Thompson A2/1 Pacifics
Posted: Sun Jan 24, 2021 1:03 pm
The London and North Eastern Railway (LNER) Thompson Class A2/1 was a class of 4-6-2 steam locomotives built at Darlington locomotive works during 1944. They were originally ordered as Class V2 locomotives, as designed by Sir Nigel Gresley, but were revised during construction into a 4-6-2 'Pacific' arrangement under the instruction of Edward Thompson.
At the time Edward Thompson succeeded Sir Nigel Gresley as Chief Mechanical Engineer of the LNER in April 1941, Darlington works was busy building Class V2 mixed traffic locomotives. Although the V2 class were competent and powerful locomotives, Thompson did not like this design as it required more servicing than his own mixed traffic B1 class 4-6-0. He also envisaged a time when the V2s would be replaced by his own design of 'Pacific' locomotives, but would not receive authority to build a new class during the war. He therefore decided to build the final four V2 already authorised as experimental 'Pacific' locomotives along similar lines to his recently rebuilt A2/2 class. The revised design was authorised in August 1943 and the new locomotives built between May 1944 and January 1945
The pony truck of the V2 class was replaced by Thompson's own design of bogie and they had an extended smokebox. They retained the same boiler as the V2 class although the pressure was increased to 225psi, giving an increased tractive effort of 36,390 lbf (161.87 kN). The firebox was also the same as the V2 although these were the first LNER locomotives to be fitted with a rocking grate and ashpan. Rather than have all three cylinders driving a single axle Thompson adopted divided drive with the middle cylinder driving the first pair of driving wheels and the outside cylinders the middle pair. Thompson also abandoned the Gresley conjugated valve gear and instead fitted independent sets of Walschaerts valve gear to each cylinder. The four locomotives of this design performed adequately but proved to be under-boilered for their size and lacked adhesion. They were less problematic than the A2/2 class, but did not distinguish themselves.
Quite a large collection of over 35 photos
Starting with this photo of
60509 Waverley near Edinburgh Waverley station
https://tinyurl.com/y2yh7qmp
LNER era starts here
509 still unnamed and minus smoke deflectors
https://tinyurl.com/y5py6x4r
B.R. era starts here
60507 Highland Chieftain Haymarket June 1958
https://tinyurl.com/y2xn8ssb
Neil.
https://tinyurl.com/y2yh7qmp
At the time Edward Thompson succeeded Sir Nigel Gresley as Chief Mechanical Engineer of the LNER in April 1941, Darlington works was busy building Class V2 mixed traffic locomotives. Although the V2 class were competent and powerful locomotives, Thompson did not like this design as it required more servicing than his own mixed traffic B1 class 4-6-0. He also envisaged a time when the V2s would be replaced by his own design of 'Pacific' locomotives, but would not receive authority to build a new class during the war. He therefore decided to build the final four V2 already authorised as experimental 'Pacific' locomotives along similar lines to his recently rebuilt A2/2 class. The revised design was authorised in August 1943 and the new locomotives built between May 1944 and January 1945
The pony truck of the V2 class was replaced by Thompson's own design of bogie and they had an extended smokebox. They retained the same boiler as the V2 class although the pressure was increased to 225psi, giving an increased tractive effort of 36,390 lbf (161.87 kN). The firebox was also the same as the V2 although these were the first LNER locomotives to be fitted with a rocking grate and ashpan. Rather than have all three cylinders driving a single axle Thompson adopted divided drive with the middle cylinder driving the first pair of driving wheels and the outside cylinders the middle pair. Thompson also abandoned the Gresley conjugated valve gear and instead fitted independent sets of Walschaerts valve gear to each cylinder. The four locomotives of this design performed adequately but proved to be under-boilered for their size and lacked adhesion. They were less problematic than the A2/2 class, but did not distinguish themselves.
Quite a large collection of over 35 photos
Starting with this photo of
60509 Waverley near Edinburgh Waverley station
https://tinyurl.com/y2yh7qmp
LNER era starts here
509 still unnamed and minus smoke deflectors
https://tinyurl.com/y5py6x4r
B.R. era starts here
60507 Highland Chieftain Haymarket June 1958
https://tinyurl.com/y2xn8ssb
Neil.
https://tinyurl.com/y2yh7qmp