Rotary valve with pressurized energized seal

A rotary valve is provided including a valve element mounted within the flow path of a valve body and rotatable about a stem axis. A peripheral seating surface on the valve body surrounds the flow path through the valve body and is spaced from the stem axis for sealing engagement with the valve element when rotated to its closed position. The peripheral seating surface on the valve body is preferably annular, and more preferably has an arcuate cross-sectional configuration and includes a central annular seating line spaced closer to the center point of the valve than adjoining upstream and downstream portions of the seating surface. The valve element includes a rigid body with a peripheral resilient overlay. The resilient overlay has a peripheral pressure-responsive sealing member for flexing in response to fluid pressure into sealing engagement with the seating surface. A peripheral backup shoulder is provided on the rigid body of the valve element for preventing extrusion of the sealing member under high pressure when the valve element is in engagement with the annular seating surface. The concepts of the present invention are particularly well suited for a plug valve and provide reliable sealing engagement between the plug and the seating surface when a high pressure differential exists across the closed valve.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to rotary valves for controlling fluid flow. 
More particularly, this invention relates to a rotary valve with a valve 
member having a peripherally extending resilient overlay for sealing 
engagement with a peripheral seating surface on the valve body that is 
spaced from the valve stem axis. 
2. Description of the Background 
Rotary valves are distinct from other valves in that the valve member 
rotates within the valve body to create and break a seal with the seating 
surface, thereby effecting closing and opening of the valve. Rotary valves 
are frequently quarter turn valves, meaning that the valve member rotates 
90.degree. between its fully closed to its fully opened positions. 
One type of quarter turn rotary valve is referred to as a plug valve, which 
employs a valve element or plug having an external sealing surface and a 
cut-out or through port for transmitting fluid through the valve when the 
plug is rotated to its open position. Plug valves have long been preferred 
for controlling fluid flow in certain industries, particularly those 
wherein the fluid is a sludge or slurry, or when solid particles are 
transmitted through the valve with the fluid. U.S. Pat. No. 3,347,516 
discloses such a plug valve with valve seat spaced from the stem axis. The 
valve element or plug has a frustoconical-shaped outer surface to seal 
with an inner surface of the valve body, with a cutout in the plug 
allowing fluid passage when the plug is rotated to its open position. 
Another type of plug valve is marketed by Keystone Valve USA, Inc. under 
the "Ballcentric" trademark. The seating surface of this valve body is 
also spaced from the axis of the valve stem, and the plug has a generally 
hemi-spherical shape. When the eccentric plug is rotated to its closed 
position, the external wall of the plug seals with the annular seating 
surface on the valve body. When the plug is rotated 90.degree., the valve 
element is moved to the side of the valve body and out of the flow path to 
allow unobstructed flow through the valve. The Ballcentric valve improves 
flow characteristics through the valve and reduces pressure drop across 
the valve compared with plug valves having a conventional passageway 
through the plug. In order to improve valve sealing reliability, the 
metallic valve element has been coated with an elastomeric overlay so that 
the overlay seals with the seating surface to obtain a fluid-tight seal 
when the valve is in its closed position. 
U.S. Pat. No. 2,852,226 discloses a plug valve with a flexible sealing 
plate provided on the plug body. The plug is of the traditional type with 
a passageway through the plug to allow fluid flow through the valve. The 
sealing plate includes a circumferential flange intended to be 
continuously pressed against the inner surface of the plug valve. The 
specification indicates that fluid pressure will urge the flange into 
tighter sealing engagement with the fluid line, and a pair of sealing 
plates are provided on opposing sides of the valve stem. 
U.S. Pat. No. 3,404,864 discloses a rotary valve wherein the valve element 
is in the shape of a tube. As shown in FIGS. 13 and 14, a valving tube may 
be fitted over a valve extension tube, with an external periphery of the 
valving tube forming a lip that is biased by pressure toward the wall. 
U.S. Pat. No. 3,990,676 discloses a sealing gasket on a valve element. The 
sealing gasket may include opposing lips for shutting off flow of fluid 
under pressure from either of the upstream port or downstream port of the 
valve. 
