IMPROVEMENTS IN STEAM ENGINES
Year: 1868

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn
Fields, in the County of Middlesex, Gentleman, for the Invention
of "IMPROVEMENTS IN STEAM ENGINES."-A communication from
abroad by Edward Nicoll Dickerson, of New York, in the United
States of America.
Sealed the 22nd May 1868, and dated the 31st January 1868.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson
at the Office of the Commissioners of Patents, with his Petition,
on the 31st January 1868.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the
County of Middlesex, Gentleman, do hereby declare the nature of the
said Invention of "IMPROVEMENTS IN STEAM ENGINES," a communication
to me from abroad by Edward Nicoll Dickerson, of New York, in tho
United States of America, to be as follows:-
This Invention relates to the valve gear of steam engines required
to be reversed when in use, and has for its object the remedying
the defects whilst retaining the advantages of the "link motion" as
now commonly used.

page_text: The essential features of this Invention consist, firstly, in the use
of a reversing link which is vibrated by a single eccentric capable of
being moved in the direction of its length for reversing, suspended at
its neutral point by a radius bar or equivalent device upon which it
vibrates, and upon the opposite sides of which it works the valve for
the forward and backward niotion of the engine, the whole being
combined with any suitable independent "cut-off" apparatus for
closing the ports opened by the valve.
Secondly. In the employment of an independent "cut-off" apparatus
rendered capable of adjustment whilst the engine is in motion by
altering the angular position of the eccentric which actuates the
independent "cut off" slide in reference to the line of the crank.
Thirdly. In the combination of a pin or block fixed in the main or
crank shaft with a tubular shaft fitted upon and surrounding the main
or crank shaft, to which tubular shaft the "cut-off" eccentrics
are fixed, and with an exterior sliding collar surrounding the said
tubular shaft and provided with two grooves one of which receives
the end of the fixed pin whilst the other receive. a block or pin fixed
upon the aforesaid tubular shaft, and one or both of which grooves arc
made spiral, the whole combination having for its object the varying
the angular position of the "cut-off" eccentrics upon the main shaft.
Fourthly. Of a graduated opening of the main port or valve, the
outside edge of the port or ports being V or shaped in lieu of
the parts being perfectly rectangular as heretofore in combination with
such an arrangement of the exhaust openings as that one exhaust
aperture will be opened before the other ccses and with an independent
adjustable "cut-off" for the purpose of preventing a "cushion" of the
steam, and the shock of sudden admission without "wire drawing" the
steam through the graduated opening in "cutting off."
By the use of this Invention the steam valve is not opened until the
piston reaches the end of the stroke or a little later, and is then opened
very gradually for a short time. Whilst the steam valve remains open
it supplies the cylinder with steam without any material reduction of
pressure in consequence of a contracted opening. When the "cut off"
slide closes the port its motion is so rapid as to be practically
instantaneous. The exhaust valve does not release the steam until its
force is effectually expended and then it opens so rupidly as to release

page_text: the steam instantly. And as the opposite valve does not close until
the piston has reached the extreme end of the stroke no "cushion" of
steam is formed.
SPECIFICATION in pursuance of the conditions of the Letters Patent
filed by the said John Henry Johnson in the Great Seal Patent
Office on the 30th July 1868.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of
Middlesex, Gentleman, send greeting.
WHEREAS Her most Excellent Majesty, Queen Victoria, by Her
Letters Patent, bearing date the Thirty-first day of January, in the
year of our Lord One thousand eight hundred and sixty-cight, in
the 31st year of Her reign, did, for Herself, Her heirs, and
successors, give and grant unto me, the said John Henry Johnson, Her
special license that I, the said John Henry Johnson, my exccutors,
administrators, and assigns, or such others as I, the said Jolin
Henry Johnson, my exccutors, administrators, or assigns, should
at any time agree with, and no others, from time to time and at
all times thereafter during the term therein expressed, should and
lawfully might make, use, excrcise, and vend, within the United
Kingdom of Great Britain and Ireland, the Channel Islands, and
Isle of Man, an Invention for "IMPROVEMENTS IN STEAM ENGINES," a
communication to me from abroad by Edward Nicoll Dickerson, of
New York, in the United States of America, upon the condition
(amongst others) that I, the said John Henry Johnson, my executors,
or administrators, by an instrument in writing under my hand and
scal, should particularly describe and ascertain the nature of the said
Invention, and in what manner the same was to be performed, and cause
the same to be filed in the Great Seal Patent Office within six calendar
months next and immediately after the date of the said Letters Patent.
"
NOW KNOW YE, that I, the said John Henry Johnson, do hereby
declare the nature of the said Invention, and in what manner the
same is to be performed, to be particularly described and ascertained in
and by the following statement, reference being had to the accompany.
ing Drawings, and to the letters and figures marked thereon, that is to
say

