CA1172667A - High pressure seal for temperature cycled applications - Google Patents
High pressure seal for temperature cycled applicationsInfo
- Publication number
- CA1172667A CA1172667A CA000408465A CA408465A CA1172667A CA 1172667 A CA1172667 A CA 1172667A CA 000408465 A CA000408465 A CA 000408465A CA 408465 A CA408465 A CA 408465A CA 1172667 A CA1172667 A CA 1172667A
- Authority
- CA
- Canada
- Prior art keywords
- stem
- ring
- rings
- gaskets
- stuffing box
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
- F16K41/00—Spindle sealings
- F16K41/02—Spindle sealings with stuffing-box ; Sealing rings
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16J—PISTONS; CYLINDERS; SEALINGS
- F16J15/00—Sealings
- F16J15/16—Sealings between relatively-moving surfaces
- F16J15/18—Sealings between relatively-moving surfaces with stuffing-boxes for elastic or plastic packings
- F16J15/182—Sealings between relatively-moving surfaces with stuffing-boxes for elastic or plastic packings with lubricating, cooling or draining means
- F16J15/183—Sealings between relatively-moving surfaces with stuffing-boxes for elastic or plastic packings with lubricating, cooling or draining means using a lantern ring
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Details Of Valves (AREA)
- Sealing Devices (AREA)
- Sealing With Elastic Sealing Lips (AREA)
- Gasket Seals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Combined metal-to-metal/compliant material stem sealing means for high pressure, balanced, rising stem gate valve includes at least one seal set at each of the actuator and bal-ance stems. Each seal set comprises a pair of frustoconical metal ring gaskets between which are disposed two make-up rings of complaint, tough material of high lubricity, e.g. tetra-fluoroethylene polymer. One make-up ring is adjacent to one gasket, and the other make up ring is adjacent to the other gasket. A core ring of material that expands substantially less volumetrically upon heating than the make-up rings, e.g. com-pacted graphite, is disposed between the make-up rings. Around the inner periphery of the core ring adjacent the respective actuator or balance stem is disposed a bearing ring of material like that used for the make-up rings, e.g. tetrafluoroethylene polymer. The seal set is compressed by a packing retainer such that the metal gaskets are coined into metal-to-metal sealing engagement with the stems and adjacent valve body parts. The sandwich stack, consisting of the core ring and bearing ring disposed between the make-up rings, is deformed to conform to the shape of, and fills substantially all of the space between, the compressed metal ring gaskets. The volume of the core ring is approximately one-third of the total volume of the sandwich stack.
Combined metal-to-metal/compliant material stem sealing means for high pressure, balanced, rising stem gate valve includes at least one seal set at each of the actuator and bal-ance stems. Each seal set comprises a pair of frustoconical metal ring gaskets between which are disposed two make-up rings of complaint, tough material of high lubricity, e.g. tetra-fluoroethylene polymer. One make-up ring is adjacent to one gasket, and the other make up ring is adjacent to the other gasket. A core ring of material that expands substantially less volumetrically upon heating than the make-up rings, e.g. com-pacted graphite, is disposed between the make-up rings. Around the inner periphery of the core ring adjacent the respective actuator or balance stem is disposed a bearing ring of material like that used for the make-up rings, e.g. tetrafluoroethylene polymer. The seal set is compressed by a packing retainer such that the metal gaskets are coined into metal-to-metal sealing engagement with the stems and adjacent valve body parts. The sandwich stack, consisting of the core ring and bearing ring disposed between the make-up rings, is deformed to conform to the shape of, and fills substantially all of the space between, the compressed metal ring gaskets. The volume of the core ring is approximately one-third of the total volume of the sandwich stack.
Description
1 ~72~67 The valve in which the stem sealing means of the present invention is used is of the high pressure, high temperature, balanced rising stem gate valve type similar to those disclosed in our Canadian Patents Nos. 1,113,914, issued December 8, 1981 and 1,125,261, issued June 8, 1982.
The stem ~ealing means of the present inven-tion is related to the stem sealing means disclosed in the above identified Patent No. 1,125,261.
B~CKGROUND OF THE INVENTION
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In th.e oïl and gas industry, wells are being drilled with increasingly higher downhole temperatures and pressures, some-times in "sour" gas fields where the well fluids contain relatively high percentages of H2S. Seals for oilfield valves and wellheads have been developed recently which are relatively resistant to deterioration from the combined effects of higher pressure and temperature, and from caustic well fluids such as H S
The stem ~ealing means of the present inven-tion is related to the stem sealing means disclosed in the above identified Patent No. 1,125,261.
B~CKGROUND OF THE INVENTION
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In th.e oïl and gas industry, wells are being drilled with increasingly higher downhole temperatures and pressures, some-times in "sour" gas fields where the well fluids contain relatively high percentages of H2S. Seals for oilfield valves and wellheads have been developed recently which are relatively resistant to deterioration from the combined effects of higher pressure and temperature, and from caustic well fluids such as H S
2 -In United States Patent No. 4,056,272, issued Movember 1, 1977 to Morrill, and assigned to the owner of the present application, there is disclosed a static seal between a well-head and a pipe hanger supported therein, the seal comprising a pair of frusto-conical elastic metal ring gaskets of sub-stantially rectangular cross section, which are flattened by a lockscrew and compression ring and stressed until the edges of the metal ring gaskets flow plastically or "coin" into metal-to-metal sealing engagement with the parallel cylindrical walls of the wellhead and pipe hanger. In this static seal, a deformable ring having an initial generally trape~oidal cross `~ section and made of, for example, Teflon~ polyurethane or 30 rubber, is disposed between the metal ring gaskets and com-pressed upon flattening of the metal ring gaskets into a ~ ~7`~J~
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rectangular cross section configuration and into engagement with the walls of the wellhead and pipe hanger. The deformable ring in this static seal acts as a backup seal for the metal ring gaskets in case of less than perfect sealing by the metal ring gaskets, for example, due to scratches or machine marks in the wellhead or on the pipe hanger. The deformable ring will flow into and seal any of such scratches or machine marks.
One seal used for dynamic as well as static sealing between the stem af a valve and the valve body or bonnet employs frusto-conical elastic metal ring gaskets of rectangular cross section disposed in a stuffing box around the stem, with sandwich rings of a more compliant material disposed between the elastic metal ring gaskets. The reasons for the metal ring gaskets being eLastic, similar to ~elleville springs although not made of spring steel but a softer material, include (1) the gaskets have a larger inner diameter and a smaller outer diameter when unstressed, so that the seal unit can be easily inserted and withdrawn from the stuffing box without undue frictional engagement with the valve stem or stuffing box;
(2) the gaskets will maintain their stressed engagement with the stem and stuffing box during use of the valve despite slight changes in the valve dimensions due to, for example, temperature and pressure variations, which would change slightly the deformation or strain on the gaskets created initially by tightening of the packing retainer. In other words, the gaskets must be elastic in order to maintain their preload.
~he above referred to valve stem seal is disclosed in the aforementioned Patent No. 1,125,261 and in an ASME paper ! 1 726~ ~
entitled "Seals for Valve Stems and Wellheads in High Pressure - F~igh Temperature Service," by C. D. Morrill and C. W. Meyer, prepared for presentation at a conference in Mexico City, Mexico, on September 19~24, 1976. The seal as disclosed therein ïs compressed by a threaded packing retainer such that the metal ring gaskets are flattened, and their inner and outer peripheral edges are deformed or "coined" into metal-to-metal sealing engagement with both the outer surface of the valve stem and the ~Jalls of the stuffing box. The sandwich rings ~etween the metal ring gaskets are also deformed upon compression of the seal to conform to the shapes of the metal ring gaskets and to engage the stem and stuffing box.
The sandwich rings should therefore be elastic to some degree.
The initial deformation will usually cause the sandwich rings to take on an initial permanent set, but they will remain elastic to some degree. Materials used for the sandwich rings in such seals have included fluoroplastics, e.g. tetra-fluoroethylene polymer, and graphite materials. Such materials have also included tetrafluoroethylene polymer filled with up to about 15% molybdenum disulfide.
The sandwich rings of the valve stem seal just described are dynamic seals, acting primarily during stem motion to seal between the metal ring gaskets and the stem when the metal ring gaskets are disturbed by stem drag while the stem is in ; motion. Such sandwich rings also tend to lubricate the areas of contact between the stem and metal ring gaskets by rubbing off onto the stem to ~: -3-! 172667 .
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some degree to reduce friction between the stem and the metal ring gaskets. The sandwich rings are also lubricious so as to reduce friction between the stem and the sandwich rings, and ~etween the sandwich rings and the metal ring gaskets. The sandwich rings further act as backup seals for the metal ring gasXets, l~ke the deformable ring backup seals as described above for the wellhead-pipe hanger s~al of U.S. patent no. 4,056,272, to flow into and seal any scratches or machine marks on the stem.
The invention herein disclosed is an improvement over the valve stem seal described above.
One embodiment of the stem seal descrihed above includes three metal ring gaskets and two sandwich rings disposed therebe~
tween, and is known as an "SMT" type seal. The SMT type seal has been found to provide satisfactory stem sealing for valves having working pressures up to about 25,000 p.s.i., at temperatures from -20~F. to 300~F.
