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Published by membersonly, 2018-03-20 07:58:09


10th March 2018




,J fro*

Great.M/estern Railway

Signal Box



Great Western Railway

Signal Box


of E*hibit
at !h", British


Empire Exhibition

Wembley I9Z5

Paddington Station.

London W.2














I{E Grent WeStern Raihva,v
E:ihibit is a Standard P:rttcrn
signal box, replete witl-r the
necessarY equipment tirr the
working of trains in one
dire[tion on1v, t,i7,., ()ver a
" down main " and a " down br:anch " Iine. Thc
box is simiiar in principle to manv hundreds in

use on the Great \X'eStetn Railwar-.
For the 6rSt time in the historr- of the raiiwavs

a signal box, compietelv equipped, will be throrl'n

open to the public, and experienced signalmen

will explain and demonstrate how the signals ancl
points are worlied. IIr-.rrnl.Rs oF THI-. PUBLIC


This brochure expiains btieflv the u'orkinq of
the blocli inStrum:nts, poin:; or srvitches, sigrrals.
facing poi.nts, faciag point lock and locking bar,

clete&or loclis, d:tonator " plfcet " machines,
s:rfetv appliances and thc plinciplcs of signalling

and controlling of trains along the raih.vav from one
siqnal box to another.

Pagt h'ite




















HE situation oi a stgnal box is

verv important. The signalman

muSt have t clear view oi aP-

proaching trains, and as manv as

possible of hrs signals. Notice

the large windows in the Box.

There ar3 over 2,ooo Signal boxes on the Great

WeStern Railwav Companv's syStem, controlling the
8,287 miles of running lines. These boxes are

r.vorked by ,,ooc trained signalmen' The boxes
r.ary in size lnd equipment from small ones with

six or more ler.'ers worked bv one sienalman, to
those ere&ed atlarget Stations and iun€lions with as

many as zz4levers which require six signalmen and

three telegraphiSts to rvotk in three turns oi duty'
$tri&ly Private, and no
All signal bPoexresson^ries
alloweci to n-ranipuiatc
signals, points, bells ol in$trutlents. Signalmen

take great pricle in their boxcs and equipment,

and keep both spctiesslv clean, chamois ieathers

bcing us:d when levers are manipulated so that the
handles are kept bright and free from ruSt.

Page Seueit


Iryreruon Vlrw or rHE SrcNAr, -Bot Erslarr.



HE levers are for operating signals and
points. The,v work forward and back-
ward in the steel frame wherein thev are

fi".d- When :Fullv backward or fuily fotward
thev are held firmli' by spring catches attached
behind them. There is a separate levet for
working each signal. \When the levet' is in the
" back-rvard " position the signal is in its normal
positicn at " clanget." To lower a signal its
1".r., mu$t be puiled to thc " forward " position'

Levers arc painted in distindtive colours to assist

the signalmen in their oPerations, ui7.', distant
(caution) signals, green ; " StoP " signals (i''',
" home " and " Starting " signals) red ; points
or switches, black I facing point locks, blue;

detonatot places, white rvith black bands'

POlNT.f Oj:',\' W'11'CI1 8,,1.
OINTS or switches consiSt of pairs of
movable hinged raiis inside fixed raiis,
worked with a lever from the signal box

bi iodai"g supported on rollet bearings' The
thick hinged end is termed the " heel," and the
thin blade-like end the " toe," and arc movecl

from side to side to enabic ttains or vehicles to be

diverted from one line to another.

Page Nine



The normai position of points conneB:ed with
the main (or running) lines, is tirat which enables

trains to pass over the main iines, without being
turned on to other lines.


