Let's start with freight brake equipment first.
Reducing the air pressure in the trainline applies the brakes.
Increasing that same air pressure releases the brakes. Simple!
When an Engineer decides to "set the air" he chooses a brakepipe
(trainline) reduction that he feels will be sufficient to accomplish
what is needed to control the train under a variety of circumstances
(slowing, controlling speed or stopping). The greater the
reduction, the greater the braking effort in the train. When the
desired results have been achieved, and all other conditions allow,
the brakepipe pressure is restored to its original value and the
brakes release. On freight brake equipment the only options
available to the Engineer are set or release. Once the initial
brake application becomes effective the Engineer can INCREASE the
braking effort in the train by making additional reductions of
brakepipe pressure, up to a predetermined level. If the position of
the brake valve handle is not changed the brakes will, in theory,
remain applied forever. As soon as the brakevalve handle is moved
to a position that INCREASES brakepipe pressure ALL train brakes
began to release completely. Simply stated, the brakes on freight
equipment are either ON or OFF.
Passenger equipment, however, is designed to operate in a manner
that allows smoother stops to be made. To accomplish this the
control valve (triple valve) has a feature that allows the Engineer
to gradually reduce the braking effort in the train (garduated
release) while still maintaining control of the train and and,
eventually, stopping at the desired spot. When the control valves
(ALL the control valves) are set to the GRADUATED RELEASE position
the Engineer can move the brakevalve handle momentarilly to the
RELEASE position and INCREASE brakepipe pressure in small
increments. The control valves, when sensing this increase in
pressure, cause a small amount of brake cylinder pressure to be
vented to the atmosphere thereby GRADUALLY reducing the braking
effort in the train. Subsequent GRADUATIONS further reduce the
braking effort to the point where, upon stopping, the passengers are
not treated to "whiplash". If the Engineer feels that additional
braking is needed to accomplish his goal he can move the brakevalve
handle to the position that allows brakepipe pressure to once again
be reduced thereby INCREASING the braking effort in the train.
In the case of "The Last 32" it is believed that several brakes
(cars) were either cut out completely (a BIG no-no) or the GRADUATED
RELEASE CAPS were positioned in the DIRECT RELEASE mode. If the
former is correct all cars with their brakes cut out would have no
brakes applied - - ever. These cars would then be free to do
anything they wanted to do. If, however, the latter was true all
cars conditioned for DIRECT RELEASE would, upon sensing even a small
INCREASE in brakepipe pressure (1 to 1-1/2 PSIG), go to full release
and, as before, be free to do anything they wanted to do while the
cars conditioned for GRADUATED RELEASE would maintain the desired
level of braking effort until the brakepipe pressure is completely
restored. Consider a train where some cars a trying to slow down
while other cars in the same train are running "free". It's pretty
easy now to visualise the predicament the Engineer could find
himself in were he not notified that the ENTIRE train was not
conditioned for GRADUATED RELEASE operation.
During the remainder of 32's last trip a different method of braking
was chosen and the change greatly reduced the anomalies experienced
at Oregon, REDUCED, not elimated them.
The brakevalve applied to the engine handling 32 was the 24RL
schedule which became, after some small internal modifications, the
finest brakevale EVER invented.
Karl
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