An air filtration system comprises an airflow inverter valve, an internal diffuser and a cylindrical filtration element positioned between the airflow inverter valve and the internal diffuser. A frustoconical external diffuser is joined to the airflow inverter valve so as to at least partly surround the filtration element. If desired, the airflow inverter valve and the external diffuser may be built as a single monolithic member. In one example, the airflow inverter valve, internal diffuser, filtration element and external diffuser each have a central axis of rotation aligned along a common central axis of the air filtration system.