IMPROVEMENTS IN VALVE GEAR FOR STEAM ENGINES
Year: 1877

page_text: LETTERS PATENT to The Honorable Charles Algernon Parsons, of Connaught
Place, in the County of Middlesex, for the Invention of "IMPROVEMENTS
IN VALVE GEAR FOR STEAM ENGINES."
Sealed the 16th April 1878, and dated the 22nd October 1877.
PROVISIONAL SPECIFICATION left by the said Charles Algernon Parsons at
the Office of the Commissioners of Patents on the 22nd October 1877.
The Honorable CHARLES ALGERNON PARSONS, of Connaught Place, in the County
of Middlesex. "IMPROVEMENTS IN VALVE GEAR FOR STEAM ENGINES."
This Invention relates to a novel arrangement of valve gear, whereby the ordinary
slide valve may be worked so as to obtain higher degrees of expansion than are
possible with the use of the ordinary link motion. To this end I employ the link
commonly used in reversing gear, and connect it at one end, with the ordinary
excentric on the engine shaft, and at the other with a short crank on a by-shaft,
which is driven by spur wheels at 3 times the velocity of the engine shaft.
The link is also jointed to a pendent vibrating arm, which may be connected with
the governor or with a hand lever for adjusting automatically or otherwise the
position of the link with respect to the valve rod, and consequently the amount of
expansion desired in the cylinder. When the link is put half way over, the motion
of the valve rod will be a mean between the motions which would be derived 'from
the excentric and by-shaft separately.
In this arrangement of gear the two shafts are so set that when the excentric of
the engine shaft is at the end of its throw, the crank of the by-shaft is th of a turn
past that position, so that (the motion of the valve being a mean of the two
motions) the valve is at the end of its throw a little before the main excentric.
During the next h of a turn the motion of the valve is very rapid, since both
excentric and crank are moving in the same direction; after this the by-shaft
crank begins to move in the opposite direction to the main excentric, checking the
motion of the valve nearly completely, but (owing to the "set" of the crank and
excentric) this pause is in such a position that, though the steam port is closed, the
Price & I

page_text: valve is not sufficiently over to effect the free passage of the exhaust through the
other port; the valve remains in this position until the stroke of the piston is nearly
completed, by which time both excentric and by-crank are moving again in the
same direction, and the valve gives a sudden rush and partial return as before, but
to the opposite end of the valve chest, and a sudden admission and cut-off of steam
is the result.
It may be best for the by-crank to be slightly shorter than the half throw of the
excentric, and for the ratio of the distance of the end of the link worked by the by-
shaft to the distance of that worked by the main excentric from the valve rod to be
about as 3 is to 2. When the excentric and by-shaft are properly set, the motion
imparted to the valve rod is very rapid at one portion of the stroke, and very slow
during the rest, causing the steam port to be opened for a much shorter time than
would be possible with the single excentric. By altering the position of the link by
the vibrating arm the motion of the valve rod may be gradually varied from the
motion of the ordinary excentric (cutting off steam at the of the stroke) to the best
compound motion, cutting off steam at a little over 3rd of the stroke.
When a greater degree of expansion is required it is advantageous to use a second
by-shaft running at 5 times the speed of the engine shaft. This shaft having a
short crank should actuate a second link in connection with the valve rod and
excentric. By this arrangement a motion compounded of the motions which could
be derived from each of the three shafts separately is obtained, and (as before) the
expansion can be varied, but in this case from a cut-off at the to a cut-off at
about th

