So far, Mr. Ivatt had not designed any locomotives for the express passenger traffic of the line, his coupled engines of the No. 400 class being intended for general work which might include express passenger service, but equally comprised express goods and special traffic. About the middle of 1898, however, he produced from the Doncaster Works a passenger express locomotive of a type novel in this country, and far exceeding in power and capacity any engine so far built for the G.N.R.
This engine, No. 990, of which the accompanying illustration, Fig. 93, shows the external characteristics, had, as can be seen, outside cylinders and two pairs of coupled driving wheels, with a four-wheeled bogie at the leading end and small pair of trailing wheels under the back end of the firebox, thus embodying the general characteristics of what is now generally known as the ” Atlantic ” type. The cylinders, which were placed at a slight inclination, were 18 3/4-in. in diameter, with a stroke of 24-in., with their centre lines distant transversely to the extent of 6-ft. 5 1/2-in., and they drove the second pair of coupled wheels by means of connecting rods having the somewhat unusual length of 10-ft. between centres. The steam ports measured 1 /2-in. by 16-in.,and the exhaust ports 3 1/2-in. by 16-in., and the valves had an extreme range of travel of 4 1/2-in.
The coupled wheels had a diameter on the tread of 6-ft. 7 1/2-in., and were placed with their centres 6-ft. 10-in. apart, and the distance of the centre of the trailing axle from the centre of the driving axle was 8-ft., thus giving a total rigid wheel-base of 14-ft. 10-in. In reality, however, the rigid wheel-base is restricted to the distance between the coupled axles, as there is allowance made for lateral play in the trailing-wheel axle-boxes.
The bogie was of standard design, having four wheels each of 3-ft. 7 1/2-in. diameter spread over a wheel-base of 6-ft. 3-in., with the bogie pin 1/2-in. to the rear of the centre, and the second pair of bogie wheels was in advance of the leading pair of coupled wheels to the extent of 5-ft. 3-in. centre to centre, the total wheel-base being 26-ft. 4-in. The single inside frame plates measured 33-ft. of-in., having an overhang of 2-ft. 3-in. and 4-ft. 3 1/2-in. at leading and trailing ends respectively.
It will be noted that the trailing axle has outside bearings in a supplementary outside frame plate, thereby ensuring a greater transverse space for the firebox. Apart from the foregoing, a large degree of interest was centred in the boiler, which was of exceptional pattern and dimensions.
The barrel, which was pitched with its centre line 7-ft. 11 -in. above the rail level, measured 14-ft. 8 5/8-in. in length, with a diameter outside the smallest ring of 4-ft. 8-in. This extreme length, however, was not utilized exclusively for tube heating surface, as the leading end of the barrel was recessed to the amount of 1-ft. 11 1/4-in., so as to provide an extension of the smokebox capacity, and this arrangement curtailed the length of the tubes to 13 -ft. between the end plates. The tubes were 191 in number, and were of an outside diameter of 2-in. The firebox casing had a length of 8-ft. and a depth below the centre line of the boiler of 5-ft. 6-in. in front, and 5-ft. at back, and these ample measurements allowed of the use of a firebox having the very generous heating surface of 140 sq. ft., and with a grate area of 26.75 sq. ft. The total heating surface equalled 1,442 sq. ft., the tubes contributing 1,302 sq. ft., and a working pressure of 175 lbs. per sq. in. was provided.
It is obvious that a still larger nominal heating surface could have been obtained by reducing the diameter of the tubes and increasing their number, but this would be in opposition to Mr. Ivatt’s theory and practice.
In full working order the engine weighed 58 tons, distributed as follows: bogie wheels 15 tons, first pair of coupled wheels 15 tons, driving wheels 16 tons, and trailing wheels 12 tons.
An unusually large tender was provided, having a capacity for 3,670 gallons of water and 5 tons of coal, and weighing 40 tons 18 cwt. when thus loaded, the total weight of engine and tender being 98 tons 18 cwt.
This engine, which has recently been honored by receiving the name ” Henry Oakley,” was given the running No. 990, its works number being No. 769, and it has proved so successful that ten new engines have been built of practically similar design and dimensions. It may be interesting to note that in these big engines Mr. Ivatt has placed the regulator in the steam dome, and has reverted from the standard G. N. R. push and pull handle to the two-armed pattern moving across the back of the firebox in a sector plate.
