The Trim Kit (CAL-NA553372) provides components to accommodate water expansion, separate air and fill a hydronic heating system. It includes an AMT-30 4.4-gallon expansion tank, a 1-1/4in NPT DISCAL air separator, an AutoFill fill valve with backflow protection and 1/2in NPT connections, a tank check valve and brass nipples. The expansion tank uses a diaphragm to separate system water from its air cushion.