My Austrian type 12SA lever frame: Exclusions between routes

The locking table shows that many routes exclude each other. There are only a few pairs of routes that are possible at the same time:

• Li-E1 and Re-A1 (through-train on main track no.1 from left to right)
• Re-E1 and Li-A1 (through-train on main track no.1 from right to left)
• Li-A1 and Re-A2; or Li-A2 and Re-A1 (leaving from different tracks into different directions after a meet)

and also (even though it is probably useless in practice, but poses no risk)

• Li-A1 and Re-A1; or Li-A2 and Re-A2 (leaving from the same track into different directions)

All other exclusions are accomplished by one of the following three possibilities:
(a) simple exclusion, when two incompatible routes are on the same route bar;
(b) special exclusion, where a custom-purpose mechanical lock prevents locking two incompatible routes;
(c) as a special case, this 12SA allows some pairs of routes to be locked, but it is not possible to clear both signals! (This is done for the routes E2 and A2 on both sides.)

In principle, there is a fourth possibility:
(d) Two routes are incompatible when a route element (usually points) is not in the same position for both routes. In this station, this criterion would prevent the pairs E1+E2 and A1+A2 on both sides. However, these pairs are already excluded because of (a)!

Why did the designers of the 12SA not place entry and exit route for one track on the same route bar, i.e., use criterion (d)? After all, this would have saved this special mechanical exclusions for case (b) above! In many other types of interlocking, like the Austrian standard type 5007, but also the Austrian electro-mechanical types 42733 and EM55, this was done quite often. But there is a problem with this assignment of routes to route bars: If two routes behind a single signal (e.g. a home signal!) are placed on different route bars, this requires the mechanical equivalent of a logical "or". After all, the signal lever must be free to move if one or the other route bar has moved from its normal position. Examples of such "mechanical ors" are the "neutral bar" (Neutralschieber) of the 5007 or "group locks" ("Gruppenverschluss") and "group drive" ("Gruppenantrieb") of the German "Einheits-Type". However, such a "mechanical or" is a tricky element; and not at all advisable for the rugged type 12SA, which was usually located on the platform, where it had to cope with snow and ice and rain. Therefore, putting routes behind one signal on the same route bar and using additional devices for special exclusion actually simplified the locking apparatus!

Let us take a closer look at these special exclusions: My lever frame has three of them, of two different types. One of them lurked at the bottom of a picture shown in the posting about locking points levers:

Then the route bar is shifted left or right, the exclusion turns by about 45 degrees:

Seen from below:

The route bars whose movement is to be prevent contain stops, which cannot move when the hooks of the exclusion point upwards. The following picture (which shows the other exclusion of this form) shows such a stop:

The pairs of excluded routes are defined by placing the stops at different locations on the route bars.

The third special exclusion device (which prevents opposing movements) is built differently: The second route bar turns a locking disc via a pin:

The disc lies in front of the front route bar:

When it is turned, a notch on the disc and a corresponding pin on the route bar prevent the movement of the bar:

When, on the other hand, the front route bar has moved left or right, the pin locks the disc in place so that it cannot be turned by the second route bar:

Obviously, this type of special exclusion device fulfills its job like the one explained previously.

Our list of locking concepts has again grown by one entry:

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)
e. Special exclusion device between route bars