Plug valves are preferably designed so that the valve element seals fluid 
flow when the valve is closed regardless of the direction fluid pressure 
is applied to the valve. Plug valves may be installed with the intent of 
fluid passing primarily in one direction through the valve, e.g., from an 
upstream high pressure side of the valve to a downstream low pressure side 
of the valve. The valve should ideally be able to seal fluid flow in the 
reverse direction, however, so that a leak occurring between two plug 
valves in a system can be isolated, with high pressure being maintained on 
opposing sides of the two closed plug valves. 
One of the problems particularly associated with rotary valves having 
seating surfaces offset from the valve stem axis concerns the difficulty 
of maintaining sealing engagement between the plug and the seat when fluid 
pressure is pressing the plug toward the valve stem axis and thus away 
from the seat, while maintaining long seal life if opposing fluid pressure 
forces the plug toward tighter sealing engagement with the seat. This 
problem is compounded when the valve member includes a resilient overlay 
to enhance sealing reliability, as explained above, since the metallic 
plug body moves with respect to the valve stem axis in response to the 
fluid pressure differential, and since the resilient overlay also moves 
with respect to the metallic plug body in response to this same pressure 
differential across the closed valve. Traditional techniques for dealing 
with this dilemma have included the use of harder or less resilient 
overlays on the plug, increased plug-to-seat interference, and/or 
reduction in the "play" or maximum axial movement of the plug with respect 
to the seat. However, the benefits of an overlay are reduced if the 
elastomer becomes less resilient. Increased plug-to-seat inference results 
in increased torque requirements to operate the valve, thereby resulting 
in larger and more expensive stems, bearings, operators, and related 
components. Reducing play between the components results in increased 
manufacturing costs, use of more durable, and thus more expensive, 
components, and more frequent valve maintenance. 
Thus, there has been a long-felt but unfulfilled need for an improved 
rotary valve that offers high sealing reliability and long seal life with 
a resilient overlay on a valve element adapted for engagement with a seat 
spaced from the valve stem axis. 
The disadvantages of the prior art are overcome by the present invention, 
and an improved rotary valve is hereinafter disclosed for reliably sealing 
fluid flow. The techniques of the present invention are particularly well 
suited for use with a plug valve having a resilient overlay on a rigid 
valve body wherein the annular seating surface is offset from the valve 
stem and the plug responds to varying fluid pressure by slight axial 
movement. 
SUMMARY OF THE INVENTION 
A rotary valve body has a fluid flow path with a central axis and the valve 
element such as a plug mounted therein and rotatable about a stem axis. An 
annular seating surface on the valve body is spaced from the stem axis for 
sealing engagement with the plug when rotated to its closed position. The 
valve member includes a rigid body and a resilient overlay secured to the 
rigid body for fluid-type sealing engagement with the annular seat. 
According to the present invention, the intersection (or approximate 
intersection) of the flow path axis with the stem axis defines a center 
point of the valve. The annular seating surface on the valve body includes 
a central annular seating line formed by center seating points within 
cross-sectional planes including the flow path central axis. The rigid 
body of the valve element has an exterior annular reference line defined 
by reference points each coincident with a side of a reference cone having 
a base defined by the central annular seating line when the valve is in 
its closed position and a vertex defined by the center point of the valve. 
The resilient overlay includes a pressure-responsive, peripheral sealing 
member spaced from the sides of the reference cone and outwardly with 
respect to the center point of the valve from an adjoining portion of the 
overlay spaced further from the reference cone for flexing into sealing 
engagement with the peripheral seating surface when the valve is in its 
closed position. In a preferred embodiment, the sealing member and seating 
surface are annular. In a more preferred embodiment, the rigid body of the 
valve element includes an annular backup shoulder spaced outwardly from 
the exterior annular reference line with respect to the center point of 
the valve for preventing extrusion of the sealing member under high 
pressure when the valve member is in engagement with the annular seating 
surface. In another embodiment, the resilient overlay includes a central 
annular portion coincident with the sides of the reference cone for 
sealing engagement with the annular seating line of the seating surface, 
and a pressure-responsive, annular portion spaced from the sides of the 
cone such that the central annular portion and the pressure-responsive, 
annular portion form a conterminous seal with the annular seating surface. 
