The Indian locomotive class SP (Standard Passenger) is a class of Indian4-4-0passenger steam locomotives which was built around 1905. It was one of the BESA locomotives developed by the British Engineering Standards Committee, later called the British Engineering Standards Association (BESA).
The SP class was catalogued in the first edition (1903) of the BESA report on standard locomotives for the railways of the British Raj.[2]4-4-0 (American) locomotives were preferred in India as they had good riding qualities, even on poor track conditions.[citation needed] The SP class used the same boiler as the SG class standard goods locomotives, which had a diameter of 4 feet 8+1⁄4 inches (1,429 mm).[2] In the 1910 BESA report, a variant with a larger boiler was developed, which had a diameter of 5 feet 1+1⁄4 inches (1,556 mm), as used in the PT class passenger tank locomotives.[3]
The locomotives were delivered to different railways, but only the Indian States Railways (ISR)-operated railways referred to them as the SP class. Beyer Peacock delivered 10 locomotives to the North Western Railway (NWR), which operated lines around the modern-day border of India and Pakistan.[4]
The locomotives were designed with two inside cylinders, a Belpaire firebox,[2] and used saturated steam. The grate was arranged between two driving wheels. Between the frames were the two cylinders and the Stephenson valve gear.[2] A small pilot was fitted to the locomotive's buffer beam. The cab was completely enclosed, with the cab's rear wall being formed by the tender.
A later version was designed with a superheater and designated SPS (Standard Passenger, Superheated); SP locomotives retro-fitted with superheaters were usually reclassified as SPC (Standard Passenger, Converted).
^"Third report of the Locomotive Committee on Standard Locomotives for Indian railways". Indian Industries and Power. March 1910. p. 275. Retrieved 2020-08-31.
