thunderfvck
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Trouble with vacuum filtration/better source of filter paper?
Okay, I got a vacuum awhile ago and now I'm really trying to use it.
I have a buchner funnel, a filtering flask and a rubber thing to sit the buchner funnel on so there's better suction in the filtering flask. Only
thing I'm missing is filter paper, so I'm using coffee filters which I cut out in circles to cover the bottom of the buchner funnel
(COMPLETELY cover).
Now, I connect the tube to the filtering flask and start the vacuum. When I put liquids into the buchner funnel nothing happens. The drip rate is as
slow as ever. However, I know there is a vacuum because when I remove the buchner funnel and put my hand over the rubber thing, my hand gets sucked
down. I tried it without the coffee filter paper and it sucked the juices down nicely. So there must be something wrong with the coffee filter. WHY?
And what else can I use aside from this instead of buying filter paper?
Thank you
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Magpie
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stuff to try
I can't speak from experience as all I've ever used is regular laboratory grade filter papers. But I don't know why you couldn't
buy fiberglass furnace filters and cut a circle to lay in your Fuckner funnel. If this is too porous lay a thin coat of diatomaceous earth (DE) over
it using an aqueous slurry. DE is used in swimming pool filters where it performs Herculean duty removing suntan lotion and other human detritus.
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vulture
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Most likely air is getting sucked in between the filter paper and the wall of your Büchner. Also, it could be that coffee filters are too permeable
to gas for this application.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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axehandle
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Yes, but coffee filters are good, especially when you run out of toilet paper.
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thunderfvck
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You see, I could imagine myself using my mouth to suck out the liquid from a coffee filter. I mean, if gravity will do it, surely my mouth can. So why
can't this vaccuum do it? What's the difference?
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Organikum
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You wetten your filter with solvent - same as to filter - wetten it well and start your vacuum source. You should see now if the filter gets sucked
onto the Buchners plate - if yes - good - if not you made something wrong.
Of course the liquid to filter has to cover the whole filter well - or this wont work at all. Say your liquid should be at least 2cm high in the
Buchner.
Another possibility is that the filtrate clogs the filter rapidly and almost completly. Then you should first filter the shit through a glasswool plug
in a usual funnel - reapeat this some times using the same plug if you are not satisfied with the results in the first run and finefilter then in the
Buchner with vacuum.
Gypsum/chalk and such stuff clogs every filter - the prefiltering with glasswool is very helpful.
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thunderfvck
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Okay, well it worked fine with another little thing I have going at the moment. So I guess the last time I did it (and had trouble filtering) the
filtrate was just full of garbage...I'm trying to remember what it was I was filtering...I don't know...I just can't remember for some
reason. Anyway, glass wool, huh? This sounds good. Where can I find this?
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Organikum
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Glasswool? Thats easy! Just melt some glass and press it through a very fine nozzle. 
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I am a fish
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Brewing/Winemaking suppliers sell pretty good filter papers. Coffee filters by comparison are next to useless.
1f `/0u (4|\\| |234d 7|-|15, `/0u |234||`/ |\\|33d 70 937 0u7 /\\/\\0|23.
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axehandle
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| Quote: |
Anyway, glass wool, huh? This sounds good. Where can I find this?
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Eeeeh..... it's not entirely uncommonly used as insulation when building houses.....
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Son of Northern Darkness
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Fibreglass?
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Hermes_Trismegistus
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Yup, but the white stuff often used in the middle of furnace (intake air) filters
seems far superior, the strands are much thicker and seem to resist breaking up and powdering much better.
another possibility is to solve the root problem.
Not enough vacuum (volume).
So either use multiple aspirators in a manifold, buy a better vacuum pump, or have the vacuum you do have operate over a smaller area.
Try getting a thistle tube, before the advent of cheap and humungous high vac sources they were the last word in filtering.
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Organikum
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| Quote: |
another possibility is to solve the root problem. Not enough vacuum (volume)
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Thats nonsense.
Vacuum filtration doesnt need high vacuum at all - it is even possible to clog filters by using a too strong vacuum source - a aspirator running half
power is perfect.
A layer of celite on the filter paper often helps a lot against clogging - the basic problem of clogging is either a mismatch between particles and
pores size or plain a to low a surface area of the filter.
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Hermes_Trismegistus
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| Quote: | Originally posted by Organikum
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another possibility is to solve the root problem. Not enough vacuum (volume)
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Thats nonsense.
- the basic problem of clogging is either a mismatch between particles and pores size or plain a to low a surface area of the filter.
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Not necessarily......I could not see his equipment, but I got the feeling that his problem might be that he was using a small glass aspirator with an
11 inch buchner funnel.
Remember, that Thunder didn't say that the paper was clogged, but rather that the flow rate didn't seem to get much faster than the
normal flow rate with gravity
(however I agree with everything else you had mentioned about clogging)
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Organikum
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There is no problem in using a small glass-aspirator with a 11" Buchner.
Also when the filter is clogged some liquid will dissipiate through - almost always. Slowly, but it will. A perfect tight seal isnt so easy to get -
ask a shipbuilder or a plumber....
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thunderfvck
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I'm using a vacuum pump that works well for every other filtration I try. Flow rate is good, it was just for one particular filtering that I was
having trouble. So it must have been "dirty" with thick stuffs which prevented it from filtering nicely. I'll have to use glass wool
next time. Thanks for all the responses, it's appreciated.
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