Which safety feature is essential in preventing boiler overpressure?

The safety valve is crucial in preventing boiler overpressure because it is specifically designed to automatically release excess pressure from the boiler to maintain safe operational limits. When the steam pressure in the boiler exceeds a predetermined setting, the safety valve opens, allowing steam to escape until the pressure drops back down to a safe level. This mechanism is vital for protecting the boiler from catastrophic failures that can result from excessive pressure, which can lead to explosions or structural damage.

The other options serve important functions but do not directly prevent overpressure in the same way. For instance, a pressure regulator controls the pressure within certain limits, but it does not act automatically in response to an overpressure situation. A blow-off valve, often used for removing sludge or sediment from a boiler, isn't designed to handle pressure relief. Meanwhile, a low-water cutoff prevents damage from low water levels, but it does not have a role in managing pressure levels within the boiler. Thus, the safety valve stands out as the critical safety device for preventing boiler overpressure situations.