THE SIGNAL BOX

PHOTO GALLERY

London, Brighton & South Coast Railway

MITCHAM

Opened: 1891

Closed: 1982

Location code: S31/10


Mitcham signal bixMitcham box and station was to be found on the Wimbledon to West Croydon route, a piece of railway that has been totally transformed today as a part of Croydon's tram network. The first signal box is recorded as having opened as early as 1856, but this is the third to serve the station.

This box was erected because the previous one (of 1868) had become "dilapidated" at an estimated cost of £360, according to the company's Engineering Committe minutes.

Architecturally, it was a variation of the company's 1891 design, as seen at Plumpton.

Although it appears that the signalman has no staircase, the original one had recently been replaced by access from the embankment side at the time of this photograph.


Inside Mitcham boxStepping inside the box, we find an interesting lever frame. At first glance, it appears to be to Saxby & Farmer's Rocker design, but this is in fact a straightforward tappet design built by the LB&SC themselves. This type appeared around 1879 when the company started to carry out some signalling work themselves, but the similarity of their frames (and box designs) to Saxby & Farmer's own products are astonishing - Oxted illustrates this.

Significant identification features of this home-built model are the lack of any fittings between the lever quadrants for the rocker mechanism (see Heckington) and a much smaller catch-handle mechanism pivoted at a higher point on the lever.

The signal and the signalling instruments seen in this view are described below.


Syke's Lock & Block instrument at MitchamThe line between Mitcham and Mitcham Junction was double track, and this short section was securely signalled by the Sykes Lock & Block system. These cumbersome and complicated instruments interlocked with the levers to ensure only one train could be between two signals at any time, whether in the block section or station limits.

Block Section

A section of railway line between the last stop signal controlled by one box and the first stop signal controlled by the next

Station Limits

The section of line between stop signals controlled by the same box

In the view above, the accepting instruments for the Down line can be seen mounted above the signal levers they apply to. Beneath them, the interlocking rods can be seen stretching down to floor level.

At the other end of the shelf, above lever 4 (the Up Starting signal) is the corresponding sending instrument. The top indicator shows the state of the block section (clear with the miniature signal arm lowered) and the indicator below shows the starting signal (4) and a shunt disc from the Down line (17) to be locked. When Mitcham Junction accepts a train, a loud clunk is heard from the instrument as the red tablet changes to green with the word FREE, and the signals are released. As the lever is pulled, it returns to showing LOCKED until the train passes the signal, allowing the lever to be replaced far enough to put the signal back to danger in emergency, but preventing the lever being put fully back until the train has been detected entering the section by a rail treadle. Activation of that treadle again changes the instrument to FREE, until the lever is replaced. Whilst the train is in the block section, the top indicator changes to horizontal - this is worked by the signalman at the box ahead.


Webb-Thompson Electric Train Staff instrument In the opposite direction, the line to Merton Park was single, protected by Electric Train Staff.

This huge cast-iron contraption was invented by the London & North Western Railway, but later produced under licence by the Railway Signal Company and sold to railway companies throughout the UK and overseas.

The principle is simple. The driver of every train on the single line between two boxes must be in possession of a train staff. A stock of these staffs is kept at both boxes, stacked in a slot in the machine. These staffs bear a brass inscription identifying the section of line concerned, and are painted a specific colour to avoid confusion at boxes which control more than one section. Additionally, rings on the staff ensure that they cannot be placed in the wrong machine.

When a signalman wants to dispatch a train to the next box, he offers the train using the bell tapper at top right on the instrument. When the train is accepted by the other box, that signalman holds his tapper down on the last bell beat, which electrically releases the instrument for one staff to be withdrawn. This is achieved by raising the staff up the slot, and twisting it upwards and outwards through the polished brass part. The hand-worked pointer (top left) is used by the signalman as a reminder of the state of the section.

Once a staff has been withdrawn, the instrument is locked against release of another until that staff has been replaced in the instrument at one or other end of the section, which would be accompanied, of course, by the usual exchange of bell signals.


LB&SC lower quadrant signal at MitchamHere is a better view of the signal glimpsed through the window of the box in the interior view above.

This was one of the very last LB&SC lower quadrant signals to survive. Its longevity was justified by sighting considerations - behind the cameraman, at the other end of the station, was another bridge which limited the driver's view. Had the signal been converted to upper quadrant, the arm would have not been fully visible from a distance when pulled off. The normal solution in such circumstances would be to reposition the arm lower down the post, but here the post is already so low that repositioning of the arm could make it not visible at all with a crowded platform. Thus it outlived other such signals by many years. Perhaps, though, through the fact that all trains stopped here, it was eventually replaced by an upper quadrant around 1978.

Notice the grey-painted shield to conceal the blue glass from being lit by sunlight to give a false indication. The glass was blue, incidentally, because the flame of an oil lamp is yellowish. Using a blue glass ensures a good green colour is visible at night.

The replacement signal did not survive long, and the box closed on 23rd May 1982 when the line became controlled from the "Victoria Signalling Centre". Later, the line closed altogether, and the route is now followed by the Croydon Tramlink.

Additional notes kindly provided by Stuart Johnson and Geof Smith



Buy prints of photographs
at 433shop
Click here

All photographs copyright © John Hinson unless otherwise stated