Abstract: A sliding closure unit includes at least one stationary plate having therethrough a discharge opening, and a movable plate mounted in sliding contact with the stationary plate, the movable plate having therethrough first and second discharge openings and including a closing area. Guides define alternative first and second paths of movement of the movable plate in directions along respective first and second tracks extending between the closing area and the first and second discharge openings of the movable plate. A single drive is connected to the movable plate for moving the movable plate along a selected such path between a closed position whereat the closing area is aligned with the discharge opening of the stationary plate and a selected open position wherein one of the discharge openings of the movable plate is aligned with the discharge opening of the stationary plate.