Railway Construction

by William Hemingway Mills

[Fig. 506] shows the arrangement applied to a double line with the outlying siding turning out of the UP main line, the points lying in a trailing direction for the running trains. Before the special and only key can be withdrawn from its seat in the interlocking frame of the signal cabin, all the UP main line signals must be set to danger, and cannot be moved from danger until the key is restored to its proper seat again. When the key is removed from the signal cabin, it can be taken to the ground frame at A, inserted in the key opening, and by turning it partly round, will release the bar which locks the levers of the facing point bolt-lock and the points. When these two levers are free the points can be opened, and vehicles moved into or out of the siding B C, but the special key cannot be withdrawn from the ground-frame A, until the points and facing point bolt-lock are put back again into their normal position for main line working. When the operations at the siding are completed, the special key can be removed, and taken back to its proper place in the signal-cabin, and ordinary working be resumed.

[Fig. 507] shows the application of the detached locks on a single line, and is a sketch of a portion of railway on which there is a small station B, with a goods siding F G, where the traffic is too small to require anything more than ground frames and detached locks. An engine-driver before leaving the station A, receives a train staff, which gives him possession of the line as far as C, including of course the intermediate station B, and this staff he must carry with him and hand over to the signalman on his arrival at the end of the section at C. At each of the points D and E is placed a two lever ground frame, similar to the one shown in [Fig. 506], and attached to the train staff is a key, which will operate either of the two ground frames, but only one at a time, as the key must be inserted before the levers can be moved. When the train is proceeding in the direction from A to C, it will be more convenient to shunt vehicles into or out of the siding F G, by means of the points E, but when proceeding from C to A, the points D will be more convenient.

Whichever of the points be used, they must be set, and bolt locked for the main line before the train staff and its key can be withdrawn from the ground frame and restored to the engine-driver. As the siding is trapped at F and G, it is impossible for any vehicles to be moved out on to the main line except through the medium of the train staff and key. The same arrangement of detached lock is equally available for a single siding with only one set of points.

Electric Repeater.—It will sometimes occur that on account of a curve or other obstacle, the arms and back lights of a distant or other signal cannot be seen from the signal cabin, and it is necessary to introduce an electric repeater. This little instrument consists of a miniature semaphore signal fixed in a metallic box with a glass front, and placed on a stand about a foot above the floor level immediately in front of the signal lever for which it is intended to serve as an indicator. Like the signal proper, the normal position of the miniature semaphore is at danger, but when the signal lever is pulled over in the cabin, the rod that pulls down the arm on the signal post effects a contact with an electric circuit which lowers the arm of the miniature semaphore at the same moment that the signal arm proper is lowered, and gives visible indication in the cabin that the signal is working. [Fig. 508] is a sketch of one form of electric repeater.

Detonators or fog signals are largely used in foggy weather and snowstorms, when the out-door signals cannot be seen from an approaching train. At such times the atmosphere is so dense, and the surrounding objects so obscured, that an engine-driver is totally unable to distinguish the usual landmarks which guide him on the approach to a station or semaphore, and he might easily pass by a signal unless he received an audible signal to indicate the position of the one that is invisible. Detonators are usually made in the form of a circular tin or metallic case about two inches in diameter, and three eighths of an inch thick, with soft metal clips on opposite sides for bending over and securing to the rails. The case is filled with detonating powder, which is crushed by the first wheel passing over it, and explodes with a loud report. It is customary to use these detonators in pairs placed a short distance apart in case one of them should fail to explode.

Fog-signalling regulations vary on different railways, but

the arrangements are generally carried out somewhat in the following manner. During the prevalence of a fog or snowstorm, a fog [signalman] is placed near each of the signal-posts to be protected, and is supplied with a hand signal-lamp, hand-flags, and a packet of detonators. So long as the arm of the signal-post at which he is alongside stands at danger, he must keep two detonators on the rail of that line which the signal controls, and also show a RED hand-signal (hand-flag by day, and hand-lamp after dark) to the approaching train. When the signal arm is lowered to show that the line is clear for the passage of the train, the fog signalman must remove the two detonators, and show a GREEN hand-signal (flag, or lamp) to the approaching train. When an engine driver hears the report of a detonator crushed by his engine, it is his duty to shut off steam immediately, and bring his engine to a stand, after which he must proceed very cautiously, until he receives further signals by hand or otherwise, or receives the line-clear signal to continue on his journey. Detonators are also of great service both in fine or bad weather, in cases of a wash away, a failure of works, or obstruction on the line, when a hand-signal may not be seen, but a detonator must be heard.

Mechanical Gates.—Mechanical gates, worked and controlled from the inside of a signal-cabin, are now very largely adopted for public road level-crossings instead of ordinary hand-gates, opened and closed by a gateman walking from side to side of the line across the rails. Being worked from inside the cabin, they remove all possibility of the gateman being struck by a passing train; they move simultaneously, and can be opened or closed in very much less time than hand-worked gates, which have to be moved one by one, and being interlocked with the signals, the mechanical gates cannot be placed across the lines of rails until the train-signals in each direction are set at danger. When set for either train traffic or public road traffic, the gates are held firmly in position by metal stops, rising out of cast-iron boxes lying flush with the ground, and worked by a separate lever in the signal-cabin.

Assuming the gates to be set for train traffic, and it is desired to open them for the public road traffic, the first operation will be to pull over the levers, and raise the signals in each direction to danger, and thus release the stop-lever, which can then be pulled over, to lower the gate-stops and allow the gate-winch to be turned, and the gates moved round into correct

position. The stop-lever must then be set back to raise the stops and hold the gates secure. The train-signals will be retained at danger by the interlocking gearing, and cannot be lowered until the gates are set back again across the public road, and the gate-stops raised.