Dissecting a Dutch point mechanism

Deutsche Version dieses Postings

This next posting about Dutch mechanical interlocking technology contains some information about the operation of points, which is distinctly different from their counterparts in Austria and Germany as well as in Britain. For fans of steam engines, I have added a few pictures of ZLSM's SJ 1040.

Remark: In my translation of the original German text, I have tried to use the terms of IRSE from this document.

i) Signal and points mechanisms: with double wires, without tensioners, with chains at bends = "Austrian"

In the Netherlands, points connected to mechanical interlocking frames are in general moved by double wires, following German and Austrian practice. At bends of the wire line, chains were spliced into the wires, as is customary in Austria and also in Britain (but not in Germany, where thin steel cables are used instead). There were no separate tensioners, as they were used in Germany; rather, the linkages for reversing points and moving signal arms had to be constructed in such a way that they would tolerate some slack in the wire lines during hotter times.

The following picture shows, on the left, the point mechanism and on the right the facing points lock. One can clearly see the chains that are wound around the wheels inside the mechanisms:

Point mechanism und FPL, points no.32, Wijlre-Gulpen, 16.8.2015

The stepped rods of the FPL run above the point mechanism:

Point mechanism und FPL, points no.32, Wijlre-Gulpen, 16.8.2015

j) Points: Without blade locks = "English", but ...

k) Points: ... can be run through = "Central European"

The following picture shows that the rods moving the blades are directly fastened to them via a simple joint. This is in contrast to the blade locks that had to be used throughout Germany and Austria to press the blades against the stock rails:

Point mechanism und facing point lock, points no.32, Wijlre-Gulpen, 16.8.2015

Here is a detail of the joints at the tip of a blade: The thinner rod is the detection rod of the FPL, whereas the thicker one is the drive rod of the blade. One can see that both rods are isolated from the blades (the white isolating separators can be seen at the places where the rods are bolted to the joints), therefore these rods can be used with track circuits. It can be clearly seen that no blade locks are in place. There is a small "hump", over which the blade is lifted by a roller at its very tip during reversal. The hump's incline will help the blade to move towards the stock rail more easily. But the distance between the roller and the bottom of the incline is so large (certainly more than one centimetre) that this mechanism cannot be responsible for preventing a dangerous gaping of a blade:

Blade with detection rod and drive rod, points no.32, Wijlre-Gulpen, 16.8.2015

Therefore, we must look somewhere else for the safety-critical element that pushes the blade reliably against its stock rail. To find it, I lifted (against some rules, certainly – I apologize for this) the lid of the point mechanism. Here is what can be seen inside:

Opened point mechanism, points no.32, Wijlre-Gulpen, 16.8.2015

Opened point mechanism, points no.32, Wijlre-Gulpen, 16.8.2015

One can see the peg on the driving wheel that fits into a slot in the drive rod. When the wheel is turned by the wires (which are in turn pulled by the lever in the signal box), the peg will clearly move the rod and therefore the blade that is connected to it. Looking more closely, one can see the following details:

• The peg moves the drive rod of only one blade. The other drive rod is below the wheel, where it is moved by another, similar peg.
• The driving wheel is turned by about 120° when the points are reversed. Thus, the peg is not at the dead center, and therefore, moving the rod by some external force (e.g. on the blades by a train) could move the wheel and hence open the points, which is clearly very dangerous.
• However, the peg is not directly attached to the driving wheel. Rather, it sits on a separate small lever. Hence, moving the drive rod from the blade will not turn the driving wheel, but try to move that small lever. If, below the wheel, this lever rests against some fixed stud on the bottom of the mechanism, the drive rod cannot be moved. If, additionally, the housing of the point mechanism is securely mounted on two ties that are also rigidly connected to the stock rails, the blade cannot move from its position and hence will be tightly pressed against or at least be very near to its stock rail.
• This decoupling of the position of the drive rod from the driving wheel is necessary for another reason: Because of temperature expansion and contraction, the double wires cannot position the driving wheel at a precise angle at the end of its movement. In other words, the linkage must tolerate some slack in the movement up to the driving wheel.
• Last, but not least, the peg moving the drive rod of the open blade could be freely movable so that the blade could turn the wheel. This would allow running through the points without destroying the mechanism—a typical requirement in Central Europe!

