Inline directional pneumatic valves are fundamental components in pneumatic systems that control the direction of airflow. These valves are installed directly in the path of compressed air and regulate its flow to activate pneumatic actuators like cylinders and motors. By opening or closing specific pathways, inline directional valves determine the direction in which air travels, allowing for precise control over the movement of pneumatic components. They are crucial for directing airflow to achieve desired motion and functionality in various pneumatic applications.