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facing point lock operation


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The Stationmaster wrote:-

"If the locking bar isn't already down when a wheel passes over it it will be depressed by that wheel and thus force the facing point lock bolt into the port on the front stretcher bar, duly locking the point. This could well damage the rodding but the force generated by a passing wheel is likely - usually - to be greater than that which a Signalman could ever exert on the rodding so it wouldn't be surprising if it did go."

 

Thank you. I understand now. My misapprehension was that I thought the bar went up and over while the FPL was being moved. It hadn't clicked with me that it stays raised as long as the FPL is withdrawn.

 

Could I be right in my recollection of a bar connected to the point operating mechanism which went up and over as the points were moved? I'm going back over 50 years to Glasgow Buchanan St.

 

Allan F

 

 

 

In my limited experience the bar doesn't stand proud, it goes up and over, and if the bar isn't down you haven't been able to get any signals off. as the bolt passes through the FPL stretcher bar and moves the sliderods that clears the path for the detector slides on the signal wires and so allowing the route to be cleared for the train to advance/set back.

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The Stationmaster wrote:-

"If the locking bar isn't already down when a wheel passes over it it will be depressed by that wheel and thus force the facing point lock bolt into the port on the front stretcher bar, duly locking the point. This could well damage the rodding but the force generated by a passing wheel is likely - usually - to be greater than that which a Signalman could ever exert on the rodding so it wouldn't be surprising if it did go."

 

Thank you. I understand now. My misapprehension was that I thought the bar went up and over while the FPL was being moved. It hadn't clicked with me that it stays raised as long as the FPL is withdrawn.

 

Could I be right in my recollection of a bar connected to the point operating mechanism which went up and over as the points were moved? I'm going back over 50 years to Glasgow Buchanan St.

 

Allan F

 

The usual design of FPL locking bar (and there were variations on the theme) is supported by a series of what almost look like small eccentrics which are pivoted at the bottom. These move in an arc parallel to the running rail so as the bar rises or falls it also moves a few inches laterally and remains parallel to the railhead.

 

Buchanan Street was converted to colour light signalling in, I think, the 1930s and I would expect by then that point locking would be by track circuit (the only photo I can quickly find doesn't show any locking bars) but it is quite likely that fouling bars were provided and I'm sure depression bars would have been used in some places where track circuits could not be relied on. These bars would usually have their pivot at a right angle to the rail and would, in effect, 'tilt' towards the rail when depressed and turn back to horizontal when unloaded. It might be these that you are thinking of?

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In many places where they have concrete sleepers under the pway through points the back drives are been fitted in the four foot as the sleepers have a series of cast holes in them so when installing them you do spent hours destroying the sleeper ends

 

The choice of where the backdrive is located depends on the physical considerations on site. The current standard is to have the cranks and roding mounted on the sleeper ends on the opposite side to the point machine. On the Southern region however the provision of 3rd rail electrification prevents this hence the use of the four foot in this area (Points on non electrifed SR lines like the Uckfield branch still use the four foot method as this is what maintence staff are used to). However in the Stechford photo shown above the placing of the backdrive in the four foot looks to be the result of its proximity to the platform ramp which may have prevented the placing of the first crank on the sleeper end. Incidentally for those wondering about them, the two small grey things beyond the point machine in the six foot are suplamentary detectors, usually used on long turnouts to prove that the switch rail is closed up to the stock rail throught its length, the point detection circuit pasing through both detectors as well as the machine itself.

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Although slightly encumbered by switch heater cabling this view shows the sort of thing Phil was talking about although as the switches are fairly short there's no supplementary detection involved (and of course no sign of the FPL as it is inside the point machine, so sorry for going slightly off the, er, point).

