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anyone using a gravity filter
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Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: nick on 11/08/2006 15:26:34 MST Print View

> one filter (from Sawyer) claims to eliminate non-filtrable (as they were always previously known) viruses

The lab report says a pressure of 40 psi was used to push water through the filter. That's equivalent to 30 metres or 100 feet of water head. This is a LOT of pressure - a LOT! And I bet the flow at the far end was not fast.

Look guys, there's an old rule in the marketplace. "If it seems too good to be true ..."
So be careful.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Re: Re: nick on 11/08/2006 15:44:56 MST Print View

Dr. C, many thanks for the "heads up" on the pressure issue. you said, "a LOT!" - you ain't kiddin'; "a LOT!" is perhaps a bit of an understatement!!!

aaron eshelman
(djaaronreed) - MLife

Locale: Central Rockies
40 PSI for conditioning. on 11/12/2006 14:57:08 MST Print View

The 40 psi was for the initial conditioning. The actual test was performed at 20 psi.

"The test waters were passed through the water filter in a manner similar to
how they would be used by the consumer (20 psi)."

Anyone know if this is a "normal" psi for drinking through a tube?

I too am curious about these filters. They are a little pricey though.

william hutchinson
(okuncool) - F

Locale: midwest (boo hoo)
Re: Re: nick on 11/13/2006 18:59:17 MST Print View

hey nick, i was just wondering about that flow rate on the general ecology filter setup you are using. i am just wondering about how long it takes to filter one liter. i know i am going to use it to filter larger quantities of water somtimes, so if it is going to take 20 minutes a liter that wont work. anyway
thanks for your info.

Aaron Lastname
(Cloudveil9) - F
Sorry to Revive This Thread... on 03/03/2009 09:30:00 MST Print View

But I have a question I'm hoping someone -Might- be able to answer. Earlier in this thread Nick (Who doesn't look like he's been on in a while and I can't PM him) stated he was able to get a 2-3 minute per liter flow rate out of a gravity fed First Need cartridge. I currently use a First Need purifier as it's the only thing I have found that:

1) Removes bacteria, viruses, and protozoa

2) Reduces heavy metals and chemicals in water

3) Improves taste, removes tannin etc. (IE pumps blue water clear!)

4) Does not use chemicals. (More concerned about long term exposure than taste here, but taste too...I filter my water at home for example to remove chlorine etc, don't want to introduce it to my backcountry water if possible)

5) Is fast. While tiring, I can fill up all water containers for 2 people very quickly and it's instantly ready to drink...No waiting 30 minutes - 4 hours.

Of course the drawback is weight of course but I have found no other option. I was thinking about trying Nick's method of just using a water bag and the canister to save about 8oz but I tried last night and got a 1 liter / 13.5 minute flow rate! This was with a canister that is almost new. I removed the pump assembly, then setup the waterbag system that is included with the First Need system and used the included hose (3 feet?) and hung the full bag as high as it would go with that hose above a Nalgene bottle. 13.5 minutes later I had a full bottle.

Does anyone have any ideas how he achieved the flow rate he stated? Or are you out there Nick? I also compressed the water bag to get it going etc but still 13.5 minutes. Do I need a longer hose, etc? Thanks for any tips!

Michael Davis
(mad777) - F

Locale: South Florida
Re: Sorry to Revive This Thread... on 03/03/2009 10:31:28 MST Print View

Aaron, I use a Sawyer viral filter, which has very similar specs compared to First Needs, in a gravity configuration. I haven't timed it but I know it doesn't take anywhere near 13.5 minutes per liter.

However, the trick with this one at least, is to prime the filter before your trip by backflushing is with the faucet attachment and leave the water in it!

This system doesn't save weight; the gravity bag + hose + dry filter weighs 9.6oz but with the wet filter, it all adds up to 14.9 oz.

However, it does save work and it filters everything, including viruses from swamp water, without any waiting or chemical side effects.

I use a Steripen Adventurer in clear mountain streams and with either system, I carry chlorine dioxide tablets as back-up.