page_text: The said Invention relates to a new and useful improvement in the
valve gear of steam engines, which when in use require to be reversed;
the object of which improvement is to remedy the defects and retain and
improve the advantages of the "link motion" as now commonly used.
At the time of the introduction of the "link motion" by Mr.
Stephenson, all steam engines which worked steam expansively did so
by the use of some form of independent cut-off; the most simple and
effective of which was a slide working upon the back of the main valve
and alternately closing the ports which passed through it. In loco-
motives this form of cut-off was sometimes made adjustable through a
portion of the stroke; either by altering the travel of the cut-off slide
by increasing or diminishing the length of the rocker arms which
transmitted the motion from the eccentric to the slide, or by dividing
the slide into two parts and by means of a screw separating those two
parts to a greater or less distance from a centre bar moved by the
eccentric. In these two forms the independant cut-off retained a value
in the estimation of some locomotive builders above the "link motion "
for several years; but, finally, the superiority of the "link motion "
over all forms of the independent cut-off has been universally acknow-
ledged, and all locomotives are now constructed with that apparatus
or an equivalent for it and without an independent cut-off.
The advantages of the "link motion" which have thus brought it
into universal use are two:-First. That it forms a cut-off variable
from almost full stroke to about one-fifth of the stroke readily
adjustable by the same lever which reverses the engine; and, second,
that as a reverser the link holds the main valves at all times in positive
connection with the hand gear, so that in the attempt to reverse the
engine there is no possibility of a failure of the motion of the valves if
the reversing lever is thrown into the proper position. The "link
motion" also has the merit of simplicity.
The main disadvantages of the "link motion" are four :-First.
When used as a cut-off it opens the steam valve before the piston has
reached the end of the stroke, by reason of which the steam is admitted
to resist the travel of the piston before the stroke is completed; second,
it contracts the opening into the cylinder very gradually while cutting-
off, in consequence of which the steam is "wire drawn," and thereby
ses a considerable part of the boiler pressure before it acts upon the
piston; third, it opens the exhaust valve too soon and releases the

page_text: steam from the cylinder before it has expended its force in driving
the piston to the end of the stroke; and, fourth, it closes the exhaust
valve, through which the steam that has already performed its work is
escaping before the piston which is driving it out of the cylinder has
reached the end of its stroke, in consequence of which the steam
which has done all the work it is capable of doing is confined and
compressed by the piston in the end of the cylinder resisting its motion
and forming what is called a "cushion." The first of these disadvantages
causes a total loss of the entire power necessary to force back the steam
at boiler pressure during the period of premature admission as well as
of the friction upon the journals for the same time. If that admission
is for one half an inch (it generally is more) of the stroke of the piston
(or one forty-eighth part of the stroke) and the steam is of the pressure
of one hundred and thirty pounds to the square inch, the loss of power
from this disadvantage will be equal to two and three-fourths pounds to
the square inch average pressure for the entire stroke, which is about
The
seven per cent. of the ordinary working power of a locomotive.
second of these disadvantages causes a loss of all the elastic force of
which the steam is deprived by being squeezed through an aperture too
small to permit the passage at boiler pressure of the quantity needed to
fill the cylinder as the piston moves. The amount of this loss varies
with the varying sizes of the ports and the varying speed of the piston,
but it is not less than ten per cent. of the whole steam power of the
locomotive. The whole amount of the loss from this cause is not
exhibited by an "indicator diagram' because the water which is
mechanically suspended in the steam and carried with it from the
boiler into the cylinder during the "wire drawing" process (but less of
which would be carried if the port were sufficiently opened for a shorter
The third of
time) produces no sensible effect upon the indicator.
these disadvantages causes a total loss of all the clastic force remaining
in the steam which might be employed in driving the piston to the
end of the stroke if the exhaust valve were kept closed until near that
point. The amount of this loss varies, in extreme cases when the
average cylinder pressure is high the loss amounts to full six per cent. ;
its average is not less than three per cent. of the working power of the
ordinary locomotive. The fourth of these disadvantages, the "cushion,"
causes a loss which varies with the speed of the engine, the amount of
"clearance" (or vacant space between the piston at the end of the
stroke and the valve), and the size of the exhaust nozzles; this loss

