What component in a locomotive boiler is used to increase the volume of the steam space?

The steam dome is an essential component in a locomotive boiler, designed specifically to increase the volume of the steam space above the water level within the boiler. This added space allows for the collection of steam that is less saturated and more suitable for use in driving the locomotive's cylinders. By having a larger steam space, the steam dome helps to ensure consistent steam pressure and quality, minimizing the chances of water being carried over into the steam piping, which can lead to poor engine performance and potential damage.

In contrast, while the boiler drum is a critical part of the boiler that contains water and steam, its primary function is not solely to increase steam space but to act as a reservoir. The steam gauge is a measure of steam pressure but does not contribute to steam volume. The superheater, on the other hand, is responsible for increasing the temperature of the steam but does not directly affect the volume of the steam space itself. Thus, the steam dome is uniquely positioned to enhance the steam capacity of the locomotive boiler effectively.