Series ETX tanks are designed for use in closed-loop hydronic heating systems to absorb the increased volume of water created when water is heated. These tanks maintain system pressure below the relief setting of the relief valve. The Series ETX's pre-pressurized steel tank features a durable expansion membrane that prevents contact of the water with the air in the tank. This rugged diaphragm minimizes loss of the air charge and ensures a long and trouble-free life for the system. Maximum pressure of the ETX tanks is 75psi.