This non-potable water expansion tank is designed for use in commercial and residential closed loop hydronic heating system piping to control the thermal expansion of hot water and maintain system pressure below the relief setting of the relief valve. This carbon steel tank is pre-charged at 12 psi, tank volume is 4.5 gallons and features a durable expansion membrane that prevents contact of the water with the air in the tank. This rugged butyl diaphragm minimizes loss of the air change and ensures long and trouble-free life for the system. This tank is made of carbon steel with epoxy finish, mounts to supply piping, 1/2 inch MNPT system connection and a 0.302-32 inch charging valve connection (standard tire valve) to facilitate on-site charging of the tank to meet system requirements. The maximum working pressure is 75 psi