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Designing a water-balanced railway

Product analysis

The market
The water-balanced railway is used by visitors to the Centre for Alternative Technology. It is particularly helpful for elderly people, those with disabilities and families with young children, who struggled to walk up the steep path to the Centre in the past.

Technical specification
The water-balanced railway has two carriages, each of which can transport 20 adults at a time.

Vertical height of lift: 30m
Track length: 53m
Angle of inclination: 55°
Speed of carriages: 0.7m per second
Time taken to travel from top to bottom of the cliff: about 75 seconds
Time taken to fill the tank with 1600 litres of water from the reservoir: 50 seconds
Number of runs per hour: 10 to 12 during peak hours

Product function
The railway consists of two carriages fixed together by a cable that is wrapped around a large drum at the top of the lift. The carriages run on steel tracks attached to a concrete base. When one carriage is at the top of the cliff, the other is at the bottom.

Underneath each carriage there is a water tank that can hold 1600 litres of water. The top carriage's tank is filled with rainwater taken from a reservoir behind the station, so that it is slightly heavier than the carriage at the bottom. This difference in weight moves the top carriage and its occupants down the hill, while the lower lift (including its passengers) travels to the top.

So that it functions efficiently and safely, the railway is controlled by a computer. The computer compares the weight of the two carriages and calculates how much water needs to be added to the tank under the top carriage to make it heavier than the bottom one (if there are a lot more passengers going down than up, only a little water is needed). A valve opens to allow this measured amount of water into the tank under the upper carriage.

When the tank is full enough, the valve is closed, the railway operator releases the braking system, and the top carriage moves down. The carriage's speed is controlled by a hydraulic pump attached to the rotating drum. If the drum is turning too fast, the pump slows it down. The braking system also stores energy, which is used to run the control systems and help pump 10% of the water back up the hill for reuse.

The railway uses 100kw of electricity, which is mostly generated from wind, water and solar power at CAT. A small amount of electricity is created by the water being passed through a turbine on its way to the railway.

Materials
Production
Because the water-balanced railway is the only one of its kind, the materials and manufacturing methods were chosen for their simplicity and reliability.
Safety
The railway is built so that it is safe to use in unusual circumstances, for example if more than the recommended number of people are travelling, or if a carriage has to brake hard in an emergency. The unusually large gauge of the track (about 1.6 metres) and the low centre of gravity of the carriages helps to stabilise the railway and increase passenger comfort and safety.

The speed of the moving carriages is carefully regulated to ensure that the ride can be stopped easily at any time. There are a number of braking systems used:
Cams on the undercarriage clamp onto a central wooden rail and prevent the carriage from moving. These are completely mechanical and are operated by a centrifugal governor.

Barriers and fencing at the stations prevent too many people entering and leaving the railway. An emergency escape route is built into the lift track, in case passengers need to be evacuated. The carriages also have windows, which could be used as an escape route in an emergency.

To ensure the railway operates safely and efficiently, the track bed and cables are inspected daily and the cable rollers are lubricated. The railway is also inspected twice a year by the insurance company and once a year by the railway inspectorate. It is given a complete overhaul annually and the cables are replaced every 18 months.

Ergonomics
When designing the railway carriages, the designers needed to consider:
Aesthetics
The water-balanced railway's appearance is largely determined by its function. However, its use of natural materials and simple construction mean that it is in keeping with its surroundings.

Ten cliff railway facts

The computer-controlled system



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