Singer models 106-SC and 206-SC solenoid control valves are based on the Singer model 106-PG or 206-PG main valve.
The solenoid pilot valve provides on-off position operation. The solenoid either admits inlet pressure into the main valve operating chamber or releases pressure from the operating chamber. The pilot system is usually piped to discharge at the valve outlet, but can be piped to discharge to drain (atmosphere).
The SC valve is available either with the main valve closed when the solenoid is de-energized (NC -Normally Closed) or with the main valve open when the solenoid is de-energized (NO- Normally Open). (NC or NO refers to the main valve, not the solenoid.)
For more information on the 106 / 206-SC Solenoid Control Valve: