The Watts 0067370 PLT-5 Potable Water Expansion Tank is designed to protect potable water systems from pressure increases caused by thermal expansion. Commonly used with water heaters, boilers, and domestic hot water systems in HVAC and plumbing applications, it features an internal diaphragm that absorbs excess water volume as temperatures rise. This helps maintain stable system pres... https://www.partshnc.com/0067370-watts-plt-5-expansion-tank