Abstract: A classifier has a rotor, driven by a motor, mounted between two opposed walls of a housing. The housing also has a curved wall which extends between the walls and around the rotor to define therewith an annular zone. A fluid and finer particles outlet opening is provided in one of the walls. The curved wall has an inlet opening for at least fluid and a fluid and coarser particles outlet opening which is registered with the inlet opening of a receptacle from which the coarser particles can be removed. A plate is located immediately upstream of the outlet opening to divert particles adjacent to the curved wall away therefrom. Similar diverting means can be located remote from the plate such as plate or secondary air inlet openings. Baffle rings are provided concentrically with the rotor to restrain particles forced to the outer peripheries of the annular zone from moving inwardly towards the rotor.