Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BI-DIRECTIONAL SEAL ASSEMBLY FOR USE WITH VALVES
BACKGROUND
[0001] Valves are commonly used in process control systems to control the flow
of
process fluids. Sliding stem valves (e.g., a gate valve, a globe valve, a
diaphragm valve, a
pinch valve, etc.) typically have a closure member (e.g., a valve plug)
disposed in a fluid
path. A valve stem operatively couples the closure member to an actuator that
moves the
closure member between an open position and a closed position to allow or
restrict the flow
of fluid between an inlet and an outlet of the valve. Additionally, to provide
a desired and/or
to achieve certain flow characteristics of the fluid, valves often employ a
cage that interposes
in the path of fluid between the inlet and the outlet of the valve. A cage can
reduce capacity
flow, attenuate noise, and/or reduce or eliminate cavitation. Additionally, a
cage surrounds
the closure member to provide stability, balance, and alignment to the closure
member.
[0002] To effect a seal between a cage and a closure member, the closure
member
typically includes a channel or groove that receives a seal and/or piston ring
that engages an
inner surface of the cage. Typically, the size of the valve, industrial
process conditions such
as pressure conditions and operational temperatures (e.g., temperatures
between -100 F and
450 F, temperatures greater than 450 F with the use of an anti-extrusion ring,
etc.) of the
process fluids are used to determine the type of valve and valve components
that may be used
such as, for example, the types of seals that may be used to effect a seal
between a cage and a
closure member. For example, a valve having a process fluid that experiences a
relatively
high pressure differential across its flow passageway typically employs a
pressure-balanced
closure member to minimize or reduce the thrust or force to be exerted by an
actuator to
move the closure member to a closed position. Additionally, valves having
larger sized ports
or flow passageways (e.g., greater than 1 inch in diameter) may employ spring-
loaded seals
to provide a tighter seal. Typically, a bidirectional seal assembly is often
employed with
pressure-balanced closure members to provide bidirectional sealing between the
cage and
closure member to minimize or eliminate leakage in forward and reverse fluid
flow
applications.
[0003] Some known bidirectional sealing assemblies include spacer rings to
maintain
opposing seals separated or spaced apart from each other. The spacer rings are
often sized to
provide a clearance between the spacer ring (e.g., an outside diameter of the
spacer ring) and
a surface of the cage (e.g., an inner surface of the cage). However, due to
wear,
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manufacturing tolerances, etc., the spacer ring may engage or contact the
surface of the cage
as the valve plug moves between an open position and a closed position,
thereby increasing
friction between the closure member or the seal assembly and the cage. While
spacer rings
made of metal material can be used to prevent excessive or rapid wear of the
spacer rings,
such metal spacer rings may mare or damage the cage surface, thereby causing
unwanted
leakage and reducing the life of the cage.
SUMMARY
[0004] An example seal assembly for use with valves described herein includes
a first
seal and a second seal opposite the first seal. The first and second seals are
to sealingly
engage a closure member of a valve and a sealing surface opposite the closure
member. A
spacer ring is disposed between the first and second seals to prevent the
first and second seals
from contacting each other. The spacer ring has an aperture therethrough to
enable
pressurized fluid to flow from a first side of the spacer ring and a second
side of the spacer
ring opposite the first side.
[0005] In another example, a seal assembly includes a first seal having a
first leg and
a second leg forming a first cavity therebetween and a second seal having a
third leg and a
fourth leg forming a second cavity therebetween. A spacer ring is disposed
between the first
and second seals to maintain the first and second seals in spaced apart
relation to prevent the
first and second seals from contacting each other. The spacer ring is at least
partially
positioned within the first cavity such that the spacer ring and the first leg
define a first
portion of the first cavity and the spacer ring and the second leg define a
second portion of
the first cavity. The spacer ring is at least partially positioned within the
second cavity such
that the spacer ring and the third leg define a third portion of the second
cavity and the spacer
ring and the fourth leg define a fourth portion of the second cavity. The
spacer ring includes
an aperture to enable pressurized fluid to flow between the first and third
portions of the
respective first and second cavities and the second and fourth portions of the
respective first
and second cavities.
