Locking the levers for starting signals is simple, because those signals only had a single arm. Therefore, for both routes on which a train could leave the station in the same direction (from the main track or from the loop), this single arm had to be raised. Both such routes are locked by the same route bar, therefore locking the signal is done by a single locking pin. In the normal position of the route bar, it sits below the locking bar of the starting signal lever, which prevents moving the locking weight and hence—via the standard pin on on the locking bar—turning the chain wheel. When the route bar is moved to the left or to the right, the pin no longer locks the bar, and hence the locking weight can be raised and the signal lever be reversed.
The notch that points downwards when the signal lever is reversed is somewhat less deep than the other one: Therefore, the locking bar is a bit lower when the signal is clear, which locks the route bar in place. The following picture shows the locking pin for signal B (there are three visible pins—the one for signal B is the last one):
And for signal C:
"Verschlusstück für Signal C ..." = locking pin for signal C for routes Li-A1 and Li-A2
Both images show additional locking pins for the levers of the starting signals—I'll explain them below.
The locking for home signals, which secure routes into the station, is somewhat more intricate, as the lever must be moved to different positions for the routes E1 and E2: One arm raised for E1, two arms for E2; and of course, only one position must be possible.
For signal A, my interlocking has a lever that is similar to the FPL levers, i.e., it ist moved from the normal position in the middle to an upper or lower position. Locking is accomplished as follows:
- Interlocking between the route bar and the signal lever is similar to the levers for starting signals.
- In order to allow the lever only one movement (up or down), but not the opposite one, there are three more locking pins (which look somewhat ad-hoc):
- On the right side of the chain wheel, there is a long "nose"—here it can be seen when A is clear with a single arm (it seems there was another "nose" on the other side which was sawed away at some time):
- The route bar contains two catches, which let the nose pass in only one direction, depending on whether the route bar was moved left or right. The following picture was shot along the route bars. A's lever is in its normal position, therefore the nose points down. In the background, one can see the locking pin which prevents the lowering of the locking bar and hence reversing the signal lever: "Verschlussstück für Signal A ..." = locking pin for signal A for routes Ri-E1 and Ri-E2 "Nase ..." = locking pin on chain wheel of signal lever A
- "Rückhaltung ..." = catch for ...
For the moment, I skip signal lever D—I hope I find time to explain this double lever in a later posting.
Anyway, the nose-plus-catch concept has shown us a new locking method. Therefore, our list is now as follows:
a. Locking pin against locking weight lever (for points lever) or locking bar (for FPL lever)
b. Position check against chain wheel (for points lever)
c. Locking pin hook against chain wheel (for FPL lever)
d. Catches holding nose on chain wheel (for home signal levers)