THE SIGNAL BOX

BLOCK SYSTEM

BRITISH RAILWAY SIGNALLING INSTRUMENTS

London & North Western Railway signalling instruments

LNW Three-Wire Three-Position Permissive block

LNW Three-Wire Three-Position Permissive block

The London & North Western Railway built their own block instruments at their signal works at Crewe (and, for a while, at Stockport) and this view demonstrates how they followed their own design ideas. It is a combined instrument (bell and indicators all in one unit) and the bell was mounted at the base. The bell tapper is just above it, to the right.

This particular instrument varies from the standard product in that it is designed for Permissive Block lines, and just above the commutator is a small window where the number of trains accepted into the section are indicated. The plunger on the right of the instrument has to be operated each time the commutator is turned; this is a means of preventing the commutator being turned too enthusiastically and counting too many trains!

Whilst this is an LNW instrument it was located on former Midland Railway territory at West Hampstead. The LMS (and BR(LM) for a while) continued the production and use of these instruments, and many were installed in the 1950's on the former Midland to replace the unsatisfactory bell-only working that had existed until then.

More details about West Hampstead will be found in the Photo Gallery.

Webb-Thompson Electric Staff Instrument

Webb-Thompson Electric Staff Instrument

The LNW also built their own electric staff instruments for single lines, and in accordance with their signal engineer's habits they were massively constructed in cast iron.

As with other types of single line instrument, the purpose was to allow only one staff to be available at any time for each single line section but to maintain the flexibility of more than one train travelling in the same direction prior to one coming the other way.

The LNW subsequently allowed these instruments to be manufactured under licence by the Railway Signal Company, who sold them to many other companies, at home and abroad.

This particular example is at Ockendon on the London, Tilbury & Southend Railway. more details of which will be found in the Photo Gallery.