Burst disk

A burst disk ruptures when the pressure gets to a certain point, allowing the gas to propel the projectile down the barrel. Due to this meathod of "opening", they have the fastest opening time of any valve in existance. They are nearly always used for hybrids, and occasionaly as the main valve in a pneumatic cannon.

They are a very close rival to a ball valve in cost, at roughly 13$ for a 2" union in sch 40 PVC. More expensive (but conveinent) devices exist, such as cam couplings. To use, solvent weld your chamber to one half of your union or cam coupling. One then 'loads' the valve by puting a layer of some weak material (such as multiple layers of aluminum foil, or a peice of a beverage container)in between the 2 halves of the union or coupling. The union or cam coupling is then tightened down, locking the disk of material in place.

In a hybrid cannon, they fail when the pressure builds due to the combusting gasses. Prior to this, they where containing the flamable gasses at a relitivly low pressure. They are also sometimes used on combustion cannons - for their noisemaking capabilities, and/or their (debated) preformance improvement.

In a pnematic cannon, they can be used in the same way, simply pointing the cannon in the correct direction and filling it untill it fires. However, many opt to use another system because of the inherent saftey issues with this. Such systems include puncturing it with a pointy object (such as a nail) attaced to the end of the object, and a 2 burstdisk system.