Note: Descriptions are shown in the official language in which they were submitted.
~2~Z4~6
FIRE-SAFE BALL VALVE
Background of the Invention
This invention relates to the valve art, and,
more particularly, to fire-resistant or fire-safe ball
valves.
When employed in the valve art, the term
"fire-safe" has come to mean a valve that satisfies
certain specified conditions when subjected to a fire.
See Arant, Fire-Safe Valves--An Overview, Proceedings,
Thirty-Sixth Annual Symposium on Instrumentation for the
Process Industries (Texas A~M University, 1981).
Unfortunately, different sets of conditions have been
promulgated by different organizations and the valve
industry has not yet recognized a uniform standard.
Basically, according to one of the standards (American
Petroleum Institute 607), if a valve will substantially
maintain a fluid seal in a closed position at a valve body
temperature of at least 1100 degrees F. for at least ten
minutes, it may be certified as "fire-safe". Valves which
include desigll characteristics to resist leakage upon
exposure to fire but cannot meet this standard are
commonly referred to as "fire-resistant".
The invention is particularly applicable to a new
and improved soft-seated fire-safe ball valve and seat
assembly for a valve of the type having a so-called
"floating ball" and will be described with particular
reference thereto~ However, it will become readily
apparent to those skilled in the art that the invention is
capable of broader applications and could be adapted for
use in other types and styles of valves.
Ball valve constructions in commercial use
typically employ annular seats or seat rings formed of a
,
~24Z6
-- 2
resilient and deformable plastic such as Teflon ta
registered trademark of E.I. duPont de Nemours and
Company) for sealing engagement with the ball. A pair of
such seat rings are positioned adjacent the valve inlet
and outlet openings. The ball itself is mounted for a
slight amount of free movement or shifting axially of the
seats when the ball is in a valve closcd position un(ler
fluid pressure conditions. Such shifting causes the ball
to act against and to flex and deform the downstream seat
ring to enhance its sealing engagement with the ball. The
amount of such flexing varies in accordance with ~he fluid
pressure involved.
When subjected to a fire, the soft annular seat
of a conventional floating ball type of ball valve is
substantially damaged by the heat of the fire to the
extent that leakage through the valve may become
unacceptable. Typically, downstream of the ball, the
sequence of seat destruction is such that the plastic
first softens and begins to flow out or extrude through
the valve port. Continued exposure to excessive hea-t
ultimately causes the seat to char and sublimate or
evaporate. The destruction of the plastic seat allows the
ball to further shift under fluid pressure conditions
until the ball engages a secondary seat. Such a secondary
seat typically comprises a metal or non-flammable radially
inwardly extending projection of the valve body, such as a
support shoulder for the plastic seat. Normally, such a
surface is not specially designed for a high degree
sealing engagement against the ball and allows substantial
leakage.
Another particular problem occurs where the
plastic seat is only partially destroyed by a fire. For
example, where a valve is exposed to radiant heat from a
fire on one side only, or in a low intensity fire, only
~LZ42426
-- 3
tha-t portion of the valve seat nearest the fire may soften
and extrude into the valve port. The ball may then shift
under fluid pressure toward that area made available to it
by the extrusion and, being unable to even]y contact the
secondary seat, expose a large leak path. Alternatively,
the ball may be held back from making any contact with the
secondary seat by the undestroyed por-tions of the plastic
seat and similarly expose large leak paths. Under either
situation fluid may rush through the leak paths and quench
the valve. The quenching action operates to prevent
further deterioration of the seat in spite of a continuing
fire and typically maintains a massive leak through the
valve.
An additional but often unrecognized problem
which occurs during a fire is the rapid increase in fluid
pressure by heated fluid which is trapped between the
inlet and outlet seats around the ball. The heat of the
fire may heat and even vaporize such fluid in the center
of the valve between the seats. Often the fire is so
intense that the fluid is so rapidly vaporized that it
cannot escape past the seats quickly enough to prevent an
excessive increase o pressure within the valve. Such an
increase in pressure can easily exceed the valve rating
and rupture the seals at the stem packing and the body
joints, or rupture the valve body itself.
Another practical problem occurs when a fire hose
is trained upon a valve in a volatile liquid system that
has been heated by a fire. The quick-cooling action of
the hose water causes a violent condensation of heated
vapor in the valve that dislodges the ball and churns llp
char, waste and contaminants that may become lodged
between the ball and the ball sealing surface and thereby
provide additional leak paths.
~Z'~24~
,~
One overall objective of fire-resistant or
fire-safe ball valve seat designs is to obtain a valve
which will seal with conventional valve seat materials at
normal operating conditions and will also seal when
subjected to a fire. Various forms and types of ball
valve seat designs have heretofore been suggested and
employed in the industry for purposes of obtaining a
fire-safe or fire-resistant ball valve, all with varying
degrees of success. It has been found that the defects
present in most prior fire-safe or fire-resistant ball
valve designs are such that the devices themselves are of
limited economic and practical value.
A common type of fire-resistant ball valve design
includes a primary soft seat of a plastic material such as
Teflon, and a secondary seat of metal or a high
temperature composite material to seal the valve upon
destruction of the primary seat in a fire. The secondary
seat typically comprises a metal rim or washer interposed
between the soft plastic primary seat and a valve body
support shoulder. This design suffers from the problems
naturally resulting from any type of metal-to-metal seal.
