The Working and Management of an English Railway/Chapter 6
CHAPTER VI.
Telegraphs.
Telegraphy might not inaptly be termed "the hand-maid of steam," for it plays an important part in almost every operation connected with railway working. By its means the trains are started from the stations and conducted safely from point to point throughout their journey; the signalmen who regulate their passage are placed in an unbroken chain of communication one with the other; the nature of the train and its destination, and the fact of its punctual running, or otherwise, are flashed ahead from signal cabin to signal cabin as it speeds on its journey; while the faithful telegraph warns the signalman if his signals are not acting freely or if his lamps are not burning brightly. By telegraph the marshalling of goods waggons, the loading of trains, and the movements of empty waggons are intelligently controlled, and the whole business of the railway is carried on with a promptitude and despatch that could not otherwise be attained. In short, the uses of telegraphy as applied to railways are so numerous, and so diversified, that it would be a formidable task even to catalogue them, and one still more formidable to attempt their description in detail.
In the earlier days of railways, and before electricity had been brought to bear upon their working, the only means for providing for the safety of the line was by erecting fixed signals at certain points, and keeping them at "danger" for a specified time after the passage of one train, before another was allowed to follow. Obviously, under a system of this kind, only a very limited number of trains could be dealt with within a given period of time, and as the traffic increased and trains were multiplied it was found quite inadequate, and some better plan had to be devised. The electric telegraph had already been utilised for transmitting from station to station the times of departure of the trains, and about the year 1853 Mr. Edwin Clark introduced the absolute block telegraph system, by means of which the number of trains which may be passed over a given section of line, with perfect safety, may, by the multiplication and shortening of the sections, be said to be almost unlimited.
Mr. Clark's apparatus took the form of what is known as the "three-wire" block telegraph for double lines, and this form has held its own up to the present time—that is, there is one wire with an instrument at each end of the section for the up line, the same for the down line, and one wire for the bell circuit, the latter being common to both lines. Besides this, there is in use a "one-wire" system, also for double lines, but which shows only two positions of the indicator instead of three. The advantages claimed for the "one-wire" system are (1) that on railways where there are four lines of rails only two wires are required, instead of the six that would be needed under the "three-wire" system; and (2) that where the sections are long, the "one-wire" system is less expensive, although in sections half a mile or less in length the "three-wire" proves to be the cheaper of the two, for the reason that, although the wires cost more, the instruments cost less. In addition to these, there is a single-line block telegraph, which is worked by two wires, one for the block instrument and one for the bell.
All the different kinds of block telegraph apparatus may be worked either on the "absolute" or "permissive" system, according to the requirements of the case
Fig. 12.
Three-wire "Tell-tale" Block Telegraph Instrument.
and the regulations in force; the meaning of the "absolute block " being that there can only be one train in a given section at the same time, while, under the "permissive" system, there may be more than one train in the section. Prior to the year 1879 it had not been found practicable to work with the block telegraph through busy station yards, and the passage of the train was, in such cases, regulated by a special code of electric bell signals, but this plan was very unsatisfactory, and the difficulty was at length met by the introduction of the "Tell-tale" instrument. This is really a form of block telegraph, worked under "permissive regulations"; but there is a special apparatus, by means of which a reminder is given to the signalman at a station of the number of trains there are in the section in the rear, (See Fig. 12.)
A block instrument of any kind consists of an indicating dial and a commutator or handle. The indicator is attached to an axle, on which a magnet is centred, being suspended either within, or in close proximity to, a coil of silk-covered wire, and deflected to the right or left according to whether a "negative" or "positive" current flows through the coil. The commutator is so arranged as to alter the direction of the current at will. The bells are generally of the single-stroke type, and are used for calling attention, and for giving the complete code of signals descriptive of the nature of trains, as agreed to by all the railway companies.
The normal state of the indicator of the three-wire block instrument is vertical ("Line closed") when no current is flowing; the deflection when a negative current is flowing is to the right, meaning "Line clear," and with a positive current to the left, indicating "Train on line." (A set of the three-wire apparatus is shown in Fig. 13.)
Briefly the modus operandi is as follows:—Attention is first called on the bell, and then station A will give to station b what is called the "Be ready" signal, consisting of a certain number of strokes of the bell, varying so as to indicate the nature of the train. The man at station B, if the previous train has passed his cabin and he knows the section between A and B is clear, repeats this signal. The train is then despatched from A, the signalman at A gives the signal "Train on line," the signalman at B acknowledges this by moving his own indicator and the one at A to "Train on line," and at once gives the "Be ready" signal to C, and so on throughout. As soon as the train has passed B the man at B moves his own indicator and the one at A over to "Line clear," and
Fig. 13.
