GNR signalling/interlocking

[chaz harrison]

I have just been looking at a signalbox diagram for Bottesford East which was a junction on the GNR line between Grantham and Nottingham. It's in "Signalling in the Age of Steam" by M Vanns.
It says in the text "The GNR was the first to use cast iron plates incorporating the lever's number, the piece of equipment it operated and a list of the numbers of other levers in the locking sequence.

In a table under the diagram it lists the levers, so.....

28 Up main distant - 25 - 26 - 27

25 - up advanced starter
26 - up main starter
27 - up main home

If this is the order it would seem to imply that the up levers had to be pulled contrary to what might be expected,
However it also lists....

1 - down distant - 2 - 3

2 - down home
3 - down starter

which seems to me to be correct.
Can anybody shed any light on this apparent anomaly - is 25, 26,27 just a typesetter "helpfully" putting the numbers in numerical order, or is there a reason why the advanced starter, starter, home would be the sequence?
I do realise that the distant would be locked unless all three stop signals were cleared - the question is what sequence.

Chaz

[BHornsey]

Hi Chaz.

The lever leads merely state which levers must be out of the frame to release that lever, in numerical order.
If a sequence is needed, the other levers (25 - 27) would have a requirement for the required levers to be reversed.
Regarding the sequence quoted, it's unlikely there would be any mechanical locking preventing you clearing in reverse order (i.e. adv. starter, starter, home) but later absolute block systems may enforce sequencial locking electrically.

As someone that worked quite a few mechanical SBs, I always wondered why they only listed the levers that were required to be reversed. Sometimes, it was necessary for another lever to be normal but normal locks were never shown.

Brian

[chaz harrison]

OK Brian that's clear. The interlocking "doesn't care" which order the required levers are pulled in, but am I right in thinking that usual practice would be for signals to be pulled off in the order in which a train encounters them (ie home, starter, advanced starter - and only then distant)? After all the train could be accepted and the home cleared even if the box in advance hasn't accepted it? The distant then would be locked at danger and the train would be stopped by the starter.

Chaz

[chaz harrison]

Isn't the reason that normal locks were never shown is that the assumption is that all the levers start in their normal position?

Chaz

[BHornsey]

Isn't the reason that normal locks were never shown is that the assumption is that all the levers start in their normal position?

Yes, that's right, but annoying if you are on a busy frame and you can't get a lever out because another lever in the frame is already out which should be locked normal!! Once you have worked a frame regularly, you don't bother looking at the lever leads. However, I was a relief signalman with 20 odd boxes to work and sometimes got to places only rarely. On complex frames you could have multiple routes set.

OK Brian that's clear. The interlocking "doesn't care" which order the required levers are pulled in, but am I right in thinking that usual practice would be for signals to be pulled off in the order in which a train encounters them (ie home, starter, advanced starter - and only then distant)? After all the train could be accepted and the home cleared even if the box in advance hasn't accepted it? The distant then would be locked at danger and the train would be stopped by the starter.

Yes, that correct. In fact the rule book is quite clear on this; unless a train is accepted by the box in advance, you should check the train down almost to a stand at the home before dropping it up to your next signal. A few exceptions did occur to this where the home signal could be cleared immediately when the starter was at danger, usually authorised in the sectional appendix.
As stated though, the mechanical locking wouldn't enforce any of this (except to lock the distant); it's up to the signalman.

Brian

[chaz harrison]

Thanks for your help Brian. A friend of a friend is planning a GNR model railway and wants to signal it correctly.
Bringing a train almost to a stand before allowing it up to a signal at danger is not something you see very often on models.

Chaz