This is an idea for a venting piston actuated by the combustion pressure. I made the animation long ago, I can see a few ways to improve upon this thing.
Operation: the chamber itself is to the right. when the cannon is fired, the blue piston is pushed to the left, taking the yellow venting piston with it. Between the chamber and venting cylinder is a check valve, the venting piston also needs a check valve.
After the combustion pressure has disappeared, the blue piston will be returned by the big spring, but the venting piston will be held back with magnets (far left). The small center spring will not be strong enough to pull it loose form the magnets, but when the blue piston has almost returned to its initial position, the force of the big spring will be put on the venting piston, it will be pulled loose from the magnets and the center spring pulls it all the way back, forcing fresh air into the chamber.
This was ment as a solution to the problem illustrated here with a simpler design someone else posted:
http://www.hostanyimage.com/files/71byr ... hzp3lk.gif
Problems: the forces of two springs and a set of magnets must be balanced for this to work. the center piston is also far too big and will have very high forces acting on it while taking energy away from the projectile. In reality, the piston could probably have a diameter smaller than the barrel. If made to travel further than in the drawing of the simple design, or if the diameter of the venting cylinder was made larger than the chamber, the simple design would work. The problem with this design is that the venting cylinder takes up at least as much space as the chamber itself.
I had designs for recoil-operated venting, but I can't seem to find the drawing or 3D model I made and I don't recall the exact mode of operation. It did involve some of the principles of the first valve though, letting the entire cannon slide backwards from the recoil, then have it move forwards (using a spring or counterweight) while a piston inside the chamber is held back by a catch. This makes the piston move through the chamber, venting it. When the cannon returns to its original position, the catch is released and the piston returned by a spring.
The advantage to doing things like this is that the recoil force only cocks the mechanism, while the actuation is done by the predictable and adjustable forces from springs, counterweights and/or bungee cords. This principle of operation can be used for any mechanism actuated by combustion pressure or cannon recoil, including loading, venting and fueling mechanisms.
Hope this can inspire someone
We also need research on something that was mentioned in another thread, which is venting through reed valves in the rear of the chamber, using the momentum of the combustion gasses (or if that's not enough, using vacuum from the projectile in an overly long barrel).
PS: Why doesn't phpSpell work? It says I need Opera 6+, I have Opera 9.63.
). Some kind of system is needed to ensure that you don't just push the combustion products into the barrel and then suck them back into the chamber again, but there are several ways to solve this problem. The piston could also be connected to a bolt action loading mechanism.
