What safety device prevents excessive pressure build-up in the boiler?

The pressure relief valve is an essential safety device in a boiler system, designed specifically to prevent excessive pressure build-up. This valve automatically opens at a predetermined pressure limit, allowing steam or water to escape, thus mitigating the risk of a potential explosion or damage to the boiler from over-pressurization. It acts as a fail-safe mechanism, ensuring that the pressure within the boiler remains within safe operational limits.

The other options serve different functions that do not directly relate to pressure control. The water level gauge monitors the water level in the boiler but does not alleviate pressure. The temperature control switch regulates the temperature within the boiler but also does not prevent pressure build-up. Similarly, a flow meter measures the flow rate of water or steam but does not affect pressure management. Each of these devices plays a critical role in boiler operation, but the pressure relief valve is the primary safety device for controlling pressure.