Bell & Gossett expansion tanks absorb the force of thermal expansion in hydronic heating and potable domestic water systems. The butyl diaphragm separates system water from the air in the tank thereby preventing water-logging problems. Series HFT tanks are for standard hot water heating systems while PT tanks are for potable domestic water systems, both have a maximum working pressure of 100 psi and a maximum operating temperature of 240°F. Series PT tanks use a polypropylene liner to protect the water from contaminants. Special ASME designated Series PT tanks can also be ordered.