However, for all facing points which are traversed with 60kph or more, an additional lock is required that firmly locks the blades in place. In mechanical interlockings, these additional lock (called "Riegel") is moved by one or two separate levers. In lieu of another term, I call them FPLs (facing point locks), although they do not at all work like FPLs in England. On my lever frame, the two points in the main track (points no.1 and no.5) required such FPLs; the points in the loop track did not need them, as a train entering the loop would already have slowed to 40 kph or less when travelling over them. The blade locks mentioned above would suffice for securing these point blades.
Here is the mechanics of locking the FPL lever by the route bars in a 12SA-type interlocking. The normal position of the FPL levers is in the middle, from where they can be moved up or down:
- When in the normal position, the points are not locked and hence can be reversed by the points lever.
- When the FPL lever points upwards, the points are locked in the normal position.
- When the FPL lever points downwards, the points are locked in the reverse position.
The handle of the FPL lever can be pulled out. Here you can see how I lock points no.5 in reverse position (the points are already in the reverse position, their lever points upwards):
First, I pull out the handle of the FPL lever completely:
Then I lift the locking weight with my left hand, ...
... move the lever downwards, ...
... and finally let the locking weight drop so that its locking pin engages in the corresponding notch in the chain (or lever) wheel:
How do an FPL lever and a route bar lock each other? To find this out, we take a closer look at the levers and the various locking parts. Here is a picture of the lever—three notches are cut into the wheel, one for each lever position:
- "Ausnehmung und Loch für Plus-Stellung" = notch and hole for upper position
- "Ausnehmung für Grundstellung des Riegels" = notch for normal position of FPL lever
- "Ausnehmung für Minus-Stellung" = notch for lower position
The following picture shows the location of a lever; the lever itself has been removed:
Here is the same picture, with annotations for the locking parts:
- "Sperrgewichtshebel" = locking weight lever
- "linkes Verschlussstück" = left locking pin
- "Sperrbalken mit Klinke" = locking bar with pin
- "linkes Verschlussstück" = right locking pin
In contrast to the points levers (from the previous posting), the locking weight for the FPL levers—and also for all other levers—is situated higher up. The weight lever turns around the same axle as the lever itself. Via an oblong hole at its back end and a threaded bolt, the weight lever slides the locking bar up and down. On the locking bar, there is a pin which fits into notches on the lever wheel. The left locking pin has the form of a hook (which will move into a hole in the lever wheel); but in addition, this pin also has a lower part which looks like the left locking pin for lock a points lever—we will see this part of the lock in a later picture.
Here is another picture of the weight lever (with part of the weight visible on the left), its oblong hole, and the vertically sliding locking bar which crosses over the route bars:
When the FPL lever is in the normal position, route Li-E1 (route bar moves right) is prevented because there is no hole opposite the hook of the left locking pin. Route Li-E2 (route bar moves left) is prevented because the locking bar is in an intermediate position (resulting from the medium-deep notch in the lever wheel), and therefore the high right locking pin collides with the locking bar.
For this route, the FPL lever must be locked in the upper position. The following picture shows to contact locations for locking (the contour of the lever wheel is a little weird):
- "Kontur der Hebelrolle" = contour of lever wheel
- "unterer Teil des linken Verschlussstücks" = lower part of left locking pin
Lockingis done by the notches in the lever wheel: The lower part of the left locking pin prevents the locking bar from moving downwards (i.e., you cannot lift the locking weight!). The pin of the locking bar sits in the notch of the lever wheel, so that this wheel cannot turn. In addition to this, the hook of the left locking bar sits in the hole of the lever wheel—however, I am quite sure that this is not for locking. After all, pulling forcefully at the FPL lever, one could certainly bend that hook, which is only about 1/3" thick. Therefore, that hooks sits in the hole only loosely.
Why isn't it possible to select route Li-E2 when the FPL lever is in the upper position? First of all, this is prevented as points no.5 are in the wrong position for this route. But moreover, the right locking pin would collide with the locking bar when the route bar moved to the left.
For this route, the FPL lever must be locked in the lower position. In this lever position, the pin of the locking bar sits in the lever wheel's deep notch, and therefore the high right locking pin can move below it and thus lock the locking bar (it cannot move downwards):
Selecting route Li-E1 is prevented similarly to the normal position of the FPL lever: The hook of the left locking pin cannot move into the hole in the lever wheel.
Lock principles of type 12SA
The following is a short list which parts take part in mutual lockings in a 12SA-type interlocking. Up to now, we have seen the following combinations—but there will be more!
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)