Note: Descriptions are shown in the official language in which they were submitted.
1080tit~'~
1 I BACl;GROUND OF THE INVEN'rIO~
2 1. Pield of the Invention.
I
3 I The present invention relates to sealing mechanisms
4 land more particularly to seal rings adapted to serve as seat
5 ! rings in a valve.
6 12. Description of the Prior Art.
? ¦~ In U.S. Patent No. 3,642,248, issued to Robert E. Benware
8 lland owned by the assignee of the present invention, there is
g Idisclosed a valve sealing mechanism in the form of a shouldered
10 Iwear ring confined in an undercut circumferential groove. The
11 wear ring has a continuous central rib extending radially beyond
12 ithe shouldered portion through the opening in the groove, the
13 circumferential surface of the rib serving as a seating surface
14 ¦~in mating contact with a complementary valve member sealing
15 ~surface.
16 1 The wear ring in the Benware patent preferably is
17 'combined with an elastomeric 0-type backing rin~ positioned
18 Ibetween the bottom of the groove and the shouldered portion
~9 lof the wear ring. The backing ring serves the dual function of
20 ,urging the wear ring out of the groove into firm contact with
21 Ithe sealing surface and of sealing against leakage of fluid under
22 ~pressure behind the wear ring.
23 An important application of butterfly valves of the
24 general type described in U.S. Patent ~o. 3,642,248 is in systems
25 handling fluids at high pressure and temperature or flammable
26 fluids that present a substantial risk of fire and resultant
27 high temperatures. The patent recommends for such applications
28 that the wear ring be fabricated of fully work hardened stainless
29 s~eel and have a pair of outwardly flared side flanges extending
3o one from each side of the shouldered portion in a generally
lO~Uti8~1
1 radial direction op~osite to the central rib (c~lumn 10, line 30
2 Ithrough column 11, line 32).
3 The flare of the side flangec is designed to provide a
4 Ipreloaded lateral sealing force aaainst the sidewalls of the
~ Igroove. The inner circumference of the wear ring seating surface
6 lis designed to provide a preloaded radial sealing force between
7 Ithe wear ring seating surface and the sealing surface of the
B Ivalve member. By thus laterally and radially preloading the
9 stainless steel wear ring, positive sealing is provided both at
10 !the seating surface-sealing surface interface and at the lines
11 lof contact between the side flanges and the walls of the groove,
12 I!even if excessive temperatures should damage or destroy the
13 Ielastomeric backing ring.
14 ¦ Although the stainless steel wear ring is an effective
15 ¦"fire-safe" seal, the hard metal-to-metal contact yields a leakage
16 ! rate higher than that experienced with wear rings fabricated
17 ! from various plastic materials.
18 ~ A subsequent patent (U.S. Patent No. 3,986,699 issued
~9 Ito ~oseph A. Wucik, Jr., et al. and also assigned to the
20 lassignee of the present invention) describes a "fire-safe" seal
21 Ihaving a soft nonmetallic seal ring of the Benware type arranged
22 ¦in an undercut groove of revised design. The downstream lip
23 10f the groove in the Wucik et al. Patent No. 3,986,699 is in
24 the form of an annular thin-walled skirt having an inner
circumference adapted to make preloaded sealing contact with a
26 mating sealing surface of the valve member.
27 .Thus, the improved arrangement of the Wucik et al.
28 '699 patent provided a soft seating ring, for superior sealing
29 under ordinary temperature conditions. The soft seating ring was
3 then backed up by a hard metal-to-metal seal between the skirt-
'.' '
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1 like lip and the sealing surface of the valve m~mber.
2 ~¦ Although the Wucik et al. "fire-safe~ seal design is
3~leffective for its intended purpose, it has several practical
4 Idrawbacks. First of all, it can be usec only for installations
Iwhere pressure is exerted always from the same direction, since
6 Ithe backup skirt seal must be downstream of the soft nonmetallic
7 Iseal ring.
8 I Secondly, the sealing lip, as disclosed, forms one side
9 lof the groove in a seating region of a valve, such as a butterfly
10 Itrunnion valve. The dimensional tolerances of the lip are much
11 jcloser than are needed for the rest of the grocve elements, and
12 jconcentricity of the lip with the valve member is important.
