IMPROVEMENTS IN THE VALVE GEAR OF LOCOMOTIVE AND OTHER ENGINES
Year: 1855

page_text: LETTERS PATENT to Alexander Allan, of the City of Perth, North Britain,
Engineer, for the Invention of "IMPROVEMENTS IN THE VALVE GEAR OF
LOCOMOTIVE AND OTHER ENGINES."
Sealed the 22nd January 1856, and dated the 2nd August 1855.
PROVISIONAL SPECIFICATION left by the said Alexander Allan at the
Office of the Commissioners of Patents, with his Petition, on the 2nd
August 1855.
I, ALEXANDER ALLAN, of the City of Perth, North Britain, Engineer, do
hereby declare the nature of the said Invention for "IMPROVEMENTS IN THE
VALVE GEAR OF LOCOMOTIVE AND OTHER ENGINES" to be as follows:-
This Invention relates to improvements upon that combination of mechanism
known as the link motion," commonly used for working the valves of loco-
motive and other engines requiring a frequent reversal of motion. Before
describing it I may explain that the link motions now commonly in use are
generally divided into two classes, namely, those in which the link moves upon
the "block," through which its motion is conveyed to the valve, and those in
which the block moves in the "link;" the first class are generally distinguished
as the "shifting link," and the latter as the "stationary link" motions.
both classes the "link" is curved either to the radius of the excentric rods with
which it is connected, or to that of the valve connecting rod, the concave side
of the link being placed towards the excentrics in the shifting link arrange-
ment, and towards the valves in the stationary link arrangement.
In

page_text: Now, this Juvention consists in a new combination of this mechanism, the
novelty of which is, that the peculiar features of both the shifting and station-
ary link arrangements are combined, as both the link and block in connection
with the valve spindle are moved to get the block in the required position in
its link, and as a consequent of such an arrangement a straight link is
employed. It will be found, in the improved combination just referred to, that
the curves or arcs described by the movement of the ends of the excentric
and valve connecting rods will neutralize or compensate each other, and thus
effect the object of the curve of the "link" in the common motions. The
movements of the link and block I accomplish simultaneously, by jointing the
rod corresponding to that by which the link is sustained or suspended in the
"stationary link "motion to an arm from a shaft, corresponding to the reversing
shaft, connecting the valve-connecting or radius rod by a rod with another
arm from the opposite side of the same reversing shaft, by which arrangement
it will be seen that the movement of the reversing shaft will give to the link
and valve rod or block, novements in opposite directions, of such extent as
will be regulated by proportioning the lengths of the arms from the axis or
centre of the reversing shaft. From the improved combination here referred
to the following advantages are obtained over the common "link" motions:-
The mechanism is more easy of construction and more easily maintained in
repair it requires less room than the shifting link; the angular position of
the excentric rods as compared with the one class, and the valve-connecting rod
as compared with the other class of common link motions, is much reduced;
consequently the excentric and valve rods move through less space and are
more direct acting; the excentric rods and link and valve-connecting rod
and block in a great measure balance each other, and to such extent dispense
with a counterbalance weight; and less power is required to move the valve
gear than in the common link motions.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Alexander Allan in the Great Seal Patent Office on the 3
29th January 1856.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
ALLAN, of the City of Perth, North Britain, Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Second day of August, in the year of our Lord 3
One thousand eight hundred and fifty-five, in the nineteenth year of Her

