Signalling

SIGNALLING DETAILS


The original signalling on the line was rather primitive and reflected the origins of the northern and southern sections, the Somerset Central and Dorset Central Railways respectively.

The Somerset Central, as a broad-gauge line, and one which was confidently expected to fall into the Great Western empire, was signalled on standard Brunel practice with disc and crossbar signals exactly like those used on the Bristol & Exeter Railway and on the Great Western itself.
Display of the red disc facing the train was the proceed signal. The signal turned through a right angle, to place the disc edge-on and display the crossbar at right angles to the track, this was the stop indication. These disc and crossbar signals were used throughout the Somerset Central portion, from Burnham to Cole.

Typical 'Disc & Crossbar' signalThe Dorset Central section of the line took on a London & South Western Railway influence. A slightly different type of disc signal was used. In the danger position a red half-disc was shown to the driver, only the upper half of the complete signal. The outer periphery of the circle was continued round the bottom half, but the interior portion below the horizontal centre line was open. In the proceed position the disc was turned edge-on, and virtually no positive indication of a clear line was shown to the driver.
The distant signals on the Dorset Central part of the line, when they were introduced, were of similar construction to the stop signals except that the division between the red half-disc and the open portion was made on the vertical centre line, instead of the horizontal, and the left-hand portion was red, with the right-hand portion open.

On the single-line sections there were certain stations having no passing loops. These came in the middle of single-line block sections, and were not equipped with signals of any kind. The scheduled stops at some of these stations were conditional only, and after the introduction of semaphore signals some of the old disc and crossbar signals were installed at these intermediate stations to indicate when a station stop was required to pick up passengers or goods.
The last remaining signal of this type was at Spetisbury station and was removed around 1901.

After the setting-up of joint ownership, the London & South Western Railway took over responsibility for civil engineering and signalling, and standard LSWR semaphore signalling practice became established. While many wooden posts remained until the grouping era, the majority of the actual masts were of the standard South Western lattice pattern.
In Southern Railway days when there was an acute shortage of steel, many of the older posts, when due for renewal, were replaced by a new standard type developed on the Southern, using two old rails braced together.
Gradually the old LSWR semaphores were replaced by modern upper-quadrant arms. In the last few years of the line's operation a few Great Western type semaphores were erected as replacements - the down starting signal at Midford, for example, and the down distant at Masbury.

Backing signal at Midford
Backing signal at Masbury station
 

Between Midford and Combe Down Tunnel were some unusual signals. These were 'Backing Signals' and were put in place to enable drivers of heavy freight trains who were unable to continue the steep climb through the tunnel to safely reverse back down to Midford.
The driver would stop his train short of the tunnel entrance and call the signalman in Midford box on the lineside telephone to advise him of the problem. The signalman would then 'pull off' the backing signals, thus authorising the driver to reverse back down to Midford station, passing on his way the down home and starting signals at danger. The train would then either take another run at the bank, or summon assistance from Bath Shed if required.

THE WHITAKER TABLET-EXCHANGING APPARATUS


The tablet-exchanging apparatus used on the Somerset & Dorset was designed by Alfred Whitaker during his term as locomotive superintendent of the Joint line. (British Patent Specification No. 861 of 1905).

Whitaker Tablet Catchers at MidfordOn the engine was a combined 'deliverer' and 'receiver'. When out of use this was close to the side of the engine and was pushed out when required. The tablet to be given up was placed in a leather pouch with a steel ring, carried at the rear end of the apparatus, and kept in position by a spring clip. The receiver consisted of a gunmetal jaw with two triggers in the front and with a rubber pad at the back.
At the lineside at the tablet station were mounted the familiar standards. The jaws of the apparatus on the engine engaged with the loop of the tablet pouch carried on the lower arm of the standard, and a similar receiver on the upper arm of the standard seized the loop of the tablet pouch from the engine. The arms of the standard were normally parallel with the running line, and were turned to a right angle with the line by the signalman when putting out a tablet ready for exchange. The standard was provided with two bevel wheels, but these had teeth on only a quarter of their faces and were provided with a stop to prevent them moving further than the correct distance. When that point was reached, the weighted lever was slightly past the perpendicular. The shock given by the receipt of the tablet into the receiver was such as to throw the weight over the centre. It then fell, and the bevel wheels turned the standard so that the arms were cleared of the running line. This was a very good feature, and the apparatus in general gave excellent service with speeds of exchanging sometimes even in excess of 60 m.p.h.

The margin of error was limited with a pouch loop of such small diameter. When the apparatus was fitted on the tender, variations in height caused by weak springs or track insulations which caused the tender to roll at the critical moment would result in a 'miss'. Drivers were always prepared for this with a hand raised toward the brake handle. If the enginemen were smart, very little loss of time occurred by the fireman having to turn back for the tablet after stopping.
In placing the tablet into, or removing it from, the engine catcher, the fireman had to expose himself to some danger, but in the history of the line there was no record of anything worse than a badly bruised arm sustained by a fireman who had left his action so late that he was struck by a lineside catcher.

Tablet exchanging apparatus fitted to the near-side of a tender.
The apparatus fitted to the near-side of a locomotive tender.

To ascertain whether the catchers were correctly aligned, a locomotive inspector on the engine would insert a circle of cardboard into the pouch hoop prior to delivery from the engine. The cardboard was secured to the end of a length of string by which it was drawn back on to the footplate after delivery of the pouch; the cardboard would then bear an imprint showing where the lineside catcher had struck it, and if the imprint was not central, the catcher had to be checked with a special gauge.
Engines not fitted with catchers had to exchange tablet pouches by hand, in which case the code word 'POUCH' was relayed to all signalmen, who then made use of the pouches with large hoops. Bath locomotive department kept a stock of clamp-on catchers which could be fitted at short notice to any engine arriving from the North which had to be pressed into service over the S&D.

For more information on S&D and other
companies signalling visit the Rail West site.

Also, go along to The Signal Box Home Signal Page for a
picture of Wellow signal box and other signalling info

 

Copyright © Kevin Clapcott
Most recent revision Tuesday August 24, 2010