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Charles Algernon Parsons in the Great Seal Patent Office on the 20th
April 1878.
The Honorable CHARLES ALGERNON PARSONS, of Connaught Place, in the County
of Middlesex. IMPROVEMENTS IN VALVE GEAR FOR STEAM ENGINES."
"
This Invention relates to a novel arrangement of valve gear, whereby the ordinary
slide valve may be worked so as to obtain higher degrees of expansion than are
possible with the use of the ordinary link motion. To this end I employ the link
commonly used in reversing gear, and connect it at one end with the ordinary
excentric on the engine shaft, and at the other with a short crank on a by-shaft,
which is driven by spur wheels at three times the velocity of the engine shaft.
The link is also jointed to a pendent vibrating arm, which may be connected with
the governor or with a hand lever for adjusting automatically or otherwise the
position of the link with respect to the valve rod, and consequently the amount of
expansion desired in the cylinder. When the link is put half way over, the motion
of the valve rod will be a mean between the notions which would be derived from
the excentric and by-shaft separately.
In the accompanying Drawing, Fig. 1 shews in side elevation an arrangement of
single slide expansion gear, constructed according to my Invention, and Fig. 2 is a
plan view of the same.
In these Figures, A is the engine shaft carrying the ordinary excentric B. Keyed
to this shaft is a spur wheel C, which gears into a pinion D, of one-third its diameter,
keyed on a by-shaft E, which is fitted with a crank F; G is a link similar to that
used in reversing gear, and to it is fitted the slide rod H. This link is connected at
its lower end with the excentric B on the engine shaft by means of the excentric
rod I, and at its upper end the link is connected by a rod K with the crank F of
the by-shaft E. Pendent from the upper end of the link is a vibrating arm L, which
at its lower end is jointed to a weighted rock lever M, having for its fulcrum a
pin N. Keyed to this fulcrum pin is an arm O, to the upper end of which is jointed
a connecting rod P, leading to a ball or other governor.
In this arrangement of gear the two shafts A and E are so set that when the
excentric of the engine shaft is at the end of its throw the crank of the by-shaft is
one-fourth of a turn past that position, so that (the motion of the valve being a
mean of the two motions) the valve is at the end of its throw a little before the
main excentric. During the next one-eighth of a turn the motion of the valve is
very rapid, since both excentric and crank are moving in the same direction. After
this the by-shaft crank begins to move in the opposite direction to the main excentric,
checking the motion of the valve almost to the extent of stopping it, but (owing to
the relative "set" of the crank and the excentric) this pause occurs at such a stage
of the motions of the slide valve that, though the steam port is closed, the valve is
not sufficiently over to affect the free passage of the exhaust through the other port.
The valve remains in this position until the stroke of the piston is nearly completed,
by which time both the excentric B and crank F are moving again in the same
direction, and the valve gives a sudden rush and partial return, as before, but to the
opposite end of the valve chest, and a sudden admission and cut-off of steam is the
result.
It may be best for the crank of the by-shaft to be slightly shorter than the half
throw of the excentric, and for the ratio of the distance of the end of the link
worked by the by-shaft to the distance of that worked by the main excentric from
the valve rod to be about as 3 is to 2. When the excentric and by-shaft are properly
set the motion imparted to the valve rod is very rapid at one portion of the stroke,
and very slow during the rest, thus causing the steam port to be opened for a much
shorter time than would be possible with the single excentric. By altering the
position of the link G by the vibrating arm L, the motion of the valve rod may be
gradually varied from the motion of the ordinary excentric (cutting off steam at

page_text: three-fourths of the stroke) to the best compound motion, cutting off steam at a
little over one-fourth of the stroke.
The expansion gear above described, it will be understood, is applicable to
stationary and marine engines generally, that is, whether vertical or horizontal.
In Sheet II. of the Drawings, I have shewn the gear as applied to a horizontal
engine, Fig. 3 being a side elevation of the engine, and Fig. 4 an end elevation of
the same.
In this arrangement it will be seen that the bearing for the by-shaft E is placed
below the level of the engine shaft A, for the purpose of supporting it from the bed
plate of the engine. The connecting rod K of this by-shaft is jointed to the lower
extremity of the link G, while the rod I of the excentric is connected to the upper
end of the link, thus reversing the relative position of the parts, as compared with
Fig. 1.
In other respects the two arrangements of gear are alike, and similar letters of
reference being used for pointing out the various parts, no further description will
be required.
In the case of reversing and marine engines, I propose to use the ordinary arrange-
ment of reversing link, and to connect the forward end of the link with the link of
my expansion gear by means of the sliding block of the valve rod. This enables
me to apply the compound motion above described while the engine is going ahead,
and thereby to obtain the requisite expansion either by moving the reversing link
or by shifting the link of the expansion gear, or the position of both links. This
arrangement I propose especially to apply to oscillating paddle engines.
When greater degrees of expansion are required than that above mentioned, I may
obtain this result by using the common slide valve with a greater lap; thus a side
cutting off steam at with the common excentric (such as is used in marine
engines) will, with my improved gear, give a variable cut-off from to about of
the stroke.
I also propose when a greater degree of expansion is required than is provided for
by the above-described arrangement, I propose to use a second by-shaft running at
five times the speed of the engine shaft. This arrangement is illustrated at Fig. 5,
which is a modification of the horizontal arrangement shewn at Fig 3, and contains
all the parts therein exhibited. In addition thereto however there is the second by-
shaft E with its crank F* and connecting rod K*, which rod is jointed to a rock
lever G*, pivotted at its centre to the link G at the point where the rod K, in the
arrangement, Fig. 3, is attached. In this case however the rod K is jointed to the
rock lever G* at the opposite end to that with which the rod K* is connected. By
this arrangement a motion compounded of the motions which could be derived from
each of the three shafts separately is obtained, and (as before) the expansion can be
varied, but in this case from a cut-off at the to a cut-off at about one-eighth.
Having now set forth the nature of my Invention of "Improvements in Valve Gear
for Steam Engines," and explained the manner of carrying the same into effect, I wish
it to be understood that, under the above in part recited Letters Patent, I claim
working the slide valves of steam engines by means of links, to which a compound
oscillating motion is imparted in the manner and for the purpose above described.
In witness whereof, I, the said Charles Algernon Parsons, have hereunto set my
hand and seal, the 17th day of April, in the year of our Lord One thousand
eight hundred and seventy-eight.
CHARLES ALGERNON PARSONS. (L.S.)