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Post by spsmiler on Jan 29, 2024 21:53:03 GMT
Today I used a station that I've never used before - Stockwell. Its not a part of London I have any need to visit but I was curious because the station was more or less completely rebuilt for the Victoria line and I was wondering if any of the older 1920s tiling still remained. So whilst passing through I stopped to explore.
Whilst on the escalator up from southbound platforms to the ticket hall I experienced something that is in the 'a blast from the past' category.
A slow handrail (ie: the handrail was moving more slowly than the steps). Several times I had to briefly let go.
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Post by zbang on Jan 29, 2024 23:28:51 GMT
More often I notice that the handrail is running fast, but AFAICT it's common enough all over.
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Chris M
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Post by Chris M on Jan 30, 2024 11:18:35 GMT
I too find a handrail running fast to be more common than one running slow. Getting the two synchronised is (as I understand it) one of the most complex parts of escalator design.
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Post by ted672 on Jan 30, 2024 11:20:48 GMT
There's an LT Museum Hidden Hangout that visits Stockwell, here:
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Post by AndrewPSSP on Jan 30, 2024 15:15:05 GMT
The handrails at Tooting Bdway tend to run slower than the steps. I once tried to maintain my grip on the escalator going down to see how far back my hand would go, and around 3/4 of the way down it was already an arms length behind me! Another problem I have with some escalators on the Underground is the oily residue it leaves behind on my hands  |
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Post by d7666 on Jan 30, 2024 23:01:00 GMT
I too find a handrail running fast to be more common than one running slow. Getting the two synchronised is (as I understand it) one of the most complex parts of escalator design. In a new install, getting the design right for simple synchronisation is straightforward. What causes the different speeds is wear over time - the step mechanism is different to the handrail mechanism in that, while linked, there are enough independant parts within each to wear at different degradation rates; it is near impossible to fully re-synch once significant wear starts, which, obviously starts from day one. Getting the design right that takes into account differing wear rates is not so easy. None of this is aided by assets never ever get as much maintenance as they need. Since KGX fire, and general station refurbs, and any recent new stations even several years old, means there are proportionately more new installs than say 30 y ago, and the differential wear rates have not diverged enough yet, which is why we notice this less. However. The above is the engineering answer. An alternative urban suggestion is deliberate design to allow the handrail to run faster in some sort of alleged safety things about keeping user alert, and running it faster so the body CoG shifts forwards if gripping the rail, rather than backwards if slower. I am not convinced by any of this argument, and I think the suggestion, which you will find plastered all over the web, arises from people thinking too hard about it. IMHO Occams Razor applies : the simplest and less convoluted answer is probably the right one. |
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Post by brigham on Jan 31, 2024 8:29:23 GMT
It suggests that there is a friction element in the drive between the steps and the handrail. Is there a reason for such an arrangement?
A safety measure, perhaps.
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Post by zbang on Jan 31, 2024 17:27:53 GMT
A reason? Friction drives are easy. And the friction point is probably the final drive wheel to the handrail itself. (Pure speculation, but then I'm not an escalator mechanic).
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Post by d7666 on Jan 31, 2024 21:02:22 GMT
It suggests that there is a friction element in the drive between the steps and the handrail. Is there a reason for such an arrangement? A safety measure, perhaps. Errrr not sure I follow that; there is friction in all drives - and none of it works unless there is. As I posted, ITYF the issue is differential wear. |
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class411
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Post by class411 on Feb 1, 2024 2:37:12 GMT
If the bottom of the handrail were toothed, you wouldn’t need a friction element, but presumably there are goood reasons why this is not possible.
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Post by brigham on Feb 1, 2024 8:36:16 GMT
To clarify: I was referring to a friction drive element in the system.
Think of a locomotive; steel wheels running on smooth rail. Slip can occur; wheel diameter decreases with wear. Both alter the distance travelled per revolution of the wheels.
Compare this with a rack locomotive. One turn of the wheels always produces a fixed amount of travel.
There is clearly a friction-drive element in the motion which connects the escalator hand-rail and the steps together. If the hand-rail can run faster than the steps, then it obviously isn't between the hand-rail itself and the device which drives it.
I'm curious to know how the phenomenon occurs.
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Post by d7666 on Feb 2, 2024 21:24:07 GMT
I think I have explained it with the word independent where I said there are enough independent parts for wear differential to occur. I don't know a clearer form of words .
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Post by brigham on Feb 3, 2024 8:39:52 GMT
With the locomotive, the variation is at the wheel/rail interface.
I wonder where it is on the escalator?
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class411
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Post by class411 on Feb 3, 2024 9:27:52 GMT
I think I have explained it with the word independent where I said there are enough independent parts for wear differential to occur. I don't know a clearer form of words . It’s obvious that with any friction interface, wear will lead to synchronisation problems, and no simple adjustment is possible. But why not use a toothed handrail so that it could be locked to the step drive with gears? I’m guessing some potential safety problem. |
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Post by johnlinford on Feb 3, 2024 9:43:18 GMT
At a guess, a much higher risk of entrapment from loose clothing. But also probably a significant cost reduction in machining and manufacturing the handrail and running surfaces, as well as ongoing maintenance.
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Post by brigham on Feb 3, 2024 14:48:02 GMT
A minor discrepancy between steps and handrail wouldn't seem like a major problem in operation.
I'm just curious to know what allows it to happen.
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Post by zbang on Feb 4, 2024 6:24:23 GMT
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Post by brigham on Feb 6, 2024 9:55:15 GMT
That looks like the answer.
I couldn't grasp the idea of something running FASTER due to slip or wear, and the idea of the STEPS being belt-driven seemed quite alarming!
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