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Semaphore operation

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Semaphore operation

Unread postby madscientist » Tue May 12, 2015 4:19 pm

Hi I started this discussion in the Overseas board area, but I have a general question

assuming a platform starter is present and so is the advanced stater , which presumably is the " section" signal. IN the absence of suitable calling on , shunt or ground disc, can the platform starter be pulled off, to signal a loco to perform a run round. ( track circuits are in place). I always assumed that the AS would have to be cleared , then the starter cleared ( and a line clear obtained etc) . or can the starter be operated independently of the advanced stater

I suppose the more general question , is within station limits , can signals , junction , starter etc , be used to signal shunt movements where discs or calling or shunt etc arms arnt provided
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Re: Semaphore operation

Unread postby edwin_m » Tue May 12, 2015 9:01 pm

As a general answer, Yes. A semaphore main stop signal when clear indicates that the train can proceed as far as the next main stop signal, which in your case would be the Advanced Starter. However it probably wouldn't be cleared until the train stopped in the platform, in case the driver forgot there was another signal (and that his train was terminating!) and started accelerating away.
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Re: Semaphore operation

Unread postby Mike Hodgson » Tue May 12, 2015 10:48 pm

To answer your general question, you would use a running signal for shunting wherever it is appropriate (ie the same movement as the running movement for which the signal was necessary), and it is not normal practice to provide a shunt signal where the running signal will serve. It would only be provided in addition to a running signal to give access to routes which are not normal running moves - eg a crossover to the wrong line, entry to a siding etc. A calling on arm would only be provided under a main arm, and only where movements are made regularly to an occupied track. Which arm the signalman clears tells the driver whether or not the platform is occupied. A shunt signal might be used instead of a call-on; both signals convey the message that the driver may only proceed as far as the line is clear.

What you could get is a "Shunt Ahead" signal (which may look the same as a call-on) where you have to pass the starting signal but no advanced starter is provided. This would allow allow you to enter the section, but only as far as necessary for the shunt movement.

In general you only need to get a Line Clear for the most advanced signal (ie the Advanced starter if present, or if not then the Starter, or if both are absent then the Home).

General practice is to clear signals in the same order the train reaches them, so an advanced starter would not be cleared before the starter. This may be enforced by "sequential locking".

A calling on arm would not normally be appropriate for a run-around; these are only used to enter occupied platforms, and you obviously can't use an occupied track to reach the other end of your train. If there is an advanced starter, you would keep that at danger, and clear the starter to allow the loco to draw forward clear of points. There would normally be a shunt signal to authorise the return via a crossover to another platform (although on a single line, there would be a Home signal there so no shunt signal would be necessary).

You need to rejoin your train having passed it on another track. That is where a calling-on arm could be appropriate (as the platform is occupied by the coaches), or more often a shunt signal may be used.

edwin_m wrote:A semaphore main stop signal when clear indicates that the train can proceed as far as the next main stop signal, which in your case would be the Advanced Starter. However it probably wouldn't be cleared until the train stopped in the platform, in case the driver forgot there was another signal (and that his train was terminating!) and started accelerating away.


Indeed it would be contrary to Rule 39a to clear it until the train is close to it and the speed is clearly under control. Sometimes this is enforced by locking the signal until a timer has expired ("compulsory Rule 39a")
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Re: Semaphore operation

Unread postby madscientist » Wed May 13, 2015 8:54 am

Thanks. ( there's two threads on this ) , I always thought that semaphores were cleared in reverse order, " unless " rule 39 A was being . Because anything else could show clear to a driver yet find that a further stop signal was not clear.
This reverse order is clearly the case for distant a, a distant cannot be cleared until ALL stop signals ahead are clear , clearly that is reverse order
I understand your comments re using running signals for shunting movements seems reasonable

In my specific case the platform starter had a disc under it. Are you saying the disc would ONLY. Be used to signal an secondary movemrent , ( there was a head shunt siding immediately after the points to connect platform 1 to the main line , which was typically signalled by the running signal normally ) , would the disc not be used instead of the starter to indicate ANY movement forward instead of using the starter or just into the head shunt
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Re: Semaphore operation

Unread postby John Hinson » Wed May 13, 2015 10:08 am

Madscientist wrote:Thanks. ( there's two threads on this ) , I always thought that semaphores were cleared in reverse order, " unless " rule 39 A was being . Because anything else could show clear to a driver yet find that a further stop signal was not clear.
This reverse order is clearly the case for distant a, a distant cannot be cleared until ALL stop signals ahead are clear , clearly that is reverse order
I understand your comments re using running signals for shunting movements seems reasonable

In my specific case the platform starter had a disc under it. Are you saying the disc would ONLY. Be used to signal an secondary movemrent , ( there was a head shunt siding immediately after the points to connect platform 1 to the main line , which was typically signalled by the running signal normally ) , would the disc not be used instead of the starter to indicate ANY movement forward instead of using the starter or just into the head shunt


You are causing a little confusion by posting in two sperate discussions.

