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Post by Deleted on Jul 23, 2012 9:23:39 GMT
I was at King's Cross St Pancras (eastbound) on Saturday morning waiting for a train to Ladbroke Grove and an S8 stock on a Metropolitan line service arrived at the platform. Whilst the doors were closing, a couple held open one set of doors so that they could get off the train. All the other doors had closed and the couple were still moving through the doors that they had held open when the train started rolling backwards! It rolled backwards for perhaps half a metre or so until the final set of doors closed and the train continued forwards as normal.
I'm pretty sure this shouldn't happen, but does anyone know what went wrong here?
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Post by Deleted on Jul 23, 2012 9:33:51 GMT
I thought trains had "run-back detectors" these days, or am I wrong? If they have, I don't know what the "setting" is for it to kick in. Over to our technical experts ?
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Deleted
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Post by Deleted on Jul 23, 2012 9:36:03 GMT
The driver tried to take power without checking they had traction interlock? The brakes released but as the driver couldnt take power the train rolled backwards on the rising gradient?
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Post by Deleted on Jul 23, 2012 9:37:46 GMT
I thought trains had "run-back detectors" these days, or am I wrong? If they have, I don't know what the "setting" is for it to kick in. Over to our technical experts ? 4 mph is the usual speed before the brakes are automatically applied if there is no traction interlock. |
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Post by 1018509 on Jul 23, 2012 20:51:14 GMT
Half a metre isn't far enough for the run back to kick in, I think it's about one wheel revolution. You maths experts can square your pi and tell us what distance that is; in feet please.
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Colin
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Post by Colin on Jul 24, 2012 0:42:20 GMT
I'm open to correction, but I'm sure its 2 metres before the run back protection activates.
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Post by t697 on Jul 24, 2012 20:47:05 GMT
4 mph is the usual speed before the brakes are automatically applied if there is no traction interlock. S stock is not specified that way and I don't think any LU stock is actually. S stock doors close automatically if speed exceeds a low value, as with 09TS. Re the 2m quoted by Colin, on S stock the whole runback should be constrained within 2m so the brakes come on earlier. I forget the exact distance. It was very sensitive indeed originally but has been relaxed to a sensible amount. None of this is intended to be a comment on the incident described by the OP, so apologies there! |
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Post by Deleted on Jul 24, 2012 22:10:38 GMT
4 mph is the usual speed before the brakes are automatically applied if there is no traction interlock. Re the 2m quoted by Colin, on S stock the whole runback should be constrained within 2m so the brakes come on earlier. I forget the exact distance. It was very sensitive indeed originally but has been relaxed to a sensible amount. I always understood it to be 2 meters distanceair 2 wheel reolutions. |
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Post by Deleted on Jul 24, 2012 23:40:27 GMT
Thanks for all the answers everyone, very informative indeed. Glad to hear that there is a rational explanation for the incident and I wasn't simply hallucinating!
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