Signal Box Block Shelf Equipment

[The Stationmaster]

3 hours ago, 5BarVT said:

That’s awful expensive, you need a lock on every signal rather than just one on the interlocking lever.

However, I might be getting mixed up with direction levers for block lines.  They need the track circuit(s) clear before you can change direction, effectively transferring ‘route locking’ from one box to the other.  With the interlocking levers you are making sure that trains aren’t signalled in from both ends at the same time, but not proving the loop clear in order to change direction.

As an example, changing a loco requires in one end, remove loco, new loco in from the other end, but the track will have remained occupied.

Paul.

Exactly so.  Interlocking levers are not like Acceptance Levers (which do require track circuits clear) and Interlocking Levers were used between 'boxes on sections of line which were not track circuited.   But without reference to any locking charts or control tables it is difficult to give an accurate answer  - which would hopefully provide the answer.    I think that Interlocking Levers worked the opposite way round from  from an Acceptance Lever - in other words when reversed it mechanically released levers working signals in the frame in which it was situated signals.  In the first example I found in the locking chart for (Malago Vale) the Interlocking Lever does exactly that - when reversed it releases the levers for signals reading to the line to which the interlocking lever applies.

 

Thinking a bit further about somewhere where I remembered they had been employed I have looked at Royal Albert Bridge and Saltash 'boxes between which the single line was converted to be worked by interlocking block instruments and Interlocking Levers.  At both 'boxes the Interlocking Lever released certain of its own signals reading towards the single line.  There are no control tables shown for either 'box but as interlocking block instruments were used I presume the Interlocking Lever was released by 'Line Clear'  - when I get a chance I'll have look in Larry Crosier's book to if any more information can be gleaned but of course we are talking here about a single line worked under Absolute Block. 

Edited September 1, 2021 by The Stationmaster
Typos

[uax6]

11 hours ago, LNERGE said:

I doubt under normal circumstances it would be possile to pull both levers together. As part of testing the circuitry it would be possible to arrange for both levers to become reversed by the application of test straps or manipulation of the electric locking. The cross protection between the circuits will prevent any release being given.

 

The acceptance levers we have for our single line certainly, in normal circumstances, lock each other in the frame.

 

I say under normal circumstances, as there is a tiny window of opportunity to get both out together. It is tiny, something like 20 milli-secs.... but it can be done, and I've witnessed it twice! (but not been at fault). The net result of getting both out is that no-one gets a release, and both levers are locked out of the frame until physically reset by S&T unlocking the gravity lock covers and lifting the lock bolt by hand, and shoving the lever to normal. IIRC the lever at the other end is then electrically released (still no acceptance) to allow it to go back into the frame. Normality then returns.

 

Andy G 

[The Stationmaster]

Further to my post last night (very early today I suppose). one thing I forgot to mention is that because the Interlocking Lever would release 33 mechanically there is no need for an electric lock and plunger on 33.   And there might well have been a plunger on 29 (and possibly a 'Locked/Free' indicator?) but it is far from clear in this situation how it worked

 

Obviously the Interlocking levers for the Up & Down Goods Line at Malvern Road could not be released by the block as the line was Permissive and I could read by implication from the Sectional Appendix that in theory it would have therefore had permissive block instruments as it is listed in Table A and not in Table B.  However it was a fairly short line so that might possibly have not been the case and if it did have them it's not really clear how they would have been arranged but there is   apossibility that they might have been interlocked so that only one could peg up 'Line Clear' at a time and the other could not peg 'Line Clear' until the first had been returned to normal which might explain why the line was track circuited although that doesn't entirely fit with the way a Home Signal berth track circuit interlinked with the block on the Western (see note below).   So we still have some mysteries and a need for someone somewhere to see if they can come up with some relevant control tables.

 

A Western berth track circuit at a Home Signal worked in a rather strange way if you know are familiar with Welwyn Control - which it very definitely was not.  If the berth track circuit was occupied with the block at 'Line Clear' the block would drop to 'Normal' and not go to 'Train On Line',  and 'Line Clear could be immediately re-pegged once the track had cleared.  So all the track circuit  effectively did was prevent 'Line Clear' being pegged if it was occupied or had dropped - simple as that.     Thus if a train was cancelled before entering the section the block was simply returned to 'Normal' with no need to do anything else - a long way from proper Welwyn Control.   I suspect this simple arrangement went back a long way because berth track circuits interlinked with the block were being installed on the GWR before 1914 and the arrival of the Great War resulted in a planned extensive installation programme being cancelled.

