IMPROVEMENTS IN STEAM ENGINES
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by James Shaw at the Office of the Com-
missioners of Patents on the 18th March 1876.
JAMES SHAW, of Ovenden, near Halifax, in the County of York, Manufacturer.
"IMPROVEMENTS IN STEAM ENGINES."
This Invention relates to the class of engines known as compound engines.
The object of the Invention is to produce a vacuum in all the cylinders alike, and
to dispense with the back pressure which has hitherto existed in the high-pressure
cylinders of compound engines heretofore employed. Now, my present improve-
ments consist in dispensing entirely with the ordinary slide valve which has
heretofore been employed in the low-pressure cylinder, and, instead of the said
slide valve, I make a port of suitable dimensions at one end of the cylinder if one
high-pressure cylinder be employed, and one at each end of the said low-pressure
cylinder if more than one high-pressure cylinder be employed; and I place a
revolving valve intermediate or between the high and the low pressure cylinders,
and this valve receives its motion by means of gear wheels driven from the fly-
wheel shaft, and the action of the same is as follows:-
Suppose there is a full exhaust port presented from the high-pressure cylinder,
there is a direct thoroughfare, opening, or passage for the steam to escape to the
low-pressure cylinder, and at such time the valve by its revolving has closed the
exhaust opening (which is within the valve), by which the residue steam from
the low-pressure cylinder is conveyed to the condenser, and when the time for
exhausting from the low-pressure cylinder has arrived, the valve has revolved the
required distance and presents an open port or passage for the exit of the residue
steam to the condenser. The passage from the high-pressure to the low-pressure
cylinder always remains open. The steam chest of the high-pressure cylinder I
place at one end, and at the time that steam is admitted to the high-pressure
cylinder for propelling or actuating the piston, the exhaust port is closed or shut in
the said high-pressure cylinder, and the steam only propels or actuates the piston
one way; when the piston has arrived at its furthest extent the exhaust port is
opened, and part of the steam rushes through the thoroughfare or passage before
alluded to in the revolving valve to the low-pressure cylinder and part passes
through a thoroughfare constructed on the said high-pressure cylinder to the back
of the piston, thereby causing an equal or thereabout amount of steam on both
sides of the said piston, which destroys entirely the back pressure which is found
to exist in high-pressure cylinders heretofore employed. When the said high-
[Price 2d1

page_text: pressure piston has travelled back again, or has arrived at what I may term the
starting point, the steam which was contained in the cylinder is used up by
expansion and by giving off its force to the low-pressure cylinder, and at such time
the low-pressure cylinder begins to exhaust to the condenser, and a vacuum is
formed in both high and low-pressure cylinders alike and at the same time.
The said revolving valve I construct within a casing, and I make it taper by
preference, and construct it in such a manner that a portion extends below the
casing, and upon this I place a bevel wheel for operating the same, as before
described, and the bottom of this portion rests and revolves in an adjustable step;
and I employ a spindle, whereby I can adjust the amount of pressure on the step
or bearing surface of the revolving portion of the valve, so that whatever amount
of pressure of steam is caused to bear on the revolving portion of the said valve in
passing from one cylinder to the other, the valve can be made to revolve quite
easily and freely.
By my construction of the low-pressure cylinder and revolving valve, and the
arrangement of the same with the high-pressure cylinder, the steam in passing
from one to the other expands only about one twelfth, whereas in the ordinary
compound engines it expands a considerable greater amount. I propose to admit
the exhaust steam in at the bottom of the low-pressure cylinder in horizontal
engines, so that the condensed steam or any water which may be contained within
the said cylinder, upon the action of the piston will be conveyed at once through
the exhaust opening of the revolving valve.
It will be obvious to engineers that I am enabled to place the high and low-
pressure cylinders side by side or in a direct line with each other, as may be
convenient or as required, without departing from the main features of my
Invention.