Amtrol ST-12 (Therm-X-Trol) is a water heater expansion tank, designed for use in domestic hot water heating systems to eliminate the potential hazards of water expansion.  Water heater expansion tank is commonly installed in a domestic hot water system that contains a backflow preventer, a check valve or a pressure reducing valve.    The HydroClaw Expansion Tank Support Bracket provides a safe and reliable option if you prefer to mount your expansion tank. This expansion tank bracket is easy to install and will hold any tank with a diameter of 11" nominal.    Amtrol ST-12 Advantages:  Eliminates the waste of energy and water, thus saving money Protects the water heater and plumbing fixtures from premauture failure Reduces potential safety hazards associated with thermal expansion Prevents a dangerous pressure build-up in the system Prevents the relief valve from going off Therm-X-Trol brand is the #1 choice of Professional Installers.