Pneumatic cannon
A pneumatic cannon is a cannon powered by pressurized gas, usually air or CO2. They generally require a little more work to build than combustion cannons, but using typical compressor pressures of 120 psig or so and a decent valve, they will outperform most combustion launchers of the same size.
Basic Elements
Pneumatic launchers consist of five basic elements:
- Compressed gas storage reservoir (chamber for short)
- Filling valve (bicycle Schrader valves, quick disconnects, etc.)
- Firing valve (ball valves, sprinkler valves, piston valves, bolt-style valves(see piston valves) quick-exhaust valves, and burst disks are the most common)
- Barrel
- Pressure gauge (for safety & repeatable launches)
Operation & Theory
In order to fire, the operator loads a projectile into the barrel, fills the chamber with a compressed gas (see Pneumatic air sources for common filling methods), and activates the main valve thus dumping the air in the chamber to the barrel.
The expansion of the compressed gas propels the projectile down the barrel. The barrel length determines the amount of energy transferred to the projectile and ultimately the velocity of the projectile.
Higher performance launchers use techniques such as:
- Faster valve opening times - see sprinkler valve modification
- Higher flow valves to maximize the airflow through the valve (Especially true for cannons with very long barrels)
- Using higher gas pressures.
Less common, but also effective in increasing power, some people will also use a gas with a higher speed of sound and particle speed (e.g. helium).
Common types of launchers
Piston valve launchers
Piston valve launchers use a pistonin a valve that either seals the barrel or chamber. releasing air from the back of the valve will set the piston away from it's sealing position and air will go out the barrel.
More to come
Related Links
Downloading the GGDT (Gas Gun Design Tool) is highly recommended to those interested in pneumatic launchers.