Concerning your first point:
That's not true for UK signalling. That may be how some signalmen worked by choice but it was not specified. I cannot speak for Claremorris.

Concerning your second point, I take it this refers specifically to Claremorris although you don't say so here. I will repost that question at viewtopic.php?f=7&t=7103 .

Would all correspondents please use this thread to discuss generic UK issues and viewtopic.php?f=7&t=7103 for matters concerning Claremorris, Eire.

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Re: Semaphore operation

Unread postby madscientist » Wed May 13, 2015 10:24 am

I started two posts too specifically seperate the issue from Irish practice , though I know that Irish semaphore practice differs very little historically from the UK, ( if in practice at all)

Hence why I didn't refer to claremorris in this thread and I did specifically refer to UK practice




Again, as refers to standard semaphore practice in the UK , and not recent practice by the way , lets pick post war. I was always of the view that signals were cleared towards an approaching train and not away from it

ie, a distance is only cleared if all stop signals are clear etc . Otherwise Rule 39A applies , the debate ( my question) is whether stop signals ( and specifically stop signals ) are cleared away or towards the train direction

So are you suggesting that the sequence of clearing is say outer home, inner home, starter and advanced starter and THEN then distant is cleared, surely that introduces problems that if any signal in advance failed to clear, the driver would be faced with a stop signal at normal , when the assumption would be that all previous cleared stop signals indicate that the forward ones are also clear. ( unless rule 39A is being applied of course , but then that is applied in such a way to show the driver that the route ahead is NOT clear )


As I understand it, and yes that may be faulty , this isn't a sequential locking issue, as that is primarily to ensure that signals are replaced to normal , before the sequence can be started again. This question is about the direction of the sequence
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Re: Semaphore operation

Unread postby madscientist » Wed May 13, 2015 11:07 am

Actually I have answered this myself having just read http://dickthesignals.co.uk/onewebmedia ... rcuits.pdf , the sequence is as stated above in this thread, Home, starter , distance and that is enforced by sequential locking where fitted, i.e. the starter has to be replaced to normal before the home can be pulled off confirming that sequence

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Re: Semaphore operation

Unread postby John Hinson » Wed May 13, 2015 11:18 am

It really wasn't as big a deal ats you think. Before sequential interlocking was introduced you could clear you signals how you liked - it really didn't matter. You were supposed to observe the signals as they cleared and you could quickly react to a failure.

Most of all, despite the requirements of Rule 39 there was nothing to say, from a driver's point of view, that he might not come across a signal at danger after passing a home "off". Most drivers would creep ahead if the couldn't see all the signals ahead, and often look for an unofficial "tip" from the signalman before opening up.

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Re: Semaphore operation

Unread postby madscientist » Wed May 13, 2015 12:52 pm

Thanks for that , I gather rule 39A is actually now called 7.3 ?
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Re: Semaphore operation

Unread postby Wilkinstown » Wed May 13, 2015 1:18 pm

The main reason for clearing semaphore signals in the opposite direction to an approaching train would be to minimise movement by the signaller - advance starter, starter, home, outer home and distanct would typically be operated by levers placed one after the other or at least one left/right of the other in the frame. If you don' do it this way you have go back to clear the distant !

Sequential interlocking would not normally (or ever ?) allow signals to be cleared in the manner described above.
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Re: Semaphore operation

Unread postby Pete2320 » Wed May 13, 2015 2:58 pm

Wilkinstown wrote:The main reason for clearing semaphore signals in the opposite direction to an approaching train would be to minimise movement by the signaller - advance starter, starter, home, outer home and distanct would typically be operated by levers placed one after the other or at least one left/right of the other in the frame. If you don' do it this way you have go back to clear the distant !

Sequential interlocking would not normally (or ever ?) allow signals to be cleared in the manner described above.

Interestingley the North Eastern Region had a tendency to move the distant signal lever "inboard" of the starter when sequence locking was provided so the lever sequence became home-starter-distant.
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Re: Semaphore operation

Unread postby kbarber » Thu May 14, 2015 8:03 am

As John says, it wasn't a big issue in everyday operation.

Where there was no sequential locking, signalmen learned to clear signals in the order that most suited them - usually what was easiest (I have yet to see a bobby deliberately do it the hard way, unless the marks are being taken).

