swiTcH ES Al)N SIGNALS, RAILROAD. Roan Staxsi.s.—The practice has become quite in favor of the use of semaphore signals for the purpose of protecting the movements of trains, as the semaphore most easily lends itself, through the simplicity of its form, to all of the many requirements of traffic. The most prominent forms of the semaphore are the home, distant, and dwarf signals, all of them modifications of the same idea. Home home signal. Fig. 1, consists of a blade about 5 ft. long, with a square end, mounted on a post about 23 ft. above the rail level. It is usually painted red on the side toward approaching trains which it governs, and white on the other side. On double track, right-hand running. the blade points to the right ; on double track, left hand running, the blade points to the left in some cases, and in others to the right. When in a horizmital position, or showing a red light at night, it indicates danger or stop. When inclined at an angle of from fi0 ' to W°, or showing a white light at night, it indicates safety, or go ahead. It is only used in connection with movements in the direction of the traffic on the main track, cr to control movements from the main truck to facing point diverging tracks, or facing point cross-overs.
Distant Signal.—The distant signal, Fig. 2, consists of a blade about 5 ft. long, with a forked end, mounted on a post about 25 ft. above the rail level. It is usually painted green on the side toward approaching trains which it governs, and white on the other side. Its location with regard to the tracks and the direction in which it points is the same as that of the home signal. When inclined at an angle of from 60 to 91)', or showing a white light at night, it indicates that the home signal in connection with which it works is in the safety position, and that trains may proceed with speed. When in a horizontal position, or showing a green light at night, it indi cates that the home signal is probably at danger, and that trains must proceed with sufficient caution to enable them to stop before reaching the home signal, if necessary. It is used always in connection with a 110111e signal, and serves only to show the position of the home signal, which con trols movements over the fastest and most important route.
Law," dwarf signal, Fig. 3, consists of a blade about 12 in. long, with a square end. mounted on a post about 2 ft. above rail level. The painting of the blade, its relative positions of danger and safety, and the position with regard to the tracks are the same as described in the ease of the home signal. It is, in fact, a diminutive home signal, but is used only to control movements in a reverse direction on double track. and for move ments from side track to main track, and from side track to side frac'.:.
The great advantage of the semaphore form is, that identically the same signal can be used for both block and interlocking purposes.
IlLocE SIGNALS.—The question of blocking a piece of track has resolved itself into the two principles of time and positive block signaling. The time signals are most prominently represented by the Fontaine signal, which consists of a track instrument controlling a dash-pot and the operation of some clock-work which may be set to run any desired number of minutes after the passage of a train. The two great objections to this method are : First, that it is not at all certain that a train has passed out of the block simply because the hand indicates that it has been gone a certain number of min utes; and, second, that the indications of the signal are visible at only a short distance.
Positive Block Systems are to be divided into two classes: First, that class which is op erated by men stationed in cabins a certain distance apart, but having electrical com munication with each ether, and, second, by those signals which are controlled entirely by the presence of a train in their section, or automatic sig nals. The most successful of
the first of these two methods is the Sykes system. The Sykes system is the applica tion to an ordinary block sys tem of certain electrical and mechanical devices which in sure the fact that the signal governing the entrance to a given block cannot be cleared until the last train which en tered that block has passed out of it. and the operator at the end of the block has given his consent. These results are se cured by the use of a Sykes lock instrument and an interlock ing relay, which are illustrated in Fig. 4, and a very short in sulated section of track, with proper metallic circuits con necting the same, together with a bell wire or telegraph line for communication between ad jacent block stations. The Sykes lock instrument is lo cated in the operator's office, immediately over the lever by which he controls his signal. The interlocking relay is lo cated in any convenient place, usually in a closet. The in sulated section of track is located at the entrance of the block, and is usually about 60 ft. long. The bell-wire push buttons are located near the signal lever and the Sykes instrument. The operation in practice is as follows, everything being normal ; levers home, signals at danger, and tracks unoccupied. If the operator desires to allow a train to enter one of the blocks which his signals control, he notifies the operator next in advance by his bell wire or telegraph line ; the advance operator, if everything is all right, responds by " plunging" on that instrument which connects with the signal lever of the man in the rear. This has the effect of releasing the signal lever at the original block station.
The only function of the Sykes system so far alluded to is that by which one operator, en request of an adjacent operator, may plunge " and thus release the latter's signal lever.
The additional and important function of the combined apparatus is to prevent an operator from plunging a second time until the train for which the preceding operator desired to clear his signal has passed into, through, and out of the block in question. This result is secured by the combined action of the Sykes instrument, the interlocking relay, and the insulated section of track. When an adjacent operator "plunges" he passes a current through the electromagnets of his neighbor's instrument, and in that manner releases the signal lever.
When the plunger, however, is released and forced by a spring at its rear out of its original position, a rod is released, which drops down in front of the plunger and prevents it from being forced in again until the signal lever above which it is situated is reversed. The func tion of the insulated section of track is to automatically restore the interlocking relay to its normal position, which has been disturbed by the act of plunging. This method of block signaling has been applied to a limited extent in the United States. It is, however, extremely expensive to operate, and in its simple form is somewhat objectionable from the fact that if a train should leave the main track between any two block stations it would be necessary to send the following train past a block station with a hand signal, for the reason that the towerman in advance would be unable to release the man in the rear more than once between the passage of any two trains.