IMPROVEMENTS IN RAILWAY- SIGNALLING APPARATUS
Year: 1881

page_text: LETTERS PATENT to John Nevil Maskelyne, of the Egyptian Hall, Piccadilly,
in the County of Middlesex, for an Invention of " IMPROVEMENTS IN RAILWAY-
SIGNALLING APPARATUS."
(Void by reason of the Patentee having neglected to file a Specification in
pursuance of the conditions of the Letters Patent.)
PROVISIONAL SPECIFICATION left by the said John Nevil Maskelyne at the
Office of the Commissioners of Patents on the 31st January 1881.
JOHN NEVIL MASKELYNE, of the Egyptian Hall, Piccadilly, in the County of
Middlesex. " IMPROVEMENTS IN RAILWAY SIGNALLING APPARATUS."
The object of this Invention is to provide simple and efficient means for working
the distance and other signals on railways, whereby the stretching and contracting
of the wires or rods used for that purpose (whether such variations in the length of
the wires or rods be due to atmospheric changes or to other causes) will be
compensated for.
It is well known that this property of metals, viz., to expand and contract under
the influence of heat and cold, is, in the case of signal wires and rods, often the
cause of railway accidents, as it materially interferes with the proper working of
the signals.
Many attempts have been made to overcome this difficulty, but hitherto with
only partial success.
In carrying out my Invention I attach to the semaphore arm, by preference in
front of its pivot, a rod which extends downwards to within a few feet of the
bottom of the signal post. The lower end of this rod is pivotted to one end of a
short rock lever, which has its fulcrum on the side of the post. To the other end
of this lever is fixed a pin or projection, against which a lug on a weighted bar will
strike at the proper time and rock the lever, which by means of the rod will raise
the arm to danger. The semaphore arm will in general be lowered by its own
weight, which will be sufficient for the purpose when the weighted bar is removed,
but a second lug on the weighted bar, and acting on the under side of the pin, may
be used. The wire from the signal box is passed round suitably placed pulleys,
and is attached to the top of the weighted bar.

page_text: This bar is so arranged as to be free to lift any distance within the possible
length of draught at the signal box, but a rise of about two inches will allow the
semaphore arm to fall; thus, should the wire stretch, the pull from the signal box
will first take up the slack, and then lift the bar a sufficient distance to allow the
semaphore arm to fall, but should the wire contract the pull from the signal box
will lift the bar considerably higher than is necessary to work the arm. A stop is
provided so as to prevent the rocking of the lever more than is absolutely necessary
to bring the signal to "caution."
It will thus be seen that where the draught of the hand lever is sufficient to
allow for the variations in the length of tho wire the sliding bar will compensate
for such variations in a more effectual manner. It may not however be convenient
to obtain sufficient draught at the signal box to allow for the whole of the variations
of the wire, and in such case I mount on the pivot pin of the hand lever, or in any
other convenient position, a toothed sector, over which a chain is passed and secured
in the centre. One end of this chain I connect to the signal wire, and upon the
other end I hang a counterweight. The throw of this sector should be about equal
to twice the greatest amount of expansion and contraction of which the wire is
capable.
Upon the hand lever I pivot two weighted pawls, which, when at liberty, will
take into the teeth of the sector. These pawls are held clear of the sector teeth by
an arrangement of bell crank levers in connection with the ordinary spring catch
of the hand lever. The sector will thus be free to rock upon its axis as the signal
wire expands and contracts, the slack being taken up by the counterweight, and
the contraction being allowed for as the counterweight is lighter than the weight
at the signal post, and therefore it will be raised by the contracting of the wire.
When the spring catch is actuated to allow the lever to be pulled over, the pawls
are set free and fall into the teeth of the sector.
The teeth of the sector are so arranged as to allow both of the pawls to enter
between any two teeth at one time, and the pawls are so placed that they will
admit one tooth of the sector entering between them; consequently there will be
no point at which the sector can rest without one or the other or both of the pawls
dropping into its teeth.
This simple arrangement of double pawls entirely overcomes a difficulty which
many have experienced who have employed toothed wheels or racks for this and
other purposes, as it has been found that the wheels or racks were at times resting
in such a position that a single pawl or double pawls placed the same distance apart as
the teeth of the wheel or rack were liable to catch upon the points of the teeth, and
when pressure was applied slip and break the teeth, thus rendering the apparatus
useless. Teeth with sharp points like dogs' teeth have also been used to overcome
the difficulty, but they have signally failed, as their natural tendency is to separate,
and they require considerable force to keep them together.
It will be evident that this arrangement of the toothed sector and double pawls
may be attached to any existing lever, and used without altering the mole of
working the semaphore arm, but I prefer to employ it with the sliding bar for
working the arm, inasmuch as it effectually prevents any unnecessary strain and
consequent stretching and breaking of the wire, and it also assists in compensating
for the variations of the length of the wire.
The semaphore arm may be controlled from several points by increasing the
length of the pin or projection upon the short lover, and providing a weighted bar
for each signal box, each bar being sufficiently heavy to keep the arm at danger,
and if either wire should break the arm will remain at danger.