"X" signals

[towerman]

Are there still X signals on the Underground?If I remember correctly they were the last auto signals before a controlled area & had to be trated as a semi automatic.

[Deleted]

Yes all over the place on conventional signalling lines

[Dstock7080]

Jun 11, 2018 21:30:08 GMT towerman said:

If I remember correctly they were the last auto signals before a controlled area & had to be trated as a semi automatic.

Normally the last . . .
there are several instances where they are followed by another automatic,

[PiccNT]

And on the Picc, we have 5 varieties of X signals to make things even more interesting :-)

[Deleted]

Jun 12, 2018 0:21:59 GMT PiccNT said:

And on the Picc, we have 5 varieties of X signals to make things even more interesting :-)

5 types?

Your referring to signals like WDX ### and WLX ###

[MoreToJack]

Jun 12, 2018 10:02:46 GMT @aetearlscourt said:

Jun 12, 2018 0:21:59 GMT PiccNT said:

And on the Picc, we have 5 varieties of X signals to make things even more interesting :-)

5 types?

Your referring to signals like WDX ### and WLX ###

Last time PiccNT made this assertion it was established that there are six "types", even if it is pushing the definition to the extreme.

Dec 21, 2016 15:04:23 GMT @wr24 said:

Dec 21, 2016 14:48:55 GMT PiccNT said:

The X signals by T5 are related to the adjacent evacuation shaft. Yes, the last auto before a controlled area is two, floodgate X signals is three, surface stock detector X signals is four and data collection signals X855 between Manor House and Turnpike Lane and X883 between Wood Green and Bounds Green. These data collection signals are to do with the signalling control at the east end of the line and the need to stop trains entering the section if the signalling system which was then run on an old computer failed, or so I'm told!

Ah - well if you're counting the various different reasons for non-prefixed X signals then I would suggest there's 6 'varieties' on the Picc, because (as I mentioned) X402a/b/c are Xs for a different reason to X400 (and X399).

It was also established that multiple X signals in a row is not particularly unusual, e.g. between Royal Oak and Edgware Road on the eastbound/outer.

[North End]

Jun 12, 2018 10:02:46 GMT @aetearlscourt said:

Jun 12, 2018 0:21:59 GMT PiccNT said:

And on the Picc, we have 5 varieties of X signals to make things even more interesting :-)

5 types?

Your referring to signals like WDX ### and WLX ###

I can think of:

* approaching semi-auto areas
* approaching Tube tunnels at Hammersmith and Hounslow
* floodgate signals
* on the T5 section which are to do with ventilation sections
* a couple of strange ones north of Manor House whose purpose I have never had fully explained but it seems like they’re to do with the transition into what was the computer controlled area, perhaps something to do with train description continuity?

So that does sort of make 5!

[PiccNT]

I thought this had been discussed before. North End is indeed right. On the T5 section, X402 and X399 are to prevent more than one train occupying a tunnel fan ventilation section. The 3 X signals east of Manor House, X855, X883 and X887 are explained as data collection signals. This was indeed to do with the archaic computer that controlled that area (known as Metal Mickey). Now that the PICU signalling upgrade has taken place, those X signals will revert back to standard automatic signals at some stage.

[revupminster]

The X signals purpose was to prevent two trains entering a controlled area and approach locking the following semi automatic signal if at Green therefore preventing the signalman returning the signal lever fully to normal, after the first train had passed, and changing the points.

If there is an illuminated A displayed the X signal can be passed as the following semi which will also have an A illuminated must be operating by the king lever and the stick relay fully energised.

I don't know if it still holds true with computerised signalling.

[towerman]

Thanks for all the info.

[roythebus]

The X signals between Westbourne Park and Paddington Met were there to protect the e/b Met in case a goods wagon derailed on the adjacent BR sidings. The X signal approaching Westbourne Park from Hammersmith was used in conjunction with the BR track which crossed the Met at the Hammersmith end of the station to allow goods trains to access the sidings on the w/b side of the Met.

From Royal Oak towards Paddington there were high metal angles on the BR sidings and derailed wagons would short whatever circuit was there to drop the X signals back to red.

But this has probably been discussed before..

[Deleted]

Correct

[Tom]

Jun 18, 2018 14:11:13 GMT roythebus said:

The X signals between Westbourne Park and Paddington Met were there to protect the e/b Met in case a goods wagon derailed on the adjacent BR sidings. The X signal approaching Westbourne Park from Hammersmith was used in conjunction with the BR track which crossed the Met at the Hammersmith end of the station to allow goods trains to access the sidings on the w/b side of the Met.

Before my time, but i think there was a separate derailment detector in those days. The rash of 'X' signals in the Westbourne Park to Paddington area has only really taken hold in the last three years.

[rheostar]

Jun 12, 2018 10:58:45 GMT PiccNT said:

I thought this had been discussed before. North End is indeed right. On the T5 section, X402 and X399 are to prevent more than one train occupying a tunnel fan ventilation section. The 3 X signals east of Manor House, X855, X883 and X887 are explained as data collection signals. This was indeed to do with the archaic computer that controlled that area (known as Metal Mickey). Now that the PICU signalling upgrade has taken place, those X signals will revert back to standard automatic signals at some stage.

Actually, that's not quite right.

The X signals between Manor House - Turnpike Lane, Wood Green - Bounds Green are not data collections signals. They were introduced to protect the PEECS (Piccadilly East End Computer System (Metal Micky/Evil Edna)) system.

When the computerised signalling system was introduced there were so many problems. Trains were taking 30/40 minutes to travel between Wood Green and Cockfosters, it was an absolute nightmare. The computers kept losing data and instead of having the correct number on the diagram each train was labelled '000' as it's data was lost.

It was discovered that if a train applied the rule at A855, as soon as it passed over the next block joint and entered the occupied section ahead, the computer wouldn't recognise it when the train ahead left the signalling section. The computer thought there was a track circuit failure as the track stayed down so put up the three zeros.

Us Motormen found out about this, so boys being boys, as soon as we arrived at A855 and the stick was on, we'd wait exactly one minute then apply the rule knowing that the train's data would be lost.

To stop us doing this, the automatic signals on the boundaries to PEECS were changed to X signals, eliminating some problems. However, most of the problems remained until the introduction of PICU last year.