SEmG

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 Tablet Instrument

 
Electric Train Tablet Instrument Another variation on the theme were the various Electric Train Tablet Instruments of which the Tyer's Nº3 is just one example. The appearance of the Nº3 and Nº6 (left) were to all intents and purposes identical, though the operation of them was quite different. In the case of the Nº3 system when the Signalman at B accepts a train from the Signalman at A, A holds in his plunger for about three seconds which allows B to hold down his side lever and withdraw an empty slide from the base. B will then turn his commutator from right to left which will change his lower indicator from 'In' to 'Out'. The galvanometer needle at the top will reset to normal whereupon B will hold down his plunger changing the upper indicator at A from 'In' to 'Out' and enabling him to withdraw his slide with a Tablet. When the train has cleared the section B will place the Tablet for A to B in his slide and give Train Out of Section to A. A will then acknowledge the signal and hold down his plunger. B will now replace his slide and turn the commutator from left to right, changing his lower instrument to show 'In'. When the galvanometer needle is normal he must hold in his plunger, enabling A to return his slide to normal who, ensuring his galvanometer shows normal, will send one beat to B after which both Instruments are once again ready for use.

Nº3 Instruments are non-returnable! This means that once issued the Tablet has to travel through the Section to be replaced in the Instrument at the other end.

photograph by Dave Hudson, courtesy of Chris Osment

 
With the Tyer's Nº6 Instrument, when Signalman B accepts a train from Signalman A he holds his plunger down enabling A to turn his commutator to the left, whereupon his lower disc will show 'Out'. He will then withdraw his Slide, extract a Tablet and send one beat to B which will change his upper disc to 'Out' which B will acknowledge by one beat. On arrival of the Train at B, the Signalman there will obtain the Tablet for the A to B section from the Driver, lift his side lever, withdraw the empty Slide and having inserted the Tablet in the Slide, push the Slide home. He will then send to A the Train Out of Section Signal, pausing on the last beat so that A may reverse his commutator, which he will turn to the right, then push the empty Slide home and acknowledge the Train Out of Section Signal. This will reverse the upper disc at B from 'Out' to 'In' and prove to B that A has replaced his Slide. B will then give one beat to A which will place the lower disc at A to 'In' and show that both Instruments are again ready for use.

Nº6 Instruments are returnable, allowing a Tablet to be restored to the issuing Instrument if required.

 
Tyer's Nº6 Tablets
Three Tyer's Nº6 Tablets that were used on the Meon Valley line, showing 'A' configuration (round notch + round hole), 'B' (rectangular notch + square hole) and 'C' (elongated, stepped notch + triangular hole).

photograph by Chris Osment

 
With the Tyer's Nº7 Instrument, when Signalman B accepts a train from Signalman A, A must hold down his Bell Plunger for a few seconds, which will ring the Bell at B, B must depress his Switch Plunger with his left hand and at the same time withdraw his lower Slide (which will only come halfway out) with his right hand. The partial withdrawal of the Slide will reverse the commutator in the Instrument and will bring the signal Up Train Approaching into view at B. The Signalman at B will then depress his Bell Plunger, ringing the Bell at A, where A will hold down his switch plunger with his left hand and fully withdraw his lower Slide with his right hand which will then bring up the signal Up Train on Line at A. He will then give one beat on the Bell to B to denote that the Tablet is out of the Instrument, remove the Tablet and place it in the pouch before giving it to the Driver. When the Train arrives at B the Signalman must obtain the A to B Tablet from the Driver, withdraw the upper Slide in his Instrument, insert the Tablet and push the Slide fully home. He must then push home his lower Slide which will bring up the Signal Line Closed on his Instrument. He will then send Train Out of Section to A, holding down his plunger on the last beat whilst A holds down his switch plunger and pushes home his lower Slide which will restore his Indicator to Line Closed. He must the acknowledge the Train Out of Section to B after which both Instruments are ready for use again.

Nº7 Instruments are returnable, allowing a Tablet to be restored to the issuing Instrument if required.

Electric Train Tablet Instrument

photograph by Dave Hudson, courtesy of Chris Osment

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

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