FFIXED to ail levers ate plates bearing the
numbers consecutively from r upwards'

Exhibited in the Signai box, in view of
,fo rrg"ulman as he faces the levers, is a diagtam
shewing ptainly ail the lines, sidings, signals, etc''
workeJfto* the signal box, and the numbers of

the levers bv which the respe&ive points, signals

and other apParatus are worked' The diagram

shews also the normal positions of the points, these

corresponding in every case to the lever being in
the backwardposition. Some of the levets, when
in the normal or " backwatd " position, cannot be

reversed unless cefiain other levers (calied leading

levers) are firSt placed in the " forward " position'
This is because the working of various levers is
" interlocked " with the working of others, e'g', the

diStant signal cannot be lowered until the home and
Starting iignals have fi.rSt been iowered' The

" home " and " Starting " signals are therefore
" leads " for the diStant signais' In a similar
way any points conne&ed with the running lines

muSt be in corre& position for the passage of a train

before the " home " ot " Starting " signals can be
Iowered,' and this is secured by intedocking

between signals and points, thus ensuring the

Page Eleuen


corret,t \Morking of points and signals, and safe-

guarciing againSt the exhibition of confli€ting sisnals.

.'ICN.,1L.'' - lND THEIR L,,JE.'.

45 lerr{E sisnal posts on the Great $Testern
Railway are gencrallv p)aced on the left-
gLl:_,[email protected]
hand side of the line as vicwed bv the

driver on the engine footplatc. The signal arms

are ofl the lef1-hand side of the poSts, and are

painted in red with a u'hite \.ertical stripe (^t

seen bv the engine-driver) in thc case of " stop "
signals, and a ) stlipe for diStant signals, the

latter in somc cases being rrellow with " blacl< " )
; on the sAitdtaechthedet'to^ttehepasiingtneacli
Stripe bl:ck l'everse
'with Stripe.

poSts are cases containing lamps, urhich on

the Great Weftern Raihvav are burning con-

tinuouslv dr)' and nieht (except when being

trimmed and cleaneC). .{ special form of lamp

econo;nical in oil consumption has bccn adoptcd,

which requires attention and replenishment with

oil once a w-eeli onlv. To the signal arms arc

attached colourecl glasses, termed spe6tacies,

throuqh u,hich the light of the lamps is vierr,'ed bl

the oncoming engine drivers. When the arm is

in the " all right " ot " ofi- " position, a green light

is seen, and when in the " danger " or " on " posi-

tion, a red light shervs. In some inftances distant

signals now shew a yellow light in the "on" position.

It is the duty of a signalman to satisfv himself

that the signal arm obeys the lever movement,

Pege Twelue


ancl that the signal light is burnins propedy. It
witl be noticed that the home signals have their

backs to the signalman, they have, thetefore, small

white back-lights as an indication to the signalman

that the arm; ^te worliiog, and that the lamps are

Ele&ric "repeaters" are

provided in signal boxes for

signals v-hich are noi visible
from the signal box, in order

that the signalman may knou,

when the ievers operating the

signals have done their work.

The arm itself is repeated by a

miniature tlag in the signal box

inStrument shewing " Ofl " or

" Off," and the signal lamp by
a fr,agshewing "In" or "Out."

In the case of a lamp failing and the flag she-wing

" Out," a bell is made to ring in order to attraet the
signaiman's attention. The

distant signal is so equipped.

Signais ^re so designed that
arm worked bv
should the signal

wire from signal lever to signal

poSt thii to worli properlv orving

to a slack or brolien ririre, the

rveight and heavr. spectacle hold

the arm in the danger or safetv
pos.ition. Scrcu' adiu$ters are provided in signal
boxes for tightening or slackening signal wires.

Page 'L'hirteen


(HE firSt signal seen bv the engine-driver

of a trainapproaching a signal box from

either dire6tion is a considerabie distance

from tne signal box" Its position gives it the
name of " diStant " signal. Be-

tween this signal and the next

one will be a diStance of perhaps

rrooo yards or so.

I Now, whenever afi. engine-

lrl driver sees a distant signal at

lli " danger " he is not expe&cd to

li. Stop at it, but to regard 7t as a caution signai, indi-
cating.that he mu$t reduce the speed of his train


l'. and be prepared to. Stop at the next'signal, if it

1,, should be at " daflger."

\7here the diStance between two signal boxes is

too short to enable a distant signai to be placed

sufficiently far. fuomthe Home Signal, to give ample

warning to engine-drivers it is fixed on the same

poSt as ihe Starting or Home Signal of the previous

box. In this case it is the lower of the two arms.

It will be'noticed that the arm of the distant

signal has a diftin&ive shape, being notched at the

end, or " fish-tailed."

