WO2018093384A1

WO2018093384A1 - Valve with friction reducing dimpled sealing surfaces

Info

Publication number: WO2018093384A1
Application number: PCT/US2016/062937
Authority: WO
Inventors: Peter K. Cheung; Peter R. EHLERS
Original assignee: FMC Technologies Inc
Current assignee: FMC Technologies Inc
Priority date: 2016-11-18
Filing date: 2016-11-18
Publication date: 2018-05-24
Anticipated expiration: 2019-05-18

Abstract

A valve includes a valve body, a flow bore extending through the valve body, first and second seat members positioned in the valve body across the flow bore, each of which has a corresponding seat bore aligned with the flow bore, and a closure member movably positioned between the seat members. The closure member has first and second sides each positioned opposite a corresponding one of the first and second seat members when the closure member is in a closed position. At least one of the first and second seat members includes a first sealing surface and at least one of the first and second sides includes a second sealing surface which, when the closure member is in the closed position, sealingly engages the first sealing surface preventing fluid flow through the flow bore. At least one of the first and second sealing surfaces comprises a plurality of dimples effective in reducing friction between the first and second sealing surfaces.

Description

VALVE WITH FRICTION REDUCING DIMPLED SEALING SURFACES The present disclosure is directed to a valve, such as a gate valve or a ball valve, which includes a closure member that is slidably disposed between two seat members. More particularly, the disclosure is directed to a valve in which the closure member or seat member has at least one sealing surface on which a plurality of friction-reducing dimples are formed.

BACKGROUND OF THE INVENTION

Gate valves and ball valves are used in a variety of industries to control fluid flow. For example, gate valves are used extensively in the oil and gas industry to control the flow of produced fluids at various stages of production. Most gate valves used in this industry comprise a valve body having a

longitudinal flow bore, a transverse gate cavity which intersects the flow bore, a pair of spaced apart seats which are mounted in the flow bore, and a closure member in the form of a gate which is slidably positioned between the seats and which includes a gate opening that extends transversely through the gate. The gate is movable by a variety of means between an open position in which the gate opening is aligned with the flow bore, and a closed position in which the gate opening is offset from the flow bore. In the closed position, the gate seals against the downstream seat to prevent fluid from flowing through the flow bore.

Typically, when the gate is in the closed position, the upstream side of the gate is exposed to the full working pressure of the fluid in the flow bore while the downstream side of the gate is at ambient pressure. This pressure differential generates a very high force pushing the gate against the downstream seat, which in turn results in significant friction between the gate and seat sealing surfaces. Prior art gate valves normally depend on flat, smooth sealing surfaces at the gate-to-seat interface to seal against the fluid pressure, and liquid lubrication is often required to minimize the friction between the gate and seat sealing surfaces when the gate is stroked between the closed and open positions. However, the smoothness of the gate and seat sealing surfaces can allow the liquid lubricant to be squeezed out or washed away during valve operation. The loss of lubricant can result in significant increases in valve friction and possible galling of the sealing surfaces.

Several options to reduce the friction between the gate and seat sealing surfaces have been used in the past. For example, a diamond-like carbon coating may be applied to the seat and/or gate sealing surfaces. However, this involves using a plasma vapor deposition process, which can be costly. Also, under very high load and temperature, the coating can wear rapidly. Further, the coating thickness is typically minimal, which may not be ideal for abrasive wear resistance, (e.g., resistance to sand slurry). Another option for reducing friction between the gate and seat sealing surfaces involves applying a low friction coating (made, e.g., from a solid lubricant such as molybdenum disulfide) to the seat and/or gate sealing surfaces. However, solid lubricants have limited service life due to high wear rates, and they lack the ability to flow and replenish the contact area between the seat and gate sealing surfaces. Another option for controlling friction between the gate and the seat sealing surfaces is to roughen the surfaces to promote lubricant retention. However, the most common methods of surface roughening (e.g., grinding or lapping) change 100% of the contact area, which can lead to higher contact stresses at the surface asperities and a subsequent increase in wear. Also, the surfaces polish themselves during running-in, which eventually reduces their ability to retain lubricant.

