1288

THE COLLIERY GUARDIAN

December 24, 1915.

Principles of Visual Signalling.*

By HAROLD GREEN.

The author said the main object of the paper was to
promote a discussion whereby some, if not all, of the
requirements for a satisfactory visual signal indicator
might be decided. The wording of the regulations was
such that one frequently met with different interpreta-
tions, and, as a consequence, manufacturers were at a
disadvantage in endeavouring to design and produce an
indicator which would satisfy everyone’s requirements.
Those responsible for the drafting of the regulation in
the first instance had apparently failed to appreciate
the difficulties incidental to designing suitable apparatus
—a view borne out by the fact that, when the regula-
tion came into force (or, rather, on the date originally
fixed), there was not a satisfactory or reliable indicator
on the market. Furthermore, everybody concerned
appeared to be in the dark over practically every detail
of visual signalling, and, as an outcome, the date of
enforcement of the new regulation was postponed.
Meanwhile, the inspectors, generally, were satisfied if it
could be shown that some steps were being taken to
provide the visual indicator prescribed by law. In the
circumstances, it was only natural that most managers
were content to instal the cheapest apparatus. The
results, in most cases, were far from satisfactory, and it
seemed at one time that protests were likely to be made
against the enforcement of the regulation, chiefly on
that account. Before that actually happened, however,
some manufacturers of visual indicators advanced the
claim that their apparatus had passed the Home Office.
If that assertion was correct, and the indicators in ques-
tion had been officially recognised as complying with the
regulation, then, in his opinion, such recognition was
only granted to justify the inspectors’ claim that satis-
factory apparatus was at least possible. He thought he
should be quite safe in saying that, even now, the visual
indicators worth any consideration at all, as practical
solutions of the problem, were few and far between.
It was quite obvious that, until the definite requirements
of such an indicator were fully recognised and under-
stood, any apparatus designed upon hard and fast lines
would scarcely satisfy all conditions. The ideal indi-
cator, therefore, should be one easily capable of modi-
fication, to satisfy different theories of what was correct.
To any non-electrical person it might appear an easy
matter to design a suitable apparatus to meet the regu-
lation. When the attempt was made, however, diffi-
culties speedily asserted themselves, to overcome which
some very ingenious arrangements had been devised;
but the complete apparatus was rarely satisfactory. As
regards mechanical indicators, it appeared to him almost
impossible to design apparatus sufficiently sensitive and
applicable to all conditions. The same remark applied
to those which were really mechanical indicators,
although depending for their operation upon electro-
magnets, actuating a step-by-step mechanism. He ven-
tured to suggest that the real solution of the problem
of an ideal visual indicator was to be found in the
employment of a series of sensitive, but reliable, electric
relays. The regulation stipulated that any signal must
remain visible until complied with. That raised the
question : “ What constitutes compliance?” Did it
mean that a signal should be cancelled immediately the
engine started, or that the signal should remain visible
until the engine stopped? He thought it was now
generally accepted that the former was the correct inter-
pretation. It would be very awkward, to say the least
of it, if the latter rendering were accepted, inasmuch
as it might easily happen (supposing the signal had to
remain until the completion of the wind) that a second
signal became necessary whilst the engine was still in •
motion. Thus, when the engine finally came to rest,
the second signal would be cancelled, although it had
not then been complied with.

He suggested that the correct interpretation was, that
any signal should, be cancelled immediately the engine
was started, and that any succeeding signals which
might be given whilst the engine was still in motion
should remain ” on ” until the engine was started
again. It was scarcely necessary to add that, what-
ever the design of the indicator in other respects, an
essential requirement was that every signal should
cancel a preceding one given from the same point. In
other words, the indicator should be non-cumulative.

One of the greatest stumbling blocks for the manufac-
turers of visual signalling indicators had been the
devising of a suitable method of cancellation by means
of the winding engine. The ideal aimed at was, of
course, cancellation on any and every movement of the
winding engine. Furthermore, the period between such
cancellation, and the readiness of the indicator to
receive another signal, must be negligible, so that any
attempt to signal during the transition period would be
successful. The latter problem was important, and it
would be interesting to hear how many indicators satis-
fied that condition. At first sight, it appeared a simple
matter to devise a means of automatic cancellation, and
one’s first idea was to arrange for a contact of some kind
to be fixed to one of the hand levers. A little reflection,
however, would show how uncertain any such arrange-
ment must prove in practice. Nearly every winding
engine differed from every other in one or more details,
and probably no two men used the same engine alike.
In actual practice it was difficult to find a case where
the engineman invariably made use of one particular
lever. Even assuming such a case to be forthcoming,

* From a paper read before the Manchester Geological and
Mining Society on December 21.

it would be seen that, when nearing the end of the
wind, the engineman was “ feeling his engines ” by
using that particular lever. In other words, the lever
he normally used, and to which such a contact making
or breaking device would be fixed, was in frequent
motion. The contact device would, therefore, be estab-
lishing a series of “ makes ” and “ breaks,” so that any
signal which might be given during that time would
be hopelessly muddled.