Page Fourtee*


HE second signal reached bY an aP-
proaching train is generally situated in
the neighbourhood of the signal box.

r,t p.iliion gives it the name of the " Home "
slgnal. It is a Stop signal, and *"1-"":le passed

at " dartget." The Home Sig-
nal is usually Placed a few
vards short of the firSt siding

conne€tion or other Points on

the line to which the signal

appiies. This enabies an
proaching tr.ain to be

whete it will Stand clea"r of anY

shunting or other operations to be done over
the points. At iun&ions the Home signals are

placid where, in a similar wa1l: they " prote& " thd
lines which other trains may require to Pass over'

In the exhibit the two signals on one po$t, a

" bracket " signal, nearest to the signal box, are the
Home signals. The left hand signal is for the left

hand or main line, and the right hand signal for the

branch line. It should be noticed that the Home
signal for the more important line is made a

little higher than the other.

The signal wires oPerating these two signals pass

tirrough *t r, is termed a " detector iock " to each'-

of the switch tongues, and it wiil be seen that unless

the points or switches are right tor the main line
it is impossible to iower the main line Home

Signal No. i in the diagraur*, and similarly unless

Page Fifnen



the switches are right for the branch line the Home
I Signal for the branch No. , in the diagram cannor

be lowered. The lowering of either arm is there-

fore an indication to the driver of the exa& position
of the facing points.

Farther: on ahead of a Station platform and points t

of any sidings worked from the signal box, and

generally some little distance beyond the signal box
itself, is another signal. Its purpose is to govern

the Startin g away of trains from one se&ion into the
se&ion in advance. The name given it, thereforc,

is the " starting " signal.


W{ffiHE ele&rical or block telegraph inStru- t
5f BR ments seen on a shelf above the levers
@l @) are for communicating with the signal-
m:n in the next boxes, in advance or in the rear,

and most of the signalling between signalmen is

done bv bell-codes. 'Iherefore u,e will

TApnsn BILL. call three consecutive

signal boxes " A,"
" Br" and tt Cr" the
signalman at (' B ')
will have an in$tru-
ment bv v'hich he
can ring a bell in
",{. " and another bv

u,irich he can ring a

Page |'ixteen


bell in " C." He will also have a beli that can
be rung bv the signalman at " A " and another

that can be rung b), the signalman at " C.."

The in$trument containing the key or " tapper,"
bl which the signalman at " B " can ring in

I one of these boxes, has afiixed to it the beii

t which is rung from that signal box. All Lrelis in

,t a signal box have difi'erent tones, which enable a

signalman soon to associate their respe&ive

sounds with the iines to which thev appiy. The

line between the immediate areas of two signal
boxes is called a " se€tion " and the obje& of the

system known as Block Telegraph $7orking, which
we are about to describe briefl-y, is to pre venr more
than one train being in a se&ion on the same line

at the same time.

t In having an up and down main line, a signalman
at (( B " is concerne(l rvith tour " se6tions."
Regarding (( A " to " C " as the Up dire€tron,

these se&ions will be'-(r) The up line betu,een
(( A " and " B." (z) The up line between (' B r)

and " C." (3) The dou,n lirre between " C " and

" B." (a) The down line betu'een " B " and " A."

Now, for each of these " Se6tions " is afi

inStrument, called a Block Indicator. The purpose

of these four inStruments is to exhibrt, at all times,

indications of the occupation ol otherwise r:f the

" se€tions " to which thev, respe€tively, apply.

h Of these Block Indicators onlv two are operated

br. the signalman at " 8." They are the ones

applving to the " sections " v'herein ttains run

tI Page S'euenteen

towards " B's " signal box. So, in othet words,

the signalmartat" B " works the inStrument for the
Up line from (( A " to " Br" arrd that for the
Down line from " C)' to " B."

The Block Indicator for the Up line from (( B "

to " C " will be worked at " C," and that for the
Down line from <( B )) to " Ar" at " 4."

