A manifold apparatus for an air seeder includes a manifold housing defining a output ports equally spaced around a perimeter thereof. An input port is defined in a bottom side of the manifold housing, and an input conduit extends downward therefrom. A distributor component is formed by a bottom side of a top plate of the manifold housing above the input port and directs product granules moving upward in an air stream in the manifold interior outward toward the perimeter of the manifold housing. A relative lateral position of the distributor component with respect to the input port is adjustable, and interference members extend an adjustable distance into the input conduit and/or manifold interior to contact the particles and change their flow path. The variables are manipulated to achieve positions where a rate of product flow through each output port is within a selected range.
