Check it out. Basic idea is the same as a super soakers. Yes, I've been disecting their internals
The other valve (ball valve) closes when you're not in combat and opens when you are. This is to prevent extra leakage.
The other, very simple valve, works with a spring that pushes the lever down. That blocks air that goes through the vinyl tubing. Pull the trigger, you pull the spring back, air goes through.
Should even work with a magazine.
I'm working to combine the Taiwanese guy's P90 design (hey, I'm belgian and so is the P90
) with semi auto, better air tank (check other topic) and a magazine 
