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Re: Real Long Read On NYCPropulsion/Braking

Posted by Jeff H. on Sat Nov 4 00:33:07 2006, in response to Real Long Read On NYCPropulsion/Braking, posted by chicagopcclcars on Thu Nov 2 20:32:01 2006.

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There are a number of technical errors in this posting, especially
this fixation with supplemental presure (brake cylinder buildup
above inshot pressure under high SAP pressure)...this feature was
only seen on A1 operating units with B relay valves, i.e.
pre R26. I'm not certain why it was changed on the later units,
but my guess is Car Equipment felt more comfortable going with
a higher dynamic brake load current and this would be sufficient
for handling the full 3.0 MPHPS brake call at maximum load.

With regard to the 1995 accident, these minor errors do not diminish
from the underlying point, which was fully reported in the NTSB
report: The emergency braking rate was knowlingly diminished
when the relay valves were "upgraded" from a J16C to a J14D.
This delivered 20% less cylinder pressure, both in service and
emergency. The result was that the emergency brake rate, which
relies entirely on friction braking, was actually lower than the
full-service rate, which generally relies on the dynamic brake and
not the relay valve.

The great fleet neutering was a component of the response to this
report. The braking rates were quietly dialed back up and all
car classes were tested to see that they achieved 3.2 MPHPS.
Finally, there have been probably thousands of signal locations
were the home control lengths were increased.

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