The Block In-

dicator is operated

by t\il/o keys (one

white and the other

red) which protrude

in front of the

inStrument. The in-

strument has three

positions : " Line
Cleat," " Line

Blocked " (normal)

and "Train ofl

Kuy Drsc. Line." When the

white liey is depressed, an indicatorin the face

of the inStrument exhibits the words " Line Clear."

When the red key is depressed, the indicator shews

the words " Train on Line." \X/hen neither key is

depressed, the indicator shou-s a half of each of the

indications juSt mentioned and is described as being

in the " normal " position. This in$trument is

called a " key-disc " Block Indicator.

Near the keys is a sliding wire clip bv rvhich

either of the keys (but not both together) may be

irStened in the depressed position.

I>age Eigbteer

" In the signal box a^t the other end of the
Se6tion " to which (' key-disc "
Block lnrli-

cator applic-s, is a " lievless disc " in$trument. The

two are eie€trically

conne€ted and ah.vavs

exhibit the sarne in-

dications as one


Applying to the
two "sections" for

rvhich the "kev-disc"

instfulrents are
operated at <c A2'
and " Cr" respe6t-

aivtetityB, "thheassigana"klmeavn- Ksvlrss Drsc.
less disc " Illock


Sometimes the key-disc and keyless-disc Block
Indicators for a se6tion are combined in a single


As a rule, there is also a telephone, or telegraph

in$trr,rment, between neighbouring signal boxes.

Page Nineteen

-!*-21d-._ '=.1)
ir o;r,,,



T of the communications
between signalmen, for sig-
nalling trains, are made by
beIl-codes. In addition, the
proper block indicators are
used for every train signalled.

A Train Register Book, with columns appropriatelv
headed, is provided in signal boxes, and signalmen

enter therein the times at which all signals are

forwarded and received.

One beat on the bell calls attention. This
signal muSt always be given before an)' other

signal, except where special inStru&ions are issued

to the contrarl. On receipt of this signal the
signalman immediatelv acknowledges it b,v

repeating it.

Except where special inStruftions are issued to

the contrarv, all signals are acknowledged by

repeating them.



We -,xzill take the three " Block PoSts " or Signal
Boxes, A, B and C, in successioa. On receipt

of the bell signal, " fs Line Clear ? " from A, B

has to satisfy himself that there is lo train in his
se&ion, i.e., between B and A, and that the line

is clear for a diftance of a quarter of a mile (thc

" clearing point ") i.r advance of his home signal.
If this is the cas:, B repeats the bell signal to

A's signal box and brings into use his (B's) key-disc

in$trument. \When a t:i.,a;in can be accepted from

A's. signal box, B after repeating the bell

signal, pegs the key-disc inStrument in his signal

box to sher.v " Line Clear," and his a&ion simul-

taneously records " Line Clear " ifi a keyless disc
inStrument in A's signal box. (The disc in$tru-

ment in the box in the rear, being keyless, is onh-

under the control of the signalman in the box in

advance). Permission is thus given for: the train tr>

be sent forward. It should be noted that B's distant

signal is ele&rically interlinked with his block

instrument so that " Line Clear " cannot be sent to

A unless B's distant is in the danget position ;

tdhi$istanetnasguariensStthitautn^til approaching B has B's
Clear ?'
B has obtained " I-ine

from C. A, after loweting his Starting signal

for the train to proceed, at once sends another

bell signal to B's signal box, " Train entering

Section." Upon receipt of this, B alters his key-

disc inStrument from " Line Clear " to " Trair

on Line," and this indication is also simultaneousiy

shewn in the keyless disc inStrument in A's box.

Page Twenty-one

B tl:en in turn offers tire train to C's box, and if thete

is no train in C's se&ion, and it is clear up to the
clearing point, C gives " Line Clear " to B,

pegging his kev-disc accordingly, which gives the

?' iit-,. Clear " indication on B's keyiess disc'

B may then lorver his signals. The operatjon as
between A and B's signal boxes is then repeated

between B's and C's signal boxes, and in each
parr of signal boxes aiong the line as the train


\X/hen the train arrives at B's signal box and is
found t<> be complete (which fa6t is known bv all

trains carrying a " tari " lamp, painted red for

daylight Purposes and shewing a red light at night,
on the laSt vehicle) B, having replaced his distant,

home, and starting signals tc) " danger," sends a
bell signal to A, " Ttain out of Se&ion," and
unpegs his key-disc inStrument from " Ttain on
Line," which then shews the normal indication
which means " Line blocked."

