# Gravity filter speed-up



## samuel-a (Jul 18, 2011)

I've been wanting to try this idea for a while now...

With a dremmel tool i "carved" these trenches in the plastic funnel.
With a turbid solution (Ar+AgCl), the speed improved from about one drop every 1 - 1.5 seconds to 1.5 - 2 drops per second, that's almost twice as fast...
I guess the dipper they are, the higher the speed could be...

Though i usually use vacuum, occasionally, i do find myself needing to use gravity filtration.

Edit: spelling


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## goldsilverpro (Jul 18, 2011)

They sell funnels with a spiral groove cut in them but I haven't tried them. Similar idea.

I do a lot of gravity filtration and, except for things like gold powder, I often "flute" the paper and have learned do it very quickly. It increases the surface area of the paper and speeds things up considerably. The folding doesn't have to be perfect. 
http://www.chem.ubc.ca/courseware/235/danalabsess/flutedfilterpaper.html

https://encrypted.google.com/search?hl=&q=fluted+filter+paper+done&sourceid=navclient-ff&rlz=1B3MOZA_enUS408US409&ie=UTF-8&lr=all


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## 4metals (Jul 18, 2011)

You can also cut a re-useable circle out of fiberglass window screening, and fold it into a cone shape along with the paper. Place the screening against the funnel and the filtration rate will increase. 

Screening also helps with a Buchner funnel but the screen must be smaller in diameter than the paper.


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## dtectr (Jul 18, 2011)

Though I haven't tried it personally, the good Dr. from Costa Rica recommended gathering a bunch of coffee stir straws into a bundle, rubber-banding the bottom, then fanning them from the top to form a cone, then place this inside the funnel, under the filter paper. This, as well as the other suggestions, allow for filtration to occur from the sides of the funnel, rather than just at the bottom.

just my dos centavos.


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## 4metals (Jul 18, 2011)

If you're inclined to buy one, they come in many sizes from 3" diameter to about 10" diameter


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## goldsilverpro (Jul 19, 2011)

This is very easy to do but hard to explain without a picture. For those that have my book, there's a drawing of it on page 73. 

The standard way of folding filter paper is to fold it in half and then fold it in quarters. The problem with this is that the cone fits the funnel so perfectly that all the paper seals flat to the funnel when wet. For fast filtering, this is undesirable. To improve this, don't make the second fold all the way over to the edge. For 6" - 8" paper, only bring the second fold to 1/2", or so, from the edge. That way, the top diameter of the paper cone is larger and, when it seals to the funnel upon wetting, there will be an air gap between the lower parts of the paper cone and the funnel.


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## Acid_Bath76 (Jul 19, 2011)

GSP, outstanding book by the way! I use this method with fantastic results. I still get a chuckle out of it. KISS method.. *K*eep *I*t *S*imple *S*tupid.


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## samuel-a (Jul 19, 2011)

Thanks for the added information guys.

I deepened the trenches today with the dremel tool... boy, now it's filtering almost as fast as i pour in the filter.
1 liter in about 15 minutes, that's great. And without any added costs.


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## glondor (Jul 19, 2011)

Now that is just brilliant. Small details, huge results.


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## goldsilverpro (Jul 19, 2011)

Acid_Bath76, thanks for the compliment concerning my book.

It is interesting to note that, without exception, all of the excellent "tricks" in this thread had one thing in common: to prevent at least some of the filter paper from "sealing" flat against the inside surface of the funnel.

BTW, here's the drawing from my book of the paper folding method referred to in my previous post. I didn't think this up. I saw it in several old books, tried it, and it worked.


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## dtectr (Jul 19, 2011)

Patnor1011 shared some suggestions in this thread: 
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=10273&p=99038#p99038


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## goldsilverpro (Jul 19, 2011)

Except for carving out the funnel with a Dremel, I've used every method discussed on this thread, including a version of the straw method - I just distributed several drinking straws in the funnel before putting the paper in (that proved to be a pain in the butt). I even owned some very large glass Mooney funnels like 4metals mentioned. 

Of all these things, the one that made the biggest difference in speed, by far, was to "flute" the paper. It is the only method I know of that both keeps much of the paper away from the funnel surface and at least doubles the effective surface area of the paper. An improvement would be to use both the window screening, that 4metals mentioned, and also "flute" the paper.

I haven't tried these, though. In combination with fluting, they might really be great.
https://www.vwrsp.com/catalog/product/index.cgi?product_id=4829651


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