The pressure-responsive, annular sealing member may define a resilient lip 
protruding outwardly from the center point of the valve and defining an 
annular groove between the lip and an inward portion of the resilient 
overlay spaced toward the central axis. When the lip is spaced opposite 
the stem axis with respect to the sides of the reference cone, the annular 
backup shoulder is spaced between the sides of the reference cone and the 
stem axis. The central annular seating line of the seating surface is 
preferably closer to the center point of the valve than remaining 
adjoining upstream and adjoining downstream portions of the annular 
seating surface. The seating surface may have a generally arcuate 
cross-sectional configuration, with an arc center spaced outwardly from 
the center point of the valve with respect to the seating surface and 
substantially along a line passing from the center point of the valve 
through the central annular seating line. 
The valve element may be a Ballcentric valve as described above or any plug 
valve with a cut-out flow path therein for transmitting fluid through the 
valve when the valve member is rotated to the open position. Both first 
and second pressure-responsive portions of the sealing member may be 
provided each for flexing into sealing engagement with the seating surface 
in response to fluid pressure applied to either the upstream or downstream 
side of the valve, and a backup shoulder may be provided on each side of 
the reference cone for preventing extrusion of the pressure-responsive 
portion on the opposite side of the reference cone, which otherwise would 
tend to occur in response to a high fluid pressure differential across the 
sealing member. 
It is an object of the present invention to provide an improved rotary 
valve with a pressure-responsive, resilient, peripheral overlay on the 
valve element for reliable sealing engagement with a peripheral seat on 
the valve body. 
It is a further object of this invention to provide an improved rotary 
valve capable of a fluid-tight seal when the closed valve element moves 
with respect to the valve body in response to fluid pressure on either the 
upstream or downstream side of the valve. 
It is yet another object of this invention to provide a relatively low cost 
and highly reliable valve that does not require high maintenance. 
It is a feature of the present invention that a resilient overlay is 
provided on a quarter turn plug having a metal seat on the valve body 
substantially offset from the stem axis, and with the valve element 
including an annular backup shoulder positioned for preventing extrusion 
of the resilient sealing member when subject to high fluid pressure. 
Yet another feature of the invention is that a seating surface on the valve 
body has an arcuate cross-sectional configuration with a center seating 
line lying closer to the center point of the valve than upstream and 
downstream portions of the seating surface, and that the resilient overlay 
has a central portion coincident with the sides of the reference cone and 
a pressure-responsive, annular portion spaced from the sides of the 
reference cone, with these resilient overlay portions forming a seal 
conterminous in cross-section with the annular seating surface. 
Still another feature of this invention is that the resilient overlay 
includes a center portion for sealing engagement with the center annular 
seating line of the seating surface and a pressure-responsive, annular lip 
for sealing engagement with an adjoining portion of the seating surface, 
with the center point and lip forming a seal with the annular seating 
surface conterminous in cross-section. 
It is an advantage of the present invention that material for the resilient 
overlay may be selected with little concern for extrusion, since the 
backup shoulder substantially minimizes or prevents extrusion. 
It is a further advantage of the invention that the valve may be 
manufactured from materials and according to component tolerances that 
allow axial movement of the valve element with respect to the valve body, 
while nevertheless maintaining highly reliable sealing engagement between 
the valve member and the seat on the valve body when subject to high fluid 
pressure. 
These and further objects, features, and advantages of the present 
invention will become apparent from the following detailed description 
wherein reference is made to the figures in the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A rotary plug valve 10 according to the present invention is generally 
shown in FIGS. 1 and 2. Valve body 12 includes a flow path 14 therethrough 
for passing fluid through the valve. The flow path 14 has a central axis 
CA that is preferably a straight line through the valve body, although the 
concepts of the present invention may be utilized with a valve having, for 
example, one port oriented at 45.degree. or 90.degree. with respect to the 
other port. 
For the valve as depicted in FIGS. 1 and 2, the valve body forms a fluid 
inlet flange 16 and an outlet flange 18 each having a circular port 
therein formed about axis CA. Each flange 16, 18 may include conventional 
holes 20 for securing the valve body to respective pipe flanges. An upper 
cap or bonnet 22 may be secured to the top of the valve body by bolts 24. 
