CA1046479A

CA1046479A - Plug valve

Info

Publication number: CA1046479A
Application number: CA261,012A
Authority: CA
Inventors: John G. Macleod
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1975-10-24
Filing date: 1976-09-13
Publication date: 1979-01-16
Also published as: JPS5253529A; FR2328906A1; BR7607103A; AU1783376A; BE847602A; DE2647879A1; CH598519A5; NL7611740A; SE7611697L; ES452609A1; ZA765546B; GB1541270A; AR211784A1

Abstract

PLUG VALVE
Abstract of the Disclosure A tapered plug valve comprising a casing having a passageway therethrough for flow of fluid and a tapered bore intersecting the passageway, a taper plug rotatably mounted in the tapered bore adapted to block the passageway in valve closed position of the plug and the plug having a port adapted to connect and be in communication with the passageway in valve open position, the plug and casing defining a chamber at one end of the plug, a stem rotatably mounted within the casing and mechanically coupled to the plug to rotatably drive the plug, the casing having an annular rib surrounding the stem at one end of the chamber, the stem having an annular rim thereon and located on the portion of the stem which is in the chamber, an annular thrust bearing and seal surrounding the stem and abutting the opposed lateral faces of the annular rib and the annular rim to provide a seal therebetween.

Description

~46~79 PLUG VALVE
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Background of the Invention The present invention relates to plug valves and, more particularly, to tapered plug valves of the lubricated variety.
The pr;or art is replete with various forms of tapered plug - Yalve assemblies, many of which are directed to solving the pr~blem of field maintenance and, in particular, to solving the problem of ~ removing the primary seals from the valve casing while the valve is in ,- place and under pressure.
This problem, if not properly resolved, can cause serious -downtime of the line in which the valve to be maintained is located.
" For example, if the valve was located in a continuous process line and : .
the valve became faulty, the entire line would have to be shut down to allow for the replacement and repair of such faulty valYe. One of the ~' major causes for failure of such a valve is the breakdown or deterioration .,.
of the primary valve stem seal ~hich results in a leaking valYe.
Certain prior art forms of tapered plug Yalves have included features which allow for partial replacement of the primary seals when the valve is exposed to line pressure. These features have been only ~' ' 20 partially successful and no prior art valve has yet been found that is ;' entirely satisfactory for this purpose until the valve contemplated by this invention. ~ ' ,.'~
''Summary'of the Invention ;
It is therefore a primary object of the present invention to provide a plug valve which is highly effective and efficlent and which ; may be maintained while the valve is in~place and exposed to line pressure.
' It is another important object of the present invention to ' '~ provide a plug valve which is inexpensive to manufacture, yet highly ~-'~ reliable and easily mainta1ned ' 1 ~ ,, 1~46~79 It is another primary object of the present invention to provide a plug valve comprising a casing having a passageway therethrough for flow of fluid and a tapered bore intersecting the passageway, a taper plug rotatably mounted in the tapered bore adapted to block the ~ passagewa~ in valve closed position of the plug and the plug having a - port adapted to connect and be in communication with the passageway in valve open position, the plug and casing defining a chamber at one end of the plug, a stem rotatably mounted within the casing and mechanically coupled to the plug to rotatably drive the plug, the casing having an annular rib surrounding the stem at one end of the chamber, the stem having an annular rim thereon and located on the portion of the stem which is in the chamber~ an annular thrust bearing and seal surrounding ~-~
the stem and abutting the opposed lateral faces of the annular rib and the annular rim to provide a seal therebetween.
~ t is a further object ~f the present invention to provide a tapered plug valve wherein the annular rib is further provided with an annular groove complementary to the thrust bearing and seal for accepting the seal therein, the thrust bearing and seal remaining substantially stationary with respect to the casing, the seal being primarily provided by the opposed lateral faces of the thrust bearing and seal and the annular rim.
It is another object of the present invention to provide a tapered plug valve wherein the width of said opposed lateral faces of said annular rim and said thrust bearing and seal are equal.
It is still a further object of the present invention to provide a tapered plug valve wherein a seal is provided in the casing surrounding the shaft above the annular rib, the seal removable from the top of the valve without disturbing the operational position of the thrust bearing and seal.

