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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146
CHAPTER V.
PERCENTAGE OF BRAKING POWER.
Definition.
313. The term “per cent, of braking power” requires definition
in order that its significance in the different ways it has been in use
may not be confused. Three distinct usages have been made of the
term in this report, they are:
A.—Nominal per cent, braking power has been used in the common
acceptance of the term, viz.: the ratio of the total shoe pressure, cal-
culated from the basic nominal brake cylinder pressure contemplated
in the design, to the light weight of the car.
B.—Actual per cent, braking power based on brake cylinder pressure
obtained, is referred to in several cases and is the ratio of the total brake
shoe pressure, calculated on the basis of the brake cylinder pressure,
actually obtained in any given test, to the weight of the car.
C.—The ratio of the net resultant normal brake shoe pressure to
the actual weight of the car in any given case. It involves an allowance
for the actual cylinder force developed and all losses in transmission
included in the general term brake rigging efficiency. This ratio, which
is, properly, the net effective per cent, braking force is seldom referred
to in this report, except in connection with the study of the performance
of brake shoes under known conditions of pressure and wheel loading,
as in the case of the laboratory tests of brake shoes, Chapter VII. In
accordance with common usage this ratio has been referred to as per
cent, braking power” in this report.
314. It should be noted, however, that the term “braking power”
is recognized to be a misnomer and should properly be replaced by the
term “braking force,” but as braking power is the generally accepted
term, it was thought best to conform to common usage throughout this
report.
Present Standard.
315. The present nominal braking power on P-70 class cars with
PM air brake equipment is, for service applications, 80 per cent, based
on 60 pounds brake cylinder pressure, and for emergency applications
113 per cent, resulting from a nominal emergency brake cylinder pres-
sure of 85 pounds, the brake pipe pressure being 110 pounds.
Braking Power as Used During Test.
316. The service tests with PM equipment were made with the
above mentioned standard percentage of braking power and for emer-
gency tests, braking powers of 80 per cent, and 144 per cent, were used
in addition to the standard 113 per cent.