IMPROVEMENTS IN VALVE SEATS
Year: 1867

page_text: LETTERS PATENT to James Robert Napier, Marine Engineer, and William
John Macquorn Rankine, Civil Engineer, both of Glasgow, in the
County of Lanark, North Britain, for the Invention of "IMPROVEMENTS
IN VALVE SEATS."
Sealed the 8th October 1867, and dated the 10th April 1867.
PROVISIONAL SPECIFICATION left by the said James Robert Napier
and William John Macquorn Rankine at the Office of the Commissioners
of Patents, with their Petition, on the 10th April 1867.
We, JAMES ROBERT NAPIER, Marine Engineer, and WILLIAM JOHN
MACQUORN RANKINE, Civil Engineer, both of Glasgow, in the County of
Lanark, North Britain, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN VALVE SEATS," to be as follows:-
This Invention relates to seats for such valves for engines driven by steam
or other vapor or gas as act by sliding either on straight or on curved
surfaces, and it consists in making any such seat in such a manner that while
the parts of it which lie between the exhaust port or ports and the cylinder
ports remain fixed those parts which lie at the other sides of the cylinder

page_text: are movable. The last-mentioned parts of the valve seat being moved by
the engine, contract and enlarge the cylinder ports alternately, and thereby
affect the duration of admission of the steam in a way which enables variable
expansion gear to be used more conveniently and advantageously than hereto-
fore. The movable parts of the valve seat may be connected so as to move
together, or may move independently. It is preferred to use as a means of
moving them together an eccentric upon a rotating shaft. When either of
the movable parts of the valve seat is moved so as to contract its port, the
cutting off of the steam takes place earlier in the stroke than it would
otherwise do, and that without affecting the release or the compression.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said James Robert Napier and William John Macquorn Rankine
in the Great Seal Patent Office on the 9th October 1867.
TO ALL TO WHOM THESE PRESENTS SHALL COME, we, JAMES
ROBERT NAPIER, Marine Engineer, and WILLIAM JOHN MACQUORN RANKINE,
Civil Engineer, both of Glasgow, in the County of Lanark, North Britain,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Tenth day of April, in the year of our Lord One
thousand eight hundred and sixty-seven, in the thirtieth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto us, the said
James Robert Napier, and William John Macquorn Rankine, Her special
licence that we, the said James Robert Napier, and William John Macquorn
Rankine, our executors, administrators, and assigns, or such others as we,
the said James Robert Napier and William John Macquorn Rankine, our
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, exercise, and vend,
within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN VALVE SEATS,"
upon the condition (amongst others) that we, the said James Robert Napier
and William John Macquorn Rankine, our executors or administrators, by an
instrument in writing under our, or their, or one of their hands and seals,
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

page_text: 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 we, the said James Robert Napier and William
John Macquorn Rankine, do hereby declare the nature of our said Inven-
tion, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement in writing,
reference being had to the accompanying Drawings, that is to say :-
Our said Invention relates to seats for such valves for engines driven by
steam or other vapor or gas as act by sliding either on straight or on curved
surfaces, and it consists, according to one modification, in making any such
seat in such a manner that whilst the parts of it which lie between the exhaust
port and the cylinder ports remain fixed, those parts which lie at the other
sides of the cylinder ports are movable. The last-mentioned parts of the
valve seat being moved by the engine contract and enlarge the cylinder ports
alternately, and thereby affect the duration of admission of the steam in a way
which enables variable expansion gear to be used more conveniently and advan-
tageously than heretofore. The movable parts of the valve seat may be con-
nected so as to move together, or they may move independently. We prefer
to use as a means of moving them together an eccentric upon a rotating shaft.
When either of the movable parts of the valve seat is moved so as to contract
its port the cutting off of the steam takes place earlier in the stroke than it
would otherwise do without affecting the release or the compression.
And in order that our said Invention and the manner of performing the
same may be properly understood, we have hereunto appended a Sheet of
explanatory Drawings to be herein-after referred to, and representing an
example of the practical application of our improvements and a diagram
relating thereto.
Figure 1 is a section of a slide valve and seat; and Figure 2 is a face
view of the valve seat; Figure 8 is a diagram showing how the proper dimen-
sions for the various parts of the valve, the seat, and the valve motion are to
be determined. The kind of slide valve shewn is one iu which the pressure
of the steam on the valve is approximately balanced, by the help of a ring
at the back of the valve, which ring slides on the inner surface of the back
of the valve box; but our Invention is applicable to any kind of slide valve.
In Figures 1 and 2 A is the centre of the exhaust port B, B; B, C, B, C,
are the bars or fixed parts of the valve seat; C, D, C, D, are the cylinder
ports; C, C, the eduction edges; D, D, the induction edges; D, E, D, E,
are the movable parts of the valve seat, formed upon the outer face of a

