Semaphore distant signal

[MDP78]

This question is about distant signal operation where two signal boxes are close together. 

 

I understand that Box B's distant would be slotted with one of Box A's starters. However how would Box A's distant work (not one slotted on one of Box B's signals).

 

I have 4 volumes of 'An Illustrated History of GWR stations'. Some diagrams do explain how Box A's distant would work. In the case of Hartlebury Junction, the distant was apparently worked by Hartlebury Station Box. There are also examples where the distant is slotted.

 

Are there any other ways for the distant to work? For example would Box A's distant level be mechanically interlocked with the level in Box B that cleared its starter?

Edited August 12, 2022 by MDP78

[SM42]

I would say that this is one of those "it depends" answers 

 

Signalling control tables  vary for the particular idiosyncrasies of the location. 

 

Andy

[Ian Smeeton]

Assuming that we are talking a single direction of travel:

 

Box A -> Box B 

 

Box A's distant can only be set clear when all the Stop signals in his section are clear:

 

Lever 1 = Distant

Lever 2 = Starter

Lever 3 = Section signal

 

Order of clearing would be 3, 2, 1 as the distant can only be cleared when the complete section is clear. 2 cannot be cleared until 3 is clear, and 1 cannot be cleared unless BOTH stop signals are clear.

 

Box B has a similar set up to A, but its distant is 'slotted' with A's Section signal. i.e. the distant is on the same post as A's Section signal.

 

Box B's distant can only be cleared when B's Starter and Section signal are cleared AND box A's Section signal has been cleared.

 

If I could draw a diagram on here it would be much simpler - A picture paints a thousand words!

 

Regards

 

Ian

[micknich2003]

Attached layout of a signalbox I worked in the '80's, "Short Section" either way about 600 yards each. The "Special Instructions" stated No29 only to be cleared when Beverley and Beverley North had "Pulled Off", Not shown on the drawing, No29 was also Beverley's Down Distant in fact a "Slot" and as it had been a few years earlier when mechanical. Like said above, much depends on local circumstance.

[Edwin_m]

Where boxes A and B were so close that A could only clear its distant if B had also done so, this was often achieved not by a mechanical slot or some electric arrangement, but by the signalman at A observing B's distant directly if visible, or an indicator in box A.  This always struck me as a major loophole in the system, and was contributory to the collision of a Pullman at Knowle & Dorridge in 1963.  

 

https://www.railwaysarchive.co.uk/docsummary.php?docID=513

[The Stationmaster]

It very much depended on how short the distance was between the two 'boxes.  

 

In the most basic of cases if the braking distance to B's Home Signal puts it's distant in the vicinity of A's stop signals a lower arm distant would be added to all of A's stop signals within the braking distance for B's distant.  All of these lower arm distants wouldv be slotted by the stop signal arm above them and could be worked either mechanically or electrically.

 

However on someparts of the railway - notably parts of what became BR's Eastern Region instead of lower arm distants you could occasionally find a separate distant signal (for B) onlya fairly short distance beyond A's most advanced stop signal (a good example could be found at Ipswich at one time - but it was far from unique.

 

Things got more complicated if the necessary braking distance for B's distant signal put it in rear of A's Home Signal (i.e. A's rearmost stop signal).  Thus while A's stop signals would in most cases still have lower arm distants for B there would also be a need for B to additionally control A's distant signal - usually done electrically but it was possible to do it mechanically although generally such installations went as soon as various electrical controls became more readily, and cheaply, available.  On the GWR  a special Signalling Regulation was sometimes used instead (and in later years in addition to) a control on A's distant signal - the Knowle & Dorridge collison showed what could happen if the Regulation was not correctly applied

 

It got a bit different when the distance between A's Home Signal and B's Home Signal was even shorter and in this case A's distant became the distant for both 'boxes (so also controlled by B) and very often there would be no lower arm distants on A's stop signals.  This also impinged on the block working between the two 'boxes and the time at which A was permitted to clear his stop signals so while the technology was unchanged it required a very different application of the Regulations and the working of stop signals.  At r ts most extreme A's most advanced stop signal would also be B's Home Signal so it was slotted by 'box B.

 

N.B.  the terms in advance and in rear are the least ambiguous way of explaining the relative position of things on the railway.  They are always used in relation to the direction of travel.  Thus a train progresses from signal box A to signal box B and then to signal box C;  B is in advance of A and C is in advance of B.  Thus A is in rear of B.  Smple way to understand is to imagine you are standing in the four foot facing in the direction of travel of a train on that line - all that you see in front of you is in advance and that which is behind you is in rear (and you could even tap part of your anatomy to remind you what is in rear.