For valves having working pressures up to 30,000 p.s.i. or greateE, however, the SMT type seal will not always provide a satisfactory seal or the valve stems undèr conditiGns expected to be encountered during service. Graphite materials alone, for example, are not desirable for SMT type stem seals for valves in the 30,000 p.s.i. class because such materials tend to extrude past the metal ring gaskets upon flattening the gaskets to ener-gize the seal, since the graphite begins to extrude before the gaskets become flattened sufficiently to form a seal with the valve stem and stuffing box. Moreover, graphite materials tend to be worn or eroded away by movement of the valve stem as the graphite is deposited onto the stem and carried by the stem past the gaskets and out of the stuffing box. Such extrusion and wearing away of the graphite material under 30,000 p.s.i. service conditions may lead to leakage of well fluids past the seal and the need to replace the graphite ring.
i 1 7~667 .
Likewise, tetrafluoroethylene polymer ("TFE") materials alone, or such materials including MoS2 as an additive, are not suitable for SMT type stem seals for valves in the 30,G00 p.s.i.
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class because such materials are not capable of always maintain-- ~ng a tight seal against such pressures after the valve is put -- through temperature cycling. A valve in oilfield;service through wh~ch high pressure well fluids are 1Owing from deep wells may be heated by the well fluids to a tempeFature of about 300F.
When the well fluids stop flowing through the valve, for example if the well is shut in, the valve may cool down to ambient tempe-rature, for example 70F., and if the well is reopened and the well fluids begin flowing again, the valve wlll heat back up to 300F. Thus, the valve's temperature is cycled between about io~F. and about 300F. A valve stem seal must be capable of remaining tight at all times, at all temperatures and through all temperature cycles to which the valve will be subjected in ser-,~ vice. An SMT type seal usiny TFE rings, or MoS2-filled TFE
rings, will seal against well fluids at pressures of about 30,000 p.s.i. at ambient temperatures, e.g. 70~F., and again at elevated temperatures, e.g. 300F., but when the valve is put through a thermal cycle from ambient temperature to 300F. and back to ambient temperature, the SMT type seal will not always remain tight; sometimes the seal will exhibit minor leakage, either during valve stem movement or when the valve stem is stationary, or both. Although the leakage can be stopped by further tighten-ing of the packing retainer, leakage will reoccur upon further -temperature cycling.
It is an object of this invention to overcome the problems described above by providing a reliable valve stem seal suitable for valves havin~ working pressures of the order of 30,000 p.s.i.
or more and subject to temperature cycling, between temperatures in the range of -20F. to 300F. It is another object of this _nven~ion to provide such a seal that will remain tig~t and will ! 1~266~
not leak when subjected to well fluids having pressures of 30,000 p.s.i. or more and when the temperature of the valve is cycled from ambient temperature to about 300F. and back to ambient temperature, without the need to retighten the packing retainer. It is also an object of this invention to provide such a seal that is simple, compact and economical, and easy to manufacture, install and service. It is also an object of this invention to provide such a seal that is low friction, durable and relatively resistant to deterioration due to fluctuations and extremes in temperature, high pressure and chemical activity of the well fluids sealed against.
SUMMARY OF THE INVENTION
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According to the invention, there is provided apparatus for sealing in high pressure, temperature cycled applications hetween the walls of an axially movable valve stem and a stuffing box around the valve stem, the stuffing box having a port in its bottom and the valve s-tem extending : through the port and out of the stuffing box, comprising:
, : first and second elastic metal ring gaskets disposed in such stuffing box around such valve stem, and annular compliant seal means dispos.ed in such stuffing box around such valve stem and sandwiched between said gaskets, said seal means including first and second annular portions of tough, compliant material adjacent said first and second gaskets~ respectively, and an annular core portion disposed between said first and second por-tions and composed of a material having a lower coefficient of thermal expansion than said material of said first and second annular portions.
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BR:[EF DESCRIP~ION OF T~IE DRA~INGS
For a detailed description of a pre:~erred embodiment of the invention, reference will now ~e made to the accompany-ing drawings wherein:
" FIGURE 1 is a vertical section through a valve embodying the invention; and FIGURES 2A and 2B are fragmentary sectional views taken in the same plane as Figure 1 ~ut to a larger scale~ and showing one embodiment of the actuator stem sealing means of the present invention in which the frustoconical metal ring gaskets point away from the pressure ~eing sealed against inside the valve. Figure 2B illustrates the stem sealing means of the present , ~ ,~
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invention as installed in the valve but prior to its being ener-gized by tightening the packing retainer. Figure 2A illustrates the stem sealing means as energized.
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D~TAILED DESCRIP~ION OF PREFERRED EM30DIMENT
Referring to Figure 1, there is shown a valve including a hollow body having a chamber part 21 and a bonnet part 23 secured .hereto by studs 25 and nuts 27. The bonnet part 23 is sealed to the chamber part 21 by a suitable pressure energized gasket 29.
Seats 31, 33 mounted at the inner ends of passages 35, 37 cooper-ate with a pair of ported gates 39, 41 whicX control flow of fluid, e.g. water, oil or gas, through the valve. Sealant material is stored in reservoirs 43, 45, and sealant is supplied automatic-ally through the sealant distribution passages 47, 49 to the interfaces between the gates and seats and between the seat necks and valve body to effect sealing at such interfaces;
Gates 39, 41 are reciprocated by a generally cylindrical actuating~stem Sl between a closed position, shown in Figure 1, where flow of fluids through passages 35, 37 is prevented, and an open position permitting such flow in which gate ports 53, 55 are in register with ports 57, 59 in seats 31, 33. The upper end of actuating stem 51 extends out of valve chamber part 2l and through port 61 in bonnet 23. Seal means 63 according to the invention seals between stem 51 and a generally cylindrical stuffing box 65 in bonnet 23. Seal mean 63 is compressed in stuffing box 65 by a packing retainer 67 which is screwed into internally threaded neck 69 on the top of bonnet 23. A bleeder port 71 is used to checX for leakage of fluids from between stem 51 and port 61 after backseating the stem.
The exterior of bonnet neck 69 is also threaded and receives 2 bearing cap 73 screwed thereon. An actuator nut 75 is screwed onto the threaded upper portion 77 of actuator stem 51 and has a -iange 79 thereon disposed between upper and lower axial thr~st ~ 1 72667 bearings 81, 83. The lower thrust bearing 83 engages the top of a washer 85 disposed on top of packing retainer 67. The upper thrust bearing 81 engages the upper inside end of bearing cap 73.
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A hand wheel 87 includes a,noncircular aperture 89 fitted over a -`~orrelativel-y shaped porti'on'91 of actuator nut 75. ~and wheel ~ -87 is he'ld in place by a retainer nut 93 screwed onto t~e upper en~ of actuator nut 75. A bleed port 9~ allows fluid to escape '' from between threaded portion 77 of s*e~ 51 and actuat~r nut 7~.
A generally cylindrical balance stem 97 is connected to the lower ends o~ the gates and extends out of the valve chamber through port 99. Seal means 101 according to the ,i,nvention seals ; between balance stem 97 and a generally cylindrical stufing box 103 in the valve body. Seal means 101 is compressed in stuffing box 103 by lower packing retainer 105 which is screwed into a threaded socket 107 coaxial with port 99 and stuffing box 103. A
bleeder port 109 is used to check for leakage of fluids from . between balance stem 97 and port 99 when the enlarged portion on the upper end of the balance stem is fully seated in the annular seat in the valve body around port 99. A lower cap 111 is secured to the valve body over lower packing retainer 105 and the lower end of balance stem 97, by screws 113.
When hand wheel 87 is turned, actuator nut 75 turns and causes actuator stem 51 to raise or lower gates 39, 41 to which the stem is connected by hub 115. This in turn causes balance stem 97, connected to the gates by hub 117, to move up or down.
~hus, there is relative axial motion between each o stems 51, 97 -and the respective stem seal means 63, 101. Seal means 63, 101 must remain tight before, during and after such relative axial motion.
Seal means 63, 101 are alike, so only one need be described in further detail. Referring to Figures 2A and 2B, seal means 63 includes an upper seal set 119 and a lower seal set 121. A base adap.er rlng 123 is disposed in the botto~ o ~nnular stuffing ~ 172~67 -box 65 below lower seal set 121. The bottom of base adapter ring 123 engages flush with and is correlative to the bottom of the stuffing box. A follower adapter ring 125 is disposed between --~he lower face 127 of packing retainer 67 and upper seal set 119.
- -~ ~e upper end of follower--adapter ring I25 engages flush with and . ._ ----is correlative to lower face 127 of packing retainer 67. An .= .
intermediate adapter ring 129 i5 disposed between seal sets 119, 121. The upper face of base adapter ring 123, the lower face of follower adapter ring 125, and both upper and lower faces of in-termediate adapter ring 129 are frustoconical in configuration, having the desired cone angles for the shapes of the seal sets 119, 121 in their final assembled positions. In this regard, it should be noted that Figure 2B-illustrates the seal means of the present invention as installed in the valve but prior to its being energized by tightening the packing retainer; Figure 2A
illustrates the seal means 2S energized, with the packing re-tainer screwed farther into its threaded receptacle and the seal sets a~d adapter rings in their final assembled positions.- As is explained in more detail hereinafter, the metal ring gaskets of the seal sets are more sharply conical, that is, they have smaller cone angles, in their relaxed states shown in Eigure 2B than in their final energized states shown in Figure 2A. If desired, either or both of adapter rings 123, 125 may be omitted, the bottom of the stuffing box and/or the lower end of retainer 67 being provided instead with a frustoconical surface of the de-sired cone angle and area. If used, adapter rings 123, 125, and adapter ring 129, should be made of fairly hard material such as, for example, 4140 steel. The valve body and bonnet need only be made of any steel conventionally used for high pressure valves.
