Nonfloating seat for expanding gate valves

To prevent pressure induced floating of the interference fitted seats of expanding gate valves, a seat ring body is provided which is press fitted within the upstream seat recess of a valve body. The seat ring body defines a sealing face of circular form which is disposed for sealing engagement with the segment portion of an expanding gate and segment assembly. The seat ring body also defines an axial extension tube extending upstream from the seat ring body with a circular sealing lip defining the outer periphery thereof being in radial sealing engagement with a reduced diameter portion of the seat recess. The radial extension is pressure yieldable to enhance the radial sealing capability thereof and defines a pressure responsive area that is equal to or less than the pressure responsive area of the sealing face.

FIELD OF THE INVENTION 
This invention relates generally to gate valves, and more specifically 
concerns nonfloating seats for parallel expanding gate valves. 
BACKGROUND OF THE INVENTION 
Parallel, expanding, through-conduit gate valves are widely utilized in 
high pressure fluid controlling service such as is typically found in the 
petroleum industry because the sealing capability thereof can be 
mechanically controlled to accomplish the necessary seat/gate force for 
efficient metal-to-metal sealing capability. Moreover, the sealing 
capability of the valve mechanism can be mechanically controlled both in 
the open and closed positions thereof through external application of 
linear force on the expanding gate mechanism. Where gear actuators and 
hand wheels are employed to accomplish opening and closing movement of the 
valve mechanism, personnel will simply rotate the hand wheel sufficiently 
to apply an adequate amount of torque which, through the gear train 
mechanism, applies desired linear force to the valve stem interconnecting 
the expanding gate mechanism with the valve actuator. Expanding gate 
mechanisms take a number of different forms but one widely accepted 
expanding gate mechanism is representative of the prior art shown 
generally at 10 in FIG. 1. The parallel expanding gate assembly of FIG. 1 
consists of two wedge pieces, namely a gate member 12 and a segment member 
14, which are held together by means of arched wire springs 16 having 
curved extremities 18 and 20 in engagement with pin members 22 and 24 
positioned at the upper and lower extremities of the gate member. The 
intermediate portions of the arched spring wires 16 are positioned in 
engagement with a pin members 26 which are centrally located on opposite 
sides of the segment member 14. The force developed by the spring wires 16 
on the pins on the gate and segment urge the free segment member toward a 
fully seated relationship with the gate member so that surfaces 28 and 30 
of the segment are disposed in intimate seated, fully engaging relation 
with both of the angulated surfaces 32 and 34 of the gate member. The 
angulated surfaces 28 and 30 of the segment and 32 and 34 of the gate are 
in fact planar cam surfaces which control the position of planar sealing 
faces 36 and 38 formed respectively on the gate and segment members. 
The gate member is movable linearly by means of one or more valve stems 40 
and 42. Typically, one of the stems 40 functions as a gate actuating stem 
while the opposite stem 42 functions as a pressure balancing stem. The 
valve body structure 44 which defines a valve chamber 46 within which the 
expanding gate assembly is linearly movable also defines internal stop 
pads 48 and 50 which are engageable respectively by the upper and lower 
extremities 52 and 54 of the segment as the segment reaches its limits of 
travel in either direction. The gate and segment members also define 
circular port openings shown in broken line at 56 and 58 which become 
aligned with one another and also aligned with circular flow passages 60 
and 62 of the valve body when the expanding gate assembly is in the fully 
opened and sealed position thereof. The valve body is also formed to 
define opposed seat recesses 64 and 66 within which seat members 68 and 70 
are received. In expanding gate valves it is typical for the seat members 
68 and 70 to be press fitted within the seat recesses 64 and 66 so as to 
establish a nonfloating, interference fitted relationship. 
