I'm going to hop onto the chain of people asking for help with blasters that aren't working. Sorry.
Anywho, I recently acquired a 4B from a friend who was thinning out his arsenal, but it hasn't worked for a couple years. When I disassembled it, it worked a bit. I tried pumping it, but mostly it didn't work. I think that either the O-ring or the OPRV aren't sealing. To test the tank's seal, I manually inflated the tank by blowing into the tube where the pump went.
At first, the tank would fire when pumped carefully or inflated by lung, but something happened and the tank won't pressurize or depressurize.
Pictures won't really help; should I record video?