Damn right it's a sport.
Some people do like to build cannons small..like me
By the way, people here won't spoonfeed. It's not cause we hate people (thunderlord hates everyone, don't take it personally..jokes thunder). It's because if we tell someone what to do, and they stuff up then parents try to get spudgunning banned. If they learn about the concepts, then they figure out how to build their own, then they don't get hurt. No different from any other hobby..such as pyro
Pnematics work on the same principles as paintball guns, except:
We use a less efficient, higher flow, faster, higher duration valve. Hence why most of our cannons get one shot on a fill, and paintball guns get..a lot more.
The valve is open to imagination, and can be in any form. Hammer valves and spool valves have been used, however ball, sprinkler (diaphragm) and piston valves are more common. Burst disks are also used.
Ball valves you can buy for a few dollars and are simple as, so I'll just link to a few things:
How piston valves work
You should recognise that as basically an unbalanced spool valve
Valves are also used in combination; for example many of BTB's guns use hammer valves to pilot QEV's.
Combustion is epicly simple. Gaseous fuel in chamber, spark ignites fuel, increased temperature and number of molecules creates pressure, forcing the prokectile out of the barrel.
Hybrid is still easy. No different to a combustion, except you add extra fuel (referred to as X), then add 15 more psi for every extra charge of fuel, this, in conjunction with moar's law gives moar power.
If you want more help, give us a bell. However, we will not give plans for complete cannons.
By the way, a schrader valve is an automotive valve...you'll see at least four on every car
