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Working Monitors

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. 

 Normal conditions:

 

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.

Normal conditions:

 

Conditions upon downstream regulator failure:

 

2 Replies

  • Nathan,

    thank you for this informative post. I would like to mention that configuration explained above correspond to monitor and regulator in "fail open" safety mode. Configuration with working monitor could be also set as : monitor "fail close" and main regulator "fail open". During my work i have also meet configuration as: monitor "fail close", main regulator "fail close" but it is not clear for me what useability is for this configuration.

    Artur I.
  • In reply to Artur Imiolczyk:

    Hello Artur!

    Monitors are overpressure protection devices which engage only if the outlet pressure begins to rise. To ensure continuous gas service when a regulator fails in the closed position, an additional station feeding the same network or a parallel run of regulators can be utilized as discussed here:
    emersonexchange365.com/.../ensuring-continuous-gas-service---redundancy