Train Graphic
Great Western Passengers' Forum Great Western Coffee Shop - [home] and [about]
Read about the forum [here]. Register and contribute [here] - it's free.
Random Image
Train Running @GWR Twitter Acronyms/Abbreviations Station Comparator Rail News GWR co. site Site Style 1 2 3 4 Chat on off
April 23, 2018, 04:14:22 pm *
Welcome, Guest. Please login or register.

Login with username, password and session length
Forgotten your username or password? - get a reminder
News: A forum for passengers ... with input from rail professionals welcomed too
 
   Home   Help Search Login Register  
Pages: 1 2 3 [4] 5
  Print  
Author Topic: Waterloo station - collision and derailment, 15 Aug 2017  (Read 6206 times)
stuving
Hero Member
*****
Posts: 3080


View Profile
« Reply #45 on: August 30, 2017, 08:47:23 pm »

I would also have  expected the point in question to be clipped and padlocked as well as relying on "A temporary modification to the points control system". Might burn the point motor out!

It is a double slip crossover, with four routes/positions.    IIRC from other discussions there are four separate points machines, and four possible positions of the crossover.   AIUI they cannot be partially clipped out of use because of the way the moving blades have to interact.   Clipping it in one position, say UMR to P12/13, would have taken P11 out of use. (or vice versa.)

Paul

That doesn't sound quite right. Surely the four routes only occur in two pairs, i.e. it has just two positions. If all the movements are linked, however many motors do the pushing, then you can't lock out one route without blocking the other route linked to it. If they all moved independently that might not be true - though detection might be an issue.
Logged
SandTEngineer
Hero Member
*****
Posts: 1923


In a Linemans Hut in the far Southwest


View Profile
« Reply #46 on: August 30, 2017, 09:34:27 pm »

I would also have  expected the point in question to be clipped and padlocked as well as relying on "A temporary modification to the points control system". Might burn the point motor out!

It is a double slip crossover, with four routes/positions.    IIRC from other discussions there are four separate points machines, and four possible positions of the crossover.   AIUI they cannot be partially clipped out of use because of the way the moving blades have to interact.   Clipping it in one position, say UMR to P12/13, would have taken P11 out of use. (or vice versa.)

Paul

That doesn't sound quite right. Surely the four routes only occur in two pairs, i.e. it has just two positions. If all the movements are linked, however many motors do the pushing, then you can't lock out one route without blocking the other route linked to it. If they all moved independently that might not be true - though detection might be an issue.
The point end approached by the passenger train that was incorrectly set is operated as a double slip pair.  The third end, controlled by the same point identity, was under the barrier train.  On a double slip each end is a pair that operate together from a single point operating mechanism.  I'll post up a drawing later.

In the meantime here is a video that shows the principle of operation.  Its not in the UK but the principles are the same: https://youtu.be/VpfJdm71u6g
« Last Edit: August 30, 2017, 09:43:23 pm by SandTEngineer » Logged

Out of this nettle, Danger, we pluck this flower, Safety.
[Henry IV, Part 1, Act 2, Scene 3]
stuving
Hero Member
*****
Posts: 3080


View Profile
« Reply #47 on: August 30, 2017, 10:29:05 pm »

The point end approached by the passenger train that was incorrectly set is operated as a double slip pair.  The third end, controlled by the same point identity, was under the barrier train.  On a double slip each end is a pair that operate together from a single point operating mechanism.  I'll post up a drawing later.

Ah - so it is linkage (mechanical or not), but not what I said. After all, even if two routes can be set through that crossing at once, only one can be signalled - so there's no need to bother about their compatibility. It's more like linking the two ends of a crossover, and extending that to a third point end that can't usefully be moved independently.

And then trying to quickly alter it temporarily.
Logged
paul7755
TransWilts Member
Hero Member
******
Posts: 4393


View Profile
« Reply #48 on: September 02, 2017, 12:14:30 pm »

The point end approached by the passenger train that was incorrectly set is operated as a double slip pair.  The third end, controlled by the same point identity, was under the barrier train.  On a double slip each end is a pair that operate together from a single point operating mechanism.  I'll post up a drawing later.

