A pump assembly may include a rotor having a rotor shaft portion; a stator having a bore portion defining a bore for receiving the rotor shaft portion; and a circumferential protrusion extending radially into the bore between the bore portion and the rotor shaft portion, wherein at least one of the protrusion and a corresponding surface of the rotor shaft portion or the bore portion is configured to be abraded by the other upon experiencing contact therewith. In this way, the gap between the bore portion and the rotor shaft portion may be at least partially filled by the circumferential protrusion in order to provide a seal. The protrusion and one of the bore portion and the rotor shaft portion may be formed from different hardness materials.