Great Western Railway Power and Weight Classification
From 1920, the cab side of Great Western Railway steam locomotives bore a letter on a coloured disc, which enabled staff to assess the capabilities of locomotives without the need to check tables of data. The letter showed the power classification, the coloured disc showed the weight restriction; this system continued. On 1 July 1905 the Great Western Railway introduced a system for denoting both the haulage capabilities and the weight restrictions which applied to their various classes of locomotive; this was used only in record books, but from mid 1919 began to be shown on the locomotives themselves. The weight restriction was shown in the form of a coloured disc, the power classification was denoted by a capital letter placed upon the disc. At first these were painted high on the cab side, but during World War II the blackout precautions meant that staff had to be careful using lights at night, so the disc and letter were moved downwards to a position just above the engine number plate, to make them easier to see.
When locomotives were loaned by other railways to the GWR during World War II, these were allotted GWR power and weight classifications, so that GWR staff responsible for locomotive rostering could select the most suitable engine for the task without needing to learn an unfamiliar system. The GWR was nationalised in 1948. In 1949, BR decided to adopt the London and Scottish Railway system of power classification for all locomotives. Despite this, the use of a letter to denote power classification continued to be used on former GWR steam locomotives, as did the coloured disc for weight classification. Certain ex-LMS and BR Standard steam locomotives allocated to the Western Region were given GWR style route classification discs without the power class letter; some of these had the BR power class shown on the disc as a figure. The coloured disc was applied to some diesel locomotives allocated to the Western Region; the letter represents the power of the locomotive, is proportional to the starting tractive effort, thus: The "Special" classification was not shown on the "King" class, but in the case of no. 111 The Great Bear, "Special" was shown by a cross on its red route restriction disc.
Locomotives loaned during World War II were given GWR power class letters, in order to avoid confusion with different systems used by the lending railway. For example, the Southern Railway used letters, but with A representing the highest power. During World War II, it was decided that some classes of two-cylinder engines would be permitted to haul loads heavier than those specified in the working books for their power classification; these engines were distinguished by a white letter "X" painted above the number plate. The GWR system was divided into "red", "blue", "yellow" and "uncoloured" routes, according to the maximum axle load which the Civil Engineer would permit: for example, engines of axle load greater than 16 tons were not permitted onto "yellow" or "uncoloured" routes. In between these were "dotted red" and "dotted blue" routes, where overweight engines were permitted subject to speed restrictions. In addition, there were the "hatched red" routes, where any locomotive was permitted: the 6000 class were barred from all except the "hatched red" routes.
In August 1938 a summary of the GWR routes by colour was published: The "hatched red" routes comprised Paddington to Bristol Temple Meads, both via Bath and via Badminton. Further routes were raised to this category after Nationalisation: Wolverhampton to Chester via Shrewsbury. Up to two coloured discs were painted on the cabside of GWR steam locomotives and some Western Region diesel locomotive classes, to show that the maximum axle load of the engine did not exceed a particular value, the absence of such circles meaning that no restrictions applied to the locomotive: As with the power classifications, locomotives loaned to the GWR in World War II were given GWR weight restriction colours. For example, engines of LNER Class J25, which were Route Availability 3 on that line, were placed in GWR route restriction "Yellow". There were occasional amendments in the light of operating experience. Abc British Railway Locomotives: Combined volume Part One- Western Region. Shepperton: Ian Allan. March 1999.
ISBN 0-7110-0506-0. 9903/A2. Allcock, N. J.. K.. M.. N.. J. T.. J.. White, D. E. ed. Part 1: Preliminary Survey; the Locomotives of the Great Western Railway. Kenilworth: RCTS. ISBN 0-901115-17-7. Bradley, D. L.. Locomotives of the L. S. W. R.: Part 1. Kenilworth: RCTS. Fry, E. V. ed.. Part 5: Tender Engines - Classes J1 to J37. Locomotives of the L. N. E. R. Kenilworth: RCTS. ISBN 0-90111
Scrap consists of recyclable materials left over from product manufacturing and consumption, such as parts of vehicles, building supplies, surplus materials. Unlike waste, scrap has monetary value recovered metals, non-metallic materials are recovered for recycling. Scrap metal originates both in business and residential environments. A "scrapper" will advertise their services to conveniently remove scrap metal for people who don't need it. Scrap is taken to a wrecking yard, where it is processed for melting into new products. A wrecking yard, depending on its location, may allow customers to browse their lot and purchase items before they are sent to the smelters, although many scrap yards that deal in large quantities of scrap do not selling entire units such as engines or machinery by weight with no regard to their functional status. Customers are required to supply all of their own tools and labor to extract parts, some scrapyards may first require waiving liability for personal injury before entering.
