An air distribution apparatus including a manifold body having ports with a delivery conduit connected to each port. A port valve is configured to communicate an interior of the manifold body with the delivery conduit associated with each port. A supply conduit is connected at an output end thereof to the interior of the manifold body and connected at an input end thereof to receive a product air stream with entrained agricultural products. An exhaust orifice is defined in the supply conduit and an exhaust valve configured to control a flow of pressurized air from an interior of the supply conduit through the exhaust orifice. The port valve and exhaust valve are controlled to operate oppositely to each other between their open and closed positions. The port and exhaust valves are also adjustable to intermediate positions between the open and closed positions.
