Compared to fire tube boilers, water tube boilers require?

Water tube boilers usually require less water than fire tube boilers due to their operational design and efficiency. In water tube boilers, water is contained within the tubes, and steam is generated in the space surrounding the tubes. This design allows for a smaller water volume in the boiler system compared to fire tube boilers, where water fills the larger shell.

With less water volume, water tube boilers can respond more quickly to changes in steam demand and typically operate at higher steam pressures. This can increase efficiency and make them more suitable for certain industrial applications. Furthermore, because of their design, they can effectively handle high temperatures without the risk of overheating, which often necessitates maintaining a larger water volume in fire tube boilers to keep the heat within safe limits.

The other choices involve aspects that do not necessarily relate to the direct comparison of water usage between these two types of boilers. While water tube boilers might require more maintenance due to their complexity, this isn't universally applicable and depends on operational conditions and how well maintenance is performed. Additionally, while water tube boilers can operate at higher pressure ratings, this does not imply they use more water.