Attempts had also been made to cancel by means of a
switch or similar device actuated by the index finger of
the depth indicator. When cages with more than one
deck were employed, such an arrangement was useless
because the signal given for every deck should be can-
celled by the act of decking. That would entail a
multiplicity of contacts on the depth indicator, an
impracticable arrangement, having regard to the com-
paratively small range of movement of the latter in
decking. Where single deck cages were employed, the
matter was simplified. Probably only one contact
would then be fitted to the depth indicator, and
arranged to cancel at some pre-determined point in the
wind; half-way down the shaft, for instance. That
arrangement, also, scarcely complied with the regula-
tion, inasmuch as no provision was made for signals
given after the engine had started, and before the can-
celling point was reached in the wind. As a conse-
quence, such signals, which should remain “ on,” would
be cancelled by compliance with the signal which pre-
ceded it. Another difficulty attaching to that system
of cancellation was due to mouthings in the shaft. In
order to deal with signals originating at those mouth-
ings, more cancelling contacts would have to be fitted
to the depth indicator, and it was not difficult therefore
to see that such an apparatus was not practicable. The
only instance, therefore, in which such a method of
cancelling was at all possible was in the case of a shaft
with no intermediate landings, and using only single
deck cages—a rather limited scope for the indicators
which embodied that method.

Another important condition which the ideal indicator
should fulfil was that it must be capable of responding
to any signals, however quickly given. He thought
colliery officials would appreciate this point, particularly
where electric signals were installed. Decided advan-
tage in point of time rested with the electric press button
or key, over the mechanical pull, and with the former
very rapid signalling was possible. Given the ideal
indicator, alterations to the existing electric signalling
circuits should be unnecessary, because, quite apart
from cost, complication of electrical circuits down the
shaft or elsewhere about the colliery ought to be avoided.

He had heard of an interesting claim made for a
certain type of indicator, which required a multiple
shaft cable or cables and a number of press buttons at
each landing, corresponding to the highest number of
rings it was required to give at any time. That indi-
cator did not function on the step-by-step principle, so
that immediately a given button was pressed, the nature
of the signal was shown, and the engineman could read
the signal before the full complement of rings could be
heard. It was claimed that that saved time. The
question to his mind was : “ Did it not also constitute
a danger?” The winder might easily fall into the habit
of starting his engine immediately the signal became
visible; otherwise it was difficult to see how any appre-
ciable time could be saved.

From the onsetter’s point of view, the indicator had
no advantages; consequently, if he were called upon to
select a particular press button or key in order to give a
certain signal, he would be saddled with another respon-
sibility for which there was no compensating advantage
to him. When the onsetter had to select one out of
several press buttons, it was comparatively easy for him
to make a mistake; and should the winder, as suggested,
act upon the visible signal instead of waiting for the
audible signal to be completed, serious results would
accrue.

His own opinion with regard to multiple cables was
that they should be avoided if possible. They were very
costly, usually entailing a greater expenditure at the
outset than for the indicator itself; and, to say the least,
they were distinctly undesirable in a pit shaft.

As regards the cost of the visual signal installation,
it was false economy to put in an apparatus which was
not absolutely satisfactory and reliable. Once the
winder lost confidence in the indicator, he took no
further notice of it; and if he reported to the manager
that it was unreliable, the latter was placed in rather
an awkward position should an accident happen after-
wards.

He had heard the argument advanced that visual
indicators were of little use because, in the case of an
accident, there was no record to show who was to blame.
He inclined to the opinion that a really good indicator
was an additional safeguard, and a means of preventing
accidents, rather than for the purpose of apportioning the
blame to a particular individual after the accident had
happened. There was absolutely no doubt that where
satisfactory indicators had been installed, the winder
had experienced the benefit, and there had certainly
been cases where accidents had been avoided by the
presence of the indicator. If only one accident was
avoided during the lifetime of the apparatus, its cost
was covered.

There was, he suggested, an unfortunate ambiguity in
the present official signalling code, where one ring
meant both ” stop ” and “ go on.” It might easily
happen that the winder received the signal to stop,
which, of course, remained displayed until the next
signal came along, or the engine was again moved.
Some time might elapse between the receipt of that

signal and another, perhaps from a different landing.
Assume an error in distinguishing between two or more
bells was possible, and, indeed, probable, where there
were several levels. The winder glanced at his indi-
cator for confirmation, saw the “ start ” signal, and acted
upon it, with possibly disastrous results. There were
other instances where that double meaning was apt to
lead to error.