Set of Three-wire Block Telegraph Instruments with Bell.
upon this being acknowledged by A the indicator is left vertical, signifying "Line closed," and thus the operation has been completed so far as that particular train and that particular section are concerned. Of course it will be apparent that if this system is properly carried out, it is an absolute impossibility for two trains to be between A and B at the same time.
A new form of instrument devised by Mr. G. E. Fletcher, one of the Company's officials, has been recently introduced on the London and North-Western Railway, by means of which the whole of the apparatus shown in Fig. 13, viz., the indicating dials for both up and
Fig. 14.
Fletcher's Combined Block Telegraph Apparatus and Bell.
down lines, and the bell, are combined in one instrument. (See Fig. 14.) The novelty lies, not so much in the combination, as in the mode of actuating the indicators, the advantages claimed for the invention being (1) a reduction in cost, and (2) considerable economy in space, which is a great desideratum in the smaller signal cabins.
The one-wire system differs from the three-wire, in so far as the indicator of the instrument is moved over to the different positions by a momentary current, and is
Fig. 15.
One-Wire Block Telegraph Instrument.
afterwards held there by induced magnetism, the wire being left free for any succeeding signals. The mode of working is about the same, only that there are but two positions, viz., "Line clear," and "Train on line," and no vertical position, (See Fig. 15.)
The "Tell-tale" instruments are somewhat similar in construction to the three-wire, the difference being that the commutator is provided with a revolving disc, lettered "line closed" (indicator vertical), "line clear," and "train on line," and Nos. 2 to 6 on the remaining five sections of the disc. Up to the point of getting one train in the section, the operation is exactly the same as with the ordinary three-wire instruments, but as each additional train is admitted into the section a corresponding disc is brought forward; and also as the trains pass out of the section the same disc is moved back, section by section, until the line is again clear, and the indicator is left at the normal position of "line closed."
It only remains to say that the single-line block telegraph is worked by a similar kind of instrument to the three-wire (absolute biock), only there is a commutator at each end, which is blocked over by the station towards which the train is running, keeping the indicators at both signal boxes at "train on line" until the arrival of the train, when they are again released.
Important as the block telegraph is, it is, of course, only an auxiliary to the working of the outdoor semaphore signals, without which it would be impossible to conduct the traffic; and the maintenance of these in a state of perfect efficiency has much to do with the punctual running of the trains. It not infrequently happens that a train will run from London, say, to Liverpool or Manchester without a single "danger" signal being exhibited, or, in other words, that there is a clear road throughout. This efficiency is to a great extent secured by the application of electricity. As is well known, expansion and contraction of the signal wires take place owing to change of temperature, the former preventing, by the elongation of the wire, the pulling of the signal "Off," and the latter, by shortening the wire, preventing the signal from getting properly "On." It is essential that the signalman should know the exact state of his signal, although, by reason of curves or other circumstances, it may be out of his sight, and, in order that he may be so informed, electric signal repeaters have been introduced, the function of which is to send currents from the signal-post, by means of
Fig. 16.
Electric Signal Repeater and Light Indicator
electric contacts, to a miniature signal-post fitted in the repeating instrument at the signal-box. Up to about three years ago the arm was only shown "On" by current, and "Off" by gravity, but since that time it has been found possible to show "On" and "Off" by current and "Wrong" by gravity; and, in addition to this, the apparatus now in use shows "Light in" and "Light out," one wire, only, being required for the five indications. (See Fig. 16.)
