Except in automatic blocking, the signals are operated from signal towers, built beside the tracks, by means of levers resembling the reverse lever of a locomotive, which are con nected with the signals by wires or pipe. If wire is used, there should be two lines for each signal, one for pulling it to "danger" and the other for pulling it back to "safety." To ensure the signal being set at .°danger" in the event of the breaking of the wires, the blade should be provided with a counterweight. Usually there is a lever for each signal, but in some in stances, as at an interlocked point, one lever may be used to operate several signals, by means of a device known as a selector.
Manual In manual blocking each signalman controls the block signals at his station and, in the absence of other means, the code signaling between the block stations is done by means of electric bells. The more important lines use an indicator, giving a vis ual indication of the condition of the block. On the dial of the indicator appear the words "line clear," "train on line" and "line closed." By placing the hand of the indicator over any of these formulas the instrument at the other end gives a like indication. The instrument is not interlocked with the outdoor signals. The term "line closed" means that the instrument is out of service as there is no traffic in the block for the time being. This is the normal position of the pointer, giving a negative indi cation. In many of the larger signal towers the indicator is equipped with small red electric lamps which light up with the passing of trains into the block and remain alight until the block is again clear. In the Mozier manual system the passage of a train into a block is controlled by the train dispatcher, no train being allowed to enter a block without his permission. When a train enters a block the dispatcher is notified of the fact by wire and he then directs the signalman at the station in advance of the train what signal to display to the train on its arrival there.
Controlled Manual In con trolled manual blocking the manipulation of the outdoor signals at the entrance to a block is controlled, electrically, by the signalman at the block station in advance. In what is some times termed the automanual system there is at each block station a track circuit of at least two or three rail lengths, which is used in actuating an °electric slot" for automatically replacing the home signal to "danger" when the rear end of a train passes that signal. The
locking instruments are generally placed in front of the signalman and over the levers with which they operate. Each block station has one of these instruments for each block. the two instruments at the opposite ends of a block being connected by an electric circuit. The code signaling between the stations is sometimes accomplished by bell.
In some instruments the signal-operating levels are normally locked, except when un locked by the signalman at the station in ad vance, while in others the signals are locked only when the line is blocked by a train, thereby leaving them free to be thrown to either "danger" or "safety," as may be de sired, when the line is clear. In some instru ments the electrical apparatus and the levers are connected electrically; in others they are connected mechanically.
The "electric slot" is an appliance for auto matically cutting out the block signal from its actuating lever, and is used to automatically return the signal to "danger" behind a train. It is actuated by a track circuit, as heretofore mentioned, placed ahead of the signal, and forms a removable connection between the sig nal counterweight and the signal rod, which connection, if removed when the signal is in the "clear" position, permits the signal to re turn to "danger" by force of gravity. The signal cannot again be placed at "safety" until the signal lever has been placed in its normal (€clanger” position. This device, therefore, prevents a signalman, after having allowed a train to enter a block, from carelessly and prematurely releasing the signal at the rear station while a train is in the block.
To ensure absolute safety for the main track in a block, including the territory for at least 1,000 feet ahead of the home signal at the station in advance (or a greater distance on a down grade), the main track switches at such advance station (including those within the 1,000-foot limit), and all outlying switches in the block, must be electrically interlocked with the block station in the rear, so that the signals at the station in the rear, which con trol the entrance to the block, cannot be placed at "clear" when the main track is occupied, or is fouled by a train on a side track, or when a main track switch is thrown for a side move ment, or a main track "back up)) signal is set for a backward movement. This system ap plies only to the operation of trains under the absolute block system.