Mechanical Interlocking - Am I going in the right direction?

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James Walters
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Mechanical Interlocking - Am I going in the right direction?

Postby James Walters » Sat May 14, 2022 12:37 pm

Hello everyone, I hope I might be able to trouble a signalling expert for some advice regarding mechanical interlocking of a lever frame.

Having successfully built a couple of the society lever frames, my thoughts have naturally turned to the interlocking. I have been helped in this respect by the loan of a lever frame which once resided in the Waterloo signalling school. There were two boxes at Bexhill West, I am currently working on Box No. 2.

Lever Frame 1.jpg

Locking Tray.jpg



I have prepared a signalling plan for No. 2 Box at Bexhill West by copying the original, as is the locking table showing the locks and releases. Which I have attached below.

From this original information I have started to design the layout of the locking, which I have so far completed for levers 1 - 4, these control the crossover arrangements for Platform 1.

Bexhill West Signal Box 1 Locking.jpg


Box 2 signalling plan and locking table V2.pdf
(107.01 KiB) Downloaded 9 times


Notes:
1. I have shown Lever 1 (Tappet 1) locked in reverse which I understand is Southern practice.
2. The cross-over release levers (1,5,9) were in themselves mechanically released from box 1. I intend to electrically lock these with solenoids, so will not affect the interlocking I am referring to here.
3. I am aware that the locking does not allow for movements past signal 2 into the carriage dock siding off of the Platform 1 loop. I have been told that this is not unusual for rarely used sidings, and that it is likely a flag would be used to allow movements.
I think that this ground signal arm should be yellow (as well as No. 4), but photo evidence suggests that it was always red.

Would there be an expert who might be able to cast an eye over my drawing to check that I've understood things correctly?

This is a surprisingly complicated yet interesting subject, any thoughts and advice would be very much appreciated,

Best wishes,

James

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grovenor-2685
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby grovenor-2685 » Sat May 14, 2022 2:14 pm

James Walters wrote:1. I have shown Lever 1 (Tappet 1) locked in reverse which I understand is Southern practice.

I don't know Souther practice for a release lever but your locking table does not agree with your statement. Your locking table shows "3 released by 1", your dog chart shows "3 locks 1" so you need to make your mind up and choose one or the other.
I would go with "3 locks 1" as this avoids lever 2 being an awkward pull between as well as agreeing with your understanding of Southern practice.
Everything else looks fine.

Mind you, you will still be left with pull betweens on other signals, you can't completely avoid them.
Regards
Keith
Grovenor Sidings

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Noel
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby Noel » Sat May 14, 2022 2:47 pm

James Walters wrote:I think that this ground signal arm should be yellow (as well as No. 4), but photo evidence suggests that it was always red.

The change to yellow for conditional signals was a very late change, no earlier than the late 1930s, and not retrospective unless there were more substantial changes as well. Previously the arms were red, but the lights were green and white [GWR practice, I don't know if the SR did something different], rather than green and red. Drivers could pass the white on a road to which it did not refer.
Regards
Noel

James Walters
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby James Walters » Sat May 14, 2022 3:16 pm

Thank you Keith, I appreciate your wisdom.
I hadn't thought about the awkward pull between levers, despite reading about such things just last night.

I have amended the dog chart, and altered the locking position of lever 1, such that it is locked in the normal position, which should avoid the problem.

Bexhill West Dog Chart.jpg


I think that now, 1 should release 3, which when reversed should allow 1 to be put back to normal (locked) and allow either 2 or 4 to be pulled-off into their correct positions given that Lever 3 is now reversed.

I imagine that this locking situation must be about as simple as it gets. Given that I'm struggling with suggests I must be simple too. :D

James Walters
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby James Walters » Sat May 14, 2022 3:20 pm

Noel wrote:
James Walters wrote:I think that this ground signal arm should be yellow (as well as No. 4), but photo evidence suggests that it was always red.

The change to yellow for conditional signals was a very late change, no earlier than the late 1930s, and not retrospective unless there were more substantial changes as well. Previously the arms were red, but the lights were green and white [GWR practice, I don't know if the SR did something different], rather than green and red. Drivers could pass the white on a road to which it did not refer.


Thank you Noel, that's really helpful and makes perfect sense.
The signalling diagram above is from the 1940's, although there had no substantial changes to these ground signals since the line opened in 1092.

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grovenor-2685
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby grovenor-2685 » Sat May 14, 2022 7:16 pm

Sorry James, I checked out the locking table but I seem to have ignored the dog chart except for the lever 1 and 3 bit.
Looking at your latest you have 2 locks 4 included twice, its only needed once as the converse is automatic with mechanical locking.
Then you have omitted 2 released by 3, and 4 released by 3 completely so you can pull either of the signals without moving levers 1 and 3 at all.
Looking back at the original it has the same problem except you have the 2 locks 4 in there 3 times.
So the dog chart does need a bit of work still.
Regards
Keith
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James Walters
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby James Walters » Sun May 15, 2022 9:19 am

I've had another go at this, and struggled to come up with an arrangement which ensured that both 2 and 4 remained locked when lever 1 was unlocked.
This is my solution, which adds an additional lock on 2 & 4 when 1 is reversed which is not ideal as this extra lock is clearly not on the locking table.
It does however satisfy the demands of the locking table and signalling diagram, (I think), and was the only way I could visualise to do it.


Thoughts please...

Bexhill West Dog Chart V3.jpg

bécasse
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby bécasse » Sun May 15, 2022 11:41 am

Noel wrote:The change to yellow for conditional signals was a very late change, no earlier than the late 1930s, and not retrospective unless there were more substantial changes as well. Previously the arms were red.


Sorry that isn't correct. Yellow faces for conditional dollies date from c1930, certainly on the SR and probably on the LMSR and LNER too. The GWR ignored the recommendation to change and yellow faces didn't appear at former GWR locations before the 1950s; the GWR did, though, introduce the use of the white rather than red light in certain circumstances which didn't necessarily coincide with the circumstances in which the other companies used a yellow face.

The actual changeover would have taken time although the SR seems to have made the changeover quite quickly where standard Westinghouse ground signals were concerned, probably because it was changing red miniature arms to red shaped discs at the same time, while retaining the use of yellow miniature arms for conditional signals.

Everywhere there would have been some existing ground signals that never got changed, I have never seen a definitive photo of a Stevens flap signal painted yellow, for example, although that doesn't mean that examples didn't exist.

JFS
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby JFS » Sun May 15, 2022 1:29 pm

Just to mention that for each Ground signal / Crossover / Ground signal combination, a butt is much the simplest solution:-

BUTT 2.jpg


Thus, just two components provide both releases and the lock.

More details in the Locking Assembly Guide here:-

https://blockpostsoftware.co.uk/L_frame.html

Good Luck!

Howard

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grovenor-2685
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Re: Mechanical Interlocking - Am I going in the right direction?

Postby grovenor-2685 » Sun May 15, 2022 2:14 pm

James, I think you are getting lost here, the dog chart has to do what the locking chart specifies. JFS has given you an easy way of building the locks between the point lever 3 and the two signals.
All you need otherwise is 3 released by 1. It must NOT be possible to restore 1 to normal whilst 3 is reverse so you need to remove the extra notch in lever 3. Restoring lever 1 would defeat the locking between the two boxes allowing moves in to be signalled by the other box while 3 is reverse.
There should not be any other locking on lever 1. The 1 locks 2 and 4 you have added defeats the object. Your 2 locks 4 and 2 released by 3, 4 released by 3 are OK although JFS method is probably less work to build
Regards
Keith
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