Since the ball in a floating ball type valve is never
perfectly spherical and the secondary metal seat is not
made perfectly circular, leakage across the secondary seal
after destruction by fire of the primary seal is usually
high, as the ball cannot make a full annular contact with
the metal seat. For a metal-to-metal seal to be anywhere
near leak-tight in a fire-safe or other application, the
sealing surfaces must be match lapped or burnished, one
into the other. Since such a procedure is very expensive,
match lapping is an economically impractical procedure for
a manufacturer of fire-safe or fire-resistant ball
valves. In addition, a match-fitted secondary seat would
likely be marred by the hazards and consequences of normal
~Z~ 6
-- 5
valve operation, such as corrosion, pitting, scaling,
erosion and the like, to the extent that during a
subsequent fire the advantages of match fitting would have
been lost. Ball valve designs incorporating the secondary
metal seat or high temperature composite seat also suffer
from the problems of partial deterioration and quenching
of the primary seat and the problems of loose and blocking
char and waste materials associated with quick cooling.
A suggested improvement over the mere metal
secondary seat design has been to add a secondary seat
comprised of a heat resistant material which is more
deformable and resiliant than metal. Typically, carbon or
graphite rings have been used. While such designs may
provide improved operation when new, it has been found
that such designs are particularly susceptible to damage
in normal service. Normal wear through cycling the valve,
erosion while opening, or abrasion by foreign matter can
easily damage the secondary seat materials since they are
typically brittle and of low strength compared to a normal
plastic seat. Therefore, such designs usually still
include a metal lip or rim as a final or tertiary seat to
restrict leakage if the secondary seat is damaged. Such a
multiplicity of seats increases the size, complexity, and
cost of the valve without adding a reliable redundant
seal. Whatever elements of wear, erosion or other foreign
matter might damage one of the seats is likely to damage
all of the seats since they are all equally exposed during
normal service.
One alternate suggestion for obtaining a
fire-safe valve is to include packing a conventional valve
in enough insulation to insulate the valve for a
sufficient amount of time to obtain a fire-safe rating.
Another suggestion is to dispose a sprinkler near the
valve which will quench the valve during a fire. Both of
~Z4Z~;26
these designs are unsuitable for practical cost reasons in
that they would involve expensive installations and
maintenance. In addition, an insulated valve would suffer
from the problem of uncertainty as to whether the
insulation would be properly reattached or installed each
time the valve received maintenance.
I-t has, therefore, been desired to develop a
fire-safe ball valve and seat assembly which woul~
satisfactorily operate at normal operating conditions and
also seal the valve in a valve closed position upon
exposure to a fire. Preferably, such a design would
eliminate the necessity for utilizing costly sprinklers or
insulation packings to protect the valve.
The present invention contemplates a new and
improved construction which overcomes all of the above
referred to problems and others and provides a new and
improved fire-safe floating ball type valve and soft seat
assembly which provides improved sealing capabilities and
efectively resists leakage upon exposure to any realistic
fire. The invention further comtemplates being useful
with a wide variety of seat designs and materials which
effectively seal at a wide variety of normal operating
conditions.
Brief Description of the Invention
Generally, the present invention contemplates a
new and improved fire-safe ball valve and seat assembly
wherein a composite seat member assembly includes a
primary soft plastic seat member or ring, and a secondary
seat member of deformable, heat resistant material. The
secondary seat member operates to seal the valve upon
partial or complete destruction or deterioration of the
primary seat ring caused by fire or other extreme heat. A
2~26
-- 7
pair of such assemblies are (lisposed on opposite sides of
the ball member and are continuously urged toward the ball
for maintaining it properly positioned in a valve body and
for providing valve sealing.
More specifically, the subject invention is
particularly applicable to use in a Yalve of the type
having a valve body with a central passageway and a ball
member which includes a fluid flow opening positioned in
the passageway. The ball is mounted for selective
rotation between valve open and closed positions to
control fluid flow through the valve. A pair of radially
inward extending shoulders are disposed circumferentially
of the passageway on opposite sides of, and in a facing
relationship with, the ball member. The passageway
includes a pair of counterbores disposed on opposite sides
of the ball member with each of the counterbores having an
inner end wall facing an associated one of the shoulders.
A pair of composite seat assemblies are positioned axially
in the passageway on opposite sides of the ball member for
fluid sealing engagement with the ball member. Each of
the assemblies includes a reinforcing ring, a primary seat
member comprising a soft plastic seat ring and a secondary
seat member. The reinforcing ring includes a central
opening and abuts an associated one of the counterbore end
walls. The soft seat ring is adapted for rotational type
flexure generally toward and away from the reinforcing
ring and abuts the reinforcing ring opposite to the
counterbore end wall. The seat ring includes a central
opening and a ball-engaging surface facing the ball member
for sealing engagement with the ball member. The
secondary seat member is interposed between the seat ring
and an associated one of the shoulders. The secondary
seat member comprises a deformable, heat resistant
secondary seat ring which preferably includes expanded
~z~ ~;26
-- 8
carbonaceous material whereby upon fire damage to the seat
ring, the secondary seat ring engages the ball to seal the
valve.