SUMMARY OF THE INVENTION

These and other disadvantages in the prior art are overcome by providing a valve which comprises a valve body; a flow bore which extends through the valve body; first and second spaced apart seat members which are positioned in the valve body across the flow bore, each seat member comprising a

corresponding seat bore which is aligned with the flow bore; and a closure member which is movably positioned between the seat members, the closure member being movable between an open position in which a through bore in the closure member is aligned with the seat bores and a closed position in which the through bore is offset from the seat bores, the closure member comprising opposite first and second sides which are each positioned opposite a

corresponding one of the first and second seat members when the closure member is in the closed position; wherein at least one of the first and second seat members comprises a first sealing surface and at least one of the first and second sides comprises a second sealing surface which, when the closure member is in the closed position, sealingly engages the first sealing surface to thereby prevent fluid from flowing through the flow bore; and wherein at least one of the first and second sealing surfaces comprises a plurality of dimples. In accordance with one embodiment, the dimples may comprise a semicircular cross section. Also, the dimples may be arranged in a generally circular pattern on said at least one of the first and second sealing surfaces.

Further, where at least one of the first and second sealing surfaces comprises an inner diameter and an outer diameter, the dimples may be arranged such that the number of dimples is greater closer to the outer diameter than the inner diameter.

In accordance with another embodiment, said at least one of the first and second sealing surfaces may be coated with a solid lubricant layer. The solid lubricant layer may be configured to follow the contour of the dimples.

Alternatively, the solid lubricant layer may be configured to completely fill the dimples.

In accordance with a further embodiment, said at least one of the first and second sealing surfaces may comprise a wear-resistant coating which is disposed over a substrate from which the corresponding seat or gate is

comprised, and the dimples may be formed in the wear-resistant coating. Also, the wear-resistant coating may be coated with a solid lubricant layer. Further, the solid lubricant layer may be configured to follow the contour of the dimples.

In accordance with yet another embodiment, the substrate may comprise a plurality of initial dimples, and the wear-resistant coating may be configured to follow the contour of the initial dimples to thereby form the dimples. Also, the wear-resistant coating may be coated with a solid lubricant layer. Further, the solid lubricant layer may be configured to follow the contour of the dimples.

The present disclosure is also directed to a method for reducing friction between sealing surfaces in a valve, the valve comprising first and second spaced apart seat members and a closure member which is movably positioned between the seat members, the closure member comprising opposite first and second sides which are each positioned opposite a corresponding one of the first and second seat members when the closure member is in a closed position, at least one of the first and second seat members comprising a first sealing surface and at least one of the first and second sides comprising a second sealing surface which, when the closure member is in the closed position, sealingly engages the first sealing surface, the method comprising forming a plurality of dimples on at least one of the first and second sealing surfaces.

In accordance with one embodiment, the method further comprises coating said at least one of the first and second sealing surfaces with a solid lubricant layer. Also, the solid lubricant layer may be configured to follow the contour of the dimples. Alternatively, the solid lubricant layer may be configured to completely fill the dimples.

In accordance with another embodiment, said at least one of the first and second sealing surfaces may comprise a wear-resistant coating which is disposed over a substrate from which the corresponding seat member or closure member is comprised, and the method may comprise forming the dimples in the wear-resistant coating. The method may also comprise coating the wear- resistant coating with a solid lubricant layer. The solid lubricant layer may be configured to follow the contour of the dimples. Alternatively, the solid lubricant layer may be configured to completely fill the dimples.

In accordance with a further embodiment, the step of forming a plurality of dimples on at least one of the first and second sealing surfaces may comprise forming a plurality of initial dimples on at least one of the first and second sealing surfaces, and configuring the wear-resistant coating to follow the contour of the initial dimples to thereby form the dimples. The method may further comprise coating the wear-resistant coating with a solid lubricant layer. The solid lubricant layer may be configured to follow the contour of the dimples. Alternatively, the solid lubricant layer may be configured to completely fill the dimples.

Thus, the valve of the present disclosure includes a closure member and/or a seat member having a sealing surface which comprises a plurality of dimples for reducing friction between the sealing surfaces when the gate is stroked between the closed and open positions. The dimples may comprise any practical configuration, such as hemispherical, and the dimple pattern may have a higher density of dimples towards the outer diameter of the sealing surface. The dimples aid in reducing friction between the sealing surfaces by acting as lubricant reservoirs and debris traps. The dimples may also promote micro- hydrodynamic lubrication between the sealing surfaces. These and other objects and advantages will be made apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers are used to denote similar

components in the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross sectional view of an example of a gate valve in which the gate and/or seat members are provided with the dimpled sealing surfaces of the present disclosure;

