YT2095
International Hazard
Posts: 1091
Registered: 31-5-2003
Location: Just left of Europe and down a bit.
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Mood: within Nominal Parameters
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Positive Pressure filtering?
I don`t have a vacuum pump or even a simple aspirator, but I do have an air pump that`s infinately variable from 0 to 2L of a air per minute.
currently all filtration is done in funnels and purely gravity driven, sometime this can take the best part of a day just to clear 250ml.
using 2 identical funnels one set up as normal and the other with an air feed at the base and placing one over the other (vaseline to form a rough
seal) this time can be reduced dramaticaly.
the idea seems so simple, and yet I`ve never encountered it before, so I`m thinking that perhaps I`m missing something in way of drawbacks as to Why
it`s not used regularly.
the only thing in way of complaint I`ve found with such a system as opposed to the Vacuum type is that you can only add a finite amount of liquid at a
time before breaking the seal and having to top it back up again.
and that seems a little trivial as a reason not to use this set up.
what am I missing ?
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Aurum
Harmless
Posts: 34
Registered: 19-5-2006
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I would guess it's because with a vacuum you can never get more than 1 bar pressure difference. With compressed air the pressure difference could be
as high as the compressor is capable of and cause an explosion.
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not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
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I think it's both the increased difficulty of adding further liquid, including for washing, and the tendency of the pieces to pop apart from the
pressure.
I've used it for clarifying, where there is only a small amount of solids to be removed, by pumping the air into a carboy with the solution in it, and
having the solution be forced out another tube and through an inline fritted filter. I had to wire all the connection really tight, as they tended to
slide apart otherwise.
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