. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . ich the engine may be called upon tostart the train from rest. We must alsoknow the tractive power of the engine andits total weight in working order; alsoweight of tank loaded. The formula for tractive power isd=PL usuallv stated as T^ Dwliere T:=tractive power in pounds atdrivers. d^ diameter of cylinder in inches. P = mcan effective pressure in cyl-inders. L= length of stroke in inches. D=diameter of driving wheels in inch^soutside tires. The value of P may be taken as 85 per Tonnage ratin
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . ich the engine may be called upon tostart the train from rest. We must alsoknow the tractive power of the engine andits total weight in working order; alsoweight of tank loaded. The formula for tractive power isd=PL usuallv stated as T^ Dwliere T:=tractive power in pounds atdrivers. d^ diameter of cylinder in inches. P = mcan effective pressure in cyl-inders. L= length of stroke in inches. D=diameter of driving wheels in inch^soutside tires. The value of P may be taken as 85 per Tonnage rating :S T-E d = PL — E. R In this equation it is evident that ton-nage rating is a function of botli T andR, since they are both variable varies as the grade and curvature, while dPL T depends for its value on . or Dtractive effort. Now d, L and D arc con-stant for any given engine, while P is avariable depending upon the steamingcapacity of the boiler and the distriliutionof the steam to the cylinders. It is evident that if an engine is ratedcorrectly and it stalls on the ruling grade. C-VLKIH )X1 \.\ \;S. cent, of the boiler pressure at slow speedsand long cut-off. The available drawbar pull at back oftank is equal to the tractive effort T, lessE, the total resistance of the engine andtank which consist of the machine fric-tion and rolling resistance of the engine,the rolling resistance of the tank and thegrade and curve resistance of the engineand tank. Resistances are all figured inpounds per ton moved and the values areknown very accurately from tests with thedynamometer car under all sorts of con-ditions. The total train resistance R is made upof the grade, curve and rolling resistancesand may be regarded as a form whichmust be balanced, or rather over-balanced,in order to keep the train in motion. The rating of the engine will be equal,then, to the drawbar pull S in pounds,divided by R, the total train resistance ex-pressed in pounds per
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