page_text: reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said Alexander Allan, Her especial licence that I, the said Alexander
Allan, my executors, administrators, and assigns, or such others as 1, the said
Alexander Allan, my executors, administrators, and 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, exer-
cise, and vend, within the United Kingdom of Great Britain and Ireland, the
Channel Islands, and Isle of Man, an Invention for IMPROVEMENTS IN THE
VALVE GEAE OF LOCOMOTIVE AND OTHER ENGINES," upon the condition (amongst
others) that I, the said Alexander Allan, by an instrument in writing under
my hand and seal, 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 Alexander Allan, do hereby declare
the nature of my said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement and accompanying Drawings, that is to say :—
My Invention relates to improvements upon that combination of mechanism
known as the "link motion," commonly used for working the valves of loco-
motive and other engines requiring a frequent reversal of motion. Before
describing it I may explain that the "link motions" now commonly in use are
generally divided into two classes, usually called the "stationary link" and
shifting link motions." The stationary link motions may be divided into two
classes, namely, those in which the block" is connected to the valve connect-
ing rod through which its motion is conveyed to the valve, and those in which
the excentric rods are connected to the "block;" in the former case the "link"
is curved to the radius of the valve rod, and the concave side of the link is
placed towards the valve, and in the latter case the "link" is curved to the
radius of the excentric rods, and the concave side of the "link" is placed
towards the excentrics. In the shifting link motions" the excentric rods
are usually connected to the link which is worked on the "block," the link
being curved to the radius of the excentric rods with the concave side placed
towards the excentrics.
Now, my Invention consists in a new combination of this mechanism, the
novelty of which is, that the peculiar features of both the shifting and
stationary link arrangements are combined, as both the "link" and "block"
(or parts corresponding thereto) are moved to get the block pin or centre at
the required position in or on its "link" or centre. As a consequent of such

page_text: an arrangement, a "link" may be made with a varying or unlimited radius or
combination of radii, or the centres of the double lever; parallel motion may
be employed by attaching radius rods to a central bar Z (see the Diagram in
the Drawings annexed hereunto, Fig. 1), which carries the valve radius rod
centre. The other ends of radius rods are connected to the excentric rods,
which are kept at the required distance apart by a strap or plate or straps and
plates (c.) I, however, prefer to employ a straight link, which may be a box,"
open," or "bar" link, according to convenience, as it will be found that the
curves or ares described by the movement of the excentric and valve con-
necting rods will neutralize or compensate each other, and thus effect the
object of the usual curve of the link in common motions. The movements
of the "link" and "block," or parts corresponding thereto, I accomplish
simultaneously, by jointing the rod corresponding to that by which the "link"
is sustained or suspended in the "stationary link motion" to an arm from a
shaft or shafts, corresponding to the reversing shaft, connecting the valve-con-
necting or radius rod by a rod with another arm from the opposite side of the
same reversing shaft, by which arrangement it will be seen that the movement
of the reversing shaft will give to the link and valve rod and block or parts
(corresponding thereto), movements in opposite directions, of such extent as
will be regulated by proportioning the lengths of the arms from the axis or
centre of the reversing shaft or shafts. This simultaneous movement may be
obtained in a variety of ways, such as by a "forked lever," or a combination
of cranks and levers; but for simplicity of mechanism as well also for stability
I prefer the method above described. From the improved combination of
valve gear just described, the following advantages are obtained over the
common link motions." namely:-The mechanism is more simple in con-
struction, and more easily maintained in repair than common link motions;"
it requires less room than the "shifting link" the angular position of the
excentric rods as compared with the one class, and the valve-connecting rod
as compared with the other class of common link motions, is much reduced;
consequently the excentric and valve rods move through less space and are
more direct acting; the excentric rods and link and valve-connecting rod and
block, or parts corresponding thereto, balance each other, or nearly so, and
thus dispense with a counterbalance weight; and, lastly, less power is required
to move to or fix the valve gear in the required positions than in the common
link motions.
The preceding explanation of my Invention, and the mode of carrying it
into effect, will be rendered quite clear by the Sheet of Drawing hereunto
annexed, and the following description thereof.

