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fire-tube boiler[′fīr ‚tüb ‚bȯil·ər]
a cylindrical steam boiler with fire tubes extending inside the water area of the boiler from one end plate to the other. A fire-tube boiler may have one or two fire tubes, sometimes more.
Fire-tube boilers appeared in the early 19th century as a result of efforts to increase the steam-producing capacity of simple cylindrical boilers while preserving their overall dimensions by developing their internal heating surfaces. Be-cause of their extremely large size and the significant consumption of metal in their construction, fire-tube boilers have not been made in the USSR since 1951; they have been re-placed by more advanced models.