In accordance with another aspect of the present
invention, the secondary seat member comprises a disc
spring in combination with a sheet of expanded
carbonaceous material. The disc spring has a generally
frusto-conical configuration in an unstressed condition.
The sheet of expanded carbonaceous material is generally
radially coextensive with the disc spring and is
interposed at least between the spring and the primary
soft plastic seat ring. The disc spring operates to
continuously urge the facing sheet of carbonaceous
material and the soft seat ring toward the ball member.
Upon damage to the primary seat ring by a fire, the facing
sheet of carbonaceous material contacts the ball member to
effect fluid sealing.
In accordance with yet another aspect of the
invention, the secondary seat member includes a pair of
sheets of expanded carbonaceous material. The pair
sandwich the disc spring and are generally radially
coextensive therewith. A first sheet faces the ball
member for engagement with the ball member upon damage to
the primary soft seat ring. A second sheet faces the
associated one of the pair of the radially inward
extending shoulders for sealing engagement with the
shoulder upon damage to the primary seat ring.
According to a further aspect of the invention, a
weir ring is included in the primary seat ring and is
interposed generally between the primary seat ring and the
secondary seat member.
According to another aspect of the present
invention, the ball member includes a second opening
normal to the principal fluid flow opening of the ball
~242~6
g
member. The second opening faces the valve inlet when the
ball is in the closed position to CommlJnicate fluid
contained in the center of the valve to the inlet fluid.
The principal object of the invention is the
provision of a new and improved fire-safe ball valve and
seat asscm~ly which has improved fluid sealing
characteristics upon fire or heat exposure to th~ valve.
Another object of the present invention is the
provision of such a ball valve and seat assembly which
will avoid metal-to-metal fluid sealing engagements.
Still another object of the invention is the
provision of a ball valve which will maintain fluid
sealing upon partial or complete destruction by fire of a
primary soft plastic seat member.
Yet another object of the invention is the
provision of a ball valve seat assembly which will prevent
the interposition of primary seat ring extrusions or
fire-caused char and contaminants between the ball member
and ball engaging and sealing surfaces.
Another object is the provision of a secondary
seat which will function upon fire damage to the ball
valve regardless of the design and construction material
of the primary seat.
Still another object is the provision of a
secondary seat which will not deteriorate with age in
normal service.
Another objec~ is the provision of a fire-safe
ball valve which prevents the accumula-tion of
destructively high pressures within the valve body and
seat assemblies when the valve is exposed to high
temperatures.
Still another object is the provision of a ball
valve seat assembly which includes a secondary seat that
is removed from the deterioration and wear forces of fluid
flow associated with normal service.
~2~2~:6
- 10 -
Still other objects and advantages of the
invention will become apparent to those skilled in the art
upon a reading and understanding of the following
specification.
Brief Description of the Drawings
The invention may take physical form in certain
parts and arrangements of parts, a preferred and several
alternative embodiments of which will be described in
detail in this specification and illustrated in the
accompanying drawings which form a part hereof and wherein:
FIGURE 1 is a longitudinal cross-sectional view
through a ball valve which incorporates the preferred
embodiment of the invention;
FIGURE 2 is an enlarged cross-sectional view of a
portion of the downstream seat assembly of FIGURE 1 just
prior to valve makeup and with the ball member deleted for
ease of illustration;
FIGURE 3 is an enlarged cross-sectional view of a
portion of the downstream seat assembly of FIGURE 1, but
with the valve in a closed position under the influence of
elevated fluid system pressures;
FIGURE 4 is a cross-sectional view similar to
FIGURE 3 but with the valve having been exposed to fire
and heat such that the soft plastic seat ring has begun to
flow outwardly through the valve port;
FIGURE 5 is a cross-sectional view similar to
FIGURE 4 where the ball has made contact with the
secondary seat;
FIGURE 6 is a cross-sectional view similar to
FIGURES 4 and 5 where the soft plastic seat has been
completely destroyed;
FIGURE 7 is a substantially plan view of -the
valve taken along lines 7-7 of FIGURE 1 with a portion of
2~
- 11 -
the valve body broken away for showing an improved bolting
arrangement;
FIGURE 8 is an enlarged cross-sectional view of a
seat assembly which incorporates an alternative embodiment
of the invention;
FIGURE 9 is an enlarged cross-sectiona.l view of
yet another alternative embodiment of the invention;
FIGURE 10 is an enlarged cross-sectional view of
a seat assembly of a ball valve which incorporates another
alternative embodiment of the invention;
FIGURE 11 is an enlarged cross-sectional view of
still another alternative seat assembly embodiment which
incorporates the invention;
FIGURE 12 is an enlarged perspective vi.ew of th~
seat assembly of FIGURE 10 after partial destruction upon
exposure to a fire and having been removed from the valve
body for ease of illustration; and
FIGURE 13 is an enlarged perspective view of -the
seat assembly of FIGURE 1 after partial destruction upon
exposure to a fire and having been removed from the valve
body for ease of illustration.
