The Wolverine Brass Hydronic Water Thermal Expansion Tank is a 2.1 gallon silver tank designed to absorb the excess volume of water that results from heating, preventing a dangerous buildup of pressure in the system. This protects the boiler, pipes, and other components from damage caused by excessive pressure, which can lead to leaks and other failures. It works by providing a space for the expanding water to go, which in turn compresses the air inside the tank, acting as a shock absorber for the system.   systems. Made of brass, this expansion tank is manufactured by Wolverine Brass and has a manufacturer part number of 80754. It has a sleek design that is compatible with various systems.