This disclosure relates generally to control valves and, more particularly, to apparatus and methods to align a closure member and a valve stem.
Control valves (e.g., linear valves, rotary valves, etc.) are commonly used in process control systems to control the flow of process fluids. Linear valves such as, for example, a gate valve, a globe valve, a diaphragm valve, a pinch valve, etc. typically have a valve stem (e.g., a sliding stem) that drives a closure member (e.g., a valve plug) disposed in a path of fluid between an open position and a closed position.
In some known control valves, a valve stem is threadably coupled to a closure member (e.g., a valve plug) via threads at a threaded opening of the closure member such that the valve stem is oriented substantially perpendicular to the closure member. In other known control valves, the valve stem is welded to the closure member. In yet other known control valves, the valve stem and the closure member are integrally formed (e.g., via injection molding) as a substantially unitary or single piece. However, manufacturing tolerances, installation misalignment and other factors, can cause misalignment (e.g., an axial misalignment and/or a concentric misalignment) between the valve stem and the closure member when coupling the valve stem to the closure member via threads, welding, and/or integrally forming (e.g., via injection molding) the stem with the closure member as a substantially unitary or single structure.
In operation, a misalignment of the valve stem and the closure member can cause seat leakage (i.e., undesired leakage passing through the valve when the valve is in the fully closed position due to a misalignment of the closure member and the valve seat). Furthermore, the misalignment of the valve stem and the closure member can cause the valve stem to slide against an inner bore of a packing system causing packing distortion and/or wear, which may cause leakage of process fluid through the pressure barrier. Although a packing system can typically be field serviced (e.g., removed and replaced), such service usually requires time consuming and/or difficult removal of a valve actuator and/or other components from the valve.
An example valve described herein includes a stem and a closure member having a first aperture to receive at least a portion of the stem. The valve further includes a positioning member having a first portion and a second portion. The first portion has a first cross-section and the second portion has a second cross-section that is greater than the first cross-section. An area between the first portion and the second portion forms a positioning surface to engage the first aperture of the closure member to align the stem and the closure member. A fastening member couples the stem to the closure member.
In another example, a closure member and valve stem for use in a valve includes a first aperture of the closure member to receive at least a portion of the valve stem. A shoulder disposed along a length of the valve stem or a positioning member engages the first aperture of the closure member. Engagement of the shoulder or the positioning member with the first aperture substantially axially aligns the valve stem and the closure member. A fastening member couples the stem to the closure member.
In general, an example closure member (e.g., a plug) and valve stem assembly described herein may be used with valves having a sliding stem such as, for example, control valves, throttling valves, on/off valves, etc. An example closure member and valve stem assembly includes a valve stem coupled to a closure member via a fastening member. In particular, a positioning member engages an aperture of the closure member to align the valve stem and the closure member when coupled together with the fastening member.
The positioning member includes a first portion having a first cross-section and a second portion having a second cross-section that is larger than the first cross-section. An area between the first portion and the second portion forms a positioning surface that engages an aperture of the closure member to align the valve stem and the closure member. In this manner, the example closure member and valve stem assemblies described herein can achieve both axial and concentric alignment of a valve stem and a closure member. Axial and concentric alignment of a valve stem and a closure member may reduce packing distortion and/or wear (i.e., minimize valve stem contact against an inner bore of the packing) and provide a substantial alignment of the closure member and the valve seat to provide a tight seal (i.e., prevent seat leakage). Furthermore, the example closure member and valve stem assembly described herein also facilitates disassembly of the valve stem and closure member for field repair or replacement of the valve stem and/or closure member. Additionally, the example closure member and valve stem assembly described herein may be provided as a factory installed option or, alternatively, can be retrofit to existing valves in the field.
Before describing the example closure member and valve stem assembly, a brief discussion of a known pneumatically actuated control valve is first provided in connection with
As described above, the valve stem 108 and the valve plug 112 may be integrally formed as a single piece or structure, or may be formed in separate pieces for connection by common fastening methods. Also, as discussed above, rigidly coupling a valve stem to a closure member can lead to axial and concentric misalignment of valve stem and closure member, which may cause undesired leakage (e.g., due to misalignment of a closure member and a valve seat) and/or packing distortion or wear (i.e., a misaligned valve stem sliding against an inner bore of a packing material).
