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This blog chapter is in celebration of the centenary of the Royal Liver Building WT clock installation. Not to mention the timely publication of Colin Reynolds' fascinating record of its construction. These were the largest electrically driven clock dials in the world when installed in 1911. Colin Reynolds' book covers the story of its construction from within the Gent company. With many unique, original illustrations and photographs from the time. Bringing the entire clock installation to life despite the intervening century.
Colin Reynolds' excellent book detailing the construction and installation is available from Formby-clocks or from Reprint.
Books on Church or Turret clocks - Jeffrey Formby Antiques
The Great George Liver Clock : Reprint [No longer available?]
Gent enjoyed considerable, global publicity from the prestige of providing such a record breaking installation. Particularly for their newsworthy meal for 40 dignitaries around one of the completed dials. This led to WTs, for public dials, being sold right around the world. No doubt the sales of their impulse clocks systems increased as a result. WTs could be added to any impulse clock system. Often without the necessity for the special architectural details always needed by weight driven clocks. Not least finding room for the weight chutes.
This image was taken from an old book on aspects of electrical engineering.
I scanned the illustration into my computer and then lightened it and improved contrast in PhotoFiltre.
The WT was a truly revolutionary public clock movement. Providing a compact, reliable and incredibly accurate performance independent of weather conditions. Moreover it did not need arduous, regular winding or bulky weight shafts to house massive weights. Nor was it subject to the wear and breakdowns to which the far more complex, weight driven clocks were prone. Thanks to its relative simplicity a WT did not require a skilled turret clock maker to maintain it. This made it particularly attractive in undeveloped countries. Even haphazard mains electricity supplies were no real hindrance. Because the impulse clock systems and WT movement usually ran on trickle-charged batteries. Allowing the WT system to cope with power cuts.
Click on any image for an enlargement. Back click to return to the text.
Four, highly exposed, 25' dials are mounted 220' above the ground on two towers of the Royal Liver Friendly Society building in Liverpool. Three dials are mounted on one tower facing the sea and up and down the Mersey. With a fourth dial on another tower facing the city. The hands on each dial are driven by a single, large, Gents' Waiting Train movement. (tower image borrowed from Wikipedia) A Liver Bird surmounts each tower like a perfectly proportioned clock finial.
Royal Liver Building - Wikipedia, the free encyclopedia
These large WT movements were designed and hand built specifically to drive the hands of these enormous dials. Bigger, even, than the dials of the Westminster Clock which strikes the hours on Big Ben. The loads were made worse, on the Liverpool clock dials, by their exposure to Atlantic gales. Loads on exposed clock hands increase as the cube of wind velocity.
No practical mechanical clock could ever cope with such a task. Many unique problems were overcome in the manufacture and supply of the complete clock installation including the dials.
Accuracy, reliability and long life were essential. The WT is renowned for its accuracy under the most appalling weather conditions. Being also, and quite uniquely for a turret clock, as accurate as the master clock which controls it. With enormous reserves of torque to cope with icing and fierce, storm force winds on the giant hands.
Here is a view of just one of the four WT movements and the dial motionwork beyond. They are each mounted in separate, glazed, iron framed cases. These keep the mechanisms clean and avoids accidents to the unwary. The cases also provides unprecedented visibility of the clockwork mechanisms for visitors.
A view behind one of the 25'6" diameter, iron and opal glass, skeleton dials. The hour pipe can be seen supported on a massive cantilevered bracket. Due to the enormous loads, on the slowly rotating components, Gent's engineers came up with a unique system of rollers. The hour pipe itself is supported and restrained against lifting by three outboard rollers. The minute arbor is itself supported on rollers attached to the hour pipe. The huge bracket, cantilevered off the building's masonry, supports the roller bearings for the clock hands close behind the dial.
The darker roller assembly can be seen at the centre of the huge dial in the image above. Plain bearings would have had far too much friction and potential corrosion problems over time. Particularly in a maritime environment. While the rollers have provided reliable, low fiction bearings for 100 years.
The many tie rods and turn-buckles can be seen holding the cast framework of the huge dials onto the inner masonry of the tower. Lighting is provided so that the dials can be seen and read from a great distance at night. This stand-off dial design allows the tower to be closed behind the dial. Otherwise a huge hole would have been necessary right through each face of the tower to allow the dials to be evenly lit at night.
A general view of one of the WT movements. The large electromagnets (protectively wrapped in red) provide the driving impulse to the massive pendulum. The electromagnets are switched on via a Hipp toggle and electrical contacts. Smaller electromagnets lock the electrical contacts closed to provide an extended impulse. At the end of the swing a pin on the crutch unlocks the contacts again.
The main frame is diagonally braced against twisting. Resisting the reaction forces of the giant wormwheel as it drives the exposed hands. Frame bracing, in depth, is provided for the massive pendulum. A brass, hand setting dial is provided on the free end of the wormwheel shaft. The, long, bright steel, horizontal shaft near the bottom of the movement frame is the worm arbor (or shaft).
