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Mixing mechanical and automatic signalling

British signalling of the past (UK, excepting Northern Ireland)

Mixing mechanical and automatic signalling

Unread postby Crepello » Fri Aug 11, 2017 6:38 pm

Good evening; I'm interested in the North London Line in the 1950s, so there would have been parts with the LMS 1930s signalling scheme I believe.

As a person with only a naïve understanding, I'd like to know more about how boxes controlled a section that was, say, fitted with automatic lights for a main line but also had control of a branch section that was mechanically signalled. I.e a facing branch from the main line ( electric signal ) and thence mechanical signals. Would the FPL have been electric, and would it be controlled from the box at the junction or from a box elsewhere?..
I presume the combination of detection and electronic locking assisted where such sections met? hope you learned people out there know some answers!
Cheers
Al
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Re: Mixing mechanical and automatic signalling

Unread postby John Hinson » Sun Aug 13, 2017 1:39 am

G'day Al,

There was no automatic signalling on the North London at that time. everywhere was worked on the Absolute Block system. There were some LMS colour-light signals but these were just substitutes for semaphore signals.

I am wondering if you are thinking of the Camden-Watford New Line? The signalling here was automatic except in the vicinity of signalboxes (when switched in). There weren't many interfaces with other signal boxes but in the few instances signals were either slotted (where sections were short) or Absolute Block applied . . . or both. For example, on the City Passenger lines between Willesden New Station and Kensal Green Junction boxes, Absolute Block applied but each box's Starter was slotted as the other's Outer Home - this allowed trains to be freely accepted despite trains being signalled through on the busy main routes at each box.

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Re: Mixing mechanical and automatic signalling

Unread postby Fast Line Floyd » Mon Aug 14, 2017 9:55 am

Crepello wrote:Good evening; I'm interested in the North London Line in the 1950s, so there would have been parts with the LMS 1930s signalling scheme I believe.

As a person with only a naïve understanding, I'd like to know more about how boxes controlled a section that was, say, fitted with automatic lights for a main line but also had control of a branch section that was mechanically signalled. I.e a facing branch from the main line ( electric signal ) and thence mechanical signals. Would the FPL have been electric, and would it be controlled from the box at the junction or from a box elsewhere?..
I presume the combination of detection and electronic locking assisted where such sections met? hope you learned people out there know some answers!
Cheers
Al

The FPL would have been mechanical if the points were mechanical and such points and FPL's would be worked from the same signalbox that controlled the signal reading over the points. However the detection of the points and FPL would have been electric so as to complete the colourlight signal circuits.

Please don't confuse Electric and Electronic, there was nothing electronic in 1930's signalling.
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Re: Mixing mechanical and automatic signalling

Unread postby StevieG » Tue Aug 15, 2017 8:56 pm

Fast Line Floyd wrote:
Crepello wrote:Good evening; I'm interested in the North London Line in the 1950s, so there would have been parts with the LMS 1930s signalling scheme I believe.

As a person with only a naïve understanding, I'd like to know more about how boxes controlled a section that was, say, fitted with automatic lights for a main line but also had control of a branch section that was mechanically signalled. I.e a facing branch from the main line ( electric signal ) and thence mechanical signals. Would the FPL have been electric, and would it be controlled from the box at the junction or from a box elsewhere?..
I presume the combination of detection and electronic locking assisted where such sections met? hope you learned people out there know some answers!
Cheers
Al

" .... However the detection of the points and FPL would have been electric so as to complete the colourlight signal circuits. .... "
May I just add though, FLF, that there were instances (not specific to the North London line, also fairly rare I believe, and usually quite old) where colour-light protected mechanical points/FPLs had mechanical detectors, as used for mechanically-worked semaphores.
From these, the signal wires then ended at mechanically-actuated electric contact boxes ('circuit controllers') on, or close to, the signal(s) structure(s), from which electrical circuitry then controlled the colour-light signal aspects.

On the North London line, in 1969 before the severely rationalised Broad Street area layout and signalling was concentrated on BS No.2 Box, I saw that the two Up lines' (admittedly ancient-looking) multi-routed colour-light Home signals at Skinner Street Jn. Box operated in this way (even to the extent of also being mechanically slotted by SSJ and one other box or ground frame for every route).
BZOH

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Re: Mixing mechanical and automatic signalling

Unread postby Fast Line Floyd » Wed Aug 16, 2017 8:16 am

StevieG wrote:
Fast Line Floyd wrote:
Crepello wrote:Good evening; I'm interested in the North London Line in the 1950s, so there would have been parts with the LMS 1930s signalling scheme I believe.

