What is the approximate level of water in the gauge glass at the normal operating water level (NOWL)?

At the normal operating water level (NOWL), the gauge glass should display a level that is half full. This indicates that there is enough water installed in the boiler to allow for effective heat transfer and steam production while also providing a safety buffer. By maintaining this level, it helps ensure that the boiler does not run dry, which could lead to overheating or damage to the boiler.

The reason the gauge glass is typically half full at the NOWL is also tied to boiler design, where a sufficient amount of water is needed to both carry away heat effectively and give a visible indicator to operators that the system is functioning properly. A full gauge glass could suggest excessive water or potential flooding, while an empty or quarter full gauge would indicate low water levels, which could potentially jeopardize the safe operation of the boiler.

Understanding the function of the gauge glass in relation to NOWL is critical for safe boiler operation and maintenance practices.