Pilot solenoid valve on the regulating valve role

You said that is not called pilot solenoid valve, but safety (limit) interlock solenoid valve. Its role is to have a certain condition (or not), the solenoid valve action, regardless of the original state of the regulating valve, are turned to open or close the state, the common is to cut off the membrane head of the gas source, and make it directly to the atmosphere (pressure relief).