Amtrol® invented the thermal expansion tank to absorb expanded water in closed, hot water systems and protect the water heater. Since the beginning, we've kept the pressure on our competitors with features they just can't match; like our patented Turbulator™, antimicrobial liner, patent-pending InSight™ service indicator cap and 50 PSIG precharge. When your water heater is on the line, we deliver. Amtrol® Therm-X-Trol® Thermal Expansion Tank, Vertical Free Standing, Series: ST Series, 34 gal Tank Volume, Acceptance Volume: 34 gal, 150 psig, ASME Yes/No: No, 22 in Dia, 30 in Height, Drawn Steel, 50 psig Pre-Pressure Rating, 200 deg F Maximum Temperature, FNPT, 1-1/4 in, Urethane Topcoat, Domestic