After a visit to Carterton to look at the inside of a sleeper lock, thinking about comments in Semaphore to CTC and reviewing what I saw at Masterton recently, I have decided that things are more complicated than I thought.

The following are some notes I have made as a memory jogger - my conclusions may or may not be correct. Further research is needed!

Two Types Of Lock

Semaphore To CTC says that there are two types of sleeper lock: Spring Locks in which the key can be removed after the locking bar has been raised and deadlocks, which impound the key. Spring locks can presumably be closed and locked without the key - as in a spring door latch. Both type lock the points in one position only, as they rest against the switch when in the locked position (photo in Semaphore To CTC).

Carterton Example The Carterton example (photo below) does not have a nib that would stop the slide moving to the lock position after the lock bar has been raised. This means the key is not impounded. The photo is therefore probably of a spring lock. Note that the slide is in the "locked" position. It slides to the left to unlock the bar.

Masterton At Masterton the requirements were to lock the loop and main points Normal or Reverse. The key must not be impounded in the loop sleeper lock but must be impounded in the main sleeper lock if the points were not Normal. The solution was to mount deadlocks parallel to the rails with a square ended lock bar (unusual) fitting in notches in a spreader bar. The main line points sleeper lock had a shallower than normal reverse notch, so stopping the bar going fully down and releasing the key.

A - Sliding plate. Shown in locked position. Moves to left to unlock locking bar.    B - Slot for key tongue. When the key is placed in the lock the tongue is horizontal and pointing to the right. The key is turned anti-clockwise, so raising the tongue and moving the sliding plate to the left.   C - Engages tab on locking bar, so locking the bar horizontal.    D - On a deadlock a nib on the slide fits into a slot on the locking bar when the bar is horizontal (locked). When the locking bar is raised the nib stops the plate moving to the right, which impounds the key. This example is a spring lock so, the nib is missing.

Locking Bar in thrown back position.   

E Latch on sliding plate locks bar horizontally.  

F On a deadlock this notch must be horizontal to allow the slide to move to the locked position, thus freeing the key.