Limuru - point with safety bar

[John Ashworth]

I have to confess I don't know what this is. At first I thought it might be an unusual sort of derailer, but it looks more like a treadle of some sort. Anybody know what it is?

Photos by John Ashworth 13th July 2008

[Kevin Wilson-Smith]

Very odd - operated from a lever close by or a signal box?

[John Ashworth]

Operated from the signal box on the platform via wires. The treadle thingie is apparently linked to the operation of the point via the levers in the metal box and the levers that can be seen in the first photo.

[Gabor Kovacs]

Hi John!

If you are reffering to the piece of steel, which is attached to the further most rail, just in front of the point blade, then you are looking at a "Safety Bar".
These Safety Bars are normally located on the "leading" side of a set of points, and the safety bar moves if there is no wheels in the way to prevent the movement, in a circular type motion to above the rail head and then back down to clear the flange way, while the points are being turned from "normal" to "reverse" postion.

The Safety Bar, is there to prevent the points from being turned / switched while a train, or vehicle is either on or near this set of points!

If you remember from our classes at Koesdoespoort, and not too long ago at Uncle Cliffs' home, in the semaphore section of our books, we learnt that there are Safety Bars located on all running lines in the middle of the station and usually opposite a signal cabin, and that drivers of short trains, motor trolleys' ect have to stop on the Safety Bar which will prevent the signalman from placing a semaphore signal which is already at danger behind the train, into the "All Right" (clear) position, onto a line that is otherwise occupied!

In the first pic, notice the "facing points lock" located between the points blades. Very similar to the ones used on the remaining semaphore stations here in SA!

[John Ashworth]

Thanks, Gabor. I think you're right - in fact I think a safety bar was going through my mind when I dredged up the word "treadle", but I couldn't pin it down. It's interesting to see the thing in real life after learning about it in the Train Assistant course.

I've been to quite a few Kenyan stations recently and this is the first example I have seen.

[Kevin Wilson-Smith]

That's logical - makes a lot of sense.Looking at the photos this looks right too. Any other comments?
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So is this approach is used here? Any examples?
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The other day I was admiring a derailer in Roodepoort - controller from the signal box interestlingly enough. Are these also common?

[John Ashworth]

In South Africa derailers are common. In fact there's one just outside our new depot at Hercules.

I don't know whether safety bars are still common in South Africa - I suspect not with the increase in CTC, track circuits, wheel counters, etc, but maybe others can answer?

[Gabor Kovacs]

John asked;

I don't know whether safety bars are still common in South Africa - I suspect not with the increase in CTC, track circuits, wheel counters, etc, but maybe others can answer?

John, safety bars are only common to the remaining Semphore Stations on our National Network, and to my knowledge, the only section in the Gauteng province that is controlled with Semphore and Van Schoor Train Instruments is the Spring - Nigel Section.

Should we arrange a mini trip down to Nigel, with Uncle Cliff in attendance, and we can get some "practical" revision in, on Semaphore signalling, Van Schoor Train Instruments and telegraph orders?
At the same time we can see how point safety bars, and general safety bars work in a semphore station!
Anybody interesed?

[Steve Appleton]

Interesting post and pictures, John.
I believe Gabor is correct. This is a facing-points safety-bar or treadle that locks the points and prevents them from being moved (and maybe a signal from being pulled 'off') while a train or vehicle is stationary on, or approaching the points. The safety-bar should be at least the length of the longest vehicle's wheelbase so that at least one wheel flange would be depressing it at all times. This would prevent the signalman from accidentally 'splitting' a train by switching the points under a train. My guess is that, for economy, this is probably only fitted where the points, or a train on them, cannot be easily seen from the signal box, or otherwise might be forgotten.
What is interesting is that the points locking seems to be done by the bar that slides longitudinally into a 'pocket' on the stretcher-bar between the rails rather than on an extension of the operating-bar beside the rails. Perhaps this might also be a way of positively and mechanically 'proving' the position of the points, possibly interlocking with a signal as well.
The second picture shows another interesting thing. There is a cable pulley located directly over the points operating-bar. It seems as though this is also an interlocking mechanism, whereby the pulley is only free to rotate when a groove in the bar is directly under the thick flange on the right side of the pulley wheel. From the picture it is difficult to see this clearly, so this is an assumption: but why else locate the pulley in a frame directly over the bar and why have the thick protruding flange?
In CTC working, such a safety-bar is unnecessary because the track circuits ahead of and immediately beyond the points, together with the relay interlocking, perform that same task. Also, the physical points position is generally relayed back to the interlocking from switches that are operated by a second, separate stretcher-bar on the points, not from the points operating stretcher-bar. This ensures that it is the actual points blades' position that is read back into the interlocking and not the position of the operating-bar, which might have become bent or even disconnected from the points blades. The physical points locking is also effectively done by the points machine.