Seal sets 119, 121~are alike, so only one need be àescribed in further detail. Seal set 119 includes a pair of frustoconical metal ring gaskets 131 between which are disposed two identical make-up rings 133. Make-up rings 133 are made of tough, compliant, .
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- . ~ 1 7 2 ~ ~
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soiid lubricious material having a lower elastic modulus than metal ring gaskets 131. One make-up ring is disposed adjacent to one of the metal ring gaskets, and the other make-up ring is .. . .
disposed adjacent to the other of the metal ring gaskets.
- ~ ~ A core-ring 135 is disposed between make-up rings 133 Core ~~ ring 135 has a lower coefficient of volumetric thermal expansion th'an make-up rings 133. The inside diameter of core ring 135 is ' greater ~han the inside diameter of make-up rings 133. Around the inner periphery of core ring 135, between it and valve actuat-ing stem 51,- is disposed a bearing ring 137 of tough, compliant, solid lubricious material which may be of the same. type'used for make-up rings 133. Bearing ring 137 makes a sliding fit within the aperture in core ring 135.
The metal ring gaskets 131 in their relaxed state have a generally rectangular cross-section which lies at about a 30 angle to the horizontal.~ Thus, the cone angle for the gaskets 131 in relaxed condition is about 120. Gaskets 131 in such relaxed` condi'tion have a radial clearance with both stem 51 and stuffing box 65 so that neither the stem nor the stuffing box ' will be damaged upon installing gaskets 131 in the valve. Gas-kets 131 are just dropped into place. Upon ener~izing the seal means by tightening the packing retainer, the gasket-s are flat-tened such that the inner diameter of each gasket is reduced and the outer diameter of each gasket is increased sufficiently that the inner peripheral edge on the concave side of each gasket and the outer peripheral edge on the convex side of each gasket are -deformed or "coined," i.e. they flow plastically, into metal-tc-metal sealing engagement with the stem and stufing box, respec-tively. In order not to gall or mar the stems, the metal ring gaskets should be made of softer metal than the valve stems. The valve stems may be made of K Monel, for example, but a comparable steel would be suitable. It is preferred that the stem have a hard coating on it, such as a tungsten carbide coating of 3 to 5 ! 172667 .
mils thickness, to increase the hardness of and enhance the durability of the stem. Such a coating would raise the hardness of the stem from about 30 to about 60 Rockwell hardness. The metal ring gaskets should have sufficient plasticity to 2110w o~ning of the peripheral edges through high stress to effect the -metal-to-metal seal, and should have sufficient strength to wlthstand the high preload and well fluid pressures found in service. They may be made, for exam~le, of annealed (austenitic) stainless steel, such as No. 316 stainless steel, or of other metals such-as carbon or alloy steel. To urther reduce the possibility of galling or marring the stems, the inner peripheral edge on the concave side of each gasket is rounded, preferably with a radius e~ual to about one-half the gasket thickness, e.g.
a radius of 0.02 inches for a gasket that is 0.04 inches thick.
In flattened condition, the metal ring gaskets 131 make an angle of approximately 15~ to the horizontal, corresponding to a cone angle of about 150~, conforming to the ~rustoconical faces of adapter rings 123, 125 and 129 which are also disposed at an angle of about 15 to the horizontal. It will be understood, of course, that while the metal ring gaskets are preferably frusto-conical, shapes for the metal ring gaskets other than frusto-conical may be employed.
The material used for make-up rings 133 and the bearing ring 137 should have a low coefficient of friction, that is, it should be a highly lu~riciou~ material. The material for make-up rings 133 and bearing ring 137 should also have sufficient strength and toughness to remain integral under high pressure, and should be resistant to chemical activity of the fluid being controlled by the valve, and should be able to withstand temperatures through-out the range expected to be encountered during service, e.g.
300~F. down to -20~F. Such material should also be sufficiently compliant or elastic to flow into any minute gaps which may be left between the metal ring gaskets and the s~em and stuf f ing DOX
! 1 7 2 6 6 7 due to scratches or machine marks on the stem or stuffing box, or between the metal ring gaskets and the newly adjacent stem sur-ace during and after movement of the stem. Gaps of the latter type might occur, for example, because during and after movement ~f-the stem, the inner pe'ripheries of the metal ring gaskets will not~instantaneously, and perhaps might not ever, 1OW further pl-astically to conform to the newly adjacent stem surface. The make-up and bearing ring materials wi11 flow into and seal any of these minute gaps. Therefore the make-up and bearing rings may also be considered to be sealing rings. Materials suitable for the make-up rings 133 and bearing ring 137 include! for example, tetrafluoroethylene polymer, such as that sold under the trade-mark "Teflon," and "Moly-Teflon," which is like Teflon but in-ciudes up to about 15 percent molybdenum disulfide, MoS2. A
particular material found to be suitable is one having 5% by weight MoS2 and 95% by weight TFE, and sold by Allied Chemical Company under the designation'"No. 2021."
Th-e'material used for core ring 135 should, lîke the m'ate-.
rial used for rings 133, 137, have sufficient strength to with-s~and the high stress re~uired for preloading the seal, and should also be resistant to chemical activity o the well fluids being sealed against and able to withstand temperatures through-out the range expected to be encountered during service, e.g.
300F. down to as low as -75F.
Further properties of the core ring 135 may be best'appreci-ated from applicants' discovery of what they believe to be the cause of the leakage of the SMT type seal at high pressures upon extreme temperature cycling, although it is to be understood that the herein described seal solves the leakage problem regardless of the theory of its operation.
The leakage exhibited by the SMT type stem seal using TFE or ~oS2-filled TFE rings at pressures in the 30,000 p~s.i. range af.er temperature cycling apparently results from partial loss of the preload on the seal. Compare the loss of preload in pure ~ 172~67 .
elastomer packings disclosed in the ASME article referred to above. When the SMT type seal is first made up or energized, mechanical compression is placed upon the seal through tightening ...
the packing retainer such that the seal is stressed to a greater -~ ~egree than it would be''stressed by the high pressure well fluids.
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When a v'alve including the SMT type stem seal-hea~s up from - -~ambient temperature to 300F., the TFE rings try to expand, but cannot do so to any great extent, ince they are substantially confined on all sides by metals which expand less rapidly .han the TFE rings. This causes the preload stress on the seal to increase from what it was originally, that is, bef.ore heating.
When the valve cools down to ambient temperature, the preload stress not only diminishes from its elevated level attained when the valve was heated, it becomes lower than it was originally.
This is apparently due to one or the ot'her, or perhaps both, of the following effects. When the valve is heated to about 300F., the elevated stressj over and above the already high preload stress', on-the seal and surrounding metal containment structure caused by thermal expansion of the TFE rings might cause slight permanent deformation or set, that is, yielding, of such surround-ing metal containment structure so as to increase the volume occupied by the seal when the seal cools back down to ambient temperature, thereby reducing the stress on the seal belo~ its preload. Alternatively, or perhaps cumulatively, when the TFE
rings are stressed at the elevated level due to thermal expansion upon heating the valve to 300~F., the TFE rings could undergo a permanent deformation beyond that caused by the preload stress, that is, they might take on a further compressive set, which remains after the valve cools down to ambient temperature and results in a stress relief in the TFE rings which offsets somewhat the effect of the packing retainer's compressing of the seal.
Thus, after temperature cyclin~, in order to regain the proper preload, the packing retainer would have to be retightened.
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Without such retightening, the valve would be unable to seal against pressures of the order of 30,000 p.s.i. without slight leakage.
According to the present invention, some of the preferred TFE-or MoS2-filled TFE material between the metal ring gaskets of the SMT type stem seal is replaced by a'mate'ria~ wh'ich exhibits relatively little expansion when heated as compared to the TFE or MoS2-filled TFE material. I~ the preferred embodiment of this invention, this low thermal expansion material lS comprised in core- ring 135, which is clad on its three sides adjacent the metal ring gaskets and stem by ~ake-up rings 133 and bearing ring 137. Thus, core ring 13S must have a coeficient of volumetric thermal expansion that is lower than that for rings 133, 137.
One such material suitable for core ring 135 is compacted graphite, such as lS sold under the trademark "Grafoil.'i See U.S. patent no. 3,404,061. It is believed that the coefficient of volumetric thermal expansion for TFE, for example, is substantially greater _;f ' ~ than that for Grafoil, indeed several times greater', although precise values are not known to applicants. Published data ' ~ ' indicate, however, that Grafoil, which is manufactured in such :, forms as thin flexible layered sheets or ribbon, has a coeffic-ient of linear expansion of about -0.02 x lQ S in/inF. in direc-tions parallel to the graphite layers, that is, along their length and width, over the range of 70~F. to 2,000F., and of about 1.5 x 10 5 in/in~F. in directions normal to the layers, that is, through their thickness, over the range of 70F. to a~ooo~F~ TFE has a coefficient of linear expansion of about 7.0 - 10.0 x 10 in/in~F. over the range of 78F. to 500~F. For solids, the coefficient of volumetric thermal expansion is approxi-mately three times the coefficient of linear thermal expansion.
