Model railroads - model railways and trains > Train signals

Train signals

Train signalsThe signals on a model railway can be disposed as a glorified form of ornamentation, or can be correctly arranged as a definite means of controlling the train service. In the former case a few signals are located at strategic points near the track, and manually operated by a lever at the bottom of the signal post. This is not good practice, and a great deal of the interest and instructional value of the model is lost.

When the railway is permanently installed, all the signals and points can be operated from properly positioned signal cabins, and it is quite feasible entirely to control the trains from the signal cabins when electrical devices are installed. Between these extremes it is practicable to arrange for a combined hand and automatic control system, or to make it as complex or as simple as circumstances and personal inclination may dictate.

Signals are quite cheap to buy ready made, or can be constructed at home for a small sum; alternatively, a middle course can be followed and prepared sets of parts purchased and assembled. Signals are usually controlled by a small hand lever on the base, or by wires from a signal cabin. The usual arrangement of a single-arm semaphore signal is shown in Fig. 7, where it will be seen that the signal arm is normally held at danger, or "stop," that is, in the horizontal position, by the lever and weight at the base of the post.

When a lever is pulled in the signal cabin a wire connecting from it to the counter­weight lever on the signal post is pulled downwards, and the connecting rod between the lever and arm is pushed up, thus pushing the signal arm to the "clear" position, that is, in a downwards sloping direction. When the the cabin lever is put back to normal the counter weight falls and the signal arm returns to danger. The connecting wires are guided in any convenient way by means of small screw eyes, or through proper guide-posts with pulleys. Other levers in the signal cabin are connected by thin metal rods to the points and crossings, which can by their aid be moved in either direction.

These rods are guided in a similar manner to the signal wires, but bends and curves are traversed by the use of cranked arms pivotally mounted on bases screwed to the baseboard of the track. On real railways the levers in the cabin are interconnected in such a way that it is impossible to move any lever which might conflict with another; for example, it would be impossible to move any given point-lever until a controlling signal ahead of it had been set to "danger." Space limitations forbid more than passing mention of this most intriguing aspect of model railway working.

Signal arms are not always mounted singly on one post; sometimes there are two arms on one post, the lower arm having a V-shaped notch in the end and acting as a "distant" or warning signal, indicating to the engine driver the need for extra caution or a reduction in speed, as a signal not far ahead is at "danger."

Two or more signal arms are not mounted on one post to control two lines of track except occasionally for an "up" and "down" single line the practice is to mount each arm on a separate post ; but often one of them is shorter and supported on a platform or bracket attached to the main post. Such an arrangement is known as a bracket signal.

A development of the idea is the gantry, such as that in Fig. 42, where two sub-stantial uprights carry a beam over several tracks, and the signal posts are fixed to the beam over their respective roads. These signals are, however, actuated in the same manner as for a single post except for the use of rods and bell cranks on the gantry, the various wires being connected near the bottom of the gantry posts to their respective levers or bell cranks.

The levers employed in the cabin can be elaborate affairs with interlocking bars, but a very simple arrangement, as shown in Fig. 43, is serviceable, inexpensive and well within the constructive ability of most amateur railway engineers. The lever frame consists of a wooden baseboard with uprights at each end, their upper parts connected by wooden longitudinals. A sheet of tinplate slotted and notched for the levers covers the top part, as shown in the diagram. The levers are made from umbrella ribs notched for the connecting wires and pivoted at the bottom in the same way as an umbrella. The lever frame is fastened to the baseboard of the railway, and connections made as before described. The signal cabin is separately made and simply stands in place as a covering to the levers.

An idea of a suitable signalling system for a continuous single line with a loop at a station is shown in Fig. 6, and comprises a bracket signal controlling the main and loop line. Two single "home" signals control the approach to the station, and the remaining pair, known as "starters" regulate the departure of trains from the station.

Signals should always be so placed that the distance between them is sufficient to accommodate the longest train on the system -a space technically known as the train berth. This is an important rriatter, as should the end of a train overlap the previous signal point or crossing it would necessarily block it and upset the operation of the system. For example, the distance from A in Fig. 6 to the inner home signals is the train berth, but if the train were much longer, then it would foul the points and the bracket signal would be blocked, or an accident might easily occur.

The signalling of a goods yard or siding is often controlled by small signals known as ground signals, because they are situated low down near the ground. One example of a semaphore-type ground signal, Fig. 45, shown in the "off" or "clear" position, indicates how such a signal is employed. It is always placed to face a train coming into the points, and the green light, or depressed semaphore arm, indicates that the point is set for the train to turn off the main line; but when the red light shows, or semaphore arm is up, the point is clear for the passage of a main-line train.