Introduction of ground disc signals

Many thanks Tubeprune. I presume those GWR ground discs would have been operated in the conventional GWR way, i.e. mechanically by wire, and assuming that to be the case, my follow up question is when were pneumatically operated ground discs signals first introduced on the system?

Btw, apropos the 1920 date, what kind of shunting signals/ground discs would have been present on those parts of the Paddington to Hammersmith line where GWR signal boxes were present (which was considerably before 1920)?

Russ

A question on the rotation of ground signals: do they rotate anticlockwise or clockwise when moving to the off position?

Q8's official leaflet extract (i7.photobucket.com/albums/y279/Q8stock/LTS2.jpg) indicates anticlockwise, as befits LT's inheritance of the (primarily) lower-quadrant semaphores from the District and Metropolitan, whereas Tubeprune's page (www.trainweb.org/tubeprune/signalling3.htm) appears to indicate both clock and anticlock movements.

Pictures in the off position seem most elusive!

Russ

Well here's one

There is one of these rare yellow discs near me on the exit to the Marchwood military branch onto the Fawley branch 'main'. It is on a post and is a 'distant' or repeater for the BR-style white/red shunt just before the points, as there is a curve to the right and it is impossible to see the main signal.

www.roscalen.com/signals/Greenford/060429/YellowDisc.jpg

from Adrian's website. www.roscalen.com/signals/index.htm

There is also another in Eastleigh yard, but that's it..never seen any more, Were they ever used on the Underground?

Also, photos of these 'semaphore' style signals at Harrow & Wealdstone:
www.roscalen.com/signals/London/Camden-Watford/8212/0451.jpg
removed in the early 1980s, which were the very last semaphore-style signals used by LU trains, as the Richmond branch semaphores had gone in the resignalling of 1981ish.

BM64 is indeed correct - a disc with a yellow bar (they can have either a black or white background, though black was more common) applies to a permissive shunt signal. These signals are sited in rear of a diverging junction, often a crossover between a main line and yard with a headshunt accessible when the crossover points are normal.

The yellow disc can be passed when 'on' (bar horizontal and shewing a yellow light) because the road is set for the headshunt and therefore not going to interfere with the main line. Moves across the crossover reverse require the crossover points to be reverse and the disc turned 'off' (bar at 45 degrees and shewing a green light).

I'm using 'turning' here to imply rotation in both a vertical and horizontal axis. Vertically rotating point discs are much older and were often used as point indicating discs that were connected directly to the drive bars of the offending points; they are now officially 'not liked' by the powers that be.

Other railways (particularly the LSWR) used vertically rotating discs as variable 'Limits of Shunt', as 'station limits' would change when adjacent signal boxes sitched 'in' or 'out'.

I'm reasonably sure that the first recognisable horizontally rotating disc signal came out just before the Great War as a product of the GWR <spit>, prior to that small semaphore arms were used particularly by the Midland and LNW, but also by the Hampstead and Bakerloo (Golders and Queen's Park respectively).

Other railways were very reticent to adopt disc signals; the Belfast and County Down, well into GNR (I) days used rather spiffing minature somersault semaphore arms; the other GNR used 'bowtie' arms (rectangular with two triangular cut outs for facing shunts); the Highland used 'bowtie' arms shaped !><! and a large 'S' at the joined apices to denote a shunt; LSWR use a 'bowtie' as a backing signal for a bang road move.

Ah. Oh dear, I digress...

Exiting Marchwood MoD:

At Danger
www.btinternet.com/~gmhistorian/shunt4.jpg

Off:
www.btinternet.com/~gmhistorian/shunt1.jpg

You can see that MW10R is a repeater for shunt MW10:

www.btinternet.com/~gmhistorian/shunt3.jpg


Is this unique then?