What device is critical to prevent overheating in a superheater?

The pressure relief valve is essential in preventing overheating in a superheater because it provides a critical safety function by regulating pressure within the system. In the context of a superheater, which heats steam beyond its saturation temperature, maintaining the appropriate pressure is crucial. If the pressure exceeds the design limits due to excessive heat or a failure in the system, the pressure relief valve opens to release steam, thus preventing potential damage from overheating or even catastrophic failure.

A thermostatic trap helps manage condensate but does not directly address pressure issues. A feedwater regulator controls the flow of water into the boiler to maintain the desired water level, which is important but not specifically focused on the superheater's temperature regulation. A flow control valve adjusts the flow of steam or water in the system but is not primarily designed to relieve pressure or prevent overheating. Therefore, the pressure relief valve stands out as the most critical device to protect the superheater from the dangers associated with overheating.