GB2298024A

GB2298024A - Plug valve assembly

Info

Publication number: GB2298024A
Application number: GB9600630A
Authority: GB
Inventors: David Lamarr Bowers; Robert Joseph Brown; Royce Chaffin; Donnie Ray Hammock; Gerald Patrick Mcdermott
Original assignee: Duriron Co Inc
Current assignee: Flowserve Corp
Priority date: 1995-02-16
Filing date: 1996-01-12
Publication date: 1996-08-21
Also published as: DE19605332A1; GB9600630D0; GB2298024A8; CN1136148A

Description

PLUG VALVE ASSEMBLY 2298024

Background of the Invention

The present invention relates generally to plug valve assemblies, and more specifically, to plug valve assemblies employing metal encapsulated valve seats.

Users of valves have long desired a valve which is capable of satisfactory sealability at higher pressure drops and temperatures. Higher pressure drops place more stress upon the seals or seats inside the valve. As a result, the valve seals begin to leak or fail completely (a condition known as "blow- out,'). To remedy such problems, current higher pressure operations often use plug-type valves.

Plug valves are frequently adjustable and, thus, can be compensated for leakage. To provide greater sealability, most plug valves employ,soft" or plastic seats. Soft seats allow for greater sealability between the seat and the plug, thereby preventing leakage. However, soft seats, while providing a greater degree of sealability, increase the problem of blow-out.

Due to the lower rigidity of soft seats, they commonly suffer blow-out at higher or throttling pressures.

To prevent blow-out of soft seats, they are commonly reinforced by a pair of spines or ribs extending outwardly from the chamber wall on either side of the flow channel. These spines or ribs hinder the ability of pressure from the fluid passing through the flow channel from pushing out the soft seats and causing blow-out. However, inclusion of spines or projections from the chamber wall prevents the chamber wall from being easily machined, leaving the chamber wall with a rougher as-cast surface.

A rougher chamber surface requires greater sealing loads which in turn contributes to the major drawback of plug valves in modern applications, i.e. turning torque. Modernization in many production facilities has led to automation of valve operation. Valve automation requires, an actuator to turn the valve stem between an open and closed position. As actuators represent a significant portion of the cost of an actuated package, the larger the actuator required, the greater the expense. Unfortunately, due to a rougher chamber surface and the amount of surface contact between the plug and the seat supports, plug valves have an rather large amount of friction, increasing the necessary turning torque an actuator need apply to turn the valve stem. Consequently, when plug valves are employed, larger actuators and greater costs are required.

Additionally, a rough, as-cast chamber wall hinders potential sealability of the valve. Thus, traditional plug valves must increase torque levels to acheive sealability. That is, a machined or smooth chamber wall allows for improved sealability between the valve seats and the chamber wall. Clearly then, a plug valve having a machined smooth surface without increasing torque or sacrificing blowout protection is desirable.

U.S. Patent 3,199,835 to Freed discloses the traditional, and still most popular, type of plug valve for chemical processing purposes. In Freed, a sleeve liner fits into the interior of the chamber and functions to seal the plug. The sleeve liner also provides a smooth surface for sealability between the plug and sleeve. However, a sleeve liner contacts the plug on all sides as it surrounds the entirety of the plug. This drastically increases the amount of required turning torque due to the increased surface area in contact. Further, the valve includes ribs to prevent blow-out of the sleeve. Thus, the chamber wall is a rough, as-cast, surface thereby increasing the valve's torque.

U.S. Patent 3,360,236 to Huslander discloses a different type of plug valve seat. The seat in Huslander comprises a thin flexible core of a material such as steel with a sealing material, such as polyurethane, bonded thereto. The seat fits into grooves on the plug and rotates with the plug rather than remaining in a fixed position. However, it appears from the figures that the seat in Huslander is not encapsulated in it's entirety. Rather, only the edges have been coated with a plastic material. Further, the seat is thin and flexible, providing littl e or no support against blow-out. And, the seat rotates with the plug in pair of grooves in the plug surface. Grooves in a machined surface, such as the plug in a valve, are difficult and exceedingly expensive to machine.