In order to close the valve of FIG. 1, which shows the gate and segment 
assembly in an intermediate position, a downward force is applied to the 
gate and segment assembly through the valve stem 40. The gate and segment 
assembly moves downwardly together until such time as the lower extremity 
54 of the segment comes into contact with the stop pad 50. At this time, 
further downward movement of the segment is prevented by the stop pad 
while the valve stem continues to move downwardly thereby also causing the 
gate member to be moved downwardly. This further downward movement of the 
gate member while the segment member is restrained against downward 
movement by the stop pad causes relative movement of the angulated planar 
cam surfaces of the gate and segment. Downward movement of the gate member 
under this condition causes camming reaction to take place between planar 
surfaces 28 and 32, thus causing the segment member to be moved 
transversely to the longitudinal axis of the valve stem. When this occurs, 
angulated surfaces 30 and 34 become separated and the sealing surfaces 36 
and 38 of the gate and segment are moved apart (expanded relative to one 
another) until they firmly contact the respective sealing faces 72 and 74 
of the seat member 68 and 70. The seating force of the gate and segment 
against the seat members can be increased simply by applying sufficient 
linear force to the valve stem 40 which, through camming activity of the 
inclined surfaces, develops sufficient expansion force of the gate and 
segment against the seat members to provide a proper seal and thus obtain 
efficient shut off. In the closed position, sufficient sealing force can 
be developed at the face of the upstream seat 68 by wedging the gate and 
segments tightly against the seats in the closed position to develop an 
upstream seal. 
Under normal operation, when the stem 40 is moved upwardly to open the 
valve, the gate also begins to move upwardly. The upstream pressure acting 
on the segment 14, assisted by the urging force of the arched spring wire 
16 causes movement of the segment away from the upstream seat 68, thus 
moving the segment back into the notch of the gate with the inclined 
surfaces 28 and 30 of the segment in fully seated contact with the 
intersecting inclined surfaces 32 and 34 of the gate member as shown in 
FIG. 1. Further upward movement of the gate and segment assembly occurs 
together with only the downstream sealing surface 36 of the gate dragging 
against its respective downstream seat 70. In this condition, the segment 
member 14 is disposed in spaced relation with the upstream seat 68. With 
only the downstream sealing surface 36 of the gate in contact with the 
downstream seat 70, the gate and segment assembly can then be moved to the 
fully open position with relatively little effort at the hand wheel. 
VALVE BINDING PROBLEM DUE TO "FLOATING" UPSTREAM SEAT 
As mentioned above, the valve seats 68 and 70 are press fitted into their 
respective seat recesses, resulting in a radial interference pressure and 
the related friction force that secures the seats in immovable position 
within the seat recesses. In some applications, however, the upstream 
fluid pressure present in the recess behind the upstream seat can overcome 
the frictional force due to the interference fit of the seat, thus forcing 
the upstream seat to "float out" and become forced by pressure against the 
upstream sealing surface 38 of the segment. This problem has been 
especially prevalent when fluids are handled at high pressures and in the 
larger size valves. The problem is also prevalent in applications where 
differences in thermal expansion of the seat and body materials result in 
a loss of radial interference pressure at the operating temperature range 
of the valve. When the upstream seat 68 "floats out" due to the resultant 
force developed by pressure acting on the surface area of its back face, 
the sealing surface 72 of the upstream seat develops an additional 
frictional drag force on segment surface 38, thus increasing the required 
operating torque or actuating stem force in excess of that required for 
normal operation where only downstream seat drag is present. In the case 
of high pressure valves, the force developed between a floating upstream 
seat and the segment can be sufficiently large to impede the upward 
movement of the segment when the actuating stem 40 is being moved upwardly 
to open the valve. With the upward segment motion being stopped due to the 
frictional drag of a floating upstream seat, any further upward motion of 
the valve stem 40 results in an upward movement of the gate member with 
respect to the segment. This results in camming activity between the 
inclined surfaces 30 and 34 which are caused to slide relative to one 
another while the cam surfaces 28 and 32 are moved apart. This activity, 
of course, causes expansion of the gate and segment assembly, thereby 
driving the sealing surfaces 36 and 38 apart and in a direction toward the 
respective seat members. Thus, as more force is applied in an attempt to 
open the valve (by moving the gate and segment assembly to the upward 
position), the gate and segment elements begin to expand more and wedge 
tighter between the seat faces instead of moving the gate and segment 
assembly upwardly toward the open position. Under this condition, if even 
greater force is applied to the actuating stem 40 thus attempting to force 
the gate element toward its open position, the result is not opening 
movement of the gate and segment assembly but rather the development of 
additional expansion force of the gate and segment assembly. Such activity 
frequently causes the gate and segment assembly to become tightly wedged 
or "locked up" in the closed position, and the valve cannot then be opened 
without causing galling of the contacting sealing faces of the gate and 
segment with the respective seats. Usually, special disassembly procedures 
are required when expanding gate valves have become locked due to floating 
upstream seats or, in the alternative, abnormally high stem force must 
then be applied to attempt movement of the expanding gate assembly to its 
open position. Obviously, when abnormally high stem forces are applied 
there is a possibility of damaging the valve mechanism. This is a problem 
that has plaqued parallel expanding gate valves for many years. 
