Centrifugal fan assembly for road sweeping machines

A road cleaning vehicle comprising a debris collection arrangement, the debris collection arrangement comprising a centrifugal fan assembly, the centrifugal fan assembly comprising:

• a casing comprising a volute portion, an outlet passageway and an air inlet, the volute portion being connected to the outlet passageway and the air inlet, a corner being formed in the casing between the volute portion and the outlet passageway;
• a rotatable impeller comprising a plurality of blades, the impeller being located in the volute portion proximate the corner and arranged to draw in air from the air inlet and direct the air to the outlet passageway;
• and
• a wall separating the outlet passageway into a first and second passageway, the wall extending to an inner end proximate the impeller, the first and second passageways being sealed from one another other than at the ends of the first and second passageways,
• wherein the inner end is positioned, and the impeller is arranged, such that when a blade passes the inner end a second pressure wave is formed that destructively interferes with a first pressure wave formed by a blade passing the corner;
• and
• wherein the distance W between the inner end and impeller is greater than the distance Z between the corner and impeller, wherein a first angle about a center of rotation of the impeller between the inner end and corner is the sum of:
• a second angle between at least two of the plurality of blades;
• and a third angle, which is less than the second angle between at least two of the plurality of blades, resulting in the second pressure wave being out of phase by approximately 180° to the first pressure wave.