Figure 2 is a front perspective view of the seat member of the gate valve shown in Figure 1 ;

Figures 3-1 1 are cross sectional views of a portion of a gate member or seat member comprising dimpled sealing surfaces in accordance with additional embodiments of the present disclosure;

Figure 12 is a front elevation view of the seat member shown in Figure 2; Figure 13 is a front perspective view of the gate member of the gate valve shown in Figure 1 ;

Figure 14 is a front elevation view of the gate shown in Figure 13;

Figure 15 is a cross sectional view of an example of a ball valve in which the ball and/or seat members are provided with the dimpled sealing surfaces of the present disclosure;

Figure 16 is a front perspective view of the seat member of the ball valve shown in Figure 15;

Figure 17 is a front perspective view of the ball member of the ball valve shown in Figure 15;

Figure 18 is a front elevation view of the seat member shown in Figure 16; and

Figure 19 is a front elevation view of the ball member shown in Figure 17. DETAILED DESCRIPTION OF THE INVENTION

In general, the present disclosure is directed to a valve of the type which includes a closure member slidably disposed between two seat members. The valve includes a flow bore across which the seat members are positioned, and the closure member is movable between an open position and a closed position to thereby open and close the flow bore, respectively. The closure member comprises at least one sealing surface, and at least one seat member comprises a corresponding sealing surface, and when the valve is in the closed position, the closure member sealing surface engages the seat member sealing surface to thereby seal the flow bore. At least one of the closure member sealing surface and the seat member sealing surface is provided with a plurality of dimples which, among other functions, serve to reduce the friction between the closure member and the seat member when the closure member is moved from the closed position to the open position. Although the dimpled sealing surfaces may be incorporated into a variety of valves, for purposes of simplicity it will be described hereafter in the context of an exemplary gate valve and an exemplary ball valve.

An example of a gate valve in which the dimpled sealing surfaces may be incorporated in shown in Figure 1 . The gate valve, which is indicated generally by reference number 10, includes a valve body 12 having a flow bore 14 which extends longitudinally through the body and a gate cavity 16 which extends through the body generally transverse to the flow bore. The gate valve 10 also includes a pair of seat members in the form of seats 18a, 18b which are each positioned at least partially in a corresponding seat pocket that is formed at the intersection of the flow bore 14 and the gate cavity 16, and a closure member in the form of a gate 20 which is slidably positioned between the seats. Each seat 18a, 18b includes an axial seat bore 22a, 22b which is aligned with the flow bore 14 to thereby define a flow passage through the valve body 12. The gate 20 comprises opposite first and second sides 20a, 20b which when the gate is in a closed position are each positioned opposite a corresponding one of the seats 18a, 18b, and a gate opening or through bore 24 which extends transversely through the gate between the first and second sides.

The gate 20 is connected to a stem 26 which in turn is connected to a lifting mechanism 28. The lifting mechanism 28 forms no part of the present invention; accordingly, it may comprise any suitable manual or electrically or hydraulically operated device. The lifting mechanism 28 functions to raise and lower the gate 20 between an open position in which the through bore 24 is aligned with the seat bores 22a, 22b and fluid is therefore allowed to flow through the flow bore 14, and a closed position in which the through bore is offset from the seat bores and fluid is therefore blocked from flowing through the flow bore. The gate 20 comprises first and second closure member, or gate, sealing surfaces 30a, 30b which are formed on the opposite first and second sides 20a, 20b, respectively, and which, when the gate is in the closed position, as shown in Figure 1 , are positioned opposite corresponding first and second seat member, or seat, sealing surfaces 32a, 32b which are formed on the seats 18a, 18b, respectively. When the gate 20 is in the closed position and the pressure in the flow bore 14 upstream of the gate is greater than the pressure in the flow bore downstream of the gate, the upstream pressure will force the gate against the downstream seat 18a, 18b and thereby force the downstream gate sealing surface 30a, 30b into sealing engagement with the corresponding downstream seat sealing surface 32a, 32b to thereby prevent fluid from flowing through the flow bore.

As discussed above, when the gate 20 is in the closed position, the upstream side of the gate is exposed to the full working pressure of the fluid in the flow bore while the downstream side of the gate is often at ambient pressure. This pressure differential results in a very high force which pushes the gate 20 against the downstream seat 18a, 18b. The resulting friction at the gate-to-seat interface between the gate sealing surface 30a, 30b and the corresponding seat sealing surface 32a, 32b as the gate 20 is moved from the closed position to the open position can cause wear or galling of the sealing surfaces which in turn can reduce the sealing effectiveness of the gate valve 10.