As a person with only a naïve understanding, I'd like to know more about how boxes controlled a section that was, say, fitted with automatic lights for a main line but also had control of a branch section that was mechanically signalled. I.e a facing branch from the main line ( electric signal ) and thence mechanical signals. Would the FPL have been electric, and would it be controlled from the box at the junction or from a box elsewhere?..
I presume the combination of detection and electronic locking assisted where such sections met? hope you learned people out there know some answers!
Cheers
Al

" .... However the detection of the points and FPL would have been electric so as to complete the colourlight signal circuits. .... "
May I just add though, FLF, that there were instances (not specific to the North London line, also fairly rare I believe, and usually quite old) where colour-light protected mechanical points/FPLs had mechanical detectors, as used for mechanically-worked semaphores.
From these, the signal wires then ended at mechanically-actuated electric contact boxes ('circuit controllers') on, or close to, the signal(s) structure(s), from which electrical circuitry then controlled the colour-light signal aspects.

On the North London line, in 1969 before the severely rationalised Broad Street area layout and signalling was concentrated on BS No.2 Box, I saw that the two Up lines' (admittedly ancient-looking) multi-routed colour-light Home signals at Skinner Street Jn. Box operated in this way (even to the extent of also being mechanically slotted by SSJ and one other box or ground frame for every route).

Indeed Steve I had thought of adding this but decided not to muddy the water.
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Re: Mixing mechanical and automatic signalling

Unread postby StevieG » Wed Aug 16, 2017 11:38 am

Fast Line Floyd wrote:Indeed Steve I had thought of adding this but decided not to muddy the water.

Hmm; probably a fair point Graham.

Crepello, I hope you gain the understandings that you seek from these 'muddied waters'.
BZOH

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Re: Mixing mechanical and automatic signalling

Unread postby colin1501 » Wed Aug 16, 2017 6:51 pm

Following from Steve's point, and slightly off topic location wise, the semaphore down starter at Billingshurst was replaced by a 3-aspect c/l in the 1970s, while the advanced starter remained a semaphore. The starter cleared to yellow when pulled off, and to green when the advanced starter was pulled off. However, it sometimes flickered from green back to yellow then green again, and I assumed from this that the feed to the yellow and green aspects was via the arm repeater on the advanced starter, the flicker occurring as the arm bounced before settling. Sound likely?

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Re: Mixing mechanical and automatic signalling

Unread postby StevieG » Thu Aug 17, 2017 12:00 am

colin1501 wrote:Following from Steve's point, and slightly off topic location wise, the semaphore down starter at Billingshurst was replaced by a 3-aspect c/l in the 1970s, while the advanced starter remained a semaphore. The starter cleared to yellow when pulled off, and to green when the advanced starter was pulled off. However, it sometimes flickered from green back to yellow then green again, and I assumed from this that the feed to the yellow and green aspects was via the arm repeater on the advanced starter, the flicker occurring as the arm bounced before settling. Sound likely?

Colin
... very, Colin; in fact almost certainly I'd say.
And although not much related to the OP, this must surely still be relevant to the thread's title.

To elaborate on this sort of arrangement, until resignalling around 1973, the ECML's London area included New Southgate ("NS") and Cemetery (C) boxes.
NS's Down Fast Second Home (think 'Starter' on other railways: And about 235 yards from Box, at the departure end of that station platform) was a '4-aspect' 'searchlight' colour-light (standard 3-aspect plus additional top lens, yellow or unlit), reading towards the mechanical semaphore Starter ('Advanced Starter': 1,066 yards from Box), and with its double yellow provided to act as C's Outer Distant.

The semaphore Starter had C's mechanical semaphore Inner Distant below it.

If C was switched out or had cleared his signals before NS, then if, after clearing the Second Home 'Off' to one yellow, NS pulled the mechanical Starter vigorously, clearing both semaphore arms at the same time, it caused them (remembering the 1,066 yard-long wire run to the stop arm) to rapidly move above, through, below, and back into, the range of degrees detected as properly 'OFF', but also the actions of the usual elements of the mechanical slotting meant that the two arms did not do this in synchronisation.
So, as the aspects of the colour-light Second Home were controlled by the arm position contact boxes of both semaphore arms, the result was briefly a rapidly changing veritable light show at the end of the platform, as the signal flashed through YY, R, G, R, Y, YY etc., (sometimes managing to do the cycle around 1 1/2 - 2 times) until the arms settled at 'Off' and the colour-light became steady green.
BZOH

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Re: Mixing mechanical and automatic signalling

Unread postby colin1501 » Thu Aug 17, 2017 6:40 am

Thanks, Steve - much the same scenario, but the combination of a 4-aspect c/l, and a stop/distant semaphore clearly added a bit more interest! I visited Billingshurst a few times in 2013 before the line was resignalled, and didn't notice this phenomenon then. I wonder if the circuitry had been changed during the intervening years.

