Hoo boy. PVC cannons.....
There have been a number of threads (and discussion on other sites) related to the use of PVC in pneumatic cannons.
Many knowledgable people consider the use of PVC with compressed air to be dangerous due to the fact that it fails in a brittle fashion, potentially creating shrapnel. They point out that the ratings on PVC are for liquids, which, being non-compressible, do not have the same potential to explode, and are rated for static pressures. The firing of a t-shirt concievably creates unanticipated impact forces and sudden pressure changes. They also point to the potential for failures at joints and caps, and have provided some convincing anecdotal reports of failures.
Others have reported the successful use of PVC in pneumatic cannons over an extended period of time and confidence that using a sufficiently high safety factor should keep the PVC from failing.
And, of course, advocates for both sides of the argument are very confident that they are correct!
(Personally, I've had good success using PVC, but in an abundance of caution have replaced the high-pressure compressed air storage side of our system with black iron pipe, which IS rated for compressed air use.)
Rather than having this thread turn into another "PVC is Dangerous!"/"Not if your're careful." thread, I'll suggest we just encourage people to do their own research and make their own informed decisions.
On the main topic... we've had good luck using 12VDC from a spike to fire our sprinkler valve.
Jason