See The Handbook of Chemistry and Physics, 48th Edition, at page F-90 (Chemical Rubber Co. 1967). Assuming, then, that Grafoil were to expand volu~etrically upon heating according to three - `~ 1 726~7 .
times the larger of the values given above for linear expansion, this would still be less than one-fourth the volumetric expansion upon heating expected to be exhibited by TFE for heating of the valve from temperatures in the ranges of about 78~F. to about -_300~F.
_- The stack of rings sandwiched between the metal ring gas-kets, referred to hereinafter as the sandwich stac~, consisting of the core ring 135 with bearing ring~137 disposed around its inner periphery and make-up rings 133 disposed adjacent the upper and lower faces of rings 135, 137, is deformed to conform to the shape of, and fills substantially all of the space between, the metal ring gaskets 131 as flattened in their energized condition.
The rings of the sandwich stack typically are originally of rectangular cross-section, but may be deformed in a press prior to installation in the valve to assume the frustoconical shapes ~; shown on the right hand side of Figure 2, which are correlative to the frustoconical shaped surfaces of adapter rings 123, 125, 129 against which the metal ring gaskets are flattened. Alterna-tively, the rings of the sandwich stack may be installed ~n their original rectangular cross-section configuration, and deformed into frustoconical shape upon energizing the seal.
The material of which stress relief ring 135 is made may have the form of Grafoil ribbon wrapped tightly and compressed into a solid, endless ring. Such ribbon may be of the type sold by Union Carbide Corporation under the name Grafoil Ribbon-Pack and described in Union Carbide Corporation's Technical Informa-- tion Bulletin No. 52~-204, a copy of which is attached hereto as Appendix I. A ring of tightly wrapped Grafoil Ribbon-Pack mate-rial that has been compressed exhibits its highest thermal expan-sion in the radial direction when such a ring is installed in the stuffing box around the stem, that is, toward the stem and stuff-ing box. Alternatively, ring 135 may be cut from a sheet of \
} 17266~
Grafoil, or sheets of Grafoil stacked together. The Grafoil available commercially may be only about 70 percent compressed or compacted, but can be fully, i.e. 100 percent, compressed or compacted either in a press prior to installation, as described _~~beve, or when in place in the valve upon energizing the seal.
- ~ Make up rings 133 are thinner axially than~ring 135 and ring -13~, which have -su~stantially the same axial thickness when ring 135 is fully compacted, but are wide~ radially than elther of rings 135,137. The combined radial widths of rings 135 and 137 is substanti-ally the same as the radial width of rings 133.
Rings 133 and 137 should make a close sliding fit with the stem upon installation of the sandwich stack in the valve.~ When the sandwich stack is compressed upon energizing thP seal, the inner peripheries of rings 133, 137 are urged more tightly against stem 51, and the outer peripheries of rings 133 and 135 are urged into tight engagement with the walls of stuffing box 65.
p Although two seal sets 119, 121 are shown in the drawings, ; appllcants~have found that one seal set alone is sufficient for providing a satisfactory seal. The second seal set, that is, the one farthest from the fluids being sealed against, is provided for emergency or back-up use, in case the first seal set fails.
As another emergency or back-up sealing feature, a passage 139 is provided in bonnet 23, which passage is in register and fluid communication with a passage 141 through intermediate adapter ring 129 when the seal is energized. Passage 139 is also in fluid communication with an injection fitting 140 disposed in a threaded socket in the exterior of bonnet ~3. An annular groove 143 in fluid communication with passage 139 is provided around the walls of stuffing box 65, and an annular groove 145 in fluid communication with passage 141 is provided around the inner periphery of intermediate adapter ring 129. If seal sets 119, 121 were to fail, then sealant material can be injected through injection fitting 140 and passages 139, 141 to grooves 1~3, 145 ! 1 72667 .
. .
to provide an emergency or back-up seal around the stuffing box and stem, respectively.
The seal means of the present invention is preloaded by tightening the packing retainer to a stress substantially higher -'th-an the stress expected t'o'be caused by fluid pressure when the . _ . . . .
~valve is in service. Typical preload stress for the s~em seals for a valve such as depicted in Figure 1, which has a rated working pressure of 30,000 p.s.i., is 37,500 p.s.i.
When a valve incorporating the stem sealing means of the present invention is heated from ambient temperature, e.g. 70F., to about 300F., for example by the fluids flowing.through the valve, and is then cooled back down to ambient temperature, no further tightening of the packing retainer is necessary. Thus, the original preload on the valve is mzintained upon temperature cycling. This is due apparently to the'fact that the stress over and above the original preload stress caused by attempted thermal expansion of the material between the metal ring gaskets 131 is , not grèat en~ugh to cause the permanent deformation or set of the metal containment structure of the valve parts adjacent to the se~l due to the lower thermal expansion of the core ring 135 as compared to the make-up rings 133 and the bearing ring 137. Eor the same reason, the additional stress due to heating is appar-ently low enough to avoid the rings' 133, 137 taking on of a urther permanent deformation or compressive set, which in turn avoids loss of preload stress when rings 133, 137 relax upon cooling.
Applicants have found ~that the stem sealing means of the present invention works well in sealing 30,000 p.s.i. fluids over temperature cycles from -20F. to 300~E. without additional tightening of the packing retainer, when make-up rings 133 and bearing ring 137 are made of 5% MoS2-filled T~E, core ring 135 is made of Grafoil, ana when the volume of the stress relief ring 135 is appro~imately one-third the tot~ olume of t~- sandwich t 1 7266~
.
stack. That is, in the preferred embodiment, the combined volume of make-up rings 133 and bearing ring 137 is approximately twice the volume of core ring 135. The material used for the make-up rings 133 will not extrude past the metal ring gaskets 131 upon -`~nergizing the seal, and'wil'l confine the Grafoil core ring 135 ~ between'them during energizing the seal to prevënt lts extruding ; past the gaskets 131 before the gaskets form the metal-to-metal '' seals with the stem and stuffing box, Also, the 5% MoS2-filled TFE bearlng ring 137 around the inner periphery of the Grafoil core ring 135 reduces the friction between the stem and~the stem seal means and prevents undue wear on the core ring. Thus, a Grafoil core ring with its low thermal expansion, clad on its three sides adjacent the stem and metal gaskets by 5% MoS2-fiIl~d TFE rings and wherein the Grafoil ring has about one-half the combined volume of the 5% MoS2-filled TFE rings, is preferred for the sandwich stack of the present invention. Of course, other volume relationships for the rings of the sandwich stack may also work we-ll,~'as may other materials for the rings comprising the sandwich stack. '~
- Although Figures 1 and 2A and 2B show the cones of the metal ring gaskets and the rings of the sandwich stack pointing away from the pressure being sealed against, when sealing between parallel surfaces the inner and outer peripheries of the seal are similarly engaged and therefore the seal is reversible. Thus, the cones of the metal ring gaskets and the rings of the'sandwich stack alternatively may be arranged to point toward the pressure being sealed against. Also, it will be understood that rings 133, 137 need not be separate rings. They may instead take the form of, for example, an integral cylindrical ring with a groove around the middle of its outer periphery, that is, a ring with a U-shaped cross-section. The Grafoil ring can then be snapped into place in the ~roove prior to installation in the valve.
) 1 726~
.
.
While preferred embodiments of the invention have been shown and described, many modifications thereof can be made by one skilled in the art without departing from the spirit of the . . .
invention. Therefore, it should be understood that the details - se~ forth herein are for illustration only, and are not intended :to limit the scope of the invention as set forth in the foilowing claims.
What is claimed as invention ist-
~.
~ ~ 72~6~
rectangular cross section configuration and into engagement with the walls of the wellhead and pipe hanger. The deformable ring in this static seal acts as a backup seal for the metal ring gaskets in case of less than perfect sealing by the metal ring gaskets, for example, due to scratches or machine marks in the wellhead or on the pipe hanger. The deformable ring will flow into and seal any of such scratches or machine marks.
One seal used for dynamic as well as static sealing between the stem af a valve and the valve body or bonnet employs frusto-conical elastic metal ring gaskets of rectangular cross section disposed in a stuffing box around the stem, with sandwich rings of a more compliant material disposed between the elastic metal ring gaskets. The reasons for the metal ring gaskets being eLastic, similar to ~elleville springs although not made of spring steel but a softer material, include (1) the gaskets have a larger inner diameter and a smaller outer diameter when unstressed, so that the seal unit can be easily inserted and withdrawn from the stuffing box without undue frictional engagement with the valve stem or stuffing box;
(2) the gaskets will maintain their stressed engagement with the stem and stuffing box during use of the valve despite slight changes in the valve dimensions due to, for example, temperature and pressure variations, which would change slightly the deformation or strain on the gaskets created initially by tightening of the packing retainer. In other words, the gaskets must be elastic in order to maintain their preload.
~he above referred to valve stem seal is disclosed in the aforementioned Patent No. 1,125,261 and in an ASME paper ! 1 726~ ~
entitled "Seals for Valve Stems and Wellheads in High Pressure - F~igh Temperature Service," by C. D. Morrill and C. W. Meyer, prepared for presentation at a conference in Mexico City, Mexico, on September 19~24, 1976. The seal as disclosed therein ïs compressed by a threaded packing retainer such that the metal ring gaskets are flattened, and their inner and outer peripheral edges are deformed or "coined" into metal-to-metal sealing engagement with both the outer surface of the valve stem and the ~Jalls of the stuffing box. The sandwich rings ~etween the metal ring gaskets are also deformed upon compression of the seal to conform to the shapes of the metal ring gaskets and to engage the stem and stuffing box.
