The Isolation Valve (IV) is designed to be normally open, hence with the pressure line normally connected to the Service line, towards consumers.

When the Solenoid Valve (SV) get energized or when the Solenoid Valve is manually actuated, the consumers line is discharged to the Return and the consumers get isolated respect to Pressure line. 

The Pressure Switch (PS) integrated detects pressurizing status on the pressure line and will signal if the pressure decreases under the minimum threshold.