This potable water expansion tank is used on gas, oil, or electric, direct-fired, residential water heater and hot water storage tank applications to absorb the increased volume of water created by thermal expansion. It also maintains balanced pressure throughout the water supply system by keeping system pressure below the T&P relief valve setting. This field-adjustable steel tank is air pre-charged at 20 psi, volume 4.5 gallons, designed with an FDA-approved polypropylene liner and Butyl rubber diaphragm, copper-lined steel, and 3/4 inch male inlet connection. An expansion membrane prevents air-to-water contact in the tank ensuring a long system life. IAPMO listed and ANSI/NSF 61 certified. The maximum pressure is 150 psi (10 bar).