Therefore, at least one of the gate sealing surfaces 30a, 30b or at least one of the seat sealing surfaces 32a, 32b is provided with a plurality of dimples to reduce the friction at the gate-to-seat interface as the gate 20 is moved from the closed position to the open position. Referring to Figure 2, for example, a plurality of dimples 34 are formed in the seat sealing surface 32a, 32b of one of the seats 18a, 18b. The dimples 34 may alternatively or in addition be formed on the gate sealing surface 30a, 30b of the gate 20, as will be described below.

The dimples 34 perform a number of functions. For example, the dimples 34 may serve as reservoirs for the lubricant which is applied between the sealing surfaces. In this regard, the dimples 34 can reduce adhesive friction between the sealing surfaces by providing additional lubricant through capillary action to any lubricant-depleted areas of the sealing surfaces. Also, the dimples 34 may serve as debris traps by providing spaces into which particles can fall during movement of the gate 20, which can reduce plowing friction caused by wear particle agglomeration or foreign particle (e.g., sand) ingestion. This can also improve sealing surface life by preventing the abrasive particles from scratching the sealing surfaces. Additionally, the dimples 34 may function as micro- hydrodynamic bearings between the sealing surfaces by promoting micro- hydrodynamic lubrication when relative motion between the sealing surfaces occurs. In this regard, it is believed that a pressure rise in the converging section of the dimple, caused by the wedge effect, may force the surfaces to separate at the microscopic level. It is recommended that the dimples be kept shallow (e.g., no deeper than 0.005 inch) in order to take advantage of the rapid increase in lubricant viscosity when the lubricant is subjected to extreme pressure.

A cross section through a single dimple 34 of a portion of a seat 18a, 18b or gate 20 is shown in Figure 3. In this embodiment, the seat or gate is made from a substrate 36 over which a relatively thick wear-resistant coating 38 is applied to form the sealing surface 30a, 30b, 32a, 32b. The substrate 36 may comprise any suitable material, such as, e.g., Inconel, alloy steel, or any corrosion-resistant alloy. The wear-resistant coating may comprise any appropriate material which is applied by any suitable method, such as, e.g., a thermal-sprayed or laser-cladded layer of tungsten carbide in a cobalt and chromium or nickel matrix.

During manufacture of the seat or gate in accordance with the present embodiment, an initial dimple 34' is formed in the substrate 36, and the wear- resistant coating 38 is then applied over the top of the substrate. The wear- resistant coating 38 is configured to follow the contour of the initial dimple 34' to thereby form the final dimple 34. As shown in Figure 3, the initial dimple 34' comprises a semicircular cross section, which tends to reduce any stress concentrations that the dimple may cause in the substrate 36. However, the initial dimple 34' could comprise any practical cross section which achieves the benefits disclosed herein. The initial dimple 34' may be created through any known process, such as ball nose cutting, ball end milling, electrical discharge machining, laser ablation, or indentation. The wear-resistant coating 38 applied over the top of the substrate 36 will follow the contour of the initial dimple 34', resulting in a smaller-diameter final dimple 34 in the sealing surface 30a, 30b, 32a, 32b. The larger size of the initial dimple 34' in the substrate 36 improves ease of manufacture, while the smaller size of the final dimple 34 in the sealing surface 30a, 30b, 32a, 32b is preferred for friction reduction. Also, the relatively even thickness of the wear-resistant coating 38 across the dimples 34', 34 may help avoid severe stress gradients within the coating, which can reduce the risk of coating spallation compared to a coating with uneven thickness. Aside from the friction-reducing benefits of the dimple 34 at the sealing surface 30a, 30b, 32a, 32b, the initial dimple 34' may also improve the bond strength between the wear- resistant coating 38 and the substrate 36 by providing a larger anchoring area for the wear-resistant coating. If desired, a layer of liquid or semi-solid lubricant, such as oil, grease or paste, may be applied over the top of the wear-resistant coating 38 for friction reduction.

