SpudFiles

I have been planning to build a hybrid cannon for a couple of weeks, but I don't want to use burst disks. I can't figure out how the piston valve hybrids work. Can anybody please explain?

Exactly what part of it do you need an explanation about? Gotta start somewhere.

http://www.spudfiles.com/forums/0-22-mi ... 22465.html

Thanks for the diagram. Now I understand.

Just don't use a spring, it probably won't last long

However, air springs have been used successfully but vented designs (where the 'pilot' air is exhausted as with a pneumatic piston valve) are currently in fashion

If you've been having trouble understanding the 'vented' piston hybrids (housed in a tee fitting), they're pretty similar to the above diagrams except the spring is replaced with air pressure (an 'air spring'). This air pressure is vented via a spool valve (same role as the 'pilot valve' in a pneumatic piston valve design) when the fuel:air mixture is ignited and reaches maximum pressure. The piston shoots back as the combustion pressure peaks and the 'air spring' vents, opening the barrel to the chamber and propelling the projectile.

In case you were wondering, in the vented design:
- the 'air spring' needs to be filled with compressed air after each shot
- the piston has o-rings to seal the chamber off from the pilot

Thanks, I think I will replace the spring with air.