P C PASSENGER-BRAKE EQUIPMENT 273 



distance in which a stop could be made. Another objection 

 to the use of a 20-in. cylinder is that on account of leakage 

 the stop will be lengthened still more, it being impossible to 

 obtain packing leathers large enough and of sufficient uni- 

 formity to prevent excessive leakage. Then, too, the piston 

 rods, drivers, etc. will be so large and heavy that they will 

 take up too great a percentage of the power developed. The 

 increased weight of the cars naturally brought increased length 

 of trains, and the larger cylinders and greater train length 

 mean that a much greater volume of air must be handled 

 through the brake pipe. This would make the action of the 

 brake on a train of cars with 20-in. cylinders so slow that it 

 would be impossible to control the heavy cars with nearly the 

 same effectiveness as is obtained with the brake used on lighter 

 cars. 



Train Energy to Be Controlled. The accompanying table 

 has been compiled in order to give a clear idea of the tremendous 

 amount of energy that the brake of a modern heavy passenger 



ENERGY OF TRAIN AT DIFFERENT SPEEDS 



train has to destroy in stopping the train. The velocity head 

 multiplied by the weight of the train, in pounds, will give the 

 energy, in foot-pounds, for that speed. The third column of 

 the table gives the energy of each 1,000 Ib. of train at the differ- 

 ent speeds given in the first column. The rate of change of the 

 energy of 1,000 Ib. of train with the increase in speed is indicated 

 19 



