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Point blade detectors in signal wires - "what for"?

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Point blade detectors in signal wires - "what for"?

Unread postby hmmueller » Fri May 20, 2016 7:16 am

Hello specialists -

I do have two questions regarding the securing of facing points in mechanical interlockings - maybe someone can shed some light on it. They came up when I casually added a remark to a (translated) comment by Hanspeter Thöni in a blog posting about a Swiss station in the 1980s.

There are, I think, five problems that must be solved for securing facing points for train runs (shunting is simpler):

1. Points must be in correct position for clearing signal
2. Point blades do not move from stock rail while train is driving over them
3. Points are not occupied when reversed
4. Points remain in position even if points rodding/wires break
5. Blades are at stock rail when clearing signal even though points rodding/wires may be broken

The mechanisms devised are, as far as I can see, the following:

Great Britain:
A. Locking bed
B. Facing point lock locked by locking bar
C. Facing point lock locked by lever in signal box
D. (Later) track circuit
E. Blade detectors

Germany, Austria:
a. Locking bed
b. Blade locks ("Spitzenverschluss")
c. Facing point lock with separate lever ("Riegel")
d. Visual check
e. Only in German points: Broken wire detector (spring-loaded levers pulled back by the wires; when wires break, a stopper prevents their movement)

Switzerland:
a'. Locking bed
b'. Blade locks ("Spitzenverschluss")
c'. Facing point lock in signal wire ("Durchgangsriegel")
d'. Visual check
e'. Only in wire-driven points: Broken wire detector (spring-loaded levers pulled back by the wires; when wires break, a stopper prevents their movement)

Here are my lining up of the five problems and the respective devices for the 3 areas. For the UK, I looked into a copy of "Railway Signal Engineering (Mechanical)" by L.P.Lewis from 1912, for rest I took my "knowledge". But:
* First of all, one can question my answers; above all it is not really clear that one device fulfills only one purpose - it might, by construction, "inadvertently" help to do more.
* Additionally, there are two direct questions for the UK which I have marked with "Q:" below - could anyone shed light one them?

1. Points in correct position for clearing signal
A.
a. (also checking lie of c.)
a'.

2. Point blades do not move from stock rail while train is driving over them
B. or C. (Q: what about E.: If it also keeps blades to stock rail, why then B.? why wouldn't E. suffice? - is it not mounted or designed rigidly enough for forces?)
b. and sometimes c. (for larger speeds; e.g. in Austria above 60kph, in Germany passengers trains or above 40kph, if I remember correctly)
b'.

3. Points are not occupied when reversed
B. or D.
d.
d'.

4. Points remain in position even if points rodding/wires break
B. or C.
b. and c. if present
b.'

5. Blades remain at stock rail when clearing signal even though points rodding/wires may be broken
E. (Q: why is B. or C. not sufficient?)
Germany: b. and e.; Austria: only b.
b.' and c.' and e.' (wow!)

Thanks a lot!
Regards
Harald
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Re: Point blade detectors in signal wires - "what for"?

Unread postby Mike Hodgson » Fri May 20, 2016 8:52 am

Facing Point Locks can lock the point in the Normal position or the Reverse position or sometimes in both positions, acting on the stretcher bar nearest to the tips of the blades. They prevent the whole switch blade assembly from moving. Unlike some European railways, our points have traditionally not been designed to be trailable, that is a train running in the trailing direction when the points are in the wrong position will usually result in permanent way damage. If the stretcher bar is damaged in this way, it would be possible for the blades to be not fully closed for a subsequent facing movement.

Detectors are not constructed as robustly, and are really part of the signal mechanism rather than the point mechanism. They are connected to the blades more directly at their tips, and if the blades are not fully closed despite the FPL being locked, you should still fail to get detection, thus preventing you from clearing the signal. Detection also verifies that the FPL is locked - although the interlocking can check that the FPL lever is locked, a rodding breakage could result in the locking bolt not being engaged even though levers are all in the correct position.
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Re: Point blade detectors in signal wires - "what for"?

Unread postby Nicko » Fri May 20, 2016 8:55 am

It is uk practice also to detect the position of the open switch
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Re: Point blade detectors in signal wires - "what for"?

Unread postby Pete2320 » Fri May 20, 2016 10:16 am

Nicko wrote:It is uk practice also to detect the position of the open switch

Is it? I believe HW point machines do not do this.

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Re: Point blade detectors in signal wires - "what for"?

Unread postby JRB » Fri May 20, 2016 10:26 am

Mechanical detectors do, however and are what this discussion is mainly about.
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Re: Point blade detectors in signal wires - "what for"?

