Improvements in Steam Engines.
Year: 1889

page_text: te of Application, 17th Dec., 1889-Accepted, 15th Mar., 1890
COMPLETE SPECIFICATION.
Improvements in Steam Engines.
A communication from JAMES BROWN STANWOOD, residing at Corner of Auburn
and Eden Avenues, Cincinnati, Ohio, United States of America, Mechanical
Engineer.
I, ALFRED JULIUS BOULT of 323 High Holborn, in the County of Middlesex,
M.L.M.E. do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
แ
This invention relates to reciprocating steam engines having reference to that
class usually known as the "Corliss" type, in which separate steam induction and
eduction valves are operated by an eccentric and what is commonly termed
releasing gear" controlled by a governor for cutting-off the supply of steam at a
given portion of the stroke of the piston as required to maintain a uniform rotative
speed of the crank shaft under varying conditions of load. The constructive
conditions (as I shall explain more in detail hereinafter) are such, that, where one
eccentric only is employed, the point of cut-off in such engines is limited to about
four-tenths of the stroke: and consequently the effective power of the engine is
kept within a corresponding limit. The general object of this invention is to
increase effective power of such engines without resort to double eccentrics;
and it consists in the construction of the cylinder with exhaust ports located within
the limits of the piston stroke at the point desired for the beginning of compression
and governed by the piston itself as a slide valve, and the combination of the same
with the usual induction and eduction valves and a single eccentric and releasing
gear. Further objects of the invention are to secure a greater amount of cushion
than certain valve gears are capable of giving, also, to assist in giving greater
clearance area for exhausting the steam from the cylinder than can be otherwise
obtained without special complication.
This invention is illustrated in the accompanying drawings in which Figures 1, 2,
and 3, are longitudinal axial sections of a steam engine constructed according to
this improvement with diagram showing the crank, eccentric and releasing gear
positions corresponding with the several piston and valve positions, and Figure 4, a
diagram indicating the several angular positions of the crank and valve motion
plotted upon and in a common circle, and Figure 5, is a cylinder embodying the same
principles of construction, but with a different type of valve gear.
Before referring specifically to the drawings, a few words of general explanation in
connection with one class of valve gears will assist in defining the invention as
hereinafter described more in detail.
In steam engines with adjustable cut-offs of (what may be generally called) the
Corliss type, one most distinguishing feature is the combination of a governor with
what is technically known as a releasing gear.
This combination automatically
regulates the supply of steam at each stroke of the engine by measuring off a
sufficient amount to perform the necessary work and maintain a constant rotative
speed of the crank shaft. The releasing gear (duplicated for forward and back
piston motion) is placed in the valve mechanism at a suitable position between the
driving eccentric and the steam induction valves, and embodies a latch or some
equivalent mechanism which coming in contact with a lug or stop, adjusted as to
position by the governor, breaks the connection between steam induction valve and
driving mechanisın, allowing the former to be closed by some outside source of
stored energy such as a spring, weight, or vacuum embodied in an instrument
known as the "Dash Pot."

