So. I'm replacing my tank,and everything looks familair. Except this little disk attatched to one side. It has two hoses. One to the tank, another to a line. Every manual I own tells me it's a diaphram. But, what does it do? I'm guessing gas fume regulation. But, I'm really scratching my head on this thing. Thnx

 

Its there to prevent excessive pressure from building up in the tank.

 

Hey, everytime i open my gas cap you can hear air escaping, like pressure is building up. is this normal? or is the "diaphram" not working?

 

Its working as intended. Its there to have pressure to a certain point. Over that it relieves it.

 

Thanks for the information . I appreciate it.