What is the function of a blow-off valve?

The function of a blow-off valve is specifically designed to discharge sediment from the boiler. Over time, boilers accumulate mineral deposits and other impurities from the water used in the steam generating process. These deposits can lead to decreased efficiency and even damage to the boiler if not properly managed.

The blow-off valve facilitates the removal of these sediments by allowing operator-controlled discharges of water and sludge from the bottom of the boiler. This maintenance action helps to ensure that the water quality remains high, thus optimizing the boiler's operation and longevity.

The other options refer to functions that do not align with the primary role of a blow-off valve. For instance, allowing water to enter the boiler pertains to feedwater supply rather than sediment removal. Releasing excess steam is typically managed by safety valves designed to prevent pressure buildup, while temperature control involves different components like regulators and thermostats. Therefore, the answer reflects the blow-off valve's critical role in maintaining boiler health through sediment management.