T-Shirt Air Cannons are frequently seen at sports events and are used as an easy and fun way to distribute T-shirts among large crowds. The principles behind the air cannon aren't difficult, essentially the air cannon is two tubes that are connected by a valve. One tube contains pressurised air and another your T-shirt to be launched. Releasing the valve between the tubes releases the pressurised air, which catches the T-shirt and sends it flying through the air. While the principles are easy enough the build itself will require forethought and care.
Drill a hole in the PVC end cap and install the Schrader valve. Cement the valve in place with PVC cement.
Attach the PVC end cap to the 3" PVC pipe. You may need to cut down the length of the PVC pipe to about 2 or 3 feet depending on how large you'd like your T-shirt cannon to be. Use the saw to cut the PVC pipe and use care when using the saw. Use the PVC primer and cement to attach the end cap to the pipe. Follow the instructions on the primer and cement you purchased.
Attach the fittings to the sprinkler valve control. You will need to test at the hardware store which fittings will help you best attach the sprinkler valve control to the U shaped PVC pipe and the 2" PVC pipe you intend to use for the barrel. Make sure all fittings will create a tight seal. When attaching threaded non-PVC fittings wrap the threads in plumbers tape to help prevent air leakage.
Attach the assembled sprinkler valve control and fittings to the U shaped PVC pipe. Again use the PVC primer and cement. Make sure you have tight seal.
Attach the U shaped PVC pipe and sprinkler valve control to the 3" PVC pipe using the PVC primer and cement.
Attach the 2" PVC pipe to the rest of the assembly with the PVC primer and cement. You may need to cut this piece so it's an appropriate length for your project. About 2 to 3 feet should do. Now that the air cannon is assembled let it sit overnight so that the cement can dry.
Attach the bicycle pump to the valve on the end cap after you have allowed your assembly to dry overnight. Pump air into the air chamber you built until the pressure gauge reads at least 80 PSI. Roll up a T-shirt tightly and slide it into the 2" PVC pipe that will serve as your barrel. Pointing the cannon away from people, animals, building, and anything that might break, release the sprinkler control valve and watch the T-shirt fly. Higher pressure should result in more distance.
You may have a sprinkler control valve that requires electricity to run. You should be able to accomplish this by attaching a 9 Volt battery and small electric switch to the valve. This will function like your trigger. Test all pieces at the hardware store to make sure they fit together properly so you don't have to make a return trip.
Make sure that all pieces are securely attached and well sealed. If they aren't they may come apart when you attempt to launch the T-shirt and that can be very dangerous. Be very careful building anything intended to launch an object and be very careful with any launch. Used inappropriately any air cannon can be dangerous to yourself and those around you.