Burst disk

A burst disk consists of a thin disc of airtigit material that will rupture at a certain pressure, held in place inside a union or cam lever coupling.

Since the burst disk ruptures almost instantly when the pressure gets to a certain point, they have the fastest opening time of any valve in existence. Since they are pressure-triggered they are nearly always used in hybrids, they are also occasionaly used as the main valve in a pneumatic cannon because of their superior performance.

Burst disks 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 lever couplings.

To use, solvent weld your chamber to one half of your union or cam coupling. One then 'loads' the valve by putting one or more layers of burst disk material (such as aluminum foil, or a piece of a beverage container) in between the two halves of the union or coupling. The union or cam coupling is then tightened down, locking the burst disk in place.

In a hybrid cannon, burst disks fail when the pressure builds due to the combusting gasses. Prior to this, the chamber was containing the flammable gasses at a relatively low pressure. They are also sometimes used on combustion cannons - for their noisemaking capabilities, and/or their (debated) performance improvement.

In a pneumatic cannon, they can be used in the same way, simply pointing the cannon in the correct direction and filling it until it fires. However, many opt to use another system because of the inherent safety issues with this. Such systems include puncturing it with a pointy object (such as a nail) attaced to the end of the projectile, melting it with an electrically heated wire, or having a pneumatically triggered burst disk system using dual burst disks.