Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
42 Test Rack Data Representing a Train in Pneumatic Mode with Rear DP Many trains are run with a DP locomotive at the rear of the train in lieu of an EOT device. If an emer- gency brake application is initiated by an air hose separation that occurs in the rear half of the train, on detec- tion of loss of BPP the rear DP locomotive transmits a signal to the lead locomotive. The lead locomotive then automatically sets an emergency brake application from the front of the train. Conversely, if the lead locomotive detects the loss of BPP, it transmits a signal to a DP locomotive to set an emergency brake appli- cation in both directions from that DP locomotive. If the BP hose-initiated emergency occurs in the front half of the train, the lead locomotive sends an emergency brake message to the rear DP unit when it senses the loss of BPP, and the emergency brake appli- cation is set from both ends. Thus, the brakes on the cars behind the POD also will be set by the rear DP lo- comotive. As in the case of the EOT system, DP is more effective when the POD is in the front half of the train, and this effect is stronger the closer the derailment is to the front of the train. When the emergency braking is initiated in the rear half of the train (on the basis of BP length), trailing DP configurations offer no brake signal propagation advantage over pneumatic brakes without DP configurations. TEST RACK DATA RECEIVED FROM NYAB IN DECEMBER 2016 Figure F-10, which was provided by NYAB, displays test rack data simulating an ECP-only brake sys- tem. The data were generated by manually synchronizing the simultaneous separation of the car-to-car elec- trical coupling and the air hose. The software in the CCDs was modified to remove some delay between air hose separation and emergency brake application that was observed in the test rack data submitted in October 2016. According to NYAB, the software modification caused an overall reduction of 1.5 seconds in the delay exhibited in the data submitted previously. The overall reduction resulted from a 0.75-second reduction in the CCD response time and a 0.75-second reduction in the brake cylinder fill time. FIGURE F-8 Pneumatic system experiences air hose separation 115 cars from the rear of a 150-car test rack. Brakes fully actuated after 18 seconds. Car numbers refer to the car position trailing the POD. Car 1 is the first trailing car. BP = brake pipe; BC = brake cylinder.
43 FIGURE F-9 Pneumatic system with rear DP or two-way EOT after air hose separation at first car behind the lead lo- comotives of a 150-car test rack. Brakes fully actuated after 16 seconds. Car numbers refer to the car position trailing from the POD. Car 1 is the first trailing car. BP = brake pipe; BC = brake cylinder. TEST RACK DATA RECEIVED FROM WABTEC IN DECEMBER 2016 Wabtec provided graphs that were created by using data obtained from the companyâs AAR-certified 150-car test rack in Germantown, Maryland, in December 2016. The test setup consisted of a 75-Wabtec overlay brake system, with 50 feet of BP per car. Wabtec indicated that the test results are specific to this train configuration but should be comparable with similar pneumatic or ECP train configurations. The test rack data for a train in pneumatic brake mode or ECP-OL mode were generated by separation of the air hoses between the parts at the point of interest. Figures F-11 through F-16 compare the performance of pneumatic brakes and ECP-OL brakes during various POD scenarios. In its submittal Wabtec indicated the following: As can be seen in the graphs, the closer the POD is to the front of the train, the more significant effect ECP has on braking performance. Although the brake application rates over time are captured and graphed, this comparison is very specific to a train break-in-two and does not include any correspond- ing data representing in-train forces, stopping distance or magnitude of potential derailment severity. In addition, the requested braking data represents only a fraction of the benefits of ECP braking. There- fore, the reader should be cautioned that drawing wide conclusions from a very narrow set of data could lead to missing extremely important performance factors not being considered. Wabtec also provided these summary points: 1. The Wabtec plots show that the first cars behind the POD begin to apply their brakes because of the dropping of the BPP and that ECP braking across the entire train initiates about 1 second later. Some cars start out applying their ECP brakes and then switch over as the BPP drop propagates to their loca- tion.
