Brake Tests

5 rest. Not only has the best previous performance for steel cars been excelled in these tests, but with a train of twelve cars having four wheel trucks and averaging about 122,000 pounds each and a locomotive and tender weighing 200 tons, better stops were made than are on record for much lighter cars. Factors to be Considered in Obtaining EFFICIENT Brake Operation. 9. In considering the improvements desirable in those particulars mentioned in Paragraph 3, four factors were given special attention:— (A) The available adhesion between the car wheels and the rails. This is fixed so largely by circumstances beyond any con- trol that the only course open is to determine in the first place what can be accepted as the maximum rate of re- tardation consistent with reasonable protection against slid flat wheels, and base further considerations upon this fundamental limit. Manifestly this limit can not be so low as to absolutely insure against the possibility of oc- casional slid flat wheels under combinations of unfavorable conditions which may be expected now and then, but it should be established upon the basis of practical service conditions and requirements as any braking power which is chosen can only be proven as satisfactory by a thorough trial in train service. (B) The efficiency of the brake shoe in transforming the pressure imposed upon it into retarding force at the rim of the wheel. (C) The efficiency of the mechanical transmission of the force of compressed air, developed in the air brake cylinders, through the rods and levers of the brake rigging to the brake shoes. (D) The characteristics of the mechanism available for controlling the pressure of the compressed air in the brake cylinders. This, in turn, bears a direct relation to the length of the emergency stop, which is, to a considerable extent, dependent upon the interval of time required between the start of the application and when the maximum brake cylinder pressure is reached. It also determines the reliability and flexibility of the brake in service applications and the certainty of release. 10. In outlining the program of tests, representatives of the Pennsylvania Railroad Company and the Westinghouse Air Brake Company in conference, agreed that the tests should cover improved types of brake rigging and air brake apparatus as compared with those now used on our P-70 cars and, therefore, the investigations were directed particularly towards obtaining as much information as possible with regard to the four factors just mentioned.