Detailed Description of the Preferred Embodiment
Referring now to the drawings wherein the
showings are for purposes of illustrating the preferred
and several alternative embodiments of the invention only
and not for purposes of limiting the same, FIGURE 1 shows
a ball valve A having a pair of opposed seat assemblies B
disposed on opposite sides of a floating type spherical
ball member C.
More particularly, and with reference to FIGURES
1 and 7, ball valve A includes a body or housing generally
designated 10 having a main or central body section 12 and
~a~2~2~
- 12 -
opposed end ~ittings 14,16. Seat assemblies B and ball C
are mounted within the main body section 12 and the ball
member is arranged for selective rotation by a stem and
actuating handle assembly generally designated 18. Ball
member C includes a first or principal fluid flow opening
15 extending the diameter of the ball for communicating
fluid flow from the inlet to the outlet when the valve is
in a valve-open condition. A second opening 17 is
included in the ball C normal to the principal flow
opening 15 and generally facing the valve inlet when the
valve is in a closed position to communicate fluid and
fluid pressure in the center of the valve to the valve
inlet fluid. Substantially all of the details of the
portions of the valve illustrated in FIGURE l, except for
the seat ring assemblies, may be modified as desired
and/or necessary to accommodate different types or styles
of ball valve constructions.
In general, however, and for purposes of
describing the subject invention, the valve body includes
a generally cylindrical central passageway or
axially-extending fluid flow opening 20 which is only
slightly larger in diameter than ball member C. Each of
end fittings 14,16 is releasably connected to central body
section 12 by a plurality of longitudinally extending tie
bolts generally designated 22 received through bolt bores
designated 24 of opposed end fittings 14,16 and fittedly
received in main body section 12 (FIGURE 7). It has been
found that the use of a plurality of tie bolts 22 received
in main body section 12 is particularly advantageous for a
fire-safe application to avoid the problems of yielding or
breaking of longer tie bolts which may occur after a valve
has been heated in a fire and rapidly cooled with water
from a fire hose or sprinkler. During a fire, the metal
components of the valve will naturally expand upon being
~Z~ 2~
heated. When a fireman has craine~ a hose on such a
heated valve, the periphery of the valve, including the
tie bolts, will cool and will contract more quickly than
the body of the valve. Such quick cooling and contraction
may ultimately result in yielding or breaking of the tie
bolts 22. Where a plurality of shorter9 fitted tie bolts
are employed, such problems are minimized. The end
fittings 14,16 are also provided with internal threads
26,28 or any other convenient means to accommodate
connecting the valve to an associated fluid system or
piping.
The stem and actuating handle assembly 18
illustrated includes a stem member 30 having a lower end
32 configured as shown for sliding receipt in a slot or
groove 34 included in the upper end of ball C. This
arrangement allows the ball to be rotated between valve
open and closed positions while~ at the same time,
permitting the ball to have some freedom of movement for
shifting axially in valve body passageway 20 when the
valve is in a closed position and fluid pressure is acting
on the ball.
Stem member 30 extends outwardly through an
opening 36 in central body section 12. Packing rings
38,40,42 suitable for elevated temperatures are positioned
in opening 36 and sealingly engage the opening and stem
member 30. As shown, lower packing ring 42 rests upon an
inwardly extending flange 44 formed within opening 36. A
thrust washer 46 suitable for elevated temperatures is
positioned below flange 44 and is clamped thereto by an
outwardly extending shoulder or flange 48 formed at the
base of stem member 30. The stem is held in position by a
packing gland 50 and a packing nut 52. As shown in ~IGURE
1, tightening of packing nut 52 applies a compressive
force to packing rings 38,40,42 to effect radial expansion
into a fluid-tight seal about the stem.
~2~2~21~
- 14 -
Although it is possible to actuate the valve stem
by many different types of actuators, including both
manual, mechanical or automatic, a handle member 54 has
been shown. This handle is releasably secured to stem
member 30 by a nut 56 which clamps the handle to the top
of packing nut 52. A cooperating flat 58 is
advantageously formed on the exterior of the stem for
association with a flat (not shown) in the handle opening
for properly positioning the handle on the stem. However,
the position of the handle and, in turn, the position of
ball member C are limited by depending stop members 62,64,
carried by handle 54. These stop members engage suitable
surfaces on central body section 12 to provide fixed stops
for the valve in the full open and full closed positions.
With continued reference to FIGURE 1, the ball
seat arrangement utilized in the subject invention
includes a pair of seat ring assemblies B disposed on
opposite sides of ball member C. As shown, the seat ring
assemblies are clampingly retained in position on opposite
sides of the ball adjacent opposite ends of the main body
section passageway 20. The seat ring assemblies are
located substantially equidistant from and on
diametrically opposite sides of the axis of rotation of
the ball member and include central openings 66,68. While
the seat ring assemblies could be maintained in position
by many different or alternative arrangements, they are
shown as being located by shoulders 70,72 defined by end
faces 74,76 of end fittings 14,16, respectively. The
inward limit of movement of the seat ring assemblies is
defined by a pair of shoulders or steps 78980 which are
formed by the inner end walls of counterbores extending
inwardly of valve body passageway 20.
