The Grundfos 506174 Cartridge Assembly Kit is a replacement cartridge assembly designed for compatible UP15 circulator pumps, including UP15-18B models operating at 115/230V. It integrates the shaft, bearings, and impeller into a single assembly that rotates within the pump housing to circulate water through the system. This cartridge is commonly used in HVAC hydronic heating equipmen... https://www.partshnc.com/grundfos-506174-cartridge-assembly-kit-15-18b-115-230-volts