Sentinel class Y3
The LNER Class Y3 was a 0-4-0 geared steam shunting locomotive with a vertical water-tube boiler and two-speed gearbox, introduced in 1927.
The LNER class Y3 was built by Sentinel Wagon Works for the London and North Eastern Railway and introduced in 1927, later passing into British Railways ownership in 1948 with Nos. 68154–68185. It was a 0-4-0 geared steam locomotive designed primarily for shunting duties in yards and on small branch lines where track conditions were less robust.
The class Y3 used a superheated vertical water-tube boiler, similar to those in Sentinel steam wagons, allowing steam to be raised quickly compared to conventional fire-tube boilers. It was equipped with poppet valves and a sliding camshaft for reversing. The class featured a two-speed gearbox, which could only be changed while stationary, and a sprocket chain drive to the wheels. Some locomotives had a 19:19 sprocket ratio, giving a maximum speed of 36.5 mph in high gear and 13.5 mph in low gear. These locomotives were highly efficient, consuming only about 15 lb of coal per mile. The vertical boiler had a cylindrical shape with an inner firebox, spiral boiler tubes, and a removable superheater for maintenance.
The class Y3 was considered ideal for shunting in yards and on lightly laid tracks due to its chain drive, which avoided hammer-blow effects on the rails. At least one class Y3 was based at Immingham in 1950. A total of 32 class Y3s were built, making them more numerous than the single-speed class Y1.
The main difference between the class Y3 and the class Y1 was the two-speed gearbox of the class Y3, allowing higher speeds when required, whereas the class Y1 was a single-speed locomotive. Both shared the vertical boiler and geared drive design, derived from Sentinel steam wagons.
While many Sentinel locomotives survive worldwide, only a few of the class Y1/Y3 design remain in the British Isles. The class Y3 itself does not have a surviving example, but the design principles are preserved in heritage collections.