Boiler Gauge glass Operation and SOP


                   A Gauge glass has two different compartment Top side and Bottom side connected to two different sections of a boiler. The top side of the gauge glass is connected to the steam and bottom side is connected to the water. the pressure on both sides will equalize and level of water can be seen in the gauge glass. 

TO TAKE IN SERVICE: This procedure is applicable wherever maintenance activities of gauge glass has completed, and cleared for service. Assume that all the isolating valves on steam and waterside are closed and drains and vents are open. Follow the below steps to take boiler gauge glass in service.

  • Close gauge glass vent valve (s). 
  • Open steam side isolation valve partly.  
  • Allow steam to flow through drain to heat up gauge glass at least for fifteen minutes. 
  • Close drain and see that steam is getting condensed in the gauge glass to build up level. 
  • When condensate level in gauge glass is found to be more that 50%, open water side valve gradually. 
  • See that the level is stabilized at 50% of gauge glass. 
  • Open both steam and water side valves full. 
  • Match level of gauge glass with that of control room indication.




Follow the steps given below to flush the gauge glass. Flushing of gauge glass should be carried out at least once in a day.

  • Close steam side valve. 
  • See that gauge glass is filled with water. 
  • Close waterside valve and open the drain valve of gauge glass. 
  • Crack open steam side valve. 
  • See that gauge glass gets emptied. 
  • Repeat above said activities at least twice. 
  • Normalize the gauge glass valves and match local level with that of control room indication.

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Thermal Power Tech.

Boiler Gauge glass Operation and SOP Boiler Gauge glass Operation and SOP Reviewed by Thermal Power Tech on March 02, 2023 Rating: 5


  1. Boiler gauge glass operation refers to the procedure and process of monitoring and maintaining the water level inside a boiler using a gauge glass. The gauge glass is a transparent tube or sight glass installed on the boiler that allows operators to visually observe the water level inside the boiler.

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