A valve stem 26 is rotatable with respect to the body about stem axis SA. 
Bushings 28 are provided for rotatably mounting both the upper and lower 
ends of the stem to the valve body. Fluid-tight sealing between the stem 
and body is provided by conventional sealing members. The valve body 12 
defines a cylindrical lower cavity 30 therein to receive the lower end of 
the stem so that the valve element and stem may be removed from the valve 
body by unbolting the bonnet 22 and lifting the components through the 
opening in the top of the valve body. 
With reference to FIG. 1, the valve element 32 is fixedly secured to the 
stem 26 and includes a metallic rigid body 34 with an elastomeric, and 
thus resilient, overlay 36 secured to the body 34. The valve element 32 
has a generally semi-spherical shape, with a semi-cylindrical center 
portion 38 providing a "full bore" passageway through the valve when the 
element 32 is rotated to its open position. The overlay 36 may be formed 
in a conventional manner by injection molding the elastomer on the body 
34, with the body 34 centrally positioned within a mold cavity having 
generally the same shape but being slightly larger than the body. The 
generally cylindrical shape of the inner resilient layer 40 on the inner 
surface of the body 34 provides corrosion protection and longer life of 
the valve element. The outer, generally spherical-shaped layer 42 serves 
the same function and provides a resilient seal for sealing the valve 
element with the valve body. 
With reference to FIGS. 1, 2, and 3, the metal seating surface 44 on the 
valve body surrounds the flow line central axis CA and is substantially 
spaced from the stem axis SA. The intersection or approximate intersection 
of central axis CA and stem axis SA defines a center point CP of the valve 
body and thus the valve. Seating surface 44 has an arcuate, convex 
cross-sectional configuration within a cross-sectional plane including the 
flow path central axis; the axis CA lies entirely within the 
cross-sectional plane. With reference now to FIG. 3, the arcuate, convex 
cross-sectional configuration of the seating surface has an arc center AC 
spaced radially from the center point CP of the valve body with respect to 
the seating surface. The annular seating surface is convex in the sense 
that it has a central annular seating line SL formed by center seating 
points SP closer to the center point CP of the valve body than the 
remaining upstream and downstream portions of the seating surface (see 
FIGS. 1 and 3). In other words, each cross-sectional plane of the seating 
surface includes two such points SP on opposite sides of the axis CA, and 
the rotation of the cross-sectional plane about axis CA creates a seating 
line SL formed by these points. The arc center AC of each cross-sectional 
configuration of the arcuate seating surface is preferably spaced 
substantially along a straight line passing from the center point CP of 
the valve body through a corresponding central annular seating point. 
Again, under the assumption that fluid flow is from the left to the right 
through the valve depicted in FIG. 1, the cross-section of each seating 
surface as shown in FIG. 2 thus includes an upstream portion 44 and a 
downstream portion 46 on opposing sides of the seating point SP. The 
entirety of the cross-sectional seating surface 42 is spaced in the valve 
body between an adjoining interior upstream valve body surface 90 and an 
adjoining downstream valve body surface 92 on the downstream side of 
seating line SL, with neither of the surfaces 90 or 92 serving a sealing 
function with the valve member 32. 
With reference to FIG. 4, the rigid body 34 of the valve member has a 
generally spherical-shaped outer surface 48 with a resilient overlay 42 
that includes a pressure-responsive, peripheral sealing member 50. Sealing 
member 50 is spaced outwardly from the surface 48 with respect to the 
central axis CA, and takes the form of an annular lip 52 protruding 
outwardly from the valve stem axis and defining an annular groove 54 
spaced between the lip and an adjacent portion 56 of the overlay spaced 
from the lip toward the central axis CA of the valve when the valve is in 
its closed position. The groove 54 thus lies along a line extending 
between the cantilevered end 51 of the lip and the center point of the 
valve (in a cross-sectional view). 
