The DFRobot 6V 2-Position 3-Way Air Valve for Arduino is used to change the direction of the air outlet, also can be used as a valve switch. Like a relay.
It has a common interface (COM), a normally open interface (NO), and a normally closed interface (NC). You can determine which interface to be connected to the common interface by powering on and off the valve.
1x DFRobot 6V 2-Position 3-Way Air Valve for Arduino