Semaphore signals

Discussion in 'Infrastructure & Stations' started by najaB, 3 May 2015.

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  1. najaB

    najaB Veteran Member

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    Hi all,

    Travelled the Welsh Marshes line on Friday and noticed there are a lot of semaphores - and mostly lower quadrant ones at that. Two questions that came to mind - is the line likely to be resignalled to colour-light before ECTS is introduced or are the semaphores safe for the next decade or so? Second, were lower quadrant signals ever popular outside the western region? Related, how comes the Western region never converted them to upper quadrant?

    Thanks.
     
  2. LNW-GW Joint

    LNW-GW Joint Established Member

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    The Marches is due to be resignalled in the near future, using the modular system already installed between Crewe and Shrewsbury.
    It will also be controlled from Cardiff.
    Shrewsbury is not included in this (too difficult!), but the semaphores and historic signal boxes along the route are not long for this world.
    The southern end of the line (Pontypool) has already been resignalled as part of the Newport scheme.

    The LMR took over the line north of Craven Arms in 1963 and gradually replaced lower quadrants with LMS-pattern upper quadrants (also across the ex-GWR lines in the west Midlands).
    That's why Shrewsbury has such an eclectic mix of upper/lower quadrant semaphores and colour lights.
    The Western (aka "Wales") is now in control again from Cardiff, also to Crewe and along the North Wales coast, but I haven't seen a new lower quadrant installed anywhere yet.

    Going back to pre-grouping, most lines, including the LNWR and Midland used lower quadrants, of a different pattern to the GWR.
    They all changed to upper quadrants between the wars, but there are still a few lower quadrants left.
    I remember a forest of LNWR lower quadrants at the east end of Chester into the 60s, probably later.
    Don't ask me why the GWR/Western never went upper quadrant!
    Just to be different I expect.

    It's worth remembering that Hereford-Shrewsbury was a joint line (LNWR/GWR) and signalling control varied over the years.
    That's why Severn Bridge Junction box is an LNWR structure with a mix of original and later kit.
    The line was never a GWR monopoly.
     
    Last edited: 3 May 2015
  3. TheEdge

    TheEdge Established Member

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    On a semi related point are lower quadrant signals not as safe as upper ones? I've always thought the preference for upper quadrant signals is that if the cable were to snap the signal will display a danger aspect. With a lower one surely in the event of a snapped cable the signal will display a proceed one. Or do they drop beyond the vertical or similar?
     
  4. najaB

    najaB Veteran Member

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    As I understand it, that is that is the main reason why upper quadrant semaphores are more common. The GWR design uses a heavy weight on the short end of the semaphore arm to cause it to return to danger if the cable breaks.
     
  5. Tomnick

    Tomnick Established Member

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    I'm only aware of one non-GW lower quadrant signal on the national network - Ketton's Down Starter, which is a fine ex-Midland example.

    The arm is connected to the weight bar by a solid rod rather than a wire, so there's less chance of it breaking. I understand that the spectacle casting is sufficiently heavy to return the arm to the 'on' position even if that does happen though.
     
  6. John Webb

    John Webb Established Member

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    Lower quadrant signals were derived from the early signals where, for 'clear', the arm disappeared into a slot in the post and was pulled out and up to the 'Stop' position. But after several accidents, particularly Abbot's Ripton (1876), where several signals were frozen into the post and failed to show 'Stop' or 'Caution' , the use of slotted posts declined, and signals were placed outside the post, but still went down for 'clear'. To ensure safety, however, the arm was driven by a rod rather than wire from a balance arm near the bottom of the post. And in case the rod failed, the 'Spectacle' casting containing the coloured glass had to be made big and heavy enough to return the arm to horizontal on its own.
    It was eventually recognised that the upper-quadrant arm could be made of lighter (and therefore less expensive) materials, but still return to the 'Stop' position by its own weight.
     
    Last edited: 3 May 2015
  7. scott118

    scott118 Member

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    x2 - it's the only one of that type that, I've seen 'north'..
     
  8. matchmaker

    matchmaker Member

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    The last in Scotland - at Stirling Middle. Now with the SRPS.

    signal.jpg
     
  9. Jamesb1974

    Jamesb1974 Member

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    All semaphores are designed to drop/rise totheir most restrictive aspect in the event of a cable breaking. An upper quadrant will drop under its own weight and a lower quadrant has weights (explained by other posters) to return it to danger/caution (in the case of a distant signal).
     
  10. John Webb

    John Webb Established Member

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    We've a couple of Midland Railway lower-quadrant signals in the garden at St Albans South:
    [​IMG]

    The one nearest the camera is in the style of post-1916, with a metal arm, vertical white stripe and cast iron finial. (Picture taken shortly after installation and before we'd finished adjusting things - the arm should be at 45 deg.) You can see the rod from the balance weight going up to the spectacle end of the arm just right of the post.
    The one further away is an earlier version and has a turned wooden finial, wooden arm (replica) and the white dot on the arm; the post and finial are also painted in the more complex MR colour scheme of that period.
    (Also visible are an MR ground disc, a stack of three LMS lower-quadrant disc signals and a more recent BR upper-quadrant distant arm on a Great Northern lattice post!)
     