13 ¦Consequently, more than usual care and expense is involved in
1 14 machining and assembling valves having this type of dual seal.
15 ¦ Increasingly stringent environmental requirements,
16 ,placed particularly upon petroleum drilling and proce~sing
17 Ifacilities, have resulted in a need for valves having the
18 Icapability to withstand very hiqh temperatures that may result
19 from a fire, for example, and still provide very high sealing
effectiveness after such a fire. The dual type of soft seal
21 and hard metal backup seal have not proved able to meet such
22 stringent requirements when installed in a wafer trunnion valve.
23 In fact, it'has been considered in the industry that only ball
24 valves would be capable of providing the required ~fire-safe"
operation.
26 For example, the Oil Companies Materials Association
27 (OCMA) has issued test specifications (OCMA Specification No.
28 FSV-l: Fire Safe Test For Soft Seat Ball Valves) for a ball
29 valve having a soft seat (e.g., a nonmetallic plastic or soft
3 metal seat) for a high degree of sealing effectiveness under
10~V~
l ~!normal conditions. After exposure to test t~mperatures that
2 Icompletely destroy the soft seat the valve must subseq~ently
3 !have a lea~age rate at full rated pressure of no m~re than lO
4 jmilliliters per minute per inch of valve diameter. In nG case
5 jshall the leakage rate after destruction of the soft seal be
6 ¦greater than lOO milliliters per minute.
7 I Another well-known oil industry specification of
B I similar stringency is EXXO~ BP 3-14-l. Up to the present time
9 ¦Ino standard productior.-line ball valve has been able to meet
lO lleither of these specifications, and wafer trunnion valves have
~ performed even less well.
12 I SU~RY OF THE INVENTION
13 It is an object of the present invention to provide
14 ¦an improved seal ring for use as a seat ring for valves in
15 lextended-temperature range service.
16 I Another object of the invention is to provide a metal
7 li seal ring adapted for "fire-safe" service and having improved
18 isealing characteristics under normal operating conditions.
l9 ~ Another object of the invention is to provide an
20 lextended-temperature range seal ring adapted for retrofi~ into
21 jconventional valves already installed in field service.
22 It is a further and important object of the invention
23 to provide a ~soft seat" type of seal ring that is adapted for
24 use in butterfly trunnion valves that will meet or exceed the
requirements of the Oil Companies Materials Association
26 Specification No. FSV-l and EXXON BP 3-14-l for fire safe service.
27 The foregoing and other objectives are achieved by the
28 improved seal ring of the present invention. This ring is of
2g the type having a hard metal body formed with a cylindrical
3~ shoulder portion, the shoulder portion being defined by a circum-
..
1080ti~
1 Iferential front surface, an opposed circumferential rear s~r'ace,
2 and tw~ ends. A pair of circ~mferential flances extend frGm the
3 ljrear surface of the shoulder portion at each of the res2ective
4 ljends, each flanQe having a circu~lferential edge spaced radially
5 Ifrom the rear surface of the should~r portion. A circumf~rential ¦
6llrib extends from the front face of the should~r portion inter-
7 ¦Imediate the ends, and terminates in a circumferential seating
gjlsurface, the width of the rib being less than the distance between !
9 jsaid ends of the shoulder portion.
lQ I The seai ring is adapted to fit within an undercut
11 Icircumferential groove in a seating region of a valve, such
12 jgroove having substantially parallel sides spaced apart by a
13 Idistance greater than the distance between the ends of the
14 jshoulder portion of the ring and an opening narrower than the
15 Idistance between the sides of such groove. The rib of the
16 ~seal ring is adapted to extend through such a groove opening for
slidable interference engagement of the rib seatina surface with
;a complementary sealing surface of such a valve.