THE PRIOR ART 
A number of attempts have been made to overcome the floating upstream seat 
problems of parallel expanding gate valves over the years. Some success 
has been obtained but, for the most part, success has been accomplished 
only at the expense of introducing other disadvantages such as increased 
expense, major valve redesign, other mechanical problems, etc. One attempt 
to overcome the floating seat problem is evidenced by U.S. Pat. No. 
3,823,911 wherein an expanding gate valve incorporates two spacer plates 
which are inserted between the faces of the upstream and downstream seats. 
The width of these spacer plates is larger than the width of the gate and 
segment assembly in its collapsed or contracted position. Thus, the 
upstream seat is prevented from contacting the upstream sealing surface of 
the segment when the gate and segment assembly are moved to the collapsed 
position thereof to facilitate upward movement while opening the valve. 
Since the upstream seat cannot impose a frictional drag on the sealing 
surface of the segment, the gate and segment move together in the upward 
direction when the valve stem is moved upwardly without any tendency for 
the development of camming sliding activity relative to one another. Thus, 
no undesirable expansion of the gate and segment occurs when attempting to 
move the valve mechanism from the closed position to the open position. 
One of the major limitations of the design set forth in the patent, 
however, is that a complete redesign of the valve castings is required to 
accommodate the thick spacer plates necessary to resist the force of the 
upstream "floating" seat and to keep it in place. Since the inside 
diameter of the valve body is designed to be as small as possible to 
minimize the size and thus weight of the body casting and thus also 
minimize cost, the amount of space inside presently existing valve body 
designs is logically insufficient to accommodate the thick spacer plates 
necessary to maintain stresses in the spacers below the yield point 
thereof. Stresses in the spacer plates that can be fitted in the space 
available in existing valve body designs for high pressures are typically 
in excess of about 200,000 PSI--well above the yield strength of most 
practical materials suitable for typical use such as in oil field service. 
Thus, an expanding gate valve constructed in accordance with the above 
patent requires body castings of larger inside diameter as compared to 
those presently used, resulting in more weight and uneconomical design. 
This competitive disadvantage has in fact prevented any commercial success 
of the design shown in the patent. 
Another development to overcome the floating seat problem of parallel 
expanding gate valves is evidenced by U.S. Pat. No. 3,929,316 which 
teaches utilization of a plastic insert at the back of the seat to prevent 
pressure from acting on the full area defined by the back surface of the 
seat. However, this valve improvement relies on a relatively soft insert 
composed of any one of a number of suitable plastic materials to establish 
a seal and prevent pressure from acting on the entire back face surface of 
the seat. This soft seal design is not pressure energized and therefore it 
does not work reliably in keeping the high upstream pressure from leaking 
around it and acting on the backface of the upstream seat. Other proposals 
have also been entertained for correction of the floating seat problem, 
namely the valve structures set forth in U.S. Pat. Nos. 2,954,960 and 
3,006,601. 
As a result of the deficiencies described above, neither of the solutions 
set forth in the above patents has been found reasonably attractive from 
the standpoint of practical implementation and reliability. 
SUMMARY OF THE INVENTION 
It is a primary feature of the present invention to provide a novel 
nonfloating seat for expanding gate valves which will not cause valve 
binding due to gate/seat friction and reduce the operating forces required 
to open the valve. 
It is also a feature of this invention to provide a novel seat for 
expanding gate valves which establishes a seal with the valve body, which 
seal is enhanced in direct response to the pressure of the fluid being 
controlled by the valve. 
It is an even further feature of this invention to provide a novel seat for 
expanding gate valves which is pressure balanced and therefore is not 
subject to pressure induced floating as is typical with other expanding 
gate valve seats. 
It is also a feature of this invention to provide a novel seat for 
expanding gate valve mechanisms which is capable of compensating for 
slight angular misalignments of the parallel surfaces of the expanding 
gate. 
