What device is used to observe the water level inside a steam boiler?

The device used to observe the water level inside a steam boiler is a sight glass. A sight glass is a transparent tube or a panel that allows operators to visually monitor the level of water within the boiler. This is crucial for ensuring that the water level remains within safe operating parameters, as low water levels can lead to overheating and potential damage to the boiler.

The sight glass is typically mounted on the side of the boiler and is filled with water that matches the internal boiler water level, providing a direct visual indicator. The accurate monitoring of the water level is essential for safe boiler operation, as it helps prevent issues such as water carryover into the steam system, which can affect equipment downstream.

In contrast, a pressure gauge measures the pressure within the boiler but does not indicate water level, a pigtail is a flexible piping arrangement that connects a pressure gauge to the boiler, and a thermometer measures temperature but does not provide information about water level. Thus, the sight glass is the specific device designed for observing the water level inside a steam boiler.