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The railway system in India began 140 years ago with experimental lines built in 1853 from Bombay to Thana and in 1854 from Howrah (close to Calcutta) to Houghly. Both were broad gauge (5ft 6in) and it was originally the intention to adopt this as the standard gauge throughout the peninsular. The Government of India considered that there was an urgent need to build an extensive railway system both to move freight (coal, cotton etc.) and to cope with the large potential passenger traffic. Various UK companies were interested in promoting the extension of the railway system but costs were considerable and the potential profits possibly small. In order to ensure the building of the requisite railways the Government provided a favourable financial package. This involved the provision of free land and a 5% guarantee on capital and loan stock for a 99 year lease. The Government controlled the construction and infrastructure, the costs of which were high and correspondingly the profitability was low.
In 1870 the government itself had to finance further development and accepted metre gauge lines which could be built at half the cost of the broad gauge and were quite adequate for many areas. Ten years later, in 1880, this argument was extended further and many miles of feeder line with a 2ft 6in gauge were built at half the cost of the metre gauge. The carrying capacity was kept high by the ability to increase the coach width relative to the track gauge. For example, the ratio of coach width to gauge was 2.0 for the broad gauge, 2.7 for the metre gauge and 3.0 for the 2ft 6in gauge. (For the Bure Valley Railway, the corresponding figure is 3.15.) The Barsi Light Railway also built some 2ft 0in gauge lines but the War Department in London decreed that 2ft 6in should be the standard for all narrow gauge railways throughout the Empire.
In 1921 there was still under-capacity and at that time a Committee of investigation found that of the 27,000 mile owned by the Government only 9,000 miles was Government operated, the remainder was worked by London based Companies as agents or managers. Slowly these Companies were taken over by the Government as leases expired.
There has always been a strong UK involvement in the Indian Railways and the first standardisation of locomotives was undertaken in 1903 by the British Engineering Standards Association (BESA). In 1920 the Locomotive Standards Committee recommended five new Indian Railway Standard (IRS) designs XA, XB, XC, XD and XE for the Broad gauge. Only the outline specification was prepared, the detail design was worked out in London by consultants and prospective builders. The corresponding Y classes were involved for the metre gauge lines and the Z classes for the 2ft 6in gauge lines.
The ZB class became one of the most popular 2ft 6in gauge designs, the detail design work was undertaken by Bagnall & Co Ltd of Stafford in collaboration with the London consultants Rendell Palmer & Tritton. The first was built in 1926 and the design continued to be built by various builders including Hudswell Clarke of Leeds, Corpet Louvet of France (8 in 1951), Krauss Maffei in Germany (15 in 1952-53) and Duro Dakovic in Yugoslavia (6 in 1959). Some variants were built: for later operation in Pakistan, Bagnall & Co built two with Caprotti valve gear in place of Walschaerts Valve gear whilst in 1950 Hudswell Clarke built four with short wheel tenders at a cost of £42,500 for the Dehri Rhotas Light Railway. At one time 40 locomotives of the class were operating on the Gaekway of Barodas State Railway some 200 miles north of Bombay. In all about 100 locomotives were built.
Locomotives No 6 and 7 on the Bure Valley Railway are half the size of the standard ZB but offer two thirds of the tractive effort. The wheel arrangement is 2-6-2 (a front pony truck, 3 coupled driving axles and rear truck under the cab). Like the original there is a wide gap under the firebox to permit easy removal of the ashpan. The driving wheels, cylinders and piston valves are, relatively, slightly larger than the original. Walschaerts valve gear is fitted and there in an axle driven generator in the tender, behind the coal bunker and water tank in order to provide a supply for lighting, radio communication etc.
Nos 6 and 7 were built by Winson Engineering Ltd at Penrhyndeudraeth in North Wales and at Daventry and were delivered to the railway at Easter and Whitsun 1994 respectively.
No 8 and No 9 are mechanically identical to No 6 and No 7, but are tank locomitives, fitted with side tanks rather than a tender. No 9 has a 2-6-4 wheel arrangement.
No 8 is styled as a Vale of Rheidol locomotive. Components were provided by Winson Engineering at Daventry for assembly at the Aylsham works of the Bure Valley Railway. It was first steamed on 19th December 1997 and originally an oil fired loco, during it's latest overhaul, the loco was rebuilt as a coal fired engine and re-entered traffic in 2008. However it has been altered in such a way that it could be easily changed back to oil firing within a matter of days.
No 9 was origally built as an oil fired locomotice by Winson Engineering in 1999 to a 'County Donegal' design. It has subsequently been rebuilt as a coal fired 'Leek & Manifold' design locomotive by Alan Keef Limited of Ross-on-Wye. Arriving at the Bure Valley Railway during 2003 (Originally numbered as No.10 and renumbered as No.9 in January 2005), this loco entered full passenger traffic in July 2004.
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