|Driving Wheels||5ft 9ins|
|Cylinders||Inside – 18in x 26in|
|Valve Gear||Stephenson (slide valves)|
The 55116 (CR class 19) was the original Caledonian McIntosh design of 0-4-4T, built for suburban and branch line work. They were very successful engines and a further enlarged engines were built of the 55119, 55237 and 55260 classes.
Thirty-two engines were built in total and the first of the class was withdrawn in 1946. They were all originally fitted with Condensing apparatus for working over the Glasgow Central low level lines but this was later removed from most of the engines. A number of engines were later fitted with stovepipe chimneys.
The first ten engines were fitted with smaller tanks and they were known as the 19 class.
The remainder were known as the 92 class and they were a later development (built 1897-1900) with larger tanks and a high sided coal bunker.
|55116 – CR class 19 introduced in 1895 by McIntosh|
|55125 – CR class 92 introduced in 1897 by McIntosh|
|55189 – CR class 439 introduced in 1900 By McIntosh|
The 439 class engines were developed from the 55116 class and were known as the Standard Passenger class. They were a direct development of the 92 class, but they were not fitted with condensing apparatus.
Seventy-eight engines were built, the first being withdrawn in 1946. A number of engines were later fitted with stovepipe chimneys.
The last ten engines (55227-55236) were built by Pickersgill and had detail differences.
The arrangement of four driving wheels and a four wheel trailing bogie gave these locomotives a short rigid wheelbase which helped them negotiate tight curves. For a tank engine, the driving wheels are large diameter – 5ft 9ins. As a result, the locomotive travels further for every revolution, and so these locomotives had a good turn of speed. The two steam cylinders are as large as can be accommodated between the locomotive frames. Their size ensured that these locomotives could develop adequate power, and their position inside the frames, in preference to outside, reduced the twisting couple created by the connecting rod forces so that these were smooth running locomotives.
To work its trains, the Caledonian Railway adopted the air brake invented by the American George Westinghouse in 1869. This kind of brake, now used by railways everywhere, is worked by compressed air. The brake must fail safe (i.e. it must automatically apply in the event of a failure). So that each vehicle in a train has air available to operate the brake in an emergency, each carries an auxiliary air tank, and it is air from this tank that is admitted to the brake cylinders. This leads to the difficulty that the air available is limited by the size of the tank, and if the brake is released and reapplied in close succession, without the auxiliary tank having had time to recharge, the brake force will be lost. To avoid this difficulty, drivers used a technique of applying the brake with increasing force, without release, up to the point where the train stopped.
These locomotives were thus ideal for suburban passenger work – their large wheels ensured that they could accelerate fast from station stops, and the air brake ensured that they stopped rapidly as well.
In 1922 Pickersgill introduced the 431 Class with larger cylinders and cast-iron front buffer beam for banking. The idea was, presumably, to move the centre of gravity forwards and put more weight on the driving wheels. However, it seems strange to use a large-wheeled 0-4-4T (rather than a small-wheeled 0-6-0T) for banking. The 431 Class was numbered 431–434 by the Caledonian, 15237–15240 by the LMS, and 55237–55240 by British Railways.
In 1925 the LMS introduced their own version of the 439 Class and these were numbered 55260-55269 by British Railways.
In the 431 and LMS classes, the cylinder bore was increased to 18¼” and this increased the tractive effort to 19,200 lbf (85,000 N).
Seventy-four Class 439s passed into British Railways ownership in 1948 and they were numbered 55159-55236 (with gaps).