19 ¦ The improvement of the present invention comprises a
20 Icircu~ferential groove formed in the seating surface of said rib,
21 Ithe groove having an opening narrower than the width of an
22 jinterior portion thereof, and a seat ring of material softer
23 Ithan the hard metal of the seal ring, the seat ring fitting tightl~
24 ¦against the sides and bottom of the groove in the rib and
25 ¦extending through the opening of the rib groove beyond the rib
26 jseating surface to provide a primary valve seat surface, said
27 ¦primary valve seat surface of said seat ring being adapted to pro-
28 ¦vide the only sealing engagement with such a complementary valve
29 ¦sealing surface unless the temperature inside such valve exceeds
3o ¦the destruction temperature of the seat ring material.
1080ti~i~
1 I The material of the seal ring is preferably work-
2 1l ~.ardened stainless steel, while the soft seal ring inserted in
3 jthe rib groove is preferably a resilient nonmetallic material
4 such as polytetrafiuoroethylene. For certain applications, the
seat ring may be a soft metal, however, such as lead or copper.
6 In one preferred embodiment of the invention, the rib
7 groove of the seal ring has a dovetail cross section, and the
8 jseat ring has a complementary solid trapezoidal cross section.
g IAn alternate embodiment of the seat ring has a V-shaped cross-
10 Isection, th~reby permitting the seat ring to be inserted in the
11 dovetail groove by compressing the arms of the V-section together.
12 iIn a third preferred embodiment, the rib groove and the seat
13 jring both have T-shaped cross sections. This embodiment provides
14 iincreased resistance against blow-out of the seat ring from the
~5 Igroove when the valve is opened under very high pressure condition~ .
16 ~ To permit use of a seat ring having a solid cross
17 isection, the invention also includes a method of fabricating the
18 Iseal ring which comprises forming a groove wider than necessary
~9 lin the face of a rib of a shouldered metal seal ring, the
20 Iremaining portions of the rib forming two side walls of the
21 Igroove with at least one of the side walls being undercut in
22 Irelation to the opening of the groove; inserting a relatively soft
23 Iseat ring into the groove, the seat ring having one side wall
24 Ithat conforms to the one side wall of the groove, a rear surface
25 Ithat conforms to the bottom of the groove, and a front surface
26 ¦which is narrower than the opening to the groove; and plastically
27 ¦deforming the other side wall of the groove into close-fitting
28 ¦contact with the other side of the seat ring to provide a fluid-
29 ¦tight seal between the seat ring and the side walls of the groove.
30 ¦ The foregoing and other objects, features and
I
__ _. I
lO~V~
1 advantages will become more apparent from the following detailed
2 description of the preferred embodiments and the accompanying
3 drawings.
4 BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of a conventional
6 butterfly trunnion valve suitable for incorporating the improved
7 seal mechanism of the present invention.
8 FIG. 2 is a partial cross section of a preferred embodi-
9 ment of the seal ring in combination with a conventional backing
ring in the valve of FIG. 1, with the valve disc open.
11 FIG. 3 is a partial section view similar to FIG. 2, but
12 with the valve disc closed.
13 FIG. 4 is a partial section view similar to FIG. 3, but
14 showing the seal ring after destruction of the soft seat ring
insert and the backing ring.
16 FIG. 5 ~s a partial perspective view in section of an
17 alternate embodiment of the seal ring at an intermediate stage
18 of assembly.
19 FIG. 5a is a partial perspective view in section,
similar to FIG. ~, showing the comPleted seal ring assembly.
21 FIG. 6 is a partial perspective view in section of
22 another alternate embodiment of the seal ring at an intermediate
23 stage of assembly.
24 FIG. 6a is a partial perspective view in section, ;
similar to FIG. 6, ~howing t~le completed seal ring assembly;:
26 FIG. 7 is a partial cross section of the alterna~e
27 preferred embodiment of FIG. 6a in combination with a conventional
28 backing ring in the valve of FIG. 1, ~ith the valve disc-shut.
