Introduction

This page describes the single-line Electric Train Tablet instruments of the former narrow-gauge Lynton & Barnstaple Railway (L&BR) in North Devon. Please see the separate Introduction page for general background information and details of other pages on RailWest about the signalling of the L&BR. Click here for more general historical details about the L&BR and a Bibliography.

Basic Working

When the L&BR was opened the single-line was divided into a number of separate sections Barnstaple Town - Pilton Bridge - Chelfham - Bratton Fleming - Blackmore - Wooda Bay - Lynton, with a signal-box provided at each of those locations. From the outset all the single-line sections were worked by the Electric Train Tablet (ETT) system, which had been invented by Edward Tyer. At each end of each section there was an ETT instrument, the two instruments at opposite ends of an individual section being connected together electrically. Normally these instruments would be located in the signal-boxes at each end of the section, but because of the small size of most L&BR signal-boxes the ETT instruments were housed instead in the station buildings, except at Barnstaple and Pilton. (After 1923 the instrument at Barnstaple Town was moved from the L&BR signal-box to the separate ex-L&SWR signal-box, which controlled the main line to Ilfracombe.)

The L&BR was equipped with the very rare Tyer's No 7A pattern of ETT instrument. Each instrument contained a number of 'tablets' - round metal discs engraved with the names of the signal-boxes between which they applied. No train was permitted to enter a single-line section unless the driver was in possession of a tablet for that section. The tablet were locked electrically within the instruments and a signalman could remove one to give to a driver only with the co-operation of the signalman at the other end of the section to provide the necessary electrical release. Click here for an extract (72KB) from regulations issued by the Southern Railway (SR) in 1934 for operation of the L&BR tablet instruments.

Once a tablet had been removed from an instrument then both instruments for that single-line section were locked, so that no other tablet could be removed from either instrument until the first tablet had been replaced. This ensured that only one tablet for a section could be removed at any one time and therefore only one train could enter a single-line section at a  time - obviously a critical safety factor. Normally when a tablet was taken out it would be carried through the section on the engine and placed into the instrument at the far end (thus clearing the section), but in the event of a train failing to proceed then it was possible to return the tablet to the same instrument from which it had been removed.

Tyer's No 7A Instruments

Edward Tyer patented a series of different types of ETT instrument from 1878 onwards and at first the different patterns were identified by numbers - 1, 2, 3 etc. Some patterns were modified at a later date and these variations were given letter suffixes, eg 5A, 6A etc. Tyer's instruments were sturdy, quality items well-suited to their purpose and it is a tribute to their design and construction that many still survive to this day in private collections, on some preserved railways, and even a few in use by Network Rail. However the early patterns were not cheap and it would appear that, with an upsurge in the construction of minor railways, Tyer turned his attention to producing designs that were mechanically and electrical simpler.

After the No 6 design Tyer started using different descriptions for his instruments and this is where the situation gets confusing. In 1896 he patented the "Automatic Tablet Instrument", but this term - or variations of it - was used subsequently also for other patterns of instruments. Then he produced the No 7 instrument, which was based on the "Automatic" but designed for more general use, and this was patented by late-1898. Two sets of the "Automatic" instruments were supplied to the Isle of Wight Central Railway by 1898 and these were described there as "No 7A", even though in fact the No 7A pre-dated the No 7. The term '7A' therefore has been adopted to describe the 1896 patent design (click for patent drawings (64KB)) in order to avoid confusion with later "automatic" instruments and to reflect the similarity with the No 7.

Tyers 7A Instrument

Photographic evidence and other research has established that the L&BR was equipped with the No 7A pattern. Apart from two sections on the Isle of Wight (later replaced), the six sections on the L&BR are the only other sections known to have been fitted with this equipment. (There were a few single-line sections of the London & South Western Railway (L&SWR) recorded as having "automatic tablet instruments", but no firm evidence exists to prove that the L&SWR equipment was the No 7A pattern and all those sections had different instruments in later years.) The L&BR ETT instruments were described in a Southern Railway Appendix as "No 1 Hopper" instruments, but this is not a term used by Tyer. It is probable that, after the L&BR was taken over by the SR in 1923, this term was invented by someone in the SR simply in order to describe a type of machine previously unknown to them - it is unlikely that railway staff in Devon would have been familiar with equipment on the Isle of Wight.