page_text: increases rapidly as the rapidity of the strokes increases; and the
accumulated resistance from this cause at high velocity practically
fixes a limit to the locomotive. In locomotive cylinders, with the
usual "clearance," the absolute loss from the "cushion" averages
seven per cent. The clearance is an evil unavoidable in connection
with the "link motion," but in engines provided with the improved
valve gear and with a clearance diminished to the practical minimum
a saving of full twenty per cent. will be effected in consequence of
avoiding the "cushion." In stating that the absolute loss from the
"cushion "
averages seven per cent., proper deduction has been made
for the reduced rate of expansion of the steam which is driving the
piston incident to the higher mean pressure required to overcome the
resistance of the "cushion" and proper allowance for the re-expansion
of the cushion steam and for the saving by filling the "clearance." By
the use of the said improvement the steam valve is not opened until
the piston reaches the end of the stroke, or a little later, and is then
opened very gradually for a short time. While the steam valve remains
open it supplies the cylinder with steam without any material
reduction of pressure in consequence of a contracted opening. When
the cut-off slide closes the port its motion is so rapid as to be practically
instantaneous. The exhaust valve does not release the steam until its
force is effectually expended, and then it opens so rapidly as to release
the steam instantly. And the opposite exhaust valve does not close
until the piston has reached the extreme end of the stroke so that no
"cushion" is formed. Thus all the disadvantages of the ordinary "link
motion are remedied, and all the advantages of the ordinary "link
motion" are retained by means of a link which reverses the engine,
but which is so constructed as to reduce the wear upon itself and its
connections to an amount practically no greater than is incurred in the
valve gear of an ordinary stationary engine incapable of being reversed.
وو
When the piston is at the end of the stroke and the crank on the
centre it is apparent that no power can result from the application of
steam pressure upon the piston, but the friction upon the journals
and crank pins of an ordinary locomotive during the first five degrees
of the revolution of the engine from the centre absorbs more power
than is generated by the motion of the piston during that time. Also
the sudden admission of steam into the cylinder produces a shock
upon the crank pins and journals like the blow of a hammer, making
it necessary to reduce the slack of the connections by driving the

page_text: keys hard, in consequence of which great friction, heated journals, and
rapid destruction of the brasses are produced. With the link motion
when working at or near full stroke this sudden admission is not
neutralized by a cushion; therefore the engine must be keyed up very
close for that position, and when the cut-off is short and the cushion
does prevent the shock of sudden opening the keys are still tight,
and the friction is augmented by the resistance of one piston against
the other near the centres. The remedy of these evils is effected in
my improvement by admitting the steam through a graduated aperture
and "wire drawing" it during the time occupied by the crank in
moving through the first few degrees of the stroke, when full pressure
on the piston would be injurious. This gradual admission of steam
cannot be used advantageously in combination with the ordinary
"link motion," because when the link is cutting-off short, which is
its usual operation, the gradually accumulated "cushion" imposes a
pressure upon the piston before the steam valve opens, and thereby
prevents a shock and renders a graduated opening for the admission
of steam useless for that purpose, while at the same time the slow
closing of the graduated valve "wire draws" the steam at a time when
its pressure is needed in the cylinder, and thereby causes an absolute
loss of power; but in the improved combination where the cut-off is
effected by an independent slide a graduated opening may be used'
without loss, and there being no tendency to blow or shock, no "cushion
is needed to anticipate and prevent it, thus the disadvantage of the
premature admission of steam and of the "cushion" may be remedied.
In the ordinary "link motion" when used as a cut-off the
valve opens the port to a very limited extent and very rapidly, but
closes it very slowly, in consequence of which the piston travels five
times as far while the valve is closing as it travelled while it was
opening. The effect of this relation between the motions of the
piston and the valve is to "wire draw" the steam and diminish its
power. In the improved valve gear the main valve continues to open
during the first seventy-five degrees, more or less, of the revolution of
the crank, as in the old fashioned lap valve arrangements, so that steam
is always supplied in proportion to the demand of the cylinder if not
otherwise cut off or suppressed; but the improved cut-off valve is so
arranged as to close with almost instantaneous velocity, which is not
reduced or affected by its adjustment to different points of the stroke.
By this means the disadvantage of "wire drawing" is remedied.

page_text: In the ordinary" link motion" the point of exhaust varies with the point
of cut-off, thereby releasing the steam carlier as its quantity diminishes,
whereas if a variation in the time of exhaust were desirable, the greater
quantity should be released earlier. In this valve gear the point of
exhaust is fixed in the construction of the machine and may be set
to the best advantage. In all cases the ordinary "link motion" when
used as a cut-off exhausts too early for economy, but by separating the
cut-off valve from the exhaust valve motion this evil is remedied.
In the ordinary" link motion" the "cushion" is unavoidable. In the
improved valve gear, the blow or shock being prevented by the gradual
opening as before stated, the exhaust cavity of the main valve is
clongated so that both exhaust valves will be open at the same time
near the end of the stroke, and the bar of the valve which covers
the port is made only as wide as the port itself (line and line with
it), so that the exhaust valve does not close until the steam valve
opens, which is at or after the end of the stroke. Thus there can be
no accumulation of steam or "cushion" in the cylinder at the end
of the stroke, nor can water be caught in the cylinder, nor when
working through the engine will it produce any jar or concussion.
And in order that the said Invention may be fully understood, I
shall now proceed more particularly to describe the same, and for that
purpose shall refer to the several Figures on the annexed Sheets of
Drawings, the same letters of reference indicating corresponding parts
on all the Figures.
In the accompanying Drawings Sheet 1 represents the improved
valve gear for a locomotive engine drawn to a scale of one-cighth the
actual size.
And Sheet 2 represents the geometry of the improved link motion
in a variety of positions drawn to a scale of one-fourth the actual size.
In Figure 1, Sheet 1, S represents a part of the engine frame of an
eight wheel locomotive with the cylinder attached, and with one
driving wheel shown in red ink. The engine is represented on the after
centre.
A is the shaft or crank axle; B is the main eccentric and rod; C is
the cut-off eccentric, and G its rod; E is the link which is connected as
usual with the eccentric B at one end, but the other end is free; D is
a radius bar which is suspended by a strap on the main shaft around
which it vibrates in reversing the engine. The link E is suspended by

