Nowadays there are, as we know, modifications
of Sir William Fairbairn's bands, but by means of his bands, or by
modifications thereof, all internally flued boilers are so
strengthened that the risk of a collapse of the flue is at an end.
Boilers of this kind are well calculated to furnish--and commonly do
furnish--steam of from 40 lb. to 80 lb. pressure above atmosphere.
The piston speed is now very generally 400 feet or more, so that,
notwithstanding that there is usually a liberal expansion, the mean
pressure upon the piston is increased, and this, coupled with its
increased speed, enables much more power to be obtained from a given
size of cylinder than was formerly obtainable. The revolutions of the
engine now are as many as from 60 to 200 per minute, and thus, with
far lighter fly-wheels, uniformity of rotation is much more nearly
attained.
THE EVAPORATIVE CONDENSER.
Moreover, all the parts of the engine are self-contained; they no
longer depend upon the foundation, and in many cases the condensing is
effected either by surface condensers, or, where there is not
sufficient water, the condensation is, in a few instances, effected by
the evaporative condenser--a condenser which, I am sorry to say, is
not generally known, and is therefore but seldom used, although its
existence has been nearly as long as that of the association.
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