I'm testing out a DIY gravity filter based on the Sawyer SP122. I have a drybag for the dirty water container, ~3ft hose, the filter, and then a few more inches of hose to poke into whichever clean water container I'm using at the moment. I'm testing using plain tap water, and am trying to find out what flow rates I should be expect.

On my last test, it seemed like I was getting no more than a trickle of water through the filter. With the filter detached (drybag with 2-3L water, then just the 3ft hose), I got 16oz in 23 seconds. With the filter in place, I gave up after a minute and a half when it had only passed 1/3 that amount.

Any tips to improve my setup? How much water do I need in the dirty bag to provide enough pressure? Is 3ft hose above the filter sufficient? Do I just need to be more patient?

Were there air bubbles in the hose above the filter? Try getting some of the air out of the tubing, when i am using the quick connect, i'll disconnect until water comes to the end of the hose, then attach. 3 feet should be plenty of head. On the clean output side, try to have a shorter hose. Also try letting some air in the dry bag as you may be creating a suction on the top side, good luck!

Jay

Edited by justaddfuel on 08/31/2011 15:33:16 MDT.

Seconded. Clear all the air (in hose and in filter) and you should get very good flow. You're using 1/4" ID tubing, yes?

Cheers,

Rick

I'll double-check the tubing diameter tonight, but I'm pretty sure it's 1/4" ID. I did make sure to get rid of all the air in the upper tubing before attaching the filter. Not sure how to do the same for the lower, and within the filter itself though.

Edit: The drybag is completely open on top, so no vacuum effects. I've also tried having no hose on the output side, to see what comes out directly from the clean side of the filter.

Edited by drwestco on 08/31/2011 15:59:53 MDT.

You can also try priming the filter by using it on a faucet first. I have heard of a couple of instances where people had a slow flow rate and exchanged the filter for a new one with better results. Maybe yours is a dud?

Also you can try squeezing the drybag to push the water through.

I had the same problem until I filled the bladder totally full and had good flow after that. I think it needed to be primed or something. I use a Platy Big Zip.

I tried a new test today - filled up a 3L Platy, hooked up the filter, and squeezed to try and force the water through faster. I managed to get 16oz in 1:10 using this method. Better than before, but still seems a bit slow (and obviously I'd rather let gravity do the work instead of having to squeeze).

It may be time to try a replacement filter - I'm running out of other ideas.

Is this a new filter or used? Have you tried backwashing at the faucet? If used, have you run chlorine solution through it?

You're still at about half the rate I'd expect.

Cheers,

Rick

Back in November I posted -

"I am using a Sawyer Filter.

I primed by filling and squashing a 2 liter Platy, shaking the filter until the air was out, and the output stream was running solid.

The distance from the bottom of a 2 liter Platy to the top of the filter was 42".

I ran about 2 liters through the system getting it hung correctly and figuring out the process. It was flowing pretty fast.

Flow rate for the Filter was 55 seconds per liter, over 3 consecutive tests (6 liters total)."

Are you priming to the point of a solid output stream?

I have yet to see a solid output stream in any of my tests. No amount of shaking the filter seems to fill it to the point of removing all air. The only way I've been able to get a good stream is by hooking up the backflush attachment and forcing water through with faucet pressure.

This filter is essentially new. I've run a few liters through testing it with tap water, and that's it.

I just used a MYOG gravity filter with the Sawyer for a week in Isle Royale NP. I didn't time any of my filter sessions, but I'd say it was 2-3 minutes per liter without squeezing. When I would first hook the filter up, I'd get many bubbles coming out, but these went away after a little bit and the flow improved.

All I can really say is what was already said by others. Make sure there's no air lock somewhere and prime it with a few squeezes. Maybe just try another one for comparison. Good luck.