This distributor comprises a housing of cylindrical general shape which is formed by a casing (1) and a cover (4), between which is rotatably mounted a distributor disc (18) pierced with circumferentially spaced holes (48, 50). Inside the casing, a partition (24) delimits a vacuum channel (26) in communication with a suction shaft (2). The channel (26) comprises a crescent-shaped wide upper part (27) which is extended at its two ends by a narrow branch (28, 30). In the upper part of the descending branch (30), as seen in the direction of rotation of the disc (18), is formed a cavity (32, 33) for receiving a removable member (34) making it possible to isolate this branch from the vacuum source. The bottom of the channel is equipped with an air intake (38) of adjustable opening.
