How did coffee pot signals come about? They obviously originated from both platform and train staff handlamps, as well as kerosene lamps placed behind semaphore signals or buffer stops. In fact it is known some of the Metropolitan Railway’s signals out towards Aylesbury used a style that were essentially a coffee pot. Most of the tube’s early electric signals were of the electro-mechanical type, hence the coffee pot signal came later.
Its not an easy subject these coffee pot signals. I dont think many get excited by railway signals except semaphores (upper & lower quadrant) ground signals. Modern colour light signals do their job but are pretty bland. Eventually signals will disappear and it will be all in cab control. Back to coffee pot signals, it hasn’t been easy to work out exactly how they originated so some historical guesswork is in order.
Clearly coffee pot signals came from a similar lineage to railway hand lamps, or even carriage lamps. (Pics source Ebay.) The front bit, or the reflector, is apparent in these examples given. The one below shows the interior of the reflector painted white.
Amazingly the first electric signals on the tube, both deep level and sub-surface, seem to be invariably electro-mechanical types. There’s a picture showing one at Earls Court on the Metropolitan District Line. Its not a very clear example. These better examples are from the Great Northern, Piccadilly & Brompton Railway (Piccadilly Line naturally.) The first is these pair of signals at Holborn controlling the junction with the Aldwych branch.
Holborn junction signals. Source: Grace’s
The coffee pot lineage is not very evident here. What is important is the vent top, which clearly shows how these particular signals (and many other similar) were an evolution from oil lamps and this was carried over into the coffee pot signals. Evidently the electric lamps generated heat and so the vents were a means of keeping them cool. The moving lenses in front of the signals themselves is also important. Its a twin lens with a single lamp behind and the lens moves up or down to show either red or green.
The actual porthole through which the light shone was about half the diameter of the glass itself. Around this was a circular reflector which would be painted white. This increased the illumination and spread it so as to fit the whole area of the glass.
Like the first example this is on the Piccadilly, but this time at Finsbury Park. I believe this one is sited just before the crossover south of the station.
Finsbury Park signal. Source: Grace’s
The slightly different perspective gives enough of an angle to show part of the reflector on the signal housing. The crop below shows the reflector housing in part.
The housing and reflector is black however its inner edge will be painted white. The glass within may or may not be a Fresnel lens.
Whilst these early 1906 examples of signals on the Piccadilly Line (and the Great Northern and City) must have served their worth, the issue with these signals was of course the moving parts. These signals are actually a very cumbersome design with their electro-magnetic motors, rocker assembly and weighted balance lever.
Its amazing a simple concept such as coffee pot signals didn’t come first. The mentality of semaphore signals no doubt prompted engineers to devise these cumbersome signals.
The simple resolution to these cumbersome apparatuses was to go back to basics – dispense with the entire mechanism save for the bit housing the lamp. That housing would be made somewhat larger, accepting two lamps and a pair of reflectors.
About 1911 or 1912, the now recognisable style of coffee pot signal began to make their first appearances. Stations soon began to acquire coffee pot signals and their cheapness meant they were soon being used too as repeater signals for train guards, especially at stations whose platforms had a curve and the starter signals could not be easily seen.
We know this because photographs of the very early tube stations with curved platforms show no signals along their length apart from the station starter signal, for example in 1906 at King’s Cross northbound (eastbound in modern parlance) whilst those like Liverpool Street at its opening in 1912 came equipped with these repeater coffee pot signals.
Coffee pot signals were employed on the tube from about 1912 to about 1930. After than the new tube lines to be built came with fully modern colour light signals. However as we know, some coffee pot signals have survived for almost 90 years beyond the early tube modernisation works of the 1930s! Most lines kept their coffee pot signals until the sixties and seventies, except the Northern Line which retained its numerous coffee pot signals until 2012-13.
Liverpool Street – eastbound platform coffee pot signal – next to modern signal controlling the crossover
Liverpool Street (Circle/Hammersmith/Met) station itself still has coffee pot signals at work 106 years after their first use was recorded at the station’s deep level Central London Railway platforms. It can be claimed this station has seen the most longevity in its use of coffee pot signals.
These signals still do sterling work assisting platform dispatch staff in their job to keep the huge swathes of commuters at this station on the move, especially when the platforms are crowded and the train starter signals cannot be seen. When the sub-surface lines resignalling eventually comes the ways and means by which platform staff will do their jobs will be different, perhaps the white calling on lights seen on the Jubilee and Northern lines, or some sort of visual or audible device to let them know when it is safe to dispatch trains.
The eastbound platform’s combo of coffee pot and modern signal
The most interesting aspect of these two surviving coffee pot signals at this location is the fact the eastbound one sits next to a modern one which controls the crossover at the western end of the platforms. I am sure the modern replaced a coffee pot signal! What is remarkable is the fact whoever put the new signal in for that crossover didn’t think to replace the other coffee pot at the same time. Its clearly an unusual situation.
Liverpool Street station’s westbound coffee pot signal
There’s far more uniqueness to these coffee pot signals as we will see in the next few installments of this series.