    Last edited: 3 May 2015
  11. scott118

    scott118 Member

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    well that should at least stop, any conflicting moves within the garden! Hopefully no one has spad'd a flymo, with a signal read through..:lol:

    Thanks for the picture upload.
     
  12. craigybagel

    craigybagel Established Member

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    Its a bit strange when you go through Dorrington, you can see two signals at the same time, home and section signal, and one is lower quadrant and one upper. Wonder how many other places there are like that....

    The South Wales signalling centre in Cardiff is a very large room, that is currently mostly empty. You can see where the panels for various routes are going to go though, including the Marches line.
     
  13. edwin_m

    edwin_m Veteran Member

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    Current practice is that on the rare occasions a semaphore signal needs to be installed, it will be upper or lower to match to the ones around it. Some new lower quadrants were put in at Banbury a couple of years back to allow reversal of trains diverted to avoid work at Reading. However I don't believe there's any plan to unify the type of signals in mixed areas like Shrewsbury.
     
  14. Llanigraham

    Llanigraham Established Member

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    Planned to get rid of us mechanical signallers on the Marches line in the next 3 years, with control of the pretty lights from Cardiff.

    Because the GWR did it properly!!!
     
  15. edwin_m

    edwin_m Veteran Member

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    The answer to that question is because the GWR never converted them. It would be interesting if anyone knew why not!

    All the Regions, with the possible exception of the Southern, continued to use the components standardised by their predecessor companies. With relatively few new semaphore signalling projects most work in the BR era would be repair and upgrade of existing installations so it didn't make sense to change things. The last LMS and LNER designs were virtually identical anyway, and I think the Southern adopted this design instead of perpetuating SR practice. All these companies had adopted upper quadrant soon after the Grouping, so any remaining lower quadrants would have been old and obsolete and they had pretty much gone by 1960.

    The GWR had also developed an extensive range of standard components, applied almost universally on their network, so again it made little sense to change. However their range was based on lower quadrant signals, as well as being different from the others in almost all other respects...
     
  16. Railsigns

    Railsigns Established Member

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    Until the 1920s, every main line railway company in the British Isles was using lower quadrant signals as standard.
     
  17. CalderRail

    CalderRail Member

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  18. Railsigns

    Railsigns Established Member

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    The problem there was the signal arm freezing in the 'clear' position. Early semaphore signals had arms that disappeared into a slot in the post when cleared. In this instance, it would have made no difference if the arm had operated in the upper quadrant.
     
  19. najaB

    najaB Veteran Member

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    It's a small difference but I think an 'upper slot' signal would be less likely to freeze as any water would be running down and away from the signal arm.
    --- old post above --- --- new post below ---
    Thanks - I didn't realise the 'changeover' was as late as the 1920's.
     
  20. Pigeon

    Pigeon Member

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    ...and you can see this working, for example when waiting at a station where a box at one end controls signals at the other by means of wires strung along the face of the opposite platform. You can watch the wire go taut as the signal is pulled off and go slack again as it is returned to danger.
     
  21. edwin_m

    edwin_m Veteran Member

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    As the arm would be horizontal for danger and invisible for clear in either case, I can't see that it makes any difference.

    Abbots Ripton is said to have given rise to the practice of keeping semaphore signals at danger/caution until a train was accepted, rather than leaving them clear all the time except when a train had recently passed. This gave them much less time to freeze in the clear position. It is also said to be the reason for the GNR developing the "somersault" signal, still lower quadrant but the arm pivoted centrally on a bracket so was some distance from the post when showing clear.

    There was an accident at Chinley as late as 1958 caused by a semaphore freezing "off", but this would not have happened had the signalman checked, as he should have done, that the arm had returned to danger when replacing the lever after the previous train. This check is the reason semaphores have backlights and those that cannot be seen from the box have arm repeaters next to their levers.
     
  22. najaB

    najaB Veteran Member

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    As I said, it's only a slight difference the danger exists in either design. With an 'upper slot' gravity is helping to free a partially frozen mechanism to bring the semaphore arm to danger, with a 'lower slot' you're working against both the mechanism and gravity.

    There's no escaping the fact that the slot design is inferior compared to later designs.
     
  23. DaveNewcastle

    DaveNewcastle Established Member Fares Advisor

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    In the case of the 'Flying Scotsman' fatality at Abbots Ripton, I understood that the increased weight of snow on the arm was a contributory factor to the lower-quadrant signal remaining 'off' while the main-line was still occupied by the reversing freight, (all taking place during a blizzard in which visibility was very poor).
    [I have a connection to someone who lost their life in that incident].
     
