. Railroad construction. Theory and practice . ^ excessivepressure due to curvature. The only exception to this is thecase where the curvature is sharp. Then the front inner drivermay be pressed against the inner rail, as indicated in Fig. 181. This limits the use of this type ofwheel-base on the sharper next type—(b^) four-wheeledtrucks with shifting centers—ismuch more flexible on sharpcurvature; it likewise draws thefront drivers away from the outerrail. The relative position of thewheels is shown in Fig. 182, inwhich c represents the positionof center-pin and c the displacedtruc
. Railroad construction. Theory and practice . ^ excessivepressure due to curvature. The only exception to this is thecase where the curvature is sharp. Then the front inner drivermay be pressed against the inner rail, as indicated in Fig. 181. This limits the use of this type ofwheel-base on the sharper next type—(b^) four-wheeledtrucks with shifting centers—ismuch more flexible on sharpcurvature; it likewise draws thefront drivers away from the outerrail. The relative position of thewheels is shown in Fig. 182, inwhich c represents the positionof center-pin and c the displacedtruck center. The structure andaction of the truck is shown inFig. 183. The ^ center-pin (1) issupported on the truck-bolster (2), w^hich is hung by thelinks (4) from the cross-ties (3). The links are therefore. Fig. 183. -Action of ShiftingCenter. f 315. ROLLING-STOCK. 341 in tension and when the wheels are forced to one side by therails the links are inclined and the front of the engine isdrawn inward by a force equal to the weight on the bolstertimes the tangent of the angle of incHnation of the links. Thisassumes that all links are vertical when the truck is in thecenter. Frequently the opposite links are normally inclined toeach other, which somewhat complicates the above simple relationof the forces, although the general principle remains identical. The two-wheeled pilot-truck with shifting center is illus-trated in Fig. 184. The figure shows the facility with which
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