IMPROVEMENTS IN STEAM ENGINES
Year: 1875

page_text: PROVISIONAL SPECIFICATION left by Edmund Edwards at the Office
of the Commissioners of Patents, with his Petition, on the 1st June
1875.
I, EDMUND EDWARDS, of 38, Southamption Buildings, Chancery
Lane, in the County of Middlesex, Engineer and Patent Agent, do
hereby declare the nature of the said Invention for "IMPROVEMENTS
IN STEAM ENGINES," to be as follows:―
This Invention consists in improved methods of constructing and
arranging steam engines, by which improved methods great economy is
obtained in the space occupied and in the cost of making such engines,
the several parts being more simple, fewer in number, lighter, and more
easily made and put together than in such engines as ordinarily heretofore
constructed and used. It is more especially applicable to engines used
for driving the screw propellor in small boats, such as ships' launches
and river steamers, but it may also be applied to other purposes.
I make the frame which carries the engines consist of a plate bent to fit
or approximately fit the bottom of the boat in transverse section. This
plate is of sufficient length to contain the engines, and it has angle irons

page_text: formed on or rivetted to its front and back edges, and a transverse plate
of corresponding shape is fixed to these angle irons at each end. The
back transverse plate is preferably rivetted, whilst the front is screwed
In the
or bolted to the angle irons so that it can readily be removed.
lower part of the back transverse plate I make an opening into which is
fitted and rivetted or screwed a bush or bearing which is bored out to
receive the front end of the screw propellor shaft which revolves in it.
The upper part of the front and back transverse plates have each two
corresponding openings formed in them, in which are rivetted or screwed
bushes or bearings which receive the trunnions of two oscillating
cylinders, which are arranged to work at right angles to each other,
being parallel to one of the sides of the plate first described which forms
the frame of the engines.
each
The trunnions upon the cylinders are made of very large diameter, so
that stuffing boxes formed for the steam pipes in their outer ends may
pass through the bushes or bearings in which the trunnions work
without its being necessary to make the bearings in two parts, and also
so that there is very little wear of the trunnions and bushes. I form the
trunnions through which the steam is admitted to each cylinder, not
upon the cylinder itself, but upon the outside of the steam chest which
is bolted or screwed sufficiently firmly to the face of the cylinder, and I
make the exhaust steam pass to the opposite trunnion by means of a
belt round each side of the cylinder, which is thus perfectly balanced
and at the same time of less weight than usual, as the valve can be
driven directly from the main shaft with the intervention of links or
levers.
I make the two cylinders precisely alike, and each containing a piston
and piston rod passing through a stuffing box in a cylinder cover, and I
connect the outer end of both piston rods to the same crank pin which
drives a crank fixed to or preferably formed upon the front end of the
screw propellor shaft. Each piston rod is connected to the crank pin by
means of a plain bush or eye fixed to the end of the rod, and one of
these bushes is made double or forked, so that its parts fit and work
upon the crank pin outside the other, which is single, the crank pin being
made long enough for the purpose, and by this method of arrangement
great simplicity of construction is attained.
In order to drive the valves of the cylinders described I make a
stuffing box for the spindle of the slide valve in the usual way at the

page_text: end of each steam chest, but I make it at the upper or outer end of the
latter. And I make the bush or bearing which carries the front end of
the main shaft as first described of sufficient length to project as far as
the back of the crank, and thus to afford a bearing of great length and
strength, and I make the outer circumference of the bush so projecting
truly circular so that an excentric fitted upon it can revolve freely, but
accurately.
I use one excentric to drive the valves of both cylinders, and I make
a suitable projection upon its front side which is carried round by one of
the sides of the crank in the revolution of the latter, the projection
being of such shape and size that when it is desired to reverse the
engines the opposite side of the crank strikes the other end of the
projection at the proper time and carries round the excentric in the
opposite direction. A hand wheel may be fitted upon the main shaft in
order to start or reverse the engines; or toothed or friction wheels and
gear may be connected to it for the same purpose; or a shaft carrying a
crank which fits loosely upon the end of the crank pin may be fitted so
as to revolve in a bush opposite that in which the main shaft works as
already described, and may carry a hand wheel instead of the latter.
The excentric is made sufficiently wide on its edge to receive the rings
or straps of two excentric rods, which I make solid instead of in two
halves, and upon the top edge of each strap is formed or attached the
end of the excentric rod, which thence passes over the side of the steam
chest (at a sufficient distance to allow the latter to oscillate), and is then
bent down and jointed to the outer end of the valve spindle already
described.
Sometimes, instead of using two excentric straps as described, I use
only one, and I joint to a suitable point in it the rod which drives the
valve of the second cylinder, and sometimes I use two fixed excentrics
and four straps and rods, to which are connected expansion links
constructed in the method well understood, by which the engines may
be reversed when necessary.
The pipes by which steam is admitted to the cylinders through the
stuffing boxes in the trunnions upon the steam chests, as already
described, are connected to a central pipe fixed to the transverse plates
and preferably passing through the latter and thence to the boiler, and
a loose cover is arranged fitted over the top of the frame of the engine

page_text: so that they are entirely enclosed and preserved from dust. The exhaust
steam is conducted to the chimney of the boiler through pipes fitted to
the stuffing boxes in the trunnions at the front of the cylinders.
The screw propeller shaft may be a continuation of the engine shaft,
but I prefer to make it separate though in the same line as the latter,
the two being connected together by a coupling or joint which will
allow a certain amount of variation without throwing any great strain
upon the engine shaft, the propellor shaft being provided with suitable
bearings in the ordinary way to take the thrust of the screw when in
motion. By unscrewing the front transverse plate the engines can be
taken to pieces in a few minutes.
A feed pump may be arranged driven by the engine shaft or propellor
shaft to supply the boiler, but I prefer to use for this purpose one of the
forms of injector as ordinarily constructed and used.