US Patent 7846242 Air dryer cartridge

An air dryer desiccant cartridge, the cartridge comprising a base having an inlet and an outlet, and a casing connected to the base to define a cavity there between, wherein the cavity contains a filter and a desiccant, the filter being arranged upstream of the desiccant such that during normal operation fluid flow entering the cartridge through the inlet passes through the filter and then on to the desiccant before reaching the outlet, and during purging of the cartridge purge flow entering the outlet passes through the desiccant before reaching the filter, wherein further the cartridge includes a valve operable to permit a portion of the purge flow to bypass the filter.