Solenoid Valve Operation 

This animation shows the air flow within a solenoid valve (Max-Air Technology SV63) during manual override.
The path of the internal air is shown in blue, the path of the air from the supply to the actuator is shown in green, and the path of the air exhausted from the actuator is shown in yellow.
When air is supplied to the middle bottom port, air flows into the left port of the pneumatic actuator, which normally closes it. The air supplied to the endcap on the right normally holds the spool to the left (this force is represented by the smaller arrow on the right). However, when the coil is energized or the blue button is pressed, air is allowed to flow into the chamber on the left, which has more area so that the same pressure applies more force on the left side of the spool (represented by the bigger arrow) which pushes the spool to the right. This change of position allows air to flow into the right port of the actuator, which normally opens it.