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Heath Poulter
(antitrust311) - F

Locale: Southwest
Re on 10/08/2013 08:16:49 MDT Print View

You don't need to epoxy anything to the bag. On each side of the new bags at the bottom there are 3 sets of cutouts pressed into the plastic. I just picked one on each side drilled a hole through them and have a short section of paracord routed through it (If at some point it begins to tear I will put a grommet in it). The tubing I got at Home Depot that fits it perfectly is 3/8" on the exterior and the innner diameter is 1/4" and it fits on the outflow nipple of the Sawyer perfectly. The hose is the same size as the fitting for the dromedary drinking tube attachment so I just have to pull the mouthpiece off and use a 1/4" barbed adapter and I can plug it in.

Dean F.
(acrosome) - MLife

Locale: Back in the Front Range
Re: Gravity on 10/08/2013 08:21:41 MDT Print View

"The water flow rate through the filter will be the same in both configurations."

I don't think that's correct. As long as the tubing is big enough that resistance isn't much of an issue then putting the filter at the end of the tubing makes for a higher column of water and thus more pressure at the filter, so a higher flow rate. I.e. the higher the dirty water bag is above the filter, the higher the flow rate. Whether it's enough to be noticeable might be arguable, perhaps. I'm not an engineer, though, so maybe I'm missing something. (One of my engineer buddies once tried to explain to me how to calculate the water pressure exerted on the bottom of a dam, and it just made my head hurt. It wasn't simply the water column pressure.)

See here, though it regards the older Sawyer filter:

http://www.backpackinglight.com/cgi-bin/backpackinglight/reviews/display_reviews?forum_thread_id=5536&cat=Hydration%20%2D%20Water%20Treatment&cid=55

Edited by acrosome on 10/08/2013 08:23:53 MDT.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Gravity on 10/08/2013 08:47:10 MDT Print View

Gravity mode doesn't make much sense

Filter is 2 or 3 ounces (mini or Squeeze)

Soda bottle weighs less than 1.5 ounces.

It takes a minute or two to squeeze out a pint of water. You can do it at a comvenient location - you don't have to bend over at a stream and pump or anything.

If you use collapseable bag it weighs a little less.

Gravity mode stuff weighs more

Before Squeeze and now mini, gravity mode made a lot more sense.

Heath Poulter
(antitrust311) - F

Locale: Southwest
Re Gravity on 10/08/2013 08:54:12 MDT Print View

Well using it in a gravity configuration means I don't have to squeeze the bag so it extends the life of the bag and coming from an MSR filter that weighed 16 ounces my gravity setup weighs less than half of that. I am quite happy with it.

Edited by antitrust311 on 10/08/2013 09:11:10 MDT.

Harris Goldstein
(hmgolds) - F

Locale: Minnesota
Gravity on 10/08/2013 09:15:33 MDT Print View

Gravity or not is not a deal breaker, but it would be nice to use as gravity filter while doing other things at a campsite.

Heath Poulter
(antitrust311) - F

Locale: Southwest
Re Gravity on 10/08/2013 09:19:09 MDT Print View

I agree. The last thing I want to do is sit and squeeze 4 liters of water into my dromedary for camp use at night/morning.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re Gravity on 10/08/2013 09:45:35 MDT Print View

I have three one liter bottles of untreated water. And 1/2 liter bottle of treated water that I carry.

I don't treat water that is boiled, which is about half.

I squeeze about three 1/2 liters over the course of a day. Not enough hassle to be important. It would take longer to set up and put away the gravity mode stuff and check it as it's filtering.

During the day, I'll probably filter some water and then continue hiking so I'de rather just squeeze it rather than wait for gravity.

When I've done gravity mode, I sometimes forget about it and it runs onto the ground. Good for a laugh when I catch it.

Just seems like most of the reason for gravity mode has gone away with squeeze

Heath Poulter
(antitrust311) - F

Locale: Southwest
Re Gravity on 10/08/2013 09:49:37 MDT Print View

For water refills during the day I would squeeze but at camp and connected to the dromedary bag there is no chance that my 2 liter sawyer squeeze bag is going to overflow my 4 liter dromedary especially since its directly connected via a hose.

Rafi Harzahav
(rhz10) - F

Locale: SF Bay Area
tornado tube like attachment for clean end on mini filter? on 10/08/2013 10:00:56 MDT Print View

Hi,

I find that connecting my original Sawyer squeeze filter output to a clean water bottle via a tornado tube to be very convenient.

It appears that is no such threading for a cap at the output of the mini filter which could be used to attach the tornado tube.

Is this the case, and, if so, what to people do--just rig up a bit of tubing to some water bottle cap adapter which can be fastened to the top of a clean bottle.

Thanks,

rhz

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Filter position relative to tubing on 10/08/2013 10:34:27 MDT Print View

Dean said: "I don't think that's correct. As long as the tubing is big enough that resistance isn't much of an issue then putting the filter at the end of the tubing makes for a higher column of water and thus more pressure at the filter, so a higher flow rate. I.e. the higher the dirty water bag is above the filter, the higher the flow rate."

