Indeed CK is certainly foul and thus should lock as you describe.
On a layout such as this, I would probably expect to find point-to-point that would prevent 138 N>R unless 137R or 136R; prevent 137 R>N unless 138N. This would be the traditional way of signalling the area. Nowadays more likely to achieve much (but not exactly) the same by pure point calling by the relevant routes.
Whether or not it is worth AF locking 137 is a matter of debate. Dead track locking is primarily for hand-signalled moves and if AF were occupied with vehicle on 138B reverse, then whether train being handsignalled over 137N or 137R it is equally likely to hit it. Therefore from that perspective there is little 137 can do about it one way or another.
A train on AF would lock 138 so this would prevent to route being set up applicable to 137R, but not for one applicable to 137N. So could well decide that (AF or 138N) should lock 137R>N and largely therefore analogous to the locking that would have occurred via the point-to-point.
To be honest I don't know what the current practice would now be. I'd be tempted to omit so that 137 could be put N, because that would at least enable normal working on the Up Slow. However you are certainly not wrong to include it, and you may feel this is the wise thing to do in the IRSE exam.
Signal engineers can argue about the finer points of locking for ages; there is often a balance to be struck between one risk and another, or slight greater safety at the expense of significant operability.
For the examination it is more important to get the basics right and I try to pitch my comments on attempts to be appropriate to the level of the author, though yes I should have pointed out that CK is conditionally foul, so thanks for your comments
On a layout such as this, I would probably expect to find point-to-point that would prevent 138 N>R unless 137R or 136R; prevent 137 R>N unless 138N. This would be the traditional way of signalling the area. Nowadays more likely to achieve much (but not exactly) the same by pure point calling by the relevant routes.
Whether or not it is worth AF locking 137 is a matter of debate. Dead track locking is primarily for hand-signalled moves and if AF were occupied with vehicle on 138B reverse, then whether train being handsignalled over 137N or 137R it is equally likely to hit it. Therefore from that perspective there is little 137 can do about it one way or another.
A train on AF would lock 138 so this would prevent to route being set up applicable to 137R, but not for one applicable to 137N. So could well decide that (AF or 138N) should lock 137R>N and largely therefore analogous to the locking that would have occurred via the point-to-point.
To be honest I don't know what the current practice would now be. I'd be tempted to omit so that 137 could be put N, because that would at least enable normal working on the Up Slow. However you are certainly not wrong to include it, and you may feel this is the wise thing to do in the IRSE exam.
Signal engineers can argue about the finer points of locking for ages; there is often a balance to be struck between one risk and another, or slight greater safety at the expense of significant operability.
For the examination it is more important to get the basics right and I try to pitch my comments on attempts to be appropriate to the level of the author, though yes I should have pointed out that CK is conditionally foul, so thanks for your comments
(31-08-2011, 06:15 PM)Tony Soprano Wrote: 137 Dead Locking....
Would N>R not also require (CK or 141R) given the position of the CP near 137B points?
Also can the possiblity of AF & EM tracks being foul {(AF or 138N) & (EM or 136N)} be excluded from the dead locking if these points will always be called flank by the route?
PJW