Which safety device is essential for detecting water levels in a boiler?

The water level controller is essential for detecting water levels in a boiler because it continuously monitors the water level within the boiler to ensure it remains within safe operating limits. The water level controller typically employs floats or electronic sensors to provide accurate readings and automatically regulate the supply of water into the boiler. This is critical for preventing low water conditions, which can lead to overheating and potential damage to the boiler, as well as ensuring efficient operation.

Other devices listed, such as a pressure relief valve, flow switch, and temperature gauge, serve different functions. A pressure relief valve is designed to prevent excessive pressure buildup by relieving pressure when necessary but does not monitor water levels. A flow switch detects the presence or absence of fluid flow, which is important for different systems but not specifically for monitoring water levels in a boiler. A temperature gauge indicates the temperature of the boiler water or steam but does not provide information about water levels. Therefore, the water level controller stands out as the vital device for ensuring safe and effective boiler operation by monitoring and controlling water levels.