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It is also a further obiect of the present invention to provide a tapered plug valve wherein a radially extending port is provided in the annular rib, the radially extending port in communication ^ with a pressure relief means for determining the sealing condition of the thrust bearing and seal.
It is yet another object of the present inYention to provide a tapered plug valve wherein the pressure relief means comprises a partially threaded cavity provided in the casing in communication with the radially ; extending port, a stop means seated on a seat in the partially threaded o cavity, the ball held in place on the seat by threaded screw member.
rt is yet a further object of the present inYention to provide a tapered plug valve wherein the radially extending port is located ' intermediate the ends of the annular rib, the threaded screw member adapted to be threadably removed from the partially threaded cavity.
It is again a further object of the present invention to provide a tapered plug valve wherein the stem is coated with a self-lubricating plastic in the area of the annular rim.
; It is another object of the present invention to provide a tapered p'lug valve wherein the self-lubricating plastic is polytetra-fluoroethylene and the thrust bearing and seal is of stainless steel.
Further objects of the present invention will become apparent as the description proceeds in connection ~ith the appended claims and ' the annexed drawings described below. ~
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Description of the Dra~ings Figure 1 is a partial sectional view of a tapered plug valve in accordance with the present invention~
. Figure 2 is another sectional view of the tapered plug valve '' in accordance with the present invention wherein the tapered plug valve in Figure 1 is rotated approximately 90 degrees.
- 30 Figure 3 is a top_view of the tapered plug Yalve of Figure 1.
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Description of the Invention Referring now to the drawings, there is shown an improved tapered plug valve 10 according to a preferred embodiment of the present - invention. The tapered plug valve 10 is highly adaptable to manyapplications and requirements as is well known by those having ordinary skill in this art. For example, the tapered plug valve as contemplated by this invention may be used in oil and gas production, refining and transmission apparatus, flow systems of all kinds, and the like.
The tapered plug valve 10 is provided with a casing 12.
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Typically, the casing 12 is a cast part which in turn is machined and otherwise suitably prepared for the operational introduction of its various parts~ The casing 12 is so arranged as to receive an end cap 14. The end cap 14 may be adapted to the casing by suitable attaching means such as a series of threaded bolts 16. With the end cap removed, all the various operational parts, which ~ill be below further described, may be introduced into the casing 12. That is, the stem 18 coupling member or equalizing ring 20 and plug 22 all may be loaded or assembled within the casing from the bottom.
The stem 18 is rotatably mounted within the casing 12 and is mechanically coupled to the equalizer ring 20. The equalizer ring 20 is ~-' mechanically coupled to the plug 22 ~hich is rotatably mounted within the casing 12 at a tapered interface 24. As can immediately be seen, rotation of the stem 18 will in turn cause rotation of the plug 22 through the equalizer ring 20 which mechanically couples the stem 18 to the plug 22. The end cap 1~ is also provided with a threaded cavity 28 . i . ...
;i which is adapted to threadably receive a plug adjusting screw 30 and a . . .
protective cap 32. The plug adjusting screw 30, as the name implies, is adapted to adjust the axial position of the plug 22 ~ithin the casing 12. This adjustment is achieved through the provision of a spherical '' ' ri :

