What type of devices must steam and hot water boilers have to prevent their operational limits from being exceeded?

Steam and hot water boilers are equipped with automatic limiting devices to ensure safe operation and prevent the risk of exceeding operational limits, such as pressure and temperature. These devices are crucial for maintaining the safe and efficient functioning of the boiler system. They monitor various parameters and will automatically shut down or adjust the boiler operation when certain preset limits are reached. This feature helps to prevent hazardous situations, such as exploding pressure vessels or overheating, which could result in catastrophic failures or fires.

In contrast, while manual shutoff valves, pressure gauges, and flow meters provide essential functions related to the operation and monitoring of the boiler system, they do not possess the automatic response mechanisms that limiting devices do. Manual shutoff valves are primarily used for isolating sections of the system, pressure gauges provide readings for operators but require manual observation, and flow meters measure the flow rate but do not actively prevent the operation from exceeding limits. Therefore, automatic limiting devices play a critical role in operational safety, making them indispensable for steam and hot water boilers.