Cory,
We’ve been designing T-Shirt Canon’s for a while but have been singularly unsuccessful at getting permission to build one from the school or school district we are affiliated with.
How did you folks go through the process of obtaining permission to build and then demonstrate your shooter at school events?
Doc
Is that PVC? If so I would recommend immediately decommissioning that cannon and rebuilding it with pressure-rated ABS or metal. PVC is pressure rated for liquids, not gases. When PVC fails, it shatters, which, when filled with air sends sharp shrapnel flying. This shrapnel can easily blind or otherwise seriously injure someone. The question with PVC, as with any material, is not if it will fail but when it will fail. It might last 10 years or it might last a month. With pressure-rated ABS or metal, the risk of failure is only slightly small, but the risk of injury when said failure occurs is orders of magnitude smaller. The risk of failure is very small, but the risk or seriously injuring someone is just to great.
We just built one (over the summer, in a student’s family owned shop), then went to the administration and asked if we could use it a an assembly and at football games.
To get permission to build and use ours we had to get the okay from not only the building principal but also “Risk Management” or what ever your school division calls the department that handles safety and security.
We made sure that our plans and materials usage met or exceeded OSHA specifications for containing compressed gasses.
Everything that contains pressurized gas is either commercially produced and rated to a pressure far exceeding what we are putting it or is soldered metal pipe. The only plastic pipe we ended up using was the barrel.
Yes the material you see is PVC and ABS plastic. However, all parts that will come under high pressure are metal. The secondary storage tank is reinforced with metal. The rest of the valves and such are either metal or standard pneumatic parts. The revolver and barrel are made out of PVC but serve only to guide the t-shirt. Any unsafe build up in pressure would be vented out the back of the revolver against the spring seal (which is very easy to move) or the other pressure relief valve. Mentors looked very carefully and verified the design and materials (Our main sponsor Price Eng. is a specialist in Pneumatics, qualified GE mentors and the legendary Mr. Borchardt (Bruceb) ) so I feel very safe. There is another topic dedicated to the controversy over our materials choices 
We have since made changes. This was a prototype
As for the school: As I understand (we have been working on this a while before my rookie year) we built it with out asking. Then after we put it together, we talked to administration and the sporting event staff (and coaches) along with janitorial staff for input. We make sure to completely honor the wishes of everyone at the events to make sure we are continued to be invited. The treads were made to be scratch resistant (again plastic) to the floor. At sporting events we dial in the pressure before the event starts to a safe level. Also, our school police officer is very interested in robots so he helps us out. (Sadly the mentors don’t like to come to Friday night football/basketball games). The robot receives a lot of attention so the administration seem to be fine with it. The situation may also be determined from your relationship with the school. Our relation ship is actually quite bad and face a lot of challenges but finding a friend in the higher ranks is a major boost. It has been a challenge but we are slowly chipping away at the goal.
We recently partnered with the DEKA club to incorporate it into their multiple fundraisers. It has been a real success and you may wish to look for support from another club to help sway the administers…