. Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools . ss, for passenger-trains. The above valuesshould Hkewise be modified when the trains are run only 313days per year instead of 365. 439. Operating value of the filling of a sagin a grade- Assumethat the sag is 4000 feet long and that its depth in the centeris 35 feet, as sketched in Fig. 216. Assume that a freight trainis approaching the sag from the right-hand side (running to theleft), the speed of passing D being 25 miles per hour. The to the left will furnish a grav
. Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools . ss, for passenger-trains. The above valuesshould Hkewise be modified when the trains are run only 313days per year instead of 365. 439. Operating value of the filling of a sagin a grade- Assumethat the sag is 4000 feet long and that its depth in the centeris 35 feet, as sketched in Fig. 216. Assume that a freight trainis approaching the sag from the right-hand side (running to theleft), the speed of passing D being 25 miles per hour. The to the left will furnish a gravity pull of 6 pounds per ton,which may be more than half the force required to pull the train,and the locomotive would have but little to do, even if therewere no sag, to maintain the speed of 25 miles per hour. Assum-ing that the locomotive is doing just this amount of work inrunning to the left through the sag, it will gain in velocity head at D is that corresponding to 25 miles perhour, or feet. Adding 35 feet, the depth of the sag,we have 56,95 feet, which is the velocity head at C, which. means that the velocity of the train would be miles perhour. For passenger trains this will not be an objectionablyhigh velocity, and even freight trains, which are provided withair-brakes and standard M. C. B. couplers, which are now 522 RAILROAD CONSTRUCTION. § 439. nearly universal, may be safely run at this velocity. Thereforefor all trains which may run at a speed of over 40 miles perhour, this sag will belong to class A, or the harmless class, sofar as trains moving to the left are concerned. The effect ontrains moving to the right will depend partly on the rate ofruling grade on that section of the road. The conditions ofclass A pre-suppose that the draw-bar pull is constant, but horse-power is measured by the product of pull times velocity. As-sume that AB is 3i ruling grade— has recently been adoptedas ruling grade for revision work on the Erie R. R
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