Solenoid Valve Actuators: A solenoid, in terms of compressed air valves, is a device that allows the actuation of the air valve using an electrical signal, or the combination of an electrical signal and a compressed air signal to accomplish valve actuation.
When an air valve is actuated solely by the electrical signal, that solenoid valve is defined as being direct acting.
When a solenoid valve uses both electricity and compressed air to shift that air valve, that type is deemed a solenoid pilot valve.
Fig. 44 shows a double solenoid pilot operated air valve.
A compressed air circuit may be controlled entirely by electricity, and all the compressed air valves, the proximity switches, temperature sensors, E-stops, they all can receive signals from, and in many cases send signals back to the brain of the air circuit, the PLC. (Programmable Logic Controller)
When the solenoid valve actuator gets an incoming electrical signal, and assuming that the valve is in good shape, then the valve will shift and air will flow to the application. For your interest, here is link to a page on this site with information on how water in the lines negatively affects compressed air valves.
Solenoid actuators usually come from the factory already attached to their air valve. To power the solenoids, it is necessary to bring a power supply to each of the solenoid valve actuators either directly or through a PLC driven relay.
Rather than hard wiring directly to the air valve, and having to undo the wiring each time the valve is disconnected from the air circuit, the hard wiring need only go to the DIN connector cap once. Then, it is the DIN that is connected to the solenoid via an internal plug. Using a DIN connector allows the non-electrical-skilled maintenance person to disconnect and re-connect the wiring to the valve quickly and safely when that valve needs to be changed out.