Working monitors are an underutilized form of overpressure protection in large gas distribution applications such as city gate stations, district stations, and large industrial meter sets.
Working monitors, like an upstream wide-open monitor setup, are composed of two regulators in series where both regulators sense downstream pressure and have a pilot on the upstream regulator set above the downstream regulator pressure setting; however, an additional pilot is added to the upstream regulator to control the pressure between the two regulators. The two pilots on the upstream regulator are installed in series with the working pilot controlling intermediate pressure and the monitor pilot open and on standby in case the downstream regulator malfunctions.
The upstream regulator must be a pilot-operated regulator, but the downstream regulator can be pilot-operated or direct-operated and can even have internal registration.
Upstream Regulator Failure
If the upstream regulator malfunctions, the intermediate pressure will increase to equal inlet pressure and the downstream regulator will continue controlling outlet pressure.
Conditions upon upstream regulator failure:
Downstream Regulator Failure
If the downstream regulator malfunctions causing outlet pressure to rise, the monitor pilot on the upstream regulator will take over control of the upstream regulator. The intermediate pressure will decrease below the worker pilot’s setting causing the worker pilot to go open.
Conditions upon downstream regulator failure:
In reply to Artur Imiolczyk:
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