It is an even further feature of this invention to provide a novel seat for 
expanding gate valve mechanisms which may be effectively utilized in 
existing valve bodies and which does not require major redesign of a valve 
body for its effective utilization. 
It is another feature of this invention to provide a novel seat for 
expanding gate valve mechanisms which is capable of developing efficient 
metal-to-metal seals with both the gate mechanism and the valve body, thus 
maintaining the sealing effectiveness of the valve under extremely high 
temperatures such as during fires so that the fluid product controlled by 
the valve is not capable of leaking and feeding the fire. 
Briefly, the present invention concerns a nonfloating seat of integral 
nature which is capable of being received in the seat recesses of a valve 
body with only minor machining modification of the seat recesses. Thus, 
the invention is capable of being utilized as replacement seats for 
existing valves as well as being used as original equipment in new valves 
with seat recesses that are specifically designed to receive them. The 
nonfloating seat of the present invention is provided in the form of a 
seat ring having a substantially rigid circular body portion which is 
enabled to be received within the large diameter portion of a seat recess 
formed in the valve body. The nonfloating seat also incorporates a 
circular axial tubular extension which is integrally formed therewith and 
which cooperates with the rigid portion of the seat ring to define a flow 
port that is disposed in registry with the flow passages of the valve. The 
axially extending portion of the seat ring is of smaller outer diameter as 
compared to the outer diameter of the rigid portion of the seat ring and 
is received within a smaller diameter portion of the seat recess. The 
tubular extension establishes a seal between an outer surface portion 
thereof and a cylindrical surface portion of the seat recess, thereby 
exposing only a small back face surface portion thereof to the pressure of 
the fluid being controlled by the valve. This small back face surface is 
substantially identical to the surface area of the seat that is exposed to 
fluid pressure at the front sealing face of the seat. Thus, the seat is 
pressure balanced and, even if loosely disposed within the seal pocket, 
will not be pressure actuated into high frictional contact with the 
sealing surface of the gate mechanism. 
The tubular extension of the seat ring is sufficiently radially expandable 
responsive to fluid pressure that the sealing capability thereof in 
contact with the seat pocket wall is enhanced by pressure. Thus, as 
pressure increases, the sealing ability of the extension tube against the 
seat recess wall becomes greater and the higher the pressure, the better 
the seal. If desired, the tubular seat extension may be sealed by means of 
an elastomeric sealing member such as an O-ring seal supported in a 
circular seal groove defined by the extension. 
In a modified form of the invention, the exposed surface area at the back 
face and sealing face of the seat ring can be so designed as to develop a 
net axial pressure induced force on the seat ring which tends to force it 
back into its seat recess rather than "float" it out of the seat recess. 
Since the seat is not allowed to float out and create a frictional drag on 
the segment of the expanding gate assembly while opening the valve, the 
problems of higher torque operation due to upstream seat frictional drag, 
as well as gate and segment "locking up" activity near the closed position 
while trying to open the valve are effectively eliminated. The valve can 
be opened with very little torque effort at the hand wheel with no binding 
problems normally encountered when such valves are being utilized in high 
pressure service. 
Also, since the seat rings are not rigidly attached to the body structure, 
they can accommodate and adjust themselves to slight angular mismatches 
between the sealing surfaces of the gate and segment and their respective 
seat faces due to tolerances on the various parts and still provide an 
efficient seal at both the upstream and downstream seats. This is also a 
very important requirement for a "nonfloating" seat design to fulfill, 
otherwise the sealing ability of the seats will become ineffective. 
One major advantage of the present invention from a practical standpoint is 
that the nonfloating seat rings of this invention can be adapted to 
existing valve body structures with very minor machining modifications in 
the seat pocket area. The size of the body casting or the internal cavity 
of the body does not need to be increased to accommodate the nonfloating 
seat rings. Additionally, since the present nonfloating seat design can 
employ a metal-to-metal seal at both the sealing face and back face, the 
effectiveness of the seal is maintained even in a high temperature fire 
environment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings and first to FIG. 2, a valve mechanism is 
illustrated generally at 80 which comprises a valve body structure 82 
defining a flow passage 84. The valve body forms a valve chamber 86 in the 
same manner as discussed above in connection with FIG. 1. The only 
significant difference between the structure of FIG. 1 and that of the 
present invention is in the seat recess area of the valve body structure 
and the seat ring that is retained therein. The functional characteristics 
of the valve seats are clearly distinct from the seats of FIG. 1, however. 
