A cyclone filtration assembly unit is described. The unit is configured to mount in a vacuum cleaner, and includes a housing having a housing inlet for a dirty air stream and a housing outlet for a filtered air stream; one or more cyclone separators mounted in the housing, each of the one or more cyclone separators comprising one or more cyclone separator inlets, at least one dirt outlet, and at least one clean air outlet in fluid communication with the housing outlet; and one or more injector units configured to deliver an airstream of clean air from outside the housing and dirty air from inside the housing to the one or more cyclone separator inlets, the injector unit comprising: a diffuser duct having an inlet end in fluid communication with the housing inlet to introduce dirty air from the housing inlet to the cyclone separator inlet, and an injector tube configured to inject clean air into the diffuser duct adjacent the inlet end, the injector tube being in fluid communication with a housing aperture at an inlet end to introduce clean air from outside the housing to the diffuser duct.