A dedusting apparatus is formed with a rectangular inlet structure that assures a fully loaded feeding of particulate material over the face of the opposing wash decks. A rectangular inlet box having substantially the same width dimension as the corresponding dimension of the adjacent wash decks provides an even distribution of particulate material over the entire surface of the wash decks. A reconfiguration of the air inlet structure eliminates a rearward air plenum and manifold by passing the air flow upwardly through the bottom wall of the apparatus housing, rather than through the rear wall. Individually adjustable inlet deflectors can regulate the product flow on each respective wash deck and can be closed to stop the product flow completely to either one or both of the wash decks. Actuators control the movement of the deflectors, which can be integrated in an overall electronic control system for the dedusting apparatus.