The Viaduct Works' Handbook

80 frames. In the engravings, A is the switch lever, B and C are the signal levers, and D is the transverse locking holt. The levers are provided with segmental tail pieces, of the same curvature as the cast-iron frames, and the frames have a slot at one end to allow the tails to pass through. They are also slotted transversely, and a sliding bolt works through the slots, and is made capable of alter- nately locking the switch lever or the signal levers. The tail pieces prevent the transverse movement of the locking bolt, except when the levers are in the right position for being locked, as the tails lie along the frames and cover the holes in which the transverse locking bolt works. In the position shown in the engraving the signals in connexion with the signal levers are at danger, and locked by the locking bolt, and the switch in connexion with the switch lever is open. The locking bolt is prevented from being moved by the segmental tail piece of the switch lever, its tail piece lying along the frame, and covering the locking bolt hole, as we just stated. Thus the signals are locked to danger; whilst the switch is free to move as may be required, allowing shunting to be carried on without interfering with the signals. If the switch lever with its tail piece is now moved over, it will leave the slot in which the locking bar works clear, and this can then be moved so as to, at the same time, lock the switch lever, and free the signal levers. If the signal levers are now shifted into the position previously occupied by the switch lever, their seg- mental tail pieces will in their turn lie along the cast-iron frame, and will cover the hole in which the locking bar works, preventing it from being moved, and effectually locking the switch lever to the “all-right” position, whilst the signal levers remain “all-right.” To get the levers back into their former position, the movements are reversed; the signal levers are first put to danger ; the locking bar is moved in front of the signal levers and locks them, leaving the switch free to move as before. By this it will be seen that it is impossible to move the switch lever until the signal levers have been first locked to danger ; neither can the signal levers be moved until the switch lever is locked to the “ all-right” position. This prevents the possibility of any accident arising from a mistake in working the signals. As will be seen, this arrangement is possessed of great simplicity in the working parts, and requires no protection from the weather;