Many scrapyards sell bulk metals by weight at prices below the retail purchasing costs of similar pieces. A scrap metal shredder is used to recycle items containing a variety of other materials in combination with steel. Examples are automobiles and white goods such as refrigerators, clothes washers, etc; these items are labor-intensive to manually sort things like plastic, copper and brass. By shredding into small pieces, the steel can be separated out magnetically; the non-ferrous waste stream requires other techniques to sort. In contrast to wrecking yards, scrapyards sell everything by weight, instead of by item. To the scrapyard, the primary value of the scrap is what the smelter will give them for it, rather than the value of whatever shape the metal may be in. An auto wrecker, on the other hand, would price the same scrap based on what the item does, regardless of what it weighs. If a wrecker cannot sell something above the value of the metal in it, they would take it to the scrapyard and sell it by weight.
Equipment containing parts of various metals can be purchased at a price below that of either of the metals, due to saving the scrapyard the labor of separating the metals before shipping them to be recycled. Scrap prices may vary markedly over time and in different locations. Prices are negotiated among buyers and sellers directly or indirectly over the Internet. Prices displayed. Other prices are not updated frequently; some scrap yards' websites have updated scrap prices. In the US, scrap prices are reported in a handful of publications, including American Metal Market, based on confirmed sales as well as reference sites such as Scrap Metal Prices and Auctions. Non-US domiciled publications, such as The Steel Index report on the US scrap price, which has become important to global export markets. Scrap yards directories are used by recyclers to find facilities in the US and Canada, allowing users to get in contact with yards. With resources online for recyclers to look at for scrapping tips, like web sites and search engines, scrapping is referred to as a hands and labor-intensive job.
Taking apart and separating metals is important to making more money on scrap, for tips like using a magnet to determine ferrous and non-ferrous materials, that can help recyclers make more money on their metal recycling. When a magnet sticks to the metal, it will be a ferrous material, like iron; this is a less expensive item, recycled but is recycled in larger quantities of thousands of pounds. Non-ferrous metals like copper and brass do not stick to a magnet; some cheaper grades of stainless steel are other grades are not. These items are higher priced commodities for metal recycling and are important to separate when recycling them; the prices of non-ferrous metals tend to fluctuate more than ferrous metals so it is important for recyclers to pay attention to these sources and the overall markets. Great potential exists in the scrap metal industry for accidents in which a hazardous material present in scrap causes death, injury, or environmental damage. A classic example is radioactivity in scrap.
Toxic materials such as asbestos, toxic metals such as beryllium and mercury may pose dangers to personnel, as well as contaminating materials intended for metal smelters. Many specialized tools used in scrapyards are hazardous, such as the alligator shear, which cuts metal using hydraulic force and scrap metal shredders. According to research conducted by the US Environmental Protection Agency, recycling scrap metals can be quite beneficial to the environment. Using recycled scrap metal in place of virgin iron ore can yield: 75% savings in energy. 90% savings in raw materials used. 86% reduction in air pollution. 40% reduction in water use. 76% reduction in water pollution. 97% reduction in mining wastes. Every ton of new steel made from scrap steel saves: 1,115 kg of iron ore. 625 kg of coal. 53 kg of limestone. Energy savings from other metals include: Aluminium savings of 95% energy. Copper savings of 85% energy. Lead savings of 65% energy. Zinc savings of 60% energy; the metal recycling industry encompasses a wide range of metals.
The more recycled metals are scrap steel, lead, copper, stainless steel and zinc. There are two main categories of metals: ferrous and
Old Oak Common TMD
Old Oak Common TMD was a traction maintenance depot to the west of London, in Old Oak Common. The depot was the main facility for the storage and servicing of locomotives and multiple-units from Paddington; the depot codes were OC for the diesel depot and OO for the carriage shed. In steam days the shed code was 81A; the area is where two Great Western Railway main lines divide: the 1838 route to Reading via Slough, the 1906 "New North Main Line" via Greenford to Northolt Junction, the start of the Great Western and Great Central Joint Railway line. The former is in use for regular passenger services. The'HST' section of Old Oak Common TMD, more known as'Old Oak Common HST Depot' closed in 2018 with the removal of the Inter-City 125s from services on the Great Western Main Line; this closure was to make way for the development of the HS2 project. Maintenance of the new InterCity Express Trains is being carried out at North Pole IET Depot, situated opposite the site of Old Oak Common TMD whilst the Night Riviera was transferred to Penzance Long Rock Depot in December 2017.
