Gravity filter/ hose length

[John Gelack]

I just finished my gravity filter. I am using a 2L Platypus as my dirty container, 46" of tubing going from the Platypus to a Sawyer filter, and about 10" of tubing going from the filter to the water bottle. I'm getting a flow rate of about 1 liter in 2 minutes. Filter weight is 5.5 oz. Does this seem good? Do you think I should shorten the tubing to save some weight? I would appreciate any advice you can give me. Thanks John

[Brendan Swihart]

My experience has been that having longer hose above the filter improves flow rate but hose length below the filter does not. When I use a gravity filter I only have a couple inches of tubing below the filter.

[Ken K]

I've got about 24" above the filter (Sawyer 0.1 micron) and 5" below. I'm getting new-filter flow rates around 1:40/liter.

I think you can probably shorten up your feed tube and still keep the same throughput, but I wouldn't go below 18".

Ken

[John Gelack]

Thanks guys for your responses. I knew having a longer feed tube would improve flow rate, if I can get the same flow rate with a 24" tube as I'm getting with the 46" tube, that would be GREAT. I will also cut the output tube down to a few inches. Thanks again John

[Gary Dunckel]

John, I originally used a 24" feed tube length with my Frontier Pro, and minutes per liter weren't all that great. Another thread indicated that flow rate was dependent on the height of the water column, which means tube length from the dirty bag to the filter. Most people liked 35-45". I settled on a 42" feed tube, and my output time nearly doubled from the 24" setup. So I would suggest that if you decide to shorten your tube, do in in 1-2" increments while you figure out what works for you. If you go directly from a 42" hose to 24", you might get a surprise you don't like. Then you'll have to buy a new tube and start over.

[John Gelack]

Gary, thanks for the advice. Now that I think about it, going from 46" to 24" in one cut, is a little drastic. I will keep experimenting with shorter tubing lenghts, (cutting in smaller increments) until I find something I'm happy with. Thanks again

[Eric Palumbo]

My flow rate is closer to 5:30/liter with 36-48 inches between source and filter. Why is my flow rate so much slower?

[Bob Gross]

It's hard to say what your specific problem is, but for some, the problem has been something like a big air bubble. Once you sort of "pump" a little water through it, the air bubble dissipates and it starts to flow better.

–B.G.–

[BlackHatGuy]

"My flow rate is closer to 5:30/liter with 36-48 inches between source and filter. Why is my flow rate so much slower?"

Remove the filter from the packaging…….

Okay, seriously, is it a new filter? It needs purging first, I used to do mine in the shower. After the initial purge it should be much faster.

[Travis Leanna]

>After the initial purge it should be much faster.

Yes, and possibly after letting it sit and dry for several days as well. Many dry filters will need to be primed.

[Eric Palumbo]

I've run many litres through the filter, trying to speed it up. Wouldn't that "prime" the filter? I've tried applying pressure to the feeder bag to pump water through it. That doesn't seem to work either.

I used the filter last year and I don't remember if it was any faster back then. But now it is surely just a trickle. Wondering if it's been knocked around too much and has broken tubules or whatever they are. Very frustrating.

I think I'll get a new one from REI. If same problem at least I can return it.

[Travis Leanna]

Eric, what filter are you using?

[Eric Palumbo]

I'm using the Sawyer 3-Way Inline like http://www.rei.com/product/801824

[Travis Leanna]

Hmmmm, I just got that one myself, and with tap water, I can filter super fast.

Now, I don't mean to insult you here :)

But…. do you have the water flowing through the filter in the correct direction? I'm not even sure that would make a difference, but there is a "correct" direction of flow with that filter.

Edit: I just read that you used it last year as well. If the filter wasn't cleaned properly before storing, it may have developed some gunk buildup that is clogging the pores. Try using the sink attachment and backflushing it with some good water pressure. Let it run for a while.

I should also note that I'm purely guessing on solutions to this.

[Eric Palumbo]

OK. Here's where I feel like a dork… no i wasn't running it backwards :-)

I have the old black faucet adapter (not the shiny new bigger white one) and i've never had much luck hooking it to any of the water sources in my house so I've never really gotten any kind of high(er) pressure through the filter…. until today. I took my kitchen faucet apart so I could get that POS adapter hooked up and pumped a ton of hot water through both ways….. EUREKA!

With my 36" feeder, I filtered (if you can call it that with tap water) 2L in 3.5 minutes.

Thanks for the thoughts everyone.

[Rick Dreher]

Kudos on sorting it out. One thing I don't think was mentioned is hose diameter. The larger (1/4-inch+ I.D.) the better, depending of course on what hooks securely to the connectors. Sometimes, folks stretch on a small diameter hose and get poor flow as a result.

Cheers,

Rick

[Travis Leanna]

Another happy ending.

Glad to see it was something simple like backflushing. Though, that filter carries a lifetime 1,000,000 gallon warranty, so you probably could have gotten a new one for free.

[roberto nahue]

But what's the weight with a wet filter?

Can you guys point me to a thread on how you make these gravity filter?

I'm currently setting it up with a fp and aquamira tablets?

Do you guys use any chemicals with your filters?

Thanks.

[Zachary Zrull]

View this entire thread; there are a couple designs here.

I just read that some guide services boil, chem, AND filter. I suppose they're hiking on well-used track and have responsibilities (people).

[roberto nahue]

Zack.

I'll read that thread right now. Thanks.

[Keith Selbo]

Getting rid of air between the dirty bag and the filter is crucial to flow rate so I'd like to try to clarify the need and the process.

If you notice a lot of air in the tube and the water is flowing along the wall of the tube through the air space in a little rivulet, you are not achieving your full flow rate. Depending on how long the bubble is, you may be getting significantly less than full flow because the effective column length is reduced by the length of the bubble.

There are several ways to eliminate the bubble. The fastest is to raise the filter above the(full) dirty bag, disconnect the hose from the dirty side of the filter, slowly lower the hose letting the water rise in the hose forcing out the air. When the water reaches the end of the hose insert the filter.

If your dirty bag is of the closed type, you don't need to disconnect the filter. Just raise it above the dirty bag while gently squeezing the bag to force the air up the hose and through the filter.

If you had any significant air space in your dirty hose, you'll be amazed at the improvement in your flow rate. One contributor mentioned that he didn't get much improvement in flow by doubling his hose length. It is likely that this is due to air in the hose. Increasing hose length should always increase flow proportionately.

Remember, freezing ruins filters, and the damage isn't always noticeable. During freezing weather, store the filter in a zip-lock bag, carry it in an inside pocket, and take it into your sleeping bag at night.

[John Gelack]

The first time I used my gravity filter,I got a flow rate of 2 min/liter, with a 46" feed tube,(not realizing I had air in the line). Since then I've been experimenting with different feed tube lenghts. I've settled on a 36" lenght, making sure I get ALL air is out of the system, I'm now getting a flow rate of just under 1 min/liter. I'm THRILLED!!! I managed to cut some weight from my system and double the flow rate. Thanks again everyone for your advice. John

[Author]

Posts