Vertical fire-tube boiler

A vertical fire-tube boiler or vertical multitubular boiler is a vertical boiler where the heating surface is composed of multiple small fire-tubes, arranged vertically.

These boilers were not common, owing to drawbacks with excessive wear in service. The more common form of vertical boiler, which was very similar in external appearance, instead used a single flue and water-filled cross-tubes. Another form used horizontal fire-tubes, even where this added complexity, such as the Cochran boiler.

Where a sustained high evaporative capacity (i.e. power) was required, vertical tubes were used, but rarely. These cases were mostly for locomotives, either railway locomotives or road steam wagons.

In any boiler, one of the most prone locations for tube and plate wastage is around the water level, where agitation and boiling is most active. This is particularly so when this level is also part of the heated surface, where boiling is most intense (water-tube boiler designs also strive to submerge their directly heated surface beneath the water level, for the same reason).

In this design of boiler, the erosion area affected is part-way up the fire-tubes. Although such tubes are usually designed to be easily replaced, their working life is relatively short.

Horizontal fire-tubes are otherwise more efficient than vertical. For that reason, and to avoid the problems of tube erosion with exposed vertical tubes, many of the multi-tubular vertical boilers were instead arranged with their tubes horizontal. These could be either a parallel bank, such as the Cochran boiler, or else radial as for the Robertson.

To avoid the problem of exposed fire-tubes above the water level, the submerged multi-tube boiler may be used. The upper boiler shell is extended upwards in an annular ring, so as to always maintain the whole length of the tubes submerged. Used in steam wagons and similar, where the water-level may be disturbed as the vehicle climbs a hill.

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Wikipedia