I've been using this same tank for over a year and now i'm getting vapor in the tank. I've never changed the o-rings and I'm not even really sure when to tell it's time. This vapor lock issue is annoying as hell though. I e-mailed qp design and the customer service person said it's most likely just worn out o-rings. There doesn't appear to be anything in the threads or anything. It hits like crap once the vapor starts getting into the tank.