Brake Tests

7 of this opportunity to establish as definitely as possible the character- istics of this type of brake shoe under the influence of various combi- nations of speed, pressure, time, weather, and the condition of the brake shoe. E.—The coefficient of friction between the wheel and the rail under varying weather conditions. 12. In addition to the investigations outlined in general above, it developed during the tests that certain additional information re- garding the performance of brake shoes under various conditions was desired. In consequence a series of experiments was carried out at the laboratory of the American Brake Shoe and Foundry Co., at Mahwah, N. J. 13. In order to obtain the best data possible, instruments were devised for taking records of the friction of the rail, wheel sliding, retar- dation of the train and slack action between cars as well as for a number of minor observations which are explained in Chapter II. 14. From the outset of the tests an endeavor was made to obtain data and develop methods by which the performance of any given air brake apparatus and its related equipment could be predetermined on the basis of the action of the individual elements which go to make up the whole, and in this respect fundamental data has been obtained which will serve this purpose. It is quite apparent, there- fore, that an analysis of the time of action and the efficiency of the various operations of any brake appliance can be made which will closely predetermine what its performance as to stopping will actually be when placed in service. 15. It will be shown that the desirable stepping distance of 1,200 feet may be obtained by improvement in any or all of the controlling factors, namely, the type of air brake mechanism, the foundation brake rigging, the nominal percentage of braking power and the type of brake shoe. 16. In proportion as the efficiency and effectiveness of any one or more of these can be increased, that of the others can be corre- spondingly reduced so that a lower maximum can be employed for such factors when circumstances render this desirable. For example, the reduction in time of action, secured by the use of the electric control of the brakes, increases their effectiveness and makes a shorter stop possible, thus permitting the use of braking power 30 per cent, less than is required with a less effective brake for the same stop. Features of Equipment and Apparatus Tested. 17. The standard (type PM) air brake equipment has been in use for many years. Its possibilities are well understood and its