The Locomotive - Lighthouse Survival Blog

1001.] THE LOCOMOTIVE. |Q9
counts of long voyages, covering several thousand miles, of which records were kept of
the amount of coal burned when the engines were worked with superheated steam, and
of corresponding voyages using steam without superheating.
In the first volume of his Researches, Chief Engineer Isherwood discusses this matter
quite carefully and draws the general conclusion that, while great economy is doubtless
to be obtained by using superheated steam in engines, the extra bulk and weight of the
apparatus required to produce the superheat, and the liability of the same to destruc-
tion, but more especially the bad effects of superheated steam on the interior working
parts of the cylinders and valves of the engines, chiefly due to the destruction of the
lubricating oils before they have had a chance to perform their work, constituted real
difficulties which rendered the use of superheated steam at that time undesirable. In
spite of this carefully considered condemnation, and Isherwood's apparent attempt to
dismiss the subject as being the wrong line to pursue in steam engine development, the
question of superheating seems to have continued to attract wide attention. The saving
in the coal pile was too great to be ignored, and engine constructors and owners were
tempted by the reduction in operating expenses to take the risk of inefficient lubrication
and the other attendant difficulties, and so much progress was evidently made that we
find in Isherwood's second volume of Experimental Researches, issued only two years
later, even more attention devoted to superheating than before, and with quite different
conclusions. In fact, superheating is here distinctly recommended, and the statement is
made that an average gain in work done of about 33 per cent, may be counted upon.
He recommends the steam to be superheated not more than 135 degrees Fahr. and sug-
gests 100 degrees as an average which it is safe to assume, because of the inability of
the oil to stand a higher temperature without destruction.
The primitive form of the engine, the inefficient insulating covering, and the low
pressure used at that time were conditions which undoubtedly lent themselves to making
the use of superheated steam exceedingly advantageous, and the difficulties of lubrica-
tion, packing of stuffing boxes, etc., must have been found to be very great in order to
cause this practice to be discontinued for so long a time, as it undoubtedly was. At
the same time the compounding of steam cylinders, the introduction of condensers, the
improvement in valve gear and general construction, the increase of steam pressures, and
other radical improvements, were so rapidly brought into general use that the amount
of work done per unit of steam was raised to a higher point than ever before, in spite of
the drawbacks of moist steam.
As the superheater was lost sight of, the improvements which were being adopted
in other directions were of such a nature as to diminish its importance. Let us examine
these improvements to the steam engine. Have they in any way interfered with it as a
user of superheated steam ? On the contrary, we find the steam engine of the present
day much more suited to the use of superheated steam than formerly. We now have
mineral oils which will stand high temperatures without disintegration; we have stuffing
boxes packed with metallic packing; we have cylinders and steam pipes covered with a
much more efficient insulating material ; we have the wearing surfaces of cylinders and
pistons machined to a nicety, and the interior surfaces often highly polished; we have
improved forms of balanced and steam-tight valves, and these with our present search-
ing after every device to make the engine more economical seem to open a field for the
superheater to an almost unlimited degree.
In Europe we find much encouragement in this belief. We Americans have char-
acteristically developed the line following the path of least resistance, practically ignor-
ing the question which had seemed to be set aside. Europeans, however, particularly