No, sorry, you are misunderstanding hydrostatic pressure, and so was Keith Selbo when he posted his comment in the thread you cited. The filter itself is the rate-limiting stage in the path of the water from dirty reservoir to clean reservoir. You can imagine it like a simple bottleneck. Hydrostatic pressure of a column of liquid can be calculated using the equation:

p = dpg (easy to remember: "pee equals deerogee")

where p is the pressure (Pascals), d is depth from the surface for which pressure will be calculated (meters), rho (the second "p") is the density of the liquid (kg/m^3), and g is the gravitational constant (9.81m/s^2). So, for a three foot long tube (ignoring the water column in the dirty water bag):

p = (0.9144 meters)(1000 kg/m^3)(9.81 m/s^2)
p = 8970 Pascals (Pa) = 8.97 kilopascals (kPa) = 1.3 psi

Because water can, for this purpose, be considered an incompressible liquid, you can imagine the water column in the tube like a rod that pulls down with a force equal to the hydrostatic pressure at the bottom. At the filter, no matter where it is on the tube (the top, the bottom, or somewhere in the middle) the positive pressure from any water above the filter and the negative pressure from any water below the filter will collude to compel water through it at a pressure of 1.3 psi. The position of the filter at the top, middle, or bottom does not matter.

This only breaks down if the length of the tubing below the filter exceeds about 33 feet, if the tubing diameter is extremely narrow (causing a pressure drop due to friction), if air can enter the tubing below the filter (through a leaky fitting, say), or if the tubing is collapsible. If the tubing and all fittings below the filter are airtight, the diameter of the tubing is more than 1/64 of an inch or so, the length of the tubing below the filter is less than 33 feet, and the tubing below the filter is sturdy enough to not collapse, then the flow rate through the filter will be the same whether it is at the top, the bottom, or somewhere in the middle of the tube.

In practice, flow rates might differ due to practical obstacles. It might be easier to have an effective prefilter if the Sawyer filter is at the top, say.

Dean F.
(acrosome) - MLife

Locale: Back in the Front Range
Re: Filter position relative to tubing on 10/08/2013 12:41:17 MDT Print View

@Colin- "At the filter, no matter where it is on the tube (the top, the bottom, or somewhere in the middle) the positive pressure from any water above the filter and the negative pressure from any water below the filter will collude to compel water through it at a pressure of 1.3 psi."

OK, I grok positive and negative pressure. But for this negative pressure doesn't that assume that the tubing beyond the filter is narrow enough that it is flowing freely with a water column its full diameter, as opposed to water just running down the inside of the tube? I suppose that's what you mean when you talk about air entering the tube from below. In my head I was picturing a rivulet running down the inside wall of the output tubing rather than filling it completely, since that's what mine seems to do. When using tubing as wide as the drinking hoses on most hydration systems this is what seems to happen if the flow is as slow as a Sawyer gravity rig, and you certainly avoid this possibility if you put the filter on the end of the tubing rather than between tubing and reservoir. Or is it just me?

Because it might just be me... :)

Edited by acrosome on 10/08/2013 12:50:36 MDT.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Tube on 10/08/2013 13:44:13 MDT Print View

Ah. Yes, we were totally making different assumptions about the outlet tube. That explains it.

It didn't occur to me that you might be imagining a trickle of water through an air-filled outlet tube. You're right that a gravity setup with the filter at the top will only work if the outlet tube is full of water. I use 3/16" outside diameter tubing for mine to reduce weight and bulk, and it is always full of water during filtration.

If you want to use large-diameter tubing in your gravity setup because you already carry some for your hydration bladder, you can still put the filter at the top if you purge the air from the outlet tube by pointing the outlet end up and lowering it while it fills. If you use bottles for water storage so you don't already carry large diameter hose for a bladder, I don't see a reason to use tubing larger than 3/16".

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Tube on 10/08/2013 14:36:54 MDT Print View

"I don't see a reason to use tubing larger than 3/16"."

I assume that is outside diameter. However, all of my filter fittings go to the inside of the tubes. What is your inside diameter?

--B.G.--

Colin Krusor
(ckrusor) - M

Locale: Northwest US
tubing on 10/08/2013 15:11:46 MDT Print View

The tubing I use is 3/16" outside and 1/8" inside (wall is 1/32"). It is NSF/ANSI 61 certified drinking water grade clear polyurethane tubing from Smallparts.com. They sell 25 feet of it for about $11:

http://www.amazonsupply.com/superthane-clear-polyurethane-nsf-61-tubing/dp/B003TJ9YN8/ref=sr_1_3?sr=1-3&qid=1381265976

I cut a 2" length of larger tubing that fits on the filter, and the smaller tubing fits inside it.