What type of boiler consists of one or more water drums?

The correct answer indicates a system characterized specifically by the presence of drums designed to hold water. A drum type boiler, as the name suggests, features one or more water drums that serve key functions, such as providing space for water to circulate and allowing for the separation of steam from water in the system. This configuration is critical for the efficient operation of the boiler, as it aids in the safe and effective production of steam.

Water-tube boilers also utilize water drums, but they are defined by a different construction where water circulates through tubes and is heated externally. The focus on the arrangement of water within the drums sets the drum type boiler apart, making it the accurate choice when asked about the specific characteristics associated with these water-holding units.

Fire-tube and shell-type boilers operate fundamentally on different principles. Fire-tube boilers have hot gases flowing through tubes that are surrounded by water, whereas shell-type refers to the external structure rather than the internal configuration of water drums. Therefore, these types do not meet the specific criteria of the question regarding multiple water drums.