Brake Tests

9 heavy cars are not necessary nor are two service brake cylinders re- quired, except for cars weighing more than the limit of the service capacity of one brake cylinder. Provision is made for using one brake cylinder up to the maximum percentage of emergency braking power which it can provide, and for using two cylinders when a higher emer- gency braking power is desired. When using one brake cylinder, the maximum service pressure is controlled by means of a safety valve. When two cylinders are used the maximum service cylinder pressure is limited by the equalizing of the service reservoir and service cylinder pressures (instead of using a reducing valve for this purpose). In emergency applications the force of the second (emergency) brake cylinder is added to that of the service brake cylinder to give the desired increase in emergency over maximum service braking force. The use of one or two cylinders is optional, depending upon the amount of braking power to be employed. It should not be overlooked that the utilizing of the equalizing pressure in this way permits either one of two courses to be followed. Either smaller cylinders may be used, or the same size brake cylinders and a much lower total leverage ratio, the latter being in the direction of increased over-all efficiency. Brake Rigging. 19. Duplicate tests were made with the clasp brake rigging, two shoes per wheel, for every test made with the standard brake rigging, one shoe per wheel, in order to bring out the possibilities of the clasp brake in the following desirable features. A. Constant piston travel for all cylinder pressures. B. Smoothness of action during stopping. C.— Greater certainty of obtaining and maintaining the prede- termined braking force contemplated in the design of the air brake equipment and foundation brake rigging. D.—Less displacement of journals, bearings and trucks, tending toward greater mechanical efficiency and less cost of maintenance. E.—A coefficient of friction equal to or greater than with single shoe brake with less wear of brake shoe metal and lower wheel and brake shoe temperatures. 20. The original plan contemplated two 12 car trains of om- standard P-70 steel cars, a general outline diagram of which is shown in Fig. 1 and a photograph in Fig. 2. These cars have 4-wheel trucks with one 16-inch brake cylinder per car. One train was equipped with the clasp type of brake rigging (two shoes per wheel) and the other with the type of standard brake rigging (one brake shoe per wheel) existing on these cars since they were built, but modified by increasing the strength of the members to be suitable for 180 per cent, braking power which necessitated lowering the brake shoes 1% ins. below their former position and by anchoring the truck dead lever to the car body instead of to the truck.