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Alterations to Stevens locking

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Alterations to Stevens locking

Unread postby Chris Osment » Mon Nov 7, 2016 9:21 pm

[I’ve posted this question here, rather than in Historical, as it is more of a technical nature – but happy if the moderators wish to relocate it.]

This picture shows a 1930 copy of the SB diagram for West Pennard, including the mechanical locking-table.

This picture shows a copy of the West Pennard dog-chart with some proposed amendments, apparently incorporated in 1940. Unfortunately it is not in colour, but hopefully the various hand-drawn changes can be made out in the bottom section.

Now, my understanding of such drawings is not good enough sadly for me to work out exactly what is the proposed effect of the alterations, so can anyone help me out with an explanation please? There is a BR version of the dog-chart which shows that the amendments were indeed done, yet the BR mechanical locking table is identical to the 1930 version, so perhaps whatever was done was simply a different way of achieving the same result – but why?

Many thanks!
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Re: Alterations to Stevens locking

Unread postby RichardH » Mon Nov 7, 2016 11:11 pm

I am not an expert and I am having some difficulties making out the locking table, but net effect of the dog chart modifications seems to be adding a lock between 7 and 18, and 18 locking 10 both ways. In the lower tray 18 released by 11, and 18 locks 8, 10, and 22 is removed, but then 18 locks 7 and 8, and 10 both ways is added on the same bar working the opposite way. 18 released by 11 and locking 22 seems to be added/present in the top tray though. A lock on 7 could have been added directly to the existing arrangement, but the second notch on the lower No. 10 tappet makes the rearrangement necessary.
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Re: Alterations to Stevens locking

Unread postby davidwoodcock » Tue Nov 8, 2016 9:23 am

That seems to be an odd change to have made in wartime suggesting that it may have been in response to an incident or due to a significant change in circumstances. Perhaps this was one of the fabled inadequacies in existing arrangements shown up by the employment of signal women during the war (because they were novices rather than the because they were women it should be added).
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Re: Alterations to Stevens locking

Unread postby Chris Osment » Tue Nov 8, 2016 7:34 pm

Thanks to the useful information from RichardH, I think I now understand the basis of what may have happened here.

In late 1929 the layout at the west end of West Pennard was altered, accompanied by some renumbering and relocking; the result was as shown in the 1930 diagram. Now in 1930 lever 7 was released by 10, and 10 and 18 locked each other, so there was no need for a specific lock between 7 and 18. For some reason it was then decided to make 18 lock 10 both ways, so ‘10 locks 18’ had to be removed, which meant that a specific lock between 7 and 18 had to be added. I have also a 1932 copy of what I had thought – when I first compared them – to be exactly the same locking table as the 1930 copy, but a careful examination in light of Richard’s comments shows that in fact it now incorporates the changes which he has described.

Two issues then.... firstly, why the change? Any shunting in/out of the sidings across 11 reverse would require alternate use of shunts 7 or 18. Under the ‘old’ arrangements this would require 10 being pulled or replaced as necessary to release 7 or 18. The ‘new’ arrangements meant that both 10 and 11 could be left reverse and just 7 or 18 pulled/replaced as necessary, hence less lever movements. Might that be the answer?

Secondly, if the alterations had indeed been done sometime between the 1930 and 1932 locking tables, then why was the negative amended in 1940? The only war-time change of which I am aware (but exact date unknown) was the provision of a new Ministry of Works siding in the goods yard, accessed by a hand-point located between shunts 18 and 5, so no obvious locking implications. Might it have been the case perhaps that the alterations had simply been recorded on the local office copy until that time, when perhaps it then came to someone’s attention that the master negative was out-of-date and needed updating?
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Re: Alterations to Stevens locking

Unread postby RichardH » Wed Nov 9, 2016 11:02 pm

Chris Osment wrote:In late 1929 the layout at the west end of West Pennard was altered, accompanied by some renumbering and relocking; the result was as shown in the 1930 diagram. Now in 1930 lever 7 was released by 10, and 10 and 18 locked each other, so there was no need for a specific lock between 7 and 18. For some reason it was then decided to make 18 lock 10 both ways, so ‘10 locks 18’ had to be removed, which meant that a specific lock between 7 and 18 had to be added. I have also a 1932 copy of what I had thought – when I first compared them – to be exactly the same locking table as the 1930 copy, but a careful examination in light of Richard’s comments shows that in fact it now incorporates the changes which he has described.

Two issues then.... firstly, why the change? Any shunting in/out of the sidings across 11 reverse would require alternate use of shunts 7 or 18. Under the ‘old’ arrangements this would require 10 being pulled or replaced as necessary to release 7 or 18. The ‘new’ arrangements meant that both 10 and 11 could be left reverse and just 7 or 18 pulled/replaced as necessary, hence less lever movements. Might that be the answer?

That sums up the changes nicely, but it seems a lot of effort to save a few lever operations.
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Re: Alterations to Stevens locking

Unread postby kbarber » Thu Nov 10, 2016 9:36 am

RichardH wrote:
Chris Osment wrote:In late 1929 the layout at the west end of West Pennard was altered, accompanied by some renumbering and relocking; the result was as shown in the 1930 diagram. Now in 1930 lever 7 was released by 10, and 10 and 18 locked each other, so there was no need for a specific lock between 7 and 18. For some reason it was then decided to make 18 lock 10 both ways, so ‘10 locks 18’ had to be removed, which meant that a specific lock between 7 and 18 had to be added. I have also a 1932 copy of what I had thought – when I first compared them – to be exactly the same locking table as the 1930 copy, but a careful examination in light of Richard’s comments shows that in fact it now incorporates the changes which he has described.

Two issues then.... firstly, why the change? Any shunting in/out of the sidings across 11 reverse would require alternate use of shunts 7 or 18. Under the ‘old’ arrangements this would require 10 being pulled or replaced as necessary to release 7 or 18. The ‘new’ arrangements meant that both 10 and 11 could be left reverse and just 7 or 18 pulled/replaced as necessary, hence less lever movements. Might that be the answer?

That sums up the changes nicely, but it seems a lot of effort to save a few lever operations.

Yes, but what sort of classification scheme did they have? How much difference might those few lever operations have made to the grading of the box, and therefore to the ongoing costs? And if it was the sort of job that could be done with existing spare capacity in the drawing office and the locking fitters, so much the better - the effective cost is close to zero.
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Re: Alterations to Stevens locking

Unread postby John Hinson » Thu Nov 10, 2016 10:58 am

It is surely more likely to be related to shunts standing on the bar when it needs to be reversed?

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Re: Alterations to Stevens locking

Unread postby Chris Osment » Thu Nov 10, 2016 7:10 pm

John Hinson wrote:It is surely more likely to be related to shunts standing on the bar when it needs to be reversed?

John


A good point! As the arrangement was new in 1929, maybe someone soon found out the hard way that it had not been "thought through" enough :-)
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