IMPROVEMENTS IN THE CONSTRUCTION OF STEAM ENGINES
Year: 1875

page_text: LETTERS PATENT to Joshua Greenwood, of Manchester, in the County
of Lancaster, for the Invention of "IMPROVEMENTS IN THE CONSTRUCTION
OF STEAM ENGINES."
Sealed the 21st May 1875, and dated the 1st April 1875.
PROVISIONAL SPECIFICATION left by the said Joshua Greenwood at
the Office of the Commissioners of Patents, with his Petition, on
the 1st April 1875.
I, JOSHUA GREENWOOD, of Manchester, in the County of Lancaster,
do hereby declare the nature of the said Invention for "IMPROVEMENTS
IN THE CONSTRUCTION OF STEAM ENGINES," to be as follows:-
This Invention relates to the construction of an improved valve motion
for steam engines whereby the steam can be worked expansively and
cut off at any desired portion of the stroke of the piston.
The valve box is cylindrical, and the valve facing is in the form of a
diso, having three openings, one for each end of the cylinder, and one for

page_text: the exhaust. Against this facing works a disc-shaped valve having two
openings through (corresponding with the two steam openings in the
facing), and an elongated curved recess, which as the valve oscillates to
and fro on its centre, causes each steam passage alternately to com-
municate with the exhaust passage. This valve is caused to oscillate by 5
its being connected by a slotted link and connecting rod to the clip
of an excentric on the main shaft of the engine. On the back of this
valve is a segmental "cut off" plate which works on a long boss or
sleeve on the axis of the valve, and on the outer end of this boss or
sleeve is fixed a slotted link attached by a second connecting rod to the 1
clip of the same excentric. The connecting pin of one rod being above
the centre, whilst that of the other is below the centre, it will be evident
that the same excentric will cause the valve and cut-off plate to oscillate
in reverse directions to each other. The action of the engine is reversed
by moving the connecting pin from one end of the slot to the other by 1
means of a quick threaded screw. This arrangement may also be used
for reversing ordinary slide valves with only one excentric.
In order to allow of altering the "cut off" so as to work tho steam
more or less expansively, the "cut-off" plate is made in two sections,
and these sections are capable of being expanded or contracted by means 2
of toothed gearing worked by a worm or screw in such a way as to "cut
off" the steam at any desired portion of the stroke.
Another improvement consists in a self-acting junction valve for
controlling the admission of steam to the engine; the steam from tho
boiler is admitted into a cylindrical steam box through two or more 2
openings in a circular facing, against which works a disc valve with
similar openings. In the side of this steam box is the steam pipo
leading to the engine, and in the upper part of the box is a valve or
piston which is pressed downwards by means of two balance springs.
The rod of this valve or piston is attached to a bar, the other end of 8
which is connected by a link to a crank fixed on the axis of the disc
valve, so that when the pressure of steam increases the valve or piston
is lifted, and raising the bar causes the crank to close the valve and
diminish the amount of steam admitted to the steam engine.