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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Fig. 7.—Eccentric
10 All About Engines
of the valve is large enough to cover the middle
or “ exhaust ” port, and one of the steam ports, but
not both. As the valve moves backwards and for-
wards it not only uncovers each steam port in turn,
so that steam can enter the cylinder, but it also places
the covered port in communication with the exhaust
port, through which the steam escapes into the open
air or into a condenser. If this valve, then, moves
backwards and forwards, always in the opposite
direction to the piston, steam
is admitted to each end of
the cylinder alternately, at
the right moment for con-
tinuous working.
The usual device for
securing this motion of the
slide valve is called an eccen-
tric (Fig. 7). An eccentric
consists of a cast-iron disc
or “ sheave,” keyed on to
the shaft, with a strap fitting
closely round it and connected
by a jointed rod to the slide
valve. Now if the hole in
the sheave through which
the shaft passes were in the centre the sheave would
merely turn with the shaft like a wheel. But this
hole is out of the centre—hence the term eccentric—
and as the sheave rotates with the shaft the valve is
moved backwards and forwards over the cylinder
ports. The distance from the centre of the sheave