page_text: the pin T to the end of the radius bar farthest from the shaft, in the
same manner as the ordinary link is suspended to the reversing hand
gear; R is a hanger, the upper end of which is suspended upon the
frame by a pin upon which it swings. To the lower end of this
hanger the ordinary link block is suspended by a pin which passes
through it; F is a connecting rod which connects the hanger and block
pin with the main rocker arm II to work the main valve L in the usual
manner.
Figure 2 is a horizontal section taken through the block, con-
necting rod, and hanger end, showing how for greater rigidity the
end of the connecting rod has a hollow pin forged upon it, which
passes through the block from the centre of the main shaft to the
centre of the link pin T through the radius bar the distance is thirty
inches, and from the centre of the eccentric to the centre of the pin U
is twenty-seven inches and four-hundredths; from the centre of the
pin U to the centre line of the link is three and one-eighth inches.
The hanger is eight inches from centre to centre, and the link is cut
in a circle, the radius of which is twenty-eight and one-half inches
to the centre line. The throw of the eccentric is five and one-half
inches, and the travel of the main valve four and half inches. The
tumbling shaft K is connected with the centre of the link in the
usual position, but around the hub of the radius bar and by its
vibration it elevates or depresses the link to the required positions
in the usual manner.
Figure 6 represents a plan of the ports and valve seat. The steam
ports instead of being rectangular have their outside edges formed
in the shape of an obtuse V, the point of the V projecting half
an inch outside of the usual edge, and the widest part of the V being
seven inches across. The triangular opening thus formed ought
to become ninth of the travel of the valve in length and one half of
the width of the port, but this V shape may be made in the inside
edges of the passages through the main valve and the ports in the
seat left rectangular. The proportion here given is suitable for
engines making one hundred revolutions a minute, but for slow
moving engines this V shaped port may be more obtuse without
producing a shock. For fast engines the ports should be cut in
the shape indicated by the red lines in Figure 6. The valve gear is
represented in the forward position in which the axis of the centre

page_text: pin of the link is in the same line and centre with the axis of the centre
pin of the hanger R and as the radius bar D holds the centre pin
of the link firmly in that position, there can be no slip of the block
in the link as it vibrates, hence all wearing of the link and block
is avoided except that which results from the slip of the block in
backing when the link is lowered and the block works in its upper
segment. When the link centre is lowered so that it coincides with
the centre of the block, the block is firmly held in the link exactly
thirty inches from the centre of the shaft, and although the engine
may be running no motion is imparted to the main valve, and all
the wear of valves when the engine is shut off is prevented; whereas
in the ordinary "link motion" the valves are never at rest when the
engine is moving. Another advantage results in this valve gear
from holding the valves still on the centre, which is that both
exhaust ports are kept open at the same time, and in running down
hill the piston is not resisted by atmospheric pressure as it is by the
ordinary "link motion," and the engine will run without steam in
many cases where steam would otherwise be required to keep the
train in motion. This peculiarity will be found of very great
advantage on railroads having heavy grades, because in running down
a grade of one to one hundred and thirty with the ordinary "link
motion" the engine requires steam enough in the cylinder to balance
the atmospheric pressure which resists the piston, and thus is wasted
a quantity of steam half as much as would be needed to drive the
engine thirty miles an hour on a level. The said improved link motion
is not capable of producing a cut-off by itself as is only valuable
in combination with an independent cut-off, but it may be used
advantageously with any of the forms of independent cut-off besides
that herein described.
The improved apparatus for effecting an independent adjustable
cut-off differs from all others in the fact that its adjustment is effected
by varying the angular position of the cut-off eccentrics on the main
shaft, in consequence of which any desired range of adjustment can
be obtained and the cut-off valve will always be closed at its highest
velocity nearly. It may be used moreover with any reversing apparatus.
Figure 1 of Sheet 1 represents an elevation of one cut off in
action adjusted to cut off near the commencement of the stroke.
The cut-off slide M is just about to close the port through the