Accordingly, a need exists for a plug valve and a seat therefore which substantially reduces the required turning torque of the valve while still providing superior sealability and protection against leakage and blow-out of the valve seats.

Summarv of the Invention This need is met by the present invention wherein an improved plug valve assembly having reduced turning torque with superior sealability and protection against seat blow-out is provided. The plug valve assembly of the present invention substantially reduces the required turning torque while maintaining sealability by providing a chamber wall capable of being machined to a smooth surface. Turning torque is also reduced by eliminating the sleeve liner insert favored by the prior art.

In accordance with the present invention, a plug valve assembly is provided. The plug valve assembly includes a valve body having an internal chamber, a plug disposed in said internal chamber and seat members for supporting the plug. The internal chamber is defined by an inner wall. Preferably, the inner wall has a substantially smooth, machined surface, allowing reduced turning torque and greater sealability. Most preferably, the machined surface has a smoothness value of about 125 rms to about 1 rms.

is The seat members function to both support the plug and to seal the valve. The seat members preferably comprise a rigid support frame encapsulated in a polymeric material. but may also be formed of a metal or ceramic material. In the preferred seat members, the rigid support is preferably a metal frame and the polymer is preferably a melt-processable polymer, such as a fluoropolymer. The seat members have a sealing surface with both the inner wall of the chamber and with the plug.

The seat members have a sealing surface with both the inner wall and the plug. The sealing surface with the plug may have a vertical taper of from about 11 to about 80. The plug then has a vertical taper corresponding to the vertical taper of the sealing surface. In addition, the sealing surface with the inner wall may also have a vertical taper on the order of 10 or 8' with the inner wall having a corresponding vertical taper.

The valve assembly may further include locking members disposed in the chamber for preventing substantial horizontal, vertical or rotational movement of the seat members. Thus, seat members are fixed in location in the present invention. Ideally, the locking members are depressions formed in the inner wall of the chamber. The plug valve assembly further includes an adjustment mechanism. The adjusting mechanism adjusts the plug vertically within the seat members thereby adjusting for leakage. Accordingly, it is an object of the present invention to provide an improved plug valve assembly with reduced turning torque while maintaining superior sealability and protection against blow-out. It is a feature of the present invention to provide a plug valve assembly having seat members comprising a rigid support frame encapsulated in a polymeric material. It is a further feature of the present invention to provide a plug valve assembly having a substantially smooth, machined inner chamber wall. other objects, features and advantages of the present invention will be apparent from the following description, the accompanying drawings and the claims.

Brief Description of the Drawings

Figure 1 is a sectional side view of the plug valve of the present invention, taken longitudinally through the center of the valve.

Figure 2 is a sectional top view of the plug valve of the present invention taken along line 2-2 in Fig. 1.

Figure 3 is a sectional side view of an additional embodiment of the present invention.

Figure 4 is a top view of the plug valve of the present invention.

Figure 5 is a front view of a preferred seat member of the present invention.

Figure 6 is a sectional top view of preferred seat member of the present Invention.

Detailed DescrilDtion of the Present Invention The present invention comprises an improved plug valve assembly. The plug valve assembly has reduced turning torque while maintaining sealability due to a substantially smooth machined valve chamber. Further, the plug valve assembly of the present invention has superior protection from blow-out due to the use of plastic encapsulated rigid seat members. Referring to Figs. 1 and 2, there is seen the plug valve assembly 10 of the present invention. The plug valve 25 comprises a valve body 12 with an internal chamber 14. A plug 16 is disposed within the chamber 14. Seat members 20 are disposed in the chamber for supporting the plug as well as sealing the valve. An adjustment mechanism 22 provides adjustability to the present invention. 30 Valve body 12, as well as plug 16 and most other items unless otherwise decribed, is formed of rigid alloy material, such as a metallic alloy, plastic or other composite material. Alternatively, valve body 12 may be internally coated with a corrosion resistant polymer such as polytetrafluoroethylene thereby providing support as well as corrosion resistance. Valve body 12 includes, along with chamber 14, flow channel 24. Flow channel 24 extends longitudinally through the entirety of valve body 12 thereby providing a passage for fluid flow. Valve body 12 may assume various configurations as desired for functionality as well as aesthetics.

