Question 55Steam Plants - Assistant Engineer

The correct answer is D) when you are in doubt about the water level. The reason this is the correct answer is that the boiler water gage glasses should be blown down whenever there is any doubt about the actual water level in the boiler. Blowing down the gage glasses helps verify the true water level and ensure safe boiler operation. The other answer choices are too prescriptive, as the need to blow down the gages may not always align with set intervals or changes in water level. Prudent boiler operation requires checking the gages whenever the water level is in question, which makes option D the best choice.