29 DESC~IPTIO~ OF THE PREFERRED EMBODIMENTS
..
To aid in understanding the arrangement and operating
108068~
1 principle of the improved seal ring of the present invention, it
2 will be described in embodiments incorporated in an otherwise
3 conventional butterfly valve or trunnion valve. FIG. 1 shows
such a valve in exploded perspective.
The trunnion valve in FIG. 1 includes a valve body 1
6 in the form of a flat annular wafer having an internal passageway
7 2 with an inlet 3 and an outlet 4. The downstream or outlet
8 face 5 of the valve body is counterbored with an annular recess 6
9 for flush mounting a retainer ring 7 by means of flat head
10 machine screws 8. Retainer ring 7 serves to hold a sealing ring
11 or wear ring 9 and a backing ring 10 within a circumferential
groove 11 machined.in the downstream edge of passageway 2.
13 A valve disc 12 ~aving a circumferential sealing
14 surface 13 is adapted to be mounted within passageway 2 for
rotation about a diametral axis between an open position in
16 which the valve disc is substantially parallel to the axis of
17 passageway 2, and a shut position, in which the valve disc is
18 substantially perpendicular to the passageway axis, and sealing
19 surface 13 makes mating contact with the valve seat structure
that includes wear ring 9 and retainer ring 7.
21 - Means for pivotally mounting the valve disc in the
22 passageway for rotation between the open and shut positions
23 includes a valve stem 14, mounted in upper and lower bushings 15
24 and 16 for rotation within a hole 17 bored dia~etrally through
the valve body. Valve stem 14 passes through.a hole 18 drilled .
26 through a diametral boss 19 on the upstream fa~e of the valve
27 disc. The disc is locked to the stem by pins 20.
28 Leakage past the upper end of valve stem 14 is pre-
29 vented by conventional stem pac~ing means including spacer 21
;30 ¦and resilient pack$ng rings 22, which are compressed $n hole 17
I
~ ' 9
~ .. , . ... . ..
10~0~i8'~
I
1 ¦against the top of bushing 15 by forcing gland 23 and follower 24
2 ¦downward by means of nuts 25 screwed down on studs 26. Valve stem
3 ¦ 14 is rotated in its bushings by a handle or motor drive (not
4 ¦ shown) attached to the squared upper end 27 of the stem.
5 ¦ The structure, operation, and method of constructing
6 ¦ the improved seal ring of the present invention are shown in
7 ¦ FIGS. 2 - 7 and are described below.
8 ¦ FIG. 2 shows a section of the assembled seating
9 ¦ arrangement of the valve in FIG. 1, but incorporating one -
10 ¦embodiment of an extended-temperature range seal ring 28 of the
11 Ipresent invention. The basic form of the shouldered hard metal
12 ¦seal ring 28 and the arrangement of the seal ring and backing ring
13 ¦10 within groove 11, are as described in the previously mentioned
14 ¦Benware U.S. Patent No. 3,642,248. (See particularly FIGS. 14
15 ¦and 15 of the '248 patent). There are several important differ-
16 ¦ences in detail and function, however.
17 ¦ Seal ring 28 is formed with a cylindrical shoulder
18 ¦portion 29 defined by a circumferential front surface 30, an
19 ¦opposed rear surface 31, and ends 32,33. A pair of flanges 34
20 ¦and 35 extend from the rear surface of the seal ring at the
21 ¦respective ends 32 and 33. Flange 34 terminates in a circumfer-
22 ¦ential edge 36 spaced radially rearward from rear surface 31,
23 and flange 35 terminates similarly in a circumferential edge 37.
24 ¦ Groove 11, in which the seal ring is positioned, has
side walls 38, 39 and base or rear wail 40. The distance between
26 side walls 38 and 39 is slightly greater than the distance
27 between ends 32 and 33 of the shouldered portion of ring 28.
28 Flanges 34 and 35 flare outward, however, so that circumferential
29 edges 36 and 37 engage the side walls of groove 11 with an
3o interference fit.
