Canals, & Waterways
The Falkirk Wheel - Section 3 - Technical Information.
TECHNICAL INFORMATION
Selected Facts
The wheel, which has an overall diameter of 35 metres (115 ft), consists of two opposing arms which take the shape of a Celtic-inspired, double-headed axe. 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 degrees 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.
Design of the Falkirk Wheel
Architectural services were supplied by Scotland-based RMJM, from initial designs by Nicoll Russell Studios and engineers Binnie Black and Veatch
How the wheel rotates
The wheel rotates together with the axle, which is supported by 4 metre (13 ft) diameter slewing bearings that are fitted to the ends of the axle and have their outer rings mounted on the plinths.
The bearing at the machine-room end of the axle has an inner ring gear which in this configuration acts as a rotating annulus. This 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. An electric motor drives a hydraulic pump which is connected to the hydraulic motors by means of hoses and drive the wheel at 1/8 revolution per minute.
Construction of the wheel
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 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, and exhibition centre.
How the caissons are kept level
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.
The docking-pit
The docking-pit is a drydock-like port which is isolated from the lower canal basin by means of watertight gates and kept dry by means of water pumps. When the wheel rotates and stops with its arms in the vertical position it is possible for boats to enter and exit the lower caisson when the gates are open without flooding the docking-pit. The space below the caisson is empty.
If it were not for inclusion of the docking-pit the caissons and extremities of the arms of the wheel would be immersed in water at 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, the viscosity of the water causing an increase in the required power and corrosion of the wheel components. Immersing lubricated moving parts of the wheel would also result in pollution of the canal.
How the canal was routed through the wheel
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 aqueduct at the top section of the wheel, the two being joined by the new 150 metre long Rough Castle 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 tunnel also passes below a road and the main Edinburgh to Glasgow railway line.
Costs and prices
The Falkirk Wheel cost £17.5 million, and the restoration project as a whole cost £84.5 million (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.
- << Prev
- Next