A decelerating device is mounted in series within a pneumatic particulate material delivery passage that communicates from a particulate material supply to a material outlet of a furrow opener for depositing particulate material into a furrow formed by the furrow opener. The decelerating device has a duct member extending longitudinally between opposing open ends for connection in line with the pneumatic particulate material delivery passage. A plurality of exhaust openings communicating through a peripheral wall of the duct member to exhaust air therethrough. A gate member is supported on the duct member so as to be movable relative to the exhaust openings to vary a cumulative exposed area of the exhaust openings. A perforated screen member spans across the exhaust openings having a smaller aperture size than the exhaust openings to ensure small particulate materials being conveyed do not escape through the exhaust openings.
