Train detection bars or treddles

[Pelham Street]

Hi guys, Iam in the procrss of building a new layout based on LSWR 1880s practice. I understand that detection bars od treddles(?) may be required. Modelling a suburban terminus in the mid 1880s period. What did they look like and where would they be placed? The signal box is on the platform ends. The crossover at the bufferstop end has a two lever ground frame forpoint and FPL. I have no idea weither that would be released from the box by rodding, or bell plunger at this period either? 

 

 

[RailWest]

Detection Bars (mechanical or electrical) are not the same as treadles.

GF release might be mechanical (rodding, or key from SB) or electrical (Sykes instruments).

A plan of your proposed layout might help a lot to enable better answer to your questions!

 

What scale? Not really relevant to the question, just curious :-)

[Pelham Street]

 The model is in 7mm scale. The terminus was proposed but not built. Enough information survives to make a model though. It was to have four platform faces.Platform 1, 25' wide by the main buildings, platform road, carriage siding. then a 30' platform, 2 & 3 with platform roads either side. A run round loop accessed from the next platform road and then platform 4. Point work from the platform ends go onto a double track with a scissors crossover. There was to be an overall roof 150' wide . I have positioned the signal box between the tracks at the end of platforms  2 & 3. The platforms were to be 450' long with the overall roof coming up to the platform ramps. The space was very constricted, with the scissors under a road bridge and covered way. Platform 3& 4 were to be for arrivals only. Presumably signalled with ground discs for shunting trains out to platforms 1 & 2 for departures. Next to the end platform 1 would have been a engine shed for six locos and a 50' turntable. This would be from a set of points beyond the scissors crossover.(I have reduced this to 42' owing to space limitations). On the other side of the station, at platform 4 end would have been a horse and carriage dock. I have accessed this from a double slip via the end of the run round loop. Sorry there isn 't a track plan. My computer skills can't do that!

 

For incoming trains a gantry squeezed under the covered wat would give access to platforms 3 & 4 9Arrivals) and i presume the centre road between plaftorm 1 & 2 for ECS moves into the carriage siding. The entry into the loco shed will be controlled with a ground signal. The whole branch was short, being 19.93 chains long. It would the have run onto the District Railway line at the western end of South Kensington station. Presumably the District would control the junction signal box, (not modelled). The heght of the covered way was 16' from rail level, so not much space. I have drawn up a signal gantry. The support wth bsuspended dolld just fits between the jack arches on the covered way.The distant signal arms may go on the platform starters, oo as a single post before the bridge which crosses the track by the scissors cross over. 

 

If I can fight with the scanner and work out how to import a drawing into this program, I will, over the week end!!

[Guy Rixon]

Detection bars lay normally down, I understand, and were raised by the point rodding when moving the points. When a train wheel was above a bar, then that bar could not rise, thereby locking the points in their current position.

 

Treadles, IIUC, normally lay in the raised position and were actively pushed down by a wheel flange. A treadle might, for example, be made to sound a gong to warn shunters of an approaching train.

 

My hazy understanding is that a turnout would be locked by a detection bar if it could be changed under a running move of a train. That, I think means if a train could be moving over the turnout after relevant signals have been put back to danger and the locking freed to move the points. E.g., consider a train running into a platform and passing over points in the station throat and later the engine-release cross-over. While the train is approaching the station, the points are locked by the home signal governing the approach. When the engine has passed that signal, the signaller can put it back to danger, and that, absent the detection bars, unlocks the points. The bars keep the train safe.

 

Another use for detection bars is to lock signals. Once a train is stopped within station limits - e.g. standing at a platform - and the signal that allowed it in has been returned to danger, nothing mechanical stops a signaller from clearing that signal to allow another train onto the same track. This is a significant risk where the view of the line from the signal box is poor. A detection bar locking the signal mitigates the risk.

 

To be fully effective, a detection bar has to be at least as long as the greatest gap between wheels in a train - i.e. the distance between the inner wheels of the two bogies of a coach.

 

Since your station is approached through covered way, it might well have had a treadle-operated gong to warn staff of trains. The gong itself would be visible on the layout, but the treadle would be out of sight on the approach.

 

I think you need detection bars on the throat point-work leading to and from your platform roads, and on your engine-release cross-over; these protect against point movements under the train. You probably don't need detection bars to tell the signallers which platforms are occupied as they can see that well from the box. If trains ever shunt onto the running lines in the covered way they may be hard to see from the box and then you should have detection bars to remind the signallers.

 

One should also consider when the full suite of safety measures came into force. Bear in mind that train brakes only became mandatory in the late 1880s. Interlocking of points and signals started in the 1860s, but was not applied everywhere until much later.

