Thanks for the advice. I just went on a 3 month vacation, but I'll try your repair suggestions when I return and report back with the outcome.

I took a standard bike pump up to 110 psi to fire my pneumatic cannon. When I tried to use the pump again, it stopped working. Even when the pump isn't attached to anything, I feel a lot of resistance in the plunger on the downward stroke (as if the pump is already attached to something at 80psi), a...