Using a plastic or fabric mesh will be even cheaper.

The prices are from here, but search around and you'll quickly find others doing them by the square foot and they may have discounts on the meshes you're after in stainless

Have a look at this bit as well, where they discuss the different weave patterns. Dutch is the toughest. Sintered won't distort but costs a lot more.

It's likely that you'll want to use the largest particle size available (or even a small grain size) if you pack a good length of the pipe, as it'll be a layer much thicker than most filters so the super fine dust will produce more back pressure. Using larger granulated material will also make the mesh to retain it even cheaper. I would recommend against packing something like the following access fitting full of fine power; enough to create a layer will do.

Anywhere from 6 months to years later, depending on what goes through it and how often, it'll need recharging. Pulling apart standard 110mm fittings is hard work or essentially impossible. You'd need to pay a little more for ones with collets that unscrew. A far, far, far, farrrrr easier option is to contruct your carbon chamber from a 'drain access', 'drain entry', 'rodding' port or 'access pipe'. That's a short length of pipe with an unscrewable port on the side. Do the same with it as above, but now when it comes to recharging you can simply unscrew the port, pour out or hoover up the carbon, pour some fresh stuff in and go.

You can also buy sewer pipe in 160mm, but it's for commercial uses (so less likely to be found in regular hardware stores) and is more expensive (for obvious reasons). There is an added bonus to using what is called 'vent soil pipe' (the black or grey stuff for above terra firma usage), in that you can make it look like a normal foul drain even if it's sticking out the side of the house by simply running it to ground level (although I've heard you crazies in the US run the foul pipes inside the walls sometimes, they're all outside here because all the walls are solid brickwork, making it hard to do the wall trick). Also, have you considered hooking the hood to the actual sewer? That way there's zero chance anyone is going to connect the smell or noise with your house. Especially so if the nearest grid in the street isn't directly outside your drive (as it is for me).

In the UK, the foul drain that leads out to the main pipe in the road is connected to it, by law, via a water trap, to prevent potentially dangerous pathogens and such flowing back up the pipe from material rotting in the public sewerage system. We don't put the traps there, they're put in by the council when they lay the main sewers and hook the houses up in the road. There is also a 'vent pipe' which runs all the way up the side of the house to the roof, where any nasty smells or germs can wash away and air can get in to keep the pressures in the pipe correct for the traps to function.

Hence, if I was to blow a hood's exhaust down my sewer, it'd blow out two stories up where no one would smell it, feel it on them or notice the noise. Even better, if the vent pipe is near the chimney, to a passing glance any persistent fuming is likely to written off as the result of a log or coal fire venting where it's supposed to. With the exit being high up, you stand a better chance of benefiting from a natural aspiration, chimney effect too. Ever seen the water in your toilet being sucked back when it's windy out? That's the aspiration effect, producing quite a fair bit of vacuum in the pipe (the effect doesn't work very much in reverse, blowing things back down it). And you have somewhere for the water from your misting nozzles to drain to. Win, win, win eh? Bar the possible need for a stronger fan (or you could get used to keeping the slash closed over, and keeping in mind that people on here go on about using baffles and adjustable fans to purposefully turn their hoods down when the sash is part closed). Someone has already built a roof mounted, water trapped exhaust for yar. Yars just need to be connectin' to her.

To pick up on the baffling point, I'm not sure how important it is or if people know about it, but baffling a number of fans causes the blades to begin turbulating and stalling and the flow numbers aren't the same as simply turning down the juice into it; the rotor isn't slowing, it's slipping through the air rather than catching it, like a cavitating propeller. Centrifugal fans are prone to this effect. When it starts happening, the flow rate doesn't fall in a predictable fashion, it vertically drops off. As was the case for the U2 spy plane, who's wings would snap off if it sped up too much or stall if it slowed down too much at it's 70 - 80k feet cruise altitude; the margin for error in the speed was 10 knots! This is called the 'death corner' of a planes aerodynamic performance. Airliners suffer a similar problem, but not as severely. Providing another example where an electronically controlled fan speed will probably be a safer bet than doing it mechanically, as the stalling won't occur when you turn the drive down. Probably why a number of modern flow hoods and benches use electronic methods over mechanical baffling, despite it being more time consuming and costly to design, pass through CE testing, produce and fit than a sliding bit of metal.