page_text: The releasing gear can only act while the valve is opening (either before or after
the actual uncovering of the steam induction port is accomplished) as at this time
only, the latch is moving toward the disengaging lug or stop operated by the
governor. In practice the release of steam just uncovers the port and its maximum
open position. It is between these points that the cut off takes place.
When, as is the custom in a majority of cases, the driving eccentric controls not
only the steam induction valves but also the steam. eduction valves this period of
cut-off is limited by the position the eccentric has to take relative to the crank.
The eccentric, under these conditions, has three functions, namely: first, to admit steam
through steam induction valves at the right instant behind the piston, as it begins its
stroke; second, to open the steam eduction valves to exhaust the steam when the piston
is near the end of its stroke; third, to close the steam eduction valves at the proper
point to give the necessary compression to steam left in the cylinder when the piston
is returning to its original position. These points are known respectively as points
of "lead," of "release," and of "compression." The position of the eccentric to
regulate practically these three points must be at some angular position on the crank
shaft greater than 90° ahead of the crank in the rotative direction towards which the
shaft is turning except when a rocker, reversing the motion of valve gear is
employed, this angle in excess of 90° is termed the "angular advance." The period
as before stated, during which cut-off can take place is between point of opening
of steam induction valve (the point of lead) and the maximum opening of same
valve the eccentric positions corresponding in time are the "point of lead" and
"maximum travel" of same eccentric beyond this point.. Now as the eccentric
is located on the shaft at a greater angular position than 90° ahead of crank, and as
crank is nearly "on centre or at its "dead point" when steam induction valve and
eccentric are at their respective "points of lead," it follows that the period during
which cut-off can take place must be limited to crank positions corresponding to
eccentric positions of "point of lead" and "maximum travel." The limiting eccentric
angle of this period is an angle equal to the difference between an angle greater
than 90° beyond "dead point" and an angle 180° beyond same
"dead point"; or,
to a limiting angle equal to 180° less 90° plus the "angular advance" which is
equivalent to an angle less than 90°; and therefore the corresponding crank angles
between which cut-off can act are an angle less than 90° from "dead point." In
practice the corresponding piston position between which cut-off can act are between 0
and about 4-10 of a stroke.
The invention which I am about to describe is embodied in a cylinder so
constructed in combination with separate steam induction and eduction ports
operated by a single eccentric as that of one of the functions of the eccentric, viz. :
the closing of the steam eduction valve is performed by the piston of the engine,
relieving the eccentric of this duty and thereby allowing the period of cut-off to
be extended from 4-10 of stroke to, an extent greater than 6-10 of stroke if
necessary.
This has been accomplished in practice heretofore only by means of two eccentrics
and duplicate valve connections, one eccentric and its connections controlling, the
steam induction valves, and one. the steam eduction valves. In this case the eccentric
operating the steam eduction valves, being relieved of other duties can be placed on
the shaft at an angle less than 90 ahead of the crank, having what is called a
" negative angular advance. This increases the limiting eccentric angle during
which cut-off takes place to 90 plus the "angular advance" (now negative) instead of
as above 90 minus the "angular advance" (positive).
In this invention the eccentric has two functions only the controlling of the " point
of lead" and "point of release" and this can be done with an eccentric as above with
negative angular advance as is shown by the figures.
In the illustrations given in the drawings A designates the steam cylinder, A, B its
reciprocating piston head; a a the steam induction valves controlling the in-
duction ports from the steam chamber E; and the eduction or exhaust

page_text: valves controlling the eduction ports from the cylinder to the exhaust chamber F.
The induction ports are located in the extreme ends of the cylinder as is
usual but I locate the eduction ports (designated at x) somewhat toward
the centre or mid-stroke of the piston and construct them and the piston head
in such manner as that the piston head may pass over and govern said ports as a
valve. It will be obvious that if the ports are located sufficiently within the
extreme limits of the piston stroke and the piston head in passing over and beyond said
ports, compresses the residual steam in the cylinder thus cushioning itself upon the
imprisoned steam. The exact location of the ports will therefore be determined by the
designer or builder of the engine to produce the desired compression, such being one
of the objects of this departure from the usual construction.
"
The compression being thus provided for independently, the valve moving
mechanism and exhaust valves are entirely relieved of this function; and the relative
period of time within which the exhaust valve is to close is extended to that point in
the return stroke of the piston of which it is about to uncover the exhaust port,
thus allowing eccentric position c to be adjusted at a smaller angle in advance of
crank C.
For example in figure 1 the piston B is travelling to the left near the close of the
stroke and has just covered the exhaust port x.
The steam eduction valve b still remains wide open into exhaust chamber F and is
not fully closed until just before piston head B has returned to the same position as
shown in figure 3.
Had the duty of closing valve & been performed by the
eccentric it would have been necessary to locate eccentric on crank-shaft at an angle
ahead of crank in direction of rotation greater than V, O, Y, figures 1, 2 or 3 so that
valve b could have been closed earlier. This angle would be found in practice
greater than 9.0. The angular period during which cut-off can act is represented by
angle V, O, Z, page 2 greater than 90°. Had V, O, Y been greater than 90°
V, O, Z or angular period during which cut-off could act would be less than 90°.
It should be now obvious that the limiting crank and occentric angles at which
a single eccentric valve mechanism with releasing gear can be set in relation
to the crank to control cut-off are materially enlarged by this construction of
cylinder.
Again in figure 1 the piston B is travelling to the left near the close of its stroke
and has just covered the exhaust port . Now by proportioning the piston of
suitable thickness a primary exhaust can be effected through this same port a by
the uncovering of this port by the opposite side of the piston and this can be
made to take place before the usual opening of the exhaust valve 6' which only should
be well open before port is reclosed by piston on its return stroke; the exact thick-
ness of piston will therefore be determined by the designer or builder of the engine to
produce the desired exhaust or release of steam from the cylinder such being also an
object of this departure from the usual construction.
It will thus be seen that each exhaust port and valve can take an added function to
wit of aiding in the opening of the exhaust which in the ordinary construction
of steam engine cylinders is taken wholly by the opposite port and valve. In
other words the exhaust port and valve which at a given time in ordinary practice
remain wholly closed, may remain open to receive the preliminary portion of the
opposite side exhaust.
In the drawings I can only illustrate the releasing gear diagrammatically; since
several different forms of mechanism are in common use all however embodying
substantially the same principle and all adapted to the purposes of this invention.
The general principle of their construction I have already adverted to and in the
drawings I have exhibited in the form of the diagram in dotted lines the position of the
valve levers with plate and connections as related to the eccentric position c and
main crank C. As the constructive details of this mechanism apart from the
described construction of the cylinder and piston form no part of the present
invention my correspondent is advised that no further specific description is
necessary and therefore omit the same.

