I have had a reverse osmosis under sink water filtration system for about 5-6 years. After the most recent filter set and membrane replacement I couldn't get it to work properly - only about a half cup would come out at a time. I figured it was a pressure issue so I drained the tank completely and tried pumping more air into the bladder with a hand pump, but I couldn't get any pressure. So I disconnected the tank and took it into the garage and hooked it up to my air compressor and I still couldn't get any pressure. I thought the bladder may have a leak, however I would think that I would either feel or hear escaping air from the upper water inlet port if air was rushing in and out of the bladder, but there wasn't anything. My only remaining diagnosis is the schrader valve is not functioning properly. The tank has a warning label that the valve cap (I assume this refers to the schrader valve) should only be removed by a qualified technician to compensate for the line pressure switch setting (I have no idea what that is). I believe my best bet at this point is to buy a new tank, however I would like some confidence that this is the right direction. Any suggestions?