What will happen if the top valve is clogged on the water column?

If the top valve of the water column is clogged, the water may be unable to escape from the sight glass. In this scenario, the sight glass can fill with water to a level that does not accurately reflect the actual water level in the boiler. This leads to the possibility of indicating a false high water level. The water inside the sight glass may appear to be at a safe level, while in reality, the boiler could be operating with an actual lower water level, which is problematic and can create unsafe operating conditions.

Understanding the function of the water column is crucial; it provides a visual indication of the water level within the boiler. If there is a blockage at the top, the water cannot leave the glass, misleading operators regarding the true state of the boiler's water level. This can result in dangerous situations, such as the boiler running low on water without the operators realizing it, which can lead to overheating and possible failure.

Thus, the correct scenario in the event of a clogged top valve is that the glass will fill with water, causing the appearance of a false high level, which significantly misrepresents the actual water level in the boiler.