Single-furnace boilers have been much used in the form of a single-tube boiler standing on end, as shown in [Fig. 47], with the flame passing up the tube, which is continued in the form of a chimney on the top of the boiler. The tube passes through the steam at the top, so that the plate is not protected from overheating by contact with water; and this has caused explosion in some instances, although the tube has been lined on the inside with firebrick to shield the plate from the flame. Another great disadvantage of this Chimney boiler is that the space between the tube and the shell is so narrow that it is almost impossible to examine or clean it internally.
Fig. 48.
A further arrangement for a single-furnace boiler is the Elbow boiler, shown in [Fig. 48], where the two difficulties mentioned in the previous boiler are avoided.
Fig. 49.
Many internally fired upright boilers of various shapes have been constructed to suit various purposes. One of a large size that has been at work many years is shown in [Fig. 49], with an internal fireplace and a suspended cone and cross tube for increasing the heating surface. This boiler is set in brickwork in such a way that the heat passes through the side tubes and round the exterior shell before going off to the chimney.
Fig. 50.