Still further, a seal is provided between central
body section 12 and end fittings 14~16 by means of sealing
rings 82,84 which are received in second counterbores
3L2~2~2E;i
- 15 -
86,88, respectively. Each sealing ring is disposed about
the outer circumference or outer peripheral surface of a
portion of the associated seat ring assembly B. The
sealing rings are preferably constructed of a deformable,
resilient, heat resistant and thermally stable material
such as an expanded carbonaceous material and wire mesh
composite to avoid problems of sublimation and charring
that may occur such as when a conventional type
thermoplastic O-ring seal is exposed to a fire or other
elevated temperatures. In the preferred construction,
Grafoil (a registered trademark of the Union Carbide
Corporation) has been advar.tageously employed as the
deformable and heat resistant material. However, it will
be appreciated that other materials such as asbestos or
ceramic composites could also be employed. As the valve
main body section 12 and opposed end fittings 14,16 expand
and contract upon heating and cooling during and after a
fire, sealing rings 82,84 continue to provide a
satisfactory seal between the central body section and the
end fittings~
The structural details of ball valve A as
described hereinabove are with reference to the preferred
valve construction. It will be readily apparent to those
skilled in the art, however, that modifications may
readily be made thereto to accommodate particular
operational needs and/or requirements. Such changes are
not deemed to affect the overall intent or scope of the
present inven-tion as will be described in detail
hereinafter.
With references to FIGURES 2 through 6 and 13,
description will be made of the specific details of seat
assemblies B comprising the preferred embodiment of the
invention. FIGURE 2 shows a cross-sectional view of the
downstream seat assembly disposed adjacent end fitting 14
prior to valve makeup. The ball member C has been deleted
2~;26
- 16 -
for ease of understanding and appreciating the seat
assembly construction. FIGURE 3 shows a view of the seat
assembly of FIGURE 2 at valve makeup and with the valve in
a closed position under the influence of eleva-ted fluid
system pressure. FIGURES 4, 5 and 6 illus-trate the seat
assembly B at successive stages after the valve has been
exposed to a fireO FIGURE 4 shows a primary soft plastic
seat ring which has begun to heat flow and extrude out
through the valve port. FIGURE 5 shows the valve after
the ball has made contact with the secondary seat. FIGURE
6 shows the valve after the primary soft plastic seat ring
has been completely destroyed and extruded or evaporated
out of the valve body. FIGURE 13 shows the seat assembly
B after partial destruction such as where the valre is
exposed to a fire or radiant heat on one side only. Lines
3-3, 4-4, 5-5, and 6-6 of FIGURE 13 correspond to the
cross-sectional views of the seat assembly B shown in
FIGURES 3, 4, 5, and 6, respectively.
With particular reference to FIGURES 2 and 3, the
seat assemblies B are preferably comprised of three
components, i.e., a reinforcing or support ring 100, a
primary seat member 102 comprising a soft plastic seat
ring, and a secondary seat member 104 comprising a
deformable, non heat-flowing seat ring. Although only a
portion of one seat assembly is shown in these FIG~RES, it
will be appreciated that the other seat assembly is
identical thereto unless otherwise specifically noted.
Reinforcing ring 100 has an annular configuration
including a central opening and is constructed from a
rigid material such as steel or other suitable metal. A
first circumferentially continuous surface or end face 106
of the ring faces associated shoulder 70 of end fitting
14. A second continuous surface 108 faces and abuts
counterbore end wall or step 78 of main body section
~2~2~2~
- 17 -
passageway 20 to positively establish a forwardrnost or
home position for the reinforcing ring. A third
continuous surface 110 faces generally toward the hall
member, but is dimensioned to be spaced therefrom in order
to prevent any abutment or interference therewith and to
inhibit distortion and displacement of the associated
primary seat ring 102 between the reinforcing ring third
surface 110 and the ball member. The outer circumference
or peripheral surface 112 of ring 100 is closely disposed
to the side wall of passageway 20. Outer surface 112 and
second surface 108 may alternately include a flange or
step configured and dimensioned to engage shoulder 78 to
further extend portions of support ring 100 axially inward
of passageway 20 where overall vaive dimensions may so
require. However, such an additional flange is deleted
from the embodiment shown to obviate additional machining
steps.
With continued reference to FIGIJRES 2 and 3, it
will be seen that primary seat member 102 also comprises
an annular or ring-like member having a central opening
118 which is smaller in size than the central opening of
the reinforcing ring 100. The primary seat member
preferably comprises a soft plastic seat ring and is
adapted for ~lexure generally toward and away frc,m the
reinforcing ring 100. Seat ring 102 is configured to
exert a spring-like mechanical elasticity against the ball
member. A first surface 120 generally faces the
associated shoulder 70 of end fitting 14. Seat ring
second surface lZ2 faces reinforcing ring 100 for bearing
engagement and support against reinforcing ring first
surface 106. Seat ring third surface or ball engaging
surface 124 generally faces ball member C for fluid
sealing engagement therewith. Flange or lip 126 extends
axially outward of seat ring first surface 120 at outer
~z~
- 18 -
peripheral surface 128. Lip 126 is preferably continuous
about the seat ring and located so its radial inner
surface generally corresponds to the outside diameter of
secondary seat member 104. Flange or lip 126 is further
beveled at the radial outermost area thereof and is
slightly rolled over the radial outer edges of the
secondary seat member in the manner shown. While not
necessary, this arrangement advantageously maintains the
primary seat and secondary seat members together as a
subassembly. Preferably, seat ring 102 is constructed
from a soft resilien~ plastic material such as Teflon,
polyethylene or the like. It should be readily
appreciated, however, that a wide range of other types of
material such as acetal resins and the like or even soft
metals and ceramic composites could also be advantageously
utilized. The particular material chosen will, to some
extent, be dependent upon the normal operating conditions
to which the valve will be subjected.
