I think that at least some of your queries will be answered if you look at this thread:
http://irseexam.co.uk/thread-741.html
although it starts off with mainline (i.e. Network Rail) environment, it then continues to consider those utilised on LUL and there are some useful attachments to download.
In essence the advantages of the LU specific mechanisms for that environment include-
a) operated by air from the air main provided to operate the signals' trainstops etc; avoids the need for thick cable to carry operation current;
b) points operate extremely quickly compared to electic mechanisms. This factor is particularly important as the traditional LU features mechanical interlocking and such things as point-to-point locking, so when wanting to clear a signal, all the points have to be operated perhaps individually (i.e. needing to have really achieved their new lie before another set of points in the same route can be operated into their desired position) and once a train has passed a signal then there is normally no "sectional route release" and therefore the signal lever cannot be fully normalised until train has passed beyond the last set of points in the route- hence it is important that once points asked to move that they do so quickly as otherwise it could delay the next train;
c) fit within the rails and therefore can be accomodated in tunnel, also if in open section and maintainer has to carry out remedial work on a points failure thennot encroaching onto a parallel running line;
d) don't use hydraulic fluid etc (fire risk in tunnel)
e) mechanically simple and visibly obvious operation and accessible- minimises likelihood of failure and time to rectify;
f) Swith & Detector box positively proves the position of BOTH switch rails (as well as the lock of course), so doesn't suffer the potential failure mode of the traditional UK point machine (Greyrigg, Potters Bar accidents).
As far as circuits are concerned the electrical drive circuits terminate with the operation of the relevant air valve; a significant difference with NR is that the "power" remains applied whilst those points are demanded in that position; i.e. really the air valve is just driven off the associated lever position, there is no "time out" nor "cut out" when detection is achieved.
In fact that is the reason why " ground locks" are provided; these guard against inadvertant operation by stored air pressure. These are essentially electrically operated "bolts" that drop into positionwhen the points are in position and electrically locked; they have to be energised just prior to the attempt to move the points so that the bolt can be withdrawn from the hole prior to the drive (as otherwise the drive would just tighten the hole preventing the bolt from being withdrawn and the points would be jammed).
Hope this (when read in conjunction to the other thread) resolves; otherwise ask more specific question.
(09-12-2013, 06:57 AM)nagaraju.a@etoerail.com Wrote: Dear Anyone,
I just want to have glance regarding existing point machines used in LUL like Chair lock, Clamp lock, 4 foot and 6 foot. Its specification and right place to use with circuits, if available. Any comments and answers, please welcome.
Regards,
A Naga Raju
