Steam power plants, their design and construction . fired fire-tube boilers if this or ahigher pressure is to be carried unless the boilers are designedby an expert. Braces.—Braces are used in horizontal tubular boilers tobalance the pressure exerted on those parts of the heads of theboiler above and below the tubes and not close to the shell. Ifthese parts are not braced, the pressure would cause the flat headto bulge outw^ard. For a distance of 3 inches from the shell, andfor a distance of 2 inches from the tubes, the head is usually con-sidered to be sufficiently stiffened by the circumfere
Steam power plants, their design and construction . fired fire-tube boilers if this or ahigher pressure is to be carried unless the boilers are designedby an expert. Braces.—Braces are used in horizontal tubular boilers tobalance the pressure exerted on those parts of the heads of theboiler above and below the tubes and not close to the shell. Ifthese parts are not braced, the pressure would cause the flat headto bulge outw^ard. For a distance of 3 inches from the shell, andfor a distance of 2 inches from the tubes, the head is usually con-sidered to be sufficiently stiffened by the circumferential joint andthe tubes not to need other bracing. Figure 6 shows one of theheads in a horizontal tubular boiler and the part which has to bebraced is indicated. Braces used in this work are usually of twokinds, the direct or through stay or brace, whicli extends entirely. Figure 8.—Connecting Direct Braces. through the boiler and joins the heads together, and the diagonalor crow-foot brace. This latter is shown in Figure 7. The headis connected to the adjacent shell by it. The diagonal brace ispreferred by the boiler inspection companies, as it is much easierto get inside of a boiler to inspect the interior with this brace thanwith the direct type. If the latter are used the»y should be suffi-ciently separated to allow a man entering the manhole opening topass between them. The braces should be distributed uniformlyover the area they are intended to support. Figure 5 shows themanner in which diagonal braces may be distributed over thehead. Five direct braces are sometimes used, three being placedin a lower row and two above, all being symmetrically placed withreference to the center. When direct braces are used the headsare frequently further stiffened by channel iron or angle ironsriveted to the heads as shown in Figure 8. If manholes are STEAM POW
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