 

Sorry about the odd angle but it was the best way of getting a view of the back drive against the platform edge.

post-6859-128094861988_thumb.jpg

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The Stationmaster wrote:-

"Buchanan Street was converted to colour light signalling in, I think, the 1930s and I would expect by then that point locking would be by track circuit (the only photo I can quickly find doesn't show any locking bars) but it is quite likely that fouling bars were provided and I'm sure depression bars would have been used in some places where track circuits could not be relied on. These bars would usually have their pivot at a right angle to the rail and would, in effect, 'tilt' towards the rail when depressed and turn back to horizontal when unloaded. It might be these that you are thinking of?"

 

Buchanan St was semaphore until closure in 1966. There were many depression bars around the station (the Caley called them balanced bars). Central station had, it seemed, hundreds, and recently I found one in situ in Perth. I don't know whether it is still in use.

 

Thanks for your expertise.

 

Allan F

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StationMaster was thinking of St Enoch methinks

 

oops, Methinks you are all too right Mr Beast sir. I even checked in a book of photos - and have just done so again, to find that I looked at the wrong ruddy caption, more speed less haste would seem to be good advice when delving less familiar places :blushclear: .

 

Incidentally there was also at least one of the type I described (pivot at right angle to the railhead) still in use as a Fouling Bar at Stirling in the early 1990s but as the connection it was protecting has gone and some resignalling has since taken place it probably isn't there now.

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sorrr for waking up an old thread, but  in reference to the LNER drawing of an economical facing point lock, could someone explain how it actually work.  I dont believe they all came with fouling bars as well did they.  SO how does a single lever in the box , act as a lock and a point lever at the same time ????

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I think the first part of the movement withdraws the bolt (or unlocks whatever locks the points), switches are then able to move with the lever, and the final part of the movement locks them again.  Are there any of these still in existence?

 

In the late 80's / early 90's there were some hand points that were called switchlocks.  the stretcher bar was done away with and the actual switches operated with a bar that looked like the fletching on an arrow.  A novel design that unlocked, moved then locked the switches in one movement.  I'll try and find some pictures

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I think the first part of the movement withdraws the bolt (or unlocks whatever locks the points), switches are then able to move with the lever, and the final part of the movement locks them again.  Are there any of these still in existence?

 

In the late 80's / early 90's there were some hand points that were called switchlocks.  the stretcher bar was done away with and the actual switches operated with a bar that looked like the fletching on an arrow.  A novel design that unlocked, moved then locked the switches in one movement.  I'll try and find some pictures

I understand this part, But the idea of an FPL was that  the point lever couldn't be unlocked without  releasing a lock lever.  IN an economical  FPL, cant the signal man , just  release the combined lever at any stage and the point moves and re-locks.   was track circuiting rather then fouling bars then used to ensure the point couldn't be moved.

 

Ecomonical FPLs seem to me to be kinda rule benders, i.e. a lock is placed on the points, but infact its not in any way independent to the mechanism that moved the blades 

 

 

 

The reason I ask is I'm modelling irish railways  in the 70-80s and  in ireland economical FPLs were very common , right up till they were removed post 2000 

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The use of one lever is OK.  That is what happens with motor points, one lever controls the motor.  Inside the point mechanism the motor winds, that extracts the bolt, then throws the tie bar across and the final part of the motion reinserts the bolt.  Everything being detected by various detection circuits (If you look at some motor points you will see connections from both switch rails and the tie bar all going into the mechanism)

 

The important thing is that any move for passenger trains over the points in the facing direction is interlocked to ensure the points are locked before the signal can clear. 

 

I've probably not made that clear.  Let me know if you've understood.

 

Thanks

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The use of one lever is OK.  That is what happens with motor points, one lever controls the motor.  Inside the point mechanism the motor winds, that extracts the bolt, then throws the tie bar across and the final part of the motion reinserts the bolt.  Everything being detected by various detection circuits (If you look at some motor points you will see connections from both switch rails and the tie bar all going into the mechanism)

 

The important thing is that any move for passenger trains over the points in the facing direction is interlocked to ensure the points are locked before the signal can clear. 