The tablets were stored within a vertical cylinder inside the front of the instrument and withdrawn (one at a time) by a slide at the bottom. Tablets were replaced into the instrument through a slot at the rear of the top, inside which was a movable half-drum - when this drum was rotated downwards by means of a side lever the tablet was tipped out and slid down an inclined tube back to the storage cylinder (see patent drawings (64KB)). On the top of the machine at the front were two plungers - the 'bell' plunger was used by the signalmen for communication, while the 'switch' plunger would provide the electrical release to the remote instrument. At the rear of the instrument a galvanometer provided an indication of the passage of electric signals between the two machines.

The Tablets

The tablets for Tyers 7A instruments were round metal discs approximately 4" in diameter, engraved with the names of the signal-boxes between which they applied. To ensure that a tablet for one section could not be placed incorrectly into the instrument for an adjacent section, each tablet had a 'configuration' which was achieved by a shaped notch in the edge of the tablet. This notch engaged with an equivalent shaped nib at the back of the slot inside the receiving drum of the tablet instrument. In the centre of each tablet there was a hole, whose shape denoted the configuration for easy recognition - round for 'A', square for 'B' or triangular for 'C'. There was also a smaller hole (about 5/8" diameter) diametrically opposite the notch, although this appears to have served little function other than for the signalman to insert a finger when trying to get the tablet out of the instrument drawer!

Examples of L&BR Tyers 7A tablets click thumbnails to see larger images

Although the L&BR had six single-line sections it did not need six different configurations, as it was necessary only to ensure that adjacent sections used different configurations. Consequently the L&BR use only the 'A' and 'B' configurations, alternating them down the line as follows:-

In 1931 the passing-loop at Bratton Fleming was taken out of use and the signal-box there ceased to be a block-post, the single-line section now extending from Chelfham to Blackmoor. This caused a slight problem with regard to tablet configuration, as the tablets for the new section had to be distinguishable from both 'B' tablets at Chelfham (for the section to Pilton) and 'A' tablets at Blackmoor (for the section to Woody Bay). Although the 'obvious' answer might have been to provide 'C' configuration tablets, in fact the Southern Railway provided a set of 'A' tablets with a side notch cut much longer than normal (click here for picture - note that the spelling of 'Blackmoor' has changed from the original use of 'Blackmore').

Mysteries

Although the details of tablet usage may appear to be fairly straightforward, there do remain some mysteries arising from the limited available evidence. For example, as the tablets for the later Chelfham - Blackmoor section were configuration 'A', then one might assume that the Southern Railway would simply re-use those from the Chelfham - Bratton section and engrave the word 'Blackmoor' in place of 'Bratton'. However there is no evidence of that in the example illustrated and it is clear also that the notch is much narrower than that of the other 'A' tablet shown (Blackmore - Wooda Bay). But if these are in fact new tablets, then why not provide 'C' configurations?

On the 'Blackmore - Wooda Bay' tablet the notch intrudes on the tablet number, which suggests a later modification - but why? There are tablets known to exist for the first section on the line engraved 'Barnstaple - Pilton Bridge', and also at least one for 'Barnstaple - Pilton', but the latter has a square centre hole ('B' configuration) despite having a round notch ('A' configuration) - but why the difference? It may be that the latter were later replacements, but for what reason and why the conflicting configuration details?

Conclusion

Apart from the 1931 alteration at Bratton Fleming the basic working of the single-line sections on the L&BR remained virtually unchanged throughout the life of the railway. When the L&BR was closed in 1935 the Tyer's No 7A pattern of ETT equipment became extinct. Sadly it is reported that the machines were smashed open by the demolition men in order to retrieve the tablets and it is very unlikely therefore that a No 7A instrument will be seen again. However a set of L&BR tablets survive at the National Railway Museum in York and various others are known to be in private collections.

© Chris Osment 2001-13
Acknowledgements to David Stirling for information on Tyer's equipment, Russell Burridge for both Blackmoor tablet photographs,and Gloucestershire Worcestershire Railwayana Auctions for Barnstaple and Lynton tablet pictures.