To gain a better understanding of the present invention, it is convenient 
to define a reference cone as shown in FIG. 1, which has a base defined by 
the central annular seating line SL and a vertex defined by the center 
point CP of the valve. The rigid body 34 of the valve member 32 has an 
external reference line RL defined by reference points RP, each coincident 
with the sides CS of the reference cone when the valve element is rotated 
to its closed position. As shown in FIG. 4, the annular sealing member 50 
is spaced outwardly from the exterior annular reference line with respect 
to the center point of the valve and may flex into sealing engagement with 
the annular seating surface when the valve is in its closed position, as 
explained subsequently in detail. Sealing member 50 is spaced from the 
sides CS of the reference cone and outwardly with respect to center point 
CP from an adjoining portion of the overlay 36 spaced further from the 
reference cone. 
In a preferred embodiment of the present invention, the rigid body 34 of 
the valve member includes an annular backup shoulder 58 spaced outwardly 
from the corresponding reference point RP on the rigid body with respect 
to the center point CP of the valve. This backup shoulder substantially 
minimizes or prevents extrusion of the sealing member by fluid pressure 
when the sealing member is in engagement with the annular seating surface. 
If the sealing member 50 is spaced between the sides CS of the reference 
cone and the central axis CA, the shoulder 58 is spaced between sides CS 
and the stem axis. 
For the embodiment as shown in FIG. 4, the backup shoulder 58 is spaced 
between sides CS of the reference cone and the stem axis SA, and a 
majority portion of the annular sealing member 50 is spaced opposite the 
stem axis with respect to sides CS. The central outer surface of the rigid 
body 34 of the valve member 32 may be flattened, as shown in FIG. 1, 
thereby reducing the weight of the valve element and minimizing its 
extension of the valve member from the seating line SL with respect to the 
center point of the valve. The outer surface of the valve body 34 
extending outwardly from the shoulder with respect to the central axis CA 
may return to the generally spherical shape 48 (so that the shoulder forms 
a hump in the valve body), or may continue toward the valve stem at 
approximately the maximum diameter of the hump with respect to the center 
point of the valve, as shown in FIG. 4. 
The FIG. 4 embodiment of a valve member is depicted in FIGS. 8 and 9, 
illustrating the axial movement of the valve member in response to fluid 
pressure. This movement is typically less than 0.010 inch, but is 
exaggerated in the figures to illustrate the concepts of the invention. In 
the FIG. 8 illustration, fluid pressure is applied from the downstream or 
right side of the valve, thereby moving the valve element slightly closer 
to the seating surface 42. Engagement of the lip 52 with the seating 
surface causes the outer surface of the lip to assume the generally 
curvilinear cross-sectional configuration of the seating surface. Fluid 
pressure on the valve element causes the downstream portion 46 of the 
seating surface to be in sealing engagement with the resilient overlay, 
although a portion of the upstream portion 44 is also forced into 
engagement with a portion of the outer surface of the lip 52. Since the 
valve element is forced closer to the valve body seating surface, an 
increase of fluid pressure creates an even tighter seal to prevent fluid 
flow through the valve, even though the lip 52 itself is not subject to 
this increased fluid pressure. 
For the illustration shown in FIG. 9, fluid pressure pushes the valve 
member away from the seating surface 42, and a fluid-tight seal is 
obtained by the lip 52 pressing outwardly with respect to the central axis 
CA. Again, increased fluid pressure forces the lip into tighter sealing 
engagement with the seating surface. If the backup shoulder 58 is not 
provided, a high pressure differential across the valve element would tend 
to extrude the lip 52 between the rigid body 34 and the seating surface, 
thereby breaking the seal. The valve would, of course, then lose its 
sealing function, and the entire valve element would likely have to be 
replaced since the annular lip 52 is integral with the rigid body 34 and 
would likely be ruined. The present invention avoids this problem by 
utilizing a backup shoulder 58 to prevent extrusion, even when the rigid 
body moves away from the seating surface in response to high fluid 
pressure. 
FIG. 5 discloses an alternative embodiment of the rigid body valve member 
of the present invention. The difference between the embodiments of FIG. 4 
and 5 relates to the cross-sectional configuration of the annular sealing 
member. Even when the valve element is not in engagement with the seating 
surface, the embodiment shown in FIG. 4 forms a pressure-responsive lip 
and a groove 54 as discussed above. This lip may, however, allow debris or 
"trash" passing through the valve to become caught in the lip and thereby 
interfere with an effective seal between the seating surface and the valve 
element when the valve is rotated to its closed position. In the currently 
preferred embodiments for most valve sizes, this lip may be less 
pronounced than as shown in FIG. 4 but nevertheless is provided to 
increase sealing effectiveness when the valve element moves away from the 
seating surface in response to fluid pressure. 
