A vertical fire-tube boiler or vertical multitubular boiler is a vertical boiler

Vertical boiler

A vertical boiler is a type of fire-tube or water-tube boiler where the boiler barrel is oriented vertically instead of the more common horizontal orientation...

 where the heating surface is composed of multiple small fire-tube

Fire-tube boiler

A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...

s, 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

Vertical cross-tube boiler

A cross-tube boiler was the most common form of small vertical boiler. They were widely used, in the age of steam, as a small donkey boiler, for the independent power of winches, steam cranes etc....

. 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 locomotive

Steam locomotive

A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

s or road steam wagon

Steam wagon

A steam wagon is a steam-powered road vehicle for carrying freight. It was the earliest form of lorry and came in two basic forms: overtype and undertype – the distinction being the position of the engine relative to the boiler...

s.

Drawbacks

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,Tube replacement is a common in-service task for locomotive-pattern boilers. their working life is relatively short.

Horizontal tubes

Horizontal fire-tubes are otherwise more efficient than vertical.Harris, Model Boilers, p. 50 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.

Submerged tubes

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 wagon

Steam wagon

A steam wagon is a steam-powered road vehicle for carrying freight. It was the earliest form of lorry and came in two basic forms: overtype and undertype – the distinction being the position of the engine relative to the boiler...

s and similar, where the water-level may be disturbed as the vehicle climbs a hill.

Stanley steam car

Some steam car

Steam car

A steam car is a light car powered by a steam engine.Steam locomotives, steam engines capable of propelling themselves along either road or rails, developed around one hundred years earlier than internal combustion engine cars although their weight restricted them to agricultural and heavy haulage...

s, including the Stanley

Stanley Steamer

The Stanley Motor Carriage Company was a manufacturer of steam-engine vehicles; it operated from 1902 to 1924. The cars made by the company were colloquially called Stanley Steamers, although several different models were produced.-Early history:...

 and the Chelmsford used multi-tube vertical boilers; the Stanley design being particularly well-known.

The Stanley boiler is constructed of a seamless copper tube shell, 13½ inches in diameter and 1/16" thick. The numerous ½" tubes are densely packed, leaving a very small water volume between them and a high ratio of heating surface to volume, for rapid steam raising. Construction of the boiler is unusual, as the steel tube plates are merely held in place by friction and the tubes are only lightly expanded into them with a tapered drift. Around the outside of the boiler shell are three heat-shrunk steel rings, the compressive stress of which retains the tubeplate. For additional strength, the boiler shell is further wrapped in a helical layer of piano wire

Piano wire

Piano wire, or "music wire", is a specialized type of wire made for use in piano strings, as well as many other purposes. It is made from tempered high-carbon steel, also known as spring steel.-Manufacture and use:...

. As the boiler is fired by a flat liquid-fuel burner, no enclosed firebox is required.