Unfortunately, I cannot and could not look below the driving wheel, so I do not know how much of my guesses above is true. Insofar this point mechanism is quite "Austrian"—the mechanisms in my home country were enclosed in casings, in contrast to the easily "readable" British and German point mechanisms.

Here is a last picture:

Opened point mechanism, points no.32, Wijlre-Gulpen, 16.8.2015

In contrast to the point mechanism, the facing point lock is much simpler: A rim on the turning wheel locks into cuts in the detection rods, which are therefore unable to move and fix the blades in their respective positions. However, the detection rods in the following picture have cuts pointing upwards—which could not be locked by the wheel that is below the rods. Most probably, someone reused rods from another set of points by turning them over and filing new cuts

Update 2.11.2016: The cuts on top are most probably not there because of a reuse, but because a a second wheel on top could be used to lock the blades for a route into the loop track. This was (and will be) necessary if Wijlre-Gulpen is used as a passing station. For such FPLs with two wheels (and four chains coming out), see the posting of Simpelveld:

Opened facing point lock, points no.32, Wijlre-Gulpen, 16.8.2015

l) Locally operated points: with weighted lever = "Central European"

The next picture shows a locally operated set of points. Because the line went from double track to single track at Wijlre-Gulpen, the separation points are of a symmetrical design. When the line to Schin op Geul was also single-tracked, the relative position of the tracks was not changed, but the separation points now led to a stub track. Last, these points were moved behind the crossing, as can be seen in the first of my postings about Dutch interlockings:

Locally operated points, Wijlre-Gulpen, 16.8.2015

The lever is weighted for pressing the blade against the stock rail. Moreover, a manual lever can (probably) be used to add more pressure—untypical for Central Europe:

Locally operated points, Wijlre-Gulpen, 16.8.2015

Locally operated points, Wijlre-Gulpen, 16.8.2015

When a train passes such a set of points, facing point locks are definitely necessary, also at small speeds. However, this specific set of points is secured by a clamp:

Blade clamp on locally operated points, Wijlre-Gulpen, 16.8.2015

Finally, for steam-engine friends, here are a few pictures of ZLSM's SJ 1040, an ex-Swedish engine pulling museum trains between Schin op Geul and Simpelveld:

SJ 1040, Wijlre-Gulpen, 16.8.2015

I love this type of engine with its interior driving rods and Walschaerts gear, as one can see the elegant wheels without any view obstruction. This type's highly mounted ("Gölsdorf style") boiler and the narrow wheel rims underscore the elegance even more:

SJ 1040, Wijlre-Gulpen, 16.8.2015

Between the frame bars, one can see the parts of the Walschaerts gear and, a little bit lower, the slide of the crosshead:

SJ 1040, Wijlre-Gulpen, 16.8.2015

SJ 1040, Wijlre-Gulpen, 16.8.2015

Dutch block instruments and single-line block working

Deutsche Version dieses Postings

After quite some time, here is the next posting about Dutch mechanical interlocking. The topic of this posting is "block instruments," with a focus on single line block working.

e) Station block: Siemens block instruments, "German" version; with "Austrian" bells

The safe communication between posts, both for

• communication between the posts of one station, i.e., between the post T and the signal boxes proper,
• as well as for block working on the line,

is accomplished via Siemens block instruments (I'll explain them a little more below – some more explanations can be found in this posting about Austrian interlocking). As it happens, there are two main strands of Siemens block instruments, which I call "Austrian" and "German." Differences between the types are, among others,

• German instruments have a small eye in the visible part of magnetic anchor, Austrian ones are without that eye;
• German instruments use only red (for "instrument blocks something") and white (non-blocking position), whereas Austrian instruments use also other colours.
• In Germany, special DC instruments were used as route locks, whereas Austrian interlockings used common AC instruments.