page_text: The advantages of this system are that with exactly the same mechanism as has
heretofore been employed, first, an extended field for operation of cut-off is obtained
increasing the.capacity nearly 50 per cent more than was heretofore possible a feature
of great value where compounding is necessary; second, the facility with which ample
compression is obtained-a point in engines of certain types which has to be sacrificed
when the greatest range of cut-off is required; third, the ease with which a double
release area is obtained by the uncovering of exhaust port at one end of
cylinder when piston is at one end of stroke in addition to the usual port opening
by the usual valve.
The diagram figure 4 indicates a method of determining by plotting the relative
positions of the several parts.
The circle represents to scale the. path of the eccentric's motion. If L is
selected as "
point of lead" and T'as the point of latest cut-off for corresponding
crank positions then lay off arc T Q equal to arc L T and draw the line L Q.
Determine the " point of release " R and draw MR parallel to L Q. It is now
necessary that S the point of compression brought about by piston covering, exhaust
port in cylinder should be so taken that a vertical line H S drawn through S cuts. the
circular path of the eccentric's motion between M and T; this ensures the closure of
the exhaust port by steam eduction valve before same port is uncovered by the
piston.
*
In figure 5 I have exhibited the application of the principle of the invention to
a slide-valve steam-engine. In such case, separate induction and eduction ports
for each end of the cylinder are formed at each side of and open through a
common valve-seat upon which rides a gridiron " valve furnished with a rider or inde-
pendent cut-off valve carried with the main valve until it meets and is detained by a bar
or abutment, which is here shown centrally between the two vertical projections of
the rider-valve. The rider being thus detained the main valve beneath continues
on to the end of its stroke while the rider is thus relatively shifted in its position
and controls the admission apertures through the main valve.
The general construction and' arrangement of an independent rider or cut-off valve
acting in this manner is well-known but the combination of the same with a duplicate
set of ports by which the compression and release are primarily controlled by the
piston, leaving only for the exhaust, edges of the slide valve the function of opening
and closing the exhaust ports at the right time, so that steam will not blow through
the cylinder, is new.
For, then, the slide-valve-eccentric can have negative angular advance and the
range of cut-off for this class of valve mechanisms may be extended; which is the
prime object of this.invention as I have already explained.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is
;-
1. In a reciprocating steam engine the combination of a crank shaft, a cylinder,
two exhaust-openings from said cylinder one near each end, within the reciprocatory
limit of the piston stroke, a piston adapted to pass over said ports as a valve,
and valves governing said port independently of the piston substantially as set
forth.
2. In a reciprocating steam engine the combination of a crank shaft, a cylinder,
two exhaust ports opening from said cylinder, one near each end within the recipro-
catory limits of the piston stroke, a piston adapted to pass over said ports as a valve,
valves governing said ports independently of the piston, and a single valve operating
connection with the crank shaft for controlling the induction and eduction of steam
to said cylinder substantially as set forth.
3. In a reciprocating steam engine the combination of the following instrumen-
talities, viz. a crank shaft, a cylinder having its exhaust ports opening therefrom
near each end within the reciprocatory limits of the piston stroke, a piston operating

page_text: in said cylinder and across said exhaust ports as a valve, separate induction and
eduction valves, the latter controlling said exhaust ports independently of the piston,
and a single valve-operating connection with the shaft for operating both sets of
valves, substantially as set forth.
Dated this 17th day of December 1889
W. P. THOMPSON & BOULT,
Agents for the Applicant.