Ok i was wondering something, lets say you have tank A and tank B that are identical. Tank A is pretty much empty and tank B is full of some gas at 200psi. Lets say you hook them up with a valve but the valve is closed. After the valve opens up and they are allowed to equalize, what will the pressure be overall? Gut instinct says 100psi... but i dunno :) Also, does anyone know if something exists that regulates pressure. Say you have a tank at 40psi and dont want ti to go any higher, is there something you could attach that opens up and releases the gas until it comes back down to 40psi in the event it goes beyond that?