page_text: sliding plate which has a reciprocating motion; F, H, F, H, a plane sliding
surface on the inner face of that plate; G, I, G, I, a plane surface, forming
an inner seat on which that plate slides; K, L; K, L, the plane surface of
the face of the slide valve. The valve and its movable seat are shewn, each
of them in its middle position; for although in the working of the engine
they do not arrive at their middle positions at the same instant, except when
the valve motion is in mid gear, those are the most convenient positions in
which they can be shown for purposes of designing. The effect of the
reciprocating motion of the movable seat is to make the width of opening
of each of the cylinder ports vary from C, D, plus balf of the travel of the
movable seat, to C, D, minus half the travel of the movable seat. That
motion may be produced by means of an additional eccentric, or any
mechanical equivalent for the same.
In order to show how an engineer is to proceed in designing a valve,
valve seat, and valve motion according to our Invention, we will suppose
that there are given the four positions of the crank, at the beginning and
end of the admission, and at the beginning and end of the exhaust, when
the slider that is attached to the valve rod is in a given position in
a link of a given length, the effective length of the eccentric rods, and
the distance between the centres of the forward and backward eccentrics
which are to move the link, and which are supposed to be of equal size and
similarly placed. Draw a straight line 1-2, in Figure 3, to represent the
line of centres of the shaft and cylinder, at any convenient point, 3, in 1-2,
draw 4-3-5 perpendicular to it, and make 3-4-3-5-half the intended
distance between the centres of the forward and backward eccentrics. Then
in the perpendicular lay off 3-6-3-7 as determined by the following
statement of proportion-As half the intended length of the link is to the
given distance of the slider from the middle of the link :: so is 3-4-3-5:
to 3-6-3-7. Through 6 and 7 draw straight lines 6-8 and 7-9
parallel to 1-2. Through any convenient point 10, in 1-2, draw four
straight lines to represent the four given positions of the crank; viz., at the
beginning of the admission 10-11; at the cut-off or end of the admission
10-12; at the release or beginning of the exhaust 10-13; at the end of
the exhaust or beginning of the compres-ion 10-14, draw 10-15, bisecting
the angle 11, 10, 12, and cutting 6-8 in 15; also 10-16 bisecting the
angle 13, 10, 14, and cutting 7-9 in 16. Through 16 draw 16-17 equal
and parallel to 10-15, and cutting 1-2 in 17; then 10-17 will be the
proper half travel for the movable part of the seat; 10-16 will be the