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Re: Mixing mechanical and automatic signalling

Unread postby John Hinson » Thu Aug 17, 2017 8:27 am

I think perhaps we should pause, take a breath and await Crepello's response as we are waffling in frightening detail about things he hasn't asked about. Then perhaps we can be more defined with our answers . . .

Best regards,

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Re: Mixing mechanical and automatic signalling

Unread postby Crepello » Fri Aug 18, 2017 9:42 pm

Thanks all; that's an interesting array of replies already! So to be a little more specific, let's consider - nominally! - the Hampstead Junction line through Finchley. We appear to be saying the signals may be colour light, and those are effectively a replacement for a mechanical arm. A facing point lock may be mechanical but with electric contacts to link with the signal, so it would be controlled and operated from the section box alongside the relevant point lever??? I'm interested in both the actual and the what-might-have-been as an aid to a general understanding of the NLL signalling. Cheers!
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Re: Mixing mechanical and automatic signalling

Unread postby Fast Line Floyd » Sat Aug 19, 2017 5:49 am

Crepello wrote:Thanks all; that's an interesting array of replies already! So to be a little more specific, let's consider - nominally! - the Hampstead Junction line through Finchley. We appear to be saying the signals may be colour light, and those are effectively a replacement for a mechanical arm. A facing point lock may be mechanical but with electric contacts to link with the signal, so it would be controlled and operated from the section box alongside the relevant point lever??? I'm interested in both the actual and the what-might-have-been as an aid to a general understanding of the NLL signalling. Cheers!

Basically yes. There was nothing unusual about the NLL signalling. It's principles applied throughout the UK for its era.
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Re: Mixing mechanical and automatic signalling

Unread postby Mike Hodgson » Sat Aug 19, 2017 11:45 am

There was a policy decision in the 1920s that colour light signals would be used instead of semaphores in future.
However this has not meant that all new signals since then have been colour lights - we are still sometimes putting in sempahores as replacements even today.

What happened is that whenever there was a major resignalling scheme (a whole stretch of line or perhaps remodelling a station), the new work generally would use colour lights. But such schemes are only financially justified for major upgrades when it is commercially necessary to increase line speed or the frequency of service. On many lines (especially branches and minor cross-country routes) the existing system was perfectly adequate if antiquated and there was no budget to modernise. So when individual semaphores needed replacement (rotten wooden posts, accident damage etc), they were often replaced with a more modern semaphore for consistency, although sometimes a colour light might be used.

Like for like replacement of a semaphore can be cheaper and easier than putting in a colour light, as there need to be associated electrical work and changes to lever frames. This might mean quicker return to normal service when the work was an urgent repair. Also, mixing colour light and semaphore at the same signal box could potentially be dangerous. For example if a home signal was a semaphore with a weak oil lamp whilst the starting was colour light, a driver approaching the home at danger might "read though", that is fail to obey it on seeing the more powerful starter showing green for the preceding train still standing in the platform. So although you often did get manual boxes controlling a mixture of signal types, each case had to be considered on its merits, and in practice the policy change has taken much longer to implement than had been anticipated almost a century ago.
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Re: Mixing mechanical and automatic signalling

Unread postby JRB » Sat Aug 19, 2017 1:56 pm

A common mixture was a distant semaphore renewed as a colour light. Typically a distant would be moved further out for increased speed and be too far for mechanical operation.
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Re: Mixing mechanical and automatic signalling

Unread postby John Hinson » Sat Aug 19, 2017 5:20 pm

Here is a plan for Kentish Town Junction box (later known as Camden Road Junction) at 1950, showing the Hampstead Junction line turning off bottom-right:
https://signalbox.org/diagrams.php?id=1165

As Graham says above, there is nothing unconventional about the signalling here - in fact there is not a colour-light signal to be seen!

But things soon changed. Here is the layout at 1959, after the box had changed its name:
https://signalbox.org/diagrams.php?id=1166
Suddenly, semaphore signals are in the minority, and more track circuits have appeared. Nevertheless, working is still conventional - with Absolute Block working retained. I suspect the colour-lights were a mass replacement for some rickety semaphores - remember all was on viaduct here so erection of heavy steel bracket signals would have been difficult. Some of the new colour-lights were actually mounted on the stumps of the old wooden posts.

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