SpudFiles

Hi, this will be my first time building a pneumatic cannon, I am considering building a replica of a rifle, pump action for the first, however, I am very concerned about the valve system between the rifle barrel and the pump.

I have made some researches, and so far everyone has been using the gas to push the spring then release the shot? can anyone explain the mechanics behind that? Thanks.

Ok, WHat do you mean pump action?You mean you will have a hand pump?
What you need is a chamber,a valve,and a barrel.
The chamber is filled with pressure, the valve releases it pushing the projectile out the barrel.
Click on spudwiki at the top of teh site and it will explain everything to you.

Go on over to spudtech, and search for "mini pump" (or just "pump") by the member "clide", including archives.
It should give you some ideas.