A close-up of the Hipp toggle and block. Instead of a single Hipp V-block a multi-toothed rack is provided here. Perhaps as extra insurance against slipping or missed impulses. It may also allow a smaller pendulum arc for emergencies in very bad weather.
The freely pivoted, Hipp toggle (hanging from its bracket at top left) looks no different from that on my own relatively tiny WT. Almost hidden below the Hipp block and contacts are the contact locking electromagnets. Also wrapped in red, protective material. Just like the larger drive electromagnets. The Hipp toggle and its block form a simple, but totally reliable, electro-mechanical switch. Together, these apparently simple components constantly monitor the pendulum arc. Only giving a drive boost (via the large drive electromagnets) if the pendulum arc falls below the set limit.
Normally the toggle rattles freely back and forth across its block. Only when the pendulum swing drops low enough will the toggle catch in the block on the return swing. The toggle then depresses the block and firmly closes the attached electrical contacts. Electricity flows through the large drive electromagnets. Giving the pendulum a really strong push.
If the clock hands are struggling to overcome heavy winds the pendulum swing will drop more quickly due to the extra energy demanded. The toggle will close the contacts as often as required to maintain the pendulum's minimum arc. As often as every other swing if necessary.
So many extra drive impulses provide a massive increase in power and torque to drive the hands in poor weather conditions. When the storm has passed the toggle senses the lighter load and the impulses become very much less frequent. It was the combination of Hipp toggle and the (completely automatic) variable frequency of drive impulsing which made the WT so utterly reliable. Many weight driven clocks would run slow or even stop in very bad weather.
To the right of the toggle is the (black) pendulum impulse hook cast onto the crutch. The impulse from a roller takes place on top rather than underneath the hook. (the latter usually occurs on the smaller WTs) This detail is rather difficult to see because of the enclosing casting.
The WT movement with the large, 30-tooth ratchet wheel in the foreground. The ratchet wheel converts the oscillating motion of the pendulum into rotational movement. On smaller WTs the ratchet wheel has only half as many teeth as the Liver clock movements. Presumably the engineers decided that a larger wheel would need huge teeth if limited to only 15 teeth. Which could not possibly be gathered securely by the pawl. Not unless the ratchet wheel and its pawl were placed very low on the pendulum rod. (or on a much longer crutch)
Having two, D-shaped, lifting pins on a much larger ratchet wheel, with finer teeth, satisfied several vital geometrical requirements. The finite swing of the pendulum and the distance down from the pivot bearings provides a strictly limited stroke. The Liver movement ratchet wheel makes one complete rotation in slightly less than one minute. The teeth are large enough to be physically reliable. Without requiring an excessive swing of the pendulum to gather its teeth. Most of the critical components on the WT are made of gun metal. A tough, hard, wear and salt resistant bronze. Brass would corrode over time.
Beyond the ratchet wheel, on the same shaft, is the worm. The worm and its matching wormwheel must provide a 60:1 reduction in rotational speed and a similar increase in torque. The bottom half of the wormwheel is seen edge-on near centre top of the image above. Presumably it uses a double start worm to achieve a 60:1 reduction from the worm shaft. The wormwheel must rotate once per hour to provide the minute hand drive without extra complication in the motionwork gear ratios.
Note the heavy thrust bearings to resist the severe end-loads on the worm. The worm not only drives its wormwheel against the loads on the giant clock hands outside the building. It also locks the hands safely against any unwanted movement. Perhaps due to ice imbalances, flocks of birds on the clock hands or wind loading. Backlash would be very undesirable because it would show timekeeping inaccuracies on the minute hands of each separate dial.
Interestingly, it was the inability to limit variations between dials which excluded the use of four separate weight driven, turret clock movements. Gents were able to offer a guarantee that all the dials would show the same time thanks to their master clock control. The contract to build the Liver Clock installation stipulated 2 seconds per week accuracy. Few turret clocks can manage this.
Detail of the pendulum support bearings. A fine ratchet wheel is provided on the end of the bearing support shaft. This provides slow rotation of the bearings to avoid flat spots on the bearing races. The loads on the pendulum bearings are always predominantly downwards.
On smaller WTs a hand wheel is provided, just here, to allow random rotation of the ball races. Presumably the friction would be too great in a WT of this massive scale to turn a knob by hand. The Gent engineers have cleverly provide auto-rotation. So nobody needs to worry about forgetting to turn the knob at intervals.
Pendulum top and bearing assembly from the other side. The cylindrical, black-painted counterweight of the gathering pawl and the pawl bearing can be seen centre right. The black bar hanging almost against the main frame is the pendulum crutch. Oiler caps can be seen on the pendulum bearings. The fine ratchet wheel (bearing rotator) is well seen here. The bearing shaft, ratchet pawl is rocked between adjustable stops by the swinging pendulum.