_ .,. 10.
iO80~8~
1 The distance between side walls 38 and 39 is also
2 greater than the width of the opening of the groove, the
3 opening being formed between lips 41 and 42 which extend from the
4 respective side walls of the groove. A rib 43 extends from the
front face of the shoulder portion of ring 28 and terminates
6 in a circumferential seating surface 44. The width of the rib
7 is less than the distance between the ends of the shoulder
8 ¦ portion, such that a clearance is formed between the sides of the
9 ¦ rib and the groove opening.
10 ¦ A circumferential groove 45 (see FIG. 4) is formed
in the seating surface of the rib 43, the groove having an
12 ¦ opening narrower than the width of the groove at its base.
13 l Specifically, the cross section of the groove has a dovetail
14¦ shape. Within groove 45 is inserted a seat ring 46. Seat
15¦ ring 46 is made of a material softer-~han the metal of the seal
16 ¦ring, such material preferably being a resilient nonmetallic
17 ¦material such as polytetrafluoroethylene. The seat ring fits
18 ¦tightly within groove 45, the sides and ~ase of the seat ring
19 ¦conforming closely to the sides and base of the groove. The
20 ¦radial dimension of the seat ring is greater than the depth .
21 ¦of the groove so that the ring extends beyond the seating surface
22 ¦of rib 43 and terminates in a primary valve seat surface 47.
23 ¦ With reference next to FIG. 3 the seal ring arrangement
24 ¦is shown with the valve disc 12 in the closed positiDn. It
25 ¦will be noted from a comparison of FIG. 3 with FIG. 2 that
26 ¦sealing surface 48 of valve disc 12 engages primary ~alve seat
27 ¦surface 47 of the seat ring with an interference fit sufficient
28 to mcve the seal ring rearward towards the base of groove 11.
9 This interference fit provides a-radial preload such that sub-
3o stantially perfect sealing is obtained between the soft seat
1080ti8'~ ~
1 ring 46 and sealing surface 48. At the same time, backup ring
2 10 provides an equally good seal between the base of groove 11
3 and the rear surface of the shoulder portion of the seal ring.
The function of backup ring 10 in this regard is the same as the
function of the backup ring disclosed in the previously mentioned
6 Benware patent.
7 Turning next to FIG. 4, the sealing arrangement is
8 shown after the soft seat ring 46 and backup ring 10 have been
9 completely destroyed by excessively high temperatures. It will
be noted that now sealing engagement with sealing surface 48 and
11 the valve disc is made by seating surface 44 of the metal seal
12 ring. In particular, it should be noted that the seating surface
13 44 has a smaller cross-radius of curvature than that of the
14 sealing surface 48 on the valve disc. Thus contact is made
only by the two outside edges of seating surface 44. This small
16 area of contact results in high contact pressures and excellent
17 sealing. At the same time, the bypass path around the rear
18 of the seal ring ls closed by the preloaded circumferential
19 edges 36 and 37 bearing against the side walls of~groove 11.
In order to be able to insert nonmetallic seat ring
21 46 into dovetail groove 45, the seat ring shown in FIGS. 2 and 3
22 has a V-shaped cross section. This V shape permits the seat
23 ring to be compressed together to allow insertion through the
24 !narrow opening of the groove. The resilience of the seat ring
25 ¦material then expands the sides of the V into close contact with
26 ¦the sides of the groove.
27 ¦ Referring again to FIG. 4, it will be noted that there
28 ¦is a shallow groove or channel 49 formed in the rear surface 31
29 ¦of the $houlder portion of ring 28. This channel helps to center
3o backup ~ing 10 in groove 11, but its more Important function is
. ~
I ` ' '1~' ' ' -
. . .