44 FIGURE F-10 ECP-only brake system. Air hose and ECP cable separation, 75 cars from rear of a 150-car test rack. Car numbers refer to the car position trailing from the POD. Car 1 is the first trailing car. BP = brake pipe; BC =brake cyl- inder. There are 50 feet of BP per car. NYAB, December 1, 2016. 2. The plots show that the braking benefits of the ECP system in derailment scenarios grow as the number of cars behind the POD increases. ⢠40-car plots: There was an improvement in the average braking effort in the 40-cars-from-the-rear- of-the-train test; the peak was a 2.2-psi increase in ECP brake pressures over pneumatic brake pres- sures across the train. ⢠75-car plots: The braking effort improves further as shown in the 75-cars-from-the-rear-of-the-train test; the peak was a 10-psi increase in ECP brake pressures over pneumatic pressures across the train. 3. Another benefit of the ECP system over pneumatic brake systems is that the BC at the car farthest from the POD will reach its targeted pressure faster: 0.7 seconds faster in the 40-cars-from-the-rear-of-train test and 2.6 seconds faster in the 75-cars-from-the-rear-of-train test. 4. The graphs shown would also be expected to apply to trains in radio distributed power service, as long as the remote locomotive is in the front half of the train that has successfully passed the POD before the incident. Figure F-12 shows that the emergency portions begin to apply brakes immediately from the POD; for the cars that have not yet experienced the BPP drop, ECP braking starts about 1 second later (see Cars 25 and 51). Once ECP braking begins on a car, that carâs emergency portion is not blocked and will still impact the BC applications when the BPP drops. This can be seen on Cars 51 and 75, where the carâs emergency por- tions begin at some point after the ECP braking has been initiated. Figure F-13 plots an average pressure across all cars of the trains from Figures F-11 and F-12, and the difference between the averages is shown as the pressure differential. The pressure differential shows that the ECP system provides a peak BC improvement of 10 psi across the entire train about 6 seconds after POD. Time (sec) Pr es su re (p si g)
45 FIGURE F-11 Conventional head-end-powered train or radio distributed power train (where the remote is ahead of the POD) with the POD occurring 75 cars from the rear of the train. Car numbers refer to the car position trailing the POD. Car 1 is the first trailing car. FIGURE F-12 ECP-OL train with the POD occurring 75 cars from the rear of the train. Car numbers refer to the car position trailing the POD. Car 1 is the first trailing car.
46 FIGURE F-13 ECP-OL train with the POD occurring 75 cars from the rear of the train. Car numbers refer to the car position trailing the POD. Car 1 is the first trailing car. FIGURE F-14 Conventional head-end-powered train or radio distributed power train (where the remote is ahead of the POD) with the POD occurring 40 cars from the rear of the train. Car numbers refer to the car position trailing the POD. Car 1 is the first trailing car. Figure F-15 shows that the emergency portions begin to apply brakes immediately from the POD and, for cars that have not yet experienced the BPP drop, that ECP braking starts about 1 second later (see Cars 29 and 40). Once ECP braking begins on a car, that carâs emergency portion is not blocked and will still impact
47 the brake cylinder applications when the BPP drops. This can be seen on Car 40, where the carâs emergency portions kick in at some point after the ECP braking has been initiated. Figure F-16 plots an average pressure across all cars of the trains from Figures F-14 and F-15, and the difference between the averages is shown as the pressure differential. The pressure differential shows that the ECP system provides a peak BC improvement of 2.2 psi across the entire train about 4 seconds after POD. FIGURE F-15 ECP-OL train with the POD occurring 40 cars from the rear of the train. Car numbers refer to the car position trailing the POD. Car 1 is the first trailing car. FIGURE F-16 ECP-OL train with the POD occurring 40 cars from the rear of the train. Car numbers refer to the car position trailing the POD. Car 1 is the first trailing car.
