On the other hand, inside cylinders are
well secured, protected, and kept hot in the smoke-box, thus minimizing
the condensation of steam. The steam ports are short, and the engine runs
steadier at high speeds, while with Joy's valve gear much larger cylinders
can be got in than with the link motion. Thus modern improvements have
minimized the advantages of the outside class.
The passenger engines for the fast traffic are of two types, the six-wheel
engines with 7 ft. coupled wheels, and the new bogie engines which are
being built to replace them. The former have 17 in. cylinders with 22 in.
stroke, and a pair of coupled wheels 7 ft. in diameter, the leading wheels
being 4 ft. diameter, and the wheel base 14 ft. 3 in. The grate area is
16.1 square feet, and the heating surface 1,141 square feet. The total
weight in working order is 33 tons. The chief peculiarity of this type of
engine consists in the boiler, which is fitted with a combustion chamber
stocked with perforated bricks, the tubes being only 5 ft. 4 in. long.
These engines are very expensive to build and maintain, owing to the
complicated character of the boiler and fire-box, but as a coal burning
engine there is no doubt the class was very efficient, but no more are
being built, and a new type has been substituted.
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