Within the valve chamber 86 is movably disposed an expanding gate assembly 
illustrated generally at 88 which incorporates a gate member 90 having an 
actuator stem 92 connected to the upper extremity thereof. A pressure 
balancing stem 94 extends from the lower extremity of the gate member 90 
in the same manner as stem 42 of FIG. 1. The gate member also defines a 
port shown in broken line at 96 which is adapted for registry with a port 
98 of a segment member 100 in the open, expanded position of the gate 
assembly. When open, the ports 96 and 98 are also disposed in registry 
with the flow passage 84 of the valve body. The gate and segment define 
spaced parallel sealing surfaces 102 and 104, respectively, which are 
adapted for sealing engagement with seat members disposed within the seat 
recesses of the valve body. The gate member defines angulated planar cam 
surfaces 106 and 108 which match the angulation of planar intersecting 
surfaces 110 and 112 of the segment member 100. The gate and segment 
assembly is shown in FIG. 2 in the collapsed position thereof with the 
segment resting fully within the notch defined by the intersecting cam 
surfaces 106 and 108. On each side of the gate and segment assembly, an 
arched spring wire 114 is positioned with the extremities 116 and 118 
thereof in engagement with spring retainer pins 120 and 122. The central 
portion of the spring wire 114 is in engagement with a spring retainer pin 
124. It should be borne in mind that arched spring wire elements are 
located on both sides of the expanding gate assembly in the manner shown. 
As mentioned above, the difference in the structure shown in FIG. 1, 
representing the prior art, and that of the present invention lies in the 
internal valve body structure defining the seat recess or recesses and the 
annular seat ring disposed therein. As shown in FIG. 2, the seat recess 
defines a large diameter portion and a reduced diameter portion. The large 
diameter portion is formed by a generally cylindrical surface 126 which 
intersects a radial, planar surface 128. The reduced diameter portion of 
the seat recess is contiguous with the large diameter portion and is 
defined in major portion by a cylindrical surface 130 which functions as a 
sealing surface. Tapered surfaces 132 and 134 are transition surfaces 
respectively interconnecting the major seat recess with the reduced 
diameter recess and the reduced diameter recess with the flow passage 84. 
Surfaces 132 and 134 may be of other configuration without departing from 
the spirit and scope of the present invention and without modifying the 
function of the seat ring. 
Within the seat recess is positioned an annular seat ring shown generally 
at 136 having a substantially rigid ring portion 138 defining a generally 
cylindrical outer peripheral surface 140 engaging the cylindrical surface 
126 of the seat recess and a planar radial surface 142 which is adapted to 
be positioned in juxtaposed relation with the planar surface 128 of the 
seat recess. At the face portion of the seat ring 138 is formed an annular 
sealing ridge 144 which defines an annular planar sealing surface 146 that 
is disposed for sealing engagement with the sealing surface 104 of the 
segment member 100. 
The seat member 136 is also formed to define an axially projecting tubular 
portion 148 which may be integrally formed with the seat as shown or may 
be a separate piece connected to the seat ring. The tubular portion 
extends into the reduced diameter portion of the seat recess in close 
proximity to the cylindrical sealing surface 130. The tubular portion 148 
is formed to define a radially projecting sealing lip 150 which forms a 
cylindrical sealing surface 152. The sealing surface 152 is of slightly 
greater initial dimension as compared to the dimension of the cylindrical 
sealing surface 130 prior to insertion of the seat member into the seat 
recess. As the seat member is inserted the cylindrical sealing surface 152 
establishes an interference fit with the sealing surface 130, thereby 
providing a metal-to-metal seal at the back face portion of the seat ring. 
Although composed of a hard material such as hardened steel, the axially 
projecting tubular portion 148 of the seat ring is flexible to some 
degree. As the pressure of the fluid controlled by the valve increases, 
this pressure will act upon the internal diameter of the tubular portion 
148 by virtue of the port 154 defined within the seat ring. The pressure 
will therefore induce a force on the tubular portion 148 of the seat 
tending to expand it radially, thus urging the cylindrical surface 152 of 
the sealing lip 150 more tightly into sealing engagement with the 
cylindrical surface 130 of the seat recess. Thus a pressure actuated 
sealing capability is developed which enhances the seal established 
between surfaces 130 and 152 in direct response to the pressure condition 
of the valve. The favorable result is as pressure increases, the sealing 
capability of the seat ring also increases. 
