This Cartridge Filter Kit includes one replacement filter with O-ring attached and one replacement check valve for the SoClean 2. This kit is suitable for all SoClean machines with “SC1200” in the serial number. The filter and check valve should be replaced every six months, if you use your SoClean once daily with the default 7-minute cycle. The Cartridge Filter converts enclosed air within the system to regular oxygen as it leaves the SoClean 2 chamber. The check valve prevents water from damaging your equipment electronics.