Question about DIY Katadyn Gravity Filter

I would think you had a vacuum problem. Air has to be able to get into the Nalgene for water to come out.

I agree with Joe. With the hard Nalgene, its probably vacuum issues. I'm gonna go ahead and pimp my Nalgene/Katadyn MYOG filter. Check these threads.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=28707&skip_to_post=239457#239457

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=28728&skip_to_post=240640#240640

Thanks for the replies. I thought it might be a vacuum thing but was confused because it seems that you would have a similar situation with an air-tight drybag. I like your setup as well Travis, although I would personally want more capacity for my 'dirty' bag. Guess I'll have to try the real deal.

FWIW, the collapsible Nalgene I'm using is 32 ounces. It can also work with the larger size, providing the opening in the nalgene is the same, which I think it is.

This just gave me an idea… ;)

Uh oh. Javan's thinking again…. ; )

The filter referred to in this thread as well as all the ones I found in the links in this thread have a design deficiency. They put the filter at the source so the water pressure is much lower than it would be with the filter at the other end of the hose. It might not be too bad with a fresh filter, but I think it could become problematic as the filter starts to clog over time.

Very possibly true. I'm interested to see how this filter works over time, but so far, there's been close to 100 liters of water through this filter cartridge. I still get about 2 minutes per liter.

I'm sure a lot depends on the porosity of the filter and what's in the water. I use a Sawyer 0.1 micron filter and it definitely benefits from the high head pressure.

The Katadyn has a 0.3 micron rating, so it is a bit more porous than the Sawyer. I would imagine things would slow down a bit if the water was quite goopy. Ew.

I've tried it nearly both ways, and have always had a much faster flow with more 'space' between the water and the filter. It's worked both ways, just better with the filter lower in the hose.

As far as the filter not working at all in the Nalgene setup for Nathan, was it a brand new filter? If so, you probably just had to prime it. After that it'll probably work fine.

With the Cantene (soft Nalgene) I start it with a squeeze and then it keeps going. I cannot get any flow out of the Lexan version. (that is with the filter inside the Nalgene) Sucking works but does not create a flow when you stop.
Franco

I had a problem similar to yours and my solution may help you…I made up the whole filter thingey, hacked everything together, filled it with water, and just a couple drips came out. You have to have a hose on the nipple of the filter (and sometimes give it a little suck to get it started).

Rob,
Yes, the hose made it work for me also. I didn't get much flow without it. Something to do with physics I think.