In the embodiment as shown in FIG. 5, however, a lip and groove is not 
provided, and the relaxed sealing member 62 may have an outer surface 64 
that lies within a vertical plane; i.e., surface 64 is co-planar with the 
stem axis SA. Nevertheless, in this embodiment the majority of member 62 
is spaced opposite the stem axis SA with respect to the sides CS of the 
reference cone. Member 62 is also pressure-responsive, since it extends 
outwardly (with respect to center point CP) from its adjoining portion 63 
of the overlay spaced further from the sides of the reference cone. When 
fluid pressure is applied to the sealing member 62 and presses the 
resilient overlay 36 toward the seating surface 42, a slight lip and 
groove may be formed as a result of the compressed annular sealing member. 
Even for the FIG. 5 embodiment, however, an effective low pressure seal 
can be maintained, and the shoulder 58 substantially enhances sealing 
effectiveness by minimizing the likelihood that the sealing member 62 will 
be extruded between the seating surface and the rigid body of the sealing 
element. 
FIG. 6 discloses a double lip seal, double backup shoulder embodiment 
according to the present invention. The annular sealing member comprises a 
first pressure-responsive, lip portion 66 that is spaced opposite the stem 
axis with respect to the sides CS of the reference cone, and a second 
pressure-responsive, lip portion 68 spaced between the sides CS of the 
reference cone and the stem axis. A first backup shoulder 70 is spaced 
between the sides CS of the reference cone of the stem axis SA for 
preventing extrusion of the first lip 66, while a second backup shoulder 
72 is spaced opposite the stem axis with respect to the sides of the 
reference cone to prevent extrusion of the lip 68. For the embodiment as 
shown in FIG. 6, the outer surface 48 of the rigid body has a generally 
spherical-shaped uniform diameter on both the upstream and downstream 
sides of the backup shoulders. 
FIG. 7 discloses yet another embodiment of the present invention with a 
sealing member including lips 74 and 76 on opposing sides of the reference 
cone, but with no backup shoulders to prevent extrusion. In still another 
embodiment, which is discussed below, the double lip sealing member as 
shown in FIG. 7 may be provided in conjunction with a single backup 
shoulder. Since extrusion of the lip is more likely when fluid pressure 
moves the valve element away from the seating surface, this latter 
embodiment preferably would include a shoulder between the side CS of the 
reference cone and the stem axis for preventing extrusion of lip 74. 
FIG. 10 illustrates this embodiment in sealing engagement with the seating 
surface 42 previously described. It should be understood that the 
embodiment as shown in FIG. 7 is practically also depicted if the 
shoulders are eliminated, and that the embodiment as shown in FIG. 6 is 
practically depicted if both shoulders are provided. In FIG. 10, the valve 
element is shown in sealing engagement with the surface 42, although 
little, if any, fluid pressure is applied to the valve element. The outer 
surface of the sealing element is compressed to conform to the generally 
arcuate cross-sectional configuration of the seating surface. When little 
or no fluid pressure differential exists across the closed valve element, 
the seal is nevertheless obtained by fluid-tight engagement of the sealing 
element with the seating surface. When fluid pressure is applied to move 
the valve element away from the seating surface 42, it may be understood 
that the lip that is pressurized by the fluid pressure may be 
substantially deformed. The lip not subject to high fluid pressure retains 
substantially its original configuration, with most, if not all, of the 
effective seal being between the pressure energized lip and the seating 
surface. 
FIG. 11 illustrates fluid pressure moving the valve element slightly away 
from the seating surface, with the single shoulder 80 particularly being 
useful for minimizing extrusion of lip 74. In FIG. 12, fluid pressure 
presses the valve element closer to the seating surface. While the 
shoulder may minimize extrusion in both the FIG. 11 and FIG. 12 
embodiments, the shoulder 70 is primarily provided for minimizing 
extrusion of lip 74 in the FIG. 11 environment. Since the valve element in 
FIG. 12 is moved closer to the seating surface 42, and thus fluid pressure 
presses the sealing element into engagement with the seating surface, the 
extrusion shoulder is of less importance in this situation. 
