. The Locomotive. Fig. 7. — Three-course Boiler in Setting. [ Girth joints well away from bridge wall.] few builders have ever suggested it. So far as the cost of the boiler is concerned, there does not appear to beany reason for preferring either type; for the slightly increased cost of theplates, in a two-course boiler, is offset by the somewhat greater amount of laborinvolved in the construction of the three-course one. The real question appears to be, whether it is better to cut the stiffeningeffect of the girth joints down by one-half, and thereby save exposing onegirth joint to the furna
. The Locomotive. Fig. 7. — Three-course Boiler in Setting. [ Girth joints well away from bridge wall.] few builders have ever suggested it. So far as the cost of the boiler is concerned, there does not appear to beany reason for preferring either type; for the slightly increased cost of theplates, in a two-course boiler, is offset by the somewhat greater amount of laborinvolved in the construction of the three-course one. The real question appears to be, whether it is better to cut the stiffeningeffect of the girth joints down by one-half, and thereby save exposing onegirth joint to the furnace gases, or whether it is better to keep up the stiffness,at the cost of having two girth joints exposed, instead of one. Our experi-ence indicates that serious trouble is far more likely to come from lack of stiff-ness, than from the exposure of a girth joint to the gases of the , it is not altogether the number of the girth joints that must be. Fig. 8. — Two-course Boiler in Setting. [Girth joint directly over bridge wall] 230 THE LOCOMOTIVE. [October, considered, in deciding upon a design, for their position with respect to thedistribution of the heat in the furnace is also an important factor. At thebridge wall, for example, the highly heated gases from the furnace are concen-trated against the boiler shell, and it is desirable, in our judgment, to keep thegirth joints well away from this region of concentration. It is only fair to saythat with our plan of setting, and the care that we recommend in the construc-tion of bridge walls, we have had little or no trouble from this source witheither two-course or three-course shells. A comparison of Figs. 7 and 8, however,will make it evident that in the case of the designs here shown, at all events,the three-course boiler gives the least exposure to whatever danger there maybe in the concentration of heat at the bridge wall. Of course we are wellaware that the two-course boile
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