1080~
1 ¦to produce a predetermined thickness of metal between the ba~e
2 of groove 45 and the bottom of channel 49 such that a desired
3 ¦springiness is achieved in preloading the flanges of the ring
against the side walls of groove 11. In the prior embodiment of
5 ¦the metal seal ring shown in U.S. Patent No. 3,642,248, such
6 springiness was achieved by making the cross section of the metal
7 ring substantially uniform. That is to say, the rear surface
8 ¦of the ring was extended up into the rib portion. In the improved
9 ring design of the present invention, the rib must be solid in
10 ¦order to provide room for forming groove 45.
11 In FIGS. 5 - Sa an alternate embodiment of the seal
12 ¦ring is shown which uses a seat ring having a solid trapezoidal
13 cross section. This provides a stronger seat ring cross section.
14 In order to permit insertion of this type of seat ring into the
15 ¦groove, the present invention provides a method of assembly
16 illustrated by these figures. As shown in FIG. 5 the groove in
17 the seating surface 44 of seal ring 28' has only one undercut
18 side wall 50. The other side wall 51 is formed at right angles
19 ¦with the base of the groove. This provides an opening to the
20 ¦groove large enough to permit insertion of seat ring 52. After
21 insertion of the seat ring, wall 53 of the rib is bent or crimped
22 against the corresponding side of seat ring 52 as shown in
23 FIG. 5a. This method of construction and assembly provides a
24 fluid-tight union between the soft seat ring 52 and the metal
ring 28'. It also permits insertion of the seat ring without
26 special tools, thereby providing a low cost method of assembling
27 the completed seal ring. -
28 ~he V-shaped and solid trapezoidal cross sections of
29 the ~eat rings provide two advantages. First, this shape locks
3 the seat ring ~nto the groove. Secondly, it provides a self-
., ., ., . .
; I 13.
____~ ~ ... .. ..
1080tjt~'~
1 ¦ acting sealing effect. Any fluid that may leak around to the
2 ¦ rear of the seat ring from the high pressure side, when the valve
3 ¦ disc is shut, will exert an outward force on the base of the
4 ¦ trapezoidal section. This force urges the downstream side of the
5 ¦ seat ring into closer sealing engagement with the contiguous
6¦ wall of the rib. It also amplifies the sealing pressure between
the face of the seat ring and the sealing surface of the valve
8 1 disc by the ratio of the back and front areas of the seat ring.
9¦ With reference next to FIGS. 6 and 6A, still another
10 ¦ embodiment of the invention has a seat ring 54 with a T-shaped
11¦ cross section, which fits in a mating T-shaped groove 55 in the
12 ¦ rib of a metal seal ring 56. The design of seal ring 56 is
13 ¦essentially the same as those of the previously described embodi-
14 ¦ments, except in the shape of the rib groove. Consequently,
15 ¦elements of seal ring 56 that are unchanged from similar elements
16 ¦of the preceding embodiments are identified with the same
17 ¦numerals and will not be described again.
18 ¦ The principal difference between the seal ring of
19 ¦FIGS. 6 and 6A and the previously described seal rings is in the
20 ¦shape of the groove and the manner of installing the seat in the
21 ¦rib groove. As shown in FIG. 6, undercut groove 55 is initially
22 ¦formed in the rib with the spacing between lips 57 and 58 at
23 ¦the mouth of the groove being sufficient to allow insertion of
24 ¦the shouldered portion of seat ring 54 into the groove.
25 ¦ After the seat ring has been snapped into the groove,
26 as shown in FIG. 6, one side wall 59 of the groove is plastically
27 deformed laterally from the dotted line position to the solid
~8 line position in FIG. 6A. This step can be accomplished by
29 rolling the side wall, while seal ring 56 is held in a lathe,
3o until the seat ring fits snugly against side wall 60, and there
.
10 ~0 fc;~ L~
1 is no gap between the rib portion of seat ring 54 and the edges
2 of lips 57 and 58. The result is close seal between the hard
3 metal seal ring and the softer seat ring.
