Approach Locking and ALSR's

On LU, the signal can be returned to danger, but any points associated with the signal will be aproach locked. It will take a release for the signal [lever] to be normalised.

As to circuits, haven't got the foggiest!

I asked a collegue tonight about said book and he said it was an IRSE book. Is that correct?

Traditional LT signalling uses an ALR (not an ALSR) but it is a 'stick' relay held over its own contact once the route it controls is 'cleared' (or 'pushed' or 'OFF') until an approaching train 'drops onto' the approach track. Once the ALR has dropped the signal lever lock drops preventing the reversed signal lever from being normalised but allowing it to move (or be moved) to the mid position and thus it is possible to 'put a signal back' in a driver's face in an emergency.
However, the same route can be cleared again as it is otherwise locked but it cannot be cancelled to set a conflicting route without taking a release.
In the days of manned cabins the signalman had to 'wind in' and 'wind out' again the release handscrew handle, which took one minute each way, in order to take a release and allow him to replace a signal lever to normal. The handle would pick up the JNR (time hand release relay) and pick up the signal lever lock allowing the signal lever to be restored to normal.
Modern practice with 'V' style frames and remote control is for the release to take two minutes. This is achieved using a 2 minute JR, release lever and the JNSR associated with the signal lever which requires to be released and completing the lever lock circuits to allow the signal levers to be restored to the Normal position. Replacing the signal lever to normal picks up the ALR over a 'normal' lever contact band, thus the ALR will 'pickup and stick' as long as the signal lever remains normal even if the approach track is still down, allowing an alternative route to be selected on the same lever if there is one or by setting a route on a different signal lever where there are conflicting routes on different levers.

The approach track TR has a Front contact in parallel with the ALR stick contact so the ALR will not drop before the approach track is shunted after the route is set.

'V' style frames can be manually released by 'pulling' the route and then 'pushing' the release at the signal control room to 'wind up' the 2 minute JR, however, there is also an auto release feature which will restore the signal lever to normal automatically should it fail to do so following the proper passage of a train through the route. The rule is that the signal lever must be in the mid position (i.e. it has been 'puffed' normal but the lock has remained down and stopped the lever in the mid) and that the backlock must be clear (all the tracks in the backlock must be unoccupied). With the backlock tracks clear, the release lever normal and the signal lever in the mid the JNSR will pickup, move the release lever to the mid and cause the 2 minute JR to start winding, the JR once picked will reverse the release lever and allow the signal lever to restore to normal by cutting out approach locking and any junction protection etc from the backlock circuit, lifting the lock.

Tom,

Quite right of course, I had the UCLR in my head while writing/editing my reply but didn't want to include it in case it caused confusion. What is really silly is that just about the first thing I would tell any trainee looking at a controlled signal backlock circuit was "GAUL" as it was the easy way to remember GVCR, ALR, UCLR & Lock and easy to remember that the simplest Lock circuit might contain just a single GVCR contact.

I guess it's time for me to quit participating, my brain is definitely not as sharp as it was.

Can I echo Tom, too. Don't depart.

One thing, though why isn't it an ALSR, after all you've got the S in the JNSR? Seems odd that the S is missing.

Well as long as you keep me honest I should hopefully avoid doing too much damage.

My main retirement hobby is building telephone servers using Centos or Fedora linux and Asterisk and connecting my heritage telephone collection to other collectors using VOIP and a private worldwide collectors telephone network. I have recently been struggling to get old ISDN2e BRI equipment working, so far with lots of software issues and little success although I have managed to get my PRI 30 channel PCM equipment interfaced with no help at all and a great deal of perseverance.
Believe me when I say that I understand exactly how you feel albeit in a different discipline!