Solenoid valves can transfer an electric control system signal and release, lock or purge compressed air. The solenoid valve must be chosen according to the type of module; whether air opening/spring shutting or air opening/air shutting. For the first type, a 3/2-way solenoid valve is sufficient. For the second type, a 4/2-way or 5/2-way valve has to be used. 24 V or 230 V solenoid valves are the norm.