Of Interlockings And Other Machines ...: Nene Valley Railway

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After the Epping-Ongar Railway, my next "heavy duty signalling visit" was at Nene Valley Railway's Wansford station, west of Peterborough. Here is the signal box:

Signal box behind gates, Wansford (NVR), 22.8.2013

Here is its long lever frame:

Lever frame, Wansford (NVR), 22.8.2013

At the very right, four levers deal with the gates of the level crossing just below the signal box. The two rightmost ones are for the small gates, whereas the two on the left unlock the large vehicle gates and the wheel that opens or closes them. Even though the numbers of the levers go up to 60, the frame does not have that many levers—it has been reduced in size when it was installed here, so that the levers now start at 17, and the active ones at 22 ("up first home"):

Gate levers, Wansford (NVR), 22.8.2013

Here are the signal levers for the station's west side. In between, there is a blue-and-brown release lever for the ground frame in the "loco yard," which has the typical shortened handle of an electric release. At the bottom of the levers, one can see that there is a gap between lever 45 and 46. It therefore seems that this type of frames uses units of 15 levers; these units are then installed side by side. This fits nicely with the number of 60 levers (four units), but it does not fully explain that the levers now start at 17: Obviously, the first unit with levers 1 to 15 has not been installed; but somehow, an additional lever with number 16 also got lost somewhere in the process:

Right side of lever frame, Wansford (NVR), 22.8.2013

Here are the levers for the up starter and the shunting signal for leaving the station's main track towards Yarwell Junction in a western direction. Near them, there is an additional lever 35 called "interlocking lever:" Actually, it reversed two trailing points connecting the platform tracks. However, these points proved to be troublesome more than they were useful, and so they were removed. In order to keep the locking logic the same, their lever was kept as an "interlocking lever:"

Signal levers, Wansford (NVR), 22.8.2013

Here are detailed photos of the track diagram. One can see that there are a few track circuits for track segments on the west side that cannot be seen well or at all from the signal box—all other tracks must be visually checked for occupation:

Right side of track diagram, Wansford (NVR), 22.8.2013

Center of track diagram, Wansford (NVR), 22.8.2013

On the left, there is a small gradient diagram of the line (the distances are given in the old miles and chains units), and one can see that the points to a storage siding are not (yet; or no longer) connected to the signal box, but clamped in place:

Left side of track diagram, Wansford (NVR), 22.8.2013

Many levers are not only controlled by mechanical tappet locks, but also by electric circuits. Here is the row of locking bars going through the electrical locks. One can see that most levers can only be locked in their normal position; but that there are two that can be locked reversed, namely the fourth and the tenth. Why would that be so? Counting down the levers in the picture of the signal levers above, one finds that the first one is the release lever for the ground frame: And of course, it has to be locked in reverse if the corresponding release lever on the ground frame has been pulled, so that no conflicting routes can be set at the signal box. As for the tenth locking bar, "I leave the determination of the reason for its reverse locking to the reader."

Many of the locks seen here carry the symbol "SGE," meaning "Siemens and General Electric Railway Signal Co., Ltd." It is interesting that Siemens did some signalling business in the UK, but never defined how signalling circuits are designed there, as they definitely did in many parts of Central Europe:

Electric locks and catch handle switches, Wansford (NVR), 22.8.2013

Besides the electrical locks, there are also many catch handle switches on this frame. The contacts in these switches are used to energize the locking circuits so that the batteries are only cut in when a lever is to be reversed; this considerably reduces the amount of current needed by the signal box's circuits:

Circuit activation contacts (activated by pulling catch handle), Wansford (NVR), 22.8.2013

Like the EOR, the NVR does not (yet?) use Tyer's instruments for block working, but only a single key as a staff on each of the two sections west and east of Wansford. Here is the Annett's key that is used as staff towards the line's end at Yarwell. Locking is accomplished mechanically here:

Annett's key used as staff, Wansford (NVR), 22.8.2013

The key for the section to Peterborough is locked in this electrical lock behind the lever frame:

Staff lock to Peterborough, Wansford (NVR), 22.8.2013

Lever 43, which controls electric points 43A and 43B, is reversed here:

Points+FPL lever 43 is pulled, Wansford (NVR), 22.8.2013

English signals are traditionally moved by single wires. This makes it hard to invent a device that adapts the wire's length with changing temperatures, and so this task is delegated to the signalman. Here is a a wire tensioner, with the corresponding handle inserted for turning the large wheel via the worm gear:

Wire tensioner, Wansford (NVR), 22.8.2013

On the block shelf, there is a row of signal repeaters—here is one of them for the signal farthest away from the signal box. This instrument is crucial when the wire is shortened or lengthened: When it is pulled so short that the arm starts moving upwards (which might be interpreted as clear by a driver!), the repeater moves to the "wrong" position and hence indicates to the signalman that he must not shorten the wire that far: