Fire-Tube Boilers Through-Tube Boilers Horizontal Many Small Fire Tubes Internally-Fired

FIRE-TUBE BOILERS THROUGH-TUBE BOILERS: HORIZONTAL, MANY SMALL FIRE TUBES, INTERNALLY-FIRED Vessels of slight draft require a boiler of small diameter. This is especially true of gunboats as it is desirable to have the boilers below the water line. As there is not rooin for the returntube boiler, the through-tube, shown in Fig. 27, is sometimes used. This boiler is made up of the same parts as the return tube, the chief difference being that of arrangement. The rear plate of the combustion chamber forms one tube sheet and the end plate forms the other. The top of the combustion chamber is stayed to the shell by sling stays which are bars having forked ends fastened to the shell and to the combustion chamber.

The fire is in a flue, or flues, which leads to the combustion chamber. The- hot gases pass from the combustion chamber through the tubes to the uptake at the back end. The chief objection to this form is its length, for the heating surface is small unless the boiler is made very long.