[BeardoMcGrath]

I've used the old-style ceramic MSR filter for years, since they tend to be reliable and you can just go out and buy new ceramic elements as needed. Last fall I started having an odd issue with the filter, where air was somehow getting into the top compartment:

Air gets trapped in the compartment shown. This causes some weird pressure problems and eventually water does not get pulled into the filter.

While I was on the trip, I found removing the top screw on section would receive the pressure, and then sometimes removing and reinserting the small orange piece (see below) would help, however inevitably air would get back into the mechanism and I'd have to remove the bottom section again. This was suboptimal when trying to refill water.

Removing the orange piece and reinserting sometimes helped.

Interestingly, this started to happen after following the instructions to boil the ceramic element portion of the filter to clean, but I had done that before with no problem so that may just be coincidence. Also I don't understand how any portion of the ceramic filter would be causing the problem. All the rubber gaskets and o rings seem to be in good shape as well, so that also doesn't seem to be the problem. I plan to try a second new ceramic element just in case there is something wrong with that part, but have in general been happy with this filter and want to avoid buying a new one. However, if people have a good suggest for a lightweight filter with good throughput I would also consider buying something new. Thanks!

[InFlight]

May just be an aged o-ring that’s leaking. There’s a MSR rebuild kit ($17) on Amazon that has all rubber parts along with some silicon grease that is used. I have one of these filters, it’ the best choice for any glacial silty water. It’s a heavy filter, so I use a BeFree for normal backpacking trips.

[JonnyQuest]

You might try calling (or if you're local, visiting), MSR. They usually provide very good customer service.

[BeardoMcGrath]

Thanks both I'll try those options. Replacing the ceramic element seems to be helping, so maybe I just filtered from a silty stream a few too many times...the BeFree filter seems to have a number of positive reviews on here so I'll take a look at that too.

[hbb]

Did you put the filter lower end cap o-ring back on the filter element after boiling? Try cleaning the duckbill valve and re-lubricating the piston o-ring with silicone grease. There's a schematic on the MSR website that will show you where these parts are. That orange piece is the umbrella valve--you also want to make sure there isn't any grit caught under there. Those are the usual trouble spots for me when I've had similar issues with that model filter.