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Traction Engines
is in motion the; weight upon the rim of the wheel compresses
the blocks so that those in the lowest and
adjoining cells come in contact with the road at the same
time, forming a large and continuous flat tread to the
wheel, and so increasing its adhesion on the road. On
paved streets the use of these wheels is specially advantageous,
for not only is the tractive power of the engine
enormously increased, but any possible damage to the
paving setts, caused by the chipping action of ordinary
wheels, is entirely avoided."
Respecting the compound engines it is said: "The
additional cost is not a serious one, and is very soon
repaid by the economy in fuel it ensures; for in it the
steam is used twice over, first in the high and afterwards
in the low-pressure cylinder, and is not discharged
through the exhaust until its pressure has been reduced
almost to that of the atmosphere itself. In other words,
there is more duty obtained from the steam in a compound
engine than in a single-cylinder engine for the
same expenditure of fuel. Another advantage of the
compound engine is that of its subduing the noise of
the exhaust when at work ; for perhaps in no class of
engine is silent working more essential than for a road
locomotive, seeing that their use is chiefly in towns or
on busy suburban roads. The comparative noiselessness
is due to the low pressure at which the steam is
discharged into the atmosphere."
MESSRS. CHAS. BURRELL AND SONS
I heir single-crank compound general-purpose traction
engine is illustrated by Fig. 191. The engine is mounted
on the firm's patent system of springs under the hind axle.
It will be seen that the high and low pressure cylinders
are placed diagonally one above the other in the well-
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