Brake Tests

67 DEVICE FOR OBTAINING HIGHER BRAKE CYLINDER PRESSURE ON LOCOMOTIVE AND TENDER. 144. The standard Westinghouse No. 6 ET brake equipment as installed and in regular service on the locomotives previous to the tests was used at first without any change. As is well known the standard braking power on the locomotive and tender (considering the ordinary working loads carried) is relatively a little less or about the same in stopping effectiveness as that of the PM equipment on the P-70 cars. This is shown by the fact that in break-away tests under these con- ditions the locomotive ran but little if any farther than the cars. 145. When using the new and more effective car brake equip- ments at braking powers higher than those obtained with the PM equipment, the difference between the stopping force on the locomotive and cars was marked. The effect of this was to produce a noticeable running out of slack in ordinary train stops and in break-away stops to cause the locomotive to run several hundred feet farther than the cars. This was especially true when the electro-pneumatic equipment was used. 146. This fact made it desirable to find out what could be done to make the locomotive and tender brake more nearly equal in effective- ness to that of the improved car brake equipments. Accordingly appa- ratus was devised while the tests were in progress and applied in an ex- perimental form to the standard locomotive brake equipment. No modification was required in the existing apparatus except in the re- arrangement of piping necessary to install an additional valve device. 147. This device was a “by-pass valve,” so arranged that the service operations of the ET equipment were not affected in any way, but when an emergency application of the brakes was made the by-pass valve operated so as to short circuit compressed air directly from the main reservoirs to all the brake cylinders on the locomotive and tender. This resulted in a much quicker rate of rise of emergency brake cylinder pressure and a much higher maximum pressure being obtained than is the case with the standard ET brake. A possible effect of this high emergency braking power, if held until the speed becomes low, is to cause the drivers to slide. To protect against this the pass valve was arranged to hold the high initial brake cylinder pressure for a specified period (about ten seconds) and then, by a gradual accelerating blow- down, reduce this pressure so that as the speed of the train diminished the brake cylinder pressure would finally reach the normal emergency pressure standard with this equipment, namely, about 75 pounds. 148. The results obtained with this device will be explained in paragraph 350, but so far as its operation is concerned it may be stated here that the tests showed that such a device could easily be provided and made to give any desired rate of application, maximum initial pressure or rate of blow-down.