Here I have labelled the major components of a Liver WT movement. (Just in case you have become lost in my wordy descriptions) Click the image to enlarge it for greater detail. Back click to return to the text.
BTW: I have used both ratchet and gathering wheel interchangeably for the same component.
The "WT magnet" labelled on the left is a small "relay" electromagnet. (Wrapped in black) Connected in series with the master clock it releases the (momentarily locked) WT drive to the hands once every half minute. The rest of the time the hands advance perfectly normally.
This incredibly simple mechanism, is used in a design of pure electro-mechanical genius. It forces the giant hands of the dial to follow the master clock exactly. Maintaining an accuracy to within a couple of seconds per week. The pendulum becomes a powerful and totally reliable electric motor. The WT mechanism harnesses this enormous power to keep perfect time.
The actual Waiting Train mechanism in close-up. The 30 tooth ratchet wheel is pulled around by the swinging pendulum via the gathering pawl. (the black horizontal lever in the centre of the image) Twice every revolution of the ratchet wheel one of two D-shaped pins lifts the L-shaped lever. This lever is counterbalanced and pivoted in the relay electromagnet pivot plates on the left. A backstop (lever) resting in the teeth of the ratchet wheel stops the gathering wheel from turning backwards.
Driven by the gathering pawl, the L-shaped lever lifts until it has been locked by a step in the relay electromagnet's armature. Now the gathering pawl can no longer reach the teeth of the wheel. A forward projecting pin, on the pawl, slides freely back and forth on top of the L-shaped lever. (without the pawl able to gather more teeth on the ratchet wheel)
Moments later the short electrical impulse comes through from the master clock. The armature is instantly attracted to the relay electromagnet core. Releasing the L-shaped lever. The L-shaped lever drops. The gathering pawl can now drop back into the teeth of the ratchet wheel and immediately starts driving the hands normally. The short pause in drive to the hands goes completely unnoticed by anybody viewing the clock dials. While the drive is interrupted the worm and wheel keep the clock hands safely locked.
The Gents' Waiting Train mechanism now seems almost blindingly obvious. Until its invention there was no way to synchronise a large and powerful public clock with a precision master clock. The greatest acts of mechanical genius often seem incredibly simple with our perfect hindsight. Yet, before its invention the problem was seemingly insurmountable.
The brilliant Gent engineer, A.E.J. Ball, was the genius who provided the solution. One which totally revolutionised public timekeeping. Clock dials, driven by WT movements, could now be easily fitted into slender war memorials and industrial chimneys alike. There was no longer any need to provide easy access to clock winders and minders.
Only the arrival of the Warren synchronous electric motor finally beat the WT for compactness. The synchronous motor driven, public clock dial was several decades away when the Liver building clock system was installed in 1911.
The coupling between the WT and its dial motionwork (in the case on the left) takes the form of a gimbal. This allows for slight variations in alignment between the two mechanisms without binding. The inner set of rollers, for the hour pipe, are seen on the extreme left inside the glass case. The inner, minute hand shaft rollers are on the right of the large gear wheel in the centre of the case.
The motionwork provides the usual 12:1 ratio between the minute and hour hands. Normally the motionwork is fitted just behind the dial. In this case the loads on the giant hands are so high that an inboard motionwork is provided for each dial. The motionwork supports the inner end of the hour pipe on solid masonry. The cantilever bracket, behind the dial, supports the outer end. The great length between the bearings provides extra stability and distributes the loads more evenly. A closer view of the dial motionwork. The 12:1 reduction is provided by two reduction pairs of gears. Only two gear wheels and two pinions are required. Albeit unusually large ones in this case. Only the sheer scale of the wheels and supporting castings gives an impression of the huge size of the hands and dials involved.
The minute hand counterweight rotates once per hour on the arm between the cases housing the WT movement and its motionwork.
Another chance to admire the genius of this unique tower clock movement. Its apparent complexity merely disguises precisely the same functions as those of the smallest WTs. The top of the massive pendulum bob can be seen at the bottom of the picture. The crutch is provided with two pins which straddle the pendulum rod. This is standard clock practice and ensures the crutch closely follows the pendulum. Providing solid drive and accurate location of timed events relative to each other.
An alternative view showing details not easily seen from other viewpoints. The contact device in the foreground, on top of the frame, is related to the extended drive impulse. The long, hooked arm is released by a pin on the crutch at the end of the extended, pendulum, drive impulse.
I am most grateful to Colin Reynolds, author and ex-managing director of Gents for sharing this information. He was also able to confirm the presence of two D-shaped, lifting pins and even provided a diagram of the electromagnetic locking of the extended impulse mechanism. Original images of the WT can be found in his book shown at the top of this page.
Click on any image for an enlargement. Back click to return to the text.
Updated with much enlarged images March 2012.
YouTube video link added 21.72014 showing the WTs in action:
Sadly the resolution is rather poor.
And another YT video. The title excites interest.
The video quality is absolutely dreadful!