The example closure member and valve stem assemblies 200, 300, and 400 illustrated in
The valve stem 204 can include a positioning member 205, which may be integrally formed with the valve stem 204 as a substantially unitary piece or structure. To integrally form the positioning member 205, the valve stem 204 can include a first portion 224 having a first cross section, a segment of which may be a threaded segment 226, and a second portion 230 having a second cross-section that is greater than the first cross-section of the first portion 224. In the illustrated example, the first and second cross-sections are circular or substantially circular. However, in other example implementations, the first and second cross-sections can be polygonal (e.g., square, rectangular, etc.).
As depicted in the illustrated example, an area between the first portion 224 and the second portion 230 forms a positioning surface 228. In the example illustration, the positioning surface 228 is a shoulder that is formed along a length of the valve stem 204 that transitions the second portion 230 to the first portion 224. In the illustrated example, the shoulder 228 is a tapered surface, though a flat surface, a step-like surface, a rectangularly-shaped surface, or any other shape could be formed instead. When the valve stem 204 is coupled to the closure member 202, the shoulder 228 engages the second opening 220 of the closure member 202 to concentrically and axially align the valve stem 204 with the closure member 202.
Another example positioning member 232 is depicted as a tapered washer. The positioning member 232 has a first portion 237 having a first cross-section and a second portion 239 having a second cross-section that is greater than the first cross-section. The first and second cross-sections can be circular, square, rectangular, etc. An area between the first portion 237 and second portion 239 forms a positioning surface 240. In the illustrated example, the positioning surface 240 is depicted as a tapered surface that engages the first opening 216 when the fastening member 206 is fastened to the threaded portion 226 of the valve stem 204, thereby causing the valve stem 204 to concentrically and axially align with the closure member 202. Although the illustrated example shows a linearly tapered surface 240, any other shape such as, for example, a flat surface, a step-like surface, a curved surface, a rectangular surface, etc. may be used as well. The tapered washer 232 also includes an aperture 238 that slidably engages the valve stem 204.
The fastening member 206 couples the valve stem 204 to the closure member 202. As illustrated in
The cleft positioning member 244 also includes an aperture 246 that slidably engages the valve stem 204. The cleft positioning member 244 has a first portion 245 having a first cross-section and a second portion 247 having a second cross-section that is larger than the first cross section. The area between the first and second portions 245 and 247 forms a positioning surface 248 that engages the first opening 216 of the closure member 202. In the illustrated example, the positioning surface 248 is depicted as a tapered surface. However, in other example implementations, the positioning surface 248 can be a stepped-surface, a polygonal-surface, etc. Similar to the positioning member 232 of
Referring to
The closure member 302 may also include a second opening 318 at a second end 320 of the closure member 302. The first and the second openings 306 and 318 are substantially coaxially aligned with the aperture 304. As shown, each of the first and second openings 306 and 318 has a tapered surface. However, in other example implementations, the first and second openings 306 and 318 can be, for example, counterbores, stepped-surfaces, polygonal (e.g., rectangular) surfaces, etc., or any combination thereof. The closure member 302 can be made of steel, aluminum, or any other suitable material(s), and may be formed via machining, injection molding, or any other suitable process(es).
In the illustrated example, as the fastening member 234 is tightened, the positioning surface 228 of the positioning member 205 engages the second opening 318 and the positioning surface 248 of the cleft positioning member 244 engages the first opening 306 to cause the valve stem 204 to axially and concentrically align with the closure member 302. As described above, the cleft edge 250 collapses around the valve stem 204 to prevent the valve stem 204 from rotating due to vibration and/or other mechanical forces once the fastening member 234 has been tightened.
The shape of the positioning surfaces 240 or 248 can be substantially similar to the shape of the first openings 216 or 306 and/or the shape of the positioning surface 228 can be substantially similar to the shape of the second openings 220 or 318. For example, in the illustrated example, the angle of the tapered surface of the shoulder 228 is substantially similarly (i.e., is complementary) to the angle of the second opening 318, and the tapered surface 248 of the cleft positioning member 244 is angled substantially similar (i.e., is complementary) to the angle of the first opening 306. In this manner, the valve stem 204 is fastened to the closure member 302, and the positioning surfaces 228 and 248 of the positioning member 205 and the cleft positioning member 244 engage the first and the second openings 306 and 318 to enable alignment of the valve stem 204 and the closure member 302. In other example implementations, only a portion of the positioning surfaces 240 or 248 of the positioning members 232 or 244 engage a portion of the first openings 216 or 306 and/or the positioning surface 228 of the positioning member 205 engages a portion of the second openings 220 or 318.