[RailWest]

It might be worth asking the Exeter West Group about the arrangements for the Interlocking Levers which worked between the Middle and West boxes - it's been a very long time since I dabbled with them to remember now :-(

[The Stationmaster]

I've given a bit more thought as to how the system might have worked at Malvern Road which does explain why there was a track circuit.  I'll call the 'boxes A and B to save words.

 

First the easy bit, which assumes that permissive block instruments are used.  With the track circuit unoccupied Box A sends the 'Is Line Clear?' bell signal to Box B and when B moves the block indicator on his pegging block instrument to 'Line Clear' that is repeated on the non-pegging instrument at A and releases the Interlocking Lever at A so the Signalman at A reverses that lever.  The train etc enters the section and after exchange of relevant bell signals B places the block instrument to 'Train On Line'.   The track circuit will show occupied but will have no effect on the block instrument

 

A  can then ask 'Is Line clear?' for as many subsequent trains etc as he needs to put into the section/it has room to accommodate.  In this situation B acknowledges the 'Is line Clear?" with a single beat on the bell and should movs the commutator to the appropriate position on the counter.   All through this the Interlocking Lever at A remains in the reverse position and all relevant signals reading into the section are mechanically released.

 

If there is more than one train etc in the section as each train, with tail lamp attached ,passes B's Home Signal, B sends Train Out of Section to A and movers the counter back one place and the block remains at 'train on Line' and the Interlocking Lever at A still stands reversed.   When the final train passes B's Home Signal B again sends 'Train out of Section' and additionally replaces the block instrument to 'Normal'.

 

A new train etc may now be signalled in either direction provided the track circuit is clear.  So it is quite possible (likely?) that the track circuit is interlinked with both pegging block instruments and has to be proved clear in order for either instrument to peg 'Line Clear'   It is equally possible that the two instruments are interlinked in order to prevent both pegging 'Line Clear' at the same time.  And equally in order to peg 'Line Clear' it is possible that the Interlocking Lever would be required to be proved standing normal in the frame? (note * below)

 

Note *. The Saltash locking chart includes a reference to levers with circuit controllers (although I suspect that it might not be complete) however there is no reference to a circuit controller on the Interlocking Lever which might imply that lever does not have to be proved normal in the frame in order to peg 'Line Clear'

 

[Michael Hodgson]

1 hour ago, The Stationmaster said:

 

First the easy bit, which assumes that permissive block instruments are used.  With the track circuit unoccupied Box A sends the 'Is Line Clear?' bell signal to Box B and when B moves the block indicator on his pegging block instrument to 'Line Clear' that is repeated on the non-pegging instrument at A and releases the Interlocking Lever at A so the Signalman at A reverses that lever.  The train etc enters the section and after exchange of relevant bell signals B places the block instrument to 'Train On Line'.   The track circuit will show occupied but will have no effect on the block instrument

 

 

Coming back to terminology, I have always (perhaps simplistically) understood Acceptance Levers to be the equivalent of a pegging block as used on single lines dispensing with the need for Staff & Ticket or tokens.  A block regs supplement was issued as Regulations for Train Signalling on Single Lines worked by Acceptance Levers in May 1971 for the Western Region and the following April for the Southern.  These say it can be a switch rather than a lever, and they refer to using the same bell codes as Electric Token Block.

 

On the other hand I have never heard of Regulations for Interlocking levers.  My layman's understanding is that interlocking levers are always worked under standard AB or Permissive regulations - and perhaps also for No Block lines?  Isn't this an earlier (mechanical) form of acceptance lever working devised before we had invented fancy circuits using stick relays etc, and therefore not capable of providing quite as many safeguards? 

 

I don't see how an interlocking lever can be released by Line Clear.  Supposing the signalman puts everything back after the first train has stopped, inadvertently including the interlocking lever, perhaps so that he can do some other movement.  Can he still pull it a second time?  When the loco running round wants in from B, A can't give him a Line Clear to release the other interlocking lever.  Surely all you really need is that the other box has his lever normal to prevent a cornfield meet?  I am assuming the lever concentrates mechanically the effect of any conflicting signals in its own frame.

