Monday, February 18, 2013

My Austrian type 12SA lever frame: Locking the point levers

Starting with this posting, I try to explain the various function of my lever frame in detail.

Austrian (and German and many other) lever frames have essentially three types of levers:
  • Levers for points (for some points, there are two levers: One for reversing the points, one for locking them; maybe I will explain the reasons for this later);
  • Route levers, which lock the points levers once they are in the correct position; and release signal levers for the setup route;
  • Signal levers.
In this first part, I explain the interlocking between points levers and route levers.

With 12SA interlockings, this dependency is not at all trivial. I'll try to show the interesting mechanical parts in a series of photos. Before this, it is necessary to understand how points are reversed in this type of interlocking. Here you can see a sequence of photos that shows me (the author) reversing points no.5:

First, the left hand raises the locking weight. This releases a pin which now allows the chain wheel to turn:

Pulling the handle release with the right hand completely releases the lever, which now can be reversed with the right hand (the left hand is still holding the weight):

After completely reversing the points, one releases the handle release (right hand) ...

... and drops the locking weight (left hand):

If you look carefully, you can see that the locking weight of the reversed points is now a little bit lower than the other weights – this will be important later.

Let us look which elements must interact to lock the points lever. On the lever frame, one can see that a points lever, in contrast to other levers, has two wheels – let me call them "lever wheel" and "chain wheel". The lever wheel is riveted to the lever proper. The chain wheel is clasped by the chain, which is in turn connected to the pull wires going out to the points. I will describe a few more details later – let me just say here that the two wheels are pressed together with two very strong springs. When an engine trails the points while they are in the wrong position, the chain wheel is turned forcefully, while the lever wheel remains locked by the interlocking. The spring coupling (or "clutch") allows this without damaging the lever frame or the points.

Why is this necessary? English points cannot be run without damaging them. However, in Central Europe, it was agreed on in technical rulebooks that such a movement should not lead toa damaged interlocking.

After this general description, let us disassemble the interlocking. Here is the lever, with special cuts that result in various lockings (please excuse that I do not [yet] translate the texts in the pictures into English):

a. The lever wheel has two notches, an upper one for the normal position and a lower one for the reveres position. A pin of the locking weight lever engages with these notches (as we will see in a moment). The two notches are of different depth: The notch for the normal position is shallower, the notch for the reverse position is deeper:

b. The chain wheel has two notches for each route bar that requires these points in a defined positon:

c. This picutres shows the various parts behind the (removed) points lever that are needed for the various lockings. At the left, there is the horizontal two-armed locking weight lever, below it the route bars go from left to right:

Here are the various locking parts with [as of now still German] inscriptions:
  • "Sperrgewichtshebel" = locking weight lever
  • "Klinke" = pin
  • "Fahrstra├čenschubstangen" = route bars
  • "besonderer Verschluss" = special route exclusion device - not important here, just to give it a name:

Route Li-A1
We now concentrate on the interactions that lock points no.5 only for route Li-A1. The necessary locking parts are marked in the following picture:
  • "linkes und rechtes Sperrgew.hebel-Verschlusst├╝ck" = left and right locking weight lever pin.
  • "Stellungspr├╝fer" = position check.
  • The locking weight is hanging vertically at the left::

The following picture shows the position of the the locking weight lever in the normal position of points lever no.5. Two lines show the contours of the two lever wheels, interrupted at the positions of the notches explained above.
  • "Kontur der Kettenrolle" = contour of the chain wheel
  • "Kontur der Stellrolle" = contour of the lever wheel:

How do I know that the weight lever is in normal position? Because  – see a. above – the notch in the lever wheel for the normal position is the shallower one – therefore the back end of the weight lever is pushed down a little bit! Still, it is raised so high that the left pin (which is invisible here behind the weight lever) can move below its back end.
Moreover, the chain wheel has a deeper notch at the location of the position check on route bar Li-A1: Therefore, the route bar can be moved to the right (which is accomlished via the route lever):

During this movement, the position of the the chain wheel is checked when the position check's left, higher hump moves through the corresponding notch. However, when the route bar is fully moved, the position check no longer remains in that notch, and therefore, the chain wheel can freely rotate. This is important when an engine runs the points to avoid damaging the frame.

But how does all this lock the points? This is only effected by the left pin, which prevents the back end of the weight lever from moving down, and hence that lever locks the lever wheel with its pin.

What prevents moving the route bar into the other direction (which would wrongly allow locking route Li-A2)? The chain wheel has a deep notch - this would allow the lower hump of the position check travelling to the left! But the right pin now touches the back end of the weight lever (which is, as we remember, pushed down a little bit by the shallow notch in the lever wheel) and by this prevents the movement of the route bar to the left.

To sum it up:
  • The right pin prevents locking of route Li-A2 (i.e., it checks that the points no.5 are in normal position).
  • The position check checks (but only during the movement of the route bar) that points no.5 are not in an intermediate position.
  • The left pin locks the lever via the weight lever and the lever wheel.
It took me the better part of an hour to understand these various dependencies – even though I could touch all the parts directly and had them dissassembled. When completely assembled, most of this cannot be observed - it happens "deep inside".

Route Li-A2

How is points lever locking accomplished for this route? This image shows the position of the weight lever when the points no.5 are in the reverse position:

The back end of weight lever is now a little bit higher, as the "reverse notch" of the lever wheel is cut somewhat deeper. When the route bar is moved to the left, the right, lower bump of the position check goes throught the notch of the chain wheel and therefore checks that the points are not in an intermediate position. At the same time, the right pin moves below the weight lever and by this locks the lever wheel and the lever:

What prevents the movement of the route bar to the right, i.e., locking of route "Li-A1"? This time, this is not done by a pin, but by the position check: Its higher hump does not fit through the lower notch of the chain wheel!

To sum up:
  • The position check prevents shifting the route bar to the right, i.e., it checks that the points are in the revers position.
  • The position check also checks (when the route bar moves) that the points are not in an intermediate position.
  • The right pin locks the weight levetr and hence the points lever.
One can see that the locking responsibilities are distributed in different ways for the two routes! – a quite tricky design of this mechanical lever frame, I'd say.

Pins and positions checks for different route bars

Looking horizontally over the pins and positions checks, one can see that their heights are different for the route bars Li-A1/A2 and Li-E1/E2:

Also, the wheels' notches for the route bars seem to be of different depths. It therefore seems that each notch and pin was designed separately! However, as there are only a handful of combinations of route bar locations and lever positions, the corresponding measures could have been assembled in a "desgn catalogue" once and chosen from there for each lever frame.

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