The sandwich rings should therefore be elastic to some degree.
The initial deformation will usually cause the sandwich rings to take on an initial permanent set, but they will remain elastic to some degree. Materials used for the sandwich rings in such seals have included fluoroplastics, e.g. tetra-fluoroethylene polymer, and graphite materials. Such materials have also included tetrafluoroethylene polymer filled with up to about 15% molybdenum disulfide.
The sandwich rings of the valve stem seal just described are dynamic seals, acting primarily during stem motion to seal between the metal ring gaskets and the stem when the metal ring gaskets are disturbed by stem drag while the stem is in ; motion. Such sandwich rings also tend to lubricate the areas of contact between the stem and metal ring gaskets by rubbing off onto the stem to ~: -3-! 172667 .
- .
some degree to reduce friction between the stem and the metal ring gaskets. The sandwich rings are also lubricious so as to reduce friction between the stem and the sandwich rings, and ~etween the sandwich rings and the metal ring gaskets. The sandwich rings further act as backup seals for the metal ring gasXets, l~ke the deformable ring backup seals as described above for the wellhead-pipe hanger s~al of U.S. patent no. 4,056,272, to flow into and seal any scratches or machine marks on the stem.
The invention herein disclosed is an improvement over the valve stem seal described above.
One embodiment of the stem seal descrihed above includes three metal ring gaskets and two sandwich rings disposed therebe~
tween, and is known as an "SMT" type seal. The SMT type seal has been found to provide satisfactory stem sealing for valves having working pressures up to about 25,000 p.s.i., at temperatures from -20~F. to 300~F.
For valves having working pressures up to 30,000 p.s.i. or greateE, however, the SMT type seal will not always provide a satisfactory seal or the valve stems undèr conditiGns expected to be encountered during service. Graphite materials alone, for example, are not desirable for SMT type stem seals for valves in the 30,000 p.s.i. class because such materials tend to extrude past the metal ring gaskets upon flattening the gaskets to ener-gize the seal, since the graphite begins to extrude before the gaskets become flattened sufficiently to form a seal with the valve stem and stuffing box. Moreover, graphite materials tend to be worn or eroded away by movement of the valve stem as the graphite is deposited onto the stem and carried by the stem past the gaskets and out of the stuffing box. Such extrusion and wearing away of the graphite material under 30,000 p.s.i. service conditions may lead to leakage of well fluids past the seal and the need to replace the graphite ring.
i 1 7~667 .
Likewise, tetrafluoroethylene polymer ("TFE") materials alone, or such materials including MoS2 as an additive, are not suitable for SMT type stem seals for valves in the 30,G00 p.s.i.
.. . . .
class because such materials are not capable of always maintain-- ~ng a tight seal against such pressures after the valve is put -- through temperature cycling. A valve in oilfield;service through wh~ch high pressure well fluids are 1Owing from deep wells may be heated by the well fluids to a tempeFature of about 300F.
When the well fluids stop flowing through the valve, for example if the well is shut in, the valve may cool down to ambient tempe-rature, for example 70F., and if the well is reopened and the well fluids begin flowing again, the valve wlll heat back up to 300F. Thus, the valve's temperature is cycled between about io~F. and about 300F. A valve stem seal must be capable of remaining tight at all times, at all temperatures and through all temperature cycles to which the valve will be subjected in ser-,~ vice. An SMT type seal usiny TFE rings, or MoS2-filled TFE
rings, will seal against well fluids at pressures of about 30,000 p.s.i. at ambient temperatures, e.g. 70~F., and again at elevated temperatures, e.g. 300F., but when the valve is put through a thermal cycle from ambient temperature to 300F. and back to ambient temperature, the SMT type seal will not always remain tight; sometimes the seal will exhibit minor leakage, either during valve stem movement or when the valve stem is stationary, or both. Although the leakage can be stopped by further tighten-ing of the packing retainer, leakage will reoccur upon further -temperature cycling.
It is an object of this invention to overcome the problems described above by providing a reliable valve stem seal suitable for valves havin~ working pressures of the order of 30,000 p.s.i.
or more and subject to temperature cycling, between temperatures in the range of -20F. to 300F. It is another object of this _nven~ion to provide such a seal that will remain tig~t and will ! 1~266~
not leak when subjected to well fluids having pressures of 30,000 p.s.i. or more and when the temperature of the valve is cycled from ambient temperature to about 300F. and back to ambient temperature, without the need to retighten the packing retainer. It is also an object of this invention to provide such a seal that is simple, compact and economical, and easy to manufacture, install and service. It is also an object of this invention to provide such a seal that is low friction, durable and relatively resistant to deterioration due to fluctuations and extremes in temperature, high pressure and chemical activity of the well fluids sealed against.
SUMMARY OF THE INVENTION
.
According to the invention, there is provided apparatus for sealing in high pressure, temperature cycled applications hetween the walls of an axially movable valve stem and a stuffing box around the valve stem, the stuffing box having a port in its bottom and the valve s-tem extending : through the port and out of the stuffing box, comprising:
, : first and second elastic metal ring gaskets disposed in such stuffing box around such valve stem, and annular compliant seal means dispos.ed in such stuffing box around such valve stem and sandwiched between said gaskets, said seal means including first and second annular portions of tough, compliant material adjacent said first and second gaskets~ respectively, and an annular core portion disposed between said first and second por-tions and composed of a material having a lower coefficient of thermal expansion than said material of said first and second annular portions.
! 172~ ~
BR:[EF DESCRIP~ION OF T~IE DRA~INGS
For a detailed description of a pre:~erred embodiment of the invention, reference will now ~e made to the accompany-ing drawings wherein:
" FIGURE 1 is a vertical section through a valve embodying the invention; and FIGURES 2A and 2B are fragmentary sectional views taken in the same plane as Figure 1 ~ut to a larger scale~ and showing one embodiment of the actuator stem sealing means of the present invention in which the frustoconical metal ring gaskets point away from the pressure ~eing sealed against inside the valve. Figure 2B illustrates the stem sealing means of the present , ~ ,~
~ ?
invention as installed in the valve but prior to its being ener-gized by tightening the packing retainer. Figure 2A illustrates the stem sealing means as energized.
... .
D~TAILED DESCRIP~ION OF PREFERRED EM30DIMENT
Referring to Figure 1, there is shown a valve including a hollow body having a chamber part 21 and a bonnet part 23 secured .hereto by studs 25 and nuts 27. The bonnet part 23 is sealed to the chamber part 21 by a suitable pressure energized gasket 29.
Seats 31, 33 mounted at the inner ends of passages 35, 37 cooper-ate with a pair of ported gates 39, 41 whicX control flow of fluid, e.g. water, oil or gas, through the valve. Sealant material is stored in reservoirs 43, 45, and sealant is supplied automatic-ally through the sealant distribution passages 47, 49 to the interfaces between the gates and seats and between the seat necks and valve body to effect sealing at such interfaces;
Gates 39, 41 are reciprocated by a generally cylindrical actuating~stem Sl between a closed position, shown in Figure 1, where flow of fluids through passages 35, 37 is prevented, and an open position permitting such flow in which gate ports 53, 55 are in register with ports 57, 59 in seats 31, 33. The upper end of actuating stem 51 extends out of valve chamber part 2l and through port 61 in bonnet 23. Seal means 63 according to the invention seals between stem 51 and a generally cylindrical stuffing box 65 in bonnet 23. Seal mean 63 is compressed in stuffing box 65 by a packing retainer 67 which is screwed into internally threaded neck 69 on the top of bonnet 23. A bleeder port 71 is used to checX for leakage of fluids from between stem 51 and port 61 after backseating the stem.
The exterior of bonnet neck 69 is also threaded and receives 2 bearing cap 73 screwed thereon. An actuator nut 75 is screwed onto the threaded upper portion 77 of actuator stem 51 and has a -iange 79 thereon disposed between upper and lower axial thr~st ~ 1 72667 bearings 81, 83. The lower thrust bearing 83 engages the top of a washer 85 disposed on top of packing retainer 67. The upper thrust bearing 81 engages the upper inside end of bearing cap 73.
.
A hand wheel 87 includes a,noncircular aperture 89 fitted over a -`~orrelativel-y shaped porti'on'91 of actuator nut 75. ~and wheel ~ -87 is he'ld in place by a retainer nut 93 screwed onto t~e upper en~ of actuator nut 75. A bleed port 9~ allows fluid to escape '' from between threaded portion 77 of s*e~ 51 and actuat~r nut 7~.
A generally cylindrical balance stem 97 is connected to the lower ends o~ the gates and extends out of the valve chamber through port 99. Seal means 101 according to the ,i,nvention seals ; between balance stem 97 and a generally cylindrical stufing box 103 in the valve body. Seal means 101 is compressed in stuffing box 103 by lower packing retainer 105 which is screwed into a threaded socket 107 coaxial with port 99 and stuffing box 103. A
bleeder port 109 is used to check for leakage of fluids from . between balance stem 97 and port 99 when the enlarged portion on the upper end of the balance stem is fully seated in the annular seat in the valve body around port 99. A lower cap 111 is secured to the valve body over lower packing retainer 105 and the lower end of balance stem 97, by screws 113.