In the Netherlands, the German type was used, with eyes, red-and-white only, and DC instruments as route locks. These details can be seen e.g. in the following pictures:

Block instruments, post T, Wijlre-Gulpen, 16.8.2015

Block instruments, post T, Wijlre-Gulpen, 16.8.2015

Block instruments, post I, Simpelveld, 16.8.2015

Block instruments, post I, Simpelveld, 16.8.2015

Besides communicating safely via block instruments, it is also necessary to inform another post about some request – e.g., requesting that an instrument is blocked so that a train is permitted into a track or line section. The safety of this operation would be guaranteed by the mechanical locks and electrical circuits of that block instrument, so the request itself could be transmitted unsafely. Of course, in many instances telephones were used for this type of communication, but for routine interactions, simple bells were widely used. Those bells were of the "Austrian" design, where a lid falls down when the bell is activated from the sender. The purpose of this design is that the information about the request was permanent, so the signalman would be informed even if he happened not to be near the bell when it sounded (e.g., throwing some locally operated points). In many cases, the type of request was also stenciled on the inside of the lid, so that it could be easily seen when the lid was dropped. In Austria, it was customary to close the lid simply by pushing it up with the hand. In the Netherlands, the bells were apparently mounted so high that a short string was attached to a small lever at the lid's end; a short pull on the string would then close it:

Bell, post T, Wijlre-Gulpen, 16.8.2015

f) Block working: Siemens block instruments = "Central European"

Around 1870, Carl Frischen invented the Siemens block instrument for block working. The Dutch railways used these instruments for protecting trains against opposing as well as following trains. The mechanically intricate design uses abut twelve pulses of an alternating current for transmitting a single bit, which makes this method of communication so safe that no overlapping layer of communication is needed – in contrast e.g. to the British block instruments, which predominantly use direct current and are used together with a required system of bell signals to provide the necessary safety against failure. The Siemens block instruments lock the signal levers of all signals into a line section, as long as this section is occupied by a train. A consequence of this design is that a failure of some part of the system makes it impossible to clear the signals, so that in such a case trains must receive orders to pass signals showing a stop indication.

g) Coupling of station block and line block working: Decoupled = "German"

In Austria, some block instruments used for communication between the signal boxes of a single station are also an integral part of the line blocking system. For example, in Austria, the information that a section of a line is occupied is sent at the same time and with the same instrument as the command from the train director to the local signal box for clearing the starting signal (blocking of the "Ba" instrument in earlier types, and of the "A" instrument in later installations). Similarly, the line is signalled as clear with the same instrument that also locks a signal box's home signal after a train has arrived. In contrast to this interlocked way of operation, the actions for station and line blocking were completely separated in (standard) German installations, and this was also the case in the Netherlands. The advantage of this is that a failure in one system (station or line blocking) does not interfere with the operation of the other; the disadvantage is of course that the separate instruments are somewhat more expensive.

The decoupled operations in the Netherlands require two block instruments for each section with line blocking, one on each side:

• One instrument transmit the information "line occupied" to the other side, thereby locking its own signal in the stop position.
• The second instrument on the other side is used to signal back "line clear", which unlocks the signal.

The instruments are marked in the Netherlands as "Blok" and "Voorbijgang", i.e., "block" and "going past". The second instruments was later coupled with a electrical lock that was released by the train through some electrical contact, as is customary with practically all later block systems worldwide. Of course, the reason for this is that signalling back "line clear" was not possible if the train had not reached the end of the line section.

h) Single line block working: permission per train = nearer to "Austrian" practice

On single-track lines, it is not only necessary to protect a train against a following train, but also against opposing trains. Actually, opposing trains need not create a safety risk: For example, on a single line with three sections, two trains might enter the first and last section from opposing sides, as long as they are prevented from concurrently entering the central section. However, such a situation is of course very undesirable.

Essentially, there are two methods of securing against opposing trains:

• One method uses "single permits:" The signal box on the far side sends a signal to the other side that a single train may enter the single line, thereby locking its own signal so that it cannot send an opposing train down the line. In simple cases, the permit is given over telephone ("telephone block working"), but more advanced installations use block instruments for this.
• The other method uses a "direction permit:" At one time, one or the other side is allowed to send trains on the line. No separate action is needed for the next train following in the same direction. Only when the direction of travel has to change, one side must give up its permit to the other side.

