Re: Signalling in Victoria

[Eddie Oliver <eoliver@efs.mq.edu.au>]

David Langley wrote:

> 
> Research has shown that the control lever went in at the racecourse on 1 Nov 1915
> but the one at Showgrounds (lever 3) on 15 Feb 1973. These control levers do not
> show up on signal box diagrams, or at least the ones I have a copy of. I presume
> that although lever 61 gave control to Showgrounds to admit down trains to the
> loop, the provision of the control lever at Showgrounds enabled an electric back
> lock of the racecourse lever thus preventing the signalman at the racecourse from
> restoring his control lever and attempting to shunt a train to the loop if the
> signalman at Showgrounds was trying to send a train to the loop. Again I do not
> have access at the moment to circuit diagrams for the line. Perhaps someone might
> have an explanation for the provision of lever 3 at Showgrounds. It certainly
> acted like the signal lever towards the loop because before you can clear signal
> 2 to go to the loop, lever 3 is required to be reverse (meaning that lever 61 at
> Flem RC has to also be reverse). The points leading to the loop can be pulled
> prior to the reversal of lever 3, there is no locking between them. The table of
> locking shows that lever 3 is merely electrically released by lever 61 at
> Flemington RC.

Can we please be a bit more complete with our picture of the locking?

Is this right?

Showgrounds 3 is released by Racecourse 61 reverse, and locks 61
reverse. And 3 leads 2, which is the actual signal lever.
Racecourse 61 normal is required for the signal(s) into the loop at the
Racecourse end.

However what is to prevent the signaller at Showgrounds normalising 2
then 3 as the train passes, thereby releasing the backlock on Racecourse
61 so it can go normal before the train has actually reached the
Racecourse?

Is it possible, for instance, that even though 2 can be put full normal,
3 cannot be until the train is somehow verified as having arrived at
Racecourse? In effect, having 2 and 3 as separate levers enables the
points at Showgrounds to be normalised; whereas if you tried to get the
same basic effect by an NI lock on 2 without having 3, the points would
have to stay reverse?

Eddie