Combustion, internal or external, are not allowed, unfortunately. That would be too easy .

I will still receive major credit for constructing a pnematic launcher for effort, even if it does not hit 15 meters, but I don't want to feel like a guilty loser.

Lol, I'm back again. my dad is getting mad at me for procrastinating, so I'm going to have to be simple again. I'm just going building something like this using either an 8" or 6" rated PVC pipe as the air chamber and a 6" as a barrel. In between the pipes will be a butterfly valve that I found off ...

Would a one inch ball valve be sufficient enough to accelerate a cabbage through a 6 inch wide (5-6 feet long) PVC barrel at least 15 meters if I fill the air chamber to around 90 PSI?
I severely doubt it.

They only have 1 inch ball valves, and the trigger handles are not even springs
No ball ...

Thanks guys! You guys have been a tremendous help! I have changed my design completely to something like this , and using a tee pipe to connect two air resevoir pipes and concentrating the air pressure into one barrel. However, I will be incorporating a lot fo what yall suggested. Oh yeah, i don't ...

I cannot find a butterfly valve anywhere in my local hardware stores and and called all of them to find out that they carry the same exact valves. They only have 1 inch ball valves, and the trigger handles are not even springs, so I have to trigger my launcher by turning.

Also, my propane tank has ...

Would I have to go to a machine shop to cut my propane tank to a better fitting? When installing a filling valve such as a Schrader valve, can I use a carbide-tip and drill a hole?

Sorry if my questions are ridiculous, but my engineering skills are horrible.

Would a 5 gallon (about 20 liter) chamber be sufficient? I'm afraid I can't find an insane one (26 gallon) for free. I can pump up to 90 PSI.

One final question. Is it really that easy to install a barrel and a chamber with a butterfly valve? I need to buy a flanged adapter too also, right?

If the cannon is to be used at a public event such as a pumpkin patch, care must be taken for liabilaty issues with the spectators. Insurance requirements may limit your choices in materials. Pumpkin Chukin has eliminated plastic barrels for safety reasons.

Is the cannon for personal rec use, or ...

Thanks for the advices, guys! They were really helpful, despite the "friendly" competition between yall. I will use MrCrowleyand and use a butterfly valve to accomodate the large projectile that I will be launching. Also, thanks for the valve size tips, Technician1002.

Also, is it reccomended to ...

I am planning to build a pneumatic launcher that can launch a 400 grams cabbage (average 6 inches diameter) at least 15 meters (does not matter how high it goes). The thing is, I am not very mechnically inclined and this will be one of my first technical projects. However, I do understand the ...