Many different types of interlocking frame were used by the British railway companies. It is a whole subject for study in itself. Some were built in-house, whilst others were bought from outside contractors.
nterlocking was necessary to prevent signals for conflicting routes to be cleared, which could obviously cause a collision or mishap. The earliest designs used all sorts of ingenious methods to interlock the levers as each system was vigorously patented. Several cases occurred where one firm took another to court over alleged copying of their principles.
Stevens & Sons invented the tappet system of interlocking that became almost universal in use in later British interlocking frames. Remarkably, they didn’t bother to renew their patent, and many manufacturers adopted this simple system as their standard with almost indecent haste.
The history of the contractors themselves is complex, too, and readers are referred to the Railway Companies page for more details, dates etc.
This section does not attempt to describe in detail the methods of interlocking employed, but concentrates on the visual aspect – what the frames look like above operating floor level.
- British Pneumatic Railway Signal Co
- British Railways (London Midland Region)
- Cheshire Lines Committee
- Dutton & Co
- Evans, O’Donnell & Co
- Great Central Railway (and its constituents)
- Great Western Railway
- London & North Western Railway
- London, Brighton & South Coast Railway
- London, Midland & Scottish Railway
- McKenzie & Holland
- Metropolitan Railway
- Midland Railway
- North London Railway
- Ransome & Rapier
- Railway Signal Co
- Saxby & Farmer
- South Eastern & Chatham Railway (and constituents)
- Stevens & Sons
- Tweedy & Co
- Westinghouse Brake & Signals Co
- Miscellaneous curiosities