page_text: main valve L which is just opening the point of the V shaped port
for the admission of steam at the commencement of a stroke.
Figure 4 represents a plan of the cut-off apparatus with one
cut-off valve connected, and with the eccentric for the other valve;
Figure 3 is a section through the main shaft sleeves and adjusting
clutch of the cut-off apparatus.
The eccentrics C are fixed upon a
tubular shaft or sleeve N, which in this case is cast in two halves with
the eccentrics and bolted together. The eccentrics are at right angles
with each other in the same direction as the crank pins. This sleeve N
surrounds the shaft, but is a loose fit, so that it may be turned upon
it. In the middle of the sleeve there is a slot cut about two inches
wide, and running round the same in a plane at right angles to its
axis for one hundred and thirty degrees. The object of this slot is to
allow the pin W to be screwed into the shaft, and to permit the
eccentrics notwithstanding the pin to be moved round the shaft for
one hundred and twenty degrees. When the eccentrics are at right
angles to the cranks and ahead of them as the engine moves forward
the pin W should be screwed into the shaft at the back end of the slot.
O is the adjusting sleeve or boss which fits outside the sleeve N, and
is made in two semi-cylindrical halves bolted together. On the inside
of this sleeve O two spiral grooves are cut, as seen in Figure 5, which
are intended to receive the end of the pin W which projects beyond
the sleeve N about an inch and a half, and also the block X which
is fixed upon the inside sleeve at the end of the slot opposite to the
pin as set. When the sleeve O is moved from end to end upon the
shaft the pin W and the block X traverse the spiral grooves from end
to end, and are brought nearer together or removed farther from cach
other in the direction of rotation. But as the pin W is fixed in
reference to the crank of the engine it is apparent that the cut-off
eccentrics must change their angular position to the cranks, as the pipe
to which they are fixed is forced around the shaft by the spiral grooves
acting upon the block X, and so an adjustment of the cut-off will be
effected through as many degrees of the revolution of the engine as
the spiral grooves diverge from each other. The travel of the cut-off
slide M is eight inches, being an increase upon the throw of the
eccentric produced by a difference in the lengths of the rocker arms.
The point at which the cut-off will be effected varies about an inch
and a quarter from the centre of the travel of the cut-off slide, so that
the centre line of the eccentric must be very nearly at right angles to

page_text: The
its rod when the cut-off is effected, and therefore must throw the valve
with nearly its highest velocity at any possible point of cut-off; and
by adjusting the lengths of the cut-off slide and connecting rods the
very highest velocity will be secured at the point of usual work with
very little diminution of speed for all other points of cut-off.
longer the travel of the cut-off slide the more perfect will be the cut-off;
but eight inches are enough for all practical purposes. For the purpose
of placing the adjustment of the cut-off within the control of the
engine driver a strap Y is passed in a groove around the sleeve O
similar to an eccentric strap, but with one hinge joint for the sake of
convenience instead of two bolted joints. At opposite points in this
strap two pins Z are fixed which pass through holes in the two ends
of a reversing clutch P, which clutch is forced from one side to the
other along the sleeve N by a vertical shaft Q which has a projecting
block on one side of its axis that fits easily into a mortice in the arm
of the clutch P. The shaft Q is vibrated from the footboard of the
locomotive by means of a lever and bell cranks and rods connecting
with it in a manner well known to engineers for analogous purposes,
the shifting clutch being an apparatus well known and used on some
locomotives for altering the angular position and throw of the main
eccentrics. Other means for varying the angular position of the cut-off
eccentrics when in motion may be used for the purpose of effecting
the improved method of cut-off; but I recommend this device in.
preference to any other for similar purposes because it completely
protects the spiral apparatus from exposure.
In order to enable engineers to construct the said link motion and
apply it in all varieties of situations, Sheet 2 of the Drawings is
prepared exhibiting five various positions of the centre lines and centres
occupied by the eccentrics, connections, links, and valves in an entire
revolution of an engine. The colors, yellow, blue, red, black, and
green, indicate the connection between the valves and their connecting
parts throughout.
Figure 1 represents a case similar to the Drawing on Sheet 1 where
an intermediate hanger and rocker shaft are employed between the
link and the valve.
Figure 2 represents a case where the link block is fixed upon one
end of a rocker arm and the valve is worked from the other end as
is usual with the ordinary link motion.

