The present document discloses a rotor apparatus (20) for feeding granular or powdered material in an agricultural implement, the rotor apparatus being designed to be received in a partially cylindrical feeder space of a feeder device for volumetric feeding. The rotor apparatus (20) comprises an insert part (21 ), which in size and shape is adapted to be inserted into the feeder space and to substantially prevent air from passing the insert part when this is inserted into the feeder space, and a rotor (22), which is rotatable relative to the insert part. The insert part (21 ) defines a rotor space (218), in which the rotor (22) is rotatable, and the rotor is together with the insert part designed to provide an air lock. The insert part (21 ) comprises a wall portion (214, 215) interacting with the rotor and located radially outside the radially outermost portion of the rotor.