page_text: But before describing the general arrangement of the mechanism shewn in the
Drawings, I have to explain that any of the links of ordinary construction may
be used, those shewn in the Figures 2 to 6, herein-after mentioned, being known
as "box links." But the construction of link which I prefer to employ either
as a straight or curved link is exhibited in the Drawings by Fig. 7, which is
a side view; and Fig. 8, a plan sectional view, drawn to an enlarged scale.
This link may consist of two straight bars (e), which form the sides of the link;
these bars have pivots formed on their outsides, to joint with the forks of the
excentric rods (d) and sustaining or suspension links (h). When the pivots
are placed in the holes in the forks, the bars are connected together by pieces
placed between them at each end, secured in position by bolts (el), by which
means the pivots are kept in the holes in the forks of the excentric rods. The
block fits between and grasps the sides of the bars, as will be understood on
reference to Fig. 7 and 8. It is formed in two parts; one (e) having a boss
on it and a hole through its centre, the boss forming the journal part, and
fits into the hole in the end of the valve-connecting rod (f); the other part
of the block (e) has a pin or projection from it, that fits into the hole in
the centre of the boss in the part (e), first described. This arrangement,
while it gives the means for readily connecting or disconnecting the valve
rod from the block, will cause both parts of the block to move when put
together between the bars (e), forming the link as if in one solid piece.
Fig. 1 is a Diagram, showing, an arrangement of valve gear where the end
of the valve or radius rod is held in the required position in relation to
the ends of the excentric rods, by an arrangement of radius rods forming a
parallel motion, as herein-before mentioned and explained; the view also
shewing my improved method of acting upon the mechanism to move or
fix it in the required positions by giving movement both to the valve or
radius rod and the excentric rods. Fig. 2 is a plan view, Fig. 3 a side view,
and Fig. 4 an end view, looking from the excentrics, of one arrangement of
my improved valve gear, with a straight link having the reversing shaft below
the link. Fig. 5 is a side, and Fig. 6 an end view, looking from the excen-
tries, of another arrangement, having the reversing shaft above the link. (The
same letters of reference are placed on the same and corresponding parts in
cach Figure of the Drawings.) a, portion of valve spindle; b, crank shaft;
c, excentrics; d, excentric rods, jointed with e, the link; f, rod jointed with the
valve spindle, and with the block or part corresponding thereto, that slides in or
on the "link"; g, reversing shaft, fixed in suitable bearings; h, rods jointed
to arms on the reversing shaft and to the link (e); k, other rods jointed with
arms on the reversing shaft and with the valve rod f; 1, lever on the reversing

page_text: shaft (g), jointed with the rod m, which may be connected with the ordinary
reversing handle. But in place of the ordinary reversing handle I prefer to
employ mechanism similar in arrangement to that represented by Fig. 9, an
elevation, and Fig. 10, a plan view, which consists in attaching to or forming
on the end of the rod ma toothed rack n, to gear with a pinion on a spindle
or shaft fixed on suitable bearings, having on the end of it a hand wheel p, by
which the shaft is revolved to communicate the requisite movements to the
rod m, and thus to the valve gear. By this arrangement, in combination with
my improved valve gear, the engineer will have a large increase of power to
produce any required changes in the position of the valve gear, even while the
valves have the full working pressure of the steam upon them, the extent of
such changes being ascertained from a scale graduated on the hand wheel.
I have now particularly described the nature of my Invention, and the
modes of carrying it into effect, and claim, as my Invention,―
Firstly, a straight or suitably curved link, arranged and combined with the
excentric and valve-connecting rods, so that both the link and the block or
parts corresponding thereto can be moved to get the block or parts correspond-
ing thereto at the required position or centre in or on the link.
Secondly, I claim, as my Invention in "link motions," arrangements for
giving a simultaneous movement both to the "link" and to the "block" or
excentric and radius rods, to move to or set the block or centre at the required
position in or on the "link."
Thirdly, I claim, as my Invention, the mode of constructing "blocks
used
in connection with the "bar link," herein-before described, and shewn in the
Drawings by Figs. 7 and 8.
Fourthly, I claim, as my Invention, arrangements consisting of a toothed
rack shaft, and toothed gear in connection with a hand wheel, graduated to
any per-centage of stroke to produce the changes required in the position of
the valve gear.
In witness whereof, I, the said Alexander Allan, have hereunto set my
hand and seal, this Twenty-sixth day of January, in the year of our
Lord One thousand eight hundred and fifty-six.
ALEXANDER ALLAN. (L.S.)