The Thompson A2/1 Pacifics
After the first
Thompson rebuilt Pacifics
(the A2/2s) started to appear,
Thompson designed a Pacific version of
the V2. The front of this design was
similar to the A2/2, with the bogie
in-front of the outside cylinders and a separate set of Walschaerts valve gear for the centre cylinder.
To standardise the new inside motion with that of the
A2/2s, the coupled wheelbase was
reduced.
The V2's V-shaped cab was kept, along with
the six-wheeled tender. The V2 boiler
was also kept, although the pressure was increased to 225psi. This new design was given the
designation of A2/1.
Rather than rebuilding pre-existing locomotives,
Thompson ordered the last four
V2s to be built to the A2/1 design.
These were built at Darlington, unlike the
V2s which were all built at Doncaster.
Construction of the A2/1s occurred during 1944 and was completed by January 1945.
Compared to the
V2s, the A2/1s had a number of
innovations. The firebox had a rocking grate and hopper ashpan, which greatly simplified the process
of dropping the fire and emptying the ash from the grate.
Thompson also introduced an axle-driven
alternator and electric lighting on the A2/1, which he later used on some of his other locomotive
designs.
The A2/1s were originally fitted with wing-type smoke deflectors.
After the A2/3s appeared in 1946 with
their large smoke deflectors, it was decided to replace these deflectors with the large kind.
At an early stage, the standard 6-wheeled tenders were found to be too small.
In 1945, No. 3696 was given the 8-wheeled tender
from A4 No. 4469 Sir Ralph Wedgwood
which had suffered irreparable bomb damage. The remaining three A2/1s received 8-wheeled tenders
in 1949.
The four A2/1s were split between England and Scotland, and usually worked express passenger and
express goods trains.
All four A2/1s were withdrawn between August 1960 and February 1961.
Technical Details
| Cylinders (x3): |
|
19x26in. |
| Motion: |
Outside: |
Walschaerts |
|
Inside: |
Walschaerts |
| Piston Valves: |
|
10in. diameter |
| Boiler: |
Max. Diameter: |
6ft 5in |
|
Pressure: |
225psi |
|
Diagram No.: |
109 |
| Heating Surface: |
Total: |
3110.74 sq.ft. |
|
Firebox: |
215 sq.ft. |
|
Superheater: |
679.67 sq.ft. |
|
Tubes: |
1211.57 sq.ft. (121x 2.25in) |
|
Flues: |
1004.5 sq.ft. (43x 5.25in) |
| Grate Area: |
|
41.25 sq.ft. |
| Wheels: |
Leading: |
3ft 2in |
|
Coupled: |
6ft 2in |
|
Trailing: |
3ft 8in |
| Tractive Effort: |
36,387lb |
(@ 85% boiler pressure) |
| Wheelbase: |
Total: |
61ft 9.6in |
|
Engine: |
36ft 8in |
|
Tender: |
16ft |
| Weight (full): |
Total: |
158 tons 7cwt |
|
Engine: |
98 tons 0cwt |
|
Tender: |
60 tons 7cwt |
| Max. Axle Load: |
|
22 tons |
| Water Capacity: |
|
5000 gallons |
| Coal Capacity: |
|
9 tons |
Preservation
The last A2/1 was withdrawn in 1961, and none survived into preservation.
Models
Apple Green Engines produce a ready-to-run model of the A2/1
in 4mm scale. PDK, Nucast, and DJH also produce 4mm scale kits of the A2/1. Crownline have produced a 4mm kit in
the past, but this is no longer available.
Locomotives
Acknowledgements
Thank you to the P.H. Groom collection for permission to use the above photograph of BR No. 60509 Waverley.
Thank you to Malcolm Peirson for the above picture of No. 3698 with small wing smoke deflectors.
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