Following the reconstruction of Paddington station and the introduction of larger locomotives and new routes, the Great Western Railway required a larger depot than that at the 1855 constructed Westbourne Park, at which to service its locomotives and carriages. In 1901, a site was acquired in South Acton, south of the Grand Union Canal and on the upside of the mainline. Taking four years to layout and build, designed by G. J. Churchward, it was the largest depot on the entire GWR system, set the pattern for similar depots throughout the GWR including Tyseley, it had four 65 feet undergirder turntables, under six-spans of east-west aligned northern-light pitched roofs. The shed covered a total area of 360 feet (six bays of 60 by 444 feet or 18.3 by 135.3 metres}. The roofs were made of wood and steel rafters covered in Welsh slate tiles, supported on steel or cast iron columns, with solid London Brick Company walls. Laid out in an interconnecting 4-square pattern under the roof, each electrically operated turntable was boarded, had 28 tracks spanning from it, able to accommodate locomotives up to 75 feet in length.
The associated repair shop, termed "The Factory", was allocated to the northeast front of the depot, with 11 roads approached over an electric traverser, a 12th road direct from the depot throat. Built in a similar style to the depot, it was 195 feet by 110 feet in size, housed a 30-long-ton crane. There were separate Smithy and carpenters shops, a stores and a general office; the approach to the shed housed a standard GWR pattern coal stage, again the largest on the system. It was approached via a 1:50 gradient brick-arch supported ramp, with 1:80 beyond the stage. In 1938, the approach roads to and from the coal stage were doubled, in 1942 an ash shelter constructed to protect from Nazi Luftwaffe bombing; the four water tanks housed over the stage held 290,000 imperial gallons of water, while sand was supplied from a separate sand furnace. The whole depot came into operation from 17 March 1906, became the head of the GWR London operating division. Throughout its GWR and early BR operational life, the depot remained intact and similar to its original layout.
The only major difference by the early 1960s was the addition of a pre-war diesel refuelling stage just north of the repair shop, for use by GWR railcars. With a reduction in steam traction and the implementation of the Beeching cuts, in March 1964 the decision was taken to move the remaining steam locomotive allocation to the 1950s designed Southall MPD, reconstruct Old Oak Common as a diesel depot. Within a year the majority of the GWR 1906 depot was demolished, with only "The Factory" repair shop, furthest western turntable and parts of the stores remaining; the main service building had 3 tracks, each holding two locos, with inspection pits, fuel supply points and a washing plant on the approach road. Some of the inspection pits in The Factory were lengthened and deepened and jacks provided to allow for bogie and spring changing, it opened on 20 October 1965. It was the last of six big diesel depots built for the Western Region, the others being Margam TMD 1960, Bristol Bath Road depot 1960, Laira Traction Maintenance Depot, Plymouth, 1962, Landore TMD, Swansea, 1963 and Cardiff Canton TMD 1964.
Just south of the residual GWR buildings, in the 1960s BR built what was the storage depot for the Blue Pullman trains, what became known as the Coronation Carriage Sidings. In the late 1970s, south of this and adjacent to the Great Western Main Line, BR built a depot for the new InterCity 125 fleet; until December 2018 these maintained the Great Western Railway InterCity 125 fleet. In 1997 a new bespoke depot was constructed at the southern end of the site, between the Great Western depot and the main line, funded by the British Airports Authority to service and maintain the Heathrow Express and Heathrow Connect service trains; this was the first new funded train depot in the UK since the British railways nationalisation in 1948. The inauguration of the Heathrow Express services saw the electrification of the GWML from Paddington to Hayes and onto Heathrow Airport using 25 kV overhead catenary. On 26 July 2002, First Great Western opened a new depot on the site of the former carriage sidings to service its Class 180 fleet.