page_text: proper half travel for the slide valve, and 16-17-10-17 will be the
half travel of the slide valve relatively to the movable part of the seat.
Another construction for finding these quantities is as follows:-Through 7
draw 7-18 equal and parallel to 16-10, and cutting 1-2 in 18; also
7-19 equal and parallel to 10-15, and cutting 1-2 in 19; then 18-19
will represent the proper half travel for the movable part of the valve seat.
Also if 18 be taken to represent the centre of the shaft, 19 will represent
the
proper position at the beginning of the forward stroke, for the centre of
the additional eccentric, supposing that to be the kind of mechanism used
for giving motion to the movable part of the valve seat. To find the proper
positions at the beginning of the forward stroke for the centres of the forward
and backward eccentrics, different rules are to be followed according to the
construction of the link motion. If the motion has a fixed link the points 4
and 5 already laid down will represent the required positions, relatively to 18
as the centre of the shaft. If the motion has a movable link through
4 and 5, draw 22-23 and 24-25 parallel to 1-2; then with a radius
determined according to rules, which are given in treatises on the steam
engine, and on slide valve gearing in particular, draw a circular are through
the points 6 and 7, cutting 22-23 and 24-25.. If at the beginning of
the forward stroke the eccentric rods are to be open, make that are concave
towards 18, as 22-6-20-7-24; 22 and 24 will be the positions required.
If those rods are to be crossed, make the arc convex towards 18, as 23-6
-21-7-25; 28 and 25 will be the positions required. If the given
position of the slider in the link is at the end of an eccentric rod, the points
6 and 7 coincide with the points 4 and 5, and are themselves the required
positions for the centres of the eccentrics, whatsoever may be the construction
of the link motion. To find the proper cover or lap at the induction edge of
the cylinder ports, bisect 10-15 in 26, and about 26 with the radius 26-10
describe a circle cutting 10-16 in 28, and 10-12 in 29, 10-28=10-29,
will be the required cover. To find the proper cover or lap (if any) at the
eduction edge of the cylinder ports, bisect 10-16 in 27, and about 27 with
the radius 27-10 describe a circle, cutting 10-13 in 30 and 10-14 in 31;
10-30-10-31 will be the required cover. When 10-13 and 10-14
lie in one straight line, the circle described about 27 will touch that straight
line, and then there is to be no cover at the eduction edge. Should 10-13
and 10-14 make with each other an angle greater than two right angles,
then the circle described about 27 will cut those lines produced beyond 10,
and the length of each of the parts which it cuts off will represent an

page_text: opening required at the eduction edge in the middle position of the slido
valve. To find the greatest opening for admission with the given adjustment
of the valve motion, about 10 draw the circular arc 28-32-29, then
32-15 will be the opening sought. To find the greatest opening for exhaust
with the given adjustment of the valve motion, about 10 draw the circular
arc 30-33-31, then 33-16 will be the opening sought, if 10-33 repre-
sents cover. When there is no cover and no opening in the middle position
of the slide 10-16 will represent the opening sought. Should 10-33
represent an opening in the middle position 10-16+10-33 will be the
opening sought.
In constructing the seat and valve make G, F, Figure 1, equal to 10-17,
Figure 3, D, L, equal to 10-32, and C, K, equal to 10-33. Also, if it
be desired to take full advantage of the openings made by the valve and seat,
make K, D, not less than 10-15, and C, A+A, B, not less than twice
10-16. If it be desired to make the volumes of steam admitted to the two
ends of the cylinder different, that can be done in the usual way by altering
the cover at one or both of the induction edges of the slide valve.
The preceding is the method which we prefer for designing the slide valve,
valve seat, and valve motion, but the engineer may vary the process in detail
provided he adheres to its principles.
We have now described in detail one arrangement whereby our Invention
is to be carried into effect, but the particular arrange.nents may be varied in
detail so long as the principle of our Invention is adhered to, that principle
being to contract and enlarge alternately the openings of the cylinder ports
by giving part or parts of the valve seat a reciprocating motion. And
although in the example we have described in detail that alternate con-
traction and enlargement is effected by keeping the eduction edges of the
ports fixed and making the induction edges move, the same thing may be
effected by keeping the induction edges fixed and making the eduction edges
move, provided that the two edges of each port and the slide valve are actuated
so as to have the proper motion relatively to each other. When the latter
modification is adopted the construction for designing the valve motion is the
same as before, except that in Figure 3, 19 is to be held to represent the
centre of the shaft, and 18 that of the additional eccentric.
And now having particularly described our said Invention, and the manner
in which the same is to be performed, we have to state that what we believe
to be novel and original and claim as the Invention secured to us by the
herein-before in part recited Letters Patent is, the making of any seat for

page_text: a slide valve in an engine driven by steam or other vapor or gas in such a
manner as to alternately enlarge and contract the cylinder ports and thereby
affect the duration of admission of the steam.
In witness whereof, we, the said James Robert Napier and William
John Macquorn Rankine, have hereunto set our hands and seals, this
Seventh day of October, in the year of our Lord One thousand eight
hundred and sixty-seven.
0 Witness,
EDMUND HUNT,
Patent Agent,
Glasgow.
JAMES R. NAPIER.
(L.S.)
W. J. MACQUORN RANKINE. (L.S.)