Double Wire Frames in Victoria

Andrew Waugh

(This article was originally published in Somersault, the journal of the Signalling Record Society Victoria (inc).)

Conventional mechanical signalling in Victoria, derived from British practice, uses rodding to operate points and facing point locks. The friction involved in operating this rodding means that points have to be within 350 yards of the signalbox. In countries with signalling derived from German practice points (and signals) were operated by two wires. One wire pulled the points or signal reverse and the other pulled it normal. Such double wire operation could operate points and signals at a much greater distance as there was much less friction and lost movement in the system. In the early 1920s, the Westinghouse Brake and Saxby Signal Company developed a version of the German double wire system suitable for British conditions. In practice, of course, the system was largely sold in the colonies. In Australia, double wire equipment was manufactured by the Australian subsiduary, McKenzie and Holland.

History

Double wire interlocking was introduced into Victoria in November 1926 when a 20 lever frame (22 including conventional gate wheel and gate stop lever) was provided to work the new crossing loop at Glen Iris. Since all of the points and signals at Glen Iris were well within the operating distance of conventional mechanical equipment, this installation was, presumably, installed as a trial. A second frame (of 15 levers) was provided at Pakenham in October 1929 - this will be referred to later.

The third frame was installed at Eaglehawk in June 1930. This frame was larger (30 levers, later extended to 35 levers) and the layout significantly more complex. Again, however, the layout could easily have been worked from a conventional frame, so the equipment was clearly still on trial.

The front of the frame at Eaglehawk. The levers stood backwards in the frame about 45 degrees when normal and were reversed by operating them through 180 degrees. Operation of a double wire lever was somewhat awkward for the signaller. After lifting the catch, he or she pulled the lever to around half stroke. The grip on the lever was then reversed and the lever pushed to the reverse position.

The rear of the Eaglehawk frame. The interlocking was of the conventional tappet type and was mounted in near vertical trays on the back of the frame. The horizontal boxes at floor level are standard lever locks, in this case locking the plunger levers.

Unlike Darling and Eaglehawk, Pakenham was the forerunner of a number of other installations. Pakenham was a minimal installation provided to work a long crossing loop - 841 yards between facing points. Full signalling was not provided; instead a single home was provided in each direction and switch stands were provided to indicate the lay of the main line points.

Extended crossing loops were provided at most of the other staff stations between Dandenong and Warragul between 1930 and 1932 on an even simpler principle. In these installations the loop was extended at one end only and a single double wire lever was provided to operate the remote points and associated lockbar.

It was not until 1934 that additional double wire frames were installed. In that year the line between Bannockburn and Warrenheip was singled and the four intermediate crossing loops were equipped with 15 lever double wire frames. These followed Pakenham with a single home in each direction and switch stands on the main line points. The major difference was that the homes were placed close to the points and distant signals were provided.

The frame at Lal Lal is shown below in May 1988. This was one of the frames provided in 1934 when the line between Bannockburn and Warrenheip was singled. Each lever in a double wire frame is a self contained unit and spaces are consequently much more apparent in these frames than in conventional frames. The frame is close to original. Levers 12 and 13 are subsequent additions (working light signals), and distant signals 1 and 15 had been converted from double wire to motor operation.

The final sequence of double wire installations dates from 1938/9 when double wire frames replaced the original single double wire levers at the staff stations between Dandenong and Warragul. These frames were generally of 10 levers and worked the signals as well as the remote points. The photo shows the last of these frames, at Longwarry, in January 1987, although it had been extensively modified by this time.

The double wire frame at Longwarry was installed in a lean-to shelter on the platform. The route is set up for an Up train to Melbourne.

The last double wire frame was not installed until November 1955 at Mount Waverley. This was provided as a temporary measure pending partial duplication and it was probably constructed out of second hand parts.

Mention should also be made of isolated double wire levers installed on conventional frames; these existed at Narre Warren (1930), Moe (1931), Cressy (1937) and Redcliffs (1938). These levers worked points that were too far away from the conventional frame to be rod worked. The frame at Redcliffs remains intact in the tourist office come gift shop that took over the station building.

Only one double wire frame remains in service today, the 15 lever frame at Meredith between Geelong and Ballarat.

The Double Wire Frame

Each lever of a double wire frame was a self contained unit and was separately bolted to two angle irons which ran the length of the frame. The angle irons were supported by standards located every 5 levers. The standards also supported the locking trays. Each locking tray had 5 channels and, in theory, more than one tray could be fixed, but none of the Victorian frames were complex enough to require this.

The photo at left is a side on view of the levers at Bunyip in February 1988. By this date the frame had been reduced to three working levers which controlled the mechanical signals at the Down end of the yard.

