Indian locomotive class HP

The Class HP (Heavy Passenger) was a broad gauge steam locomotive introduced in 1906 for heavy passenger trains on the railways in British India. It was one of the BESA locomotives developed by the British Engineering Standards Committee, later called the British Engineering Standards Association (BESA).

History
The HP class was the locomotive intended for heavy passenger traffic, which was first proposed in the BESA standard of 1907. Like the AP class, the HP was offered with three different large tenders, the small one holding 3000 gallons of water, the medium 4000 and the large 4500.

The HP class locomotives were delivered to various railways, but only the Indian States Railways (ISR) gave their locomotives the designation HP. They were built by several British locomotive factories, including the Vulcan Foundry, Robert Stephenson and Company, North British Locomotive Company, Kitson and Company and William Beardmore and Company.

Later, the HPS series was introduced, fitted with the Schmidt smoke tube superheater system - the S stands for superheated, and the HPC series for the locomotives with superheaters converted from the HP series, where the C stands for converted.

Preservation
Three HPS series locomotives have been preserved:
 * HPS 30 of Bangladesh Railway in Rajshahi
 * HPS 32 of Indian Railways at the Rail Museum, Howrah
 * HPS 24467 of Indian Railways at the National Rail Museum of India, New Delhi.

Technical aspects
The locomotive was a two-cylinder saturated steam engine with a Belpaire firebox. The grate was arranged between the coupling gear sets, for which the wheel base between axles 2 and 3 was increased. The cylinders were arranged on the outside and the drive was on the second axle. The saturated HP class had Walschaerts valve gear with slide valves; piston valves were used in the superheated HPS and HPC classes. The running plate was set low, so splashers had to be fitted above the driving wheels. As with the AP class locomotives, the line of the driver's cab floor is raised in an arc to the height of the running plate. A small cow catcher was attached to the front buffer beam. The driver's cab was completely closed, with the rear wall of the driver's cab being formed by the three-axle tender. The three-axle tender was equipped with running boards and handrails along the side walls, which made it possible to reach the train from the locomotive while in motion.