Following the totally new departure in locomotive design [that is the Ivatt Atlantic], Mr. Ivatt brought out an enlarged pattern of the eight-wheeled bogie passenger locomotive, its principal features of difference from the No. 400 class being in respect to the use of a larger boiler and firebox, this latter causing a greater length of wheel-base between the coupled axles, while the larger boiler, pitched at a higher level from the rails, produced a return to the “built-up” form of chimney in place of the standard cast-iron pattern which had been in vogue during the later yearsof Mr. Stirling’s rule at Doncaster. These features of resemblance and difference are indicated in the accompanying illustration, Fig. 96, which shows No. 1321, the first of the class.
Five engines were built at Doncaster of this modified type with the following numbers : —
|Date.||Doncaster Nos.||Engine Nos.|
The leading dimensions were : cylinders 17 1/2-in. by 26-in.; diameter of bogie wheels 3-ft. 7 1/2-in., and of coupled wheels 6-ft. 7 1/2-in.; wheel-base: bogie 6-ft. 3-in., divided unequally; bogie pin to driving axle, centre to centre 9-ft. 9-in.; coupled axles, centre to centre 9-ft.; total wheel-base 22-ft ; length of frame plates 28-ft. 1-in., with an overhang of 2-ft. 5-in and 3-ft. 8-in. at leading and trailing ends respectively.
The boiler had a length of barrel of 10-ft. 1-in., its centre line being pitched 7-ft. 11-in. above the rail level, and was formed of two rings, that nearest the smokebox having an outside diameter of 4-ft. 9 1/8-in., while the second ring, which lapped inside the first ring and the firebox covering, had an outside diameter of 4-ft. 8-in. The smokebox measured 2-ft. 10 1/4-in. long outside and the firebox casing was 6-ft. 4-in. long. Inside the boiler barrel were 238 tubes, each 10-ft. 4 3/8-in. long, with an outside diameter of 1 3/4-in.
The heating surface was: firebox 119.9 sq. ft., tubes 1,129.9 sq. ft., total 1,249.8 sq. ft., the grate area being 20.8 sq. ft. The safety valves were pressed to 170 lbs. per sq. in.
In working order engines of this class weighed 47 tons 10 cwt., distributed as follows: bogie 16 tons 10 cwt., driving wheels 17 tons, and trailing wheels 14 tons. A standard tender, weighing 40 tons 18 cwt., with its full complement of fuel and water, was provided.