This assembly includes: cartridge and housing. If you have not used ASI check valves in the past, then we recommend that you purchase the complete assembly. For better performance, we recommend that you use ASI check valves for both inlet and outlet. Inlet Check Valve Assembly for Shimadzu LC-10AT, LC-ATvp (OEM# 228-32166-91) and Primary Inlet Check Valve for LC-20AT (OEM# 228-45704-92).  Replacement for 228-45557-92 and 228-45704-91.