Keith Selbo
(herman666) - F - M

Locale: Northern Virginia
Re: Sorry to Revive This Thread... on 03/03/2009 10:44:59 MST Print View

The Sawyer viral filter won't get rid of chemicals by itself so if that's an issue, you need to add a charcoal filter.

BUT, if you include a charcoal filter, you can also add a little chlorine (2 drops/liter) to the water to kill viruses. The charcoal will remove the chlorine after it does its job and many other chemicals as well. Then you can use the considerably cheaper Sawyer 0.1 micron filter which removes everything except viruses.

I never timed it, but if I had to guess, the flow must be a half liter per minute.

There's a photo of this combination in this thread:

Aaron Lastname
(Cloudveil9) - F
Thanks on 03/03/2009 10:48:32 MST Print View

Thanks Michael, I have been looking at that filter, but was scared away by the REI listed weight of 20oz, no better than my First Need. However it appears that 20oz must be incorrect or the system can be broken down into something lighter. Your system would still save me a lot of weight - My First Need with cartridge and pump weighs 22oz with a used canister. I find the listed weight of 16oz incorrect, and it seems that after you use the cartridge one time, it gains 4oz. (I have a cartridge I've used that was flushed out after use and has been sitting in my closet for 6 months, and it is still 4oz heavier than a new one) I guess with that Sawyer I would be losing that ability to turn blue water clear and remove bad taste while reducing any heavy metals and chemicals, but gaining in that I would never have to replace a cartridge. Hmmmm.

Aaron Lastname
(Cloudveil9) - F
Nice Setup on 03/03/2009 10:53:38 MST Print View

Herman, I like that setup. Kinda going against my "Mantra" to add chlorine and then take try to take it out, but hey that's the same thing I do at home (Or try to) with my Brita. Maybe I'll have to make some compromises to achieve my goal!

Aaron Lastname
(Cloudveil9) - F
Triple Post on 03/03/2009 11:07:19 MST Print View

Now that I think about it maybe Michael's viral filter with the Katadyn charcoal filter is the way to go. Don't know about flow rate, though. No chems added, however.

Justin Marney
(gotascii) - MLife

Locale: Shenandoah
anyone using a gravity filter on 03/03/2009 15:17:46 MST Print View

@Michael & @Herman Is this the Sawyer you guys are using? Is it possible to prime the filter on the trail or does it take more pressure than one could muster via lung power?

Edited by gotascii on 03/03/2009 15:30:05 MST.

mike leary
(backingit) - F
Big Berkey Gravity Filter? on 04/17/2009 19:16:32 MDT Print View

How about a Berke Filter. A smaller one like the big berkey or berkey light would be good as a base camp solution. albeit a little bulky to manage.

Walter Carrington
(Snowleopard) - M

Locale: Mass.
What diameter tube for filters? on 05/31/2009 15:15:18 MDT Print View

A possible easy way to set up a water filter is to use the top for a nalgene water bottle with nipple:
If you pull the moveable part of this nipple you have a nipple about 10mm in diameter. If this fits the tubing required for the filter, then use this wide mouth 96 oz polyethelene water bottle:
The question is the diameter the same as the filters. I'm thinking of using a 0.1 sawyer filter

Samson lee
(Samson) - F
Re:water filter on 10/28/2010 11:08:36 MDT Print View

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Locale: Western Michigan
Informational Help on Sawyer Filters on 10/28/2010 11:21:00 MDT Print View

Gary Ward
(coastalbliss) - F
Gravity filter works on 11/12/2010 15:45:51 MST Print View

I'm surprised there is not more current postings on this topic. It seems there have been some improvements in the last few years on the gravity feed filtration systems. I have an MSR that works great.

I've used the pump-MSR as well. I have one that has lasted about 15 years and still works great with its ceramic filter. It is the old standby. I tried the UV bio-killer pens, but kept having issues with them. I was not impressed. These need some further development to make them bombproof.

I had absolutely no issues this past summer with the MSR gravity feed system. My partner used the Katadyne gravity feed system with the filter in the bag and has some trouble with it being very slow. It was not as easy to flush as the MSR system and she was almost ready to give up until I told her about the MSR system. But to be fair, she was using the Katadyne system in an area with a fair amount of glacial silt washing through, whereas I wasn't.