2 gram back flush for sawyer squeeze
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Stephen Parks, it can hardly be called 'off topic' to note that a method may in fact be incorrect, although alluring. So this is in fact strictly ontopic, exceedingly so, the topic being backflushing a sawyer squeeze.
If I wasn't clear, the reason I use a tube is not to increase pressure, but to make mating the syringe tip to the sawyer work way better, no leaks or misses. Trying to jam the one they provide against the hard plastic does sort of work but it's a pain. Since I already use the clean end adapter with a hose to get the water into the clean bottle, this is zero extra weight. You can also suck the water out of the sawyer before packing it up, the benefits are significant.
I realized after posting this that this question can be fairly trivially tested. With a 2oz syringe, ideally not with the catheter tip that sawyer provides, but with the longer nozzle that lets you insert it into a soft tube firmly, you can squeeze out 2 oz of water in about 1 second, give or take. Hard to time it exactly. This yields of a flow rate of roughly 120 oz per minute, but a flow rate that starts instantly, no buildup. Now we have a standard to judge against. That's 7.5 pints, or roughly 4 quarts a minute. The thing that sawyer specifically warns against is inadequate pressure forming a center channel after which you will never achieve a full clearing out of the sawyer because the water will always then follow the path of least resistance after that point. I believe that to achieve this 1 or 2 second flow rate with a platy type bag will yield a popped bag in not too long, but it's easy to test empirically so there's no need to speculate, how hard to squeeze a bag to get this burst. Remember, you don't want to build up to this rate, you want it instant to avoid forming the center channel issue.
If it takes 2 seconds to empty the syringe, then you have a flow rate of 2 quarts per minute. I'd have to time it to see what it actually takes.
The syringe, because it is a pump, which you can apply focused force on via the plunger, because you squeeze it between your thumb and fingers, using leverage, allows you to achieve this pressure/flow rate in a consistent manner, every time.
So all alternate methods can be easily tested, simply do whatever you're going to do for between 1 and 2 seconds, measure the flow out with a measuring device accurate enough to measure ounces, and there you have it. The flow rate was either in the recommended range or it was not. If you get this 2 oz in about 1, 1.5 seconds (that's counting at normal speaking speed, one one thousand) then you do in fact have an awesome 2 gram backflushing system, if it is far under that, you do not.
However, at $29 for a sawyer squeeze filter, which for those of us using hiker pros remember, is I believe less than a 200 gallon rated, non backflushable replacement filter costs, this is not a really major problem.
My apologies to any violations of physics, which I am trying to correct by noting very simple empirical facts of actual flow rates, which are measurable, and require no speculation.
So give it a try, attach devices, start backflush, into accurate measuring device, note measurement of liquid after 1 second, then 2 seconds. This test takes a few minutes to carry out.
[added]holding the sawyer and and squeezing the syringe with one hand, it took about 1.25 seconds to get the water through, 2 oz. If I put the sawyer on the ground and held the syringe in two hands, I could do it in 1 second easily. So that's actual data point 1 for those interested in such things. lol, what we do for the sake of science….
a long nozzle 2oz / 60ml weighs 36 grams roughly.
As a side note, I'd been considering the use of smaller syringes to get more compact but this discussion has finally convinced me it's a bad idea to try to save weight that way, alluring as it is re size and weight and overall compactness. From now on I will consider the weight of the sawyer to include the syringe.
I'm going to update those postings where I suggested using smaller syringes and remove that advice, I simply had not considered flow rates over time adequately, so this thread was quite useful, as were the comments of an engineer on that blog posting who also pointed to flow rates (the tubules apparently hold roughly 1/2 oz of water in volume).
When I tested using a bag for backflush, these were my results:
I did, by the way, try using two screw on ends with hoses, to try to use a bladder bag to backflush, but I couldn’t generate enough pressure, and it felt like I’d probably end up bursting the bag over time if I tried it, and it really didn’t get much more than a dribble when backflushing.
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