When hand wheel 87 is turned, actuator nut 75 turns and causes actuator stem 51 to raise or lower gates 39, 41 to which the stem is connected by hub 115. This in turn causes balance stem 97, connected to the gates by hub 117, to move up or down.
~hus, there is relative axial motion between each o stems 51, 97 -and the respective stem seal means 63, 101. Seal means 63, 101 must remain tight before, during and after such relative axial motion.
Seal means 63, 101 are alike, so only one need be described in further detail. Referring to Figures 2A and 2B, seal means 63 includes an upper seal set 119 and a lower seal set 121. A base adap.er rlng 123 is disposed in the botto~ o ~nnular stuffing ~ 172~67 -box 65 below lower seal set 121. The bottom of base adapter ring 123 engages flush with and is correlative to the bottom of the stuffing box. A follower adapter ring 125 is disposed between --~he lower face 127 of packing retainer 67 and upper seal set 119.
- -~ ~e upper end of follower--adapter ring I25 engages flush with and . ._ ----is correlative to lower face 127 of packing retainer 67. An .= .
intermediate adapter ring 129 i5 disposed between seal sets 119, 121. The upper face of base adapter ring 123, the lower face of follower adapter ring 125, and both upper and lower faces of in-termediate adapter ring 129 are frustoconical in configuration, having the desired cone angles for the shapes of the seal sets 119, 121 in their final assembled positions. In this regard, it should be noted that Figure 2B-illustrates the seal means of the present invention as installed in the valve but prior to its being energized by tightening the packing retainer; Figure 2A
illustrates the seal means 2S energized, with the packing re-tainer screwed farther into its threaded receptacle and the seal sets a~d adapter rings in their final assembled positions.- As is explained in more detail hereinafter, the metal ring gaskets of the seal sets are more sharply conical, that is, they have smaller cone angles, in their relaxed states shown in Eigure 2B than in their final energized states shown in Figure 2A. If desired, either or both of adapter rings 123, 125 may be omitted, the bottom of the stuffing box and/or the lower end of retainer 67 being provided instead with a frustoconical surface of the de-sired cone angle and area. If used, adapter rings 123, 125, and adapter ring 129, should be made of fairly hard material such as, for example, 4140 steel. The valve body and bonnet need only be made of any steel conventionally used for high pressure valves.
Seal sets 119, 121~are alike, so only one need be àescribed in further detail. Seal set 119 includes a pair of frustoconical metal ring gaskets 131 between which are disposed two identical make-up rings 133. Make-up rings 133 are made of tough, compliant, .
~ i~
- . ~ 1 7 2 ~ ~
.
soiid lubricious material having a lower elastic modulus than metal ring gaskets 131. One make-up ring is disposed adjacent to one of the metal ring gaskets, and the other make-up ring is .. . .
disposed adjacent to the other of the metal ring gaskets.
- ~ ~ A core-ring 135 is disposed between make-up rings 133 Core ~~ ring 135 has a lower coefficient of volumetric thermal expansion th'an make-up rings 133. The inside diameter of core ring 135 is ' greater ~han the inside diameter of make-up rings 133. Around the inner periphery of core ring 135, between it and valve actuat-ing stem 51,- is disposed a bearing ring 137 of tough, compliant, solid lubricious material which may be of the same. type'used for make-up rings 133. Bearing ring 137 makes a sliding fit within the aperture in core ring 135.
The metal ring gaskets 131 in their relaxed state have a generally rectangular cross-section which lies at about a 30 angle to the horizontal.~ Thus, the cone angle for the gaskets 131 in relaxed condition is about 120. Gaskets 131 in such relaxed` condi'tion have a radial clearance with both stem 51 and stuffing box 65 so that neither the stem nor the stuffing box ' will be damaged upon installing gaskets 131 in the valve. Gas-kets 131 are just dropped into place. Upon ener~izing the seal means by tightening the packing retainer, the gasket-s are flat-tened such that the inner diameter of each gasket is reduced and the outer diameter of each gasket is increased sufficiently that the inner peripheral edge on the concave side of each gasket and the outer peripheral edge on the convex side of each gasket are -deformed or "coined," i.e. they flow plastically, into metal-tc-metal sealing engagement with the stem and stufing box, respec-tively. In order not to gall or mar the stems, the metal ring gaskets should be made of softer metal than the valve stems. The valve stems may be made of K Monel, for example, but a comparable steel would be suitable. It is preferred that the stem have a hard coating on it, such as a tungsten carbide coating of 3 to 5 ! 172667 .
mils thickness, to increase the hardness of and enhance the durability of the stem. Such a coating would raise the hardness of the stem from about 30 to about 60 Rockwell hardness. The metal ring gaskets should have sufficient plasticity to 2110w o~ning of the peripheral edges through high stress to effect the -metal-to-metal seal, and should have sufficient strength to wlthstand the high preload and well fluid pressures found in service. They may be made, for exam~le, of annealed (austenitic) stainless steel, such as No. 316 stainless steel, or of other metals such-as carbon or alloy steel. To urther reduce the possibility of galling or marring the stems, the inner peripheral edge on the concave side of each gasket is rounded, preferably with a radius e~ual to about one-half the gasket thickness, e.g.
a radius of 0.02 inches for a gasket that is 0.04 inches thick.
In flattened condition, the metal ring gaskets 131 make an angle of approximately 15~ to the horizontal, corresponding to a cone angle of about 150~, conforming to the ~rustoconical faces of adapter rings 123, 125 and 129 which are also disposed at an angle of about 15 to the horizontal. It will be understood, of course, that while the metal ring gaskets are preferably frusto-conical, shapes for the metal ring gaskets other than frusto-conical may be employed.
The material used for make-up rings 133 and the bearing ring 137 should have a low coefficient of friction, that is, it should be a highly lu~riciou~ material. The material for make-up rings 133 and bearing ring 137 should also have sufficient strength and toughness to remain integral under high pressure, and should be resistant to chemical activity of the fluid being controlled by the valve, and should be able to withstand temperatures through-out the range expected to be encountered during service, e.g.
300~F. down to -20~F. Such material should also be sufficiently compliant or elastic to flow into any minute gaps which may be left between the metal ring gaskets and the s~em and stuf f ing DOX
! 1 7 2 6 6 7 due to scratches or machine marks on the stem or stuffing box, or between the metal ring gaskets and the newly adjacent stem sur-ace during and after movement of the stem. Gaps of the latter type might occur, for example, because during and after movement ~f-the stem, the inner pe'ripheries of the metal ring gaskets will not~instantaneously, and perhaps might not ever, 1OW further pl-astically to conform to the newly adjacent stem surface. The make-up and bearing ring materials wi11 flow into and seal any of these minute gaps. Therefore the make-up and bearing rings may also be considered to be sealing rings. Materials suitable for the make-up rings 133 and bearing ring 137 include! for example, tetrafluoroethylene polymer, such as that sold under the trade-mark "Teflon," and "Moly-Teflon," which is like Teflon but in-ciudes up to about 15 percent molybdenum disulfide, MoS2. A
particular material found to be suitable is one having 5% by weight MoS2 and 95% by weight TFE, and sold by Allied Chemical Company under the designation'"No. 2021."
Th-e'material used for core ring 135 should, lîke the m'ate-.
rial used for rings 133, 137, have sufficient strength to with-s~and the high stress re~uired for preloading the seal, and should also be resistant to chemical activity o the well fluids being sealed against and able to withstand temperatures through-out the range expected to be encountered during service, e.g.
300F. down to as low as -75F.
Further properties of the core ring 135 may be best'appreci-ated from applicants' discovery of what they believe to be the cause of the leakage of the SMT type seal at high pressures upon extreme temperature cycling, although it is to be understood that the herein described seal solves the leakage problem regardless of the theory of its operation.
The leakage exhibited by the SMT type stem seal using TFE or ~oS2-filled TFE rings at pressures in the 30,000 p~s.i. range af.er temperature cycling apparently results from partial loss of the preload on the seal. Compare the loss of preload in pure ~ 172~67 .
elastomer packings disclosed in the ASME article referred to above. When the SMT type seal is first made up or energized, mechanical compression is placed upon the seal through tightening ...
the packing retainer such that the seal is stressed to a greater -~ ~egree than it would be''stressed by the high pressure well fluids.
. . ~
When a v'alve including the SMT type stem seal-hea~s up from - -~ambient temperature to 300F., the TFE rings try to expand, but cannot do so to any great extent, ince they are substantially confined on all sides by metals which expand less rapidly .han the TFE rings. This causes the preload stress on the seal to increase from what it was originally, that is, bef.ore heating.
When the valve cools down to ambient temperature, the preload stress not only diminishes from its elevated level attained when the valve was heated, it becomes lower than it was originally.
This is apparently due to one or the ot'her, or perhaps both, of the following effects. When the valve is heated to about 300F., the elevated stressj over and above the already high preload stress', on-the seal and surrounding metal containment structure caused by thermal expansion of the TFE rings might cause slight permanent deformation or set, that is, yielding, of such surround-ing metal containment structure so as to increase the volume occupied by the seal when the seal cools back down to ambient temperature, thereby reducing the stress on the seal belo~ its preload. Alternatively, or perhaps cumulatively, when the TFE
rings are stressed at the elevated level due to thermal expansion upon heating the valve to 300~F., the TFE rings could undergo a permanent deformation beyond that caused by the preload stress, that is, they might take on a further compressive set, which remains after the valve cools down to ambient temperature and results in a stress relief in the TFE rings which offsets somewhat the effect of the packing retainer's compressing of the seal.