Included in primary seat ring 102 is a weir ring
130. Preferably, this ring is received in an annular
undercut or groove 132 of seat ring 102 isolated from the
valve fluid flow passageway. However, it is within the
scope of the invention that weir ring 134 could be
completely encased in seat ring 102 or, alternatively,
completely without the seat ring such as, for example, an
axially directed lip of the secondary seat member 104
extending towards the ball member at the inner diameter of
the primary seat ring 102. Preferab]y, though, weir ring
130 is generally disposed radially intermediate of seat
ring 102 between the associated secondary seat member 104
and ball member C. In this preferred location, the weir
ring 130 is isolated from exposure to the same hazards of
wear and damage that affect the soft primary seat member
102 in normal service. The weir ring is constructed of a
~Z~2~2~
- 19 -
thermally stable, non heat-flowing material, preferably a
Grafoil and wire mesh composite, similar to sealing rings
82,84; however, mere Grafoil itself, wire mesh, a ceramic
or even metal may be suitably employed.
Secondary sea-t member 104 comprises a subassembly
including a central frusto-conical disc spring 134
sandwiched between a ~irst annular facing sheet 136 facing
associated shoulder 70 and a second annular ~acing sl-cet
13~ facing primary seat member 102. Facing sheets 136,138
are preferably constructed of Grafoil and are generally
radially coextensive with disc spring 134; however, it is
within the scope of the invention that the facing sheets
136, 138 may extend only over a portion of the disc spring
as, for example9 where first facing sheet 136 may extend
only over a portion of the disc spring 134 near the outer
diameter of the disc spring, and second facing sheet 138
may extend over the portion near the inner diameter of the
spring 134. The latter embodiment may be particularly
economical and advantageous in large size ball valves.
It has further been found to be advantageous for
the facing 74 of support shoulder 70 to be knurled or
grooved for better gripping of disc spring facing sheet
136. Upon exposure of the valve to a fire, such improved
gripping inhibits slipping, flowing or extrusion of the
facing sheet and disc spring. It is possible at high
temperatures for Grafoil to become somewhat flowable. The
knurled or grooved facing inhibits such action and
facilitates the fluid tight seal.
The diameter at the outer end of the secondary
seat member 104 is such that the member may be received
within the cylindrical cavity defined by the inner wall of
the seat ring axial flange 126 and seat ring first surface
120. The inner diameter of the secondary seat member is
slightly larger than the diameter of the central opening
2~
- 20 -
118 of seat ring 102 to substantially isolate the
secondary seat member from normal service contact with the
ball member and system and associated wear and damage
hazards.
Disc spring 134 is selected so that its force is
sufficient under partial deflection to continuously urge
the seat ring 102 towards the ball. The spring must also
allow deflection thereof toward a flattened condition to
accommodate ball shifting and engagement with seat ring
third surface 124 during normal operating conditions.
With particular reference to FIGU~E 3, it may be seen that
a fluid-tight seal is effected by close containment of the
primary seat ring 102 between the ball member C, the
support ring 100, the valve main body 12, and the end
fitting shoulder 70. During normal operating conditions,
secondary seat member 104 primarily operates to bias and
contain the primary seat ring 102 without performing a
secondary sealing function.
With reference to FIGURES 1, 2 and 3, and at the
time of valve make-up, each of the seat assemblies B is
moved such that each primary seat ring 102 is slightly
rotatably flexed away from the other generally about its
outer periphery and against secondary seat member 104 in
response to engagement between the seat ring ball-engaging
surface 124 and ball member C. This action slightly
compresses the associa-ted disc spring 134 toward a
flattened condition. In addition to positioning the ball
member, this spring deflection assures a seal force
between the two seat rings and ball at ball-engaging
surface 124 regardless of how low the system pressure may
be. The secondary vent orifice or opening 17 in the ball
C faces the inlet when the valve is in a closed position
and assures that the inlet seat does not seal. Any fluid
in the center of the valve is- free to expand upon heating
~242426
or vaporizing, and relieve through the vent orifice 17
without increasing the pressure in the valve.
- Operation
With particular reference to FIGURES 4, 5, 6, 12
and 13, the operation of the above described preferred
embodiment will be specifically discussed upon destruction
of the primary seat by fire.
FIGURE 4 shows the soft plastic seat ring 102
being heated to a more fluid state and, in turn, flowing
or being extruded through the central opening 66 of the
secondary seat member 104 by fluid pressure forces in the
valve. Upon softening of the seat ring 102 the disc
spring 134 of the secondary seat member 104 deflects to
maintain a fluid tight seal against ball member C and
against end face 74 of shoulder 70.
