Abstract: An air pre-cleaner of the centrifugal type has a cylindrical housing with an annular louvred air entry structure at a first end thereof and coaxial therewith, and has an inner cylinder forming with the housing and the entry structure an annular separation chamber coaxial with, adjacent to, and axially inward of the entry structure. The inner cylinder forms with the housing a short cylindrical transfer chamber coaxial with, adjacent to, and axially outward of the separation chamber. A ring flange is disposed at the inner end of the inner cylinder along the inner ring of the annular separation chamber lying in a plane normal to the axis of the chambers. A dirt discharge slot is disposed in the side wall of the housing with one end of the slot substantially radially outward from the ring flange, the slot extending along a major portion of the axial length of the separation chamber.