According to the present invention, each of the seating surfaces 42 
preferably has a geometry as shown in FIG. 3. The seating surface 42 
includes at least a substantial portion formed about arc center AC. The 
cross-section of the entire seating surface on the valve body is between 
an adjoining upstream surface 90 on the valve body and an adjoining 
downstream surface 92 on the body, with neither of the surfaces 90, 92 
providing any seal with the resilient overlay of the valve element. 
With reference to FIGS. 8-12, the resilient overlay for each of these 
embodiments includes a first annular portion 78 coincident with the sides 
CS of the reference cone for sealing engagement with the central annular 
seating line SL of the seating surface, and a pressure-responsive, annular 
portion spaced from the sides of the cone for sealing engagement with 
another portion of the annular seating surface, with the central annular 
portion and the pressure-responsive, annular portion forming a continuous 
seal with the cross-sectional annular seating surface. For the embodiment 
as shown in FIGS. 8 and 9, this pressure-responsive, annular portion is 
the annular lip 52 previously described, and a continuous seal between the 
seating surface and the sealing element is formed extending between an 
upstream portion 44 of the seating surface through the seating point SP as 
shown in FIG. 3. For the embodiment as shown in FIG. 10, this continuous 
seal is formed between the sealing member and the seating surface and 
extends between an upstream portion 44 of the seating surface through the 
point SP to the downstream portion 46 of the seating surface. For the 
embodiment as shown in FIG. 11, this continuous seal is provided between 
at least the upstream portion 44 of the seating surface and the point SP, 
while for the environment as shown in FIG. 12 this continuous seal is 
formed between the point SP and a downstream portion 46 of the seating 
surface. It is thus a significant feature of the present invention that 
the resilient overlay includes a central annular portion that will be in 
sealing engagement with the central annular seating line of the seating 
surface when the valve is in the closed position, while a 
pressure-responsive portion is also provided for engagement with the 
seating surface, so that in cross-section a continuous seal is obtained 
for reliable sealing engagement. 
The concepts of the present invention are particularly well suited for a 
plug valve. Ball valves and other types of rotary valves frequently are 
designed so that the valve element does not substantially move in response 
to an increase in fluid pressure and, accordingly, any resilient overlay 
provided on such a valve element would not be as susceptible to extrusion. 
Although the present invention has been particularly described with respect 
to a plug valve having a generally semi-spherical-shaped element, the 
concepts of the present invention could be used for various types of plug 
valves. While the valve of the present invention has been described with 
respect to a valve with a seating surface having a generally circular 
configuration, an elliptical, generally rectangular, or generally square, 
seating surface may be provided in the valve body, and a similarly 
configured annular seat provided on the valve element. In this respect, it 
should be understood that the term "conical" with respect to the reference 
cone with sides CS is intended in its broadest sense to include a 
reference body with a base defined by the seating surface and a vertex 
defined by the center point of the valve, and that the configuration of 
the base of the reference cone need not be circular. Also, although in the 
embodiments shown in the drawings and described herein, the valve element 
is mounted for centric rotation, the invention finds particular 
application to eccentrically or double-offset journalled valve elements. 
Such plug valves are well known to those skilled in the art, who will 
appreciate the applicability of the present invention thereto. 
Since the concepts of the present invention substantially reduce or 
eliminate the likelihood of extrusion of the resilient overlay even when 
the closed valve element is subject to a high pressure differential, the 
selection of material for the overlay may be based upon primary 
considerations such as cost, resiliency of the material to contain a seal 
under high fluid pressure, and extended seal life, with concern for the 
extrusion of the overlay being substantially minimized. 
Although several embodiments of the present invention have been described, 
it should be understood that the invention is not limited to the 
embodiments described herein and shown in the accompanying drawings. Other 
embodiments should be apparent to those skilled in the art based upon the 
concepts disclosed herein, and, accordingly, the scope of the invention is 
not limited to the embodiments described and illustrated but is defined by 
the following claims.