 

Another related term is Direction Lever.  I take that to be identical to Acceptance Lever - but is that correct?

 

Then there is Tokenless Block, another supplementary set of regs issued in 1968, functionally similar to Acceptance Lever working but without exchange of bell signals and allowing acceptance of a train in anticipation of its being offered.

[RailWest]

AIUI the terms 'Direction Lever' and 'Acceptance Lever' relate to different methods of block working over single lines - sadly I can never remember the precise difference between the two :-(

 

Certainly from a GWR/BR(WR) perspective the term 'Interlocking Lever' was often used for levers which controlled one of a number of different functions, say (for example) GF releases or 'switching out' at single-line passing-loops or 'wrong direction' running on AB lines such as at Exeter St Davids etc, so not exclusively related to block working in any way.

 

[5BarVT]

10 hours ago, The Stationmaster said:

A Western berth track circuit at a Home Signal worked in a rather strange way if you know are familiar with Welwyn Control - which it very definitely was not.  If the berth track circuit was occupied with the block at 'Line Clear' the block would drop to 'Normal' and not go to 'Train On Line',  and 'Line Clear could be immediately re-pegged once the track had cleared.

I think it depends on exactly what controls were provided.  The One Acceptance Block relay unit (4 P.O. relays in a shelf type relay case) did drop back to T.O.L., and, as far as I am aware, achieved full Welwyn controls. but there were other lesser varieties around in some boxes.

Paul.

[The Stationmaster]

4 hours ago, 5BarVT said:

I think it depends on exactly what controls were provided.  The One Acceptance Block relay unit (4 P.O. relays in a shelf type relay case) did drop back to T.O.L., and, as far as I am aware, achieved full Welwyn controls. but there were other lesser varieties around in some boxes.

Paul.

Welwyn control was a rarity on the Western in the 1970s In the two West Country areas that I worked in between 1974 and 'early '79 I had a total of almost 20 'boxes working at least one double line Absolute Block section and out of all of those only one had Welwyn Control (it had only got it as a result of major layout and locking alterations in the early 1970s).   Similarly where I was working earlier in South Wales on one patch I had 4 'boxes working double line Absolute Block and none had Welwyn Control.  i know that all of those in the West Country had the old Western standard circuit as we had to do a survey of block controls and I went through it all with the Area S&T Engineer and he re-checked all the prints so we knew exactly what we had (or in terms of Welwyn Control - didn't have).  

 

I presume the same applied in South Wales because the only time I saw it happen the block dropped to Normal when the berth track was occupied and one of my Signalmen confirmed that exactly the same happened at the adjacent 'box (all of which led to the dismissal of a trainee Signalman who had been playing silly beggars with adjacent 'boxes).

 

Incidentally we also went through 'the one pull' controls for section signals and they were also a somewhat dated way of doing because if you couldn't get the signal fully off for some reason (need to tighten the signal wire etc) all that needed to d be done where there wasn't Welwyn Control was put the block back to 'Normal' and re-peg 'Line Clear' .  

 

The other thing we were asked to survey, c.1975/76, was the number of places where we were regularly making movements over 'box worked points for which no fixed signal could be cleared - we had one set of points where we were making at least 20 light engine setting back movements every weekday through them and there was no fixed signal that could be cleared for the movement.  Strangely what appeared to be originally a survey to identify the need for alterations etc would seem to have been filed in the too difficult tray an  the locking was never altered although it would have been a very simple alteration affecting only 3 or 4 levers at the most.

 

By the way as far as single line signalling systems are concerned I think that over the years I worked in areas with, and I therefore had to have fairly deep knowledge of, most of them viz, One train Working (with a train staff), Train Staff & Ticket (using paper tickets), Electric Token, No Signalman Key Token, Tokenless Block (WR version of course), And Table C2 working (without or without a peg board).   I was familiar with but never worked directly with although I have been in 'boxes where they were in use -  Acceptance Lever Working, and Single Line Track Circuit Block.  And I wrote the initial outline for the Regulations for No Signalman Token (Remote).