4 The completed T-shaped seat ring embodiment of FIG. 6A
is shown installed in a valve in FIG. 7, comparable to the
6 installation of the dovetail seat ring embodiment shown in
7 FIG. 3. Just as in the arrangement of FIG. 3, the sealing sur-
8 face 48 of valve disc 12 engages only primary seating surface 61
9 of seat ring 54. Secondary seating surfaces 62 and 63 of the
hard metal seal ring 56 are held out of contact with the valve
11 disc under normal operating conditions.
12 The embodiment of FIGS. 6 - 7 is particularly adapted
13 to service with higher than usual operating pressures because the
14 lips of undercut groove 55 prQvide superior protection against
blowout of the seat ring when the valve is opened quickly, as
16 compared with the dovetail groove and seat ring of the previously
17 described embodiments. At the same time, the essentially right
18 angle turns at the shoulders of the seat ring provide increased
19 resistance to leakage between the seat ring and the seal ring at
high pressures.
21 As with the other embodiments, rubber backing ring 10
22 performs a primary sealing function against leakage between the
23 seal ring and the valve body, and outwardly biased seal ring
24 skirt edges 36 and 37 provide a secondary seal against the
respective side walls of groove 11 in the valve body.
26 Example:
27 A wafer trunnion valve of the type illustrated, having
28 a six-inch nominal inside diameter and rated for 150 pounds
29 pressure was tested in accordance with the previously mentioned
3o OCMA standards (published as OCMA Specification No. FSV-l: Fire
_.. - . .~_ , . . .
108068 :~
1 ¦Safe Test For Soft Seat Ball Valves). This Specification
2 ¦ requires that the valve be subjected to a test pressure equal to
3 ¦ its pressure rating, the test fluid being kerosene or diesel oil.
4 ¦ The valve must next be exposed to fire, ~ith the valve in the
5 ¦ open position, for a period of time sufficient to assure that the
6 ¦ soft seat and backup ring have completely decomposed or
7 1 disintegrated. The valve must then be operated a minimum of three
B ¦ times within five minutes of extinguishing the fire. Then the
9 valve shall be shut and tested at 15 psi and at full rated test
pressure in that order. The leakage rate must not be in excess of
11 10 milliliters per minute per inch of valve diameter.
12 A six-inch valve equipped with a seal according to
13 the present invention was subjected to this test. The measured
14 leakage rates at 15 psi and at 300 psi rated test pressure after
completion of the fire test was essentially zero. Upon subsequent
16 disassembly of the valve it was determined that both the soft
17 seat ring and the backup ring had completely disintegrated.
18 A subsequent test with an 18-inch valve yielded
19 equivalent results.
In view of the previous experience of relatively high
21 leakage rates encountered with metal seal rings, as described
22 in the introductory portion of the Specification, the perfect
23 performance of the "soft seat" metal seal rings of the presènt
24 ¦ invention was completely unexpected. To the knowledge of the
inventors, no other unmodified standard production butterfly
26 ¦trunnion valve has been able to meet the OCMA Specification.
27 ¦Certainly, no other resilient seated valve has so far exceeded
28 ¦the specifi~ation that no measurable leakage has been detected.
29 ¦ It is believed that the superior performance of the
3o ¦seal ring of the present invention results from the fact that
ll
1080~
1 the "soft" primary seating surface of the nonmetallic seat ring
2 ¦takes all the wear during the normal operating life of the valve.
¦The metal seating surface of the shouldered ring is thus pro-
4 tected from wear and abrasion, thereby allowing it to provide
a perfect seal in the emergency operating situation following a
6 fire. The combined primary soft seat/backup hard seat of this
7 improved seal ring thus provides far superior results to the all
8 soft, all hard, or tandem soft and hard seat arrangements of the
9 prior art.
As mentioned earlier, the material of the soft seat is
11 preferably a nonmetallic plastic, such as polytetrafluoroethylene,
12 for most applications. In some cases the soft seat may itself be
13 metallic, but of a metal such as lead or copper which is much
17 jsofter n the hardened metal of the seal ring.
18
22ol
22
23
224
26
27
28
29
