Plenum damper and baffle plate arrangement for pneumatic distribution system

In an air seeder, a pneumatic distribution system for delivering product through a plurality of primary tubes arranged in first and second rows, said pneumatic distribution system comprising:

• a plenum housing having an upstream end and a downstream end, the upstream end of the plenum housing having an inlet and the downstream end of the plenum housing having a plurality of outlet ports arranged in first and second rows, each of said plurality of outlet ports associated with one of the primary tubes;
• a fan in fluid communication with the inlet at the upstream end of the plenum housing for generating a flow of air;
• a baffle plate having a plurality of openings extending therethrough mounted in the housing for governing the flow of air to the outlet ports;
• and
• a damper mounted in the plenum housing upstream from the baffle plate for directing the flow of air toward at least one of the first and second rows of outlet ports;
• and
• a flow divider extending from the baffle plate to the downstream end of the plenum housing for substantially isolating air directed by the damper to the first row of outlet ports from air directed by the damper to the second row of outlet ports.