In the meantime here is a video that shows the principle of operation.  Its not in the UK but the principles are the same: https://youtu.be/VpfJdm71u6g

Did you manage to find a drawing?  I'm thinking the signalling panel engraved lines means something the way they are drawn, presumably they show the default straight route (i.e. P11 left <> DMR right) with everything set normal?

I had a quick glance at the hardware from a passing train and it looks like these are "clamp lock" operation, does that affect how the pairs are linked/operated?

Paul
Logged
SandTEngineer
Hero Member
*****
Posts: 1923


In a Linemans Hut in the far Southwest


View Profile
« Reply #49 on: September 06, 2017, 04:37:03 pm »

The point end approached by the passenger train that was incorrectly set is operated as a double slip pair.  The third end, controlled by the same point identity, was under the barrier train.  On a double slip each end is a pair that operate together from a single point operating mechanism.  I'll post up a drawing later.

In the meantime here is a video that shows the principle of operation.  Its not in the UK but the principles are the same: https://youtu.be/VpfJdm71u6g

Did you manage to find a drawing?  I'm thinking the signalling panel engraved lines means something the way they are drawn, presumably they show the default straight route (i.e. P11 left <> DMR right) with everything set normal?

I had a quick glance at the hardware from a passing train and it looks like these are "clamp lock" operation, does that affect how the pairs are linked/operated?

Paul

Paul, still trying to find my drawings.  Might have to sketch it out myself......but have found a basic animation here: http://www.dccwiki.com/images/2/2f/CrossingDoubleSlip.gif

You are correct about the panel presentation and the fact the points concerned are Clamplock operated.
« Last Edit: September 06, 2017, 04:45:17 pm by SandTEngineer » Logged

Out of this nettle, Danger, we pluck this flower, Safety.
[Henry IV, Part 1, Act 2, Scene 3]
paul7755
TransWilts Member
Hero Member
******
Posts: 4393


View Profile
« Reply #50 on: September 06, 2017, 05:25:37 pm »

Thanks.   In the conversation about four positions, of course what we a looking at is analogous to a binary truth table, where Normal and Reverse are the equivalent of 0 and 1.  So two 'mechanisms' each with 2 conditions gives you four results?

N N
N R
R N
R R

...sort of thing?

Paul
« Last Edit: September 06, 2017, 06:14:40 pm by paul7755 » Logged
SandTEngineer
Hero Member
*****
Posts: 1923


In a Linemans Hut in the far Southwest


View Profile
« Reply #51 on: September 06, 2017, 06:44:27 pm »

Thanks.   In the conversation about four positions, of course what we a looking at is analogous to a binary truth table, where Normal and Reverse are the equivalent of 0 and 1.  So two 'mechanisms' each with 2 conditions gives you four results?

N N
N R
R N
R R

...sort of thing?

Paul

Correct again (I'll make a signal engineer out of you yet Wink ).  In the incident the train was signalled through the points concerned NN, but they were actually set RN.  On clamplock operated double slips each end of a pair is individually driven by separate hydraulic rams but they are connected to the same single electro-hydraulic pump unit so 2 per double slip arrangement (there is a design version that has 2 separate electro-hydraulic pump units per pair - 4 in total for a set of double slips; but for reasons of economy in design, installation and ongoing maintenance, that configuration is rarely used).
Logged

Out of this nettle, Danger, we pluck this flower, Safety.
[Henry IV, Part 1, Act 2, Scene 3]
Chris from Nailsea
Administrator
Hero Member
*****
Posts: 17321


I am not railway staff


View Profile Email
« Reply #52 on: September 08, 2017, 01:40:22 am »

Well, I'm glad to see that you two apparently understand it ...  Tongue Embarrassed

Logged

William Huskisson MP was the first person to be killed by a train while crossing the tracks, in 1830.  Many more have died in the same way since then.  Don't take a chance: stop, look, listen.

