Slotting

andrew jukes
Posts: 211
Joined: Thu Mar 05, 2009 4:15 pm

Slotting

Postby andrew jukes » Mon Mar 21, 2011 6:35 pm

I had understood the usual use of ‘slotting’ to be to prevent a distant signal co-located with a semaphore stop signal from showing clear when the stop signal shows danger. It would therefore prevent the distant arm from clearing when the stop signal was at danger even though the distant lever was cleared, allow the distant to clear ‘automatically’ if the stop signal was subsequently cleared and cause the distant arm to return to caution if the stop signal was returned to danger. In all this, the stop signal arm moves in accordance with its own lever, whatever the distant arm shows.

Reading a book on GN signalling*, however, I am now confused. To quote from the book: “The slotting was then arranged so that the distant signal only came off if the home signal was pulled to all clear, and (this is the surprising bit) if the distant signal lever was put back to normal in the lever frame before the adjacent signalman had returned his home signal lever, the slotting caused both arms to return to danger simultaneously.”

Has the writer got this the wrong way round, or is it the case that returning either lever to normal causes both arms to return to horizontal?

Andrew Jukes


* P.43 of Michael Vanns 'An Illustrated History of Great Northern Railway Signalling'

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grovenor-2685
Posts: 3108
Joined: Sun Jun 29, 2008 8:02 pm

Re: Slotting

Postby grovenor-2685 » Mon Mar 21, 2011 7:40 pm

Unless the GN had some very weird idea of its own he has got it wrong way round. Standard slotting for distants is as you expect. The words should say:
“The slotting was then arranged so that the distant signal only came off if the home signal was pulled to all clear, and if the home signal lever was put back to normal in the lever frame before the adjacent signalman had returned his distant signal lever, the slotting caused both arms to return to danger simultaneously.”

Keith


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