These two words chill the hearts of railroad managers whenever
they're used. With the data gathering systems in use today (Black
Boxes) RR's spend great amounts of time analyzing the decisions made
by their Engineers' in daily operations. One of the issues dealt
with is "POWER BRAKING".
It stands to reason, with a car or pickup truck at least, that
standing on the brake pedal while depressing the throttle is,
besides being pointless, very expensive. So also it is with train
handling when carried "out of the ball park". There is a difference
of course between cas and pickups in that neither is subject to
slack action. "Slack" in a train is the sum of the free movement
between drawbars (couplers) added to the available movement built
into the draft gear on each car (rubber or springs). Slack is a
necessary evil since starting a heavy, "slackless" train would be
very difficult if even possible. A perfect example of the
difficulty of starting a slackless train is provided by 25 car
trains of welded rail. Anyone who ever handled one of these trains
will agree.
While slack is necessary it must be controlled to avoid break-in-
twos and unnecessarliy rough train handlig. In passenger service
much greater attention must be given to the control of slack to
provide the travelling public a smooth ride both while moving over
the road and, especially, when stopping. "POWER BRAKING" is (was)
the most valuable tool in the Engineers' bag of tricks to accomplish
this feat.
Power braking is simply the application of braking effort in the
train while urging the engine to keep on pullin', within in reason,
of course. Applying the train brakes would usually result in a run-
in of slack due to the fact that train brakes apply on the head car
FIRST. If the engine is allowed to continue pulling the train you
can run ahead of the slack. With subsequent brakepipe reductions,
increasing braking effort, the throttle is gradually reduced a notch
at a time to allow the speed to decay. When the final brakepipe
reduction is made and, immediately prior to comming to a stop, the
engine brake should be allowed to apply also. This action prevents
the engine from "backing" into the train when the throttle is
finally closed. The final, GRADUATED brake application is allowed
to remain in effect until it is time to start the train. IF all has
worked well the brakes (train and engine) can be released and the
throttle advanced a notch or two (depending on grade conditions) in
order to get the train under way.
Power braking or, as the term has been modified to fit more "modern"
train handling requirements states, STRETCH BRAKING, may still be
employed as a method of controlling slack but, with the
aforementioned data recovery systems in use, just don't make too big
a reduction while working too much power. Engineers' engaging in
the profligate use of BOTH air and throttle will soon be "invited"
to visit their local, friendly Roadforeman of Engines to "discuss"
the matter. (Ah, the good ol' days)
Hope this helps.
Karl
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