The Indian locomotive class XB was a 4-6-2 (or Pacific) passenger locomotive with a 17-long-ton (17 t; 19-short-ton) axle load. It was one of several standard designs drawn up in the early 1920s as part of the Indian Railway Standard (IRS) series. The class suffered many teething troubles early in their service career, and after several modifications were made, the XBs were in service until the 1980s.
In 1924, the Indian Railway Board formed the Locomotive Standards Committee in designing new locomotive designs, as a result of an increase in traffic following the First World War and the prospect of using low-grade coal, which previous locomotive designs may not work well with. Evolved from the BESA designs of the early 1900s, three 4-6-2 passenger locomotive classes and two freight 2-8-2 designs were drawn up.[1]
Class XB, Light Type 4-6-2 Passenger Locomotive Built By The Vulcan Foundry Ltd. for Indian State
The XB was one of these 4-6-2 designs, and like the other designs, was designed with consultation with many manufacturers and the British Engineering Standards Association (BESA) by the Indian Railway Board.[1] It was comparable to contemporary designs in Britain, having American 3-point suspension with compensating levers for indifferent tracks in India. The trailing wheels were mounted on a Cartazzi truck, as it was for the rest of British Pacifics at the time. Goodall-type drawgear was fitted between engine and tender to facilitate free movement. The copper firebox had combustion chamber extension.
Like the other X series Pacifics, the XB was prone to frame fractures. One unit had nine fractures in nine years. 18 XBs of the East Indian Railway Company (EIR) spent three years in repair shop, out of eight years. Again due to it being an X series Pacific, it had chronic coupling rod failure. Tubeplates had to be replaced frequently due to the radius of flanges being prone to cracking. The boiler was poor, having pressure below 150 pounds per square inch (1,000 kPa), and the diameter was too small for the flue gas made by the firebox. Tube cross-section area to the grate was only 9%. Testing showed that the engine was unable to haul a 350-long-ton (360 t) train at 60 mph (97 km/h) at 33% cylinder cut-off. It oscillated laterally at a right-angle to the tracks causing damage to the tracks. Within nine years, there were 68 such cases caused by the XB and XC class locomotives.
The trailing bogie was moved 30 inches (760 mm) back and an American drawgear was fitted,[2][better source needed] while a 45 miles per hour (72 km/h) speed restriction was enforced on many lines.[1] In 1937, the Bihta accident occurred with the engine jumping the tracks and derailing at 60 mph (97 km/h), killing over 100 people.[1][3] The Pacific Locomotive Committee was formed on public demand, with representatives coming from Britain, France, and India.[1]
No XB's from Indian Railways have survived into preservation, but in Pakistan, No.450, an ex-EBR locomotive, survived and is preserved at Lahore workshops.
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