O2ptima EA experiment

This is untested and not suggested for use!
I have been looking at designing a refillable replacement for the extend air cartridges used by the O2ptima rebreather

Improvements to be made...
Add an indent or similar for a max fill line
find a tube to use rather than all thread so that the factory oxygen tube can still fit through the middle.
Gas deflection widget to prolong breakthrough at the top of the cartridge.

I have added a second version of the cap please see instructions