A dirt separator including a chamber having an inlet through which dirt-laden fluid enters the chamber and an outlet through which cleansed fluid exits the chamber, and a disc located at the outlet, the disc being arranged to rotate about a rotational axis and including holes through which the cleansed fluid passes. The holes are distributed over at least first and second regions of the disc, the second region being radially outward of the first region. The porosity of the second region is higher than the porosity of the first region.