Internal chamber 14 is preferably substantially tubular. However, those skilled in the art will recognize that various other shapes may also be employed and remain within the scope of the invention. Chamber 14 includes inner wall 26. Inner wall 26 may be vertically tapered to participate in vertical adjustment of the valve 10. By vertical taper it is intended that the upper portion 28 of the chamber is wider or greater in circumference than the lower portion 30. Preferably the vertical taper of chamber 14 is substantially conical in nature. That is, when viewing chamber 14 from above, the chamber appears as a cone with the upper portion 28 greater in circumference than lower portion 30. However, the vertical taper may also be a flat taper with only the sides 32 of chamber 14 in sealing contact with seat members 20 being tapered. The degree of the vertical taper, as are all other vertical tapers referred to in this specification, is measured from a vertical plane through the center of chamber 14. As will be hereinafter described, the vertical taper of inner wall 26 will correspond to the vertical taper of a sealing surface 23 with inner wall 26 and is from about 10 to about 80, preferably from about 10 to about 40, and most preferably about 20.

Internal chamber 14 and specifically inner wall 26 preferably has a substantially smooth, machined surface as opposed to the as-cast surfaces of the prior art. In other words, rather than leaving inner wall 26 with a rougher surface resulting from the casting or formation of the valve, inner wall 26 may be machined to provide a substantially smooth surface. This potential machinability is made possible due to the absence of projections such as spines or ribs extending outwardly from the chamber surface, as is common in the prior art.

A substantially smooth, machined surface significantly reduces the required turning torque of the present invention. Further, a smooth machined surface provides for greater sealability between seat members 20 and the inner wall 26. The need for sleeve-type valve seats is eliminated. Preferably, the inner wall 26 of the present invention is machined to a smoothness value of from about 125 to about 1 rms.

Plug 16 is disposed within internal chamber 14. Plug 16 may also be coated with a corrosion-resistant polymer. Plug 16 has a orifice 34 passing through the entirety of the plug. Orifice 34 may also be internally coated with a corrosionresistant polymer such as polytetrafluoroethylene. Plug 16 is adapted for rotation between open and closed positions. Plug 16 contains a top portion 18 to rotate the ball between the open and closed positions. T op portion 18 extends outside of valve body 12 so that external rotation of plug 16 is possible. When plug 16 is rotated to the open position as shown in section A of Fig. 2, orifice 34 is in alignment with flow channel 24 so that fluid is free to pass through both orifice 34 and flow channel 24. when plug 16 is rotated to the closed position as shown in section B of Fig. 2, orifice 34 is out of alignment with flow channel 24 so that plug side walls 36 block channel 24 and prevents the flow of fluid through the valve.

Returning to Fig. 1, plug 16 is held into chamber 14 by means of a top cap or bonnet 42. Meanwhile, bonnet 42 is held into position by fasteners 44 as seen in Fig. 3. Fas'teners 44 can be any common fastener suitable for the purpose such as screws, bolts, pins, etc. Preferably, fasteners 44 are screws. Fasteners 44 and bonnet 42 hold plug 16 in chamber 14 without preventing free- movement of the plug. That is, plug 16 remains free to rotate between open and closed positions. Further, plug 16 remains free to be vertically adjusted within the seat members 20. A sealing arrangement is then employed to.seal the valve top portion 18 to the valve body 12 and prevent leakage. Such arrangements may include O-rings, stem packings, bellows seals and preferably, a diaphragm 46. Diaphragm 46 can be any suitable diaphragm for sealing purposes, but is preferably a reverse-lip diaphragm of a plastic material such as a polytetrafluoroethylene. Of course, one of ordinary skill in the art will recognize that various arrangements may be employed in the present invention to prevent leakage around valve top portion 18.

