When is it permissible to tighten the packing nuts on a boiler gauge glass?

The correct scenario for tightening the packing nuts on a boiler gauge glass is when the pressure has been removed from the system. This is because when the boiler is under pressure, any adjustments to the gauge glass, including tightening the packing nuts, can pose a significant safety hazard. If the packing nuts are tightened while the system is still pressurized, it risks causing a failure or leakage, potentially leading to dangerous situations such as burns or explosions.

Removing the pressure ensures that the system is not in a hazardous state, allowing for safe maintenance and adjustments to be made. This practice of working on the gauge glass only under safe conditions is crucial for ensuring both the integrity of the boiler and the safety of operations personnel.