"Level crossings are safe, unless they are used in an unsafe manner."  Discuss.
eightf48544
TransWilts Member
Hero Member
******
Posts: 3995


View Profile Email
« Reply #53 on: September 08, 2017, 10:11:29 am »

Still doesn't answer why weren't the points clipped N N. If RN and RR would cause a collison
Logged
SandTEngineer
Hero Member
*****
Posts: 1923


In a Linemans Hut in the far Southwest


View Profile
« Reply #54 on: September 08, 2017, 10:14:16 am »

Still doesn't answer why weren't the points clipped N N. If RN and RR would cause a collison

Its not for us to speculate why.  Its for RAIB to determine that.
Logged

Out of this nettle, Danger, we pluck this flower, Safety.
[Henry IV, Part 1, Act 2, Scene 3]
SandTEngineer
Hero Member
*****
Posts: 1923


In a Linemans Hut in the far Southwest


View Profile
« Reply #55 on: September 08, 2017, 10:16:50 am »

Well, I'm glad to see that you two apparently understand it ...  Tongue Embarrassed

I have tried to explain it in 'simple' non-technical terms but a double slip is probably the most complex set of points that exist so...... Roll Eyes Tongue

I have decided that I need to do you a drawing.  Watch this space  Wink
Logged

Out of this nettle, Danger, we pluck this flower, Safety.
[Henry IV, Part 1, Act 2, Scene 3]
paul7755
TransWilts Member
Hero Member
******
Posts: 4393


View Profile
« Reply #56 on: September 08, 2017, 04:01:15 pm »

Still doesn't answer why weren't the points clipped N N. If RN and RR would cause a collison

Because if clipped to straight through i.e. "NN" there would have been no access to P13?

Paul
Logged
paul7755
TransWilts Member
Hero Member
******
Posts: 4393


View Profile
« Reply #57 on: September 18, 2017, 12:28:56 pm »

Roger Ford's monthly preview of his next Modern Railways article again quotes an unnamed source who says that the points simply "should have been clipped" so I still await the RAIB detailed explanation.   

Paul
Logged
paul7755
TransWilts Member
Hero Member
******
Posts: 4393


View Profile
« Reply #58 on: December 20, 2017, 10:58:56 am »

RAIB interim report.  I'm no expert - it is as expected all to do with stage works and testing, is very detailed and I'm hoping someone can follow it through and come up with a short precise.  Seems the point ends the train approached were physically 'mid position' as seen from the FFCCTV.

As was postulated in various forums at the time, the driver and signallers cannot be considered responsible in any way.

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/669469/IR022017_171220_Waterloo.pdf

Paul
Logged
Oxonhutch
Hero Member
*****
Posts: 441



View Profile
« Reply #59 on: December 20, 2017, 11:35:36 am »

Primarily points 1524A and 1524B should have been clipped in their normal position (as per plan) but were not.

Secondarily, a test wire was left connected which shorted out the electrical detectors to 1524A&B and fooled the signalling system into believing the point blades were correctly set and locked normal.

If only one of the above had happened the accident would not have occurred - it required the combination of the two. Holes in the cheese.

Had unclipped point blades moved without the testing wire being present, detection would have been lost and the starting signal would not have cleared.

Logged
Do you have something you would like to add to this thread, or would you like to raise a new question at the Coffee Shop? Please [register] (it is free) if you have not done so before, or login (at the top of this page) if you already have an account - we would love to read what you have to say!

You can find out more about how this forum works [here] - that will link you to a copy of the forum agreement that you can read before you join, and tell you very much more about how we operate. We are an independent forum, provided and run by customers of Great Western Railway, for customers of Great Western Railway and we welcome railway professionals as members too, in either a personal or official capacity. Views expressed in posts are not necessarily the views of the operators of the forum.

As well as posting messages onto existing threads, and starting new subjects, members can communicate with each other through personal messages if they wish. And once members have made a certain number of posts, they will automatically be admitted to the "frequent posters club", where subjects not-for-public-domain are discussed; anything from the occasional rant to meetups we may be having ...

 
Pages: 1 2 3 [4] 5
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.2 | SMF © 2006-2007, Simple Machines LLC Valid XHTML 1.0! Valid CSS!
This forum is provided by a customer of Great Western Railway (formerly First Great Western), and the views expressed are those of the individual posters concerned. Visit www.gwr.com for the official Great Western Railway website. Please contact the administrators of this site if you feel that the content provided by one of our posters contravenes our posting rules (email link). Forum hosted by Well House Consultants