The same processes are gone thtough with
regard to trains on both " Up " and " Down 2'
lines respe&ively, and it will now- be realised hov'
these operations ensure that only one train can

be in one se&ion on the same line at one time'

Page Twentlt-two


IGNALMEN are assisted in tl-eir
duties bv numerous appliances

designed with a view to safe
working. One of the moSt im-

portant of these is, perhaps, what

is known as "Track Circuiting,"
of which the following is a brief description. A
length of raihvav is insulated to form a complete

eie&rical circuit bv having insulated fishplates on

the rail joints at cach end. The rails betvu'een these

insulated fishplates are joined together br. wire

bonds to enable the cleCtric current to be con-
tinuous. The ele&ric current is provided bv
means of a battery fixed at one end, and the

current is made to pass through a mechanism cailed

a " relay " at the opposite end of the length of
line tracl< circuited. In the signal box is provideC
an indicator which shews " Track Clear " rilhen no

train is on the track-circuited portion of line, and

is immediatelr.

altered to

" Track Occu-

piecl " as soon

as a train enters

rlpon the tracli

circuit. Bv

these means a

signalman is

able to tell
rvhen his line is " Clear " or " Occupied " br

Paqe Twen/)'-tltree

a ttain, even although the train on iine is entireiv
out of sight. It is also possiblc fot the lever
working the signal leading on to the track
circuited portion of line to be ele€trically locked
at danger when the track circuited portion of the
iine is occupied, so as to prevent an "All Right"

signal being given when the line is not clear.



grffi{PN theii continued e{lorts to increase the
ffi P& safety of raiirvay travel, the Great \WeStern
U\W[ Railway has inStalled at some points on its

syStemu-hat is

known as the


System of
Train Con-


u'ith Audible

SiEnals. The

primary ob-
ie& of this
svStem is to

give audible

u,'arning to an


Auorur StcNal IN ENctNu Cen' when his train

is approach-
i.g a diStant

Page Twenll foar

signal in the " or] " position, and, in the event of

this warning beinq disregalcied, aurcrmaticallv to
eppiv the brakes so as ro cnsure the train being

puiled up before it reaches the llomc Signal.

Another and cliStin&ir..e audibie indication is alscr

given on the engine when the diStant signai is " off."

The value of this lattel indication is that it faciiitates

the running of the ttatn when the semaphore

canflot be seen during fogs and snorvStorms. The

audible signals given are the souncling of a siree
indicating " $isnal O.r," and the ringing of a
bell indicating " Signal O.6i-."

The apparetus fixed on the permanent way for

operating th: audible signals on the engine is an

immovable ramp about 4o feet long fixed between
the running raiis, consiSting of a fteel inverted T-bar

mounted on a baulk of timber. The ramp at its
highest point is four inches above rail-ier.el. A

teiegraph rvire conne6ts the ramp with a srvitch in
the signal bt>x. This switch is attached to the lever

controlling the diStant signal. The apparatus on

the engine comprises a conta& shoe, an ele&ricallv

controlled bral<e valve and siren combined, and an

ele&ric bell. The contadt shoe is fixed in the
centre line of the engine and proje&s to within
z$ inches above rail-level. It is capable of being

raised verticallr., and, being in line with the raflp,

it will be seen that it is lifted r* in:hes whenevet
a rump is passed over, this lift opening a switch
attached to the contaat shoe. The mechanism
is adaptabic to doubie or single lines of railwar-.

Page TwenU-.fu,




N order that facing points mav bc held
firm1y in position, Facing Point Locks
and Locking Bars with Dete6tors are

provided at all Facing Points in passenger lincs.

