What feature distinguishes a blow-off valve?

A blow-off valve is primarily designed to discharge water and sludge from the bottom of a boiler. This function is crucial for maintaining the efficiency and safety of the boiler system. By removing sediment and impurities that accumulate at the bottom, the blow-off valve helps prevent corrosion and scaling, which can lead to reduced efficiency or even damage to the boiler over time.

In contrast, the other options refer to different functions of boiler components. Regulating steam pressure pertains more to safety valves or pressure control devices that maintain the desired pressure level within the boiler system. Controlling the fuel supply is related to valves that manage fuel flow to the burners for combustion. Ensuring proper ventilation typically involves systems designed to allow air supply and exhaust, which is separate from the specific function of the blow-off valve. This focus on discharging water and sludge distinguishes the blow-off valve and highlights its role in boiler maintenance and operation.