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Author: Subject: Filtration - any issue with using positive pressure instead of vacuum?
RogueRose
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[*] posted on 7-11-2015 at 09:44
Filtration - any issue with using positive pressure instead of vacuum?


I was devising some improvised filtration devices and was wondering if I increase the pressure above the media to be filtered to like 30-60 PSI, would that work to help increase speed of filtering?

Also, if I have a container that is 12" diameter where the air-space is and then a reduction down to 6" where the filter is located. There is more surface area where the air pressure is, so would that increase the pressure over the filter medium? So would I get more pressure with what I just explained vs a 6" straight pipe?
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Magpie
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[*] posted on 7-11-2015 at 10:41


yes, no, no.



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Fulmen
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[*] posted on 7-11-2015 at 10:59


Short and to the point, Magpie :-)

Using high pressure rather than vacuum is a valid approach and has some benefits over vacuum as well. Filtering saturated solution with vacuum can be a challenge as the pressure drop causes evaporation and cooling that can cause the solute to precipitate out in the filter. You can also achieve far greater pressure differences than vacuum will permit.




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subsecret
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[*] posted on 7-11-2015 at 11:49


Keep in mind that it's much easier to keep an apparatus together if it's under vacuum, rather than under pressure.



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aga
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[*] posted on 7-11-2015 at 12:11


Pressure instead of Vacuum kinda makes it hard to do any washing.



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Xenoid
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[*] posted on 7-11-2015 at 13:27


Pressure filtering works wonderfully well, and is commonly used on an industrial scale.

Check out this thread, http://www.sciencemadness.org/talk/viewthread.php?tid=9630 a pressure filter built from PVC plumbing parts! Note the WARNING.

Cheers, Xenoid
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Mesa
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[*] posted on 7-11-2015 at 22:34


Flow rates are a hell of a lot slower with positive pressure in my experience. I had the same idea in the past but quickly abandoned it.
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Pumukli
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[*] posted on 8-11-2015 at 11:50


Once I tried applying a bit of pressure over a diethyl-ether containing solution/solid particles mixture, although not for filtering purposes, by a hand bicycle pump. Could not even finish the first "stroke", the ether vapour "detonated" in the pressurized chamber - a plastic hypodermic syringe in this case!

(We all know that it was not a real detonation, but this word seems to be the most accurate to describe the emotional effect it had on me.) :D

Based on this experince I would avoid pressurizing anything flammable with air. Maybe with inert gas it would be different.
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