Nearly all locomotives are equipped with two devices designed to limit certain
speeds. One is the Diesel engine overspeed protection device that immediately
acts to shut down the prime mover in the event of an overspeed (RPM's)
condition. The action of this safety device has no effect on the train as it
shuts down only the prime mover affected with the overspeed condition.
The locomotive (train) overspeed protection does effect the train. When the
pre-set speed is exceeded this protection device acts to notify the Engineer of
the condition and demands immediate action (6 to 12 seconds) to reduce the the
speed to a value less than that set in the speed sensing equipment. On the old
speed recorders this device was mechanical and, so I'm told, lent itself to
"re-calibration" while enroute. The newer speed sensing equipment is electronic
and, as a result, is less susceptible to enroute "adjustments".
When an overspeed condition exists long enough to activate the protective
equipment all prime movers in the MU'd consist will go to idle, the main
generator is unloaded (PC switch opens) and a penalty application (brake pipe
reduction at SERVICE rate) of the automatic air brakes is initiated. The
automatic brake valve handle must be placed in the SUPPRESSION position and the
throttle moved to IDLE for 60 seconds.
Of interest to some may be the equipment, or lack thereof, with which the Q
E5's were fitted. NO SPEED RECORDERS and NO TRAIN OVERSPEED. Also, a gear ratio
that invited an Engineer to "experiment".
It should be noted that the above description of events may NOT be the same on
ALL railroads as the mechanical and operating departments make the decisions
relative to the functions mentioned.
Karl
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