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Author: Subject: Vacuum filtration - fewer holes vs many holes in filter plate?
RogueRose
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[*] posted on 16-7-2016 at 11:07
Vacuum filtration - fewer holes vs many holes in filter plate?


I'm planning on using an old plastic tub, about 1.75 gallons in size. It is kind of like the tubs that protein powder comes in - a really over-sized mayonaise jar. The bottom seals well on another container that has a vacuum attachment/vent.

The question I have is whether putting 7 holes (maybe 1/4-3/8"), one centered and 6 evenly spaced in a ring 1/4 of the way from the edge of the container. The other option is to drill lots of smaller holes all over the bottom, space them evenly as possible, but put maybe 50-80 1/8" holes.

Another option I was thinking was this tub can be filtered at a ~45 degree angle so the edge of the bottom of the tub would be the lowest point of the vessel, allowing the fluids to accumulate at this point. I could put a number of holes around this area and attaching a filter material is actually pretty easy, so that isn't difficult. I guess this would act kind of like a funnel in a way.

The liquid to be filtered has a viscosity close to water, +/- ~15% in "thickness" if that matters much.

Can anyone shed any light on the effect of the number of holes? I would think with vacuum less holes might allow for more "pull" at each hole vs where gravity filtration - the more holes allows for more flow as all are even.
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[*] posted on 16-7-2016 at 13:56


I would imagine more smaller holes would be the better choice. If using larger holes, you run a higher risk of tearing filter paper and having a non-uniform net filtration. Although smaller holes could limit the flow through the paper and the filter plate,I think it would likely be worth the extra time spent per filtration run.



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Sulaiman
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[*] posted on 17-7-2016 at 02:09


For vacuum filtration I would definitely go for many small holes as wet paper is very weak

don't forget to leave the area around the edge of your paper with no holes so that the papers do not leak around the edges, something like 5% of diameter.

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[*] posted on 17-7-2016 at 13:30


You need a large area exposed to vacuum. You cannot filter "sideways" through the paper, only the parts exposed to vacuum will pass any significant amount of fluid through it.
I have on occasion used a disc of very fine plastic fabric under the paper in my Buchner-funnel, and it increases the output noticeably. Basically something coarse and permeable that is thin enough to allow the paper to lie smooth around the edge.




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[*] posted on 18-7-2016 at 12:12


You might look into wire mesh products, like stainless steel wire mesh, or epoxy coated steel mesh:

http://www.mcmaster.com/#standard-mesh-filters/=13c8bir

http://www.mcmaster.com/#standard-mesh-filters/=13c8bya

http://www.mcmaster.com/#standard-mesh-filters/=13c8c40

http://www.mcmaster.com/#standard-mesh-filters/=13c8cc5

Dutch weave mesh could be used as the filter medium directly without paper:

http://www.mcmaster.com/#standard-mesh-filters/=13cf32v

Then there is Monel:

http://www.mcmaster.com/#standard-mesh-filters/=13c8d5j

And plastic mesh:

http://www.mcmaster.com/#standard-mesh-filters/=13c8dio

Shoot, I thought those would like directly to the item pages - they seemed to in my browser. But you can pick out the products from the survey page easily enough.

[Edited on 19-7-2016 by careysub]
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[*] posted on 18-7-2016 at 20:30


I really wish more filtering products were available with mesh as a paper support. As careysub said, you could use it as a support or as the filter directly. Strong and highly "perforated."



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[*] posted on 19-7-2016 at 04:04


sintered glass buchner funnels come in many capacities and porosities
e.g. http://www.ebay.co.uk/itm/350ml-G3-Filter-Funnel-Buchner-24-...

for diy, why limit to only circular papers, square or rectangular is more convenient;
Vogel has a nice description of a 'filter box'
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