Pneumatic Valve Symbol Directional air valves, in particular, spool valves, are the building blocks of pneumatic control. Pneumatic circuit symbols provide detailed information about the valve they represent. A valve schematic is made up of boxes, each containing a number of lines and arrows. The number of boxes that make up a valve symbol indicates the number of possible positions the valve has. Flow direction is indicated by the arrows in each box. Watch the video and answer the question. What