The Facing Point Lock consists of a " Stretcher
Blade " ioining the two srvitch blades and pierce.d

with two holes, and aplunger wotked bv separate
Iever from the signel box, rvhich passcs through
one of the holcs in thc Stretcher Blade accorditg
to which dir:e&ion the Facing Points are sgt, and
this prevents any movement of the points until the

plunger is withdrawn. The movement of the
Facing Point Lock Lever is rendered compulsory

by the locliing, as the Home Signal cannot be
lowered until the Facing Point Locli lever has been



O prevent the signalmanv,'itl:clravving the
plunger rvhile a train is passing over thc

@@"1 points, a locking bar, 5o feet in length, to

cover the wheel-base of the ionge6t vehicle in use,
is fixed inside or outside the rails iudt to the rear of
the Facing Points. It is fixed on a series of cranks

ir such a manfler that urhen moved it rises and faIls,

and when rising would be Stopped by the flanges of

Prtgt Tnrn1,-six

any whcels, or if outsidc the rail by thc rvheels the m-

sch,es, passing over the points. The Locliing
Brr is rvorked bv the same lever as the Facing
Point Lock, and it is consequentiy impossible to
unbolt the points when a trin is standing or

passing over them.


S applied to Facing Points, these dete€tor

locks serve to dete& anvthing vrron{l
with the points in the event of the
Facrng Point Loc.k faiiing to a& and prevent the

signals governing such points being lowered until

the points are in corre& pc:ition.

The rodding conne&ing the Facing Point Lccl<
with the signal bo:i might eithet break or be out

of adjuStment, or the Stretcher Blade before
referred to might break. Anl' such contingencv

would be dete&eC bv the Dcte€tor Locli.
The Facing Point Lock is similarly dete6tecl to

ensur3 that the points are a€tually boltgd before thc

signal can be lowerecl.

The main idea of a Dete6tor Locli is that a

blade or some similar device worked in conne&-ion

with the points shell cross the path of another
blade or bhdes woriied in conncttion rvith the
Stop Signal, prote6ting the points, iri such m nnei

that should the points be out of adiuStmcn^t in anr'

respedt, the blade working off the points shall
form an obstru&ion to the pulling of the signal


Page Twenlt-seuen


ETONATOR " Pl^cer " Machines

worlied bv a lever from the signal bo^rxc,
bv means of which the signalman is able
to place two detonators on the rail in advance oi
the Home Signal. $7hen the Detonator " Placer "

lever is in the normal or forward pos.ition
(i.e., awav from the signalman) the detonators
are under cover in an iron caSting fixed close
to the ratl and slightlv below rall level, and

when the lever in the box is reversed, the detonatots
ar:e thrust forward upon the rail heacl.

These machines are used for the Purpose of

calling the attention o[ the driver in emergencies.

Page Twen4'+igbr


HE Great WeStern Railwav were

the pioneers in schools of
signalling. The firSt of such
schools rvas inStituted at Pad-

dington on N{onday, October
r9th, r go3, to give facilities to
members of the Staff to extend their knowledge of

railwav operating.

The illuftration given is of the model fixed in
the school. This model, which is z 5 feet in length,
is of a complete double line iun&ion with a
crossover road and refuge siding. Stanciard
fsaigcninagllinpgoinetquloipcmk,eniotciksinpgrobvaidr,edde, tien&colurdlioncglis^,
discs at the trailing points, catch-point in tefuge

The signais and conne&ions are interlocked in

a locking frame consi$ting of z5 levers, of which

, afe spare.

An engine and 5 vehicles rePresenting Passenger

$retopcrek,seanntidnq^fgl oeondgisneS, to4cktr,uaclkssoatnhdebfroallkoewYinagn
apparatus, were provided :-

(r) A Standard semaphore arm compiete with

lamp case, iamp sPettacles, .lamP and

arm ele6trical repeaters.

(r) A pair of ele&ric train staff inStruments

with occr-rpation kev box'

Page Twenti-nine

@ Detonator Placer machine.
I (+) Set of Permissive Block lnStruments'
(t) \Wooden Train staff and Tictr'et box ;

I thus enabling all manner of operations to bc


tT::$t:f, r.r,oor, have since been inaugurated

h^atveryattpernodveidncthiael centres. Over ,,ooo Students

le€tures at these schools, and sat

for the examinations at the conclusion of the




Page Tbirty

KEr-LY €y' rrrrv

LONDoN, E.C.2.



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