Thus, after temperature cyclin~, in order to regain the proper preload, the packing retainer would have to be retightened.
1 1726~7 :
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Without such retightening, the valve would be unable to seal against pressures of the order of 30,000 p.s.i. without slight leakage.
According to the present invention, some of the preferred TFE-or MoS2-filled TFE material between the metal ring gaskets of the SMT type stem seal is replaced by a'mate'ria~ wh'ich exhibits relatively little expansion when heated as compared to the TFE or MoS2-filled TFE material. I~ the preferred embodiment of this invention, this low thermal expansion material lS comprised in core- ring 135, which is clad on its three sides adjacent the metal ring gaskets and stem by ~ake-up rings 133 and bearing ring 137. Thus, core ring 13S must have a coeficient of volumetric thermal expansion that is lower than that for rings 133, 137.
One such material suitable for core ring 135 is compacted graphite, such as lS sold under the trademark "Grafoil.'i See U.S. patent no. 3,404,061. It is believed that the coefficient of volumetric thermal expansion for TFE, for example, is substantially greater _;f ' ~ than that for Grafoil, indeed several times greater', although precise values are not known to applicants. Published data ' ~ ' indicate, however, that Grafoil, which is manufactured in such :, forms as thin flexible layered sheets or ribbon, has a coeffic-ient of linear expansion of about -0.02 x lQ S in/inF. in direc-tions parallel to the graphite layers, that is, along their length and width, over the range of 70~F. to 2,000F., and of about 1.5 x 10 5 in/in~F. in directions normal to the layers, that is, through their thickness, over the range of 70F. to a~ooo~F~ TFE has a coefficient of linear expansion of about 7.0 - 10.0 x 10 in/in~F. over the range of 78F. to 500~F. For solids, the coefficient of volumetric thermal expansion is approxi-mately three times the coefficient of linear thermal expansion.
See The Handbook of Chemistry and Physics, 48th Edition, at page F-90 (Chemical Rubber Co. 1967). Assuming, then, that Grafoil were to expand volu~etrically upon heating according to three - `~ 1 726~7 .
times the larger of the values given above for linear expansion, this would still be less than one-fourth the volumetric expansion upon heating expected to be exhibited by TFE for heating of the valve from temperatures in the ranges of about 78~F. to about -_300~F.
_- The stack of rings sandwiched between the metal ring gas-kets, referred to hereinafter as the sandwich stac~, consisting of the core ring 135 with bearing ring~137 disposed around its inner periphery and make-up rings 133 disposed adjacent the upper and lower faces of rings 135, 137, is deformed to conform to the shape of, and fills substantially all of the space between, the metal ring gaskets 131 as flattened in their energized condition.
The rings of the sandwich stack typically are originally of rectangular cross-section, but may be deformed in a press prior to installation in the valve to assume the frustoconical shapes ~; shown on the right hand side of Figure 2, which are correlative to the frustoconical shaped surfaces of adapter rings 123, 125, 129 against which the metal ring gaskets are flattened. Alterna-tively, the rings of the sandwich stack may be installed ~n their original rectangular cross-section configuration, and deformed into frustoconical shape upon energizing the seal.
The material of which stress relief ring 135 is made may have the form of Grafoil ribbon wrapped tightly and compressed into a solid, endless ring. Such ribbon may be of the type sold by Union Carbide Corporation under the name Grafoil Ribbon-Pack and described in Union Carbide Corporation's Technical Informa-- tion Bulletin No. 52~-204, a copy of which is attached hereto as Appendix I. A ring of tightly wrapped Grafoil Ribbon-Pack mate-rial that has been compressed exhibits its highest thermal expan-sion in the radial direction when such a ring is installed in the stuffing box around the stem, that is, toward the stem and stuff-ing box. Alternatively, ring 135 may be cut from a sheet of \
} 17266~
Grafoil, or sheets of Grafoil stacked together. The Grafoil available commercially may be only about 70 percent compressed or compacted, but can be fully, i.e. 100 percent, compressed or compacted either in a press prior to installation, as described _~~beve, or when in place in the valve upon energizing the seal.
- ~ Make up rings 133 are thinner axially than~ring 135 and ring -13~, which have -su~stantially the same axial thickness when ring 135 is fully compacted, but are wide~ radially than elther of rings 135,137. The combined radial widths of rings 135 and 137 is substanti-ally the same as the radial width of rings 133.
Rings 133 and 137 should make a close sliding fit with the stem upon installation of the sandwich stack in the valve.~ When the sandwich stack is compressed upon energizing thP seal, the inner peripheries of rings 133, 137 are urged more tightly against stem 51, and the outer peripheries of rings 133 and 135 are urged into tight engagement with the walls of stuffing box 65.
p Although two seal sets 119, 121 are shown in the drawings, ; appllcants~have found that one seal set alone is sufficient for providing a satisfactory seal. The second seal set, that is, the one farthest from the fluids being sealed against, is provided for emergency or back-up use, in case the first seal set fails.
As another emergency or back-up sealing feature, a passage 139 is provided in bonnet 23, which passage is in register and fluid communication with a passage 141 through intermediate adapter ring 129 when the seal is energized. Passage 139 is also in fluid communication with an injection fitting 140 disposed in a threaded socket in the exterior of bonnet ~3. An annular groove 143 in fluid communication with passage 139 is provided around the walls of stuffing box 65, and an annular groove 145 in fluid communication with passage 141 is provided around the inner periphery of intermediate adapter ring 129. If seal sets 119, 121 were to fail, then sealant material can be injected through injection fitting 140 and passages 139, 141 to grooves 1~3, 145 ! 1 72667 .
. .
to provide an emergency or back-up seal around the stuffing box and stem, respectively.
The seal means of the present invention is preloaded by tightening the packing retainer to a stress substantially higher -'th-an the stress expected t'o'be caused by fluid pressure when the . _ . . . .
~valve is in service. Typical preload stress for the s~em seals for a valve such as depicted in Figure 1, which has a rated working pressure of 30,000 p.s.i., is 37,500 p.s.i.
When a valve incorporating the stem sealing means of the present invention is heated from ambient temperature, e.g. 70F., to about 300F., for example by the fluids flowing.through the valve, and is then cooled back down to ambient temperature, no further tightening of the packing retainer is necessary. Thus, the original preload on the valve is mzintained upon temperature cycling. This is due apparently to the'fact that the stress over and above the original preload stress caused by attempted thermal expansion of the material between the metal ring gaskets 131 is , not grèat en~ugh to cause the permanent deformation or set of the metal containment structure of the valve parts adjacent to the se~l due to the lower thermal expansion of the core ring 135 as compared to the make-up rings 133 and the bearing ring 137. Eor the same reason, the additional stress due to heating is appar-ently low enough to avoid the rings' 133, 137 taking on of a urther permanent deformation or compressive set, which in turn avoids loss of preload stress when rings 133, 137 relax upon cooling.
Applicants have found ~that the stem sealing means of the present invention works well in sealing 30,000 p.s.i. fluids over temperature cycles from -20F. to 300~E. without additional tightening of the packing retainer, when make-up rings 133 and bearing ring 137 are made of 5% MoS2-filled T~E, core ring 135 is made of Grafoil, ana when the volume of the stress relief ring 135 is appro~imately one-third the tot~ olume of t~- sandwich t 1 7266~
.
stack. That is, in the preferred embodiment, the combined volume of make-up rings 133 and bearing ring 137 is approximately twice the volume of core ring 135. The material used for the make-up rings 133 will not extrude past the metal ring gaskets 131 upon -`~nergizing the seal, and'wil'l confine the Grafoil core ring 135 ~ between'them during energizing the seal to prevënt lts extruding ; past the gaskets 131 before the gaskets form the metal-to-metal '' seals with the stem and stuffing box, Also, the 5% MoS2-filled TFE bearlng ring 137 around the inner periphery of the Grafoil core ring 135 reduces the friction between the stem and~the stem seal means and prevents undue wear on the core ring. Thus, a Grafoil core ring with its low thermal expansion, clad on its three sides adjacent the stem and metal gaskets by 5% MoS2-fiIl~d TFE rings and wherein the Grafoil ring has about one-half the combined volume of the 5% MoS2-filled TFE rings, is preferred for the sandwich stack of the present invention. Of course, other volume relationships for the rings of the sandwich stack may also work we-ll,~'as may other materials for the rings comprising the sandwich stack. '~
- Although Figures 1 and 2A and 2B show the cones of the metal ring gaskets and the rings of the sandwich stack pointing away from the pressure being sealed against, when sealing between parallel surfaces the inner and outer peripheries of the seal are similarly engaged and therefore the seal is reversible. Thus, the cones of the metal ring gaskets and the rings of the'sandwich stack alternatively may be arranged to point toward the pressure being sealed against. Also, it will be understood that rings 133, 137 need not be separate rings. They may instead take the form of, for example, an integral cylindrical ring with a groove around the middle of its outer periphery, that is, a ring with a U-shaped cross-section. The Grafoil ring can then be snapped into place in the ~roove prior to installation in the valve.
