A port interface for a pneumatic distribution system includes a first flow passage configured to receive fluidized particulate material from an outlet port of a header and to output the fluidized particulate material to an outlet line. The port interface also includes a second flow passage configured to receive a purging airflow and to output the purging airflow to the outlet line. In addition, the port interface includes a knife valve having a blade with a first opening and a second opening. The blade is configured to move between a first position in which the first opening is substantially aligned with the first flow passage and the second opening is substantially aligned with the second flow passage, and a second position in which the first opening is substantially aligned with the second flow passage and a solid portion of the blade is substantially aligned with the first flow passage.