The Eastman Thermal Expansion Tank is designed to protect residential water heaters from excess pressure caused by thermal expansion. Built with a butyl rubber diaphragm and a 304 stainless steel system connection, this tank provides durable and reliable performance while helping extend the service life of your water heater. Factory pre-charged at 40 PSI, it installs easily with a 3/4 in MIP connection. The tank is rated for a maximum working pressure of 150 PSI and a maximum operating temperature of 210 degrees F. Backed by a 6-year limited warranty, it offers dependable protection for your water heating system.From the ManufacturerThis Thermal Expansion Tank prevents hot water from back flowing into the cold water line. This tank also prevents hot water from escaping through the pressure relief valve and onto the floor. The thermal expansion tank prevents constant fluctuations in water pressure that damage the heater.