Falkirk Wheel

From Wikipedia, the free encyclopedia

The Falkirk Wheel

The Falkirk Wheel, named after the nearby town of Falkirk in central Scotland, is a rotating boat lift connecting the Forth and Clyde Canal with the Union Canal, which at this point differ by 24 metres, roughly equivalent to the height of an eight storey building. The structure is located in the village of Tamfourhill. It was designed by the architectural practice RMJM.

On 24 May 2002, Queen Elizabeth II opened the Falkirk Wheel as part of her Golden Jubilee celebrations. The opening had been delayed by a month due to flooding caused by vandals who forced open the Wheel's gates.^[1]

1 Design of the Falkirk Wheel
2 How the wheel rotates
3 Construction of the wheel
4 How the caissons are kept level
5 The dry well
6 How the canal was routed through the wheel
7 Costs and prices
8 Future rotating boat-lifts
9 Photographs
10 See also
11 References
12 Further reading
13 External links

The wheel, which has an overall diameter of 35 metres, consists of two opposing arms which extend 15 metres beyond the central axle, and which take the shape of a Celtic-inspired, double-headed axe. Two sets of these axe-shaped arms are attached about 25 metres apart to a 3.5 metre diameter axle. Two diametrically opposed water-filled caissons, each with a capacity of 80,000 gallons (302 tons), are fitted between the ends of the arms.

These caissons always weigh the same whether or not they are carrying their combined capacity of 600 tonnes of floating canal barges as, according to Archimedes' principle, floating objects displace their own weight in water, so when the boat enters, the amount of water leaving the caisson weighs exactly the same as the boat. This keeps the wheel balanced and so, despite its enormous mass, it rotates through 180° in less than four minutes while using very little power. It takes just 22.5 kilowatts (kW) to power the electric motors, which consume just 1.5 kilowatt-hours (kWh) of energy in four minutes, roughly the same as boiling eight kettles of water.

The wheel is the only rotating boat lift of its kind in the world, and is regarded as an engineering landmark for Scotland. The United Kingdom has one other boat lift: the Anderton Boat Lift in Cheshire. The Falkirk Wheel is an improvement on the Anderton Boat Lift and makes use of the same original principle: two balanced tanks, one going up and the other going down.

The wheel rotates together with the axle, which is supported by four-metre-diameter slewing bearings that are fitted to the ends of the axle and have their outer rings mounted on the plinths, which in turn are constructed on top of piled foundations.

The slewing bearing at the machine-room end of the axle has an inner ring gear which in this configuration acts as a rotating annulus. The rotating annulus is driven by ten hydraulic motors which are assembled on a stationary bearing and motor assembly known as the planet carrier which in turn is also mounted onto a plinth similar to the one at the other end of the axle. The driveshafts of the motors have pinion gears which act as stationary planetary gears in this train of gears and engage the rotating annulus ring gear. Electric motors drive a hydraulic pump which is connected to the hydraulic motor by means of hoses and drive the wheel at 1/8 revolution per minute.

The wheel was constructed by Butterley Engineering at Ripley in Derbyshire under Millennium Plans to reconnect the Forth and Clyde Canal with the Union Canal, mainly for recreational use. The two canals were previously connected by a series of 11 locks, but by the 1930s these had fallen into disuse, were filled in and the land built upon.

The Millennium Commission decided to regenerate the canals of central Scotland to connect Glasgow with Edinburgh once more. Designs were submitted for a lock to link the canals, with the Falkirk Wheel design winning. As with many Millennium Commission projects the site includes a visitors' centre containing a shop, café and exhibition centre.

The Falkirk Wheel in action. The wedge-shaped building on the right is the visitors' centre. Click on image to view the Docking Pit at the bottom canal.

The caissons need to rotate at the same speed as the wheel but in the opposite direction to keep them level and to ensure that the load of boats and water does not drop out when the wheel turns.

Each end of each caisson is supported on small wheels which run on the inside face of the eight-metre-diameter holes at the ends of the arms, allowing the caissons to rotate. The rotation is controlled by means of a train of gears: an alternating pattern of three eight-metre-diameter ring gears and two smaller jockey gears, all with external teeth. The central large gear acts as a stationary sun gear. It is fitted loosely over the axle at its machine-room end and fixed to a plinth to prevent it from rotating. The two small jockey gears are fixed to each of the arms of the wheel at its machine-room end and act as planet gears. When the motors rotate the wheel, the arms swing and the planet gears engage the sun gear, which results in the planet gears rotating at a higher speed than the wheel but in the same direction. The planet gears engage the large ring gears at the end of the caissons, causing them to rotate at the same speed as the wheel but in the opposite direction. This keeps the caissons stable and perfectly level.

For a demonstration of the principle, click here.

The dry well is a drydock-like port which is isolated from the lower canal basin and kept dry by means of water pumps. If it were not for inclusion of the docking-pit the caissons and extremities of the arms of the wheel would be immersed in the lower canal basin each time the wheel rotates. This would result in a number of undesirable situations developing, such as providing buoyancy to the bottom caisson and the viscosity of the water causing an increase in the required power.

The route chosen to take the Union Canal to the site of the wheel involved building a completely new section of canal, leading from the original terminus at Port Maxwell to link up with a new basin to the south of the wheel. The water level in this basin is the same as the top section of the wheel, the two being joined by a 150 metre long tunnel with elliptical cross section. There are two locks to drop the canal level from that of the Union Canal to this basin. The tunnel was required because the canal had to pass underneath the route of the Antonine Wall without disturbing its archeological remains. Just at this point the canal also passes below a road and the main Edinburgh to Glasgow railway line.

The Falkirk Wheel cost £17.5 million, and the restoration project as a whole cost £84.5 million^[2] (of which £32 million came from National Lottery funds).

The Falkirk Wheel Visitor Centre offers scheduled one-hour, round trip boat tours, called "The Falkirk Wheel Experience," that include passage on the wheel. The tours start below the wheel in the Forth & Clyde Canal, ascend via the wheel to the Union Canal, visit nearby areas on the Union Canal, and then return. As of 2007, the boat tour costs £8 for adults, £4.25 for children aged 3-15 (free for children under 3), OAP concession £6.50, student/UB40 concession £6.50, and family price of £21.50 (2 adults and 2 children) with a discount of 10% for a group of 20 or more.^[3]^[4]

A similar design of boat-lift has been suggested for a proposed new canal which would run along Marston Vale in Bedfordshire, as part of a large-scale project creating an area of leisure and tourism facilities linked to the future expansion of Bedford and Milton Keynes. The canal would link the Grand Union Canal at Milton Keynes with the River Great Ouse at Bedford.^[5]