thermocouple
06-06-2010, 09:55 PM
Recently the manufacturers of backpacking gear have introduced a line of gravity water filters. These are designed on the same basic principle as the Berkey water filters, but obviously without the heavy, bulky and rigid containment features on a counter top system. I wanted to let these systems ride the market for awhile before jumping in myself, but I recently made the switch before my last backpacking trip.
Initially I purchased the MSR AutoFlow, mostly because I have (and do) own many MSR products and have always been satisfied.
http://img.photobucket.com/albums/v19/cbatson73/autoflow.jpg
However this is a ONE bag system, designed to allow you to mate the output hose to a reservoir or bottle of your own. I found that it was not compatible with my existing (older) Platypus hydration bladder, so this went back. Also, there is a major flaw with the one bag design, if the intention is to filter from the "dirty" bag into a rigid container, such as a bottle. I will describe this flaw later.
The next filter I brought home was the Platypus CleanStream.
http://img.photobucket.com/albums/v19/cbatson73/CleanStream.jpg
It was put through very challenging conditions on my last trip, very difficult filtering with fine suspended sand and silt. The idea behind the design is to fill the "dirty" bladder with unfiltered water, hang it from a elevated position and allow gravity to force the water through the filering medium, filling the "clean" bladder. I was very impressed with the performance of this system, and my fellow backpacking buddies were as well. After one round of pumping through their pump filter, having to service halfway through due to the silt and sand, all four of us easily relied on my filter for the remainder of the trip.
Another interesting filter in this line is the Sawyer.
http://img.photobucket.com/albums/v19/cbatson73/sawyer.jpg
I didnt purchase the Sawyer mainly because I didnt like that bags are not clear, or at least having a window to see the water level. Totally clear would be best, I learned on the trip. However, its interesting to note that Sawyer boasts a 1 million gallon guarantee. They admit that they have not run a million gallons through their filters in test, but make the point that the filter design is such that it's lifespan is virtually indefinite.
I point that out because all of these filter designs use the same basic filtering medium, "hollow fiber technology". The durability of this filtering medium allows for constant re-use, the only service being a back-flush. This is a critical function in the process of keeping the filter flowing in challenging conditions. As impurities invade the filter medium they are trapped, as would be the case with all filters. However, raising the "clean" bag above the "dirty" bag (for a few seconds) effectively reverses the flow of water, flushing the clogging impurities out of the system. When performed at the completion of a filtering cycle, the small amount of backflushed water in the dirty bag is simply poured out.
In really bad conditions the dirty water can be poured into the dirty bladder through a rag or bandana, as a pre filter, to minimize the major chunks able to enter the filter. This is the reason that it became evident to me on the trip that the clear bags are better, since we were able to see any large debris in the dirty bag, and remove it, before it entered the filter, which would have slowed the flow rate.
I like the system a lot, although I dont like that Sawyers bags are not clear and that MSR only provides one bag with their system. You could add a bag to MSR's system for additional cost, but the Platypus is already sold at the same price point. The Sawyer system comes with the neat addition of a faucet attachment, for a serious backflush servicing at home, but their complete 4-liter system was significantly higher cost than Platypus' complete 4 liter system, and if I really want a faucet flush I can make one relatively easily and cheaply.
Berkey filters are in their own category, they are meant to last a very long time on a counter top, and these portable gravity filters are not intended to compete with that market. The obvious advantages of these portables over the Berkey line is obviously the cost factor and portability. But also, the filter longevity. I know Berkeys are built to last a long time, but that is considering that you are already sending relatively clean (tap) water through the system. These portable gravity filters are designed for long, servicable life, a life intended to be spent filtering dirty, debris-filled water.
Pretty cool, worth consideration.
Initially I purchased the MSR AutoFlow, mostly because I have (and do) own many MSR products and have always been satisfied.
http://img.photobucket.com/albums/v19/cbatson73/autoflow.jpg
However this is a ONE bag system, designed to allow you to mate the output hose to a reservoir or bottle of your own. I found that it was not compatible with my existing (older) Platypus hydration bladder, so this went back. Also, there is a major flaw with the one bag design, if the intention is to filter from the "dirty" bag into a rigid container, such as a bottle. I will describe this flaw later.
The next filter I brought home was the Platypus CleanStream.
http://img.photobucket.com/albums/v19/cbatson73/CleanStream.jpg
It was put through very challenging conditions on my last trip, very difficult filtering with fine suspended sand and silt. The idea behind the design is to fill the "dirty" bladder with unfiltered water, hang it from a elevated position and allow gravity to force the water through the filering medium, filling the "clean" bladder. I was very impressed with the performance of this system, and my fellow backpacking buddies were as well. After one round of pumping through their pump filter, having to service halfway through due to the silt and sand, all four of us easily relied on my filter for the remainder of the trip.
Another interesting filter in this line is the Sawyer.
http://img.photobucket.com/albums/v19/cbatson73/sawyer.jpg
I didnt purchase the Sawyer mainly because I didnt like that bags are not clear, or at least having a window to see the water level. Totally clear would be best, I learned on the trip. However, its interesting to note that Sawyer boasts a 1 million gallon guarantee. They admit that they have not run a million gallons through their filters in test, but make the point that the filter design is such that it's lifespan is virtually indefinite.
I point that out because all of these filter designs use the same basic filtering medium, "hollow fiber technology". The durability of this filtering medium allows for constant re-use, the only service being a back-flush. This is a critical function in the process of keeping the filter flowing in challenging conditions. As impurities invade the filter medium they are trapped, as would be the case with all filters. However, raising the "clean" bag above the "dirty" bag (for a few seconds) effectively reverses the flow of water, flushing the clogging impurities out of the system. When performed at the completion of a filtering cycle, the small amount of backflushed water in the dirty bag is simply poured out.
In really bad conditions the dirty water can be poured into the dirty bladder through a rag or bandana, as a pre filter, to minimize the major chunks able to enter the filter. This is the reason that it became evident to me on the trip that the clear bags are better, since we were able to see any large debris in the dirty bag, and remove it, before it entered the filter, which would have slowed the flow rate.
I like the system a lot, although I dont like that Sawyers bags are not clear and that MSR only provides one bag with their system. You could add a bag to MSR's system for additional cost, but the Platypus is already sold at the same price point. The Sawyer system comes with the neat addition of a faucet attachment, for a serious backflush servicing at home, but their complete 4-liter system was significantly higher cost than Platypus' complete 4 liter system, and if I really want a faucet flush I can make one relatively easily and cheaply.
Berkey filters are in their own category, they are meant to last a very long time on a counter top, and these portable gravity filters are not intended to compete with that market. The obvious advantages of these portables over the Berkey line is obviously the cost factor and portability. But also, the filter longevity. I know Berkeys are built to last a long time, but that is considering that you are already sending relatively clean (tap) water through the system. These portable gravity filters are designed for long, servicable life, a life intended to be spent filtering dirty, debris-filled water.
Pretty cool, worth consideration.