With par-ticular reference to FIGURE 5, ball
member C has shifted axially downstream in valve A to
compress the secondary seat member 104 and to abut the
weir ring 130. Second facing sheet 138 which is
sandwiched between disc spring 134 and seat ring 102
contacts ball member C at its radially innermost portion
to effect a fluid-tight seal. Since second faci~g sheet
138 is preferably constructed of a heat-resistant,
deformable material such as Grafoil, the sheet will
conform to the engaging surface of the ball member C and
thereby avoid the problems of prior fire-safe ball valve
designs which incorporate metal-to-metal type secondary
seals. Similarly, first facing sheet 136 of secondary
seat member 104 engages support shoulder 70 at shoulder
end wall 74 at its radially outermost portion to effect a
fluid-tight seal. The deformable property of sheet 136
enables it ~o conform to the irregularities of surface 74
and the outermost radial edge of disc spring 134.
~z~z~
- 22 -
It is within the scope of the invention to
include a secondary seat member 104 without a first or
second facing sheet 136, 138 because it has been found
that the disc spring 134, due to its circumferential
elasticity, will form an appreciable metal-to-metal seal
with ball member C, thereby overcoming the problems
resulting from the ball member not being perfectly
spherical nor match-lapped with the secondary seat member.
The disc spring 134 of the secondary seat member
possesses a circumferential elasticity as well as an axial
elasticity and upon softening of the seat ring 102, the
secondary seat member deflects to maintain a fluid-tight
seal between the ball member C and the end face 74 of
shoulder 70. By circumferential elasticity is meant the
capability of the secondary seat member to deflect axially
in one segment more so than in another segment.
Since the ball member C is not perfectly
spherical and central opening 66 of disc spring 134 is not
perfectly round, the ball and spring will contact only at
a few high spots. The circumferential elasticity of disc
spring 134 enables it to deflect at those high spots such
that the ball makes essentially continuous contact against
the innermost radial edge of disc spring 134. Similarly,
the outermost radial edge of disc spring 134 contacts end
face 74 only at a few high spots. The circumferential
elasticity of disc spring 134 again enables it to deflect
by variable amounts around its perimeter and thereby
establish an essentially continuous line of contact
between the outermost radial edge of disc spring 134 and
end face 74 of shoulder 70. Thus, the circumferential
elasticity of the disc spring 134 compensates for
imperfections in roundness at the inner and outer radial
edges of disc spring 134, imperfections in sphericity of
ball member C, and deviations from flatness of end face 74
of shoulder 70.
Z~:6
- 23 -
The weir ring 130 acts as a "weir" or dam to
prevent excessive extrusion of the soEtening plastic seat
102 between the ball member C and the secondary seat
member 10~ into the valve port. As a practical matter, a
fire cannot always be expected to uniformly heat the
surface of a fire-safe valve, particularly where the fire
is a radiative fire near the valve and heats the closer
side of the valve, but not the opposite side. Thus, in
the course of a fire, it is reasonably foreseeable that
the plastic seat ring 102 will likely soften in only a
first portion on its circular perimeter prior to softening
in other areas. Without the weir ring 130, the first
portion may excessively extrude into the valve port under
system pressure allowing the ball member C to displace
radially or sideways perpendicular to the valve port
access. Consequently, as the ball member C moves
downstream through softening plastic to meet the secondary
seat member 104, the ball may shift too far to one side
and may contact the secondary seat member 104 unevenly,
leaving large gaps and leak paths where melting plastic
and system fluids can blow through. It has been observed
that such leak paths and gaps occur at positions generally
spaced ninety degrees from the vector of directicn of
radial shift. The point one hundred eighty degrees from
the vector of radial shift maintains a fluid seal by
contact with the remainder of the primary plastic seat
102. The rush of system fluids may then quench the
plastic seat 102 preventing further melting. A gross lea~
thus developed can remain a gross leak no matter how much
extra fire is applied to the fire-safe valve.
An additional mechanism of partial seat
destruction is illustrated in FIGURE 12. A seat assembly
which does not include a weir ring is shown which has been
exposed to a fire that has caused only a portion 141 to
- 24 -
extrude into the valve port. A large leak path 143 has
resulted due to the inability of the ball member to
contact the secondary seat member 104. The ball member C
is checked against any radial or axial shift into the
extruded portion by the substantially remaining portion of
the primary plastic seat ring 102. The quenching action
of the rushing leak quenches the primary plastic seat ring
against further destruction or extrusion in spite of
varying fire intensity.
However, with reference to FIGURE 5, weir ring
130 constrains the flow of soft and melting plastic no
matter where on the seat perimeter plastic softening first
occurs. Weir ring 130 is positioned in seat ring 102 such
that only a narrow annulus portion 144 may extrude into
the valve port. The substantial portion 146 of seat ring
102 is blocked from extruded flow by the weir ring 130.
The relatively small portion 144 which may extrude is of
lit-tle substance and upon its extrusion, the associated
displacement area into which the ball member C may then
shift is insufficient to allow formation of a leak path.