page_text: In constructing a valve gear the draftsman should first determine
the length of the link which he would desire to use, as it determines
the length of the radius bar which within certain limits bears a constant
proportion to it. The length of the hanger or rocker arm upon
which the block is fixed should be from twenty-five to thirty-three
per cent. of the length of the radius bar D which supports the centre
of the link; and the chord of the lower segment of the slot in the
link from the centre pin to the end of the slot must be of the same
length as the hanger or rocker-arm from its centre to the centre of
the block with one half the length of the block added. For very fast
engines the larger proportion is better than the smaller, because a
greater lead is thereby effected upon the exhaust valves; but tho
proportion of lead is a matter of judgment for each constructor. When
that proportion has been determined, the centre of the hanger or rocker
shaft can be fixed by measuring from the centre of the shaft, a distanco
as much greater than the length of the hanger or rocker arm as that
proportion requires; and from the centre of the shaft A an arc of a
circle x, y, should be drawn at the distance of the centre of the hanger
or rocker shaft. Upon that arc, say at 1, the centre of the hanger or
rocker shaft must be established. From that centre with a radius
equal to the distance between the centre of the hanger pin or rocker
shaft and the centre of the block suspended at the lower end of the
hanger or rocker arm describe an arc of a circle 14, 15, intersecting
the main arc at 2 and extending on either side of it somewhat further
than the eccentric throw. In this arc the centre of the block will
always travel. From the point of intersection of these two arcs 2,
describe another are 6, 7, with the same radius and the same general
dimensions. The principal arc x, y, will be the track of the centre
of the link as it is raised or lowered in reversing the engine; the
first of the small arcs 14, 15, will be the track described by the
centre of the block pin when the engine is working; the second of
the small ares will be the track described by a point in the lower
end of the link as much below its centre as the centre of the
block is below the centre of the rocker arm when the link is in
its middle position and the block is permanently held with its centre
coincident with the centre of vibration of the link. In this position
draw the line 2, 11, which will be the chord of the arc of the link
when constructed, and which is of the same length of the hanger arm.
From the point 11 and at right angles to the line 2, 11, draw the line

page_text: 10, 11, as long as the desired distance between the centre line of the
link and the centre of the eccentric link pin, which will be at 10. Take
the distance from the centre 2 to 10 as a radius and describe a dotted
curve through 10 with that radius and that will be the track of the
eccentric link pin. Describe a similar are from the centre 1. From
the point 10 draw a straight line to the centre of the shaft A and at
right angles to that line through the centre of the shaft draw another line
12, 13. From the centre of the shaft describe a circle the diameter
of which is equal to the throw of the eccentric. At the points 12, 13,
at which that circle intersects the right angle line last drawn will be
the two centres of the eccentric at the two opposite centres of the
engine. Connect these points with the eccentric link pin 10 and the
distance from the centre of that pin to either of the eccentric centres
will be the length of the eccentric rod. In this position the main
eccentric should be keyed to the shaft and never changed, and when
the engine is on either centre the radius arc x, y, will pass through
the centre line of the link at the points 2 and 11. When the line
is clevated from this position to that in which its centre is at 1, its
lower extremity will be drawn away from the arc x, y, into one of
the positions colored red or blue as the engine may be on the back
or forward centre and that departure will constitute the lead for
forward motion. The track of the eccentric link pin is traced in
yellow, and the yellow lines indicate the positions of the link at
both centres of the engine (which are the same) and at full throw
when the valves are out of action and when only the link is moved
if the engine should be running. The full throw of the link may also
then be ascertained by laying down the black and green lines, which
is done by using the eccentric rod length 10, 12, set in a pair of
dividers, one end of which is to be applied to the circle of the eccentric
throw at its points furthest from and nearest to the arc 14, 15, and
the other end to the dotted are in which the eccentric link pin travels,
by means of which the extreme throw of that pin will be known, and
from those points at a distance equal to 10, 11, on the arc 14, 15,
will be the points of extreme throw of the centre of the block pin 14
and 15. In that state of the drawing the curve of the link may be
ascertained which depends upon the travel that is desired for the
main valves in backing, and which need not generally be more than
two-thirds of their travel in going ahead. From the centre 2 measure
off on the radius are the distance 2, 3, the same proportion to the

page_text: distance 1, 2, that the travel of the valve in backing is to its travel
in going ahead. From the centre 3 sweep the arc 8, 9, of the
same radius as the arc 14, 15, and also the corresponding dotted
are, and upon those ares lay off the full throw positious of the centre
of the eccentric link pin and the centre chord of the link as shown
in the black and green lines 3, 8, and 3, 9. The point 8 or 9
will be a point of the curve of the link, the centre 3 will be another
point, and the third point will be on the arc 11, 15, and between its
ends, the exact position of which may be determined experimentally
as follows:-Sweep an are through the two first established points 3,
8, with a radius somewhat less than the radius A 1, and mark
where it intersects the are 14, 15. With the same radius sweep
another arc through the points 3, 9, when the link is at full throw
in the opposite direction and mark where it intersects the arc 14,
15. If the radius selected for sweeping this are should chance to be
the true one the two points of intersection on the arc 14, 15, will
divide the distances 2, 14, and 2, 15, on that arc in similar pro-
portions. If they do not SO divide those distances the radius
selected for the experiment is too long or too short and another
experiment with a different radius must be tried until the arcs 2,
1, and 2, 15, are similarly divided. The radius thus found will be
the radius of the link and the travel of the valve in backing
will be equal each way from the points of lead. With that radius
thus found through the points 2, 11, draw the centre line of the link
and construct the entire link around that centre line in the usual
manner. The curve of this line will coincide with the curve x, y,
only at the points 2 and 11, but it will transmit a true valve motion
from the eccentric to the valve in all positions. If it is desired to
make the backing travel as long as the forward travel the centre 3.
must be dropped nearly as far below the centre 2 as the centre 2
is below the centre 1, and in that case the experimental curves for
determining the radius of the link would intersect the arc 14, 15,
at those points. The lead in backing will be the same as in going
ahead if the travel is the same; if the travel is less the lead will be
diminished proportionately. The reversing hand gear must be arranged
so as to lock the centre 3 in the position determined by the drawing
for backing and in the position 1 for going ahead, and in the position 2
when the valves are to be held still with both exhaust ports partially
open.

