Annett's key
Encyclopedia
In railway signalling
Railway signalling
Railway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...

, an Annett’s key or Annett key is a large key
Key (lock)
A key is an instrument that is used to operate a lock. A typical key consists of two parts: the blade, which slides into the keyway of the lock and distinguishes between different keys, and the bow, which is left protruding so that torque can be applied by the user. The blade is usually intended to...

 that locks levers
Lever frame
Mechanical railway signalling installations rely on lever frames for their operation to interlock the signals and points to allow the safe operation of trains in the area the signals control...

 or other items of signalling apparatus, thereby functioning as a portable form of interlocking
Interlocking
In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. The signalling appliances and tracks are sometimes collectively referred to as an interlocking plant...

. When not in use, the key is normally held in an Annett's lock that is fixed to the lever or apparatus concerned. With the key removed from the lock, the lever or apparatus is locked and cannot be moved.

The Annett's key takes its name from its inventor, J. E. Annett of the London, Brighton and South Coast Railway
London, Brighton and South Coast Railway
The London, Brighton and South Coast Railway was a railway company in the United Kingdom from 1846 to 1922. Its territory formed a rough triangle, with London at its apex, practically the whole coastline of Sussex as its base, and a large part of Surrey...

. Annett patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....

ed his design in 1875; in 1881 that patent was bought out by Saxby and Farmer, one of the principal British companies of signalling contractors at the time.

Annett's keys have been made in a variety of forms. The keys and locks are given a matching configuration to prevent keys of a different configuration being inserted into the wrong lock.

Applications

An Annett's key is commonly used to unlock an item of signalling apparatus remote from a signal box
Signal box
On a rail transport system, signalling control is the process by which control is exercised over train movements by way of railway signals and block systems to ensure that trains operate safely, over the correct route and to the proper timetable...

, e.g. a ground frame, a set of points
Railroad switch
A railroad switch, turnout or [set of] points is a mechanical installation enabling railway trains to be guided from one track to another at a railway junction....

, a swing bridge
Swing bridge
A swing bridge is a movable bridge that has as its primary structural support a vertical locating pin and support ring, usually at or near to its centre of gravity, about which the turning span can then pivot horizontally as shown in the animated illustration to the right...

 or a turntable
Turntable (railroad)
A railway turntable is a device for turning railroad rolling stock. When steam locomotives were still in wide use, many railroads needed a way to turn the locomotives around for return trips as their controls were often not configured for extended periods of running in reverse and in many...

.

An Annett's key may be used as a single line
Single track (rail)
A single track railway is where trains in both directions share the same track. Single track is normally used on lesser used rail lines, often branch lines, where the traffic density is not high enough to justify the cost of building double tracks....

 token
Token (railway signalling)
In railway signalling, a token is a physical object which a locomotive driver is required to have or see before entering onto a particular section of single track. The token is clearly endorsed with the name of the section it belongs to...

.

In the Scottish Region
Scottish Region of British Railways
The Scottish Region was one of the six regions created on British Railways and consisted of ex-London, Midland and Scottish Railway and ex-London and North Eastern Railway lines in Scotland...

Tokenless Block system of signalling, Annett's keys are used as "shunting keys".
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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