Quote Originally Posted by Summit
silica is neat but again with the keeping it fresh (do we keep adding valves)

and for the purge valves (however you want to do it, mushroom or diaphram /w mushroom or whatever) the better you make the seal, the more you have to sorry about maintainence (make sure nothing is in there, no grit prventing the mushroom from closing, maintinence checks to make sure a diaphram isnt checking) OTOH you can make them for good long times between maintainence. the question is how long can you keep an unsealed scrubber reasonably fresh in the system? 6 months?

two other issues:
1. valves need to fail safe (open)
2. the avalung is encouraged to be breathed through while skiing through dangerous areas, not just when trapped, so that the mouthpiece is always in incase of a problem.
3. 2 combined with the filter life means the filter must be easily replacable by the user or a shope tech so that the user doesnt have to send the reavalung back to the factory
The problem with labeling how long the scrubber can be left in the system unsealed is that it's going to be hard to test whether how well it's working short of pulling out your test tubes and limewater. I think the system of easily changeable cartridges which are self sealed would work well. The way I image it working is having a plastic cylinder, approaching an inch in diameter, with soft plastic cups at each end pressed to form at seal using springs and a hard plastic plate on the inside. When this is pushed into the apparatus' filter mechanism, metal (or plastic) slides will slide up against the seal, but there wouldn't be quite enough pressure (again probably from a spring) to force it entirely open. The whole chamber would then be sealed by a top which is again lined with soft plastic which is clipped into place, forming a seal. When air is forced against the valve (This is working on a valve mechanism, not an always open one - so may have to be re-thought) it pushed against the plastic slide sitting again with another pressure to open the seal, but when the breath has passed to springs closing the seal again.

This way you will be able to easily remove the filters from the system at all - so if the plastic slides cause too much tension you won't lose the filtering ability of the cartridge, and the spring won't be forced into a different shape - but inside the system should last for a relatively long time.

This way the filter should be easily replaceable by the user, even on long trips where after a burial you would want to replace the cartridge, and they should be able to maintain a very long shelf life.

However, this is relying on seal which, if they are broken or damaged, could result in the apparatus functioning not as intended, not a good selling point...

edg