In yet other example implementations, the shapes of the positioning surfaces can be substantially dissimilar relative to the shapes of the first openings 216 or 306. For example, the angle of the positioning surfaces 240 or 248 can be angled differently relative to the angle of the first openings 216 or 306. Likewise, the angle of the positioning surface 228 (e.g., the angle of the tapered shoulder) can be angled differently relative to the angle of the second openings 220 or 318. In this manner, the dissimilarly shaped surfaces (e.g., differently tapered surfaces) can still mate or engage to achieve both axial and concentric alignment (i.e., alignment of the valve stem 204 and closure member 302).
In yet other example implementations, the size of the positioning member 205 can be different relative to the openings 220 or 318, and/or the size of the positioning members 232 or 244 can be different relative to the openings 216 or 306. For example, the positioning member 232 or the cleft positioning member 244 can have a different diameter than the first openings 216 or 306 and/or the diameter of the positioning member 205 can have a different diameter than that of the second openings 220 or 318. Regardless of the differing diameters, the positioning members 232 or 244 may engage the first openings 216 or 306 and/or the positioning member 205 may engage the second openings 220 or 318 to align the valve stem 204 with the closure members 202 or 302. Such difference(s) in diameter(s) can be caused by, for example, manufacturing tolerances, wear and tear caused to the positioning member 232, the cleft positioning member 244, the first openings 216 or 306 of the closure member, etc.
Furthermore, the positioning surfaces 228, 240 and 248 can reduce misalignment caused during installation of the closure members 202 or 302 and the valve stem 204. If the closure members 202 or 302 are misaligned with the valve stem 204 during installation, the fastening member 234, when fastened or tightened, causes the positioning surfaces 240 or 248 to engage the surface of the first openings 216 or 306 and/or the positioning surface 228 to engage the surface of the second openings 220 or 318 to cause the valve stem 204 and the closure members 202 or 302 to align axially and concentrically.
Unlike known rigidly coupled valve stems and closure members, the positioning members 205, 232 and 244 engage with respective first and second openings 216 or 306 and 220 or 318 to cause the valve stem 204 and the closure members 202 or 302 to align both axially and concentrically, thereby substantially reducing or eliminating misalignment between the valve stem 204 and the closure members 202 or 302. The positioning surfaces 228, 240 and 248 substantially reduce or eliminate misalignment caused by manufacturing tolerances, installation misalignment, misalignment caused by varying diameters of the positioning members 205, 240 or 244, the valve stem 204, the closure members 202 or 302, etc.
The closure member 402 includes an aperture 408 to receive the valve stem 204 and may include an opening 410 (e.g., a tapered opening) at a first end 412 of the closure member 202 to engage the positioning surface 228 of the positioning member 205 when the valve stem 204 is coupled to the closure member 402. In this manner, engagement of the positioning surface 228 and the opening 410 concentrically and axially aligns the valve stem 204 with the closure member 402. The opening 410 is substantially coaxially aligned with the aperture 408. In the illustrated example, the opening 410 forms a tapered surface that engages the tapered surface of the shoulder 228 when coupled to the closure member 402. In other example implementations, the opening 410 can be, for example, a counterbore, a stepped-surface, a rectangularly shaped surface, etc., or any combination thereof and/or any other suitable shape to coaxially and concentrically align the valve stem 204 and closure member 402. The fastening member 234 couples the valve stem 204 to the closure member 402. Additionally or alternatively, in some example implementations, a washer 416 can be used with the fastening member 232.
Referring to
The example closure member and valve stem assemblies 200, 300, or 400 described herein advantageously maintain the orientation of the valve stem substantially perpendicular to the closure member to axially and concentrically align the valve stem and the closure member when assembled. In the illustrated examples, the positioning surfaces 228, 240, or 248 of the positioning members 205, 232, or 240 causes the valve stem 204 to axially and coaxially align with the closure members 202, 302, or 402. Engagement of the tapered surfaces 228, 240 or 248 cause the closure members 202, 302, or 402 and the valve stem 204 to align despite manufacturing tolerance variation and/or when installation misalignment between the closure member and valve stem occurs. The axial and concentric alignment, in turn, enables the closure members 202, 302, or 402 to properly align with a valve seat to provide a substantially tight seal to restrict or prevent the flow of process fluid through the orifice when the valve is in the fully closed position. Furthermore, the axial and concentric alignment minimizes the sliding movement of a valve stem against the inner bore of a packing, thereby reducing packing distortion and/or wear of the packing material.
Although certain methods and apparatus have been described herein, the scope of coverage of this patent is not limited thereto. To the contrary, this patent covers all methods and apparatus fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.