In a pneumatic motion control system, directional control valves have a simple job: open and close. They send air to actuators, hold it back, change its direction or vent it to the atmosphere.
However, the simplicity of their function belies the complexity of the choices for specifying them. Directional control valves come in many configurations. Matching the valve with the application can improve the performance of a pneumatic system and save assemblers money on the cost of compressed air.