The locomotives had outside cylinders with inside valves and inside Stephenson valve gear. There were two variants:
Q1/1 (69925-69928) with 1,500-imperial-gallon (6,800L; 1,800USgal) tanks
Q1/2 (69929-69937) with 2,000-imperial-gallon (9,100L; 2,400USgal) tanks
The extra 500 imperial gallons (2,300L; 600USgal) of water in the Q1/2 was carried in the rear tank, under the coal bunker, resulting in a reduced coal capacity.
Withdrawal
All the Class Q1 locomotives were withdrawn and scrapped from 1954 to 1959.
References
↑Ian Allan ABC of British Railways Locomotives, part 4 (1948ed.). p.56. ISBN978-0-7110-0401-6.