The residual GWR buildings were used from the 1970s to house and maintain singular diesel locomotives, special trains, maintain carriages and fre
In both road and rail vehicles, the wheelbase is the distance between the centers of the front and rear wheels. For road vehicles with more than two axles, the wheelbase is the distance between the steering axle and the centerpoint of the driving axle group. In the case of a tri-axle truck, the wheelbase would be the distance between the steering axle and a point midway between the two rear axles; the wheelbase of a vehicle equals the distance between its rear wheels. At equilibrium, the total torque of the forces acting on a vehicle is zero. Therefore, the wheelbase is related to the force on each pair of tires by the following formula: F f = d r L m g F r = d f L m g where F f is the force on the front tires, F r is the force on the rear tires, L is the wheelbase, d r is the distance from the center of mass to the rear wheels, d f is the distance from the center of gravity to the front wheels, m is the mass of the vehicle, g is the gravity constant. So, for example, when a truck is loaded, its center of gravity shifts rearward and the force on the rear tires increases.
The vehicle will ride lower. The amount the vehicle sinks will depend on counter acting forces, like the size of the tires, tire pressure, the spring rate of the suspension. If the vehicle is accelerating or decelerating, extra torque is placed on the rear or front tire respectively; the equation relating the wheelbase, height above the ground of the CM, the force on each pair of tires becomes: F f = d r L m g − h c m L m a F r = d f L m g + h c m L m a where F f is the force on the front tires, F r is the force on the rear tires, d r is the distance from the CM to the rear wheels, d f is the distance from the CM to the front wheels, L is the wheelbase, m is the mass of the vehicle, g is the acceleration of gravity, h c m is the height of the CM above the ground, a is the acceleration. So, as is common experience, when the vehicle accelerates, the rear sinks and the front rises depending on the suspension; when braking the front noses down and the rear rises.:Because of the effect the wheelbase has on the weight distribution of the vehicle, wheelbase dimensions are crucial to the balance and steering.
For example, a car with a much greater weight load on the rear tends to understeer due to the lack of the load on the front tires and therefore the grip from them. This is why it is crucial, when towing a single-axle caravan, to distribute the caravan's weight so that down-thrust on the tow-hook is about 100 pounds force. A car may oversteer or "spin out" if there is too much force on the front tires and not enough on the rear tires; when turning there is lateral torque placed upon the tires which imparts a turning force that depends upon the length of the tire distances from the CM. Thus, in a car with a short wheelbase, the short lever arm from the CM to the rear wheel will result in a greater lateral force on the rear tire which means greater acceleration and less time for the driver to adjust and prevent a spin out or worse. Wheelbases provide the basis for one of the most common vehicle size class systems; some luxury vehicles are offered with long-wheelbase variants to increase the spaciousness and therefore the luxury of the vehicle.
This practice can be found on full-size cars like the Mercedes-Benz S-Class, but ultra-luxury vehicles such as the Rolls-Royce Phantom and large family cars like the Rover 75 came with'limousine' versions. Prime Minister of the United Kingdom Tony Blair was given a long-wheelbase version of the Rover 75 for official use, and some SUVs like the VW Tiguan and Jeep Wrangler come in LWB models In contrast, coupé varieties of some vehicles such as the Honda Accord are built on shorter wheelbases than the sedans they are derived from. The wheelbase on many commercially available bicycles and motorcycles is so short, relative to the height of their centers of mass, that they are able to perform stoppies and wheelies. In skateboarding the word'wheelbase' is used for the distance between the two inner pairs of mounting holes on the deck; this is different from the distance between the rotational centers
Newton Abbot railway station
Newton Abbot railway station serves the town of Newton Abbot in Devon, England. It is 20 miles 13 chains down the line from Exeter St Davids and 214 miles 5 chains measured from London Paddington via Bristol Temple Meads, at the junction for the branch to Paignton; the station today is managed by Great Western Railway, who provide the train service along with CrossCountry. For many years, it was the junction for Moretonhampstead and the site of a large locomotive workshop; the station was opened by the South Devon Railway Company on 30 December 1846 when its line was extended from Teignmouth railway station. It was opened through to Totnes on 20 June 1847 and a branch to Torquay was added on 18 December 1848; the Moretonhampstead and South Devon Railway opened its branch line on 26 June 1866. All these railways used the 7 ft broad gauge. Approaching the station from the town along Queen Street, people first saw. On the opposite side of the line was the pumping house for the atmospheric railway system that powered the trains for a short while.
