Indian locomotive class SP
The Indian locomotive class SP were a class of passenger broad-gauge locomotives introduced around 1905 that were one of seven standard locomotive designs developed by the Engineering Standards Committee for the broad-gauge railways of British India.
Background
British Indian railways operated numerous steam locomotives built to their own design standards, and near and at the turn of the century, this created a considerable strain on British locomotive manufacturers who could not keep up with demand. This led to British Indian railways outsourcing production of locomotives to non-British companies, which generated complaints from British locomotive manufacturers.Amidst this situation, proposals for standardisation of British Indian steam locomotives were made as early as the 1870s, in which there were prior plans to standardise locomotive designs for British Indian railways that never went through; but later, a locomotive standardisation scheme for British Indian railways was finally realised when the Engineering Standards Committee was requested by the British Indian government to develop standard locomotive classes for British Indian railways. Its first report, compiled in 1903, outlined plans for British Indian standard locomotives, being revised in 1907 and in 1910.
History
The SP class locomotives were catalogued in the first report of the Engineering Standards Committee on standard locomotives for the railways of the British Raj. Later on, in the third report of the Engineering Standards Committee of the same, a variant with a larger boiler was outlined, which had a diameter of, as used in the PT class locomotives.Engines built to this design worked the broad-gauge lines of British Indian railways; however, only government-operated railways designated these locomotives as the SP class. Beyer, Peacock & Company delivered 10 locomotives to the North Western Railway, which became the Pakistan Western Railway and the Eastern Punjab Railway upon the partition of India.
Design
The design parameters outlined by the Engineering Standards Committee were as follows: the locomotives were designed to use the same boiler as the SG class locomotives, which had a diameter of, and later the same boiler as the PT class locomotives—the latter two locomotives built to broad gauge, two inside cylinders, a Belpaire firebox, and saturated steam. The valve gear used was the Stephenson valve gear which was fitted inside the frames. The grate was fitted between the two driving wheels. The diameter of the driving wheels necessitated splashers to be fitted over the wheels. A small pilot was fitted to the locomotive's buffer beam. The cab was enclosed, with the cab's rear wall being formed by the tender's half cab.A later version was designed with a superheater and designated SPS ; SP locomotives retrofitted with superheaters were usually reclassified as SPC.