Brake Tests
År: 1913
Forlag: Pensylvania Railroad Company
Sted: Altoona, Penna.
Sider: 401
A Report Of A Series Of Road Tests Of Brakes On Passanger Equipment Cars Made At Absecon, New Jersey, In 1913
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292
with the PM equipment, the pressure is blown down as
the speed of the train decreases (Fig. 53).
7. The following is a summary of the stopping performance of
cars equipped with the PM and with the UC equipment. It should
be noted, however, that the air-brake valve and means for its operation
are only partly responsible for improved stops. The function of the
air-brake apparatus is to admit the air to the brake cylinder with the
greatest flexibility in service application and in the shortest time in
emergency stops.
(a) With the PM equipment, operating at our standard
emergency braking power, stops from 60 miles per hour
were made in about 1600 feet.
(b) Operating at 150 per cent, emergency braking power, the
UC pneumatic equipment will produce a stop 200 feet
shorter than the PM equipment. (Fig. 93.)
(c) Twelve-car trains can be stopped from 60 miles per hour
with an electro-pneumatic emergency application, 150 per
cent, nominal braking power, in less than 1200 feet.
(Fig. 93.)
(d) The shortest 60 miles per hour emergency stop with a 12-car
train was made in 1021 feet. (Par. 363.)
(e) An emergency stop of 725 feet was made by a single car
from a speed of 60 miles per hour. (Par. 357.)
The estimated train stop under the same conditions would
be 795 feet. (Par. 414.)
8. With electro-pneumatic emergency applications a given in-
crease in braking power results in a constant decrease in the length
of stop. (Par. 325.) An approximate expression for the variation of
percentage of emergency braking power and length of stop with the
electro-pneumatic equipment is that for an increase of 5 per cent, in
the braking power the stop is decreased 2 per cent. (Par. 329.)
9. The amount of wheel sliding depends more on the rail and
weather conditions than on the percentage of braking power. (Par. 337.)
(a) The determining factor in wheel sliding is not high braking
power alone, but rather the uncontrollable rail and weather
conditions in connection with it, against which no per-
manent provision can be made without a sacrifice in the
length of emergency stops during those favorable periods
of the day or seasons of the year when conditions warrant
the use of high braking power. (Par. 341.)
(b) The coefficient of rail friction increases with increasing
temperature and decreasing relative humidity, and de-
creases with increasing relative humidity and decreasing
temperature. (Par. 346.)
(c) The average rail condition changes with the seasons of the