Draft:Midland Railway 2601 Class

The Midland Railway 2601 class was the last of four classes of 4-2-2 steam locomotives designed by Samuel Johnson for the Midland Railway. They were a development of his 115 class Spinners.

Only 10 were built at Derby Works, and none were preserved.

The resurgence of singles
Towards the end of the 19th century, the age of the single-driver locomotive was obsolete because the trains, which had become heavier, required pulling forces that could no longer be provided by one drive axle alone. When steam sanding was invented by James Gresham in 1885 this improved the traction of the driving wheels enough that singles were once again a practical design. There was a resurgence of single designs across a number of railways, such as the GWR's Dean Singles, Holden's P43 for the GER and Johnson's 115 class Spinners for the Midland Railway. All of these were used for high-speed passenger services of moderate weight and not usually of the longest distances. This required a locomotive that was powerful, with the ability to run at high speeds, but only of modest tractive effort.

Most used double frames and two inside cylinders. Outside frames, and thus double frames, had become regarded as generally obsolete, but this was an issue with coupled wheels and the need for their coupling rods to use outside cranks. For singles, especially inside-cylindered singles, this was an irrelevance. The use of inside cylinders also reduced the rocking couple, which could become a problem for outside-cylindered locomotives with short wheelbases at high speed. By using double frames, Johnson's Spinners had four main axle bearings and for once, the Midland Railway had a locomotive bearing design that was not undersized and gave continual trouble.

2601 class
A few years after the 115s, Johnson followed these with the slightly improved 2601 class. The cylinder sizes remained the same and the driving wheels increased by an insignificant $1/2$inch. The only major change was that the slide valves were replaced by piston valves, although the boiler was still unsuperheated.

The boiler was enlarged, with a larger grate area and a small increase in working pressure from 170 to 180 psi. The steam dome was now directly above the driving axle, rather than noticeably ahead of it, as on the 115s. By 1900 Johnson was using the new Belpaire firebox design for the 4-4-0 Belpaires, but this firebox was wider than the previous round-topped boiler and there was insufficient space for it between the tall single drivers.

The 6-wheeled tender was replaced with an 8-wheeled bogie design. This provides a further identification feature in photographs between a 115 and a 2601.

History
Between 1887 and 1900, Johnson had no fewer than 95 single locomotives built by the railway's own workshops in Derby, which differed slightly in structural details. They were used in front of high-quality express trains and reached speeds of up to 90 mph (approx. 145 km/h).

2601 Princess of Wales, the first of the class, was exhibited at the Paris Exposition of 1900 and awarded the Grand Prix.

The last were withdrawn in 1922, and so none passed into the post-Grouping LMS.