As mentioned above in connection with FIG. 1, it is desirable that the seat 
ring remain fully seated within its seat recess so that the front sealing 
face of the seat ring does not maintain frictional engagement with the 
sealing surface of the segment after the gate and segment assembly has 
collapsed to the position shown in FIG. 1. With the seat ring in sealing 
engagement with the segment and with gate collapsing movement initiated, 
it is possible at times for pressure to enter the upstream seat recess 
behind the seat ring. When this occurs, a pressure responsive area 
differential will exist. Pressure will act upon the entire back face of 
the seat ring while sealing contact between the seat ring and segment 
reduces the pressure responsive area at the sealing face of the seat ring. 
This undesirable condition causes seat drag against the segment and can 
cause wedge locking of the gate assembly. To overcome any possibility of 
pressure responsive floating of the seat ring, the seat ring of this 
invention has been designed to be pressure balanced when in contact with 
the sealing surface of the segment member. As shown in FIG. 2, contact 
between the sealing surface 146 of the seat ring and the sealing surface 
of the gate establishes a pressure responsive area D.sub.1 at the face 
portion of the seat. Likewise, the seal established between cylindrical 
surfaces 130 and 152 at the rear portion of the seat defines a pressure 
responsive area D.sub.2. Pressure responsive areas D.sub.1 and D.sub.2 of 
the seat ring are substantially identical, thereby developing a net 
pressure responsive force of substantially zero. Even under circumstances 
where the seat ring 136 is fairly loosely retained within the seat recess, 
it will have no pressure responsive tendency to float toward the segment 
member when the segment is collapsed toward the gate portion of the 
expanding gate assembly. Further, if the seat ring 136 is loosely retained 
within the seat recess, as soon as the seal between the seat ring and 
segment is borken, the entire sealing face portion of the seat ring will 
be exposed to the pressure condition while the rear face portion of the 
seat ring is restricted to the surface area D.sub.2 by the seal between 
surfaces 130 and 152. This pressure responsive area differential therefore 
develops a resultant force tending to drive the seat ring into fully 
seated relation within the seat recess. 
It may also be desirable to provide a seat construction of the nature shown 
in FIG. 2 wherein the seat ring is retained within its seat recess by 
means of a pressure responsive force differential. If such is desired, a 
valve mechanism may take the form shown generally at 160 in FIG. 3. The 
valve body structure 162 and its seat recess 164 are of the same 
configuration as set forth in FIG. 2. An expanding gate member 166 
incorporating a gate and segment is also of the same configuration as 
shown in FIGS. 1 and 2. A seat ring 168 is provided which differs from the 
seat ring 136 of FIG. 2 only in the position and dimension of the face 
sealing surface thereof. As shown in FIG. 3, the seat ring 168 defines a 
circular sealing projection 170 defining a circular planar sealing surface 
172 which is positioned for sealing engagement with a planar sealing 
surface 174 of the segment portion of the gate and segment assembly 166. 
At the back face portion of the seat ring 168 the tubular extension 
portion 176 is of identical size and configuration as shown in FIG. 2 
thereby establishing a back face area D.sub.2 of the same dimension as in 
FIG. 2. The inner and outer peripheral edges of the sealing surface 172 
are of greater diameter as compared to the sealing surface 146 of FIG. 2, 
thereby establishing a face sealing area D.sub.3 which is greater than the 
back face pressure responsive area D.sub.2. An area differential is 
therefore defined which is greater at the face portion of the seat ring 
168 than at the back face portion thereof. Pressure acting against this 
area differential will develop a resultant force acting on the seat ring 
168 which urges the seat ring toward the seat recess. By controlling the 
dimension of the internal diameter D.sub.3 of the face sealing surface 172 
in comparison to diameter D.sub.2 at the rear face portion of the seat 
ring, a resultant force of desired character will be developed throughout 
the pressure range of the valve. The tendency at all pressures, however, 
will be the development of a resultant force tending to maintain the seat 
ring 168 within the seat recess. There will be no tendency therefore for 
the seat ring to float outwardly from the seat recess as the gate and 
segment assembly 166 becomes collapsed. 
