Hydrostatic displacement lubricator of a steam locomotive, at the Darjeeling train yard (India)
The purpose of this mechanical lubricator is to control the flow of lubricant (oil) that is injected into the steam that feeds the cylinders.
For more information about Hydrostatic lubricator, go to en.wikipedia.org/wiki/Mechanical_lubricator
The Darjeeling Himalayan Railway, locally known as the "Toy Train", is a 2 ft (610 mm) narrow gauge railway that runs between New Jalpaiguri and Darjeeling (India). It is still operated by vintage British-built B Class steam locomotives. Operations between Siliguri and Kurseong have been temporarily suspended since 2010 following a Landslide at Tindharia (view photos of the landslide).
For more information about the Darjeeling Steam-powered Train, read en.wikipedia.org/wiki/Darjeeling_Himalayan_Railway.