These potable water expansion tanks feature a 100% butyl diaphragm and plastic liner to separate the system water from the tanks air precharge. The system has a stainless steel sleeve to prevent corrosion, something no other manufacturer offers. And, the tanks are finished with appliance-quality paint to help prevent external corrosion. On top of all of this, every PH tank is comprehensively tested and backed by Flexcon's one-year limited warranty.