 

So a signal box's distant signal is in rear of the 'box

 

The photo below shows mechanical slot - not absolutely clearly but hopefully sufficiently.   The two outer balance weight levers are the ones worked from the two different lever frames so when the lever is pulled the weight on the right hand end of the balance weight rises.  The middle weight lever has its balance weight at the opposite end and you can see a plate bolted to it which extends over both of the other balance weight levers but is only bolted to one of them (that is the one which slots the signal).   The plate forces down the left hand weight from when the slot is cleared and it can go back up when either lever worked balance weight is returned to normal.  Thus when both outer levers have operated the middle lever can be forced dwnwards at its left hand end and the down rod to the right of the pivot point can rise causing the signal arm to lower.  Returningewither of the other levers to their normal position will cause the metal plate to rise and the signal to return to danger/

 

 

 

Edited August 13, 2022 by The Stationmaster

[tomparryharry]

If I remember correctly on the up Merthyr line, Clydach Court Jcn, Stormstown, Carne Park & Abercynon were all on the slotted distant. On the Rhymney section, the line above Caerphilly Tunnel was quite 'busy'.

[MDP78]

Managed to get a shot of the Hartlebury Junction diagram. The distant in question is identified as no.27.

 

Presumably though, this would still have been slotted or interlocked so that it only cleared when both boxes had cleared all of the following signals?

[The Stationmaster]

On 13/08/2022 at 16:42, MDP78 said:

Managed to get a shot of the Hartlebury Junction diagram. The distant in question is identified as no.27.

 

Presumably though, this would still have been slotted or interlocked so that it only cleared when both boxes had cleared all of the following signals?

Yes, exactly the case.   That is the meaning of the note that says 'Controlled By Hartlebury Station', i.e, the next 'box in advance.  So basically it was slotted although in this case  'controlled by' was done through relays which were probably nowhere near the signal.    Where there were a succession of short sections you would find, particularly on fast sections of route, that this sort of control could extend back through a whole succession off distant signals.  

 

For example at Slough in the Up Direction the sequence of signal boxes was Farnham Road - 1188 yds - Slough West - 506 yds - Slough Middle - 308 yds - Slough East;  on absolutely minimum GWR distant signal siting Slough East's Distant would be at Slough West and for faster speeds, as were permitted there, it would be between Farnham Road and Slough West.  Slough Middle's Up Main Distant would also as, as a minimum, be between Farnham Road and Slough West  while Slough West's Distant would be at Farnham Road or probably even further beck.  Thus there was a situation where Slough East also 'controlled' the Distant Signals for Slough Middle and Slough West. (and possibly even Farnham Road's Up Main Distant - without checking the box diagram).

[jim.snowdon]

On 12/08/2022 at 20:05, Ian Smeeton said:

Box A's distant can only be set clear when all the Stop signals in his section are clear:

 

Lever 1 = Distant

Lever 2 = Starter

Lever 3 = Section signal

 

Order of clearing would be 3, 2, 1 as the distant can only be cleared when the complete section is clear. 2 cannot be cleared until 3 is clear, and 1 cannot be cleared unless BOTH stop signals are clear.

Don't you mean, in order of travel -

 

Lever 1 - Distant

Lever 2 - Home

Lever 3 - Section (or Starter) signal

 

which would make the lever pulling order 2, 3, 1, lever 3 being conditional on obtaining a Line Clear from the 'box in advance.

[Michael Hodgson]

 

17 hours ago, jim.snowdon said:

Don't you mean, in order of travel -

 

Lever 1 - Distant

Lever 2 - Home

Lever 3 - Section (or Starter) signal

 

which would make the lever pulling order 2, 3, 1, lever 3 being conditional on obtaining a Line Clear from the 'box in advance.

 

 

That would be the usual sequence under current practice. 

In some cases that is the only possible sequence, because of Sequential locking or other controls on signals. 

• A fairly standard control is Line Clear Release, which means you can ony pull the starter if the train has been accepted forward and the block instrument is showing Line Clear.  It is of course a requirement of the rules, but it is unusual these days for this not to be electrically enforced.    This alone is not watertight, as you might clear the signal a second time, thus irregularly allowing a second train to be signalled forward if the box in advance has omitted to put his block instrument to Train Line for the first (which might be your fault for failing to send Train Entering Section or the box in advance for not responding correctly - but still your fault for not noticing his oversight).  Occupation of the Berth track  (track circuit just in rear of the Home Signal of the box in advance) usually forced the block to Train on Line if it was not already in that position as it should have been.  The block instrument was usually locked so that the section signal must be at Danger before Line Clear could be given.  Not a common problem, but this prevented a signalman on lines with a fairly sparse service from being so extremely lazy and irresponsible as to leave all his signals off all the time on the basis that the previous train would be long gone by the time another one came along.
• Line clear One Pull or Line Clear One Train are additional controls to reinforce the Line Clear Release.  The Line Clear Release is destroyed either by the act of clearing the section signal (one line clear, one pull) or by the passage of a train (one line clear, one train), either way ensuring (in conjunction with sequential locking on the signals in rear) that the signal can only be cleared for one train to pass into the section.
• Sequential locking is another control, under which you can't pull the home if the starter is already off (this applies to all the stop signals in sequence if there are several).  So you must clear them in the order in which the train passes them.  This control was typically installed on lines with a frequent service.
• The distant is invariaby locked so that if can only be cleared if all stop signals in that direction are already off, that locking would usually be mechnical; it is important to put the distant back to caution as soon as the train has passed within it, because the converse of this locking prevents you from restoring the stop signals to danger in an emergency whilst the distant remains off.
• Compulsory Rule 39(a) is another control which can be provided and affects clearance of signals.  Where the train is not being given a clear run (typically because the section in advance is still occupied), the signalman is required under that rule not only to keep the distant at caution but also to keep his stop signals at danger and only clear them one at a time once the approaching train has got its speed under control.  That procedure can be enforced electrically by ensuring that a track circuit in rear of the signal has been occupied for a sufficient period of time (obviously without encroaching onto the next track circuit!) this demonstrating it's not going very fast.  This rule was particularly important in steam days, as drifting smoke etc could cause a driver to miss the distant, so suddenly seeing a Home SIgnal at Danger gives him a second chance.
• Some times the passage of a train would automatically put the signal back to danger behind the train - standard with colour lights, but there were also automatic mechanical restorers on some semaphores. 