Historically, the first method was developed and used first. The largest disadvantage of this method is that a permit "has to be used up:" If a permit has been given to the other side, but then it is decided that another train in the opposite direction should run earlier, that second train must run against signals showing stop. In later times, when train densities on single lines became larger, the second method was introduced, predominantly in Germany. In Austria as well as the Netherlands, the older method continued to be used, even though designs for the second method were developed and installed also there.

The line between Wiijlre-Gulpen and Simpelveld was the last Dutch line using single permits. The operations of this system is explained with a sequence of images on this page at klassiekebeveiliging.com (scroll down to the middle of the page, there are two arrows for clicking through the seven steps). However, I think it is easier to understand the workings of this system if one looks at the electrical connections between the block instruments. I have reverse-engineered a rough diagram of the circuits on both sides of the single line. The diagram uses the following letters:

• B = "Blok" - this is the signal-blocking block instrument at the entry to the line.
• E = "Enkel" = "single" (permit) - the block instrument for permitting one train into the line.
• V = "Voorbijgang" - the instrument for signalling "line clear".

Here is the diagram which shows how the three block instruments on each side of the line interact with each other. Each arrow shows a possible action, where operating the instrument at the back end of an arrow will change the position of the instrument at the arrow's point:

However, I think that is not really easy to understand the block system's working from this diagram. Therefore, I have created a simpler diagram where I left out some connections which—I believe—were added in later times. Thus, the following diagram shows the "pure" circuits needed for single-line blocking. One can see that in this basic form, three instruments are interconnected in a triangle of circuits. The operation is as follows:

• When no train is near the line, the Blok instruments are blocked and lock their respective signals. Thus, no train can enter the line.
• If a train is to be permitted into the section, the Enkel instrument is blocked on the far side, which unblocks the Blok instrument on the near side. This in turn unlocks the signal lever so that the signal can be cleared.
• After the signalman has returned the signal lever, he blocks the Blok instrument, which will now unblock the Voorbijgang instrument on the far side so that it shows red (for "line occupied"). The Enkel instrument remains blocked, so that the far side cannot permit another train into the section.
• When the train leaves the section, the Voorbijgang instrument can be blocked, which will in turn unblock the Enkel instrument at the same signal box. All instruments now have the position they had at the beginning.

The circuits just described will prevent that a following train can enter the line while it is occupied. However, it will not hinder the other side of also blocking its Enkel instrument, thereby allowing an opposing train into the section. But this problem is easy to solve: As long as one Enkel instrument is blocked, it must interrupt the circuits of the other Enkel instrument—then, it is impossible to permit two opposing trains into the section.

However, this solution has a disadvantage: It is still possible to press the button of the other Enkel instrument, which will put the instrument in a position where it is "half locked" (I'll skip the details of why the instrument will react like that). Therefore, the system uses another option: When the Blok instrument is blocked in the second step, the Enkel instrument near it is also blocked (via a mechanical linkage between the two instrument buttons). This is indicated by the dark-red bent line in my first diagram. I have chosen this representation because it mimics the official symbol for mechanically connected buttons, as can be seen in this detail from Simpelveld's original operating manual:

The unblocking of the Enkel instrument of the opposing direction is done by the third step, i.e., by the blocking of the Voorbijgang instrument on the opposite side.

The operating manual from Simpelveld

The 1960's operating manual of Simpelveld's interlocking apparatus can be downloaded from this page at http://www.klassiekebeveiliging.com as a PDF file (klick "BVS" in the website and then "S"). The manual describes all operations necessary for train runs to and from Simpelveld. However, the necessary actions are sorted by post, and hence it is somewhat difficult to get an understanding of which parts of the interlocking frames work together. For the runs on the Wijlre-Gulpen side, I have therefore attempted to assemble them in a single page which shows all the actions on post T and post II (a click on the diagram opens a readable PDF file):

Although ... the information collected there is probably only of interest for severely afflicted signalling fans.

The next posting will show pictures for another topic, namely the linkage used for reversing points.