Plug 16 is supported by seat members 20 disposed within chamber 14. Seat members 20 serve the dual purpose of supporting plug 16 as well as sealing valve 10. Seat members 20 seal the valve by providing two sealing surfaces, one with the inner wall 26 and one with plug 16. Seat members 20 are preferably encapsulated with a polymeric material 50 and are, thus, of a soft seat type from the sealing standpoint. Soft seats provide a superior sealing surface to metal or ceramic seats. Additionally, soft seats require lower turning torque than metal or ceramic seats. However, for selective applications, such as high temperatures, seat members 20 may be formed of a metal or ceramic material. Of course, one of skill in the art will recognize that various seat members and configurations may be employed within the scope of this invention.

Turning to Figs. 5 and 6, there is seen the preferred seat members 20 of the present invention. Seat members 20 are substantially rectangular in nature. Seat members also include flange portions 64. Seat members 20 have a sealing surface 21 with the plug 16 and a sealing surface 23 with the inner wall 26.

The sealing surface 21 with plug 16 is preferably vertically tapered on the order of from 1' to about C, and more preferably from about 21 to about 40. Plug 16 is then vertical tapered to correspond to the taper of sealing surface 21. This allows plug 16 to be forced into the taper of seat members 20 by adjustment mechanism 22 thereby tightening both the seal. As plug 16 is forced downward into the seat members 20 into a narrower taper, seat members 20 have have a higher load or pressure applied to them. Thus, seat members 20 exert more outward force on the 5 sealing surfaces, creating a tighter seal.

In addition, the sealing surface 23 with inner wall 26 may also be provided with a vertical taper of from 11 to about 8', and more preferably from about 20 to about 40. Inner wall 26 may then be provided with a corresponding vertical taper, thereby allowing for tightening of the sealing surface 23 when plug 16 is adjusted vertically in seat members 20..

Traditional soft plug valve seats have not afforded protection against blow-out. Once the pressure drop of the valve is elevated by throttling or other means, the seats begin to leak or fail completely. To solve the problem of blow-out, spines or ribs were extended from inner wall 26 on either side of flow channel 24 to prevent the soft seats from blowing out. However, such extensions prevented the machinability of inner wall 26. Thus, turning torque was increased due to the much rougher as- cast surface. The seat members 20 of the present invention provides superior protection against seat blow-out, without increasing turning torque.

The preferred seats of the present invention comprise a support frame 52 of a rigid material encapsulated with a polymeric material 50 to provide a soft seat. That is, the support frame 52 is completely encased or covered on all surfaces in a polymeric material 50. The rigid support frame 52 may be of any suitable material such as iron, various other metal compositions and ceramics. Support frame 52 is completely encapsulated with the polymeric material 50. In this fashion, both the sealing surfaces with plug 16 and inner wall 14 have the benefit of a soft seal. Yet, the support frame 52 provides the rigidity the seats require to protect against blow-out. Thus, the seats of the present invention provide support against blow- out without sacrificing sealability. Again however, for certain applications such as higher temperatures, metal and ceramic seats may be employed.

The polymeric material of the present invention is preferably a melt -processable polymer. Melt -processable polymers are well-known. Examples of polymers suitable for such a purpose include various members the fliioropolymer family, particularly, Teflon PFAI TeflonIFEP and TefzelVall available from DuPont de Nemours & Co. of Wilmington, DE as well as Ryto available from Phillips Petroleum of Bartlesville, OK.

Preferably, the valve 10 of the present invention includes locking members 60 disposed in internal chamber 14. Turning to Fig. 2, there is seen locking members 60 disposed within chamber 14. Locking members 60 prevent substantial horizontal, vertical or rotational movement of seat members 20 within the chamber. Thus, seat members 20 are fixed within the cahmber 14. By substantial movement it will be recognized that a minimal amount of movement is possible without departing from the scope of the invention. Rather, the purpose of locking mechanism 60 is to prevent seat members 20 from leaving the position in which they will provide a sealing arrangement with plug 16.

