Single Line Instruments

Described below are more of the many forms of Single Line Instrument that have been used by the Southern railways over the years. Once again, this is more of an informative introduction than an in-depth tutorial. These notes are a brief reference to the operation of the Instruments, there are other requirements to fulfil before a Train may be allowed into the section.

The Electric Train Staff Instrument

Electric Train Staff Instrument This is the instrument used for the issuance and return of the Electric Train Staff. When a Signalman at 'box A has requested and been given permission for a train to be sent to 'box B, the Signalman at B will hold down a lever on his instrument that will unlock the Instrument in 'box A allowing the Signalman there to withdraw one Train Staff. Once the Staff has been withdrawn it is impossible to withdraw another whilst the first is out. The Staff may be replaced in either Instrument and once this has been done, another may be withdrawn from either end of the section. In addition to locking the Instruments so that no more Staffs may be withdrawn, it is also usual for the Instrument to be interlocked with the section Starting Signal so that it may be lowered just once. If for any reason this Signal needs to be replaced before the train has left, then the Staff has to be replaced and another withdrawn before the Starting Signal may be pulled again.

photograph by Peter Richards

The head of the Instrument. The dial on the right has to be moved to 'For Staff' by the Signalman withdrawing a Staff, and the lever with the black handle held down by the other Signalman, before a Staff may be issued. Whilst the second Signalman is holding down, the galvanometer in the centre dial will deflect to indicate the Instrument is able to release a Staff. As soon as the Staff is withdrawn the galvanometer in both Instruments will return to its normal position. Once the Staff has been withdrawn the dial on the left may be turned to 'Up Staff Out' or 'Down Staff Out' as appropriate as a reminder to the Signalman of the state of the Instrument. Prior to releasing a Staff, the black handled lever may be used for operating the bell at the other Signalbox providing the dial above is set to 'For Bell'.

N.B. Not all of these Instruments were equipped with the right-hand indicator.

photograph by Peter Richards

Electric Train Staff Instrument
Electric Train Staff Instrument The Staffs are stored in the base of the Instrument's supporting column. The total number of Staffs in the two connected Instruments must always equal an even number so if one becomes damaged and cannot be used, before it is taken away for repair the Lineman has to remove another Staff, and lock it in a safe place, to balance the Instruments. If more trains work in one direction than the other, then it will result in a build-up of Staffs at one end of the section. To overcome this the Lineman will remove an even number from the full Instrument, making suitable entries in both his Register and the Signalbox Register, and convey them by road to the other Instrument.

photograph by Peter Richards

One very noticeable thing from the above three photographs is the sheer size of the Electric Train Staff apparatus - far larger than those used for the issuance of Tablets or Key Tokens! A 'miniature' version was developed, though not much under half the size of the 'large' Instrument. The head was not much smaller but the Staffs were, and were kept in four vertical slots (in a similar fashion to Key Tokens) as opposed to one.

Right: A Miniature Electric Train Staff that was used between Fordingbridge and West Moors.

Miniature Electric Train Staff

photograph by Chris Osment

Example of Electric Key Token Instrument | Examples of Electric Train Tablet Instruments
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This page was last updated 4 January 2004

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