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DiveController
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Rather than hijack another thread on Facing Points Locks (FPLs), I wonder if somebody could explain the mechanical motion that occurs after a lever is pulled in the signal box.

From Mayner's post on another thread, these seem to be facing points with a FPL attached. I guess if I understood on which rod the actuation began and what moved on what thereafter, I might understand this other thread better. Sorry , I know this might be difficult to explain from the series of pictures. Incidentally is anything thrown by hand anymore or is it all done electronically/electrically/mechanically nowadays? (if I had spent more time roving carelessly along the permanent way I might know this). Apologies in advance if everyone on here knows this but me:o

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Edited by DiveController
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Rather than hijack another thread on Facing Points Locks (FPLs), I wonder if somebody could explain the mechanical motion that occurs after a lever is pulled in the signal box.

From Mayner's post on another thread, these seem to be facing points with a FPL attached. I guess if I understood on which rod the actuation began and what moved on what thereafter, I might understand this other thread better. Sorry , I know this might be difficult to explain from the series of pictures. Incidentally is anything thrown by hand anymore or is it all done electronically/electrically/mechanically nowadays? (if I had spent more time roving carelessly along the permanent way I might know this). Apologies in advance if everyone on here knows this but me:o

 

[ATTACH=CONFIG]18423[/ATTACH]

 

 

 

Nearly everything you wanted to know about points/switches Network Rail video on switch and crossing work

 

The section on detection and facing point locks from 5:10 onwards.

 

The locking mechanism is usually built into the switch machine with power operated points.

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Rather than hijack another thread on Facing Points Locks (FPLs), I wonder if somebody could explain the mechanical motion that occurs after a lever is pulled in the signal box.

From Mayner's post on another thread, these seem to be facing points with a FPL attached. I guess if I understood on which rod the actuation began and what moved on what thereafter, I might understand this other thread better.

 

IN modern electric or hydraulic point motors, both detection and FPL is implemented in the point motor assembly, even though it is logically separate

 

in mechanical systems, you have several systems on the go, Firstly the signal box, had a mechanical connection to physically move the points, Then for facing points on passenger lines, a facing point lock was added, Think of it as like locking your front door , even though the standard latch is already holding the door closed.

 

FPLs, mechanically operated , could utilise two methods of movement, One is that the point and the lock are separately connected to the signal box and operated by two levers. a black painted lever for the point movement and a blue painted lever for the lock. As you can see from the lock, its virtually like a bolt on a door. ( there were other types as well).

 

The second method used one signal box lever to move both the lock and the point. These were called " economical " FPLS and were very common in Ireland, but less so it the UK, where they had a bad reputation . In this case an arrangement of cranks and an " escapement" ( or cam ) caused , as the point lever was thrown, first to release the lock, then move the point and then re-insert the lock. These levers were painted black and blue.

 

In certain cases, before the advent of track circuiting , fouling bars were also added, especially when the signal man had difficultly sighting the points and couldn't easily tell where exactly the train was standing. In this case the action of the FPL ( either sperate or economical ) raised a long bar above the rail head, On depressing that bar the train prevent the removal of the lock and hence the operation of the points. IN those cases incidentally , the rodding could be damaged. It also prevented the signalman from also moving the switchblades if a train was standing on the bar. They were used in different situations, and sometimes called clearance bars. ( for example in engine run rounds where the signalman couldn't see the engine standing in relation to the point blades.

 

Most clearance/fouling bars were converted to track circuits and electrically locked to the lever ( hence the array of pushbuttons over the levers in many signal boxes). However I saw fouling bars on many points well into the 90s on IE.

 

Interesting , my impression was that Irish railways used the bar on the outside of the rail , but UK more often had them inside

 

 

http://catalogue.nli.ie/Search/Results?lookfor=railroad+claremorris&type=AllFields&submit=FIND&filter%5B%5D=format%3A%22Photo%22&filter%5B%5D=digitised%3A%22Digitised%22

 

Shows claremorris signalling in the 1960s, you can see there are two fouling bars on the diagram (points 29,24) which are funny as they are very close to the signal box and I find it hard to understand why they were installed , but it could be because the switch blades were so close together . see http://www.signalbox.org/overseas/ireland/claremorris.htm

 

As you can see from the second link, there were NO seperate FPLs , all were of the " ecomonical " type, certainly in excess of 10 or more because of the preponderance of facing points in bi-directional running.

 

Im not sure whether CIE and IR etc , remained true to the original pre nationalisation Board of Trade rules on facing point locks, perhaps someone could comment. I know that signalling rules began to seperate in the two jurisdictions over time. IN a complex junction like claremorris, there were lots of FPLs.

 

Interesting as was typical in signalling , crossovers were activated by a single lever. That meant that two points and their associated locks were operated in one pull. That must have been tough on the signalman.

 

Futhermore ( as you can see in the signal box.org link), often signals were slotted with the detection bars on points , so that signals could not be released if the switch bars didn't complete the move. IN many cases these were converted to electrical interlocking .

 

FPLs were not really part of the interlocking system, they were solely a means to prevent unexpected movement of the switch blades , they did not as a rule have fouling or clearance bars as well, as these provided a different protection

Edited by Junctionmad
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Signalling is a fascinating subject, but to get it right, and to get it to work right can be extremely complicated.

 

The following diagram is a simplified version of a signal interlocking system I drew up some years ago for an O gauge layout. In this version, only running line signals are shown, for simplicity there are no shunting signal or point locking levers shown. The advance starter and outer home signals are also not shown. The more signals there are the more complicated the interlocking.

 

The bars are made from flat brass strip and fit into guides which are not shown. The white vertical bars are what link the levers to the points and signals, and they have notches cut into them. The grey horizontal bars are the interlocking bars, and they have raised cams fitted.

 

The loops are only signalled for one direction running, so a train approaching from the left would take the crossover P1 into the upper platform.

As shown on the interlocking diagram, crossover P1 is set straight, and the interlocking cams between S1 and P1 prevent signal S1 from being pulled off. Once point P1 is moved to the cross position, the notch in the slide bar will permit the cams to move when signal S1 is pulled off. Once signal S1 is pulled off, the slide bar will then prevent the cams from moving back, thus locking crossover P1.

Signal S1 is also interlocked with signal S4, so that only one or the other signal can be pulled off, thus preventing two trains from arriving simultaneously.

The same process applies to signal S4 and crossover P4.

 

Once both trains have arrived, signals S1 and S4 have both been reset to stop, and crossovers P1 and P4 have both been reset to straight, along with point P2, then both signals P2 and P3 can be pulled off to permit departure. Again, by pulling off these signals, the movement of cams into notches prevents the points being changed until the signals are reset.

 

I hope all that makes sense. I have tried to make it as simple as possible to understand.

 

INTERLOCKING Simple version.jpg

Edited by Dhu Varren
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