[0006] In yet another example, a seal assembly for use with a valve includes
first
means for sealing and second means for sealing opposite the first means for
sealing. The first
and second means for sealing are to sealingly engage a closure member of a
valve and a
sealing surface opposite the closure member. The seal assembly includes means
for spacing
the first means for sealing away from the second means for sealing to prevent
the first and
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second means for sealing from contacting each other. The means for spacing
being sized so
that the means for spacing does not contact the closure member or the sealing
surface. The
means for spacing includes means for allowing fluid flow through the means for
spacing
between a first side of the means for spacing and a second side of the means
for spacing
opposite the first side of the means for spacing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view of a portion of a known valve
implemented
with a known sealing assembly.
[0008] FIG. 2 is an enlarged portion of the example valve of FIG. 1.
[0009] FIG. 3 is a cross-sectional view of a portion of a valve implemented
with an
example seal assembly described herein.
[0010] FIG. 4 is an enlarged portion of the example valve of FIG. 3.
[0011] FIG. 5 illustrates an enlarged portion of a valve implemented with
another
example seal assembly described herein.
DETAILED DESCRIPTION
[0012] The example seal assemblies described herein may be used with valves
having
a sliding stem such as, for example, control valves, throttling valves, etc.,
which may include
a valve trim arrangement (e.g., a cage). In general, the example seal
assemblies described
herein effect a seal to substantially prevent leakage between a sealing
surface or a cage and a
closure member (e.g., a valve plug) of a valve. In particular, an example seal
assembly
described herein includes a first seal and a second seal opposite the first
seal where both seals
are disposed between an outer surface of the closure member and an inner
surface of the
cage. A spacer ring is disposed between the first and second seals to prevent
the first and
second seals from contacting each other when the pressure of the process fluid
is insufficient
to assist the seals to seal against a sealing surface (e.g., the inner surface
of the cage and the
outer surface of the closure member). More specifically, the spacer ring is at
least partially
disposed within cavities of the first and second seals and is sized (e.g., has
a width or is
dimensioned) to fit within outer surfaces of the first and second seals so
that the spacer ring
does not engage or contact the outer surface of the closure member and/or the
inner surface of
the cage. The spacer ring may be made of a thermoplastic material, a polymer,
a metal, or
any other material(s).
[0013] FIG. 1 illustrates a cross-sectional view of a portion of a known valve
100.
The valve 100 illustrated in FIG. 1 includes a valve body 102 that defines a
fluid flow
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passageway 104 between an inlet 106 and an outlet 108. A valve plug 110 is
slidably
disposed within a cage 112 and moves between an open position and a closed
position to
control the fluid flow rate through the valve 100. A valve stem 114 couples
the valve plug
110 to an actuator (not shown), which moves the valve plug 110 toward and away
from a
valve seat 116. In operation, the actuator moves the valve plug 110 away from
the valve seat
116 to allow fluid flow through the valve 100 (e.g., the open position) and
toward the valve
seat 116 to restrict fluid flow through the valve 100. The valve plug 110
sealingly engages
the valve seat 116 to prevent fluid flow through the valve 100 (e.g., the
closed position). A
seal assembly 118 prevents fluid leakage between the valve plug 110 and the
cage 112 when
the valve 100 is in the closed position (i.e., when the valve plug 110
sealingly engages the
valve seat 116) as shown in FIG. 1.
[0014] FIG. 2 depicts an enlarged portion of the valve plug 110, the cage 112,
and the
seal assembly 118 of FIG. 1. The valve plug 110 includes a recessed portion
202 to receive
the seal assembly 118. The seal assembly 118 engages an inner surface 204 of
the cage 112
to prevent fluid from leaking between the cage 112 and the valve plug 110 when
the valve
100 is in the closed position. The seal assembly 118 includes a first spring-
loaded seal 206
disposed between a shoulder 208 of the valve plug 110 and a first spacer ring
210, and a
second spring-loaded seal 212 disposed between the first spacer ring 210 and a
second spacer
ring 214. The seal assembly 118 also includes a retaining ring 216 to retain
or hold the seal
assembly 118 together.