page_text: The next problem is to transfer the motion thus obtained upon the end
of a hanger or rocker arm to the valve. The throw of the hanger pin
will be dissimilar on the opposite sides of the radius arc, but it is
desirable that the travel of the valve should be equal at each portion
of its throw from the engine centres. It is therefore necessary to
convert the unequal throw of the block pin in an equal throw of
the valve, which is done as follows:-Construct the rocker arm H 16
to which the valve is to be connected so as to throw equal distances on
cach side of a perpendicular, and with a total throw equal to the desired
travel of the valve. From the centre II lay off an arc 17, 18, of about
the same radius of H 16; select a point 18 on that are for the extreme
throw of the rocker arm, and with a pair of dividers connect that point
with the point 15; then remove the dividers, retaining their distances
so that one of the points will touch 14, and mark on the are 17, 18,
where the other point touches it. The points 17, 18, will be the
extreme throw, and if the angle 17, H, 16, has been correctly assumed
the rocker arm may be so constructed; in order to ascertain which
place one of the divider points on the lead points 4 and 5 successively,
and mark with the other one where the rocker arm will be when the
block pin is at 4 and 5, which will be found at 19 and 20; then measure
the distances 17, 19, and 18, 20, and if they agree the connecting rod
length is correct, if not, spread the dividers more or less and repeat the
experiment, assuming new points on the are 17, 18, till they do agree,
when the length of the rod 15, 18, and the angle between the two
rocker arms H 17, and H 16, will be correct. If the arm II 17 is found
not to be short enough to give the throw required at 16, its length may
be altered and a new are drawn for experiment as before until the
proper length of all the parts and the proper angle of the rocker arms
is ascertained. If no intermediate hanger is employed, but the block
is hung on one end of the rocker arm and the valve is worked from
the other end as in Figure 2, then the motion of the valve will he
equalized by adjusting the angle which the valve rocker arm makes with
the block rocker arm, and that adjustment will be made experimentally
as follows: Construct a movable paper sector having drawn upon it the
lines 1, 14-1, 15-1, 4, and 1-5, and pin it on the Drawing at the
centre 1, so that it will coincide with the lines which it imitates. Turn
it till it occupies the position of 16, 16, and with the dividers measure off
and mark upon the line of the valve stem 21, 22, near the chest, the
points 21, 25, 26, and 22 being equidistant from the points 16, 23, 24,

page_text: and 16 respectively. If the distance 21, 25, is the same as the
distance 22, 26, the sector has been placed at the right angle with the
linc 1, 14; if not, move it round the centre 1 to another position
and repeat the experiment until the lead and travel of the valve agree.
The length of the arm 1-16 may require to be varied to suit the
desired valve travel, which can be done as in the other case. In this
case the valve arm will not vibrate equal distances on each side of a
line perpendicular to the valve rod, but will fall lower on one side
than the other. The valve motion, however, will be truc, and an
unequal eccentric throw will be converted into an equal valve travel.
The four valve and valve seats colored blue, red, black, and green
represent the four positions of the valve at its points of lead and full
throw, the blue and red colors representing the position of lead on
both centres. The opening made by the lead amounts to a very small
triangle three-sixteenths of an inch wide and two inches and five-
eighths of an inch long, but the elasticity of the valve gear and the
loss of motion in the joints will reduce this small opening materially,
and it is not desirable to have any opening until the engine reaches
its centre. If there were no clasticity or lost motion I would make
the valve so much longer than it is here shown as to cover the port
when the engine is on the centre and only open it afterward. The
rapidity with which the main valve is opened by this valve gear is
such that notwithstanding the great portion of the travel occupied in
opening the part of the port the pressure upon the piston is not
diminished except where it is desirable to diminish it in order to save
the loss of the friction while it is greater than the power, and
the shock is prevented without expense of power.
In constructing a locomotive I would advise the engineer not to finish
the lap and exhaust cavity of the valve till the valve gear is all erected
and the position of the eccentric is adjusted and fixed.
When the parts
are all in position except the valves let the engine be placed on one
centre and let the link be placed with its centre pin coincident with
the centre of the block pin, as shewn in Sheet 2; then with the
eccentric in a position nearly right ascertain the position of the point 10
and mark it; turn the engine to the other centre and again mark
the position of 10. If it should be the same as at first the eccentric
is in the right position; if not, turn the eccentric on the shaft dividing
the error in halves and again try the position until the point 10 will
come to the same exact position at both centres of the engine; then key

