Engineering Wonders of the World
Volume I
År: 1945
Serie: Engineering Wonders of the World
Sider: 448
UDK: 600 Eng -gl.
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228
ENGINEERING WONDERS OF THE WORLD.
Fig. 6.—SAXBY AND FARMER’S FACING POINT LOCK.
These possibilities have been negatived by
the simple but ingenious Saxby and Farmer
facing point lock, which is shown in Fig. 6,
and is worthy of examination.
A Point The points are shifted by one
set of rods, B, and locked or
unlocked by a quite separate set, H. Near
the nose of the points is a stretcher bar, C,
divided into two parts, one of which is at-
tached to each switch. These parts are
flattened out and overlap one another for
about eighteen inches at the centre of the
track. The overlapping portions ar© pierced
with, two sets of holes, which under normal
conditions coincide exactly. Should the bars
connecting the switches break, the stretcher
would divide, and the holes of the parts
coincide no longer.
Attached to the sleeper under the stretcher
is a collar, through which works a plunger
bolt, D, fitting the holes in the stretcher.
This bolt is connected by rods and a rocking
lever to a locking bar, E. The bar rides on
swinging clips, F, and can be moved in either
direction by the train of levers, HH, its
upper surface rising at half-stroke to the
level of the top of the rails. (The motions of
the bar may be compared to that of one
element of a pair of parallel rules.) If a
vehicle happens to be passing, the bar cannot
be thrown over, owing to the obstruc-
tion caused by the wheel flanges, and conse-
quently the bolt cannot be withdrawn from
the stretcher bar, which, fact in turn prevents
the shifting of the points. In the illustration
the bar is seen lying over to the right, and
the bolt withdrawn ready for the points to be
shifted. As soon as they have been moved,
the bar will be thrown to the left, and the
locking bolt shot. It should be added that,
should either of the tongues, AA, or the rods,
KK, break, the two parts of the stretcher
bar would separate, and the signalman would
know, from his inability to shoot D home,
that something was amiss.
Interlocking.
But these great improvements must appear
small when compared with the introduction
of the interlocking of points and signals.
By this the lowering of conflicting signals—
that is, those for opposing movements, such
as signals 6 and 7 in Fig. 7—is rendered