[Figs. 514, 515, and 516] are sketches of an electric train-staff instrument which has been very largely adopted on single lines, both at home and abroad.
In a similar manner to the block-telegraph instruments for double line, the electric train-staff instruments have each a bell or gong by which the adjacent signalmen can communicate their calls and answers in accordance with a regulation code. In the signal-cabins of the intermediate stations two instruments are required, one for the staffs belonging to the section to the left of the cabin, and the other for the staffs of the section to the right. At a terminal station only one instrument is required.
The head of the instrument contains the electrical and mechanical locking apparatus which controls the withdrawal of a train-staff, or is acted upon by its insertion. The circular name-plates and pointers, together with the galvanometer in the centre, serve as indicators to guide the signalmen in carrying out the various operations. The staffs usually consist of thin steel tubes, solid at the ends, with metal rings fixed upon them, as shown in the sketch, the number and position of the rings varying according to the section or pair of staff stations to which they belong; this difference in the rings effectually preventing the possibility of one set of staffs being used or inserted in either of the instruments of the adjoining sections. The staffs rest normally in the long vertical slot A, with the rings fitting in vertical grooves, which prevent the removal of any staff except by passing it along the curved slot BC, and out by the
opening D, of large diameter. The electrical and mechanical locking apparatus is placed at the curved slot, and until the locking-bolt, which stands across the passage of the curved slot, be lifted by the joint operations of the signalmen and their instruments at both ends of the section, no staff can be withdrawn. When the instruments are standing in their normal position of “staffs in,” the signalmen can arrange between them to withdraw a staff—say either from the NORTH cabin instrument or from the SOUTH cabin instrument of the section, but only from one of them; and the act of taking out that staff automatically locks both instruments, and prevents the possibility of taking out any other staff from either instrument until the staff already removed is restored and inserted in one or other of the instruments. From the above description it will be seen that the electric train-staff instrument provides for the safe working of two or more trains proceeding, one at a time, in the same direction over a section of single line, each one being supplied with a train-staff, which must be handed over at the end of a section before another staff can be issued for a following train. Should the train-staffs accumulate in one instrument, in consequence of more trains running in one direction than another, a re-distribution of staffs is effected by the authorized persons according to fixed regulations.
In the diagram sketch, [Fig. 517], a piece of single line is shown divided into sections or blocks, with loops or passing-places at the stations. At the station E a train-staff taken out of the instrument F serves for the section up to the instrument L at the station H; and on the train-staff is a key which will open the detached locks on the points of the small intermediate station, G, as described in [Fig. 507], in connection with the working of detached locks. At the station H the engine-driver receives another staff from the instrument M, which takes him to the instrument N at station K, and in like manner on this staff is a key which will open the detached lock on the colliery siding points at I. At stations H and K are shown loops, or short pieces of double line, with platform to enable an UP train to cross or pass a DOWN train. The distance apart of the electric train-staff stations will depend greatly upon the number of the trains, and for a frequent train-service it may be necessary to have the instruments at every station, whether large or small. The electric train-staff is of great advantage in the working of
ballast or construction trains, as a staff may be taken out of the instrument F at station E, which will give possession of the section as far as station H, and when the ballasting operations—which may be very near to E—are completed, the train can return to E, and deliver the staff again to the instrument F, instead of having to run the entire distance to station H. Although carrying a train-staff, the engine-driver must approach stations cautiously, and obey the fixed signals in the usual manner.