 

 

 

EDIT: while googling for some images, I discovered that the proper term for what I described above might be "fouling bar" rather than "detection bar". Whatever the name, you still need to have them. There is a rather different device called a "facing-point-lock detector" (google it for a picture) that connects the signalbox locking to the position of a FPL. "Detection bar" might be another name for one of these. FPL detectors also became mandatory on facing points in passenger lines, but possible not in 1880.

Edited May 12, 2017 by Guy Rixon

[Siberian Snooper]

Detection bars or track circuits are required where any passenger carrying train will encounter a facing turnout, to prevent the turnout being moved under the train. Not all run round turnouts at the buffer stop end were required to be so fitted.

 

As has been stated, treadles were used to operate a warning device, usually a gong.

[RailWest]

With respect, there seems to be some confusion in the above comments between 'lock bars' used with Facing Point Locks (used to prevent FPLs being moved under a train) and Mechanical Fouling Bars, normally used to prevent points being moved to one route when clearance on the other route is fouled.

 

Unlike MFBs, Electrical Detection Bars were normally foul of the flangeway.

 

Many forms of treadle were under, or on the side, of the rail and worked by the weight of the train rather than physical interaction with wheel flanges (unlike modern ones, which are effectively giant micro-switches). Most, but not all, treadles were electrical devices.

 

I would suggest that any provision of ground signals would depend on whether you are talking early 1880s (not many) or late 1880s (more extensive provision).

 

I would not expect to see many track-circuits in the 1880s.

[TheSignalEngineer]

A lot of confusion arises about the different types of bars. To try to put it simply

 

1) Facing Point Lock Bar.

A bar on the inside of the rail approaching a set of facing points. It is connected at the running-on end to the rodding coming from the signalbox. The running-off end is connected via a crank arrangement to the plunger of the facing point lock. Moving the bar will lock or unlock the points. It is raised above the flangeway during this movement so cannot be operated if a train wheel is present. The bar is usually 50' 6" long.

 

2) Fouling Bar.

This is similar to a Facing Point Lock Bar in appearance and operation, but is positioned at the fouling point in the vee of a junction, turnout or crossover. It works in conjunction with the points and cannot be operated when a vehicle is standing foul of a converging move through the points.

 

3) Depression Bar. 

A Depression Bar normally lies within the flangeway on the inside of the rail. It operates by being depressed by the wheels of a vehicle standing on it which in turn opens a switch to break a circuit connected to the signalling system. It was used in lieu of track circuits, or sometimes in addition to the track circuit in terminal platforms where track circuit operation could not be relied on due to rusty rails.

 

4) Treadles. 

A treadle id a device which either opens or closes an electrical circuit connected to the signalling system. this is a momentary operation as each wheel passes over it. These can have a mechanical arm directly operating the switch. In early days to make them safe from tampering a mercury switch which detected the flexing of the rail as a train passed over it was used. these died out around the 1970s. A modern equivalent used an electro-magnetic proximity detector.  

[micknich2003]

The attached 1904 Signal Layout Of Broomfleet, East Yorkshire NERly shows a typical use of Clearance Bars. see Nos21, 29 and 37. Incidently, the NERly painted Clearance Bar levers Yellow .

[TheSignalEngineer]

The attached 1904 Signal Layout Of Broomfleet, East Yorkshire NERly shows a typical use of Clearance Bars. see Nos21, 29 and 37. Incidently, the NERly painted Clearance Bar levers Yellow .

BROOMFLEET Signalling.jpg

A great example of how bars were used to ensure that a train going away from the points was clear of a conflicting move for example to reverse 36 points, bar 37 would have to be operated. This would not be possible if a move from signal 9 to signal 10 was still standing foul of the crossing move.

[Pelham Street]

This is a lot to take in! The station was given Parliamentary Consent in 1882, for a terminus, with the pointwork on the throat leading directly onto the eastern end of the District Railways platforms at South Kensington. As originally envisaged the existing District signal box would be extended, and all moves into, and out of the station would be controlled from there.That included shunt moves. So when stock was to be moved from the barrival platform to a departure one, it was to shunt into the platform of the District station. This was not a satisfactory situation, so the following year in 1883 another Act allowed the entire length of Pelham Street running alongside the station to be dug up and a covered way installed. This allowed the junction to be moved to the other end of the station. In doing so the LSWR had a good platform length to shunt trains on their own metals. 

