Caledonian Railway 956 Class

Caledonian Railway 956 class
Type and origin
Power type Steam
Designer William Pickersgill
Build date 1921
Total produced 4
Specifications
Configuration 4-6-0
UIC classification 2'C
Gauge 4 ft 8 1⁄2 in (1,435 mm)
Driver diameter 6 ft 1 in (1.854 m)
Locomotive weight 81 long tons (82.3 t)
Tender weight 48 long tons (48.8 t)
Fuel type Coal
Boiler pressure 180 psi (1.24 MPa)
Firegrate area 28 square feet (2.6 m2)
Superheater type Robinson
Cylinders Three
Cylinder size 18.5 in × 26 in (470 mm × 660 mm)
Valve gear See text
Performance figures
Tractive effort 27,975 lbf (124.4 kN)
Career
Operator(s) CR • LMS
Class CR: 956
Power class LMS: 5P
Number(s) CR 956–959;
LMS: 14800–14803
Withdrawn 1931–1935
Disposition All scrapped

The Caledonian Railway 956 Class were 3-cylinder 4-6-0 steam locomotives that were used on the Caledonian Railway from 1921. They were built to the design of William Pickersgill. At the time they were the largest design operated by a Scottish railway.

Introduction

The class ran to four members:

CR no. LMS no. Built Works Withdrawn First allocation
956 14800 6/1921 St Rollox 8/1931 Glasgow (Balornock)
957 14801 7/1921 St Rollox 3/1934 Carlisle (Kingmoor)
958 14802 7/1921 St Rollox 1/1936 Carlisle (Kingmoor)
959 14803 8/1921 St Rollox 7/1933 Perth (South)

source: BritishSteam[1]

Dimensions

Problems

The locomotives were large and visually very impressive, but they were not successful and never really got established in traffic. One author has described them as “that monumental flop of all time”, another as “ineffectual giants”.

Draughting was a problem from the beginning, and firemen had a lot of trouble keeping them up to pressure. There were other troubles thought to be a result of too small an ashpan causing choking of the grate. However, the chief problem was the failure of the unusual derived motion design. The valve gear was insufficiently robust and the valve spindle guides (originally cast iron) had to be replaced in cast steel, but this did not address the fundamental shortcomings of the design and the performance of these large locomotives remained woeful.[2]

By early 1922 management decided things could not be left alone and in April of that year No.s 957 and 958 were rebuilt to the strange arrangement of Walschaerts valve gears for the outside cylinders and Stephenson link motion for the inside one. At the same time No. 959 was given a modified version of the standard Caledonian equipment but with dashpots added to absorb stress that was thought to exist at some points. No. 956 was first given a different variation of the standard arrangement, then brought into line with No. 959, but by the end of 1922 both had been altered again, this time to the same mixed gear arrangement as 957/958. It would have been difficult to retrofit Walschaerts gear to the inside cylinder (because there would be no mounting-point for the combination lever) but it seems strange that a modified Walschaerts gear was not used. It would have been possible to add a second eccentric to drive the combination lever.

None of the changes seems to have achieved very much. Experienced locomotive engineers have expressed astonishment and disbelief at the "cacophony" that the mixed valve gear gave rise to, and many have stated that the whole idea was a disaster.

Withdrawal

Despite their larger size they were capable of no better work than the preceding 60 class (which did not have a sparkling reputation themselves), and the allocation of power class '5P' by the LMS was hardly deserved. Within a few years they had been relegated to freight traffic.[3] Being a non-standard class of only four locomotives the LMS showed no interest in rebuilding them further and they were all withdrawn between 1931 and 1935.

References

  1. ↑ "BritishSteam locomotive information". BritishSteam.com. Retrieved 2013-05-26.
  2. ↑ Atkins, C. P. (1976), The Scottish 4-6-0 Classes, Ian Allan, p.57
  3. ↑ Atkins, C. P. (1976), The Scottish 4-6-0 Classes, Ian Allan, p.58