PVC pressure ratings for HS student.

DWV systems are not required by ASTM code to be pressure tested and are therefore not pressure rated by any manufacturer. DWV pipe and fittings should never be used in any pressurized system.

I know you probably want to use a DWV tee due to the sweep on the leg, but if you want to pressurize you need to go to at least Sch. 40 PVC (rated for 133 psi working pressure in 4" pipe.)

Good luck with your project.

If these are the same as the push-fit waste pipe fittings found in the UK, then they have no pressure rating at all. They are designed to run with the pipe partly-full and unpressurised. Though they push together to give a leak-tight seal, a pull is all that is needed to separate them.

Do NOT rely on them for anything above a few inches of water above ambient pressure, otherwise there may be a risk of someone getting hurt, particularly in the context of a "pressurised football launcher"!

Google for potato cannons. The only difference between them and what you have in mind is the projectile launched. FYI, you should be using Schedule 40 or even Schedule 80 pipes for your purpose.

If one reads the manufacturers literature on PVC and CPVC pipe, it will inevitably state the pipe is never to be used for pneumatic pressure--at least every manufacturers spec I have read says that.

As a technical matter, pressure is pressure, and people somewhat routinely use plastic pipe in pneumatic pressure applications without trouble. I have been told by pipe distributors that there have been a few spectacular examples of catastrophic failure of the pipe which results in this limitation.

Yes, I have seen many industrial compressed air loops constructed from PVC. It's cheap, goes up fast , and is easy to modify. Unfortunately it degrades from exposure to UV or hydrocarbons (compressor oil) and does not take impacts well. When one fails, it's like a Pyrex bowl exploding.