LNWR Precursor Tank Class

LNWR Precursor Tank
No. 528 in photographic grey livery
Type and origin Power type Steam Designer George Whale Serial number 4560–4599, 4820–4829 Build date 1906–1909 Total produced 50
Specifications Configuration: ​  • Whyte 4-4-2T  • UIC 2′B1 2t Gauge 4 ft 8+1⁄2 in (1,435 mm) Leading dia. First 30: 3 ft 9 in (1.143 m) Last 20: 3 ft 3 in (0.991 m) Driver dia. 6 ft 3 in (1.905 m) Trailing dia. First 30: 3 ft 9 in (1.143 m) Last 20: 3 ft 3 in (0.991 m) Loco weight 74 long tons 15 cwt (167,400 lb or 75.9 t) Boiler pressure 175 psi (1.21 MPa) Cylinders Two, inside Cylinder size 19 in × 26 in (483 mm × 660 mm) Valve gear Joy
Performance figures Tractive effort 15,216 lbf (67.68 kN)
Career Operators LNWR » LMS Power class LMS: 2P Withdrawn 1927–1940 Disposition All scrapped

The London and North Western Railway (LNWR) "Precursor Tank" Class was a type of 4-4-2 tank steam locomotive. Fifty were built to the design of George Whale between May 1906 and April 1909, being a tank engine version of his "Precursor" Class.

Chronologically, the class was constructed three distinct blocks, from May to September 1906 (works nos. 4560–4589), March to April 1907 (4590–4599), and March to April 1909 (4820–4829). The first 30 locomotives had 3 ft 9 in (1.143 m) carrying wheels, but the size of these was reduced to 3 ft 3 in (0.991 m) thereafter.

The LNWR reused numbers from withdrawn locomotives, so the numbering system was completely haphazard. The 3 ft 9 in engines were numbered by 528, 531, 784, 1295, 1305, 1981–1985, 97, 111, 181, 196, 562, 616, 803, 1356, 1508, 2210, 139, 653, 834, 874, 1506, 1572, 1589, 1671, 1714, and 2165. The 3 ft 3 in engines were numbered 44, 527, 612, 762, 827, 875, 1427, 1764, 2196, 2446, 920, 935, 1164, 1219, 1523, 1536, 1551, 2077, 2223 and 2228.

All fifty passed into LMS ownership in 1923. The LMS gave them the power classification 2P. The LMS also renumbered them into solid block of numbers: 6780–6809 for the 3 ft 9 in engines and 6810–6829 for the 3 ft 3 in engines, in the order given above.

Due to their weight, the Precursor Tanks were unable to operate on some branch lines, but had primarily been designed for use on heavy suburban trains. In 1921, they were reported as being employed to the near-total exclusion of other locomotive types on local services between Watford and London Euston, as well as on other routes.

One member of the class was withdrawn in October 1927, and the others between December 1931 and February 1940. None were preserved.

References

Sources

• Casserley, H. C. & Johnston, Stuart W. (1974) [1966]. Locomotives at the Grouping 3: London, Midland and Scottish Railway. Shepperton, Surrey: Ian Allan. p. 77. ISBN 0-7110-0554-0.