Locking members 60 are preferably depressions 62 disposed in the sides of chamber 14 into which flange portion 64 of seat members 20 extend. By disposing depressions 62 in both sides of chamber 14 and extending seat members 20 into the depressions via flange portion 64, horizontal, vertical or rotational movement in either direction is prevented or minimized.

The valve 10 of the present invention is externally adjustable to compensate for leaks in the valve due, in part, to seat wear or increased pressure. The adjustment mechanism 22 of the present invention involves applying or reducing force on pplug 16, thereby manipulating the plug 16 vertically within the seat members 20. Application of force wedges plug 16 further into the vertical taper of sealing surface 21,. thereby applying an increased load on the sealing surface 21 and tightening the seal. Pressure on the sealing surface 21 then transfers through seat members 20 and is applied to sealing surface 23 thereby sealing the surface between inner wall 26 and seat members 20. One of ordinary skill in the art will, of course, recognize that various arrangements may be employed with which plug 16 may be adjusted within seat members 20, and that the adjustment mechanism described herein is merely a preferred embodiment of the adjustment mechanism 22.

Turning to Fig. 1, there is seen adjustment mechanism 22. Adjustment mechanism 22 comprises an adjuster 66 adapted to apply pressure to plug 16. Adjuster 66 is preferably formed as a wedge shaped collar as shown in Fig. 1. As seen in Fig. 4, adjuster 66 further includes a tab 74 extending upwardly. Tab 74, in conjunction with stop collar 76 prevents top portion 18 and consequently, plug 16 from over rotating when turning and potentially damaging seat members 20. As seen in Fig. 4, stop collar 76 is attached to top portion 18 and is preferably formed as a ring with a quarter-section removed. As plug 16 is rotated, stop collar 76 is correspondingly rotated. Tab 74 then limits the range of motion of stop collar 76 and top portion 18 to that within the removed quarter- section.

Returning to Fig. 1, adjuster 66 is preferably adapted to press against plug 16 through the use of thrust collar 68. Thrust collar 68 allows uniform pressure to be applied to plug 16. To increase the applied pressure as well as maintain the amount of pressure applied, fasteners 70 can be manipulated to apply a load through adjuster 66 to thrust collar 68. Fasteners 70 preferably comprise screws which pass through adjusting plate 66 and into bonnet 42. Fasteners 70 can be externally tightened to increase the pressure applied to thrust collar 68 and consequently plug 16.

As fasteners 70 are manipulated, adjuster 66 is drawn against thrust collar 68 thereby increasing the pressure applied to thrust collar 68 and transferring the applied load. Hollow space 72 provides an area of movement for thrust collar 68. As the load transferred to thrust collar 68 is increased, load is transferred through diaphragm 46 to plug 16. In this fashion, adjusting mechanism 22 is capable of externally adjusting valve 10. Of course, one of skill in the art will recognize that the above described adjustment mechanism is merely the preferred mechanism and that variations are possible while remaining within the scope of the invention.

Accordingly, the plug valve of the present invention provides significant improvements over valves of the prior art. The valve of the present invention allows a substantially smooth surface machined into the inner wall of the chamber, if desired. This provides for reduced required turning torque and greater sealability. Further, the valve of the present invention employs valve seats comprising a rigid support frame encapsulated with a polymeric material. This allows for the elimination of spines or ribs extending from the inner wall of the chamber, and preventing the valve seats from blowing out. Which in turn, allows for the aforementioned machinability of the chamber.

Having described the invention in detail and by reference to the preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention which is defined in the appended claims.

1

Claims

1. A plug valve assembly comprising:

a valve body having an internal chamber formed therein, said chamber being defined by an inner wall; a plug disposed within said chamber and adapted to rotate said plug between open and closed positions; seat members disposed in said chamber for supporting said plug; locking members disposed in said chamber fixing said seat members in position thereby preventing substantial horizontal, vertical or rotational movement of said seat members; and an adjustment mechanism for adjusting said plug vertically within said fixed seat members.