A 'vented soil pipe' 'access pipe' (£8.94 from toolstation.com in the UK, free next day delivery on orders of £10, free hot drinks in the store & the lowest prices available, sweeet);


There are also other handy bits available. Such as prebent angle bends (which are helpfully made with a slight off 90 degree angle to encourage draining) or this, an adjustable bend to take up errors;


Flexible couplings;


These ones are cheaper and come in lots of different configurations to couple from 110mm to various other sizes. They produce the same water / air tight seal and have big hoze clips to get them tight, as you can see (use a ring spanner or socket set for ease, screwdrivers are a pain in the ass).


There a many more, and the way you set the up is largely limited by your inventiveness.

What you've linked to is essentially a wash head. If you've seen someone going on about them on this forum, there's a good chance it was in one of my posts, as I rant on about their virtues all the time.

The only difference between mine and the one you've shown is that mine is all glass, because they're also used for analytical, experimental work that may interact with the rubbers and such in that one. E.g. HCl(g) will slowly rot orange natural rubber and DCM will make it swell up. But you can get inventive with that two and line the stoppers with PTFE tape or use silicone or poly stoppers.

If you're just using it for scrubbing, I expect that one will do you fine. Along with a number of variations on it that people have made with jars. Fritted glass is better, but the glass frits also have a tendancy to fall apart in strong base solutions, and the aquarium ones can melt in some solvents or corrode around things like HCl(g).

I would hazard a guess that the majority of nasty things you'll produce will be either going acidic or basic when in solution and likely soluble in water; HCl(g) is very soluble, for instance. To scrub HCl(g), you could take that bottle you linked to and simply fill it with extremely concentrated KOH. With no frits to dissolve, it'll sit there happy as piggies in shit (which aren't actually that happy in actual shit) until you're too old to do chemistry anymore. Any HCl(g) that attempts to get through it will immediately be raped, hard, to potassium salt. Use NaOH and you've got table salt. There will essentially zero HCl(g) at the output.

So, selecting to have a frit or not and the material it's composed of depends on the wash in progress. In some cases, plastic will work better than glass. In others, the plastic will be a molten blob on contact.

You can also stack a number in series to scrub a lot of different possibilities, or increase the efficiency again.

I'll include a picture of the wash heads & bottles QuickFit here in the UK do at the end. This one is a sintered version.

All thar best!
John

{edit}I just noticed the price on that bottle you linked to. YOWZERS! That's a good 10 to 15 times cheaper than the bottle alone for this one, used.



[Edited on 6-8-2010 by peach]

Quote: Originally posted by peach

{edit}I just noticed the price on that bottle you linked to. YOWZERS! That's a good 10 to 15 times cheaper than the bottle alone for this one, used.

I'd still consider the PVC pipe option. With the pipe, you'll know what all the seals and such are so you'll better know their corrosion properties. PVC is pretty good in terms of that. The mild steels will start corroding if things like HCl(g) go through. Some of the others components may as well. I suspect granules will do if you fill most of the access pipe. If you can still smell anything, add a handful of PAC.

Unless you've dealt with things like HCl(g), you'll probably underestimate it's ability to rot things. As an example, I can have all my tapers either greased or sealed with PTFE tape and keck clipped. If a few tiny puffs of it escape whilst I'm swapping something around, or if the grease isn't well seated or runs out, things five to ten metres away will start going. My cooker hood is about that far away from the surface I produced some HCl(g) on a few weeks ago. Despite the amounts of gas escaping being so low they are barely detectable, there was rust appearing on the stainless a week or two later. Similarly, if I clean the glass out over the kitchen sink, there will inevitably be a few traces of something left and it'll fume a little. Not enough to be dangerous, but the fumes have rotted a brand new stainless sink to look like it's a decade old, despite me blowing them away and thoroughly rinsing down the surfaces. In fact! I just remembered I have something I can show you...