,, ' ' '' ' , ' ,, "' ' ' ' ' ' ', , ' ~ ' ' ~C146~79 plug thrust ball 34 supported within a cavity 36 in the lower end of the plug 22 and on ball seat 38. The ball seat 38 is responsive to axial movement of the plug adjusting screw 30 which, for example, when threadably moved inwardly with respect to the end cap 14 drives the plug 22 and thereby drives the spherical plug thrust ball 34 toward the apex of the ; taper.
; A band seal 40 may also be provided around the juncture of the casing 12 and end cap 14 to seal the void 42 between the two members from the environment. The sealing of the void is further enhanced by the provision of a grease f~tting 44 provided in a bore 46 in the end cap 14 for applying grease under pressure to the above noted void 42.
It should be noted that the grease will completely fill the void 42 and surround the threaded bolts 16 thereby preserving the threads on the ; threaded bolt 16 from any adverse substance or environment.
A seal is maintained between the end cap 14 and the casing 12 by the provision of an annular seal or gasket 43.
The stem 18, as before mentioned, is rotatably supported within the casing 12. The stem 18 is provided with an annular rim 48 which is located in the area of the upper chamber 7~ which will be referred to further below. The annular rim 48 may be formed integrally `
with the stem. The annular rim 48 is provided with a radially extending - lateral face 49. The casing 12 is provided with a radially extending annular rib 54 which may be formed integrally with the casing 12. A
stainless steel thrust bearing and,seal 50 surrounds the ste~ 18 and ,s located between the annular rib 54 and annular rim 48 and is seated in a groove 52 disposed in the annular rib 54 on said casing 12. The thrust bearing and seal 50 is provided with a radially extending lateral face 51 which opposes the radially extending lateral face 49 of the annular .. ., :
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~L046~79 rim 48. When the plug 12, equalizer ring 20 and stem 18 are assembled in place, as above stated and in a manner as will be later described, ` the opposed lateral faces 49 and 51 of the annular rim 48 and thrust . bearing and seal 50, respectively, will be in bearin~ engagement, the :
seal 50 being relatively stationary with respect to the casing 12 while : the stem 18 being relatively rotatable thereto. Accordingly, it can be : seen therefore that the thrust bearing and seal, while in bearin~
~ engagement with the annular rim 48, provides a seal at the end of the upper chamber 76. Further, the thrust bearing and seal 50 will act as : 10 an axial thrust bearing for axial thrust exerted by the stem 18. The stem 18 may be suitably coated with a self-lubricating plastic such as . polytetrafluoroethylene in the area of the thrust bearing and seal and, in particular, in the area of its lateral face 49. The application of : the self-lubricating plastic improves the rotative characteristics of the stem. This seal may be considered a secondary seal.
The primary sealing of the stem 18 is provided by a series of . .
. , sealing members provided in the casing above the annular rib 54 disposed on the casing 12. A typical arrangement of packing or seals 56 may in-:~: clude a series of flat bottom rings and regular rings. The seals 56 may . 20 be held in their operational position by stem rings 58 and 60. The upper stem ring 60 typically may abut a stem cap 62 which may be suitably attach-: ed to the casing 12 by attaching means such as a series of threaded bolts 64. The stem cap 62 serves several functions including, as before . mentioned, the maintenance of the axial position of the stem rinns 58 and 60 and their associated seal 56; and the sealing of the stem from the environment by the provision of a weather seal 66 as typically .
. manufactured by Johns-Manville as their Wiper Construction II, Type P;
and also as a reference stop by the provision of a stop member 68. The ~, , .

