Pneumatic Components and Symbols
From DT Online
Pneumatic symbols are used to describe the function of the various valves and other devices which are connected together to form circuits and sub circuits.
Symbols for valves are shown as boxes representing the dfferent operating positions - the symbol shown for example is based on two boxes so it is a two position valve. Looking at any one of the boxes gives an indication of the number of ports on the valve - in this case there are 2 ports in each box so it would be a 2-port, 2-stage valve (2/2 Valve).
In the left-hand box, the arrow indicates that both ports are open and air would be allowed to pass through the valve in this position. In the right-hand box, the same two ports are shown as blocked. In this position, air is not allowed to pass.