Diagonal fan

A diagonal fan having a fan housing, within which an external-rotor motor and an impeller are accommodated, wherein the external-rotor motor has a stator and a rotor which at least partly surrounds the stator, and an axial flow duct runs between the fan housing and the external-rotor motor as far as a discharge opening, surrounding the external-rotor motor, of the diagonal fan, through which axial flow duct, during operation, air which is drawn in by means of the impeller and is conveyed to the discharge opening, and wherein the impeller is integrated in the rotor, and the impeller and the rotor are designed as a single piece, while an air guide apparatus with several air guide vanes distributed in the circumferential direction is arranged in a discharge portion bordering on the discharge opening, and the air guide vanes extend in the axial direction at least in an overlap portion (Ly) beyond the rotor and are spaced apart from the rotor with a radial air gap, wherein the fan housing is multiple-piece and comprises an inlet nozzle and a discharge piece, while the inlet nozzle has an intake opening and the discharge piece comprises the discharge opening, and wherein the inlet nozzle comprises an inlet portion reducing the flow diameter, which extends in the axial direction into the impeller, and wherein the impeller and/or the air guide vanes are designed such that an axial spacing between the air guide vanes and the impeller increases in the radial direction from a first spacing (A1) to a second spacing (A2), and wherein a radius (R1) of the impeller at a point of attack of the first spacing (A1) is larger than the first spacing (A1), and wherein the impeller comprises impeller vanes and a cover disk, while the impeller vanes extend from the rotor to the cover disk.