Question about FPL lever locking

[Titanius Anglesmith]

Afternoon All,

 

I'm sure this has been covered before but "FPL" comes up so often in the search it's hard to separate the wheat from the chaff.  The Hayling Island thread has aroused my curiosity regarding the locking of FPL levers, but Hayling Island looks a bit unusual to me.

 

In the example below lets assume the FPL lever 3 stands out when locked (this is just an example, it's not meant to represent a full track plan or proper numbering): 

 

 

1.  Naturally lever 4 (the home) would be released by 3 reversed.  Would there typically be any locking between levers 1 and 3?  I.e. would the FPL be used as it's there anyway, even though the move is trailing?  

 

2.  How likely would it be that the FPL would bolt 2 both ways (in which case 5 would also be released by 3)?  It seems like an unnecessary complication for a shunt move.

 

Thanks in advance

[Gordon A]

My understanding is that the FPL would not lock when the points are set for the loop.

I am assuming that as there is no platform no coaches carrying passengers would run into the loop.

I believe levers 2 , set for main and 3, locked, to release 1 or 4. 

5 would be released by points 2 being reversed.

 

Gordon A

[The Stationmaster]

There are really two questions here.

 

The first is answered by two of the basic locking rules, viz - that the indications given by signals should not conflict with the direction in which points are set.  And that proceed indications given by signals should not conflict with each other

The second is how did a particular Railway or BR Region achieve that - further taking into accointhat the same Railway/BR Region might change over the years to a different way of achieving the required locks

 

On you sketch in its simplest form the basic requirement to achieve the first rule is that Lever No.1 reversed should lock Lever No.2 at normal, which also creates the reciprocal that Lever No. 2 reversed should lock Lever No.1 at normal.  Similarly in the pure application of the rule Lever No 4 should lock Lever No.2 and vice versa.  And for the second rule Lever No.1 should lock Lever No.4 and vice versa.

 

But  there is more than one way of skinning a cat and a common practice at one time was to concentrate a lot of interlocking via the levers working FPL.  If we assume, as is most likely in past times in the situation, that the FPL only bolts the points when they are standing normal then Lever No.3 reversed could not only lock Lever No.2 normal but release Lever No. 4 from normal and Lock Lever No.1normal.  This offers the immediate attraction of no need for Levers 1 & 4 to lock each other while still achieving some of the required locking between both signals and point No. 2.  

 

So hanging locking on FPL levers could be an attractive proposition and was no doubt probably quite widely adopted.  But it has its dangers because should the FPPL Lever No.3 be disconnected for any reason, such as a fault in the FPL itself, it could remove the security of the interlocking.  so some r railways at least came away from the idea of feeding so much locking through FPL levers and went for the relevant direct locks between functions instead. Of course almost any sport of disconnection can reduce the effectiveness of the interlocking but this one was recognised as creating a particular hazard

[Titanius Anglesmith]

26 minutes ago, The Stationmaster said:

If we assume, as is most likely in past times in the situation, that the FPL only bolts the points when they are standing normal....

 

then Lever No.3 reversed could not only lock Lever No.2 normal but release Lever No. 4 from normal and Lock Lever No.1normal.  This offers the immediate attraction of no need for Levers 1 & 4 to lock each other

 

The bits in bold answer my questions perfectly, thanks Mike. We’ve still got plenty of lever frames left on LU but no FPL levers, so I’ve always wondered how they interacted with the rest of the frame. 

[Nick C]

I think the answer to both questions is "it depends" - I think different companies did it different ways. I've seen some diagrams that specify an FPL to be one-hole. I understand that signalling engineers prefer it if FPLs aren't used for trailing moves (even if the locking allows it), as a run-through with an FPL engaged would be very expensive...

[Titanius Anglesmith]

1 minute ago, Nick C said:

I understand that signalling engineers prefer it if FPLs aren't used for trailing moves (even if the locking allows it), as a run-through with an FPL engaged would be very expensive...

 

That’s an interesting observation to my modern eyes... on my patch the old point machines are steadily being replaced by modern variants with integral FPLs, regardless of where or how they’re used. At some locations we think the drivers have made it a sport to smash the points up...

[4069]

4 hours ago, Titanius Anglesmith said:

In the example below lets assume the FPL lever 3 stands out when locked

Some helpful replies here, but let's clear one thing up: when it says on a (usually Southern) box diagram that FPLs stand "out", it means that the FPL is unlocked (ie out) when its lever is normal (ie standing) in the frame. The alternative is that the FPL stands normally "in", ie it is locked when the lever is normal. So "stands out when locked" is not a phrase a signal engineer would recognise.

[Grovenor]

Well now, I recognised it, signal engineer since 1963. He did say the lever stands out, ie is reverse, not that the bolt was out. And its the lever which is of most interest when working a box. Although both versions of stand out, his and yours, amount to the same thing. Lever reverse when locked is the more common of the two options.

Edited May 1, 2020 by Grovenor

[RailWest]

A few additional comments from me, tho' Stationmaster has covered the all basics.

 

Firstly, assume a situation where 4 is sited much further out and 5 is located next to 3 as a 'running shunt', ie 3 releases 5 which releases 4. In that case, as 5 is released by 3 and also would read both ways over 2, then 3 would have to lock 2 both ways.

 

Secondly, assume an Up Advanced Starting signal some distance out from points beyond 4/5. Although 3 would be in the rear of the UAS, and any train signalled by the UAS would be going away from the station, 3 would be locked 'both ways' by the UAS, as also would 2. That ensures that neither the FPL nor the point could be moved under the tail-end of a departing train.

 

[The Stationmaster]

1 hour ago, RailWest said:

A few additional comments from me, tho' Stationmaster has covered the all basics.

 

Firstly, assume a situation where 4 is sited much further out and 5 is located next to 3 as a 'running shunt', ie 3 releases 5 which releases 4. In that case, as 5 is released by 3 and also would read both ways over 2, then 3 would have to lock 2 both ways.

 

Secondly, assume an Up Advanced Starting signal some distance out from points beyond 4/5. Although 3 would be in the rear of the UAS, and any train signalled by the UAS would be going away from the station, 3 would be locked 'both ways' by the UAS, as also would 2. That ensures that neither the FPL nor the point could be moved under the tail-end of a departing train.

 

Not 3  - because in this scenario the points are being trailed so 3 would be standing normal even if the train was coming from the platform (especially if Lever No.1 was locked by Lever No.3).  The locking rule is that the signal in this instance locks (both ways) trailing points in rear of it.  And operationally there is no way round that unless signals trailing through the points very unusually need the FPL locked (because if the locking didn't require it the Signalman wouldn't bother to bolt a trailing point).

 

18 hours ago, Titanius Anglesmith said:

 

That’s an interesting observation to my modern eyes... on my patch the old point machines are steadily being replaced by modern variants with integral FPLs, regardless of where or how they’re used. At some locations we think the drivers have made it a sport to smash the points up...

Yes, The Western increasingly went over to doing that from the 1980s (and in some cases in late 1970s schemes although it had been very unusual in the 1960s schemes).  There were two reasons for doing so - one was that the additional cost of incorporating the FPL had reduced considerably and it meant also that all point machines would be to the same detail pattern.  And secondly the view was taken that you'd never know in advance if circumstances would arise in which a facing move was going to be made over a nominally trailing point and it the point machine had an FPL (and a signalled move) there'd be no need to clip the points.