A vertical boiler in use where there are large quantities of waste gases from iron-furnaces consists essentially of a very long shell inclosed in a mason-work stack (pl. 76, .fik. 12). The intensely hot gases of combustion pass between the stack and the cylinder, to which they impart their heat. To prevent the injurious action of the flames upon the upper portion of the boiler, in which there is no water, that portion is made smaller than the lower and is inclosed with a fire-brick ring.
There are vertical cylindrical boilers in which a number of small water tubes leave the main shell just above the crown-sheet and enter above the wetter-level; the entire boiler being set in brick-work or in an iron jacket, the gases of combustion pass among and around these tubes, through which there is a constant upward circulation.
Portable l'e•rtical simplest form of portable boiler ( 3) has a single smoke-flue, extending from the crown-sheet or the top of the fire-box through the upper head of the cylindrical shell. The Shapley vertical type (fig. to) has a conical internal fire-box in two tions, the lower containing the greater part of the fire-box, the upper and smaller being principally a steam-reservoir. Short horizontal smoke-flues extend from near the top of the fire-box to an annular space between the two main cylindrical sections, and from this annular space vertical flues of small diameter lead to an annular smoke-passage around the base. The proper water-level is above the top of the fire-box, about one-quar ter of the way in the upper drum.
Figure 4 (bl. 76) has a nearly spherical boiler suspended in a cylin drical fire-box with double walls. The gases, which are deflected by the bottom of this suspended water-vessel, pass up from the fire-box through a ring of flues communicating with a smoke-drum, above.
Where vertical portable boilers have several vertical smoke-tubes, they discharge at their upper ends into a common smoke-chamber connected with the stack. In some this smoke-chamber is entirely above the boiler proper; in others it is submerged in the steam, this being the most com mon type in American steam fire-engines. In the Niles type (fig. II) this submerged smoke-drum is conical.
The Silsby Steam Boiler (fig. 2) has an inner and an outer shell with water-leg between; there are vertical smoke-flues from the upper head to the crown-sheet, from which latter there depend concentric circles of drop-tubes, each having a circulation-tube within. In a new form of steam fire-engine boiler (fig. 1) the straight drop-tubes of the Silsby are replaced by sectional coil-tubes extending from the water-leg to the crown-sheet.
Coil Boilers (usually vertical) carry most, if not all, their water in long coils of pipe of small diameter. They are characterized by rapid steaming power and by great safety; but it is necessary to have their feed much more steady and reliable than where there is a considerable mass of water. Their use is principally confined to steam fire-engine and marine service.
and Flue tubular boilers are distinguished as either "water-tube'' or "flue," the tubes of the former serving for the passage of water and the tubes of the latter for the passage of the gases of combustion. In water-tube (sometimes called " tubulous") boilers the pressure upon the tubes is from the inside; in smoke-flue or tubular boil ers the pressure is from the outside. Iu cross-tube boilers there are two parts of the shell, the lower part forming the fire-box and containing water-tubes, and the upper part surrounding the tubes and composing the water-space and the steam-space. The two parts are joined by rings and can be taken apart to clean the boiler or to repair the tubes.
The Circulating invented by Jacob Perkins, has found its way into many types of boilers. It consists essentially of a vertical tube with closed bottom, which extends into the combustion-chamber or passages for the gases of combustion, and has within it a smaller concentric tube extending nearly all the way down. The course of the water is down the central tube and up through the annular space between the two tubes. The same effect is produced by substituting for the central tube three strips of sheet iron of such width that their cross-section forms a triangle inscribed in the tube-circle. One form of vertical boiler with Field tubes is shown in Figure 6. The arrangement suspended in the centre of the combustiou-space is a smoke-deflector, which deflects the gases among the suspended circulating tubes and keeps them front going straight up the chimney without expending- their heat upon the tubes. In the original Field tubes there was a funnel-shaped enlargement of both the inner and the outer tubes, intended to facilitate circulation; but this has been found to be unnecessary. Figure 5 (/5/. 76) shows a Field tube in Sectional the double purpose of increasing the heat ing surface as compared with the amount of water contained, and of dimin the size of parts so as to lessen both their liability to explode and the damage resulting from their rupture, there have been devised what are called "sectional" generators, having heating surfaces wholly or in great part composed of tubes or spheres containing the water to be heated.