It is also preferable that weir ring 130 be placed in seat
ring 102 such that ball member C contacts the weir ring
130 simultaneously with contact of the secondary seat
member 10~l. Weir ring 130, thus, can further contribute
to effecting a secondary seal upon destruction of the
primary seat member 102~
With reference to FIGURE 6, the primary seat
member 102 has been completely destroyed such that the
substantial portion 146 ~FIGURE 5) of the soft plastic
seat ring has been sublimated or evaporated out through
the valve port. A fluid-tight seal remains between ball
member C and secondary seat member 104 as the ball member
remains in contact with the radially innermost portion of
the second facing sheet 138 which deforms in accordance
with the ball member surface. First facing sheet 136
similarly engages shoulder end wall 74 to maintain the
fluid seal between the secondary seat member 10~ and the
shoulder 70. In addition, it is advantageous that weir
ring 130 be sized to engage the ball member upon
destruction of the primary seat member and associated
downstream shifting of the ball. Such engagement
facilitates a further fluid seal.
With particular attention to FIGURE 13, along
lines 6-6 it may be seen that the ball has contacted the
weir ring 130 after destruction of the primary seat member
and has also contacted the secondary seat member to
maintain a fluid seal (FIGURE 6). Along lines 5-5, the
extrusion of the substantial portion of the primary seat
member is blocked by weir ring 130 to prevent the
formation of the leak path in FIGURE 12.
With particular reference to FIGURE 8, an
alternative embodiment of the present invention is shown.
For ease of illustration and appreciation of this
alternative, like components are identified by like
numeral~ with a primed (') suffix and new components are
identified by new numerals. Secondary seat member 104'
comprises a unitary disc member 150 of heat resistant,
deformable material such as Grafoil or a Grafoil and wire
mesh composite. Upon fire damage to the primary seat
member 102', ball member C' may shift axially downstream
in response to fluid pressure to engage the radially
innermost end portion of secondary seat member 104' to
effect a fluid-tight seal. Further, wall 74' which is
preferably knurled, engages end face 152 of the secondary
seat member to effect a fluid-tight seal between the
secondary seat member and support shoulder 70'. Secondary
seat member 104' may thereby conform to the engaging
surface of the ball C' and the wall 74'.
2~%6
- 26 -
Yet another alternative embodiment of the
invention is illustrated in FIGURE 9 where like components
are identified by like numerals with a double primed ('')
suffix. Secondary seat member 104'' comprises a disc
spring 134'' and a facing sheet 156 of heat resistant,
deformable material such as Grafoil or Grafoil and wire
mesh composite. Upon destruction of the primary seat
member 102'' in a fire, the ball member in a closed
position advances under system pressure against the
secondary seat member 104" and contorts the facing sheet
156 at its radially innermost portion to make a
fluid-tight seal. Fur~hermore, as the fire progresses,
disc spring 134'' anneals. The softening disc spring,
contorted by the ball under pressure, thereby more readily
conforms to the surface 74" of support shoulder 70" and
makes an improved metal-to-metal seal behind the spring.
Yet another embodiment of the inven-tion similar to this
embodiment would comprise use of a single facing sheet on
the disc spring surface facing the support shoulder. Such
a construction would involve a metal-to-metal secondary
seal to the ball and a facing sheet to shoulder seal. It
is preferable to employ a knurled shoulder to contact the
facing sheet.
FIGURE 10 shows another alternative embodiment of
the present invention where like components are identified
by like numerals with a triple primed ~''') suffix. This
embodiment of the invention includes a seat assembly
comprising support ring 100" ', a primary seat member or
seat ring 102'l', a secondary seat member 104" ' including
a disc spring 134" ', a first facing sheet 136' 1 1 and a
second facing sheet 138lll. Facing sheets 136l " ,138'''
are constructed of Grafoil or other heat resistant,
deformable material. A weir ring is not included. Upon
destruction of seat ring 102" ' in a fire, the ball member
~Z~ 26
- 27 -
will shift axially downstream and make a fluid seal at
second facing sheet 138' ". First facing sheet 136'''
engages knurled end wall 74''' of support shoulder 70'''
to maintain the seal.
~ inally, FIGURE 11 relates to still another
alternative embodiment of the present invention wherein
like components are again identified by like numerals with
a primed suffix. Secondary seat member 104" '' may
comprise a single disc spring, a single non heat-flowing
deformable disc constructed of material such as Grafoil or
a metal wire and Grafoil mesh composite, or a combination
of a disc spring and a Grafoil facing sheet similar to the
secondary seat member 104'' i~ strated in FIGURE 9. A
weir ring 130"'', preferably constructed of a Grafoil and
wire mesh composite, is included in primary seat member
102" " to contact the ball member upon partial or total
destruction of the primary seat member, and to block
extrusion of the substantial portion 146" " of the seat
ring 102~
Other modifications not speciically shown in the
drawings may be readily incorporated into seat ring
assemblies B without in any way departing from the overall
invention It may, for example, be desirable to slightly
modify the relative dimensional characteristics between
the primary seat members, reinforcing rings and secondary
seat members to accommodate particular operational
requirements.
The invention has been described with reference
to a preferred and several alternative embodiments.
Obviously, modifications and alterations will occur to
others upon a reading and understanding of this
specification. It is our intention to include all such
modifications and alterations insofar as they come within
the scope of the appended claims or the equivalents
thereof.