Another embodiment is shown in Figure 4. This embodiment is similar to the embodiment shown in Figure 3. In the embodiment shown in Figure 4, however, a solid lubricant layer 40 is applied over the top of the wear-resistant coating 38. The solid lubricant layer 40 follows the contour of the dimple 34 to further reduce friction. The dimple 34 may also improve the adhesion of the solid lubricant layer 40 to the wear-resistant coating 38 by providing a larger anchoring area for the solid lubricant layer.

The solid lubricant layer 40 may be made of any suitable material, for instance diamond-like carbon or other chemicals such as graphite, molybdenum disulfide, hexagonal boron nitride, tungsten disulfide, or polytetrafluoroethylene. A combination of solid lubricants may be preferred for effective friction reduction under various environmental conditions, such as graphite for high humidity conditions, molybdenum disulfide or tungsten disulfide for low humidity

conditions, and polytetrafluoroethylene for conditions where capillary stiction is a concern. The solid lubricant may be applied using any appropriate method, such as burnishing, bonding, or vapor deposition. If desired, a layer of liquid or semisolid lubricant, such as oil, grease or paste, may be applied over the top of the solid lubricant layer 40 for initial friction reduction during valve running-in.

An alternative embodiment to that shown in Figure 4 is shown in Figure 5. In the embodiment of Figure 5, the solid lubricant layer 40 is applied so as to completely fill the dimple 34. In this embodiment, the dimple 34 initially acts as a solid lubricant reservoir rather than a debris trap. However, the dimple 34 will still act as a debris trap once the solid lubricant is depleted from the dimple during valve operation. A layer of liquid or semi-solid lubricant, such as oil, grease or paste, may be applied over top of the solid lubricant layer 40 for initial friction reduction during valve running-in.

Additional embodiments will now be described with reference to Figures 6-

1 1 . In the embodiment shown in Figure 6, no initial dimple 34' is formed in the substrate 36. Instead, the dimple 34 is formed directly in the wear-resistant coating 38. The dimple 34 may be created in the wear-resistant coating 38 via, e.g., electrical discharge machining or laser ablation.

In the embodiment shown in Figure 7, the dimple 34 is formed directly in the wear-resistant coating 38, such as in the embodiment of Figure 6, and a solid lubricant layer 40 is applied over the top of the wear-resistant coating 38 so as to follow the contour of the dimple, such as in the embodiment of Figure 4.

In the embodiment shown in Figure 8, the dimple 34 is formed directly in the wear-resistant coating 38, such as in the embodiment of Figure 6, and a solid lubricant layer 40 is applied over the top of the wear-resistant coating 38 so as to completely fill the dimple, such as in the embodiment of Figure 5.

In the embodiment shown in Figure 9, the substrate 36 of the seat or gate is not covered by a wear-resistant coating 38. Rather, the dimple 34 is formed directly in the substrate 36. In this embodiment, the substrate 36 may be made of a wear-resistant material such as a cobalt-chromium-carbide alloy. Also, the dimple 34 may be created through, e.g., ball nose cutting, ball end milling, electrical discharge machining, laser ablation or indentation.

The embodiment shown in Figure 10 is similar to the embodiment shown in Figure 9. In the embodiment of Figure 10, however, a solid lubricant layer 40 is applied over the top of the substrate 36 so as to follow the contour of the dimple 34, such as in the embodiment of Figure 4.

The embodiment shown in Figure 1 1 is likewise similar to the embodiment shown in Figure 9. In the embodiment of Figure 1 1 , however, a solid lubricant layer 40 is applied over the top of the substrate 36 so as to completely fill the dimple 34, such as in the embodiment of Figure 5.

The dimples 34 may be arranged on the sealing surface 30a, 30b, 32a, 32b in any practical pattern. One example of such a pattern is shown in Figure

12. In this embodiment, which shows a circular seat sealing surface 32a, 32b having an inner diameter 42 and an outer diameter 44, the dimples 34 are arranged in a generally circular pattern which is coaxial with the inner and outer diameters. This circular pattern can be beneficial for manufacturing simplicity and for instances where the sliding direction may change, such as if the seat rotates within the seat pocket during valve operation. Also, the dimples 34 may be arranged such that the pattern density is biased towards the outer diameter 44 of the sealing surface 32a, 32b (i.e., the number of dimples is greater closer to the outer diameter than the inner diameter of the sealing surface). This region experiences lower local bearing stresses and can better tolerate surface texture features than the region near the inner diameter 42.