He saw no reason why one ring should not denote
“ stop,” and the signal to start be given by means of
two rings. There was, of course, a possible objection
in the case of the mechanical pull bells on the score of
time occupied in signalling. Such an alteration would
entail an addition to the official code, which would not,
however, be a serious matter.

Another alternative would be to dispense with the
No. 3 signal for “men,” and substitute some other
meaning for that number of rings. The distinction
between men and coal would then be made by means of
a separate indicator, the onsetter being provided with
two buttons, one for men and the other for coal. He
was fully aware that such a change would prove some-
what trying for those who had become accustomed to
the present code, but it would considerably simplify
matters so far as the design of visual indicators was
concerned.

Another point with which he would like to deal was
that most makers at present supplied their indicators
with a separate level indicator, to show the origin of
any signal. There was only one indicating device to
show the nature of the signal, no matter whence it
came, and another to indicate the level. He considered
that to be a very undesirable combination, and for the
following reason. Assume a signal to be given from
the pit bottom; the number of rings would be shown
on the indicator, together with the level from which the
signal originated. Then assume a second signal from
another mouthing. That, he took it, cancelled the
previous signal, so far as the code was concerned, and
also as regarded the point of origin, although the first
standing signal had not been complied with. Surely
such an arrangement was liable to cause great con-
fusion in the mind of the engineman concerned. In
the author’s opinion, each level should be entirely
separate, and different signals from the various levels
should appear simultaneously if necessary.

Summarising the points, he suggested the following
were essential requirements, and, unless an indicator
possessed the full complement, it could not be regarded
as entirely satisfying the regulation which enforced its
use :—

(1)	The signals to be non-cumulative.

(2)	Cancellation to take place immediately the
engine starts, and not when stopping.

(3)	Signalling should be possible during the wind.

(4)	Should respond to any reasonable signalling
speed.

(5)	No alterations to existing circuit arrangements,
or, in case of an entirely new installation, only one
line wire per level, with a common return.

(6)	Must be capable of adaptation to mechanical
pull wires.

(7)	A distinctive cautionary signal should be
embodied for “ men riding.”

(8)	Signals from every level to be separate and dis-
tinct, including indication of origin.

(9)	Must be capable of modification to suit any
reasonable interpretation of the regulation.

(10)	Reasonable over-all cost.

(11)	Reliability.

The Board of Trade have held a preliminary enquiry into
the circumstances of an explosion from a junction valve
chest, which occurred at Barrow Collieries, Barnsley, on
July 8 last, at Barrow Collieries, Barnsley. The valve
chest, which was the property of the Barrow Haematite
Steel Company Limited, Barrow Collieries, Barnsley, was
of the right-angled type, and made of cast iron. It was
6 in. in diameter of bore, the boidy was in. -in thickness,
and the flanges were 12| in. in diameter and 1J in. thickness.
The cover was 16 in. in diameter, and was secured by six
wrought iron bolts I in. in diameter, and the screwed ends
of two pillars supporting the bridge were of the same
diameter and acted as bolts. The thickness of metal in the
outlet neck-piece was in., but at one part it increased to
If in., otherwise the thickness of metal was practically
uniform. The flange on the under side of the valve was
connected by eight wrought iron bolts, in. in diameter,
to a neck-piece attached to the boiler shell; to the vertical
flange was connected, by eight wrought iron bolts in. in
diameter, the branch steam pipe which also was of cast
iron. The part of the valve chest which was connected to
the branch steam pipe fractured completely round the neck
of the flange; the parts separated about |in. and, through
the opening thus formed, the greater part of the steam
escaped from the boiler before it was possible to get near
and close the valve. The explosion was due to the extension
of a fracture which originated when the chest and steam
pipe were first jointed up, or on some subsequent occasion
when the joint required hardening up. In his observations,
the Engineer Surveyor-in-Chief remarks that the method of
connecting the steam pipe to the valve chest was unsatis-
factory, a making-up piece, in the form of a wrought iron
ring l|in. in breadth, having been inserted, with asbestos
jointing material on either side between the flanges and
inside the bolt circle, so that, unless great care was exercised
when the bolts were screwed up, an excessive stress would
be set up, tending to fracture the flange or the material
forming the neck of the chest. The objectionable features
of the arrangement have been pointed out to the management
of the collieries, and it has been decided that the packing
rings shall be done away with as the boilers become due for
cleaning.