Originally Posted by
cspan
I decided to experiment a bit here at home with a gravity feed water filtration system using my Sawyer Mini. I'm not terribly concerned with flow rate, as the plan would be to set it up and let it run while doing other camp chores. As long as it worked ... which is the catch.
I had hoped to set up a system whereby one of my 1L soda bottles would be the dirty water reservoir. I figured out a way to hang that upside down, with the mini screwed on in place of the cap, and for completeness I affixed the gray tube to the outflow side, and let it drain into another 1L soda bottle standing upright. Except - nothing.
At first, I thought, well, the mini was totally dry, it'll take some time for water to soak through the layers of filter. After 5 min, I gave the "dirty" bottle a little squeeze to help things along. As I squeezed, couple bubbles went up, a little water dripped down, and I thought I was on my way. But then, nothing more.
It occurred to me that the lack of pressure equalization in the dirty water bottle was keeping it from flowing out. It made sense to me as the only other time I used the mini (as a filtering cap to a soda bottle), the bottle collapsed as I sucked untreated water out of the bottle through the Mini, and I had to unscrew the Mini periodically to let the bottle pop back into shape and resume a good flow.
So, short of punching holes in the (top) of the dirty water bottle, it's not really going to work this way? How is this not an issue with a water reservoir/bag? Just because the sides are more flexible and more collapsible? Is it the case that the same forces are at play with the soft-sided bag, but just not as noticeable because of the greater ability to collapse? That is, theoretically: if you poked a hole in the top of a dirty water bag halfway through its emptying through filtration, the flow would likely increase due to pressure equalization? (forgive me if that's not the right physics term)
Anyway, I had hoped to have a bottle-to-bottle filtration system, but, short of finding a bottle with a cap at both ends, I don't think it's going to work, so I'll probably need to get something like an Evernew bag instead.
Thanks in advance for any thoughts on this.