Pre-filter water AZT

[Patrick W]

Hello!  I’ll be doing the Arizona Trail, starting in March and am trying to get myself geared correctly.  I normally use a Sawyer Squeeze on a smartwater bottle and have never had to prefilter (east coast).  It appears that much of the water on the AZT is from stock tanks and full of floaties and such.  I’d like to come up with a pre-filter that is ultralight, filters finer than a bandana, filters quickly.  And I might as well say that I want it to be cheap.  Good, fast, cheap.  Ideas?

Mando

[JCH]

I’m a homebrewer and recently bought some hop bags from brewinabag.com. They are a very fine mesh (they claim 210 micron) and cheap…$3 each. You could probably DIY something with one of them.

[Diane Pinkers]

Check out this blog post for a pre-filter made from a coffee filter.  I have one of these on my Sawyer, and carry an extra pre-filter in my repair kit–so light and small!

http://adropofrain.net/2012/08/simple-modifications-for-sawyer-squeeze-filter-prefilter-hose-adapter-evernew-water-bladder/

 

[DancingBear]

Diane’s suggestion looks really interesting.  If you want a finer screen you might check out Duda Diesel’s filter fabric.  I have been playing with their filter bags as a pre-filter for a Platypus system, and the results seem promising so far, though the bags are pretty heavy when wet.  But if you got some fabric and cut little circles out to act in place of the screen in Diane’s link that wouldn’t be much of an issue.

Walt

[Diane Pinkers]

What’s the thickness of the filter material, Walt?  If it is relatively thick, then it may not fit, or may get compressed enough that it may not flow well?

You could sure get a *lot* of filter circles from that material, though.

[DancingBear]

It’s about 3/32″ thick (2 mm for metric types). So it’s not quite as thick as the washer that comes with the filter. It’s a felted material, so it’s compressible to some degree.  But I would think it would only compress around the edge, where the bag spout bears on it, and the middle, where the water flows through, would be fine.

I think a thinner washer, as mentioned in the article you linked to, would be necessary.  But it looks promising, at least.  Even one of the bags, which only cost a few bucks, could yield enough circles for a lot of filtering.

I have a used 1-micron filter bag that I could sacrifice, and some thin gasket material, so I think it’s time to do a bit of experimenting.  Stay tuned!

Walt

[DancingBear]

Aaaaand, we’re back with some preliminary results.

I cut up a 1-micron filter bag to experiment with.  The fabric is surprisingly tough, at least to the scissors I used.  But, these are my shop scissors, which I also use to cut brass shim stock, aluminum windscreen material, cable ties, paper, and whatever else comes around, so that may not mean that much.  I removed the gasket in the Sawyer Squeeze and used it as a template to make a circle of the pre-filter fabric, and a new gasket out of thinner rubber.

The circle wouldn’t register on my scales.  For reference, a 1.5″ x 4.5″ chunk of the fabric weighed 4 grams.

I also cut a new gasket of 1/16″ neoprene gasket material.  I didn’t weigh that since I ended up dissatisfied with its performance.

I inserted the pre-filter material, fuzzy side out, followed by the new gasket, and screwed on a full bag of water.  I just used tap water for the preliminary leak and flow testing.

Unfortunately it leaked at the dirty water inlet.  If I really cranked down on the filter to screw it to the bag tighter, I could get the leak to stop, but when I removed the bag the pre-filter and gasket were stuck in the mouth of the bag, which would be a real annoyance on the trail.  I think the leakage was caused by defects in my homemade gasket.

I then tried using the stock gasket.  Stacked on top of the pre-filter it looked like it might be too thick, but in practice it didn’t leak.  If I over-tightened the bag the gasket and pre-filter did lodge in the neck of the bag, just as the thinner gasket did.

I was able to operate the filter as normal, either by squeezing or by simply holding it pointed downward and flowing under gravity.  Apparently there was still some gunk in the dirty water bag from the last time I used it, because the pre-filter did appear to have silt lodged in it after I filtered a couple quarts.  The pre-filter did slow down the flow somewhat, and I’m not sure how quickly it will clog, but it definitely seems to warrant further testing.  I’ll report back in a few days.

Walt

 

[Patrick W]

Some very interesting ideas.  Sounds like a lot of us are working on the same problem.  I had actually been thinking of using a melitta filter cone or something similar.

The mesh inserted in the front end of the filter (from Diane’s link) looks like a great way to deal with leaf particles and such here in Appalachia.  I doubt it can be beaten for weight.

The AZT sources (dirt tanks and livestock troughs) seem to contain big chunks, big and small particles, small worms, bees, and algae.  It’s a wide range of targets.  I am leaning toward taking a reusable coffee filter.

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