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Post by commuter on Oct 4, 2022 20:30:17 GMT
When you’re at a quiet station above ground you can often hear a clicking noise which appears to be coming from a metal plate between the porcelain pot and the underside of the current rail. Something causes the magnet to raise and then stop, causing this clicking noise.
Does anyone know what causes it?
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Post by goldenarrow on Oct 4, 2022 23:34:20 GMT
If my reading of this thread from the depths of the forum is correctly inclined, then it would appear that the noise is coming from what you describe. Metallic plates between conductor rails and porcelain insulator pots becoming magnetised then dropping. Video showing the phenomenon below. Click here if not shown |
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Post by modeng2000 on Oct 5, 2022 6:34:37 GMT
Really interesting, I wonder how much current has to flow in the conductor to lift the plate?
John
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Post by brigham on Oct 5, 2022 7:35:07 GMT
I'm more inclined to wonder why the plate is there in the first place, and if its behaviour is intentional.
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Post by Dstock7080 on Oct 5, 2022 7:47:29 GMT
I'm more inclined to wonder why the plate is there in the first place, and if its behaviour is intentional. I understood these to be spacers intended to lift the rail surface to correct contact height. |
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class411
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Post by class411 on Oct 5, 2022 8:59:06 GMT
I'm more inclined to wonder why the plate is there in the first place, and if its behaviour is intentional. I understood these to be spacers intended to lift the rail surface to correct contact height. Surely, if that was the case, they would be fixed. |
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Post by Chris M on Oct 5, 2022 11:39:03 GMT
Yes, that was my first thought - if it was supporting the rail then there would be no space between it, the rail and the pot. Then I wondered whether it was a temperature-related thing - i.e. the plate supports the rail when it is hot (or cold) but not when it's cold (or hot)?
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class411
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Post by class411 on Oct 5, 2022 11:45:39 GMT
Yes, that was my first thought - if it was supporting the rail then there would be no space between it, the rail and the pot. Then I wondered whether it was a temperature-related thing - i.e. the plate supports the rail when it is hot (or cold) but not when it's cold (or hot)? The gap seems much to large to be a result of (or in place because of possible) expansion. Watching the video full screen, it appears that the piece that moved was one of a number stacked - indeed, as if they were spacers, but they took up far too little space vertically to have any effect. We really do need a track engineer.  |
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Post by t697 on Oct 5, 2022 16:34:48 GMT
In the example in the video, probably the current rail is bearing heavily on the adjacent insulator pots either side of the one shown and the shimming isn't quite right at the one shown, leaving the shim loose.
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class411
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Post by class411 on Oct 5, 2022 16:41:00 GMT
In the example in the video, probably the current rail is bearing heavily on the adjacent insulator pots either side of the one shown and the shimming isn't quite right at the one shown, leaving the shim loose. Yes, that makes sense. So this clicking is not a particularly common phenomenon, nor an (or a side effect of) intended design feature? |
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Post by brigham on Oct 6, 2022 7:39:30 GMT
It's a ghostly reminder of the Lorain surface-contact system of current collection.
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Post by modeng2000 on Oct 6, 2022 9:03:46 GMT
So what changes to cause the spacer to move?
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class411
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Post by class411 on Oct 6, 2022 9:23:02 GMT
So what changes to cause the spacer to move? (Possibly) When a train starts drawing current from the section of which the rail in question is a part, where the current flows, a magnetic field will be induced in the rail. And as trains can draw quite a lot of current so the effect can be noticeable. |
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Post by t697 on Oct 6, 2022 16:35:51 GMT
The video was fascinating. I've often heard these clinks but vaguely assumed it was caused by thermal expansion/contraction of the rail and stiction on the mounts. The video has put me straight on the magnetic cause. Of course ideally the load would be fairly evenly spread on all insulators and one wouldn't have shims loose.
The more recent type of insulators have two sections that can be adjusted via an included coarse thread system for height so don't need loose shims.
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Post by PiccNT on Oct 6, 2022 22:30:47 GMT
I may be completely wrong here, but at certain places when I hear that clicking sound, the approach-controlled signals in advance clear, if all other clearing conditions are met. It may just be a coincidence or indeed a different clicking sound!
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Post by modeng2000 on Oct 7, 2022 6:09:41 GMT
Depending on the current rail feed point the train need not be near the loose plate to cause it to lift assuming this is the cause.
Just fascinating!
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