There are many other electrical appliances used in railway working, such as "Train-starting indicators," from platform to signal-box, to inform the signalman that trains are ready to start from certain platforms; "Route indicators" for junction cabins, by means of which signalmen are advised beforehand of the route an approaching train is required to take where the roads diverge; "Vehicles on line" indicators, to show the signalman when a line is fouled by a vehicle being detached from a train and left standing on the line; "Shunting indicators" for station yards, and a variety of other electrical apparatus of a similar character. There is, however, one special appliance which merits a somewhat more detailed description, viz., the "Electric lock" for sidings. This apparatus has been designed to lock and unlock sidings at a distance from the signal-box too far to be worked by rod and lever. There is an instrument at the signal-box, and another at the siding, each containing an electro-magnet capable of actuating an armature which constitutes the lock, fixed in connection with the locking bars of the signal frame. The normal state of the apparatus is "Signals at signal-box unlocked, and siding locked," by the constant flow of a current of electricity through the electro-magnets. If a train, arriving at the signal-box, has to call at the siding, the breakman, or person in charge, intimates the fact to the signalman, who, by the insertion of an ordinary carriage key into the electrical apparatus, disconnects the wire. This has the effect of locking the signals at the signal-box and unlocking the lever at the siding, and the key can only be inserted when the signals are at "Danger." There is a code of bell signals drawn up for the guidance of the men, but it will be sufficient to say here that when the train has finished its work at the siding and is ready to go forward, the breakman communicates this by bell signal to the signal-box, and at the same time, by the turning of a button in the front of the instrument at the siding, renews the flow of current, thereby again locking the siding lever and unlocking the signals at the signal-box. The security of the system lies in the fact that, whatever operation takes place at one end, it is only in the hands of the person at the other end to reverse it.
On all the more important main lines the signalmen are enabled to converse one with the other, either by means of the speaking telegraph or of the telephone, which latter is found to be a great acquisition in facilitating the working of the line, more especially through busy station yards.
The mileage of telegraph wires upon the London and North- Western system for purely railway purposes is 11,238 miles, in addition to which there are 6,877 miles of wire appropriated to the use of the Post Office, making up an aggregate of 18,115 miles of wire, while the number of battery cells in work for carrying on the telegraphic business of the Company amounts to 100,323 cells. With such an extent of wires, and so large a number of instruments and batteries in use, it becomes of great importance to provide for a complete and perfect system of maintenance and supervision; but the staff which has to be employed for the purpose is not so extensive as may at first sight appear to be requisite. A line of telegraph has this advantage over a line of railway, that the person charged with the duty of maintaining it in a proper state of repair need not walk from end to end of it in order to detect any fault or weakness. A man can stand at one end of a line of telegraph, hundreds of miles in length, and, by exchanging signals with the other end, may satisfy himself that the entire circuit is in efficient: working order. Thus the work of inspection and maintenance of the extensive system of telegraphs in operation on the London and North-Western Railway is carried on by nine inspectors, three sub-inspectors, and forty-eight "linemen." The line is divided for maintenance purposes into nine sections, each of which is in charge of an inspector; and the first daily duty of each inspector is, at a stated time previous to 8.0 a.m., to test all the more important circuits under his charge, and ascertain if they are intact and working efficiently, and the results of this inspection are telegraphed at once to the office of the chief telegraph superintendent, in Manchester, so that that officer has before him, by 9.0 a.m. each day, a condensed report of the exact state of the telegraphic communications over the entire system. By these means it is known where the services of the linemen are required, and some of them are told off to execute necessary repairs, while others undertake the duties of cleaning apparatus, and refreshing batteries. As a general rule, the batteries are cleaned, or refreshed, at fixed intervals varying from ten days to a month, according to the amount of work they have to perform; but it is the duty of any operator who perceives, by the failure or weakness of the indications, that his battery power shows signs of exhaustion at once to intimate the fact to the inspector in charge of the district, and to report any neglect or delay in attending to it to the chief telegraph superintendent.
Electricians are said to be somewhat divided in opinion as to the relative advantages of iron and copper wires for transmitting the electric current, but for over-head wires the London and North Western Company prefer galvanised iron wires, as having greater tensile strength and superior powers of elongation and contraction, so as to allow for a considerable variation in temperature. The gauges of wire used differ according to circumstances, but the wire chiefly employed has a standard diameter of ·171 inch with a minimum tensile strength of 1,200 lbs., and is subjected to a torsion test of 20 twists in 6 inches. The average life of the wire varies very much according to locality. For instance, in the vicinity of chemical works, as at Widnes and St Helen's, the wire corrodes and requires renewal in about three years, while, in the pure atmosphere of the island of Anglesey, there are wires that have been in use for five-and-thirty years, and which recent tests show to have been very little impaired, whether as regards conductivity or tensile strength; under ordinary conditions, however, the average life of the standard wire is about 10 years.
As regards battery power, the Company use, for speaking telegraph circuits, three wire block telegraph circuits, and electric locks, the Daniell Sulphate Battery; for bell wires the Leclanché Battery; and for signal repeaters, Fuller's bichromate battery.