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~ )46~79 stop member 68 coacts with a stop collar 70 which is affixed to the stem 18 to rotate therewith. The stop collar 70 is provided with a cut away section 72 with lands 74 at each end thereof which restrict the rotational movement of the stem to a predetermined arc. The restriction of the movement of the stem 18 is effected by the stop collar 70 abutting the stop member 68 at either of its lands 74.
As can be seen in either of the sectional yiews of the valve 10, the casing 12 and the tapered plug 22 define an upper chamber 76 and a lower chamber 78. A check valve assembly 80 is provided for the introduction of a sealant lubricant into the upper chamber 76 and said sealant lubricant may be introduced therein under pressure. The sealant lubricant as it flows into and fills the upper chamber 76 will also flow into axially extending grooves 82 and a circumferential groove 84. As ~;~
the name sealant lubricant implies, the material serves the dual purpose of lubricating the various operational parts of the valYe 10 while at the same time seals the plug with respect to the casing.
The annular rib 54 disposed on the casing 12 is provided with a radially extending port 53 intermediate the ends of said annular rib 54. The radially extending port 53 is in communication with a pressure relief screw arrangement 86. The pressure relief screw arrangement 86 includes a partially threaded cavity ~0 disposed within the casing 12.
Suitable stop meàns such as a solid spherical ball 88 is received within , ~ .
the threaded cavity 90 and is seated in said cavity 90 on a ball seat 55. The spherical ball 88 is maintained on the ball seat 55 in a sealed condition by a set screw 92 which is threadably received within the threaded cavity 90.
The present invention provides immunitY to the lockup phe-nomenon by the provision of dynamically balancing the plug 22 in the casing 12 when the plug 22 is partially or fully open, i.e., when the port 94 of the plug 22 is connected to and in communication with the passageway 96 through the casing 12. The dynamic balancing feature of the valve 10 is achieved by the provision of a first axially extending opening 98 in the plu3 22 connecting the port 94 to the lower chamber 78 and the provision of a second axially extending opening 100 in the plug 22 connecting the port 94 to the upper chamber 76. The opening g8 may be offset from the longitudinal axis of the plug 22 while the opening 100 may also be disposed from said longitudinal ax~s.
At this juncture, it can be seen that the pressure seen by the o port 94 when the plug 22 is in its partially open or fully open position is also simultaneously seen by the upper chamber 76 and the lower chamber 78. Accordingly, the pressure seen by the chambers 76 and 78 will also be seen by the smaller end 102 of the plug 22 and the larger ; end 104 of the plug 22, respectively. Hydraulic pressure exerted on the smaller end 102 and the larger end 104 of the plug 22 will tend to ; maintain the axial position of the plug 22 with respect to the tapered interface 24 within the casing 12 at all times even through pressure and temperature translent. However, there has been noted that there will tend to be a slight unequal pressure exerted toward the apex of the taper due to secondary forces such as the relatiYely large cross-sectional areas of the larger end 104 with respect to the smaller end of the plug as well as the unequal weight dis.tribution of the plug 22, i.e., the plug obviously is heavier at its larger end than at its smaller end.
Depending upon the position of the valve with respect to its associated line, gravlty therefore may also play a role in axially dislocating the plug 22 along ~ts longitudinal axis. To offset these secondary forces, a helically wound spring 106 ~hich may be disposed on the longitudinal axis of the plug 22 biases the pluy 22 along said longitudinal axis away from the apex of the taper. The spring 106 is mounted on an extension 108 of the stem and, as before mentioned, abuts and biases the plug 22.
Therefore, the plug 22 will see virtually no axially dislocating forces , .- ~ . . . i . . . .. .:.
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~ o~479 as it experiences pressure and temperature transient in its partially open or fully open position. The avoidance of such axial dislocation of the plug also avoids the lockup phenomenon in that the plug 22 maintains i:ts axial position within the casing 12 and is not driven into the taper and thus pinched by the casing after the stabilization of a pressure or temperature transient.
The second axially extending opening 100 is also provided with a spherical ball 110 seated therejn. The spherical ball, which is not biased by the spring 106, is free floating ~ithin the second axially extending opening and serves as a check valve, checking the flow of the sealant lubricant into the port 94 of the plug 22 when the sealant -~ lubricant is introduced into the upper chamber 76 under pressure.
; As before mentioned, the variou5 operational parts of the valve 10 may be assembled through the end of the casing through the opening covered by the end cap 14, i.e. the stem 18, thrust bearing and seal 50, equalizer ring 20, spring 106, spherical ball 110, plug 22, ;r' spherical plug thrust ball 34, etc. This configuration of the various " parts allows the valve stem seal 56 to be serviced while the Yalve is ;!' exposed to line pressure. More spec;fically, the seal 56 may be removed eYen though the valve 10 is connected to the line and under pressure.
This is achieved by the removal of the stop collar 70 from the stem 18 -~ and the removal of the stem cap 62 from the casing 12 by the removal of the Dolts 64. After the above noted parts are removed the seal 56 and stem rings are exposed and may be removed. At this point the primary seal is provided by the thrust bearing and seal 50. To ensure that the -i thrust bearing and seal 50 is operating properly so as to allow the `~ removal of the above noted face of the seal and its associated stem :-rings 60 and 62 the set screw 92 may be partially remoYed, therebyallowing the spherical ball 88 to unseat. The operator may immediately tell if the t~rust bearing and seal 5a is suitably sealing the stem at . . .. . . .