 

Historically however, there was a practice in some companies for trains which are being given a clear run of pulling in the reverse sequence, ie starter, home the distant.

[RailWest]

>>>Sequential locking is another control, under which you can't pull the home if the starter is already off (this applies to all the stop signals in sequence if there are several).  So you must clear them in the order in which the train passes them. 

 

There was also sometimes Rotation Locking which AIUI meant that once you had pulled (say) the Home and then put it back, it could not be pulled again until after the Starting had been pulled and replaced (and so forth if there was an Advanced Starting etc), thereby proving (in theory at least) that the train had passed onwards. Of course, if you pulled the Home only, so that the train could pull up to the Starting and then reverse back into a siding or over a crossover on the adjacent line, then because the Starting had not been used there had to be a means to release the backlock on the Home, which might have been achieved (say) by the pulling+replacing of whatever shunt signal was used to back the train out of the way.

[MDP78]

Just had a further thought. Would Hartlebury Station Box have 2 distant levels for the side of the level frame closest to Hartlebury Junction ? I.e. :

 

1. A distant lever to allow the distant shown numbered 27 on the track diagram; and

 

2. A distant lever to allow the distant attached to Hartlebury Junction's Up Main Home (no.26 on the diagram)?

 

I assume so, or some such arrangement so that it was possible to leave no.27 at caution  for an approaching train but allow the distant on no.26 to be cleared if appropriate. 

[RailWest]

AIUI from the partial diagram, the distant underneath the Up Main Home is NOT worked from Hartlebury Jcn but the next box along, so HJ would not have a lever for it.

[bécasse]

The distant signals under both up homes 24 and 26 are worked only by the next box, presumably Hartlebury station, and quite possibly by the same lever there. They would, of course, be slotted on the post by the homes above them (which would mean that no selector would be required if they worked by the same lever, the selection would effectively be done by these slots).

Edited August 19, 2022 by bécasse

[MDP78]

22 hours ago, RailWest said:

AIUI from the partial diagram, the distant underneath the Up Main Home is NOT worked from Hartlebury Jcn but the next box along, so HJ would not have a lever for it.

Yes I know that to be the case. The question was about Hartlebury Station's level frame. I am aware that the distant arm on no.26 (Hartlebury Junction's Up Main Home) was worked by a level in Hartlebury Station. 

 

The question was whether Hartlebury Station had a level for no.26 and a level for no.27. The reference to Hartlebury Jcn in the question was in reference to the levels for those signals being on the left hand side of the Station Box's lever frame I.e. the side of the box nearest to Hartlebury Jcn. 

Edited August 20, 2022 by MDP78

[The Stationmaster]

14 hours ago, MDP78 said:

Yes I know that to be the case. The question was about Hartlebury Station's level frame. I am fully aware that the distant arm on no.26 (Hartlebury Junction's Up Main Home) was worked by a level in Hartlebury Station. 

 

The question was whether Hartlebury Station had a level for no.26 and a level for no.27. The reference to Hartlebury Jcn in the question was in reference to the levels for those signals being on the left hand side of the Station Box's lever frame I.e. the side of the box nearest to Hartlebury Jcn. 

According to the information on the SRS site the same lever (No.1)  at Hartlebury Station 'box worked all the distants but that information appears to be  no earlier than the early 1970s and all the distants were electrically worked.  However looking at the information for the lever leads it does look as if it had long been the case that the same lever worked all the distants although the direct control of Hartlebury Jcn's Distant might possibly have been a later addition notwithstanding the fact that the two 'boxes were only 27 chains apart.

[MDP78]

22 hours ago, The Stationmaster said:

According to the information on the SRS site the same lever (No.1)  at Hartlebury Station 'box worked all the distants but that information appears to be  no earlier than the early 1970s and all the distants were electrically worked.  However looking at the information for the lever leads it does look as if it had long been the case that the same lever worked all the distants although the direct control of Hartlebury Jcn's Distant might possibly have been a later addition notwithstanding the fact that the two 'boxes were only 27 chains apart.

Signalmen must have been pretty happy when distant started getting motors. Working two mechanical distants from the same level must have been a decent workout, especially on route with a lot of trains timetabled to pass through at speed.

Edited August 21, 2022 by MDP78