Strange filter performance

[Mark Verber]

I was with a group this weekend doing a hike through a Utah slot canyon.  There was a beautiful fresh water spring that we were going to refill our containers.  We have a group gravity filter (based on a platypus filter I believe). Water barely dribbled out.  The owner said “Darn.  I forgot to presoak the filter. Doing that helps getting started.”   After 10 minutes still no water flow.

While waiting I pulled out my almost new HydraPak filter.  It has processed around 30l of water so far.  Last trip I used it, I saw greater than .5l/min as a gravity (platy to platy) and 1l/min when I squeezed.  On this trip nothing came through by gravity, and squeezing produces a tiny trickle.

We all gave up and people pulled out their backup bleach, or in my case Katadyn Micropur tablets.

2 days later I tried my filter using water from a stream in Portland’s Forest park. I got around 1l/min squeezing my source platypus.

Any theories?  I have never experienced this sort of thing before.  Everytime I had a clogged filter it only recovered (if it recovered) after backflushing or other recommended treatment.

[Jon Fong / Flat Cat Gear]

Utah slot canyon

That could be the key.  The water in the river needs to have the slit settled to prevent form clogging filters.  The spring?  Hard to say why that would cause a problem but it could be fine silt as well.  It seems like a combination of settling and chemical treatment is could be a way to go.  My 2 cents.

[Jerry Adams]

I have filtered noticeably silty water and it took a while to plug up

If both filters plugged up immediately, then it would have to be very silty, which seems inconsistent with “beautiful fresh spring”

Maybe if the water was very basic it could plug up filters?  That doesn’t make sense either…

 

[Todd T]

When you leave water in the filter and let it dry, whatever minerals were in that water solidify in the filter.  In my experience it takes a LONG soaking to loosen those precipitates so the filter flows again.  After a winter’s storage, I’ve had it take two or three days.

The best solution I’ve found is to run plenty of distilled (not “purified”) water through the thing before putting it away.

[Jerry Adams]

But the hydra pac filter also clogged

If it was just the gravity filter then yeah, it was probably clogged and requires the distilled water.  Or an acidic solution, CLR for example.  And warm water…

[Sam Farrington]

The performance might be strange due to diminished quality in the product.  A design for a DYI filter with replaceable  cartridges is here:  https://backpackinglight.com/forums/topic/99643/

The approach was to use filters with small filter cartridges that can be easily replaced.  And that also cut weight.

Some of the better brands mentioned on BPL are Sawyer, Platypus and Gravityworks.  The replaceable cartridges on the filter in the link above are Sawyer, weigh the least, and the solution has been to carry more than one, maybe several, in case of clogging, and depending on the length of the trek.   And to use backflushing after each use.

At one time, used ceramic filters, and they worked OK, but were quite heavy.  That’s why the approach on the above link was adopted.  As with all such products, there are some that are cheaply made, and don’t last long.  At any rate, the approach outlined in the above link has never left me clogged.  The cost was around $20 apiece for the small cartridges  in Walmart.

One regular BPL visitor, Daryl and Daryl,  who still posts occasionally, covered the clogging issue at considerable length.  And as was mentioned, use of small tablets of your choice is a must for back-up, and do not add weight.

Hope this is helpful.

[David D]

My experience is same as Todd’s

Last weekend did a 3 day group trip so prepped my Gravity Works which was in storage for 6 months, dry.  Almost no flow, even after being wetted for hours.  A 30 minute vinegar soak got it flowing halfway to new and a day later it was almost flowing like new

[Mark Verber]

Several sources have suggested (and I think they are right) that both of our filters had fully dried out since the last time we used them.  10 minutes wasn’t enough time for they to rehydrate and to start to pass the water. Mine is working fine now because the water from the spring soaked into the filter long enough to start functioning.  My lesson is add “filter a few ounces of water” to my departure check list.

 

[Jerry Adams]

or, test the filter a few days before a trip.  If it needs to be unclogged, then you’ll have time to do that

[David D]

>My lesson is add “filter a few ounces of water” to my departure check list.

This year I got a scary surprise the day before leaving when my Quickdraw failed, my son’s Quickdraw failed, and my gravity works wouldn’t flow.  So the primary filter and 2 back ups failed.   I guess there’s no such thing as being over prepared.  My Quickdraw had a micro crack, my son’s Quickdraw had mold (he stored after disinfecting, don’t know what happened there) and my gravity works was calcified (which I fixed later).

The last minute panic drive to the gear shop other side of town wasn’t the ideal start :)  Platy is warrantying my quickdraw, so now I’ll have both an extra quickdraw and an extra gravity works filter.

I still put a note in my google calendar at least 3 days before the trip to pre-wet and test the water filter in case I need to scramble to revive a new one or go shopping.

[Dan]

I always test my filter before a trip, just part of the ritual.

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