Thompson LNER block instruments

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Mickey
GNR C1 4-4-2
Posts: 716
Joined: Sun Jan 27, 2019 7:27 am
Location: London

Thompson LNER block instruments

Post by Mickey »

We had four (4) of these Thompson LNER block instruments at Welwyn Garden City s/box until the lever frame along with the track diagram, block instruments and semaphore signals were all abolished and the commissioning of the NX panel along with colour light signalling took place in September 1973. The Thompson LNER block instruments were nice block instruments to work on with a black coloured 'round handle' for 'pegging up on' the instrument instead of a 'pegging handle' that was found on the GNR block instruments see the link below-
http://www.lymmobservatory.net/railways ... _small.jpg

Also the box at Welwyn Garden City gave it's name to a railway signalling safety device that came about after the 1935 crash at the box when a signalman wrongly gave 'train out of section' back to Hatfield No.3 signal box and then wrongly accepted a second train into the already occupied block section between both signal boxes. It was found at the official enquiry into the accident that some sort of safety device was required to stop a signalman wrongly giving 'train out of section' back to the signal box in the rear and then wrongly accepting a second train into the already occupied block section before the first train had completely passed through the block section. The safety device worked electrically/mechanically in conjunction with the block instrument on the block shelf and the berth track circuit on the illuminated track diagram in the signal box and required the berth track circuit in the box to show occupied and then clear (a train passing over the track circuit that had passed through the block section) before a second 'line clear' could be given by the signalman to the signal box in the rear after the signals were returned to danger behind the train. The safety device was known as Welwyn control or Welwyn block and was widely adopted on the LNER and on other regions into British Railways days. If a train had already been accepted by the signalman at the box in advance but was then was cancelled off by the signalman at the box in the rear the commutator handle on the block instrument on the block instrument at the box in advance would be returned to the Line Blocked or Normal position (after putting any signal back to danger) and a 'winding handle' had to be wound around by the signalman in the box in advance for about 2 minutes until a letter N re-appeared in the winding mechanism on the block shelf beside the block instrument this supposedly gave the signalman time 'to think' what he/she was doing before giving another line clear to the box in the rear. Signal boxes that I worked in the London area of the former London Midland region during the 1980s had Welwyn control fitted on the signal box block instruments.
Original start date of 2010 on the LNER forum and previously posted 4500+ posts.
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