 

The station was fully described in the companies own house magazine in 1882. I am guessing it was intended to open it in late 1884 or early 1885. The LSWR was issuing signalling updates at Waterloo in 1885 advising staff that the engine shed ground signals were now operated from the signal box , and not from the points as point indicators. The station could have either as it comes in during this period. In the 1890s the South Western got a bit like the North Eastern Railway and signalled everything! However my period, fortunately it was a bit simpler 

[bécasse]

Ian

 

My suspicions are that an 1880s LSWR terminus would not have had more than the pre-1889 Act requirement of shunt dollies, i.e. protecting the EXIT from sidings on to running lines. If you look at stations on the Bournemouth Direct line (which IIRC was the last line opened before the 1889 Act) it is reasonably clear that that was how it was done there - and some of the stations never gained any additional dollies right up to electrification. (The Netley-Fareham line though, which opened the day the Act came into force, did have a full set of dollies, which is a very useful pointer of when LSWR policy changed.)

 

I also think that an fpl is unlikely to have been provided for the buffer-stop end release crossover. LSWR, and later SR, policy on such matters is a little confused, but most locations did NOT have fpls (or if they had an fpl it was not locked by a bar, only by the box interlocking). Even newly-built SR locations such as Allhallows did not have fpls on the release crossovers even though they were regularly traversed by loaded passenger stock (since, at Allhallows the normal service was worked by pull-and-push trains with the loco at the London end).

 

Shunt movements (other than from sidings on to a running line) would have been authorised by running signals or by the signalman showing a flag from the box.

 

It is possible that there would have been depression bars in places if the signalman couldn't see under the roof well. They were common fitments well into SR days (with a special blue star indicator to show their position) but I am not certain when they were first used, the 1880s may be a little early. One special use of depression bars was to electrically select whether a main or calling-on arm came off when the platform entry signal lever was pulled, but again it is possible that the 1880s is a little early.

[Pelham Street]

Thank you for that information. 1885 saw a flurry of new lines being opened, Bournemouth Direct, (I think that Bournemouth Central then was a terminus untll the connecting line and viaduct to Bournemouth West was opened.) Hurstbourne to Fullerton, Swanage and the Southsea branch.

 

I know the station at South Kensington wasn't built,but I want to make it as accurate as I can, treatin it as if it had been opened. This is why I have posted this appeal. Not a lot is known about the early 1880s signalling and if it is visable,in o gauge I think it should br modelled.

 

In the end the District never had the cash for their part of the scheme.It was intended that having kept the District out of Surrey with the LSWR New Guildford line, a jointly funded line was to be built. This was to run from Parsons Green over the Thames, down the course of the current A3 to Surbiton. Stations were to be provided at Putney Heath, Roehampton, Malden, Connection to Norbiton on the Kingston Loop, A station at Kingston Fairfield then it was to terminate on the south side of Surbiton station. The LSWR the wanted running powers over the District to a terminal site in South Kensington, thus giving them a West End terminus. Work was started at Putney when the scheme collapsed. The Putney construction was then incorporated into the Wimbledon line, which opened in 1889.

 

The signalling would have been with the Stevens company and would have been slotted wooden posts as at Swanage and Bournemouth Central when first built,. hence my request in an earlier appeal for their construction!

[bécasse]

Not a lot is known about the early 1880s signalling.

 

 

That may be true in terms of surviving original material. However by looking at a range of stations that were built in that period and their surviving (at least into recorded history) signalling, one can see what the LSWR was doing and not doing at that period. 

 

What is clear is that the signalling was (like on many other companies' lines at the time) parsimonious, fulfilling the requirements imposed by the BoT (such as dollies controlling the exits from sidings on to running lines) but doing little else. A particular feature of the LSWR's parsimony was that it made little provision for expansion of the signalling with all or most levers in a frame already assigned a use and boxes built no larger than the frame required; it was that particular behaviour which led to the development of the lever saving devices (most notably pull-push levers, but there were others) that later became such a hallmark of LSWR signalling practice.

 

Incidentally, although the LSWR did no more than it was required to, it does seem to have had an excellent relationship with the BoT inspectorate, perhaps best illustrated by the fact that the Netley-Fareham line, opened on the day the 1889 Act came into force, already conformed with the new requirements even though they differed from previous LSWR practice and the line should have opened earlier (difficulties with the local geology having caused problems). I have seen it suggested that this relationship, which wasn't typical of British railway companies, resulted from the closet links between the War Department and the LSWR.