page_text: the eccentric in that position and never let it be changed again; raise
the link to the go-ahead position, as in Sheet 1, and the rocker arm
will move the valve stem to the lead; apply a template of thin sheet
metal of the shape of a longitudinal section through the main valve
in the place of the valve to the valve seat, so that it will be worked
by the valve stem as the wheels are turned and mark upon it the points
of the V-shaped ports when the engine is on each centre; measure
from those points toward the centre of the template an amount
which is expected to be lost by clasticity and lost motion, one-
eighth of an inch more or less, and those points will be the
ends of the lap of the valve. From those points measure again
toward the centre of the template a distance equal to the breadth
of the port from the point of the V to its opposite side and the
points thus ascertained will be the ends of the exhaust cavity. Cut
the valve to correspond with the template thus made and place it in the
chest, and it will have the lead and travel which the drawing requires.
The link instead of being curved may be composed of two chords of
arcs meeting at the centre, and a rectangular block will work in it,
enough clearing being made at the angle of intersection to permit it
to pass the centre; and inasmuch as the link only uses a small
portion of its length at each end and in the centre to give position to
the valves its other parts may be of irregular form, but a true curve is
the best. In running a locomotive constructed upon this plan the
throttle valve and pipe which should have an area of one-tenth of the
area of the cylinder all the way to the chests should be thrown wide
open after the engine is fairly started, and the speed of the machine
should be regulated entirely by the lever which controls the position of
the cut-off, whereby the steam will always be admitted to the cylinder at
a pressure very near to that in the boiler, and the greatest range of
expansion which the load will permit will at all times be obtained, and
consequently the greatest economy of steam will result. By the use of
this improvement the entire theoretical power which steam is capable
of producing in a non-condensing engine of a given size and performing
a given work will be produced in a locomotive engine with no
deductions except those due to the "clearance," the radiation of heat,
and the leakage from imperfect construction; and of the power thus
produced much less will be absorbed by friction when the engine is
worked by the said improved valve gear because there is no resistance
by one piston against the other at each centre as there is with the "link

page_text: motion," and because there being no shock on the centres the keys may
all the slack, and so there will be no binding of the brasses. The loss
by leakage also will be much diminished because the travel of the valve
is constant, whereas with the "link motion" the valve is generally
moving with a small travel upon the seat, which it wears down in the
middle, and when the travel is increased, as it must be frequently, the
valve runs against an elevation left by the reduction of the middle
surface of the seat, and the effect is to wear the valve into a curved
surface touching the seat on its centre and rocking either way. The
steam then leaks under the ends of the valve and is wasted, as may be
seen in any "link motion" engine which has been running a month
by setting the slides in the centre and opening the throttle valve and
cylinder cocks.
Having now described and particularly ascertained the nature of my
said Invention, and the manner in which the same is or may be used or
carried into effect, I would observe in conclusion what I consider to
be novel and original, and therefore claim as the Invention secured to
me by the herein-before in part recited Letters Patent is,-
First. A reversing link vibrated by one eccentric capable of being
moved in the direction of its length for reversing, suspended at its
neutral point by a radius bar or other equivalent device, upon which it
vibrates, and upon the opposite sides of which it works the valve for the
forward and backward motion of the engine, substantially as herein-
before described, in combination with an independent cut-off apparatus
of any sort for closing the ports which it opens.
Second. An independent cut-off apparatus adjustable while the engine
is in motion by altering the angular position of the eccentric which
works the independent cut-off slide in reference to the line of the crank,
substantially as herein-before described.
Third. The combination of a pin or block fixed in the main shaft
with a sleeve or tubular shaft surrounding the main shaft to which
the cut-off eccentrics are fixed, and with an exterior sliding sleeve
surrounding the said tubular shaft provided with two grooves, one of
which receives the end of the fixed pin and the other of which receives a
block or pin fixed upon the tubular shaft, and one or both of which
grooves are spiral as a device for the purpose of varying the angular
position of the cut-off eccentrics upon the main shaft, substantially as
herein-before described.

page_text: Fourth. A graduated opening of the main port or valve in combi-
nation with such an arrangement of the exhaust openings as that onc
exhaust aperture will be opened before the other closes, and with an
independent adjustable cut-off for the purpose of preventing a "cushion
of the steam and the shock of sudden admission without "wire drawing"
through the graduated opening in cutting off, substantially as herein-
before described.
J. HENRY JOHNSON. (L.S.)