Abt Rack Railway and Technical Information
Most railways use simple adhesion of rail wheels on the rails to move a train along a track. In the case of mountain railways the gradient of the track means that simple adhesion does not work.
The solution is to mount a toothed rack between the running rails and provide a cog (pinion) on the locomotive. In this way the locomotive can crawl up steep gradients.
There are seven different types of rack and pinion systems for railways but by far the most popular worldwide is the Abt system as used at Snowdon. The system was invented by Dr. Roman Abt, a Swiss railway engineer in 1885. The system is cheaper to manufacture and install than other systems as it uses less steel.
The Rack at Snowdon utilises a pair of toothed racks offset by one tooth and two driven axles on each locomotive, each axle with a pair of pinions. This ensures that there are two teeth fully engaged at all times to increase safety. The braking system also uses the rack to slow and stop the trains with the brakes fitted to the pinion axles on the locomotives and carriages.
Snowdon is unique in rack railways by having a derailment protection device fitted either side of the rack which engages with fittings under each carriage and locomotive which ensures that the vehicle cannot lift out of the rack.
The Snowdon track was designed in Switzerland in 1895 meaning that the track and rolling stock are metric. The track gauge is 800mm or 2ft 71/2 inches between the rails. The total track length is 7.53 kilometers with a steepest gradient of 1 in 5.5 (or 1 meter rise every 5.5m travelled).
Snowdon Mountain Railway is the only public rack and pinion railway in the United Kingdom.
The Rack and Pinion System
The rack and pinion system used is that patented by the Swiss engineer Dr Roman Abt. The railway uses double rack rails, fastened to steel sleepers between the running rails. Each locomotive is equipped with toothed pinions (cogwheels), which engage the rack and provide all the traction necessary to scale the steepest inclines. On the way down, the rack and pinion system also acts as a brake.
The railway, laid to a gauge of 2ft 7 ½ in (800 mm) which is common to most mountain railways, consists of a single track with 3 passing loops spaced equidistantly between Llanberis and the Summit. (Hebron at 1069 ft (326 m), Halfway at 1641 ft (500 m) and Clogwyn at 2556 ft (779 m)). The average speed of the trains is 5 mph (8 kph).
The total length of the railway is 4 miles 1188 yards (7.53 km), with an average gradient of 1 in 7.86. The steepest gradient on the route is 1 in 5.5. The gradients on the route make it unsuitable for a normal adhesion railway, so a rack and pinion system was installed. Snowdon Mountain Railway is the only public rack and pinion railway in the British Isles.
The company currently operates 4 coal-fired steam locomotives manufactured by the Swiss Locomotive & Manufacturing Co. of Winterhur. Three of which are the original ones dating from 1895 and 1896, whilst the remaining one was built in 1922. The first of the original locomotives cost £1525.
The boilers are inclined on the locomotives to ensure that the boiler tubes and the firebox remain submerged when on the gradient, a standard practice on mountain railways. The locomotive always runs chimney first up the mountain pushing a single carriage in front of it. For safety reasons the carriage is not coupled to the locomotive.
Between 1986 and 1992 the company took delivery of 4 British built diesel locomotives to complement the steam fleet at a cost of £250,000 each. These locomotives are powered by 320 Horsepower (238 kW) six cylinder turbocharged Rolls Royce diesel engines of 12 litres capacity. Manufactured by Hunslet Engine Co. Leeds.
The original carriages were open above the waist and had canvas curtains, which provided little protection against the elements. Between 1951 and 1957 the superstructure of the original carriages was modified to produce the enclosed bodies. Each of these carriages had a capacity of 56 passengers, plus a guard. Every passenger carriage had its own set of pinions, with automatic brakes as an added precaution. If the train's speed exceeded 7.5 mph for any reason, the brake came on.
In 2012 the first of 4 new carriages was delivered to Snowdon Mountain Railway with the remaining 3 due for delivery early in 2013. These new coaches have been designed and built in the UK by a partnership between Garmendale Engineering Limited of Ilkeston, Derbyshire and the Hunslet Engine Company, to a performance specification defined and project managed by the Railway.
Not only do the carriages boast higher levels of passenger safety, space and comfort, but the manufacturing process is a world first in the rail industry. Although the material chosen for the carriage body had been used in the production of road freight vehicles in the recent past, it has never been used in the production of rail vehicles.
Combining strength and thermal insulation characteristics with extremely low weight made the choice of this material particularly appropriate for our carriage project. The new carriages also have a stunning new livery which will be reflected on the diesel locomotives that will power them up the mountain. Also this choice has allowed the Railway to increase the capacity of each carriage from the current 56 to the new capacity of 74 without change in seating space from previous carriages. In addition to this higher carrying capacity all four carriages will now have wheelchair access therefore allowing more users the opportunity to travel every day.
The carriage bogies have been designed and built by Hunslet Engine Company at the home of their parent company LH Group in Barton under Needwood. Rather than a revolutionary design, the bogies represent an incremental improvement to an existing design that has been in passenger service since 1986 and latterly improved in 2006 on the old carriage number 10 and the summit project flatbed truck. In this way Hunslet have built on a solid safety record but improved the performance of this safety critical piece of equipment. The original carriages will now be taken out of service with some of them going to have new bodies constructed on them for our new Heritage Steam Experience which is due to start in June 2013.
Manufacturer: Lancaster Carriage & Wagon Co. Ltd
|1||1895||Re-bodied for permanent way engineering vehicle|
|2||1895||In service Snowdon Lily re-bodied 2013|
|3||1895||Out of service|
|4||1895||Out of service|
|5||1895||Out of service|
|8||1895||Out of service|
Manufacturer: Schweizerische Industrie-Gesellschaft, Neuhausen
|6||1923||Out of service|
|7||1923||Out of service|
Manufacturer: East Lancashire Coach Builders Ltd
|10||1987||Re-engineered for summit service vehicle & rescue 2013|
Manufacturer: Hunslet bogies and brakes, Garmendale chassis and bodies 2013
Manufacturer: Rebuilt from 1895 Lancaster Carriage & Wagon Co. Ltd carriage frame.
A Traffic Controller at Llanberis, who is responsible for the overall movement of traffic, controls the movement of trains. Communication between Llanberis, the Summit and Clogwyn, as well as the guard of each train is by means of two-way radios.
OpenTrains are now running. Summit service open from 17th April.
Click here for an up-to-the-minute Snowdon Summit Met Office report.
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