2. The plug valve assembly as claimed in claim 1 wherein said inner wall of said chamber is a smooth, machined surface.

3. The plug valve assembly as claimed in claim 2 wherein said smooth, machined surface has a smoothness value of from about 125 rms to about 1 rms.

4. The plug valve assembly as claimed in claim 1 wherein said seat members comprise a rigid support frame encapsulated with a polymer material.

5. The plug valve assembly as claimed in claim 4 said seat members comprise a metal support frame encapsulated with a meltprocessable polymer.

6. The plug valve assembly as claimed in claim 5 wherein said meltprocessable polymer is a fluoropolymer.

7. The plug valve assembly as claimed in claim 1 wherein said seat members comprise metal or ceramic material.

8. The plug valve assembly as claimed in claim 1 wherein said seat members have a sealing surface with said inner wall of said chamber and a sealing surface with said plug.

9. The plug valve assembly as claimed in claim 8 wherein said sealing surface of said seat members with said plug has a vertical taper and said plug has a corresponding vertical taper.

10. The plug valve assembly as claimed in claim 8 wherein said sealing surface of said seat members with said inner wall has a vertical taper and said inner wall has a corresponding vertical taper.

11. The plug valve assembly as claimed in claim 9 wherein the vertical taper of both said plug and said sealing surface is from about 10 to about 80 as measured from a vertical plane.

12. The plug valve assembly as claimed in claim 10 wherein the vertical taper of both said inner wall and said sealing surface is from about 10 to about 80 as measured from a vertical plane.

13. The plug valve assembly as claimed in claim 1 wherein said locking members are depressions formed in the inner wall of said chamber.

-is- 14. A plug valve assembly comprising:

a valve body having an internal chamber formed therein, said internal chamber being def ined by an inner wall; a plug disposed within said chamber and adapted to rotate said plug between open and closed positions; seat members disposed in said chamber for supporting said plug, said seat members comprising a rigid support frame encapsulated in a polymeric material; locking members disposed in said chamber for fixing said seat members in position thereby preventing substantial horizontal, vertical or rotational movement of said seat members; and, an adjustment mechanism for adjusting said plug vertically within said fixed seat members.

is. The plug valve assembly as claimed in claim 14 said seat members comprise a metal support frame encapsulated with a melt-processable polymer.

16. The plug valve assembly as claimed in claim 15 wherein said melt proces sable polymer is a fluoropolymer.

17. The plug valve assembly as claimed in claim 14 wherein said inner wall of said chamber is a smooth, machined surface.

18. The plug valve assembly as claimed in claim 17 wherein said smooth, machined surface has a smoothness value of from about 125 rms to about 1 rms.

19. The plug valve assembly as claimed in claim 14 wherein said seat members have a sealing surface with said inner wall of said chamber and a sealing surface with said plug.

11 20. The plug valve assembly as claimed in claim 19 wherein said sealing surface of said seat members with said plug has a vertical taper and said plug has a corresponding vertical. taper.

21. The plug valve assembly as claimed in claim 19 wherein said sealing surface of said seat members with said inner wall has a vertical taper and said inner wall has a corresponding vertical taper.

22. The plug valve assembly as claimed in claim 20 wherein the vertical taper of both said plug and said sealing surface is from about 10 to about 80 as measured from a vertical plane.

23. The plug valve assembly as claimed in claim 21 wherein the vertical taper of both said inner wall and said sealing surface is from about 10 to about 80 as measured from a vertical plane.

24. The plug valve assembly as claimed in claim 14 wherein said locking members are depressions formed in the inner wall of said chamber.

25. A plug valve assembly as claimed in claim 1 and substantially as hereinbefore described.

26. A plug valve assembly as claimed in claim 14 and substantially as hereinbefore described.

27. A plug valve assembly substantially as hereinbefore described with reference to any of Figures 1 to 4 of the accompanying drawings.

28. A plug valve assembly comprising a seat member substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.