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r ~0~79 ; the complementary groove 52. If the thrust bearing and seal 50 is performing its function adequately, then the removal of the seal 62 can be intitated.
There is thus provided a uniquely configured plug valve 10 which may be maintained in place, that ts, when the plug valve is operationally connected to its associated line and exposed to line pressure. ~n particular, the plug valve 10, in accordance with the present invention, can have its primary sealing members removed from the valve casing 12 without any dtsruption to the flow through the valve 10.
Obviously, the present invention is not limited to the specific details as herein described, but is capable of other modifications and changes without departing from the spirit and scope of the appended . -clatms.

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Claims

WHAT IS CLAIMED IS:

1. A tapered plug valve comprising a casing having a passageway therethrough for flow of fluid and a tapered bore inter-secting said passageway, a taper plug rotatably mounted in said tapered bore adapted to block said passageway in valve closed position of said plug and said plug having a port adapted to connect and be in communi-cation with said passageway in valve open position, said plug and casing defining a chamber at one end of said plug, a stem rotatably mounted within said casing and mechanically coupled to said plug to rotatably drive said plug, said casing having an annular rib surrounding said stem at one end of said chamber, said stem having an annular rim thereon and located on the portion of said stem which is in said chamber, an annular thrust bearing and seal surrounding said stem and abutting the opposed lateral faces of said annular rib and said annular rim to provide a seal therebetween.

2. A tapered plug valve in accordance with Claim 1 wherein said annular rib is further provided with an annular groove comple-mentary to said thrust bearing and seal for accepting said seal therein, said thrust bearing and seal remaining substantially stationary with respect to said casing, said seal being primarily provided by the opposed lateral faces of said thrust bearing and seal and said annular rim.

3. A tapered plug valve in accordance with Claim 2 wherein the width of said opposed lateral faces of said annular rim and said thrust bearing and seal are substantially equal.

4. A tapered plug valve in accordance with Claim 1 wherein a stem seal is provided in said casing surrounding said shaft above said annular rib, said stem seal removable from the top of said valve without disturbing the operational position of said thrust bearing and seal.

5. A tapered plug valve in accordance with Claim 4 wherein a radially extending port is provided in said annular rib, said radially extending port in communication with a pressure relief means for de-termining the sealing condition of said thrust bearing and seal.

6. A tapered plug valve in accordance with Claim 5 wherein said pressure relief means comprises a partially threaded cavity pro-vided in said casing in communication with said radially extending port, a stop means seated on a seat in said partially threaded cavity, said ball held in place on said seat by threaded screw member.

7. A tapered plug valve in accordance with Claim 5 wherein said radially extending port is located intermediate the ends of said annular rib, said threaded screw member adapted to be threadably removed from said partially threaded cavity.

8. A tapered plug valve in accordance with Claim 1 wherein said stem is coated with a self-lubricating plastic in the area of said annular rim.

9. A tapered plug valve in accordance with Claim 8 wherein said self-lubricating plastic is polytetrafluorethylene and said thrust bearing and seal is of stainless steel.