er of the smoke-box. The boiler is the same as that in the
standard type of engine, but the wheel base is 17 ft. 7 in., and in order
to allow it to traverse curves easily, the front axle is fitted with a
radial axle-box, which is in one casting from journal to journal, and
fitted at each end with brass steps for the bearings; the box is radial,
struck from the center of the rigid wheel base, and the horn plates are
curved to suit the box, the lateral motion being controlled by strong
springs. Another peculiarity of this engine is that, instead of the
ordinary link motion, it is fitted with Joy's valve gear, which is now
being more and more adopted. This gear--which is of a most ingenious
decription--dispenses altogether with eccentrics, and so allows the inside
bearings to be much increased, those on these engines being 131/2 in. long;
and it is also claimed for it that it is simpler and less costly, weighs
less, and is more correct in its action than the ordinary link motion; the
friction is less, the working parts are simplified, it takes less oil,
and is well under the driver's eye. It also allows larger cylinders to be
got in between the frames of inside cylinder engines, as, the slide valves
may be placed on the top or bottom of the cylinders. This latter advantage
is a great one, as, with the ordinary link motion, large cylinders are
exceedingly difficult to design so as to get the requisite clear exhaust.
The action of the gear is as follows: A rod, a, is fixed by a pin at b, on
which it is free to turn, and is attached to a rod, c, at d, the other end
of which link is fastened to the connecting rod at e. At the point, f, in
this rod another lever, g, is connected to it, the upper end of which is
coupled to the valve rod, h, at i, and just below this point a second
connection is made to a block at j, sliding in a short curved piece, k.
The inclination of the block, k, governs the travel of the valve. The
total weight of the engine in working order is: On the leading wheels, 10
tons 8 cwt.; front drivers, 14 tons 4 cwt.; rear drivers, 13 tons 10 cwt.;
total, 37.75 tons. The tender weighs 25 tons in full working order. The
boiler pressure is 150 lb., and the usual point of cut-off in the high
pressure cylinders, when running at speed, is half-stroke, while the
pressure of steam admitted to the large cylinder is never to exceed 75 lb.
per square inch. The average consumption of coal between London and Crewe
is 26.6 lb.