Brake Tests

43 drawn from the brake pipe), long trains, leaky brake pipe, poor con- dition of triple valve piston packing rings or slide valves low ma reservoir pressure, or light brake pipe reductions, all tend to bring about the slow rise of brake pipe pressure at the rear end of the tra1, which results in failure to release brakes, slow release, stuck brakes an dragging brake shoes. . • 85. Briefly stated, the compressed air entering the brake pipe is being called upon to perform two functions at the same time, viz., (a) Increase the pressure throughout the entire brake pipe through- out the train at a sufficiently rapid rate to insure the releasing of triple valves in whatever condition or position in the train they happen to be. (b) Recharge the auxiliary reservoir. These two conditions are mutually antagonistic and conditions fre- quently arise where the release function is partially or almost completely nullified in the performance of the recharging function, which after a certain stage is reached may be the controlling factor in the release of the brake. EMERGENCY Brake Application. 86. In response to a rate of brake pipe reduction considerably more rapid than that established for service brake application the triple valve parts move to their emergency positions, in which the quic action parts of the triple valve are actuated so as to vent air from the brake pipe to the brake cylinder, thus . (a) Causing a local venting of brake pipe air on each vehicle and so transmitting serial quick action rapidly from car to car throughout the train. . ... : (b) Supplementing the air flowing from the auxiliary reservor to the brake cylinder, thus increasing the brake cylinder pressure, by the amount derived from the brake pipe. . ,, 87. The brake cylinder pressure in emergency is under the control of the high-speed reducing valve at all times. At first the reducing valve blows down the brake cylinder pressure at a very slow rate, but this rate gradually increases, being timed to become relatively rapid as the train nears its stopping point and the valve then closes at 60 pounds brake cylinder pressure.... 88. It is impossible to obtain a quick action application with the PM equipment after a service application of any consequence has been made. Brake Troubles Experienced During Recent Years. 89. The continual increase in weight and length of cars, length of train and speeds, since the introduction of the quick action triple va ve in 1888, has naturally resulted in taxing the PM brake equipment to its full capacity. This is particularly true with regard to the follow- ing considerations: (Par. 90 to 94).