[0015] The first and second spring-loaded seals 206 and 212 include springs
218a and
218b disposed within respective outer jackets or coverings 220a and 220b. The
springs 218a
and 218b are typically helically-shaped springs. The spacer rings 210 and 214
prevent the
first spring-loaded seal 206 from contacting the second spring-loaded seal 212
as the valve
plug 110 moves relative to the cage 112. Additionally, the spacer rings 210
and 214 retain
the spring-loaded seals 206 and 212 to prevent the spring-loaded seals 206 and
212 from
becoming dislodged or trapped between the cage 112 and the valve plug 110,
thereby
preventing impairment of the operation of the seals 206 and 212, the cage 112,
or the valve
plug 110. The spacer rings 210 and 214 are made of a metallic material to
prevent excessive
wear to the rings 210 and 214 if, for example, the seals 206 and/or 212 wear
such that the
spacer rings 210 and/or 214 engage or contact the surface of the cage as the
valve plug moves
between an open position and a closed position. While spacer rings made of
metallic
materials can be used to prevent excessive or rapid wear of the spacer rings,
such metal
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spacer rings may mare or damage the cage surface, thereby causing unwanted
leakage and
reducing the life of the cage.
[0016] FIG. 3 illustrates a cross-sectional view of a valve 300 implemented
with an
example bidirectional seal assembly 302 described herein. The valve 300
illustrated in FIG.
3 includes a valve body 304 that defines a fluid flow passageway 306 between a
first port or
inlet 308 and a second port or outlet 310. In other examples, because the
example seal
assembly 302 provides a bidirectional seal, the direction of fluid flowing
through the valve
may be reversed such that the second port 310 is an inlet port and the first
port 308 is an
outlet port.
[0017] A valve trim assembly 312 interposes in the fluid flow passageway 306
to
control fluid flow between the inlet 308 and the outlet 310. The valve trim
assembly 312
includes internal components of the valve 300 such as, for example, a cage
314, a closure
member 316 (e.g., a valve plug), a valve seat 318 (e.g., a seat ring), and a
valve stem 320.
[0018] The cage 314 is disposed between the inlet 308 and the outlet 310 to
provide
certain fluid flow characteristics through the valve body 304 (e.g., reduce
noise and/or
cavitation generated by the flow of fluid through the valve 300). The cage 314
includes a
bore 322 to receive (e.g., slidably receive) the closure member 316 and at
least one opening
324 through which fluid can flow when the valve 300 is in an open position
(i.e., when the
closure member 316 is spaced away from the valve seat 318). A cage can be
configured in
different manners to provide certain fluid flow characteristics to suit the
needs of a particular
control application. For example, the openings 324 may be designed or
configured to provide
particular, desirable fluid flow characteristics of the fluid such as, for
example, to reduce
noise and/or cavitation, to enhance pressure reductions of the process fluid,
etc. The desired
fluid flow characteristics are achieved by varying the geometry of the
openings 324. In some
example implementations, the cage 314 may include a plurality of openings
having various
shapes, sizes, and/or spacing(s) to control the flow, reduce cavitation,
and/or reduce noise
through the valve.
[0019] The cage 314 guides the closure member 316 and provides lateral
stability as
the closure member 316 travels between the open position and a closed
position, thereby
reducing vibrations and other mechanical stress. The cage 314 can also
facilitate
maintenance, removal, and/or replacement of the other components of the valve
trim
assembly 312. In the illustrated example, the cage 314 is a substantially
unitary structure.
However, in other example implementations, the cage 314 can be a two-piece
structure that
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includes an upper portion that removably couples to a lower portion. In yet
other examples, a
retainer (not shown) may be used to retain the cage 314 within the valve body
304.
[0020] The closure member 316 has an outer surface 326 sized to closely fit
within
the cage 314 so that the closure member 316 can slide within the bore 322 of
the cage 314.
The closure member 316 can slide within the cage 314 between the closed
position, in which
the closure member 316 obstructs the openings 324 of the cage 314, and the
open position, in
which the closure member 316 is clear of (i.e., does not block) at least a
portion of the
openings 324. In the illustrated example, the closure member 316 is depicted
as a valve plug
having a cylindrical body and a seating surface 328. However, in other
examples, the closure
member 316 may be a disk or any other structure to vary the flow of fluid
through a valve.