 

Changing the subject slightly and thinking further about that platform release crossover, it seems most likely that it would have been worked directly by the box as it would have been within even the 150-yard limit that applied pre-1885 and certainly within the 200-yard limit that applied after that year. If, though, for some good reason (such as lack of visibility from the box), it had been decided to provide a ground frame released by the box, it would almost certainly have been a 2-lever (Stevens) frame with one lever acting as both the release lever and working an fpl bolt on the point that was facing to arriving trains, and the other working both points; the point that was facing only to departing trains would not have had any fpl, and the other one would not have had a bar, only a bolt. I don't think that there was any exactly comparable situation on the whole LSWR system, contemporary or not, but the fpl provision at the original two-platform Exmouth terminus would suggest that this is the provision that would have been made here. The ground frame would have been mechanically locked from the box, electrical locking was probably impractical at this date.

[The Stationmaster]

A lot of confusion arises about the different types of bars. To try to put it simply

 

1) Facing Point Lock Bar.

A bar on the inside of the rail approaching a set of facing points. It is connected at the running-on end to the rodding coming from the signalbox. The running-off end is connected via a crank arrangement to the plunger of the facing point lock. Moving the bar will lock or unlock the points. It is raised above the flangeway during this movement so cannot be operated if a train wheel is present. The bar is usually 50' 6" long.

 

2) Fouling Bar.

This is similar to a Facing Point Lock Bar in appearance and operation, but is positioned at the fouling point in the vee of a junction, turnout or crossover. It works in conjunction with the points and cannot be operated when a vehicle is standing foul of a converging move through the points.

 

3) Depression Bar. 

A Depression Bar normally lies within the flangeway on the inside of the rail. It operates by being depressed by the wheels of a vehicle standing on it which in turn opens a switch to break a circuit connected to the signalling system. It was used in lieu of track circuits, or sometimes in addition to the track circuit in terminal platforms where track circuit operation could not be relied on due to rusty rails.

 

4) Treadles. 

A treadle id a device which either opens or closes an electrical circuit connected to the signalling system. this is a momentary operation as each wheel passes over it. These can have a mechanical arm directly operating the switch. In early days to make them safe from tampering a mercury switch which detected the flexing of the rail as a train passed over it was used. these died out around the 1970s. A modern equivalent used an electro-magnetic proximity detector.  

 

Agree, and Fouling Bars were sometimes called Clearance Bars by some Companies - the principle of course was no different.

[Pelham Street]

One other question, if I may, is the position of the Distant signal. The branch was 19.93 chains long, with the junction to the District Railway. Presumably the junction signal box was a District one. Even at that time there were traffic flow issues at Earls Court. I am guessing that the distant signal was slotted from the junction box?

 

I must admit I haven't got my Chains into yards measuring head on today. Where would the distant be situated.?( Still haven't finished the diagram/track plan yet. ) Would it be on each of the starting signals, or further back under the covered way. Presumably it would have to be beyond the scissors crossover that gave access to the platform roads. The double tracks leading to this would be operated in either direction. Once through the crossover it was up or down lines.

[micknich2003]

One other question, if I may, is the position of the Distant signal. The branch was 19.93 chains long, with the junction to the District Railway. Presumably the junction signal box was a District one. Even at that time there were traffic flow issues at Earls Court. I am guessing that the distant signal was slotted from the junction box?

 

I must admit I haven't got my Chains into yards measuring head on today. Where would the distant be situated.?( Still haven't finished the diagram/track plan yet. ) Would it be on each of the starting signals, or further back under the covered way. Presumably it would have to be beyond the scissors crossover that gave access to the platform roads. The double tracks leading to this would be operated in either direction. Once through the crossover it was up or down lines.

22y = 1ch, 80ch = 1mile.

[Pelham Street]

Thanks for the help with the measurements,! 

[Pelham Street]

That may be true in terms of surviving original material. However by looking at a range of stations that were built in that period and their surviving (at least into recorded history) signalling, one can see what the LSWR was doing and not doing at that period. 

 

What is clear is that the signalling was (like on many other companies' lines at the time) parsimonious, fulfilling the requirements imposed by the BoT (such as dollies controlling the exits from sidings on to running lines) but doing little else. A particular feature of the LSWR's parsimony was that it made little provision for expansion of the signalling with all or most levers in a frame already assigned a use and boxes built no larger than the frame required; it was that particular behaviour which led to the development of the lever saving devices (most notably pull-push levers, but there were others) that later became such a hallmark of LSWR signalling practice.

 

Incidentally, although the LSWR did no more than it was required to, it does seem to have had an excellent relationship with the BoT inspectorate, perhaps best illustrated by the fact that the Netley-Fareham line, opened on the day the 1889 Act came into force, already conformed with the new requirements even though they differed from previous LSWR practice and the line should have opened earlier (difficulties with the local geology having caused problems). I have seen it suggested that this relationship, which wasn't typical of British railway companies, resulted from the closet links between the War Department and the LSWR.