The passenger station was situated to the south of these buildings. It consisted to two – three – small train sheds covering separate platforms for trains running in each direction to Exeter and Torquay, it was rebuilt in 1861. On 1 February 1876 the South Devon Railway, which had amalgamated with the Moretonhampstead company, was amalgamated into the Great Western Railway; the station was known as just "Newton" but this was changed to "Newton Abbot" on 1 March 1877. The last broad gauge train ran on 20 May 1892, after which all the lines in the area were converted to 4 ft 8 1⁄2 in standard gauge over the space of a weekend; the workshops at Newton Abbot played a part in converting broad gauge locomotives and wagons to standard gauge over the following months. Plans were put forward to rebuild the station with four platforms, but World War I delayed the plans; the goods facilities were moved onto the Moretonhampstead branch line on 12 June 1911, some sidings were laid at Hackney on 17 December 1911 to replace those near the engine shed.
These alterations paved the way for the expansion of the station following the war, the rebuilt station being opened by Lord Mildmay of Flete on 11 April 1927. The station, built to the designs of the Chief Architect of the Great Western Railway, Percy Emerson Culverhouse, now faced the town along Queen Street rather than the old wooden goods shed. An old broad gauge 0-4-0 locomotive, was put on display on the station platform to provide a link with the past; the southbound platform had to be rebuilt again following an air raid on 20 August 1940, during World War II. Six bombs were dropped killing 14 people; the Moretonhampstead line lost its passenger trains on 28 February 1959. Goods trains were cut back to Bovey railway station from 6 April 1964 and from 6 July 1970 were run no further than Heathfield; the final regular traffic ran in 1996. The last trains used the former Platform 4 on 24 April 1987. Removed were the loop lines that allowed fast trains to pass the station without passing a platform.
Resignalling was completed over the following bank holiday weekend. Full operation was now controlled from the panel signal box at Exeter. A new junction was installed for the Paignton branch and the signals now allow trains to run either way on each track; some of the signalling equipment was taken to the Newton Abbot Town and GWR Museum, where it forms part of an interactive display that shows how the railway shaped the town. It was at about this time that Tiny was removed from its position on the platform and moved to Buckfastleigh railway station where it is displayed in the museum of the South Devon Railway Trust; the remaining section of the Moretonhampstead line was taken out of use in 2009 when'temporary stop blocks' were placed on the line 53 chains from the junction at Newton Abbot. The line to Heathfield has since been re-opened, seeing daily timber trains in 2012 to Chirk in Wales. South West Trains ran services until December 2009 between London Waterloo and Plymouth and Paignton, before withdrawing services west of Exeter to form an hourly service from Exeter St Davids to London Waterloo.
The station was'open' for many years after the staffed ticket gate was removed from the ticket office but in August 2017 ticket barriers were installed again, this time in a new building on the platform. Newton Abbot has proved to be an accident-prone station. On 22 August 1851 the locomotive Brigand was derailed and Switchman Bidgood had to pay one pound towards its repairs; the investigation into a collision in August 1875 revealed that it was normal practice at Newton to ignore the signal that controlled movements from the siding to the main line, as a result of which it was decided to interlock the signals and points here, one of the first such installations to be authorised on the South Devon Railway. On 21 October 1892 an engine fell on its side. In more recent times, a collision occurred on 25 March 1994 when a Class 158 DMU, working a Paignton to Cardiff service, ran into the back of a Class 43 standing in the platform with a Penzance to Edinburgh train. Thirty-one people were injured.
In June 1997 a similar train from London was derailed by a broken axle as it was slowing down on its approach to the station. The main entrance is on the west side of the station, facing Courtenay Park and Queen Street which
British Railways, which from 1965 traded as British Rail, was the state-owned company that operated most of the overground rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages between 1994 and 1997. A trading brand of the Railway Executive of the British Transport Commission, it became an independent statutory corporation in 1962 designated as the British Railways Board; the period of nationalisation saw sweeping changes in the national railway network. A process of dieselisation and electrification took place, by 1968 steam locomotion had been replaced by diesel and electric traction, except for the Vale of Rheidol Railway. Passengers replaced freight as the main source of business, one third of the network was closed by the Beeching Axe of the 1960s in an effort to reduce rail subsidies. On privatisation, responsibility for track and stations was transferred to Railtrack and that for trains to the train operating companies.