This is a pair of stainless steel scissors I had lying on the bench beside me when a small, virtually undetectable amount of HCl(g) escaped the glass, they were shiny prior to this;


Note how the opposite side is significantly less corroded, indicating just how sensitive things like this are to the flow rates and directions (it's only stained the top, where it could land, like the germs in Pasteur's broth flasks [Pasteur actually 'stole' a lot of the limelight for germ theory from the earlier Semmelwies, who was told he was nuts for thinking tiny animalcules were everywhere and he died at a young age in a psychiatric hospital, after publishing reams of papers regarding their probable existence, his evidence based control strategies and the beneficial results this achieved in hospitals]);


Despite them having stainless stamped on them, that term is strongly bastardized now to mean anything with any chrome, moly etc content in it that exceeds mild steel grades, so a lot of the 'stainless' you find around the house isn't actually all that stainless. You need graded, controlled stainless like 316, Inconel and the others. But it's a fair indicator of how aggressively things like this will attack metals.

In a lot of cases with chemistry, building your own is usually going to end up costing more in money and time, performing unacceptably or being a risk. I think the access pipe scrubber is reasonable unique in that it is likely to be cheaper, quicker, work just as well or better and present well known and controllable variables.

John

[Edited on 6-8-2010 by peach]

Quote: Originally posted by bob800

Do you think my blower will corrode too then?

.

On the grainger page, (http://www.grainger.com/Grainger/wwg/search.shtml?searchQuer...) it says the "Housing Material" is rolled steel and the "Housing Finish" is gray enamel. But I don't think that's referring to the blades. Can you tell what they're made of from the picture?

The enamel paint idea sounds good, but I don't want to paint the blades shut!

That's excellent that it's already painted with enamel, you're saving some spray painting there.

I would be very impressed if you managed to spray the blades shut, it'll be next to impossible. I guess you may have been thinking of using a brush perhaps?

Nah, don't bother. They sell enamel in spray cans at the hardware and car places. It's often called 'radiator paint'.

Take the cover off the fan and try to get the blades and the motor separate from the housing. It'll be super, duper easy to paint something like that, even easier than most things. Just give the fan a spin (with a stick, not the socket) and spray as it turns. You may want to undo the set screw and take the blades off entirely to do the back as well. Remember to keep the can 12" or so away, give it a good 2 minute shake first, put on a damp coat and add more, carefully as per the instructions. If you put your greasy mits all over the blades and don't follow the time intervals on the pack, it will mess with the paint. Remember there are 'hidden spots' as well, you need to be ducking and leaning all over it under a bright light to find where you've missed. Spraying outside usually wastes a lot of paint.

I can't really tell what the metal is from that picture, it's bright, but it's also brand new. Stainless is quite a bit more expensive to buy and process, so it's more likely it's mild steel. They may have galvanized it, but I'd have to have it in my hands to see that ideally. If it's zinc galvanized, a number of paints won't stick to that without a special primer, so get the fan first or hold onto your spray can receipt.

[off topic]I used to work in a metal fabricators. For one job, they hot dipped a bunch of supports for a railing fence at an airport. Then bought the special acid etch primer. Then were told by the spray guys one drum of the expensive commercial stuff they'd bought would do the entire job with most of it left over. They had about ten on the van. Ask first, buy later.

E.g. Email them and ask if someone can try sticking a magnet to the blades.

[Edited on 8-8-2010 by peach]

OK, I'll go with the epoxy idea. Thanks for all your suggestions.

Attached is my "final" plans for the hood, along with the dimensions.

Also, the depth doesn't have anything to do with how many cfms I need, right? The only thing that matters is the face velocity, right? How deep do you think I should make it?

[slightly off topic]. You said you're using a 1L RBF, right? I don't think I need that much capacity though. Do you think this 19/22 setup would fit in my 2.5' sq hood: [url=http://cgi.ebay.com/New-19-22-Chemistry-Laboratory-Distilling-Kit-FREE-S-H-/200383943175?pt=LH_DefaultDomain_0#ht_3129wt_1137]

Again, thanks for all your help.

Well found what I was looking for from Grainger, but as I thouth the price would be in the $1000's.


http://www.grainger.com/Grainger/PLASTEC-Blower-3MPW3?Pid=se...
But one benefit is that the noise level is only 43 dB

Quote: Originally posted by anotheronebitesthedust

Do they make blowers with ptfe or other non-corrosive, highly abuse resistant materials without charging $1000's? I found this site but they are located in China and I have a hard time trusting asians. And I still wasn't able to find a worthy model. http://www.blower.com.tw/en_pdc00.htm

You can forget that matey!

