Wide-open monitors are the most common form of overpressure protection in large gas distribution applications such as city gate stations, district stations, and large industrial meter sets.
Wide-open monitor setups utilize a second regulator (called the monitor) in series with the worker regulator where both regulators sense downstream pressure. The monitor is set slightly above the worker pressure setting, keeping it open and in standby. If the worker malfunctions and outlet pressure rises, the monitor will take over control at its pressure setting.
The monitor can be either the upstream or downstream regulator. Also, both pilot-operated regulators and direct-operated regulators can be utilized in a monitor setup as long as the upstream regulator has external registration in order to sense the pressure after the downstream regulator.
Conditions after worker failure: