Gate valve structure

An expanding gate valve with a valve seat structure which comprises a pair of "floating" seat rings (60) loosely received in annular seat pockets (52) surrounding the flow passage through the valve and each having an axial dimension which exceeds the depth of the seat pocket. The front face (61) of each seat ring is disposed adjacent the gate assembly (24, 26) and is provided with an annular groove (63) and an annular resilient sealing element (64) therein adapted to form a ring of sealing contact area about the flow passage (14) when the gate assembly is expanded thereagainst. The rear face (66) of the seat ring (60) is provided with an annular groove (63') and a second annular resilient sealing element (64'). The two annular sealing elements are coaxial and the inner diameter of the front sealing element (64) exceeds that of the rear sealing element (64') so that the front sealing element is a greater radial distance from the flow passage (14) than is the rear sealing element. When the gate assembly is expanded against the seat rings (60), the annular area of the front of the seat ring exposed to flowline pressure exceeds the annular area of the rear of the seat ring exposed to flowline pressure whereby the seat ring is pressure energized towards the bottom (54) of the seat pocket (52). The annular sealing elements (64, 64') and bottoms of the annular grooves (63, 63') are provided with cooperating frusto-conical wedging surfaces (80, 94 and 80', 94') which for the upstream seat ring wedge the front face sealing element (64) towards the gate assembly and the rear sealing element (67) towards the bottom (54) of the seat pocket when there is pressure in the flow passage. To provide for a pressure energized downstream seal in the event of an upstream leak, additional frusto-conical surfaces on the sealing elements are provided to cooperate with additional frusto-conical surfaces in the groove bottom whereby fluid pressure from the valve chamber energizes the sealing elements to provide a downstream seal. A groove in the rear face of each sealing element between its frusto-conical surfaces adds sealing capability.

BACKGROUND OF THE INVENTION 
This invention relates generally to gate valves and more particularly to an 
improved valve seat structure for expanding gate valves. 
Gate valves of the expanding gate type typically employ a gate mechanism 
which is mounted in a valve chamber and is movable therein transversely of 
the flow passage to open and close the valve. The gate assembly typically 
comprises a gate member and an adjacent segment member which, as the gate 
assembly approaches the open and closed positions, are expanded 
transversely of one another by cooperating cam surfaces whereby they are 
forced against seat rings in the valve body on opposite sides of the gate 
assembly for effecting upstream and downstream seals. The gate assembly 
includes parallel sealing surfaces which are maintained parallel as the 
gate assembly expands in the open and closed positions to seal against the 
seats. Upon movement from the open and closed positions, the gate assembly 
collapses from its expanded condition to permit reciprocal movement of the 
gate assembly without excessive friction between the gate assembly and the 
seat assemblies. 
Most generally, the seat assemblies for expanding gate valves are retained 
within seat recesses which are formed within the valve body in surrounding 
relationship to the flow passage on each side of the gate assembly. The 
valve seats are in the form of seat rings which in one widely used valve 
structure are pressed into the seat recesses to that the seat will be 
retained in a fixed position. Ideally, the seats provide essentially 
planar and parallel surfaces for the gate assembly to contact and seal 
agains where it is in the expanded configuration regardless of whether the 
gate assembly is in the open position or the closed position. As a 
practical matter, however, the maintenance of parallelism between the 
outer sides of the gate assembly and the faces of the valve seats is 
frequently a problem which impairs the ability of the valve to achieve a 
seal. In addition, the seats do not always remain fixed and they may float 
or move inwardly toward the gate assembly under high differential pressure 
conditions. In doing so, the seats move to a position tight against the 
gate assembly and drag excessively thereon thus making the valve very 
difficult to open or close. An alternative construction to the fixed 
press-fit seat ring is the floating seat arrangement wherein the seat 
member is designed to float in the seat pocket in the direction of the 
flow passageway so that it can be moved against the gate sides by the 
fluid pressure. Such floating seats have the advantage of being able to 
seal against the gate and segment members even if there is a lack of 
parallelism or if there are irregularities in the mating surfaces of the 
gate assembly and the valve seat. A potential disadvantage of this type 
design is that excessive drag can be created between the seat members and 
the gate assembly when the gate assembly is moved due to the upstream seat 
being forced against the gate assembly by fluid pressure. 
Furthermore, under high pressure service conditions in excess of 10,000 
psi, there must be a smaller clearance between the seat ring and seat 
pocket to preclude damaging of the gate sealing surface by the 
misalignment of the metal seat ring. Accordingly, a reduced ability of 
such a floating seat to compensate for non-parallelism is associated with 
the smaller clearances. In addition, the operating torques for expanding 
the gate assembly to achieve a seal under high pressure service conditions 
become extremely high so as to make valve operation very difficult. 
It is therefore an object of the invention to provide a gate valve of the 
expanding gate type with a unique improved "floating" valve seat 
construction wherein the seat element tends to be retained by differential 
flowline pressure in the open and closed conditions of the valve and as 
the gate assembly begins its movement to its collapsed condition 
intermediate its open and closed positions and is able to compensate for 
non-parallelism between the cooperating sealing surfaces of the valve seat 
and gate assembly, particularly in high pressure service conditions. 
Another object is to provide a gate valve with an expansible gate assembly 
and valve seat means comprising a "floating" seat ring adapted to be urged 
by flowline pressure towards the back of the seat pocket to eliminate 
"drag" between the gate assembly and the valve seat as the gate assembly 
moves between open and closed positions. 
A further object is to provide an expanding gate valve with "floating " 
seat rings, each with annular grooves with sealing elements in the front 
and rear faces and each sealing element having pairs of spaced 
frusto-conical surfaces adjacent its rear face for cooperating with 
conforming wedge surfaces in said grooves whereby the sealing elements in 
the upstream seat are cammed away from the flow passage to effect a seal 
and those in the downstream seat are cammed towards the flow passage to 
effect a seal in the event of leakage of the upstream seal. 
SUMMARY OF THE INVENTION 
The invention is an expanding gate valve which comprises a pair of 
"floating" seat rings loosely received in annular seat pockets surrounding 
the flow passage and each having an axial dimension which exceeds the 
depth of the seat pocket. The front face of each seat ring is adjacent the 
gate assembly and is provided with an annular groove and resilient sealing 
element therein adapted to form a ring of sealing contact area about the 
flow passage when the gate assembly is expanded thereagainst. The rear 
face of the seat ring is provided with an annular groove and a second 
annular sealing element. The inner diameter of the front sealing element 
exceeds that of the rear element so that the front element is a greater 
radial distance from the flow passage than is the rear element. When the 
gate assembly is expanded against the seat rings, the annular area of the 
front of the seat ring exposed to flowline pressure exceeds the area of 
the rear of the seat ring exposed to flowline pressure whereby the seat 
ring is pressure energized towards the bottom of the seat pocket. The 
annular sealing elements and bottoms of the annular grooves are provided 
with cooperating frusto-conical wedging surfaces which for the upstream 
seat ring wedge the front sealing element towards the gate assembly and 
the rear sealing element towards the bottom of the seat pocket when there 
is pressure in the flow passage. To provide for a pressure energized 
downstream seal in the event of an upstream leak, additional 
frusto-conical surfaces on the sealing elements are provided to cooperate 
with additional frusto-conical surfaces in the groove bottom whereby fluid 
pressure in the valve chamber energizes the sealing elements of the 
downstream seat ring to effect a downstream seal.

Referring more particularly to the drawings, there is shown in FIG. 1 an 
expanding gate valve 10 which is provided with floating seats in 
accordance with the invention. The gate valve 10 includes a valve body 12 
having an inlet passage 14 and an outlet passage 16. Flanges 18 and 20 are 
formed on body 12 at the outer ends of passages 14 and 16, respectively, 
to permit easy attachment of the valve body within a flowline. A valve 
chamber 22 is formed in body 12 between the flow passages 14 and 16 and in 
communication therewith to thereby provide a fluid flow passage through 
the body. 
An expanding type gate assembly is mounted in valve chamber 22 for 
reciprocal movement therein between an open position and a closed position 
with respect to flow passages 14 and 16. The gate assembly includes a gate 
24 located adjacent the downstream flow passage 16 and a segment 26 
located adjacent the upstream flow passage 14. On the side facing segment 
26, gate 24 has oppositely inclined surfaces 28 and 30 on its respective 
upper and lower portions. Segment 26 has similarly inclined surfaces 32 
and 34 on its respective upper and lower portions for cooperative contact 
with surfaces 28 and 30 of gate 24 to expand and collapse the gate 
assembly, as will be explained in more detail. The outwardly facing sides 
of the gate and segment are planar surfaces which continually remain 
parallel to one another and perpendicular to the flow passage. A pair of 
curved springs 36 (FIG. 1) engage pins on opposite sides of gate 24 and 
segment 26 in a manner to continuously urge gate 24 and segment 26 toward 
one another to bias the gate assembly toward its collapsed condition. Gate 
24 is connected with stem 38 which extends upwardly through a valve bonnet 
40 mounted on top of valve body 12. A handwheel 42 is mounted on top of 
stem 38 to effect up and down movement of gate 24 in a conventional 
manner. A lower stem 44 extends downwardly from the bottom of gate 23 to 
pressure balance the gate assembly. 
When the gate assembly is moved upwardly in response to turning of 
handwheel 42, the top end of segment 26 contacts a stop 46 in the valve 
body to prevent further upward movement of the segment. Continued upward 
movement of gate 24 results in a lateral expansion of the gate assembly 
due to the camming action resulting from sliding contact between surfaces 
30 and 34. When the gate assembly is in its upper fully open position as 
shown in FIG. 1, it is fully expanded and ports 48 formed through the gate 
and segment members are in alignment with each other and with the flow 
passages 14 and 16. Movement of gate 24 downwardly from the fully open 
position causes surfaces 30 and 34 to slide against one another, with 
assistance from spring 36, until the gate and segment are in the collapsed 
or minimum width condition as shown in FIG. 4. The springs 36 are attached 
to opposite sides of the gate assembly and flexed about lugs provided on 
the gate and segment members in a conventional manner to hold the gate 
assembly in its collapsed condition as it moves downwardly from the open 
position toward the closed position. As the gate assembly moves 
downwardly, the bottom of segment 26 contact a lower stop 50, thereby 
preventing further downward movement of the segment. Continued downward 
movement of gate 24 causes surfaces 28 and 32 to slide against one another 
in camming fashion such that the gate assembly is fully expanded when it 
reaches a lower fully closed position wherein passages 14 and 16 are 
blocked. When the gate assembly is moved upwardly from the closed position 
toward the open position, springs 36 urge the gate assembly to its 
collapsed condition in which it is maintained until the open position is 
reached, at which time the gate assembly expands. In the manner described 
above, the gate assembly is actuated to a fully expanded condition in both 
the open and closed positions of the valve and maintained in a fully 
collapsed condition when it is in transit between the open and closed 
positions. 
In accordance with the present invention, valve body 12 is provided with a 
pair of annular recesses 52 which are formed around flow passages 14 and 
16 at locations adjacent valve chamber 22 upstream and downstream thereof. 
The recesses 52 are of identical configuration although their orientations 
are opposite and each recess opens to valve chamber 22. The annular 
recesses 52 form seat pockets in each of which the valve seat assembly of 
this invention is inserted. Each seat pocket 52 has a planar annular 
bottom surface 54 which is oriented perpendicular to the flow passage of 
the valve and a cylindrical side wall 56 which is formed substantially 
coaxial with the flow passage through the valve. 
The valve seat of this invention is shown in an enlarged perspective view 
thereof in FIG. 2. The valve seat comprises a metallic seat ring 60, the 
central bore of which corresponds in diameter and configuration to that of 
the flow passage through the valve. The axial dimension of the ring 60 is 
slightly larger than the depth of a seat pocket 52, so that when the seat 
ring is fully seated in the pocket 52, the ring 60 protrudes into the 
valve chamber 22 and its front face 61 is disposed to engage a planar side 
wall of the gate assembly when the gate assembly is expanded thereagainst. 
Further, according to the invention, the external diameter of the seat 
ring 60 is slightly less than the diameter of the seat pocket so that a 
clearance exists between the external cylindrical wall 62 of the seat ring 
60 and the cylindrical side wall 56 of the seat pocket. Accordingly, the 
seat ring 60 is designed to fit loosely in the seat pocket in a "floating" 
relationship therewith and can therefore orient, when necessary, to 
establish a face-to-face contact with the sealing surface of the gate 
assembly when the gate assembly is expanded thereagainst. 
The front face 61 of the seat ring is formed with an annular groove 63 
therein which is concentric with the bore of the ring 60 and in 
surrounding relation to the valve flow passage. The groove 63 accommodates 
an annular resilient sealing member 64 which is adapted to establish a 
seal with the face of the segment of the gate assembly when the gate 
assembly is in its expanded condition. Accordingly, the axial dimension of 
the annular seal 64 exceeds the depth of the groove 63 so the seal 64 
protrudes beyond the face 61 of the seat ring 60. For low pressure and low 
temperature service conditions, the resilient seal 64 may be of "Teflon" 
or other similar deformable plastic material. However, for high pressure 
service, generally pressures in excess of 10,000 psi, or at high operating 
temperatures greater than 500.degree. F. (260.degree. C.), a metallic 
sealing member is required to provide the necessary structural strength. 
In such instances, an aluminum bronze alloy or a soft stainless steel, 
such as 316 stainless steel, would be suitable material. 
Also, as best seen in FIG. 2, the back face 66 of the seat ring 60 is 
provided with an annular groove 63' which corresponds in dimensions and 
configuration to the annular groove 63. A resilient sealing member 64', 
which is identical in radial cross section to the sealing member 64 and of 
the same material composition, is installed therein. Both of the annular 
sealing members 64, 64' are disposed in a coaxial relationship with the 
bore of the seat ring 60 and the flow passage through the valve. However, 
the inner diameter of the annular sealing member 64 in the front face 61 
of the seat ring exceeds the inner diameter of the annular sealing member 
64' in the back face 66 and, therefore, the sealing member 64 is disposed 
a greater distance from the flow passage than the sealing member 64' for 
purposes to be hereinafter described. 
It is also to be noted that the clearance between the seat ring and the 
circumferential wall of the seat pocket must necessarily be smaller than 
that which is permissible when using plastic annular sealing members since 
under high pressure conditions the edge of the seat ring tends to do 
damage to the surface of the gate element. In one embodiment of the 
invention, a typical diametrical tolerance between the seat ring and seat 
pocket is 0.013 inches. For purposes of illustration, the various 
clearances between the groove walls in the seat rings and the sealing 
elements have necessarily been exaggerated. 
In the invention, the configuration of the annular grooves 63, 63' in the 
front and rear faces of the seat ring 60 is as shown in U.S. Pat. No. 
4,320,890 to Meyer et al, the disclosure of which is incorporated herein 
by reference. The annular groove 63, for example, is provided with a 
bottom 76 which includes a flat bottom portion 78 that is generally 
perpendicular to and adjacent to the inner groove side 72 which is the 
side nearest the flow passage, and a frusto-conical bottom portion 80 that 
is formed adjacent the outer groove side 74. The frusto-conical bottom 
portion 80 comprises between approximately twenty-five percent (25%) and 
approximately seventy percent (70%) of the width of the annular groove 63 
and between approximately twenty percent (20%) and approximately fifty 
percent (50%) of the depth of the groove along the outer groove side 74. 
Accordingly, the frusto-conical bottom portion is disposed from the flat 
bottom portion 78 at an angle which is within a range between 
approximately thirty degrees (30.degree.) and approximately sixty 
(60.degree.). 
The annular sealing member 64 is loosely received in the annular groove 63 
for relatively unrestrained movement therein. The annular face seal 64 
includes front and rear seal faces 84 and 86 joined by inner and outer 
seal sides 88 and 90. The axial dimension of the face seal 64 is between 
approximately 1.4 and 1.6 times the thickness thereof. The rear seal face 
86 includes a flat rear portion 92 that is generally perpendicular to and 
adjacent the inner seal side 88 and a frusto-conical rear portion 94 that 
is formed adjacent outer seal side 90. The frusto-conical rear portion 94 
is disposed from the flat rear portion 92 at an angle in the range between 
approximately thirty degrees (30.degree.) and approximately sixty degrees 
(60.degree.) but in conformity with the cone angle of the frusto-conical 
bottom 80 of the groove 63. 
In a specific embodiment of an expanding gate valve of a standard 
commercial size, the front seal face 84, when the gate is in collapsed 
condition, extends past the front seat face by a distance "E" in the range 
of between approximately 0.002 inches (0.0051 cm) and approximately 0.015 
inches (0.0381 cm). With the face seal 64 sitting loosely in the annular 
groove 63 with its frusto-conical surface engaging the frusto-conical 
bottom surface of the groove, the clearance between the groove side 74 and 
seal side 90 is in the range of 0.001 inches to 0.015 inches. The 
clearance between the seal side 88 and groove side 72 is approximately 
0.021 inches which is the same as the clearance between the rear seal face 
92 and the groove bottom 78. 
The seat ring illustrated in FIG. 2 is described with reference numerals 
applied to the seating assembly used on the upstream side of the gate 
assembly. The seat ring and seat assembly used on the downstream side is 
identical to that shown in FIG. 2 and is installed in a reverse 
orientation to the upstream seat assembly. For ease of description, 
elements of the downstream seat assembly which correspond to those in the 
upstream seat assembly are identified with the same reference numerals but 
with a subscript appended thereto. 
When the gate assembly of the valve is moved to either the open or closed 
position by operation of the handwheel 42, the gate assembly is expanded 
against the seat ring elements on both the upstream and downstream sides 
of the gate assembly. As shown in FIG. 3 wherein the gate assembly is 
illustrated in the closed expanded condition, the sealing element 64 is 
compressed by the segment 26 and establishes a fluid-tight seal between 
the contacting faces of the seat ring 60 and the segment 26. The sealing 
element 64' also establishes a fluid-tight seal between the back face 66 
of the seat ring 60 and the end wall 54 of the seat pocket. 
It is to be noted that the inner edge of the sealing element 64 is located 
a distance from the flow passage 14 which exceeds the distance of the 
sealing element 64' from the flow passage 14. Accordingly, on the upstream 
side, pressurized fluid from the passage 14 will flow between the face 61 
of the seat ring 60 and the sealing face of the segment 26 to where it is 
blocked by the sealing element 64. Similarly, pressurized fluid will flow 
between the back face 66 of the seat ring and the end wall 54 of the seat 
pocket to the inner edge of the sealing element 64'. Therefore, the 
annular area of surface of the front face 61 which is exposed to fluid 
pressure exceeds the annular area of surface of the back face 66 which is 
exposed to fluid pressure and the resultant differential force acts to 
urge the seat ring 60 more tightly against the back of the seat pocket to 
establish an even tighter seal at the back of the seat ring. 
In addition, when there is initial movement of the gate assembly away from 
its fully open or fully closed position and the gate assembly begins to 
collapse, as shown in FIG. 4, this differential force resulting from the 
difference of exposed areas causes the seat ring 60 to be pressure 
actuated towards the end wall 54 of the seat pocket rather than towards 
the gate assembly. This prevents the seat ring from being forced out of 
the pocket and following towards the gate element to impose a drag 
thereon. 
Although it is usually only the upstream valve seat that presents a problem 
with respect to dragging against the collapsed gate assembly, the 
downstream seat may in some cases pose a problem in this regard, 
particularly when reverse flow conditions are encountered. Accordingly, it 
is contemplated that both the upstream and downstream seats will normally 
be constructed in accordance with the invention. 
While the relative locations of the annular sealing elements with respect 
to the flow passage results in pressure energizing of the seat ring 60 as 
to urge its retention in the seat pocket to serve the purposes of 
enhancing the sealing effectiveness of the valve seat assembly and also 
avoid any dragging contact of the seat ring with the gate assembly, the 
particular structure of the annular resilient sealing elements and the 
accommodating grooves in the front and rear faces of the seat ring enables 
the valve seats to compensate for out of parallel conditions which may 
exist between the cooperating sealing surfaces of the gate assembly and 
valve seat and between the seat ring and the valve body even though there 
is a very small clearance between the seat ring and the seat pocket. 
Furthermore, the cooperating wedging surfaces of the annular resilient 
sealing elements and the associated annular grooves in which they are 
received, act to establish more effective seals between the seat assembly 
and the valve body and gate assembly under pressure conditions and this 
effectiveness of the seals increases with increasing fluid pressure in the 
flow passage as described below. 
As the gate assembly reaches its closed position, it expands against both 
upstream and downstream annular face seals 64 and 64A so that they are 
axially compressed to form a fluid-tight seal between themselves and the 
gate assembly and their respective annular grooves 63 and 63A. Also, the 
rear face seals 64' and 64A' in the upstream and downstream seat 
assemblies are likewise axially compressed to establish seals between the 
seat rings and the seat pocket bottoms 54 and 54A. 
With respect to upstream annular face seal 64, fluid from inlet flow 
passage 14 then travels along the upstream side of segment 26 and into 
upstream annular groove 63, and is contained within a space between inner 
groove side 72 and inner seal side 88. The fluid does not leak past either 
the front or rear seal faces of annular face seal 64 due to the above 
described seal created between it and the gate assembly and upstream 
annular groove 63. As the fluid pressure builds within the space between 
the inner groove and seal sides, upstream annular face seal element 64 is 
forced to travel on its frusto-conical rear portion 94 up frusto-conical 
bottom portion 80. As upstream annular face seal 64 travels up 
frusto-conical bottom portion 80, it moves inwardly towards the gate 
assembly while the gate assembly simultaneously expands outwardly towards 
it. Fluid pressure built up in the space defined between flat bottom 
portion 78 of groove 63 and flat rear portion 92 of seal 64 also forces 
upstream annular face seal 64 to travel inwardly toward valve chamber 22 
and the gate assembly. Thus, an effective seal which surrounds the flow 
passage is created between front seal face 84 and the gate assembly, and 
between frusto-conical rear portion 94 and annular groove 63. Because 
fluid from the flowline actually forces the upstream annular face seal to 
wedge towards the gate assembly, the effectiveness of the seal created by 
the annular face seal increases with increasing flow passage fluid 
pressure. The inward travel of the annular face seal towards the gate 
assembly reduces the distance the gate assembly must move against the 
direction of fluid flow in the flow passage. It can thus be seen that the 
ability of annular face seal 64 to move inwardly in response to fluid 
pressure in the flow passage facilitates the formation of an effective 
seal on the upstream side of the gate assembly without the need for 
exerting operating torques on the gate assembly of such degrees as has 
been required in the past. 
As regards the annular sealing element 64' in the rear face of the seat 
ring 60, fluid from the flow passage enters between the rear face 66 of 
the seat ring and the bottom 54 of the seat pocket to be contained within 
the space between the inner groove side 72' and the inner seal side 88'. 
As the pressure builds within this space between the inner groove and seal 
sides, the sealing element 64' is forced to travel on its frusto-conical 
rear portion 94' up the frusto-conical groove bottom 80', thus causing it 
to move towards the bottom wall 54 of the seat pocket. The resulting 
compression of the sealing element 64' enhances the effectiveness of the 
seal between its frusto-conical surface 94' and that of the seat ring 60 
as well as the seal between the sealing element 64' and the bottom wall 54 
of the seat pocket. 
With respect to the downstream annular face seal 64A when the gate assembly 
is placed in its closed expanded position, the downstream annular face 
seal 64A remains slightly axially compressed between frusto-conical bottom 
portion 80A of downstream annular groove 63A due to the expansion of the 
gate assembly. However, because fluid does not flow into downstream 
annular groove 63A, downstream annular face seal 64A, does not wedge 
inwardly towards the valve chamber 22. 
FIG. 1 illustrates the gate assembly in its open position in which it is 
also fully expanded and the ports 48 through gate 24 and segment 26 are 
fully aligned. As the gate assembly reaches its open position, both the 
upstream and downstream annular face seals 64 and 64A are axially 
compressed to initially seal against the gate assembly and their 
respective annular grooves in a manner similar to that when the gate 
assembly reaches its closed position. However, because fluid from the flow 
passage has entered the valve chamber 22 during the movement of the gate 
assembly the fluid pressure on both sides of the upstream annular face 
seals 64 and 64' is equal, and the upstream annular face seals are not 
axially compressed any further by wedging against their frusto-conical 
groove bottoms 80 and 80'. The valve chamber pressure also precludes any 
further axial compression and wedging of the downstream seats 64A and 
64A'. 
With reference to FIG. 4, wherein the gate assembly is shown in transit 
from the closed position to the open position and has just assumed its 
fully collapsed condition, the frusto-conical rear portion 94 of the 
upstream face seal 64 moves away from the frusto-conical bottom portion 80 
of the groove 63 and fluid contained between the inner sides and flat 
portions of the upstream annular groove 63 and the face seal 64 flows past 
these frusto-conical surfaces 94, 80 to the outer sides of the annular 
groove 63 and face seal 64 thereby equalizing the fluid pressure on both 
sides of the upstream annular face seal 64. Once the fluid pressure on 
both sides of the upstream annular face seal 64 is equalized, the seal 64 
moves into a wiping relationship with the gate assembly wherein the front 
seal face 84 is spaced apart a small distance from the gate assembly which 
reduces the amount of contaminants that can enter the valve chamber 22. In 
like manner, the downstream seal 64A assures a similar wiping relationship 
with the gate assembly by means of the sealing elements 64, 64A. 
In FIG. 5, there is shown a seat ring of the invention which incorporates a 
modified form of sealing element for use in its front and rear faces. This 
particular sealing element is provided with two frusto-conical surface 
portions 94B, 95B in its rear face. The flat rear portion of the sealing 
element includes an annular groove 96B located intermediate the two 
frustoconical surface portions and also disposed in coaxial relation to 
the ring axis. The annular grooves in the front and rear faces of the seat 
ring are similarly provided with a groove bottom having a pair of 
frusto-conical bottom portions 80B, 80D, each facing a different side of 
the groove. This particular embodiment of the invention presents the 
unique advantage that if there should occur a leakage past the upstream 
seals, then fluid pressure in the valve chamber will pressure energize the 
annular sealing members 64C in the downstream seat ring thereby effecting 
a downstream seal for the valve. This is accomplished by fluid pressure 
from the valve chamber entering the annular grooves in the faces of the 
downstream seat ring 60C and urging the frusto-conical surface 95B of each 
sealing member 64C which is nearest the flow way through the valve into a 
wedged fluid-tight sealing relation with that frusto-conical surface 80D 
of the groove bottom which is nearest the flow way. In addition, the 
annular groove in the rear face of the annular sealing member provides 
flexibility to the portions of the sealing member between the groove and 
the frusto-conical surfaces which significantly enhances the sealing 
capability of the valve. Further, the flexibility of the sealing portions 
of the annular sealing member allows it to be urged deeper into the seat 
pocket by flexure towards its central axis. Accordingly, there is less 
chance of "drag" by the annular sealing members when the gate assembly is 
moved to a collapsed condition. Such, of course, increases the lifetime of 
the sealing members. 
The invention described herein is directed to floating seats for expanding 
gate valves which are pressure energized to minimize "drag" between the 
valve seats and the gate assembly and are also adapted to compensate for 
non- parallelism between the gate assembly sealing surfaces and the seat 
rings and between the seat rings and the bottoms of the seat pockets. At 
the same time, this unique seat and seal ring assembly allows the valve to 
effect a fluid-tight seal with the application of lesser operational 
torque than is generally required for conventional gate valves with 
floating seats and particularly so for operations under high pressure 
service conditions. Also, its sealing effectiveness increases with 
increasing pressure conditions. 
While the invention has been illustrated with respect to a balanced stem 
gate valve, the invention could be used as well with an unbalanced gate 
valve. Furthermore, it is to be understood that the foregoing description 
of the invention has been presented for purposes of illustration and 
explanation and is not intended as limiting the invention to the precise 
form disclosed as changes in details of construction may be made by those 
skilled in the art, within the scope of the appended claims, without 
departing from the spirit of the invention.