[0021] In this example, the closure member 316 includes channels or conduits
330 to
balance the pressures acting across the closure member 316. In this manner,
the forces
exerted across the closure member 316 by the pressure of the process fluid
flowing through
the valve 300 are substantially equalized. For example, the pressure of the
fluid in the cavity
332 exerts a force on a first side or surface 334 of the closure member 316
that is
approximately equal to and opposite a force exerted on a second side or
surface 336 of the
closure member 316. As a result, a smaller actuating force can be provided to
move the
closure member 316 between the open and closed positions.
[0022] The valve stem 320 is operatively coupled to the closure member 316 at
a first
end 338 and extends through a bonnet 340 to couple the closure member 316 to
an actuator
stem (not shown) at a second end 342. The actuator stem couples the closure
member 316 to
an actuator (not shown). The actuator (e.g., a pneumatic actuator) drives the
valve stem 320
and, thus, the closure member 316 between the closed position at which the
closure member
316 is in sealing engagement with the valve seat 318 (e.g., a seat ring) to
restrict or prevent
fluid flow through the valve 300 and the fully open or maximum flow rate
position at which
the closure member 316 is spaced away from the valve seat 318 to allow fluid
flow through
the valve 300. In the open position, fluid flows between the inlet 308,
through the openings
324 of the cage and an opening 344 of the valve seat 318 and through the
outlet 310. In the
closed position, the closure member 316 covers the openings 324 of the cage
314 and
sealingly engages the valve seat 318 via the sealing surface 328 to prevent
fluid flow between
the inlet 308 and the outlet 310.
[0023] The bonnet 340 is coupled to the valve body 304 via fasteners 346, and
the
bonnet 340 couples the valve body 304 to the actuator (not shown). The bonnet
340 houses a
packing system 347 (e.g., a spring packing), which prevents undesired leakage
to the
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environment via the valve stem 320 as the valve stem 320 moves or slides
within the valve
300 along an axis 348. The bonnet 340 also includes a gasket 350 to prevent
unwanted fluid
leakage through the valve body 304. In this example, the bonnet 340 is fixed
to the valve
body 304 to retain (e.g., via an interference and/or press fit) the cage 314
and the valve seat
318 within the valve body 304. In other examples, the valve seat 318 couples
to the cage 314
and/or the valve body 304 via, for example, fasteners, etc.
[0024] Referring also to FIG. 4, although the closure member 316 closely fits
within
the bore 322 of the cage 314, a gap 402 is formed between the closure member
316 and the
cage 314. Fluid may leak through the gap 402. For example, when the valve 300
is in the
closed position, fluid from the inlet 308 may flow via the gap 402 through the
conduits 330 of
the closure member 316, and through the outlet 310 of the valve 300. Such
unwanted leakage
affects the shut-off classification of the valve 300. For example, the
American National
Standards Institute has established various leakage classifications (e.g.,
Class I, II, III, etc.)
relating to the amount of fluid flow allowed to pass through a valve when the
valve is in a
closed position. The seal assembly 302 is disposed between the cage 314 and
the closure
member 316 to prevent leakage between the inlet 308 and the outlet 310 of the
valve 300
when the closure member 316 is in the closed position to improve the shut-off
classification
of the valve 300.
[0025] The example seal assembly 302 prevents unwanted leakage through the gap
402 when the closure member 316 is in the closed position. Thus, the seal
assembly 302
effects a seal between a first sealing surface 404a (e.g., an inner surface of
the cage 314) and
a second sealing surface 404b (e.g., the outer surface 326 of the closure
member 316). The
closure member 316 includes a shoulder 406 to receive the seal assembly 302. A
retaining or
snap ring 408 retains the seal assembly 302 between the retaining ring 408 and
the shoulder
406 of the closure member 316. A back-up ring 410 may be disposed between the
retaining
ring 408 and the seal assembly 302 to maintain the position and/or orientation
of the seal
assembly 302 relative to the closure member 316. Additionally or
alternatively, although not
shown, the seal assembly 302 may include an anti-extrusion ring (e.g.,
disposed adjacent the
shoulder 406 and/or the back-up ring 410) to prevent the seal assembly 302
from extruding
into the gap 402 as the closure member 316 moves between the open position and
the closed
position.
