All About Engines
Forfatter: Edward Cressy
År: 1918
Forlag: Cassell and Company, LTD
Sted: London, New York, Toronto and Melbourne
Sider: 352
UDK: 621 1
With a coloured Frontispiece, and 182 halftone Illustrations and Diagrams.
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322 All About Engines
length of bar and the weight of the balance on
the other side. When the engine is started the
pulley tends to carry the blocks round, but is pre-
vented by the spring balance. The speed can be
varied by
tightening or
loosening the
nuts. If P is
the force in-
dicated on
the spring
balance and
y is the dis-
tance of the
balance from
the centre of
the shaft in
feet, then the
engine is
working
against a
Fig. 180.—Rope brake
force P applied at the circumference of a circle /
feet in diameter. This circumference is 2 % r feet,
and if the engine makes n revolutions a minute, the
distance over which the force acts per minute is
2 7T / n, and the work done per minute is 2 tt y n P.
The horse-power is, therefore,
2 tt y n P
33,000.
A more usual form of brake consists of a number
of wooden blocks strung on a couple of ropes, or