    Last edited: 4 May 2015
  24. ac6000cw

    ac6000cw Established Member

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    I think a major contributory factor at Abbotts Ripton was that it was the convention at the time (on some railways at least) to have normally 'open' blocks i.e. signals were normally 'clear' unless the block ahead was occupied. This allowed the arms to freeze more easily in the 'clear' position (in the slotted posts) during the blizzard. After the accident there was a general change to having normally 'closed' blocks (so signals are at 'danger' other than to allow train movement).

    Of course we changed back to normally open blocks with the introduction of automatic block signals (in those areas)....

    Part of the reason for the delayed changeover to upper-quadrant semaphores was because a few pre-grouping railways had been looking at/experimenting with American style three-position upper quadrant power semaphores (horizontal/45 degrees/vertical for stop/caution/clear). After the IRSE set up a technical committee in the 1920s to look at the future of signalling in the UK, the installation of three-position semaphores was not permitted - colour lights were the future for 3 and 4 aspect signals - so two-position upper quadrant arms could be used without fear of confusion. (Although I think the experimental Great Central three-position semaphores in Lincolnshire lasted quite a long time before replacement - from about 1912 until the early 1970's ?).

    --- old post above --- --- new post below ---

    As for why the GWR never changed their semaphores, God's Wonderful Railway (or Great Way Round) always trod it's own path, helped no doubt by the fact that it was the least changed at Grouping of the 'big four' and that it made most of its signalling equipment at Reading. It also never really seemed to embrace power signalling in a significant way.
     
    Last edited: 4 May 2015
  25. LNW-GW Joint

    LNW-GW Joint Established Member

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    And when the WR finally did roll out power signalling, it chose a system that was incompatible with AC electrification.
    It is now having to be replaced for the present electrification scheme.
    One of the horrors about the possible break-up of Network Rail is that the Routes will go their own way (again).
     
  26. edwin_m

    edwin_m Veteran Member

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    Most of the signalling on the GW routes being electrified dates from the 1960s or early 70s so is pretty much life-expired and would have had to be replaced within a few years even with no electrification. So the WR probably called that one right, though for all the wrong reasons! Fortunately most modern signalling equipment has immunity built in so the work needed for electrification of recently re-signalled areas will be less.
     
  27. Crossover

    Crossover Established Member

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    I had a feeling upper quadrant were potentially less problematic in snow/ice and such like, as if the arm gets weighed down, it'll be weighed down to danger rather than clear. I guess a lower quadrant could be weighed down to clear, counteracting the counterbalance
    --- old post above --- --- new post below ---
    Do you know if this is still the case now? I recall being at Brough one evning towards the end of last year and the semaphore was held 'on' until about a minute before the train reached the station, and therefore the signal.
     
  28. Tomnick

    Tomnick Established Member

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    Yes, it's still one of the underlying principles of Absolute Block signalling, but there's no requirement during falling snow to delay 'pulling off' beyond the usual time that the train would be offered forward as specified in the regulations (usually upon receipt of 'train entering section') or box instructions. With the various controls (such as 'home normal control', requiring the home signal proved at danger before a 'line clear' can be given to the box in rear), anything resulting in an arm failing to return to danger would be an inconvenience rather than directly affecting the safety of the line.
     
  29. MarkyT

    MarkyT Established Member

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    The 'system' the Western Region chose was not fundamentally incompatible, rather the specification did not require the additional expense, as with many other non-electrified parts of the network, regardless of region. As Edwin_M explains there's no point in modifying the existing kit for AC compatibility as it's life expired and many parts are obsolete. Book life for signalling installations is 40 years, which might be tweaked up or down a decade or so depending on emerging condition factors of the specific sites and the fit with major enhancements such as layout changes and electrification. Beyond Paddington - Heathrow, provision for electrification also began in the early 1990s with Didcot - Swindon resignalling. That scheme, incorporating the new Relief lines between Wantage Road and Challow, was built to be AC compatible using SSI and with all major signalling structures designed for OHLE clearance.
    --- old post above --- --- new post below ---
    GW and WR lower-quadrant arms are very heavily weighted with a large iron casting the other side of the pivot which also houses the coloured spectacle glass filters, so in a broken wire scenario the much lighter thin steel plate arm should always return to the danger position. If a signal had been cleared for a long time, for instance when a box is switched out, then icing around the bearing area might feasibly seize an arm in the off position but that could apply equally for the upper-quadrant type and the signaller should observe the indicated position of signals anyway via direct vision or using arm repeating indicators. Important functions such as giving a line clear block release usually require arms to be proved in the danger position using the arm repeating contacts as well.
     
  30. Pigeon

    Pigeon Member

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    Not on the arm, on the wires. Signal operation had been disrupted for quite a while before the actual accident.
     
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