) 1 726~
.
.
While preferred embodiments of the invention have been shown and described, many modifications thereof can be made by one skilled in the art without departing from the spirit of the . . .
invention. Therefore, it should be understood that the details - se~ forth herein are for illustration only, and are not intended :to limit the scope of the invention as set forth in the foilowing claims.
What is claimed as invention ist-
Claims (13)
1. Apparatus for sealing in high pressure, temperature cycled applications between the walls of an axially movable valve stem and a stuffing box around the valve stem, the stuffing box having a port in its bottom and the valve stem extending through the port and out of the stuffing box, comprising:
first and second elastic metal ring gaskets disposed in such stuffing box around such valve stem, and annular compliant seal means disposed in such stuffing box around such valve stem and sandwiched between said gaskets, said seal means including first and second annular portions of tough, compliant material adjacent said first and second gaskets, respectively, and an annular core portion dis-posed between said first and second portions and composed of a material having a lower coefficient of thermal expansion than said material of said first and second annular por-tions.
first and second elastic metal ring gaskets disposed in such stuffing box around such valve stem, and annular compliant seal means disposed in such stuffing box around such valve stem and sandwiched between said gaskets, said seal means including first and second annular portions of tough, compliant material adjacent said first and second gaskets, respectively, and an annular core portion dis-posed between said first and second portions and composed of a material having a lower coefficient of thermal expansion than said material of said first and second annular por-tions.
2. Apparatus of claim 1, wherein said material of said first and second annular portions has a low coefficient of fric-tion.
3. Apparatus of claim 2, wherein said material of said first and second annular portions comprises tetrafluoroethylene polymer, and said material of said core portion comprises com-pacted graphite.
4. Apparatus of claim 3, wherein said material of said first and second annular portions further comprises up to about fifteen percent molybdenum disulfide.
5. Apparatus of claim 4, wherein said first and second annular portions comprise make-up rings in sealing engagement with such stem and such stuffing box and said core portion com-prises a core ring having an inner diameter larger than the outer diameter of such stem, and further including a bearing ring of tough, compliant material disposed around the inner-periphery of said core ring between said core ring and such stem.
6. Apparatus of claim 5, wherein said material of said bearing ring is the same as that of said make-up rings.
7. Apparatus of claim 6, wherein said core ring and said bearing ring together occupy substantially all of the space between said make-up rings, in the axial direction, and between such stem and such stuffing box, in the radial direction.
8. Apparatus of claim-7, wherein the volume of said core ring is about one-half the combined volumes of the make-up rings and bearing ring.
9. Apparatus of claim 1, wherein the coefficient of ther-mal expansion of said core portion material is less than one-fourth that of said material of said first and second annular portions.
10. Apparatus of claim 1, and including means for compress-ing said first and second gaskets such that said gaskets are partially flattened and their inner and outer peripheral edges are coined into metal-to-metal sealing engagement with such stem and such stuffing box, and for urging said first and second annular portions of said seal means into sealing engagement with such stem and such stuffing box.
11. Apparatus of claim 10, said core portion being annular in configuration with its outer radial periphery adjacent such stuffing box and having an inner diameter greater than the outer diameter of such stem, said seal means including a third annular portion of tough, compliant material disposed between said core portion and such stem.
12. Apparatus of claim 11, said first, second and third annular portions being composed of tetrafluoroethylene polymer, and said core portion being composed of compacted graphite.
13. Apparatus of claim 11, said first, second and third annular portions being composed of a material consisting of ninety-five percent tetrafluoroethylene polymer and five percent molybdenum disulfide, said core portion being composed of com-pacted graphite, and wherein said first, second and third annular portions and said core portion occupy substantially all of the space between said metal ring gaskets, the stem and the stuffing box when said gaskets are compressed, said core portion having a volume equal to about one-third the total volume of said space.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US28874281A | 1981-07-31 | 1981-07-31 | |
| US288,742 | 1988-12-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1172667A true CA1172667A (en) | 1984-08-14 |
Family
ID=23108452
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000408465A Expired CA1172667A (en) | 1981-07-31 | 1982-07-30 | High pressure seal for temperature cycled applications |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5828082A (en) |
| CA (1) | CA1172667A (en) |
| DE (1) | DE3228583A1 (en) |
| FR (1) | FR2510711B1 (en) |
| GB (1) | GB2103310B (en) |
| NL (1) | NL8203028A (en) |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4516752A (en) * | 1984-01-12 | 1985-05-14 | Joy Manufacturing Company | Mechanically preloaded packing assembly |
| GB2180626A (en) * | 1985-07-29 | 1987-04-01 | Orbit Valve Limited | Ball valve |
| US4886241A (en) * | 1987-09-16 | 1989-12-12 | Fisher Controls International, Inc. | Valve stem packing containment for high pressure, high temperature |
| DE3907103A1 (en) * | 1989-03-04 | 1990-09-13 | Argus Gmbh | SEALED PERFORMANCE OF A SHAFT THROUGH A BEARING EXTENSION |
| US4899899A (en) * | 1989-06-21 | 1990-02-13 | Triten Corporation | Pressure vessel |
| US5791629A (en) * | 1996-10-31 | 1998-08-11 | Fisher Controls International, Inc. | Bushing-less stem guided control valve |
| GB0004949D0 (en) | 2000-03-02 | 2000-04-19 | Needham David M | Fluid flow proportioning device |
| DE20005319U1 (en) * | 2000-03-22 | 2001-06-07 | Claret Jose | Sealing system for the control shaft of a valve |
| DE202005006553U1 (en) * | 2005-04-22 | 2005-07-14 | Vr Dichtungen Gmbh | Radial shaft seal comprises membrane and support ring with centering section on its outer rim which press-fits into seal mounting and has wedge-shaped support section on its inner rim |
| JP5061045B2 (en) * | 2008-06-27 | 2012-10-31 | 株式会社キッツ | Seal packing and seal structure using the same |
| US9010725B2 (en) | 2011-12-21 | 2015-04-21 | Vetco Gray Inc. | Valve vented redundant stem seal system |
| US9897215B2 (en) * | 2012-12-31 | 2018-02-20 | Vetco Gray Inc. | Multi-valve seat seal assembly for a gate valve |
| RU2545254C1 (en) * | 2014-04-18 | 2015-03-27 | Игорь Михайлович Каштанов | Sliding shutter |
| CN106537009B (en) | 2014-05-02 | 2019-11-22 | Bs和B创新有限公司 | Pressure reducing valve for oil extraction system |
| WO2016168250A1 (en) * | 2015-04-13 | 2016-10-20 | Oceaneering International, Inc. | Composite circular connector seal and method of use |
| CN110260034A (en) * | 2018-03-12 | 2019-09-20 | 中核苏阀科技实业股份有限公司 | A kind of big butterfly spring floating preload valve stem packing sealing device of band |
| FR3079903B1 (en) * | 2018-04-04 | 2022-12-23 | Commissariat Energie Atomique | METAL SEAL ASSEMBLY FOR SEALING BETWEEN A ROTATING SHAFT AND A FIXED FRAME |
| GB2586274A (en) * | 2019-08-16 | 2021-02-17 | Oliver Twinsafe Valves Ltd | Valve with sealing system |
| DE102020003214A1 (en) | 2020-05-28 | 2021-12-02 | Daimler Ag | Valve stem seal for an internal combustion engine of a motor vehicle |
| RU2743872C1 (en) * | 2020-05-28 | 2021-03-01 | Индивидуальный предприниматель Лёвин Сергей Анатольевич | Spindle support-sealing assembly of wedge gate valve for underground pipelines |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3179426A (en) * | 1962-06-25 | 1965-04-20 | Gen Motors Corp | High temperature actuator seal |
| GB1150645A (en) * | 1965-12-30 | 1969-04-30 | Dowty Rotol Ltd | Sealing Device |
| GB1139200A (en) * | 1966-01-29 | 1969-01-08 | Pierino Saleri | Improvements in valves for fluids |
| US4340204A (en) * | 1976-02-06 | 1982-07-20 | Smith International, Inc. | High pressure gate valve with preloaded, stacked, solid lubricated stem seals |
| DE2734794A1 (en) * | 1977-08-02 | 1979-02-15 | Mcevoy Oilfield Equipment Co | Slide valve with member supported by spindle - held in seal having metallic washers between plastics rings |
-
1982
- 1982-07-29 NL NL8203028A patent/NL8203028A/en not_active Application Discontinuation
- 1982-07-29 GB GB08221916A patent/GB2103310B/en not_active Expired
- 1982-07-30 JP JP57134635A patent/JPS5828082A/en active Granted
- 1982-07-30 DE DE19823228583 patent/DE3228583A1/en active Granted
- 1982-07-30 CA CA000408465A patent/CA1172667A/en not_active Expired
- 1982-07-30 FR FR8213363A patent/FR2510711B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2103310B (en) | 1985-07-24 |
| FR2510711A1 (en) | 1983-02-04 |
| DE3228583A1 (en) | 1983-02-17 |
| DE3228583C2 (en) | 1991-01-10 |
| FR2510711B1 (en) | 1985-11-29 |
| JPS5828082A (en) | 1983-02-18 |
| JPH0210313B2 (en) | 1990-03-07 |
| GB2103310A (en) | 1983-02-16 |
| NL8203028A (en) | 1983-02-16 |
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