VERTICAL WATER-TUBE BOILERS - CAHALL: ANNULAR STEAM AND WATER DRUM, WATER TUBES VERTICAL, STRAIGHT-TUBE, SINGLE-TUBE, NON-SECTIONAL The Cahall vertical water-tube boiler consists of an annular steam and water drum, a cylindrical mud drum, and 4-inch vertical tubes. The generating tubes connect these two drums and are placed within the brick setting. An external circulating pipe also connects the two drums. As this pipe is filled with comparatively cool water and the generating tubes with a mixture of hot water and steam, the circulation is positive and rapid. The feed water enters the steam and water drum, flows down the external pipe to the mud drum and then rises in the generating tubes to the steam and water drum.
The fire is in a brick furnace at one side of the boiler as shown in Fig. 63. The hot gases rise among the tubes. The annular form of the steam drum makes the central space conical; in this space several deflecting plates, or baffles, cause the hot gases to flow out among the tubes. After heating the water in the tubes the hot gases pass through the opening in the steam and water drum coming in contact with the metal containing the steam This thoroughly dries the steam and in many cases slightly super heats it.
The steam drum and also the mud drum are equipped with swinging manheads. The steam drum also has several handholes for use in removing and replacing tubes.