 

Changing the subject slightly and thinking further about that platform release crossover, it seems most likely that it would have been worked directly by the box as it would have been within even the 150-yard limit that applied pre-1885 and certainly within the 200-yard limit that applied after that year. If, though, for some good reason (such as lack of visibility from the box), it had been decided to provide a ground frame released by the box, it would almost certainly have been a 2-lever (Stevens) frame with one lever acting as both the release lever and working an fpl bolt on the point that was facing to arriving trains, and the other working both points; the point that was facing only to departing trains would not have had any fpl, and the other one would not have had a bar, only a bolt. I don't think that there was any exactly comparable situation on the whole LSWR system, contemporary or not, but the fpl provision at the original two-platform Exmouth terminus would suggest that this is the provision that would have been made here. The ground frame would have been mechanically locked from the box, electrical locking was probably impractical at this date.

Did the 1885 ruling on 200 yds apply to the maximum distance  signal a signal could be operated from a box? This has impications as to where I place a distant signal that may be operated by the junction box and the station box.(sorry if this is a little obvious but I don't know too much about the subject!) Your help so far has been beyond what I had expected for the period

[Guy Rixon]

I suggest that the distant would be under the outer home signal of the terminus, not on the platform starters, and the the terminus would have an outer home somewhere in the covered way so that trains could shunt out of the platforms while remaining within station limits. However, if the branch is only a quarter mile long, that puts the outer home nearly halfway to the junction, so I wonder if the station limits of the terminus and junction could actually coincide; and, if so, whether there would be any need for a distant?

 

Note that this branch is actually shorter than the normal distance from a home signal to that signal's clearing point! 

[TheSignalEngineer]

Did the 1885 ruling on 200 yds apply to the maximum distance  signal a signal could be operated from a box? This has impications as to where I place a distant signal that may be operated by the junction box and the station box.(sorry if this is a little obvious but I don't know too much about the subject!) Your help so far has been beyond what I had expected for the period

I'm not sure that there was a distance quoted for signals at that time. It was expected that most signals would be in sight of the signalman. 

The distance for points was actually quoted as 180 yards.

 

There is a copy of the 1892 reprint of the 1885 Requirements annotated with the proposed 1902 amendments on the Railways Archive site. Probably worth a read.

http://www.railwaysarchive.co.uk/docsummary.php?docID=166

[Pelham Street]

Track plan based on LSWR practice. Scissors probably further out, but put in current position in order to get it in

[Pelham Street]

Previous scan was of the original Parliamentary plan for the 1882 Act

[The Stationmaster]

I suggest that the distant would be under the outer home signal of the terminus, not on the platform starters, and the the terminus would have an outer home somewhere in the covered way so that trains could shunt out of the platforms while remaining within station limits. However, if the branch is only a quarter mile long, that puts the outer home nearly halfway to the junction, so I wonder if the station limits of the terminus and junction could actually coincide; and, if so, whether there would be any need for a distant?

 

Note that this branch is actually shorter than the normal distance from a home signal to that signal's clearing point! 

 

Then providing an 'Outer Home' effectively achieves nothing and in any case the layout allows shunting onto the outgoing line which would be far more sensible anyway in operational terms although in view of the distances involved it would mean shunting into the block section in advance.

[RailWest]

I am confused as to whether the 'distant' in question is for trains approaching the terminus, or leaving the terminus and approaching the junction?

[Pelham Street]

Hi Chris, My original concern was for trains leaving the terminus, as to where the distant would be put. (Have only just posted the track plan and the map. Hope this is a bit clearer). I did think that the distant would be slotted with the junction box.

 

To help orientate the view the .terminus would be at the bottom of the map. The top is the District and Metropolitan station at South Kensington. The 1883 scheme would have removed the District bay on the left of the station, and the covered way would have replaced Pelham Street running to the top of the page. The junction would be approximately where the text is above the map. This should help shown  how short the line would have been. The map was divided into 10'0" squares and the LSWR station drawn out on this. The measurements can help with the overall branch size.

 

I haven't finalised signalling. yet. I have had help with this, but my ideas, based on further research changed things! As mentioned before it was to have arrival and departure sides. I have made platform 1 next to the station building. Platform 2 & 3 on the middle platform and 4 by the horse dock. Thus 1 & 2 are departures, and 3 & 4 are arrivals. The busy sytation pilot would be in the crun round road between 3 & 4 or at the the station end of the track going to the dock, where it can be seen by the signalman

 

If anyone is wants to have a go at signalling this, please have a go!