In the meantime there were completed at Doncaster a series of the new engines of the smaller Atlantic, or ” 990 “class. They differed from their original in having the frames so shaped as to allow of them being fitted with the larger boilers if necessity arose, and they also had the duplicate (four-column) Ramsbottom safety valves which subsequently were fitted to all the Atlantic class, large and small. The dates and numbers of these new engines were : —
|Date.||Doncaster No.||Engine No.||Date.||Doncaster No.||Engine No.|
After exhaustive trials of the large ten-wheel passenger engine, No. 990, it was decided to place more locomotives of the same class upon the road. These later engines were generally, in so far as their main dimensions were concerned, exactly similar to their prototype.
The chief external points of difference lay in such details as an alteration of the framing at the leading end and a modification of the sanding arrangements. The steam Sander delivered the sand under the driving or second pair of coupled wheels from boxes placed between the frames midway between the coupled axles, while the boxes and pipes used in running backwards were, in most cases, done away with. These engines also are fitted with a novel arrangement for locking the reversing gear in any desired position, consisting of a friction lock on the reversing shaft which is actuated by vacuum.
The accompanying illustration. Fig. 104, showing No. 989 with its tender, also marks a slight modification adopted in the latter, the brake- blocks being applied at the front of the tender wheels instead of at the back, as had previously been the practice. Altogether, in addition to No. 990, ten engines of this class have so far been built, with the following numbers : —
|Date.||Doncaster No.||Engine No.|
A few years ago almost every locomotive superintendent of note designed a four-cylinder high-pressure engine for express traffic, more or less as a protest against the introduction of the compound system, and in 1902 Mr. Ivatt built an engine, No. 271 (Doncaster No. 974), which is shown in the accompanying illustration. Fig. 107. It will be seen that No. 271 bears a resemblance to No. 990, in that it has a leading bogie, four-coupled wheels and a small pair of trailing wheels.
No. 271 is, however, provided with four cylinders, two outside the frames and two inside, placed in line. These cylinders are each 15-in. in diameter, with a stroke of 20-in., and drive direct on the first pair of coupled wheels, with connecting rods 5-ft. 9 3/4 -in. long, the distance from centre of cylinders to centre of driving axle being 9-ft. 3-in.
The bogie and trailing wheels are each 3-ft. 7 1/2-in. in diameter, while the four-coupled wheels are 6-ft. 7 1/2-in. in diameter, and are placed with their centres 6-ft. 10 1/2-in. apart, the total wheel-base being 26-ft. 9-in., of which the bogie-wheel centres account for 6-ft. 3-in., and the distance of the trailing wheels from the rearmost coupled axle accounts for 7-ft. 6-in. Over all, the frame-plates measure 33-ft. 7 1/4-in., the overhang being 2-ft. 5-in. and 4-ft. 5 1/4-in. at leading and trailing ends respectively.
The original boiler, with its centre 8-ft. 1-in. above the rails, had a barrel 15-ft. 4 1/4-in. long, with a diameter outside the smallest, or middle ring, of 4-ft. 6 7/8-in. The smokebox had a length externally of 3-ft. 3 1/4-in., and it was extended within the boiler barrel, but not to the same degree as in the ” 990 ” class, the distance between tube plates being 14-ft. The tubes were only 141 in number, 2 1/4-in. in diameter. The firebox casing measured 8-ft. 1- length, with a breadth at the bottom of 4-ft. 0 1/2-in., giving a heating surface of 140 1/4 sq. ft., to which was to be added the tube surface of 1,162 3/4 sq. ft., making a total of 1,303 sq. ft. The grate area was 24 1/2 sq. ft. Duplex safety valves were fitted, pressed to blow off at 175-lb. per sq, in.
In its original state this engine weighed 58 tons 15 cwt., divided as follows : bogie 15 tons 10 cwt., driving wheels 17 tons, coupled wheels 15 tons 15 cwt., and trailing wheels 10 tons 10 cwt. ; and the tender was of the smaller kind, fitted with water pick-up apparatus, weighing in working order only 38 tons 10 cwt. In 1904, No. 271 was fitted with the Walschaerts valve gear, and towards the close of 1908 was again overhauled and a boiler of the standard 990 class fitted, having a total heating surface of 1442 sq. ft.