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. Railroad construction. Theory and practice . ox surface byhaving the outside boiler-plates parallel to the fire-box platesand separated from them by a space of about 3. The platesare then mutually held by stay-bolts. See Fig. 189. Theseare about \ in diameter and spaced 4 to \y, The f^ hole, 344 RAILROAD CONSTRUCTION. §318. drilled li deep, indicated in the figure, will allow the escapeof steam if the bolt breaks just behind the plate, and thus callsattention to the break. The stay-bolts are turned down to adiameter equal to that at the root of the screw-threads. Thismethod of supporting the
. Railroad construction. Theory and practice . ox surface byhaving the outside boiler-plates parallel to the fire-box platesand separated from them by a space of about 3. The platesare then mutually held by stay-bolts. See Fig. 189. Theseare about \ in diameter and spaced 4 to \y, The f^ hole, 344 RAILROAD CONSTRUCTION. §318. drilled li deep, indicated in the figure, will allow the escapeof steam if the bolt breaks just behind the plate, and thus callsattention to the break. The stay-bolts are turned down to adiameter equal to that at the root of the screw-threads. Thismethod of supporting the fire-box sheets is used for the twosides, the entire rear, and for the front of the fire-box up to theboiler-barrel. The furnace tube-sheet—the upper part ofthe front of the fire-box—is stayed by the tubes. But the topof the fire-box is troublesome. It must always be coveredwith w^ater so that it will not be ^burned by the intense must therefore be nearly, if not quite, flat. There are threegeneral methods of accomplishing Fig. 189. Fig. 190. (a) Radial stays. This construction is indicated in Fig. there is also shown the diagonal braces for resist-ing the pressure on the back end of the boiler above the fire-box. It may be seen that the stays are not perpendicular toeither the crown-sheet or the boiler-plate. This is objection-able and is obviated by the other methods. (b) Crown-bars. These bars are in pairs, rest on the sidefurnace-plates, and are further supported by stays. See (c) Belpaire fire-box. The boiler above the fire-box is rect-angular, with rounded corners. The stays therefore arc per-pendicular to the plates. See Fig. 192. Fire-brick arches. These are used, as shown in Fig. 193, toforce all the gases to circulate through the upper part of the fire- §318. ROLLING-STOCK. 345 box. Perfect combustion requires that all the carbon shall beturned into carbon dioxide, and this is facilitated by theforced circulation.
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