[0026] The seal assembly 302 includes a first seal 412, a second seal 414, and
a
spacer ring 416. In this example, the first seal 412 is substantially similar
or identical to the
second seal 414. Each of the first and second seals 412 and 414 is implemented
as a spring-
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loaded seal. The seals 412 and 414 include respective springs 418a and 418b
disposed within
respective outer jackets 420a and 420b. The springs 418a and 418b include a
ring-shaped
cantilevered finger spring and have a V-shaped (or U-shaped) cross-sectional
shape. The
springs 418a and 418b may be made of, for example, stainless steel, or any
other suitable
material. The jackets 420a and 420b are also in the form of a ring and can be
unitary or
partially ring-shaped. The jackets 420a and 420b include respective cavities
or channels 422a
and 422b to receive the springs 418a and 418b. The jackets 420a and 420b may
be made of a
flexible material that does not generate excessive friction between the
closure member 316
and the cage 314. For example, the jackets 420a and 420b may be made of a
fluoropolymer
material (e.g., Teflon ), an elastomeric material, or any other suitable
material. When
disposed within the respective channels 422a and 422b, the springs 418a and
418b provide a
load to assist or bias outer surfaces 424a and 424b of the outer jackets 420a
and 420b against
the first sealing surface 404a and the second sealing surface 404b. In other
examples, the
first seal 412 may be different from the second seal 414. For example, the
jacket 420a of the
first seal 412 may be made of a material that is different from the material
of the jacket 420b
of the second seal 414.
[0027] The first seal 412 is disposed between the closure member 316 and the
cage
314 in an opposite direction or orientation relative to the second seal 414.
In particular, as
depicted in this example, the channel 422a of the first seal 412 faces the
channel 422b of the
second seal 414. In this manner, the first and second seals 412 and 414
provide a
bidirectional seal to prevent leakage between the closure member 316 and the
cage 314
regardless of the direction of fluid flow through the valve 300.
[0028] The spacer ring 416 is at least partially disposed within the channels
422a and
422b of the respective first and second seals 412 and 414. The spacer ring 416
prevents the
first and second seals 412 and 414 from contacting each other when the
pressure of the fluid
in the flow passageway 306 is insufficient to pressure-assist or hold the
first and second seals
412 and 414 in spaced apart relation relative to each other. Additionally, the
spacer ring 416
is sized to fit within the outer surfaces 424a and 424b of the jackets 420a
and 420b. In this
manner, the spacer ring 416 is sized so that it does not engage or contact the
first sealing
surface 404a (i.e., the inner surface or bore 322 of the cage 314) and/or the
second sealing
surface 404b. As a result, the spacer ring 416 may be made of, for example, a
thermoplastic
material such as, for example, polyetheretherketone (PEEK), a metal, or any
other suitable
materials and/or materials that can withstand fluids having relatively high
temperatures (e.g.,
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fluid temperatures above 450 F, greater than 450 F with the use of an anti-
extrusion ring,
etc.).
[0029] Also, for example, should the seal assembly 302 (e.g., the outer
surfaces 424a
and/or 424b) wear, the spacer ring 416 will not engage or slide against the
cage 314 (i.e., the
first sealing surface 404a), thereby substantially reducing seal friction
between the closure
member 316 and the cage 314. In general, the seal assembly 302 substantially
increases the
life of the seal ring 416 because the seal ring 416 does not engage the cage
314 or the closure
member 316.
[0030] Referring to FIGS. 3 and 4, in operation, an actuator (e.g., a
pneumatic
actuator) drives the closure member 316 between the fully open or maximum flow
rate
position at which the seating surface 328 of the closure member 316 is spaced
away from the
valve seat 318 to allow the flow of fluid through the valve 300 and a closed
position. The
seal assembly 302 moves or slides in a direction along the axis 348 as the
closure member
316 moves between the open position and the closed position. At the closed
position, the
closure member 316 sealingly engages the valve seat 318 and blocks the
openings 324 of the
cage 314 to prevent fluid flow through the valve 300 between the inlet 308 and
the outlet 310.
[0031] When the valve 300 is in the closed position, fluid may flow into the
gap 402
between the closure member 316 and the cage 314. The seal assembly 302
described herein
prevents the fluid from traveling further and, thus, prevents the fluid from
leaking between
the cage 314 and closure member 316.
