Sawyer mini filter as a camp gravity system?

Amazon sells Tygon thin-wall silicone tubing that I used on my last build (1/4" ID, 5/16" OD). It's very light but tends to kink more easily than the thicker stuff I used previously. You have to fiddle with it during setup if you need a curved routing to shed drips.

http://www.amazon.com/gp/product/B000FP0IES/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1

Yeah, it's expensive.

Hi! Resurrecting this thread because I've found it helpful but have a question about details.

Regarding the discussion of ideal tubing length, I get that not enough tubing = not enough flow (but too much tubing = unwieldy system), but did anyone do a comparison between putting the tubing above or below the filter? I'm wondering whether flow will be different if the system is dirty bag –> Mini –> tube –> clean bag or dirty bag –> tube –> Mini –> clean bag. If nobody has done this comparison, I'll do it and post the results, but if it's been done, that'd save me putting together a mock-up system for the purpose.

I got a Granite Gear drysack (13 liters, weighs an ounce and a half), which I think will make a great lightweight version of bags like the Katadyn Base Camp if I macgyver the right attachment onto the bottom. All else being equal, it would be nice to put the hose on the clean end so that I could then use it as a drinking tube with a Platypus, but I might sacrifice this if the flow rate were better using the hose on the dirty end. (I used my Mini with a friend's Katadyn bag this summer, and it worked great as the primary water supply for a group of four. That was with the hose on the dirty end.)

Any input would be appreciated!

I have not done exhaustive testing. This might depend somewhat on which brand of filter you use.

However, I found that the overall length of tubing from dirty to filter to clean is the most important, and four feet is a good place to start. I tried some with shorter lengths, and I started getting into intermittent failures and slow operation.

I'm not exactly sure why you would use a 13L dirty bag unless you had a group of people.

–B.G.–

Rebecca, I have found that the optimal setup for my 4 L. "dirty" Big Zip Platy is 36"-42" from the outlet hose to the filter. Then I have a short 6" tube to connect from the filter to the receiving "clean" Platy. The longer top tubing adds a sweet hydrostatic head to force the water down faster.

Actually, last weekend at 8500', I had trouble getting my dirty 4 L. zip bag to zip right. There were no bugs at all, so I left the bag unzipped. The water raced through the filter faster than ever (2 L. in a minute). Thinking that either al-Qaeda messed with my filter, or that it somehow self destructed since I last used it, I bought a new Frontier Pro yesterday to replace it. But it's possible that an unzipped dirty bag allows air to help push the water faster down the outlet hose to the filter.

My real point here is, have a longish tube running from the dirty bag to the filter, not at all the other way around.

Not the answer I was hoping for, but good to know. Thanks, guys!

>I'm not exactly sure why you would use a 13L dirty bag unless you had a group of people.

Yes, that's the idea. My buddy's big Katadyn bag was so convenient–when you make camp, one person makes one trip to the stream with one bag, and you've got water for everybody's dinner and breakfast. And if you can have that with a bag that weighs about the same as a Platypus, what's to lose?

Here is my setup

Works great,, i'll either use my trekking pole, a large rock or a tree to string the dirty bag from, it'll then take just a couple of mins to filter the 2 litres of water.

As long as your tubing is small enough that it doesn't allow air in, the position of the filter shouldn't matter. Gravity will move the water through the system either by pressure or by siphon. If you are using a collapsible dirty water reservoir, air doesn't need to get in to the reservoir for water to flow out. If you are using a rigid reservoir, you will either need squeeze it or poke a hole in it for air to get in to get flow through the filter. You can rig the whole thing up as a siphon and use a bucket or pot as the dirty water reservoir. If you took a piece of rigid tubing and bent it in a "U" shape, you could use it as a dip tube in the upper vessel. To start the siphon, all you have to do is fill the system with water. You can do this by sucking on the outlet tube or filling the system with clean water from a bottle or syringe. If you are carrying the backwashing syringe, you can fill and backwash the system at the same time. The thing that I like about this approach is that you can dip your dirty water vessel and hang the filter system from it without having water drip down the outside of the tubing. From what I have read, you should be just as concerned with where your hands have been as what your water has in it. If you have had your hands in dirty water, then you should wash and dry them before you touch anything clean.

For those who live near a Meijer's store, they have silicone aquarium tubing in the pet department. It's pretty small bore and probably wouldn't connect to a Sawyer without an adapter. I would use a short piece of larger tubing that will slip over the smaller tubing. This tubing should fit the Leur Lock hose fittings and they can be found on eBay. The fitting on the end of the backwashing syringe is a Leur lock.

Prior to my last trip, I had reduced my hose lengths to be 36" above and 10" below. Then I tried to use this on the last trip, and it didn't work worth a damn. It would take an hour to filter a liter. No good.

So, I increased the lower hose length to be 20", and it sped up the flow rate about a hundred-fold.

Go figure.

–B.G.–

A bunch of tests I did last weekend:

Setup:
Sawyer Mini, backflushed with tap water
Long tube, about 3ft, silicone 3/16" ID (from my pump filter)
Short tube, about 3 inches, 1/4" ID (the straw from the Mini)
Tubes are connect to Playtupuses with the Hyperflow-like connector, but the old angled version

I filtered 1 L of water for each test. All tubes need some kind of air bubble removal for the result to be reliable (difference in time can be 2x if there are significant amount of air bubbles in the tube, thus reducing the effective length of the tubing). To do that, I raise the clean bag to back-filter some clean water into the dirty bag and wait for the bubbles to clear (this is the backflushing procedure recommended for the GravityWork filter). For the tests with just the short tube, I will just squeeze start for a few seconds.

Test 1:
Short tube above filter, long tube below
1:55 min/L

Test 2:
Long tube above, short tube below
1:52 min/L

Test 3:
Just the short tube below filter
~6 min/L

Test 4:
Just the short tube above the filter
~5 min/L

Test 5:
Just long tube above, but filter raised to only 2 ft high
~4 min/L

Conclusion: physics works (http://en.wikipedia.org/wiki/Fluid_statics#Hydrostatic_pressure)! Only the total height matters.

I brought my Mini with just the straw for the JMT and the gravity filtering speed is rather pitiful. It doesn't help that I didn't realize a squeeze start makes a huge difference (20 vs 6 min in my test).

I think from now on I'll bring an extra 0.5oz or so in quick-connect adapters so I can use my hydration tube as part of my gravity filter kit. Minimal weight gain, huge difference in flow rate.

Thanks for doing these tests. This is really great info. I assume you did several tests and averaged? Do you think the different ID tubing has anything to do with the results?

>"Do you think the different ID tubing has anything to do with the results?"

No, that tubing is large enough to support a higher flow. At the highest flow observed, 0.5 liters/min, the pressure drop due to the smaller 3/16" ID tubing was only 0.09 psi or 2.5 inches of water height. So >90% of the "head" (water pressure) went to pushing water through the filter, not the tubing.

However, the tubing wasn't MUCH too large. Don't go to a tubing ID smaller than 3/16". 1/8" = 0.125" diameter would be too small. Then most of the pressure would needed for 0.5 liters/min to flow. i.e. there wouldn't be as much pressure available for filter back pressure and the flow rate would be reduced.

A quick check for this would be run the water through the tubing without the filter. If the water flows much faster, than the tubing isn't the limit.

While the tubing isn't the limit to flow in these experiments, the tubing connections on the filter housing could be. Their ID is much less plus there are entry and exit effects.