It is also desirable that an expanding gate valve have the capability of 
compensating for slight angular misalignment of the sealing surfaces of 
the expanding gate mechanism. In accordance with the present invention, 
the seat rings 136 and 168 of FIGS. 2 and 3 are capable of compensating 
for such slight angular misalignment and yet maintaining an effective seal 
with the expanding gate mechanism. The major seat retaining surfaces 126 
and 128 as shown in FIG. 2 are so dimensioned relative to corresponding 
surfaces 140 and 142 of the seat ring 136 such that the seat ring will 
seek optimum seating relation within the seat recess as controlled by the 
respective sealing surface 104 or 102 of the gate and segment assembly. As 
the gate assembly expands, the sealing surfaces thereof will be forced 
into tight wedging engagement with the sealing surfaces 146 of the seat 
ring. Since the seat rings are not rigidly attached to the body structure 
of the valve, they can become slightly canted or angularly misaligned with 
respect to the axis of the respective seat recess. The sealing surfaces 
146 thereof will therefore establish optimum sealing engagement with the 
respective sealing surfaces 102 and 104 of the expanding gate assembly. 
The seats can therefore accommodate and adjust themselves to slight 
angular misalignment of the sealing surface of the gate due to the 
tolerances on the various parts even though an optimum seal is effectively 
maintained between the sealing lip of the tubular projection and 
cylindrical rear wall of the seat recess. 
One of the major advantages of the present invention from a practical 
standpoint is that existing valve bodies may be modified by simple 
machining to convert the seat recesses of the valve bodies from the 
configuration shown in FIG. 1 to the configuration shown in FIGS. 2 and 3. 
The strength and pressure containing capability of the valve body will not 
in any way be diminished due to such machining. The size of the body 
casting or the internal cavity of the body casting does not need to be 
increased. Valves being overhauled therefore can be provided with 
nonfloating seats according to the present invention thereby effectively 
eliminating any problems of wedge locking. Additionally, since the seat 
ring 136 is composed entirely of metal and is seated against the metal 
surfaces of the valve body and expanding gate assembly, the valve 
mechanism is capable of maintaining an effective seal even at abnormally 
high temperature conditions such as might occur in the case of a fire. The 
seat rings therefore render the valve fire safe to a greater degree than 
would be the case if O-rings or plastic materials were utilized to enhance 
the sealing capability thereof. 
Although metal-to-metal sealing capability is illustrated in the 
nonfloating seats of FIGS. 2 and 3, it may desirable to provide an 
elastomeric sealing capability in lieu thereof or in addition thereto. As 
illustrated in FIG. 4 a valve mechanism is illustrated generally at 180 in 
the fragmentary sectional incorporating a valve body structure 182 
defining one or more seat recesses 184 which may be essentially identical 
as compared to the seat recesses shown in FIGS. 2 and 3. A seat ring 186 
is received within the seat recess and defines a face sealing surface 188 
disposed for sealing engagement with sealing surface 190 of the segment 
portion of a gate and segment assembly. The seat ring also defines an 
elongated tubular extension 192 having an outer peripheral seal groove 
formed therein and retaining an annular sealing element 194 such as an 
elastomeric O-ring type sealing member. The tubular extension may be 
integrally formed with the seat ring or a separate piece interconnected 
with the seat ring in any suitable manner. The tubular extension of the 
seat ring may be loosely fitted within the seat recess if desired or, in 
the alternative, may define an annular radially projecting sealing lip 196 
disposed in metal-to-metal interference sealing relation with the the 
cylindrical surface 198 of the seat recess. The seat of FIG. 4 may be 
pressure balanced in the manner illustrated in FIG. 2, or, in the 
alternative, may be pressure energized in the manner set forth in 
conjunction with FIG. 3. 
In view of the foregoing, it is respectfully submitted that the valve 
mechanism of the present invention is capable of accomplishing all of the 
features hereinabove set forth together with other features which are 
inherent from a description of the apparatus itself. It will be understood 
that certain combinations and subcombinations are of utility and may be 
employed without reference to other features and subcombinations. The 
scope of this invention is intended to be limited only by the scope of the 
appended claims and is not limited by the specific embodiments shown and 
described herein.