Flexcon Industries PH5 FLEX2PRO Thermal Expansion Tank - 2.1 Gallon PH tanks feature a 100% butyl diaphragm and plastic liner to separate the system water from the tanks air precharge The system connection has a stainless steel nipple to prevent corrosion, something so other manufacturer offers Tanks are finished with appliance quality paint which helps prevent external corrosion PH tanks are comprehensively tested and backed by Flexcons 1 year limited warranty Volume: 2.1 Gallons