Water addition enhances sanding and WSP operation
During the last weeks of July 2020, we completed a series of demonstration trials of our Water-Trak system installed in the experimental Class 319-based HydroFLEX train, operated by The University of Birmingham and Porterbrook. Figures 1 and 2 show the train and system in operation.
Figure 1: The HydroFLEX train during a braking manoeuvre
Figure 2: The Water-Trak system in operation
The tests marked the end of our First of a Kind project entitled “improved braking through controlled water addition”. In this blog post we will review the key outcomes of the trials.
During three days of tests at Long Marston, 21 low adhesion train braking manoeuvres were conducted at an 18mph entry speed. Very slippery railhead conditions were successfully generated using both leaf matter and paper tape, at times making it hard for the driver to stop the train. The driver was instructed to release the brakes if the speedometer reading stayed at zero for more than 5 seconds, indicating a potential threat of wheel damage. Deceleration rates as low as 2%g were recorded and five braking runs had to be interrupted to prevent wheel flats. The on-train sanding system remained operational throughout as an additional wheel-flat mitigation. It was notable that all the interrupted runs occurred when the Water-Trak system was not operational and in each case the Wheel Slide Protection (WSP) system failed to prevent wheel slide. Each time Water-Trak was deployed the WSP system functioned correctly and braking was described by the driver as “good”. The deceleration delivered with Water-Trak was also far better than without – see figure 3.
Figure 3: Comparison of deceleration results, with and without Water-Trak
The test results showed a statistically significant difference in mean deceleration of 1.8%g. If each braking run had been completed without interruption at an entry speed of 18mph, the following stopping distances would have resulted:
Even when braking at a relatively low speed, the difference between the two braking distances represents more than two carriage lengths of a Class 319 train. Imagine the potential Water-Trak might have at higher train speeds to reduce the risk of SPADs and station overruns in low adhesion conditions.
If we look at one set of comparable results for successful braking runs in more details, we can gain some further insight into the differences in braking performance. Figure 4 shows a speed vs time trace for two braking manoeuvres, one with water addition (blue line) and one without (orange line).
Figure 4: Speed vs time traces for train braking with and without water addition
As expected, the blue trace is much steeper than the orange, indicating better braking. In Figure 5, we can study the WSP activity (small bumps at the bottom of the chart) in the leading carriage during the braking run without water.
Figure 5: WSP activity during braking run without water addition
The trace shows that WSP activity is present throughout the braking run until Wheel Slide Protection is disabled at 6mph. Contrast this with the WSP activity during the braking run with water added – see figure 6.
Figure 6: WSP activity during braking run with water addition
Once again, WSP activity starts soon after braking but this time only operates for about 5 seconds, indicating greatly improved adhesion in the later part of the braking manoeuvre.
We received very positive driver feedback during the braking tests - train driver, Robin Hicks of Rail Operations Group commented: “it has definitely proved to me that water does slow trains down and stops them in good distance”.
In summary the results from these recent tests have been very encouraging, demonstrating greatly enhanced braking, reduced potential wheel damage and increased driver confidence. The full presentation can be viewed here.