A pneumatic system of an agricultural implement includes a radial fan coupled with a plenum. The plenum contains outlets which distribute the airflow into a plurality of product distribution lines for application to a field. An airflow deflector plate has a back face fixed on a sidewall of a region interconnecting the fan outlet and plenum inlet to modify the airflow pattern and obtain an airflow that is at a uniform pressure and flow rate for each product distribution line. The deflector plate is tapered with a narrow edge pointed upstream and includes front face having at least one generally rectangular groove with a bottom surface extending generally parallel to the deflector back face.