Unread postby hmmueller » Fri May 20, 2016 1:22 pm

Thank you! - I have now learned from you that

  • FPLs are necessary even in the presence of detectors, as "detectors are not constructed as robustly"; FPLs are more akin to the continental blade locks, albeit not trailable;
  • detectors are useful even in the presence of FPLs, as they can detect problems with broken/bent rods in or before the points,
in addition to other details.

Danke!
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Re: Point blade detectors in signal wires - "what for"?

Unread postby Nicko » Fri May 20, 2016 7:35 pm

hw point machines do detect open switch position
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Re: Point blade detectors in signal wires - "what for"?

Unread postby Andrew Waugh » Sat May 21, 2016 11:10 am

Historically, the UK has seen a steady increase in the elaboration of facing point protection over time. The need for this elaboration is not supported by the published railway accident reports, but presumably is driven by unreported incidents of failures of the apparatus. It would also be driven by the very strong normalisation imposed by the Board of Trade requirements and by railway industry consensus.

In my view, the story really starts in the 1870s when the UK railway industry was caught in a cleft stick. On one hand traffic was booming and line capacity was becoming a real issue. This was made worse by the rapidly increasing speed of passenger trains, which not only increased the need to overtake slow goods trains, but made it more likely for trains to derail if the points weren't possibly closed, and made the consequences of derailment more serious. The consequence was that there was a desperate need to increase capacity, balanced by a strong desire to avoid facing points. The result was a rapid evolution in facing point technology which set the norms for the UK rail industry which can still seen today. Other countries did not face this challenge that early, and the railway industry consensus that developed there was different.

First, I definitely have in mind that detectors holding points predate facing point locks and lockbars (and, indeed, interlocking). I can't find examples at the moment, but I've certainly read early accident reports that discuss 'wire locks'. These were what we'd now call detectors placed in wire runs to signals to ensure that hand worked points were in the correctly set for the main line and remained so when the signal was cleared.

Rapier, in his 1874 paper, is clear that when interlocking was introduced, the interlocking and rodding was at first relied upon to hold the points. The first problem encountered was the 'frequent' reversal of points under trains. The locking bar was invented in 1867 by Livesey and Edwards to address this problem. At first it was coupled to the point lever, but in 1869 Saxby and Farmer began working the lockbar by a separate lever. Note that the facing point lock (i.e. bolting the points) had not been adopted at this time. By 1874 the FPL had been added to ensure that the point blades were fully home to one side or another and to "provide against the most dangerous class of accident."

The basic UK facing point layout had evolved by this time, but variations most certainly existed and were illustrated by Rapier. The then president of the ICE, Harrison, had introduced the most interesting on the NER. This secured the point blades individually using wedges, rather than jointly by means of a bolt in the stretcher. This system, I believe, lasted until the expiry of the NER at grouping (and, of course, examples in use survived much later).

By 1874, the problem that the facing point lock didn't prove the position of the points was recognised. Rapier mentions a couple of proposals to solve the problem. He does not, however, talk about detectors in the wire run. For this reason I believe that detectors were not in use at this date, or at least, were not commonly known.

By 1892 the Board of Trade requirements officially discouraged the use of facing points ('Facing points should be avoided as far as possible'). When they were provided they 'should' be fitted with facing point locks and lockbars. A plain English reading would suggest that this means that facing point locks and lockbars were not mandatory at this time, but this would be surprising. Detectors still weren't mentioned. When the text was revised in 1902, facing point locks, and lockbars were mandatory, as was a means of detecting any failure of the rodded connections (one method of which is a detector).

When Raynar Wilson published his 'Mechanical Railway Signalling' in about 1910 wire detectors were standard practice. Many different types are illustrated in the book.

Even by this time, 'best' practice was still evolving. Ideas that are described in Raynar Wilson, but not yet common practice, were the use of split stretcher bars to guard against the point blades becoming detached from the stretcher and from the operating lever, detection of the FPL plunger, and operation of the plunger through the lockbar. Good practice, but not universal practice at the time, was detection of both point blades.
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Re: Point blade detectors in signal wires - "what for"?

Unread postby Andrew Waugh » Sat May 21, 2016 11:14 am

Oh, and I meant to include a link to a digitised version of Richard Rapier's 1874 paper 'On the fixed signals of railways'"

https://archive.org/details/onfixedsignalsr00rapigoog

The original paper was presented to the Institution of Civil Engineers. It's the first published description of UK signalling practice. The discussion after the paper was as interesting, if not more so, as many of the early signalling pioneers were there and put their pennyworth in.
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Re: Point blade detectors in signal wires - "what for"?

