IMPROVEMENTS IN THE ARRANGEMENT AND COMBINATION OF HIGH AND LOW PRESSURE STEAM ENGINES
Year: 1861

page_text: PROVISIONAL SPECIFICATION left by Zerah Colburn at the Office of
the Commissioners of Patents, with his Petition, on the 27th August
1861.
I, ZERAH COLBURN, of No. 15, Tavistock Street, Bedford Square, in the
County of Middlesex, Mechanical Engineer, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN THE ARRANGEMENT AND COMBINATION
OF HIGH AND LOW PRESSURE STEAM ENGINES," to be as follows:-
Steam engines in which two or more cylinders are employed in such manner
that the steam escaping from one cylinder is discharged into another, and thus
worked twice or thrice over, so as to obtain, to a certain extent, the effect due
to its own expansion have long been known and used under the designations
of Hornblower's engines, Woolf's engines, compound engines, and high and
low pressure engines; so also two steam engines, with their working parts
entirely separated from each other, have been so arranged that the steam
discharged from one should, after flowing through a passage of greater or less
length, enter into and work the other at a lower average pressure per square
inch, the object being the same as in Hornblower's and Woolf's engines, to
wit, to secure the effect obtainable from the expansion of steam, in addition to
the force exerted upon the piston or pistons while the steam was flowing
directly from the boiler. In all the engines mentioned, the whole of the steam
worked at low pressure had been previously worked at high pressure. By the
present Invention a certain portion only, and not the whole of the steam

page_text: employed in working or driving a steam engine is to be previously worked at
a higher average pressure per square inch above the atmosphere, either in
another steam engine, or in a separate and independent additional cylinder or
cylinders of the same engine. Two facts are well known in connection with
steam, to wit, that equal weights of fuel will generate nearly equal weights of
either high or low pressure steam, and that steam on its discharge from a steam
engine retains nearly the whole of the "total heat," or combined sensible and
latent heat which it had on its admission to such engine. In cases, therefore,
where steam engines are being worked at pressures ranging from, say, five to
sixty or seventy pounds per square inch above the atmosphere, and where
more power is required with little or no sensible increase in the expenditure
of fuel (or where it is desired to have the same power with a lessened
expenditure of fuel) a part of the fuel may be applied, under suitable boilers,
to raise steam of a pressure considerably higher than that already worked, and
the high-pressure steam so raised, and which may have a pressure of from
seventy pounds to two hundred and fifty pounds, or more, per square inch is
then to be worked, either with or without expansion, in a separate engine, or
clse in a separato cylinder or cylinders to be added to the existing engine;
and this high-pressure steam, on its discharge from such separate engine or
such separate cylinder or cylinders, is to be allowed to mix with additional
steam, by preference, of a lower pressure, and the mixture is then to bo
admitted to and worked in the original or low-pressure engine or engines, in
like manner as the steam ordinarily supplied to such engines. The steam
may be exhausted from the high-pressure engine, either into the low-pressure
boiler, or into any vessel intermediate between and in direct communication
with the low-pressure boiler and low-pressure engine, or it may be exhausted
into either the slide valve box, or the cylinder of the low-pressure engine.
The portion of steam to be worked twice over may bear any ratio desired to
the whole of the steam worked in the low-pressure engine, that is to say, an
eighth, a half, or three-fourths more or less of all the steam worked in the
low-pressure engine may be previously made to pass at a higher pressure
through the high-pressure engine, or the high-pressure cylinder or cylinders
of the combined engine. The high-pressure steam may be superheated, if
desired, either before its admission to the high-pressure cylinder or after its
escape therefrom, and while on its way to mix with the steam of lower
pressure. If desired, a portion only of the steam from the high-pressure
engine or high-pressure cylinder may be permitted to mix with the low-
pressure steam, the rest of the high-pressure steam being taken up in a small
quantity of cold water, so as to heat it to a temperature equal to or greater

page_text: than that at which the water is maintained in the low-pressure boilers when at
work. The water so heated is then to be admitted as feed water to the low-
pressure boilers; in this case the portion of high-pressure steam to be
condensed into water is to be made to pass through a condensing vessel, into
which vessel is forced by a pump or any other means a regulated quantity of
water of ordinary temperature, this quantity being sufficient only to take up
as much of the steam as it is desired to condense into water, and so that the
final temperature of the condensing water shall be equal to or above the
temperature of the water in the low-pressure boilers. If one pound of water
at 50 deg. Fahrenheit be injected into one pound of steam at a sensible
temperature of 300 deg., about 1 lb. of water heated to 300 deg. will be
precipitated, and about pound of steam of the same temperature will remain.
The water at 300 deg. will then be under a pressure, from the steam rising
out of it, sufficient to force it into any boiler in which the pressure of steam
is less than that corresponding to a temperature of 300 deg., and thus no
pumps for forcing this heated water into the boiler need be used. The use of
a separate condensing vessel, as described, is to be preferred, but that portion
of the steam which it is intended to condense may be condensed after its
admission into the low-pressure boiler. It is to be understood that the terms
"condense," "condensing," and "condensed," as herein employed, do not apply
to the production of a vacuum, but only to the absorption of a part of or the
whole of any quantity of steam in such a quantity of water as shall preserve
a final temperature both of the condensing water and the remaining steam, if
any, equal to or greater than that of the water in the boilers to which such
condensing water and condensed steam are to be supplied as feed water.