semaphore signals

[asalmon]

I think by now most people realise I'm a bit of a newbie when it comes to railway matters I have only recently worked out that "upper quadrant" signals are ones that are up for go, and "lower quadrant" go down.

Until MSTS I'd never known about LQ, and I wonder how they came into being? I would have thought from a safety point of view UQ are better, because if the cable snaps gravity will make the signal show stop, whereas with LQ it will show go.

Or am I completely wrong.

-Alan

[JohnEyres]

You are right in theory. I don't think the cable would have snapped many times though! If you look at the default S&C signals they actually look like GWR lower quadrant with the light indicators hanging down. this is why they look odd when the signal goes up. On LMS Upper quadrant signals the light indicators are almost straight along the signal arm.

[edmundkinder]

Hi Alan

Most railway companies adopted a form of of lower quadrant signal after the use of flags was discontinued (hence the word semaphore). I think in the very early days when railway staff used flags stop was employees arm straight out and go employees arm lowered 45 degrees.

With this, the 138 railway companies (pre-1923 big four) adopted this with the use of a physical signal. However, when you had situations such as snow the arm would lower itself under the weight (also if the cable snapped). This of course would show clear when it was not and there were a series of accidents.

The LMS were the pioneers of the upper quadrant signal in the 30's and this design was adopted by British rail (formed 1948). in the 50's, a lot of lower quadrant signals were replaced by the standard upper quadrant design (apart from the western region). The Settle Carlisle route still had many lower quadrant ex-Midland types until the early 60's. As far as I'm aware, the last one to be removed on the S and C was at Mallerstang on closure of the box in 1969.

Hope this helps
Edmund

[asalmon]

A-ha, I see - that is interesting, and makes perfect sense. I'd rather stand with my arm pointing down than up!

Cheers,
-Alan

[snowcrashandy]

Alan,

the signal wire was connected to a balance weight pivoted to the signal post, the signal arm was connected to the balance weight, when the signal was at danger/caution, the balance weight would point at roughly 45 degrees towards the ground, when the signal was cleared, the balance weight would move to about 45 degrees above horizontal, so, if the signal wire broke, the balance weight would rely on gravity and return the signal to danger/caution.

An exremely simple and failsafe way of doing things. The Settle & Carlise route must be one of the longer lines still retaining semaphore signalling today.

Cheers,

Andy.

[asalmon]

Thanks Andy.

Interesting website BTW

Alan

[snowcrashandy]

Cheers, ta!

Andy.

[CaldRail]

The LMS were the pioneers of the upper quadrant signal in the 30's and this design was adopted by British rail (formed 1948)

The 30's? Upper quadrant semaphores were around in the 1850's on some lines.

[johny]

I would suggest that the balance weight was more to do with making it easier to pull the lever in the signal box then ensuring a lower quadrant returned to the stop position. Both upper and lower quadrant signals had them fitted as the semaphore arms were not exactly lightweight.

The Southern also extensively changed from lower to upper quadrant in the 1930s even right down in the far west in Devon and Cornwall, although some examples of the old LSWR lower quadrants remained in use in the West Country in BR days. The GWR, however, remained defiant to the last.

The LSWR used at some locations a three-position quadrant, the signal engineer of the time having seen this type in use in the USA.

John

[edmundkinder]

The LMS were the pioneers of the upper quadrant signal in the 30's and this design was adopted by British rail (formed 1948)

The 30's? Upper quadrant semaphores were around in the 1850's on some lines.

Oops, I stand corrected!

I perhaps should have said "the present upper quadrant signals as we know them"

[bjdick]

The point about balance weights,regarding safety is quite correct.
With upper quadrant,if the pull wire breaks,the signal "fails safe"by gravity.
With lower quadrant,if the pull wire breaks,the counterweight drops by gravity,and the signal "fails safe" also.
There would be,in the case of a lower quadrant mechanism,a rigid link between the counterweight and signal arm,so that only wire breakage faults would cause above effect.
Counterweights can be applied to both systems,to lessen signalperson(PC) fatigue,with the balance tipped toward safety.
It's obvious that upper quadrant is cheaper as it only relies on the wire,with no linkage involved.
I expect lowerQ lasted so long because of the"tradition" established on a paticular route.

[johny]

I don't think cheapness had anything to do with it. The SR UQ had the rigid link and the counterbalance was situated just below the semaphore arm, similar to the preceding LQ version.

I have always understood that the equivalent of today's Health & Safety Executive all those years ago were concerned about LQ arms falling, for whatever reason, to the off position and the resulting incidents, that the change to UQ was recommended.

Even then the conversion was never totally completed. Just two examples, Nuneaton still had LNWR LQs at the south end of the station in the mid 1950s and Seaton Junct had LSWR LQs in 1959.

John

[bjdick]

No argument there.Human nature being what it is,would always be suspicious,quite rightly,of a mechanism that would be unable to defy gravity,in a "fail safe" safety situation.No matter how well engineered.

[salopiangrowler]

Come to shrewsbury for a good selection we have signals upper and lower quad dating from 1902 - 4 right up to 1970s early 80's replacement upper quadrant signals.

R.I.P Wellington(salop) box and semaphores 2 months to go before we miss you.

[johny]

What I have just discovered is that the GWR made the spectacle frame heavier than the signal arm. This meant that in the event of a failure of the linkage between the balance arm and the semaphore their LQ signal would remain at danger.

John