My original idea was to have the performance of the QDV with the added bonus of having semi automatic operation.

@veolcity: Can a spring not work in compression and extension? In the ready to fire position, the spring will be in tension, enough to pull the piston/valve/spool enough to allow the chamber to vent into the barrel. The air will accelerate both the projectile and the piston. The piston will compress...

@POLAND_SPUD: You could stick another spool on the rod which would block off the air supply. cos aren't spool valve usually used for this kind of thing?

Isn't that what a QDV is? It seals the chamber. I thought that piston valves generally have a sealing face and have a pressure differential across them which is utilised to open them. QDV is a spool valve which, when closed has no forces (kinda) on it. is that about right? @kjjohn: Does all of the a...

This is just a random idea that popped up into my head. I decided to stick it up here for criticism/approval before I go to sleep. It is a really crappy drawing and thus I apologise in advance. It is just a normal qdv but with a spring! When the valve is closed, the trigger (orange) holds the valve ...