[0032] The outer jackets 420a and 420b of the first and second seals 412 and
414
engage the sealing surfaces 404a and 404b. The springs 418a and 418b apply a
load against
the jackets 420a and 420b to bias the outer surfaces 424a and 424b of the
jackets 420a and
420b against the sealing surfaces 404a and 404b, thereby effecting a tight
seal and preventing
undesired fluid leakage between the cage 314 and the closure member 316. For
example,
fluid attempting to leak through the valve 300 between the closure member 316
and the cage
314 from the inlet 308 presses against an inner surface 422b of the jacket
420b, thereby
pressure-assisting the outer surface 424b against the sealing surfaces 404a
and 404b.
Conversely, if the direction of flow is reversed, fluid attempting to leak
through the valve 300
between the closure member 316 and the cage 314 that is flowing through the
conduits 330 of
the closure member 316 presses against an inner surface 422a of the jacket
420a, thereby
pressure-assisting the outer surface 424a of the jacket 420a against the
sealing surfaces 404a
and 404b. This action improves the seal (e.g., provides a tighter seal)
between the closure
member 316 and the cage 314.
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[0033] Additionally or alternatively, because the springs 418a and 418b exert
a force
to bias the respective jackets 420a and 420b toward the sealing surfaces 404a
and 404b, the
spring-loaded seals 412 and 414 enable a relatively relaxed tolerance in
machining and
assembly of the valve components and/or dimensional variations caused by
temperature
changes.
[0034] In operation, the spacer ring 416 maintains or keeps the first and
second seals
412 and 414 in spaced apart relation and prevents the first and second seals
412 and 414 from
contacting each other. Failing to maintain the first and second seals 412 and
414 in spaced
apart relation may otherwise cause the first and second seals 412 and 414 to
become jammed
or stuck within the gap 402 between the cage 314 and the closure member 316,
thereby
resulting in an ineffective seal.
[0035] FIG.
5 illustrates an enlarged portion of a valve 500 that is implemented
with another example seal assembly 502 described herein. Those components of
the example
valve 500 of FIG. 5 that are substantially similar or identical to those
components of the
example valve 300 described above and that have functions substantially
similar or identical
to the functions of those components will not be described in detail again
below. Instead, the
interested reader is referred to the above corresponding descriptions in
connection with FIGS.
3 and 4. Those components that are substantially similar or identical will be
referenced with
the same reference numbers as those components described in connection with
FIGS. 3 and 4.
[0036] The example valve 500 is substantially similar to the example valve 300
of
FIGS. 3 and 4. However, a closure member 504 of the example valve 500 is
implemented
with a vent or passageway 506 to fluidly couple the fluid flow passageway 306
(see FIG. 3)
to the seal assembly 502 via the conduits 330. The seal assembly 502 includes
a first seal
508 and a second seal 510 opposite the first seal 508. A spacer ring 512 is
disposed between
the first and second seals 508 and 510 to prevent the first and second seals
508 and 510 from
contacting each other. The first and second seals 508 and 510 are
substantially similar or
identical to the seals 412 and 414 of FIGS. 3 and 4 and, thus, for brevity,
the description of
the first and second seals 508 and 510 will not be repeated.
[0037] The passageway 506 enables pressurized fluid to flow to the seal
assembly
502 between the channels 422a and 422b. The spacer ring 512 includes an
aperture or
opening 514 to enable the pressurized fluid to flow to a first side 516a of
the spacer ring 512
opposite a second side 516b facing the passageway 506. In this manner, the
passageway 506
and the opening 514 of the spacer ring 512 provides equalization of pressure
across the seal
assembly 502, thereby further reducing friction between the cage 314 and the
first and second
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seals 508 and 510 when the closure member 504 moves between an open position
and closed
position. As a result of the reduced friction between the cage 314 and the
closure member
316, the operating lives of the jackets 420a and 420b of the respective first
and second seals
508 and 510 and the spacer ring 512 are substantially increased.
[0038] Although certain apparatus have been described herein, the scope of
coverage
of this patent is not limited thereto. To the contrary, this patent covers all
apparatus fairly
falling within the scope of the appended claims either literally or under the
doctrine of
equivalents.
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