The British Rail "double arrow" logo is formed of two interlocked arrows showing the direction of travel on a double track railway and was nicknamed "the arrow of indecision". It is now employed as a generic symbol on street signs in Great Britain denoting railway stations, as part of the Rail Delivery Group's jointly-managed National Rail brand is still printed on railway tickets; the rail transport system in Great Britain developed during the 19th century. After the grouping of 1923 under the Railways Act 1921, there were four large railway companies, each dominating its own geographic area: the Great Western Railway, the London and Scottish Railway, the London and North Eastern Railway and the Southern Railway. During World War I the railways were under state control, which continued until 1921. Complete nationalisation had been considered, the Railways Act 1921 is sometimes considered as a precursor to that, but the concept was rejected. Nationalisation was subsequently carried out after World War II, under the Transport Act 1947.
This Act made provision for the nationalisation of the network, as part of a policy of nationalising public services by Clement Attlee's Labour Government. British Railways came into existence as the business name of the Railway Executive of the British Transport Commission on 1 January 1948 when it took over the assets of the Big Four. There were joint railways between the Big Four and a few light railways to consider. Excluded from nationalisation were industrial lines like the Oxfordshire Ironstone Railway; the London Underground – publicly owned since 1933 – was nationalised, becoming the London Transport Executive of the British Transport Commission. The Bicester Military Railway was run by the government; the electric Liverpool Overhead Railway was excluded from nationalisation. The Railway Executive was conscious that some lines on the network were unprofitable and hard to justify and a programme of closures began immediately after nationalisation. However, the general financial position of BR became poorer, until an operating loss was recorded in 1955.
The Executive itself had been abolished in 1953 by the Conservative government, control of BR transferred to the parent Commission. Other changes to the British Transport Commission at the same time included the return of road haulage to the private sector. British Railways was divided into regions which were based on the areas the former Big Four operated in. Notably, these included the former Great Central lines from the Eastern Region to the London Midland Region, the West of England Main Line from the Southern Region to Western Region Southern Region: former Southern Railway lines. Western Region: former Great Western Railway lines. London Midland Region: former London Midland and Scottish Railway lines in England and Wales. Eastern Region: former London and North Eastern Railway lines south of York. North Eastern Region: former London and North Eastern Railway lines in England north of York. Scottish Region: all lines, regardless of original company, in Scotland; the North Eastern Region was merged with the Eastern Region in 1967.
In 1982, the regions were abolished and replaced by "business sectors", a process known as sectorisation. The Anglia Region was created in late 1987, its first General Manager being John Edmonds, who began his appointment on 19 October 1987. Full separation from the Eastern Region – apart from engineering design needs – occurred on 29 April 1988, it handled the services from Fenchurch Street and Liverpool Street, its western boundary being Hertford East and Whittlesea. The report, latterly known as the "Modernisation Plan", was published in January 1955, it was intended to bring the railway system into the 20th century. A government White Paper produced in 1956 stated that modernisation would help eliminate BR's financial deficit by 1962, but the figures in both this and the original plan were produced for political reasons and not based on detailed analysis; the aim was to increase speed, reliability and line capacity through a series of measures that would make services more attractive to passengers and freight operators, thus recovering traffic lost to the roads.
Important areas included: Electrification of principal main lines, in the Eastern Region, Birmingham to Liverpool/Manchester and Central Scotland Large-scale dieselisation to replace steam locomotives New passenger and freight rolling stock R
Prime mover (locomotive)
In engineering, a prime mover is an engine that converts fuel to useful work. In locomotives, the prime mover is thus the source of power for its propulsion. In an engine-generator set, the engine is the prime mover, as distinct from the generator. In a diesel-mechanical locomotive, the prime mover is the diesel engine, mechanically coupled to the driving wheels. In a diesel-electric locomotive, the prime mover is the diesel engine that rotates the main generator responsible for producing electricity to power the traction motors that are geared to the drivers; the prime mover can be a gas turbine instead of a diesel engine. In either case, the generator, traction motors and interconnecting apparatus are considered to be the power transmission system and not part of the prime mover. A wired-electric or battery-electric locomotive has no on-board prime mover, instead relying on an external power station; the engine and generator set of a diesel-electric locomotive are sometimes coupled as a removable unit called "the power unit".
The power unit represents the main weight in a locomotive design, other than the body. Its position back and forth is at the designer's choice and may be used to control overall weight distribution. In most locomotives designs, the power unit is placed centrally. In some locomotives, it is offset to one end. In extreme cases, such as C-B wheel arrangements, the weight on each bogie may differ so much that the engine-end bogie is given an extra carrying axle, to keep individual axle loads more consistent. Power pack