Although the dimples 34 are shown in Figure 12 to be formed on a seat sealing surface 32a, 32b, they may alternatively or in addition be formed on a gate sealing surface 30a, 30b. Referring to Figures 13 and 14, for example, a plurality of dimples 34 may be formed on one or both sealing surfaces 30a, 30b of the gate 20. In this embodiment, the dimples 34 may be arranged in rows which are aligned longitudinally along the gate sealing surface 30a, 30b. Also, the dimples 34 may be arranged such that the pattern density is biased towards the regions where lubricant depletion is most likely to occur and where the local bearing stresses are low enough to tolerate surface texture features.

As mentioned above, the dimpled sealing surfaces may be incorporated into a variety of valves. Referring to Figure 15 for an additional example, the dimpled sealing surfaces are shown incorporated into an exemplary ball valve, generally 100. The ball valve 100 includes a valve body 102 comprising a flow bore 104 which extends transversely therethrough and a valve cavity 106 which intersects flow bore. Referring also to Figures 16 and 17, the ball valve 100 also includes a pair of seat members in the form of seats 108a, 108b. Each seat 108a, 108b is mounted in a corresponding seat retainer 1 10a, 1 10b which is positioned at the intersection of the flow bore 104 and the valve cavity 106, and each seat includes an axial seat bore 1 12a, 1 12b which is aligned with the flow bore 104. A closure member in the form of a ball 1 14 is rotatably positioned between the seats 108a, 108b. The ball 1 14 comprises generally diametrically opposite first and second sides 1 14a, 1 14b which when the ball is in a closed position are each positioned opposite a corresponding one of the seats 108a, 108b, and a through bore 1 16 which extends through the ball generally 90° offset from the first and second sides.

The ball 1 14 is connected to a stem 1 18 which in turn is connected to a turning mechanism 120. The turning mechanism 120 forms no part of the present invention; accordingly, it may comprise any suitable manual or electrically or hydraulically operated device. The turning mechanism 120 functions to turn the ball 1 14 between an open position in which the through bore 1 16 is aligned with the seat bores 1 12a, 1 12b and fluid is therefore allowed to flow through the flow bore 104, and a closed position (shown in Figure 15) in which the through bore is offset from the seat bores and fluid is therefore blocked from flowing through the flow bore.

The ball 1 14 comprises first and second closure member, or ball, sealing surfaces 122a, 122b which are formed on the first and second sides 1 14a, 1 14b, respectively, and which, when the ball is in the closed position, as shown in Figure 15, are positioned opposite corresponding first and second seat member, or seat, sealing surfaces 124a, 124b which are formed on the seats 108a, 108b, respectively. When the ball 1 14 is in the closed position and the pressure in the flow bore 104 upstream of the ball is greater than the pressure in the flow bore downstream of the ball, the upstream pressure will force the ball against the downstream seat 108a, 108b and thereby force the downstream ball sealing surface 122a, 122b into sealing engagement with the corresponding downstream seat sealing surface 124a, 124b to thereby prevent fluid from flowing through the flow bore.

Referring also to Figures 18 and 19, at least one of the ball sealing surfaces 122a, 122b or at least one of the seat sealing surfaces 124a, 124b is provided with a plurality of dimples 34 to reduce the friction at the ball-to-seat interface as the ball 1 14 is rotated from the closed position to the open position. As shown in Figures 16 and 18, the dimples 34 are arranged on the seat sealing surface 124a, 124b in a generally circular pattern which is generally concentric with the seat opening. Also, the pattern density of the dimples 34 may be biased toward the outer diameter of the seat sealing surfaces 124a, 124b and/or towards the regions where lubricant depletion is most likely to occur and where the local bearing stresses are low enough to tolerate surface texture features. The dimples 34 may alternatively or in addition be formed on one or both of the ball sealing surfaces 122a, 122b. As shown in Figures 17 and 19, the dimples may be arranged on the ball sealing surfaces 122a, 122b in a generally circular pattern, and the pattern density of the dimples may be biased towards the regions where lubricant depletion is most likely to occur and where the local bearing stresses are low enough to tolerate surface texture features. The dimples 34 may be formed using any of the techniques described above, and the sealing surfaces 122a, 122b, 124a, 124b may include any configuration of wear- resistant coating and/or solid lubricant layer depicted in Figures 3-1 1 .

It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.

