I don't really have any ideas to add, but if this works it would probably solve the question of how to make a pneumatic flour/ airsoft mine.
Also; Joe, do you mean kind of like the two semicircles would be together with the flat ends touching, and the rod holding against the chamber's pressure? In that case, it would still require you to remove the entire rod very quickly for maximum flow. Great idea though, I can't think of any major flaws in it.