 

I've probably not made that clear.  Let me know if you've understood.

 

Thanks

Yes I have usually seen the relevant signal slotted with the point /FPL. , though not always. I always thought the idea of the lock lever was to prevent the point lever being pulled. , ie that the tappett locking in the cabin was used. With a single lever I don't see the advantage of FPL.s.

 

Was it that they were always paired with fouling bars or track circuit protection ?

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The locking of the lever in the frame is separate from locking the points. If you look at lever plates. There are often numbers underneath, that indicate other levers that need to be reversed to free the locking on a particular lever. I'll sort out some pictures to illustrate and post them.

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The only purpose of the FPL is to prevent the point blades moving under a train in the facing direction. The Economic FPL achieves this by the design of the "Z" bar. The prevention of moving the point lever is by way of interlocking in the normal way.

Edited by meil
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Interlocking does not entirely prevent the points being moved as they would be free immediately the protecting signal is returned to danger (hence the Rules relating to the working of such signals).  The facing point lock bar is what physically prevents the facing point lock from being unlocked by premature movement of the operating lever - and there is no reason - apart from the weight of the throw - why an economical FPL can't work with a facing point lock bar, and of course they did.

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Interlocking does not entirely prevent the points being moved as they would be free immediately the protecting signal is returned to danger (hence the Rules relating to the working of such signals).  The facing point lock bar is what physically prevents the facing point lock from being unlocked by premature movement of the operating lever - and there is no reason - apart from the weight of the throw - why an economical FPL can't work with a facing point lock bar, and of course they did.

 

Yes this is my point I suppose, I have seen installations with and without fouling bars.  But fouling bars as I understand it were primarily installed because of sight lines to the box, meant the signalman couldn't  determine where the train was standing.  the classic case being  engine run arounds etc 

 

I also understand these were phased out in favour of track circuit protection.  I can see the point of FPLs if you ALWAYS have  fouling or track circuits, but cant see the point if not.  What  protection was added, by FPLs on their own , especially since many point blades were slotted with the appropriate signal anyway 

Edited by Junctionmad
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The only purpose of the FPL is to prevent the point blades moving under a train in the facing direction. The Economic FPL achieves this by the design of the "Z" bar. The prevention of moving the point lever is by way of interlocking in the normal way.

 

so without a fouling bar or track circuit locking how is that achieved.  other then  either locking in the box , or slotted with signals ( which have nothing to do with the FPL per se), whats stops the signalman with an economical FPL from  just releasing lever.  If he's stopped by signal or box interlocking, he's stopped from releasing the lever anyway.

 

I can see the point of a seperate locking lever, as it acts as a consciousness  decision to release the FPL and then  pull the point lever.  But in an economical FPL, what additional protection is being added in the absence of any other form of locking.  It seems to me to be a " rule bender" , i.e. the physical point lock is present , but in fact no additional safety has been added.  

 

 

are you saying that the only purpose is to add a " dubious" additional protection preventing the point blades moving under their own volition , rather then an additional to locking safety 

Edited by Junctionmad
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so without a fouling bar or track circuit locking how is that achieved.  other then  either locking in the box , or slotted with signals ( which have nothing to do with the FPL per se), whats stops the signalman with an economical FPL from  just releasing lever.  If he's stopped by signal or box interlocking, he's stopped from releasing the lever anyway.

 

I can see the point of a seperate locking lever, as it acts as a consciousness  decision to release the FPL and then  pull the point lever.  But in an economical FPL, what additional protection is being added in the absence of any other form of locking.  It seems to me to be a " rule bender" , i.e. the physical point lock is present , but in fact no additional safety has been added.  