Claims

What is Claimed is:

1 . A valve comprising:

a valve body;

a flow bore which extends through the valve body;

first and second spaced apart seat members which are positioned in the valve body across the flow bore, each seat member comprising a corresponding seat bore which is aligned with the flow bore; and

a closure member which is movably positioned between the seat members, the closure member being movable between an open position in which a through bore in the closure member is aligned with the seat bores and a closed position in which the through bore is offset from the seat bores, the closure member comprising opposite first and second sides which are each positioned opposite a corresponding one of the first and second seat members when the closure member is in the closed position;

wherein at least one of the first and second seat members comprises a first sealing surface and at least one of the first and second sides comprises a second sealing surface which, when the closure member is in the closed position, sealingly engages the first sealing surface to thereby prevent fluid from flowing through the flow bore; and

wherein at least one of the first and second sealing surfaces comprises a plurality of dimples.

2. The valve of claim 1 , wherein the dimples comprise a semicircular cross section.

3. The valve of claim 1 , wherein the dimples are arranged in a generally circular pattern on said at least one of the first and second sealing surfaces.

4. The valve of claim 3, wherein said at least one of the first and second sealing surfaces comprises an inner diameter and an outer diameter, and wherein the dimples are arranged such that the number of dimples is greater closer to the outer diameter than the inner diameter.

5. The valve of claim 1 , wherein said at least one of the first and second sealing surfaces is coated with a solid lubricant layer.

6. The valve of claim 5, wherein the solid lubricant layer is configured to follow the contour of the dimples.

7. The valve of claim 5, wherein the solid lubricant layer is configured to completely fill the dimples.

8. The valve of claim 1 , wherein said at least one of the first and second sealing surfaces comprises a wear-resistant coating which is disposed over a substrate from which the corresponding seat or gate is comprised, and wherein the dimples are formed in the wear-resistant coating.

9. The valve of claim 8, wherein the wear-resistant coating is coated with a solid lubricant layer.

10. The valve of claim 9, wherein the solid lubricant layer is configured to follow the contour of the dimples.

1 1 . The valve of claim 9, wherein the solid lubricant layer is configured to completely fill the dimples.

12. The valve of claim 8, wherein the substrate comprises a plurality of initial dimples, and wherein the wear-resistant coating is configured to follow the contour of the initial dimples to thereby form the dimples.

13. The valve of claim 12, wherein the wear-resistant coating is coated with a solid lubricant layer.

14. The valve of claim 13, wherein the solid lubricant layer is configured to follow the contour of the dimples.

15. The valve of claim 13, wherein the solid lubricant layer is configured to completely fill the dimples.

16. A method for reducing friction between sealing surfaces in a valve, the valve comprising first and second spaced apart seat members and a closure member which is movably positioned between the seat members, the closure member comprising opposite first and second sides which are each positioned opposite a corresponding one of the first and second seat members when the closure member is in a closed position, at least one of the first and second seat members comprising a first sealing surface and at least one of the first and second sides comprising a second sealing surface which, when the closure member is in the closed position, sealingly engages the first sealing surface, the method comprising:

forming a plurality of dimples on at least one of the first and second sealing surfaces.

17. The method of claim 16 further comprising coating said at least one of the first and second sealing surfaces with a solid lubricant layer.

18. The method of claim 17, further comprising configuring the solid lubricant layer to follow the contour of the dimples.

19. The method of claim 17, further comprising configuring the solid lubricant layer to completely fill the dimples.

20. The method of claim 16, wherein said at least one of the first and second sealing surfaces comprises a wear-resistant coating which is disposed over a substrate from which the corresponding seat member or closure member is comprised, and wherein the method comprises forming the dimples in the wear-resistant coating.

21 . The method of claim 20 further comprising coating the wear- resistant coating with a solid lubricant layer.

22. The method of claim 21 , further comprising configuring the solid lubricant layer to follow the contour of the dimples.

23. The method of claim 21 , further comprising configuring the solid lubricant layer to completely fill the dimples.

24. The method of claim 16, wherein the step of forming a plurality of dimples on at least one of the first and second sealing surfaces comprises:

forming a plurality of initial dimples on at least one of the first and second sealing surfaces; and

configuring the wear-resistant coating to follow the contour of the initial dimples to thereby form the dimples.

25. The method of claim 24 further comprising coating the wear- resistant coating with a solid lubricant layer.

26. The method of claim 25, further comprising configuring the solid lubricant layer to follow the contour of the dimples.

27. The method of claim 25, further comprising configuring the solid lubricant layer to completely fill the dimples.