Early in 1866 a need arose for new engine power in order to deal with the growing goods traffic between the over-ground railway at King’s Cross and the goods yards round about Farringdon Street and Blackfriars, which necessitates a large amount of tunnel work on a road having gradients of 1 in 35 and 1 in 39. Accordingly, two very powerful engines were obtained from the Avonside Engine Co., of Bristol, one of which was put to work early in the year 1866, and the other a few months later. They were numbered in the railway company’s books as Nos. 472 and 473, and No. 472 bore upon it the maker’s No. 633.
These two engines were in general design and leading dimensions almost exactly similar to two previously supplied to the Vale of Neath Railway, and were, as can be seen from Fig. 31—which is an illustration of No. 472—side-tank locomotives with eight-coupled wheels and outside cylinders.
The wheels were 4-ft. 6-in. in diameter, and were distributed over a wheel-base of 15-ft. 10-in., the spacings being 4-ft. 10-in., 5-ft. 5-in., and 5-ft. 7-in. respectively, starting from the leading end. Both leading and trailing wheels were allowed a transverse play of 5/8-in., subject to the control of an arrangement of check springs patented by Messrs. Slaughter & Caillet. The cylinders drove the third pair of wheels, as can be seen from the illustration, and they were of somewhat unusual size, having a diameter of 18 1/2-in. and a stroke of 24-in., thus allowing of the exertion of considerable tractive force — 152 lbs. for every lb. of effective steam pressure. A boiler of ample dimensions, the barrel measuring 13-ft. 8 1/2-in. in length and 4-ft. 4-in. in diameter, and containing 184 tubes each 2 1/8-in. in diameter, produced a total heating surface of 1550-1 sq. ft., of which 100 sq. ft. were contributed by the firebox and the remaining 1450.1 sq. ft. by the tubes.
It will be noted that provision was made for the condensation of steam in working through the tunnels, and that the side-tanks were of unusual size. Each engine weighed a total of 56 tons in working order, which was so equally divided over the four pairs of wheels that the load on the rails under no one wheel greatly exceeded 7 tons. Both engines were broken up in 1880.
