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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. The boiler has the advantage of simple robust construction, in particular requiring little regular maintenance. It is relatively inefficient, which was not a serious drawback to the purposes for which it was used. However it was also of limited heating surface, thus limiting its sustained output power, compared to other boiler designs. For that reason it was rarely used when power was required continuously, such as for locomotives. However as the boiler is of relatively large internal volume relative to its power, this acts as a transient reserve of steam. Applications such as cranes only require steam intermittently, allowing the boiler to recover pressure between lifts. == Construction == The boiler consists of a cylindrical vertical external shell, with a large firebox inside this, filling perhaps half of the total height. A single large vertical flue or ''uptake'' leads to an external chimney. Some boilers use vertical rod stays between the firebox crown and top of the boiler shell. The main evaporative surface is provided by a pair of large water-filled cross-tubes across this firebox and directly exposed to the radiant heat of the fire. As these tubes are large in diameter they remain mostly filled with water, rather than filling with steam,〔Large diameter gives a low ratio of heating surface to water volume, thus a low boiling rate.〕 and so the boiler is not classed amongst the usual water-tube boilers. These tubes are horizontal,〔 or slightly inclined〔 so as to encourage circulation in a single direction without turbulence. As usual, there is a manhole in the upper part of the shell for internal access and inspection. The boiler may be distinguished externally from other types of vertical boiler by the additional presence of two smaller handholes, in line with the end of each tube and used for internal cleaning. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Vertical cross-tube boiler」の詳細全文を読む スポンサード リンク
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