PTFE = big cash even for objects that can be easily made from standard solids without excess machining or special moulding methods. A centrifugal fan blade is reasonably complex by comparison and theres basically no demand outside of very odd chemical handling problems, meaning they can charge whatever they like, leaving you with you're anus stinging.

I think it might be worth modifying your attitude towards Asians a little there. I get your point, that it's easy to get ripped off from those distances and be able to do nothing about it. However, I have ordered quite a few items from China and actually had the guy send it quicker, cheaper, better and with less hassle than people in my highly developed home town of England.

Also remembering, China is a highly mechanized, technology leading country (a ton of the big name US / European countries have plants out there, not at home). If you pay for rubbish, they'll give you rubbish. If you pay a decent amount, they can produce equally good products, or better (given that 'they' work a lot harder most of the time). As you can see from the photo, I am not 'one of them'.

Besides, if you scrub the gas stream a little prior to it hitting the fan, as per Bob's suggestion in his 3 year old looking paint diagram (jk), most of the corrosives / solvents should be massively diluted down before they get to the blades.

@bob800

>>>>A video reply!<<<<

[Edited on 10-8-2010 by peach]

Wow, thank you so much for making that!. I guess it makes up for your MS paint insult!

[EDIT] I just bought the wood, plexiglass, and blower for the hood. It's going to be 2.5' sq with 2' depth. Hopefully that'll fit a 19/22 setup...

[Edited on 10-8-2010 by bob800]

Glad you liked it. Pictures are a lot more useful most of the time. I'll be stalking you for photos of said fume hood.

[Edited on 10-8-2010 by peach]

I have to bring out my negative nancy hat here and say, that's a bit of a poor excuse. If you can't read the thread, it kind of suggests you might not be too careful using things that require the hood in the first place.

Acetone isn't much of a fire problem. I smoke and play with my lighter sat right in front of it, with it all over the glass (as I rinse it), the surface, the paper I'm writing on, tissues, rags, me... I've never seen it ignite, ever, and I've gone through tens of litres of it.

Ether is another issue altogether.

That's where I'd start considering the benefits of a sparkless motor.

With the doors and windows open as I work with misbehaving solvents, the escaping vapour is rapidly diluted by air passing through. In a hood, it'll puddle up and all have to go out past the fan.

The only time I've had a fire was with cyclohexane. Again, I'd been sat smoking with it all over the place all night. Then someone else came into the room, tried to light a candle and the piece of paper a few drops had landed on immediately burst into flames; within 30s of them coming into the room. Indicating that it's not so much the ignition source, as who's controlling it.

I'm clinically insane (quite literally, according to the NHS). They've had me on their special person pills, checking in for hour long chats with psychiatric teams every two weeks for a year and I only mention it because you mentioned ADHD. I can still read the threads and think they should be merged.

[Edited on 11-8-2010 by peach]

Quote: Originally posted by peach

Acetone isn't much of a fire problem. I smoke and play with my lighter sat right in front of it, with it all over the glass (as I rinse it), the surface, the paper I'm writing on, tissues, rags, me... I've never seen it ignite, ever, and I've gone through tens of litres of it. ..... The only time I've had a fire was with cyclohexane. Again, I'd been sat smoking with it all over the place all night. Then someone else came into the room, tried to light a candle and the piece of paper a few drops had landed on immediately burst into flames; within 30s of them coming into the room. Indicating that it's not so much the ignition source, as who's controlling it. ........ I'm clinically insane (quite literally, according to the NHS).

My two cents..

I'll definitely be building one when I finally return to the US, and my house.

The room I'd set it up in has swamp cooler provided cooling. Maybe I could figure a way to reverse that???

One thought on PVC. As I recall from my woodworking days, moving stuff through PVC can build up some serious static electricity. You're always warned to ground such systems. I don't know if that would be an issue in the ones discussed here though.

Do most of you just run it out a convenient window? I do have one thing in my favor. I'm just downhill from an extremely large, hitech manufacturing plant. One that some folks in my town are always berating/accusing/investigating this company for releasing all sorts of bad, smelly chems. At least I won't get blamed

Quote: Originally posted by albqbrian

One thought on PVC. As I recall from my woodworking days, moving stuff through PVC can build up some serious static electricity. You're always warned to ground such systems. I don't know if that would be an issue in the ones discussed here though.