 

 

are you saying that the only purpose is to add a " dubious" additional protection preventing the point blades moving under their own volition , rather then an additional to locking safety 

I think you mis-understand. The need to lock a facing point is because it can, or it is perceived it can, move whilst a facing move is underway and hence derail the train. So the points are locked to prevent that. Trailing points don't cause a derailment because the wheels can push the blades over (points are not usually locked for trailing moves even when they have a FPL). The FPL has nothing to do with protecting the movement of the point per se. That is achieved by interlocking of the points and signals and the use of fouling bars in the normal way.

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I think you mis-understand. The need to lock a facing point is because it can, or it is perceived it can, move whilst a facing move is underway and hence derail the train. So the points are locked to prevent that. Trailing points don't cause a derailment because the wheels can push the blades over (points are not usually locked for trailing moves even when they have a FPL). The FPL has nothing to do with protecting the movement of the point per se. That is achieved by interlocking of the points and signals and the use of fouling bars in the normal way.

I see , yes thanks , 

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I would suggest that this is a complicated subject for the layman.  It might be better doing more research and reading some historic accident reports that highlight the various ways of doing things.

 

There is a very interesting report into a head on collision at Hull Paragon, where despite the most modern of equipment, the signalmen managed to route two trains into a head on collision http://www.railwaysarchive.co.uk/documents/MoT_Hull1927.pdf

 

Please note that this response isn't meant to be patronising in any way.

Edited by The Bigbee Line
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I would suggest that this is a complicated subject for the layman.  It might be better doing more research and reading some historic accident reports that highlight the various ways of doing things.

 

There is a very interesting report into a head on collision at Hull Paragon, where despite the most modern of equipment, the signalmen managed to route two trains into a head on collision http://www.railwaysarchive.co.uk/documents/MoT_Hull1927.pdf

 

Please note that this response isn't meant to be patronising in any way.

I was always under the impression that FPLs were part of an improving locking strategy, but as "Meil" pointed out , they are purely an additional means , situated at the point itself to prevent something other then the rodding from moving the blades. I stand corrected.  

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There seems to be a confusion creeping in regarding terminology.  Before the widespread use of track circuit (and an electric circuit controller on the lever working the facing point lock, or economical lock) the facing point lock was held in position - or rather prevented from moving during the passage of a train - by the facing point lock (or locking) bar.

 

Although mechanically similar a fouling bar serves a total different purpose in that it is there to detect if a vehicle is standing or passing foul of the fouling point at a point (so therefore basically at the trailing end of the point) in order to prevent a conflicting route being set or to avoid the potential for a collision.  As already noted fouling bars were used where visibility was restricted or in other circumstances - possibly where a train was standing to make sure it was 'in clear'.  It is (was) therefore serving a  totally different purpose from the one of making sure that a facing point was not moved under a train which was passing over it.

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An additional danger when points were operated by a local lever rather than a remote frame was that the shunter might suddenly get the mistaken impression that he hadn't set the points correctly and try to reverse them at the last moment - the human psyche does odd things like that.

 

In North America this was generally protected against by regulations requiring the crewman to cross the track away from the switch-stand, thus preventing sudden brain-farts of that sort from being acted on, but AFAIK there was never any similar rule in the UK, where it seems not to have ever become a major problem.

 

Or am I wrong about that?

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An additional danger when points were operated by a local lever rather than a remote frame was that the shunter might suddenly get the mistaken impression that he hadn't set the points correctly and try to reverse them at the last moment - the human psyche does odd things like that.

 

In North America this was generally protected against by regulations requiring the crewman to cross the track away from the switch-stand, thus preventing sudden brain-farts of that sort from being acted on, but AFAIK there was never any similar rule in the UK, where it seems not to have ever become a major problem.

 

Or am I wrong about that?

The Rules clearly required hand points (which of course only existed in sidings) to be correctly set and properly closed before a movement was made over them and the Shunter (or Guard) working them was required to ensure that was the case - Rule 111 in the BR 1950 Rule Book, within Section J of the 1972 Rule Book (where it is even more explicit than in the 1950 book).

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