THE BLOCK SYSTEM
Southern Railway instruments
SR Three-Wire Three-Position
When the Southern Railway was formed in 1923, it inherited a motley collection of instruments from its predecessors. Most main lines were signalled using Sykes Lock & Block instruments (which were clunky and cumbersome but a safe system) whilst lesser lines mostly used very basic one-wire two position instruments from a wide range of manufacturers. The Southern Railway quickly developed plans to replace the latter, but the programme was never fully completed and many older instruments laboured on into BR times – some right through to abolition of their boxes around 1990.
Most, if not all, of the instruments were manufactured by W R Sykes & Co and in shape and form they bore great similarity to the Sykes Lock & Block instruments in use on the Southern’s main lines. A few actually show signs of the wooden cases of Lock & Block instruments being re-used.
In 1926, the Southern issued two standards of these instruments that would be used:
1: Closed Block
This was to be provided with three features:
- Line Clear Release on the signal governing entry into the next block section, i.e. electrically locked until the instrument shows “Line Clear”
- Home Normal Control and Distant Normal Control, with the distant and first home signal reached by a train required to be “On” before the “Line Clear” indication can be given on the block instrument
- Sequential Locking, requiring each signal at a signal box to be “On” before the previous one could be cleared.
The proving of signals to be in the “On” position would be by the position of the lever – plus, if the signal was electrically repeated, the indication on the repeater.
Over the years, many additional features were developed which were used in some places, the most common being co-operative cancel buttons which were required to be pressed simultaneously by both signalmen concerned in the case of cancelling of a “Line Clear” indication. This feature was found along the South Coast lines and can be seen here behind a small rectangular glass cover:
2: Open Block
The Southern classed anything that didn’t meet the standards of Closed Block as Open Block; this would appear on lesser lines.
In BR days another variation was defined:
3: With British Railways Controls
This was basically similar to the Closed Block except a Welwyn Control Release for cancelling the Line Clear indication replaced the co-operative cancel buttons.
This system was not widely found on the Southern Region but examples can be seen in this view showing those that replaced Sykes Lock & Block instruments on the line through Redhill in the 1980s:
The Southern Railway, and the Southern Region of British Railways, operated a policy of re-cycling instruments released by using them to continue with the replacement programme of two-position blocks through to the 1980s. They never had cause to use the so-called “BR Standard” bakelite block instruments.
One curiosity which has never been satisfactorily explained was the presence of a handful of Southern Railway instruments in Cheshire Lines Committee signal boxes, possibly introduced by the London Midland Region when they upgraded the instruments along the line in the 1950s. Another possibility is that they were purchased directly from W R Sykes & Co as there are minor differences to those found on the Southern Railway.
In this picture it can be seen that the “Commutator Locking Slide” found on most SR instruments is absent, and instead a reminder device that simply hangs over the the commutator is provided. This hangs on a hook beneath the instrument and looks very much like the similar devices provided for ex-L&NWR instruments.
But we really don’t know how they came to be there. Given the SR’s re-use policy, they would have no sound reason to have parted with any.