Even if a signal failed, there should be no safety issue regardless of the order of clearing. If 39(a) (later C4.6) is being worked, the train will be dropped down signal to signal until it reaches the failure. If the signalman knows it's a failure before pulling off and there's no signal post telephones, he'll stop the driver at the box to instruct him (or give a handsignal). If, on the other hand, the signalman discovers the failure as he pulls off with full line clear, he'll just put back those already cleared. He should, as John says, be checking the signal has answered the lever - a rather dim view would be taken of a bobby who pulled all off without checking and left a clear distant reading up to a failure. But even that won't endanger the train - the failure reads towards a clear section - although the driver might be somewhat less than happy. So the only difficulty is likely to arise if the bobby gets line clear just as he was going to pull off his outermost home under 39(a), starts pulling off then has the wire break on the starter as the train passes the home. In this case the driver could argue he'd been misled by a second signal being cleared well in advance (if he'd SPADed the starter, that is) but there would be no safety implications. And such a situation would be pretty rare in any case.

Quite frankly, when I was in the box, I never gave those considerations a thought. I just worked the signals (in accordance C4.6 when necessary) and kept the trains moving.
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Re: Semaphore operation

Unread postby StevieG » Fri May 15, 2015 10:16 am

Madscientist wrote: " .... As I understand it, and yes that may be faulty , this isn't a sequential locking issue, as that is primarily to ensure that signals are replaced to normal , before the sequence can be started again. .... "
Hi Madscientist.
Having only just read through this thread. I get the impression that your understanding is now good.

I just thought it worth making clear that sequential locking is only about enforcing the sequence of clearing stop signals at the time of attempting to clear them, and has no bearing on any sequence of replacing them to Danger, as, in case of emergency, it normally ought to be possible to place any main running stop signal to Danger at any time, irrespective of the position of other stop signal levers reversed for the same train.

'Sequential' could be achieved either mechanically (through proving only lever positions by means of the mechanical locking of the lever frame). or electrically using electric locks / detection of lever Normal (and making it possible to also include proving of the next signal's actual arm position/aspect).

Also, sequential locking has no relevance to when it is possible to pull or normalise a Distant signal lever : A Distant should not be clearable until all the stop signals to which it applies have been cleared and should have to be replaced to Caution before any of its stop signal levers can be put back to Normal, whether or not there is any sequential locking in place between those stop signals.

P.S. Just in case of interest, there have been installed instances in boxes of some pre-grouping companies where what might be regarded as a more restrictive form of sequential locking has been provided, and dating from the era when either there were few if any, track circuits, their reliability had yet to be proved or widely accepted, or they were regarded as overly expensive for widespread introduction where not fully justified.
This is known as Rotation locking : As well as enforcing the clearing of stop signals in the order that they were approached, this locking included a form of preventing accidents by trying to ensure that each main signal leading to another of the same box could not be cleared when the line ahead to the next stop signal ought* to be occupied.

* - E.g. at a box with rotation locking, having one Home and one Starting signal for a line, and one or more crossover and/or siding connections in between them, if the Home lever was reversed and then placed back to Normal, it became locked even though the Starting signal lever was Normal ; this was because the rotation locking was designed around protecting the assumed presence of a train now located between the Home and Starter.
The Home lever would only become free again once either the Starter signal lever had been reversed and put back to Normal, or one of the points levers (and, if provided, the correct shunt signal lever) had been reversed and re-normalised.

[ I have no idea whether any Irish practice ever embraced any type of rotation locking.]
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Re: Semaphore operation

Unread postby Mike Hodgson » Fri May 15, 2015 10:12 pm

StevieG wrote:I just thought it worth making clear that sequential locking is only about enforcing the sequence of clearing stop signals at the time of attempting to clear them, and has no bearing on any sequence of replacing them to Danger, as, in case of emergency, it normally ought to be possible to place any main running stop signal to Danger at any time, irrespective of the position of other stop signal levers reversed for the same train.


The sequence of clearing signals may not be laid down by the rules, but putting them back is. You should put each signal back as soon as the train has completely passed it, with a proviso about waiting till it has passed any junction points. So they would be put back sequentially. And if you have omitted to restore the Distant to Caution, the locking will prevent you putting back stop signals should you need to do so in emergency.
Last edited by Mike Hodgson on Sun May 17, 2015 10:23 am, edited 1 time in total.
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Re: Semaphore operation

Unread postby StevieG » Sat May 16, 2015 12:05 am

Mike Hodgson wrote:
StevieG wrote:
Madscientist wrote:I just thought it worth making clear that sequential locking is only about enforcing the sequence of clearing stop signals at the time of attempting to clear them, and has no bearing on any sequence of replacing them to Danger, as, in case of emergency, it normally ought to be possible to place any main running stop signal to Danger at any time, irrespective of the position of other stop signal levers reversed for the same train.]


The sequence of clearing signals may not be laid down by the rules, but putting them back is. You should put each signal back as soon as the train has completely passed it, with a proviso about waiting till it has passed any junction points. So they would be put back sequentially. And if you have omitted to restore the Distant to Caution, the locking will prevent you putting back stop signals should you need to do so in emergency.
Would you care to re-examine your "...wrote:" 'quotes' Mike? : I'm unclear on which comment/s or part/s thereof that your point is meant to be relevant to.
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