The mechanism for operating the tappets can be seen in the photo of the Bunyip frame and was exceedingly clever. The locking was operated by the catch handle and was transferred between the catch and the tappet by a boomerang shaped crank. When the lever was normal the pin connection between the catch handle extension and the boomerang crank was slightly below the lever pivot. Lifting the catch moved the tappet, via the boomerang crank, half its travel. With the catch up the pin connecting the catch rod extension and the boomerang crank was aligned with the lever pivot and so the crank (and tappet) did not move as the lever was reversed. When the catch was dropped to hold the lever reversed, the catch rod extension pushed the pin connection to the boomerang crank away from the lever pivot, however, because the lever was now reverse 'away' meant that the boomerang crank moved in the same direction as the first movement, giving the second motion to the tappet.

Detail of the frame at Lal Lal in 1998 showing the broken wire detection and rear of the Annett lock. Note that the Annett lock was installed in 1988 - after the earlier photo was taken!

The detail photo above shows the detail on the non locking side of a double wire pulley. The "E" shaped casting on the side of the lever is the broken wire detector. This is only in operation on point (and lockbar?) levers. If a wire breaks during a lever movement the broken wire detector will rotate and catch in the teeth seen on the drum. This locks the lever and prevent the completion of the lever movement and the interlocking will consequently prevent signals being cleared over points that may have been disconnected. The "E" shaped casting terminates the two wires. If one wire breaks, the casting rotates to engage with the teeth on the side of the lever casting and prevents the lever from moving any distance. The broken wire detectors on signal levers are secured by a setscrew in the cover. In the foreground of the photo an Annett lock can be seen. On a double wire frame, Annett locks took the place of a lever and directly operated the tappet. Annett locks were surprisingly common on double wire frames; examples can be seen on photos of the frames at Eaglehawk and Longwarry.

Signals at a double wire installation could either be operated by double or single wire. With single wire operation the signal was operated conventionally with a balance arm and weight on the signal to haul the signal wire back through the wire run when the lever was restored to normal. Double wire operation of a signal was significantly more expensive than single wire operation and so was only resorted to when the signal was too far from the frame to operate by single wire. In fact, double wire operation of signals was relatively uncommon in later years as signals a long way from the frame were often fitted with motors.

The left hand end of the Longwarry frame shows three single wire levers (1, 2, and 3), and a double wire lever (5).

At Longwarry, for example, only three levers were actually double wire levers - numbers 5, 7, and 10 - and only one of these (lever 5) worked a signal. Lever 10 had worked the Down distant by double wire, but this had been converted to motor operation. A double wire lever has a full circular drum. Single wire levers have a half drum of much smaller diameter. The drum on a single wire lever is adjustable to allow the wire travel to be varied. The adjustment mechanism can be clearly seen on all three single wire levers shown in the photo of Longwarry. The front end of the drum has a slotted extension which is bolted to the lever. By loosening the bolt, the front top end of the drum can be moved closer to or further from the lever pivot. This alters the average radius of the drum, and hence the amount of signal wire wound onto the drum each time the lever is reversed.

The Wire Lead

Solid steel wire is used for double wire operation as the normal signal cable would stretch too much. No 8 gauge wire is normally used, but No 6 gauge wire has been used for point operation. Special 3/16 inch chain is used around all wheels in the wire lead and a connection between a wire and a chain is shown below. The wire lead uses special 3 inch pulleys to reduce friction. Pulleys are normally situated 15 yards apart, but may be closer where required. The wheels in the wire lead are provided with roller bearings, again to reduce the friction. Turnbuckle adjusting screws are provided in each wire lead near the operated unit to allow for small adjustments in wire length.

Joint between the solid steel wire and the chain to work around pulleys.

The wire compensator

Unlike conventional signal wire, the wires in a double wire system are always under tension. This tension is adjusted automatically by compensators situated between the signalbox and operating mechanism. Two slightly different designs of compensator were used, but all remaining in recent years were of the type shown below. The compensator is a simple mechanism - it consists mainly of two weighted levers each acting on one wire. The compensator shown was located at Longwarry and compensates two double wire units. Some idea of the tension in the system can be gained by the size of the cast iron weights - this is even more impressive when it is realised that the lever arm for the weights is about four times that of the moveable pulleys.

The double wire compensators at Longwarry. The compensators ensured that the tension in the wires remained constant. One compensator was provided for each wire, hence two compensators were provided for each double wire lever - one for the normal wire and the second for the reverse wire.