Unread postby hmmueller » Sat May 21, 2016 5:45 pm

Andrew, thank you very much for your long essay (which I expected from you, I have to confess :) ). I'll digest it slowly over the next days, and also the paper or Rapier.
Re the split stretcher bars, the book by Lewis is critical of them, as they seemed to malfunction (due to dirt?) too often ... but I have to check this once again.

Regards
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Re: Point blade detectors in signal wires - "what for"?

Unread postby Frank » Sat May 21, 2016 8:07 pm

Hello,


for that some hints:

Germany, Austria:
a. Locking bed
b. Blade locks ("Spitzenverschluss")
c. Facing point lock with separate lever ("Riegel")
d. Visual check
e. Only in German points: Broken wire detector (spring-loaded levers pulled back by the wires; when wires break, a stopper prevents their movement)



blade locks are not only of the Type Spitzenverschluß.

There is a line of evolution from the british Type of Blade locks in the Beginning here in germany over several Types to the least Spitzenverschluß.

Here a Type of Gelenkverschluß
http://www.drahtkupplung.de/0_Weichen/0_Teile/WT27.html

Here a Type of Hakenverschluß
http://www.bahnbilder.de/bild/Deutschla ... nbahn.html


Also the Type of
'. Facing point lock in signal wire ("Durchgangsriegel")

was common here by the old mechanical Lever frames of the Länderbauart



There
c. Facing point lock with separate lever ("Riegel")


the Riegel is a second Lock mechanism and points are locked by a Riegel are not trailable.
Originaly the Riegel was developed for Handoperated Points to lock them by the Signal wire on Branch lines.



Here:
http://www.drehscheibe-online.de/foren/ ... 7,page=all

Picture 74 there shows the Point Number 10 with the point drive on the left side and the Riegel mechanism on the right side of the Track
Picture 156 shows a Hand operated Point secured by a Riegel

Also a view of a typical Bran line Station over 100 Years until 2011. Now all mechanical is gone and the controll is in a Center far away.
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Re: Point blade detectors in signal wires - "what for"?

Unread postby Mike Hodgson » Sat May 21, 2016 9:36 pm

The Hakenverschluß and Gelenkverschluß photos both look like point operating linkages for moving the blades between their alternative positions, and I can't see how they actually they lock the points if their operating rods should break. However I suppose the same is true of a British Economical Facing Point lock unless the covers are removed so that you can see the parts which do the locking.

Although the working parts are not obvious on photo 74 of the Riegel, in photo 156 it seems to have some similarity to our mechanical detectors; however the shunt signal appears to be worked directly from the position of the points.
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Re: Point blade detectors in signal wires - "what for"?

Unread postby hmmueller » Sun May 22, 2016 7:34 am

Mike Hodgson wrote:The Hakenverschluß and Gelenkverschluß photos both look like point operating linkages for moving the blades between their alternative positions, and I can't see how they actually they lock the points if their operating rods should break.

In short:
  • With points moved by a crank lever, a separate stop is provided that prevents the points reversing themselves when a wire is broken. In my recent posting about a Swiss station in 1988, one can see such a drive inthe sixth picture. I have marked the relevant parts in a copy:

    Image

    The stop mentioned above is circled red; and the springs that will pull small levers when a wire breaks which will touch that stop are circled yellow.
  • Austrian points with a different, simpler kind of drive had to have a weight on the lever to keep them in their position.
The Spitzenverschlüsse (Hakenverschluss and Gelenkverschluss) only keep the blades to the stock rail during the hard blows of a vehicle running over them.

Although the working parts are not obvious on photo 74 of the Riegel, in photo 156 it seems to have some similarity to our mechanical detectors; however the shunt signal appears to be worked directly from the position of the points.

There is no shunt signal here - this is the points indicator, which shows the lie of the points. A shunt signal indicates that a move over some stretch of tracks is permitted (in the UK as in Central Europe); a points indicator just informs someone who will permit a shunting move whether the points lie in the correct position.

And re similarity to detector: As you explained, detectors are - if I understand you correctly - not intended to keep the blades at the stock rails while a train is running over them, as they are not built robustly enough. They are "only" a means of making sure that the points mechanism is working correctly when the signal is pulled. The Riegel, on the other hand, guarantees due to its small tolerances (3..5mm) that the blades are securely lying at the stock rails in all circumstances (except when the whole mechanism is completely damaged - even then, the Spitzenverschluss would give some security). So I wouldn't (now!) say that a Riegel is similar to a detector - rather, a Riegel does more the work of a FPL (similarity between them: Both have - except for EFPLs - their own lever; and are locked in the locking bed). But the purposes do overlap - that was the reason for list of my questions at the beginning ...

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