A propane cannon is a device that produces a fireball using propane gas.
A propane connon has several parts
1) Propane tank 2) Hose to connect the tank to the reservor 3) Reservor 4) Valve 5) Launch Tube 6) Ignitor
Descriptions of each below.
There are two types of valves suitible.
1) Solinoid Operated Valves 2) Manually Operated Whistle Valves.
Soliniod valse use a solinoid to operate the valve. A variant is the pilot operated soliniod valve. In this valve the soliniod opens a pilot valve which then uses the gas pressure to opperate a diaphragm which opens the main valve.
The advantage of pilot operated valves is they can use a smaller soliniod operate the valve. The downside is that they typically require 5-10psig to operate. Which is usually not a problem.
Many DC soliniod valves a pilot operated. This is because it is hard to build large DC soliniods. An AC soliniod limits the current through the soliniod via the AC impedance of the windings. A DC soliniod in contrast l9imits the current via a DC resistance. The upshot is DC soliniods generate more heat.
12V DC operated soliniod valves are good for this application as they can be easily run of a 12V lead acid battery.
Whistle valves are very good for this applications. They are basically spring loaded globe valves. Globe valves use a round 'globe' and a rubber seat to seal. The gas pressure tends to hold the valve closed. When the valve is opened the pressure is much reduced which causes the valve to snap open, which is what you want with a Propane Canon.
If the propane canon needs to be computer controlled or remotely controlled a 12DC pilot valve is a good choice. Otherwise a manually operated whistle valve is best.