There is one complication to the compensator as it is necessary to compensate both wires separately. If one wire jammed (or was prevented from moving by a detector slide), the Signaller may still be capable of completing the lever stroke because the wire would simply raise the compensator weight. To prevent this, it is necessary to lock the compensator when the lever is being moved. The mechanism for doing this is shown below. Normally, both compensators will move together and when this happens the clutch mechanism shown will slide up and down the vertical bar. When the Signaller operates a lever, the tightening of one wire and the slackening of the other causes weighted levers to become locked in the position they then occupied by means of the grip blocks which lock tightly on the vertical square rod. On completion of the lever movement, the balancing of the tensions of both wires releases the lock and permits free movement of the weighted levers.

Detail of the compensator locking device. This locked the two compensators in the wire lead (one each in the normal and return wires) when the lever in the frame was operated.

The signal mechanism

The signal mechanism was complicated by the necessity to prevent the signal from clearing if the "return" wire broke. If this occurred the tension in the "pulling" wire could clear the signal. To prevent this the signal mechanism is separated into three major components: pulley wheel A, cam plate B, and operating crank K. The operating wires drive pulley wheel A, and cam plate B drives the operating crank (and thence the signal arm). In normal working, clutch D ensures that pulley wheel A and cam plate B rotate together. As pulley wheel A is rotated, roller G on clutch D engages in a notch in projection E on the cam plate, and so the cam plate is rotated. Clutch D is kept securely in the notch by the tension in the �return� wire; if this breaks the clutch disengages and the weight on the cam plate brings the arm back to danger. Note that no equivalent protection was given to the point mechanism, although a break in either wire would cause points to move. It appears that reliance was placed in the point detector to hold the points if necessary during the passage of a train in the facing direction (note that plunger would only hold the points if it was worked by a separate lever).

The front and back of the signal mechanism on the Down Home (Post 2) at Lal Lal. The cam slot in the cam plate can be clearly seen in the photo on the right. Idle travel is provided in both the normal and reverse positions so that crank K travels through a fixed angle with full travel of the mechanism.

The point mechanism

The point mechanism commonly used in Victoria is known as the "Type H" and was patented by F.W. Harvey around 1935. This mechanism was broadly similar to the original McKenzie and Holland mechanism. Harvey was described as the "Assistant Engineer, Signal and Telegraph Division, Victorian Government Railways". Using the Type H mechanism it was possible to operate the points up to 850 yards from the signalbox. The diagram below shows the details of the mechanism.

The operating wire is lead around the upper channel of the motion wheel B (the lower channel is used to drive the plunger motion wheel if both the plunger and points are worked by one lever, as at Longwarry). Fixed to the motion wheel are two rollers, C, which work in a cam slot D in an arm pivoted on pin F. To reverse the points the motion wheel turns anti-clockwise. The rollers move along the cam slot until they strike the end at the top right after the motion wheel has turned approximately 45 degrees. The motion wheel then pushes the arm around, and the last 45 degrees of movement simply moves the rollers back to the end of the cam slot. The free movement before and after moving the points allows the plunger to unlock and lock the points when both are worked by one lever. The crank arm E is also pivotted on pin F and is connected to the operating arm by sheer pin H. If the points are trailed, sheer pin H will break before the rest of the mechanism is damaged. Before the Type H there was the "McK&H" type which had a broadly similar operation.

The arrangement of double wire equipment at points are illustrated by the points at Eaglehawk and Longwarry. At Eaglehawk seperate levers were used to operate the facing point lock and points while at Longwarry one lever was used to operated both the facing point lock and the points.

A double wire set of points at Eaglewawk. The point operating wires come in from the top of the picture to drive the point mechanism (the square box). The wires operating the facing point lock come in from the bottom left and run around the motion wheel at the bottom of the picture. A pin in this wheel drives the rod connected to the plunger of the facing point lock (centre). The bell crank to the lower left of the plunger drives the rod to the point detector which is off the picture to the right.

At Longwarry, the layout is a mirror image to that at Eaglehawk. The point mechanism is at the top right, the facing point lock and bell crank in the middle, and the motion wheel for the plunger at the bottom left. The operating wires for the points enter the picture at the top right and directly work the point mechanism. Note the two adjusting screws in the operating wires to alter their length. The facing point lock motion wheel is worked by a secondary chain. This is driven from the point mechanism. The second pin in the facing point lock motion wheel (which can be seen in all of the photos of point layouts) drove the lockbar, however by the time I began photographing signalling equipment all of the lockbars had been replaced by lever locks worked from track circuits. The point rodding on the far side of the points drives a second stretcher bar half way along the point blades as these are a set of "high speed" points.

A view of Points 14/Plunger 15 at Eaglehawk showing the point mechanism, plunger, detectors, and plunger pulley.

(Copyright Andrew Waugh, 2004)