Pneumatic circuits can be controlled by electric circuits. The interface between these two circuits is a solenoid valve. Solenoid valves perform the same function as normal pneumatic valves but there are operated electrically.
Inside the solenoid valve, there is a coil of wire through which an electric current is passed. It produces a magnetic field which attracts an iron armature. The movement of the armature operates the valve.
Solenoid Operation Off: When the electric current is not flowing, a spring pushes the iron armature out of the coil. A seal connected to the armature blocks port 1. Air can flow between ports 2 and 3.
Solenoid Operation On: When current flows, the iron armature is attracted into the coil by a magnetic field. The spring pressure is overcome and the seal moves to block port 3. Air can flow between port 1 and 2.
When the solenoid valve is on, an electric current will flow through the coil. When current flows through the coil, the iron armature is attracted by magnetism. The solenoid has control of the valve. Port 1 is connected to port 2 and air flows to inflate the soft robot.
When the solenoid valve is off, the coil is de-energized and the spring has control of the valve. Port 2 is connected to port 3 and air flows out of the soft robot.