A four-eccentric c-type ball valve

Abstract

This application relates to the technical field of ball valves and discloses a four-eccentric C-type ball valve, including a valve seat, a valve core, an upper valve stem, and a lower valve stem. The valve seat has a receiving cavity. The valve core is detachably connected to the upper and lower valve stems and rotatably connected within the receiving cavity. The upper valve stem is rotatably mounted on the valve seat, and the lower valve stem is mounted on the valve seat. The valve seat has a mounting hole communicating with the receiving cavity. A mounting plate for sealing the mounting hole is detachably connected to the valve seat. A movable structure is movably mounted on the valve seat, with a connecting strip and a support strip. The support strip supports the valve core. When the support strip abuts against the valve core, the movable structure drives the support strip to move along the flow path. This application uses the movable structure to remove the support strip from the mounting hole, achieving separation or installation of the valve core and valve seat, thereby reducing the possibility of damage to the valve core or valve seat during disassembly and installation.

Description

Technical Field

[0001] This application relates to the technical field of ball valves, and in particular to a four-eccentric C-type ball valve. Background Technology

[0002] The four-eccentric C-type ball valve is a rotary shut-off valve that abandons the traditional ball valve's positional sealing method that relies on squeezing and friction. During the rotation of the valve core, the sealing surfaces can completely disengage, achieving a wedge seal only at the final moment of closure, thus completely eliminating friction and wear.

[0003] Referring to the prior art CN119393551A, the ball valve includes a valve seat, a valve core, an upper valve stem, and a lower valve stem. The valve seat has a cavity for the valve core to rotate and a flow channel communicating with the cavity. The upper valve stem is rotatably mounted on the valve seat, and the lower valve stem is mounted on the valve seat. The valve core is detachably connected to the upper and lower valve stems. The valve seat has a mounting hole communicating with the cavity for the valve core to be mounted on the upper valve stem. The valve seat has a mounting plate for sealing the mounting hole.

[0004] When maintaining or replacing the valve core, the operator needs to first disassemble the upper valve stem and valve core, as well as the lower valve stem and valve core. The valve core needs to be moved in the direction of the medium outflow in the flow channel to completely detach the valve core from the flow channel, that is, the valve core is located in the receiving cavity. Then the valve core is taken out from the mounting hole.

[0005] For four-eccentric C-type ball valves used in large-diameter, high-pressure applications, the valve core is large and heavy, making the valve core replacement operation cumbersome. When moving the valve core, it is difficult for operators to accurately control the distance the valve core moves, making the valve core and the inner wall of the receiving cavity prone to accidental collision due to center of gravity shift or limited operating space. Such collisions can directly damage the precision sealing surface of the valve core or the sealing surface of the valve seat, resulting in a permanent decline in the sealing performance of the ball valve, and even the risk of scrapping the ball valve. Summary of the Invention

[0006] To address the issue of potential collisions between the valve core and valve seat during valve core installation, this application provides a four-eccentric C-type ball valve.

[0007] This application provides a four-eccentric C-type ball valve, which adopts the following technical solution: A four-eccentric C-type ball valve includes a valve seat, a valve core, an upper valve stem, and a lower valve stem. The valve seat has a receiving cavity. The valve core is detachably connected to the upper and lower valve stems and rotatably connected within the receiving cavity. The upper valve stem is rotatably mounted on the valve seat, and the lower valve stem is mounted on the valve seat. The valve seat has a mounting hole communicating with the receiving cavity. A mounting plate for sealing the mounting hole is detachably connected to the valve seat. A movable structure is movably mounted on the valve seat. The movable structure has a connecting strip, and the connecting strip has a support strip. The support strip and the movable structure are horizontally arranged, while the connecting strip is vertically arranged. The support strip supports the valve core. When the support strip abuts against the valve core, the movable structure drives the support strip to move along the flow path.

[0008] By adopting the above technical solution, the operator first removes the mounting plate from the valve seat and separates the upper valve stem and valve core. Then, the operator inserts the support bar into the mounting hole and extends it into the receiving cavity through the moving structure. After that, the operator separates the valve core and lower valve stem, so that the support bar can support the valve core. The operator moves the support bar in the receiving cavity through the moving structure, so that the valve core can move in the direction of medium flow out of the flow channel. The operator then removes the support bar from the mounting hole through the moving structure, realizing the separation or installation of the valve core and valve seat, reducing the possibility of accidental collision between the valve core and valve seat, so as to reduce the possibility of damage to the valve core or valve seat during disassembly and installation.

[0009] Optionally, the movable structure includes a first movable strip, an elastic element, and a second movable strip. The elastic element is disposed between the first and second movable strips, and the connecting strip is disposed on the second movable strip. The elastic element is used to drive the second movable strip to move in the direction of the first movable strip so that the support strip can be inserted into the mounting hole.

[0010] By adopting the above technical solution, an elastic element is set between the first and second moving strips, and the elastic element is used to drive the second moving strip to move in the direction of the first moving strip, so that the support strip can be smoothly inserted into the mounting hole. When the operator pulls the second moving strip away from the first moving strip, the support strip can be disengaged from the mounting hole, realizing the separation between the valve core and the valve seat.

[0011] Optionally, a mounting sleeve is rotatably connected to the valve seat, the movable structure is disposed on the mounting sleeve, a movable block is provided on the second movable bar, a limiting sleeve is fixedly connected to the valve seat, a first movable groove for the movable block to be inserted is provided on the limiting sleeve, and a second movable hole communicating with the first movable groove is provided on the limiting sleeve, the second movable hole for the movable block to pass through; when the movable block slides in the first movable groove, the supporting bar slides in the direction of the flow channel in the receiving cavity; when the movable block slides in the second movable hole, the supporting bar can disengage from the receiving cavity at the mounting hole.

[0012] By adopting the above technical solution, the operator rotates the mounting sleeve, causing the moving structure to move on the limiting sleeve. This allows the moving block to move along the direction of the first moving groove, and the support bar to slide along the flow channel within the receiving cavity. Then, the operator moves the second moving bar, allowing the moving block to move in the second moving hole, and the support bar to detach from the receiving cavity from the mounting hole, thus allowing the valve core to detach from the valve seat. The rotation of the mounting sleeve achieves the rotation of the moving structure, distributing the force borne by the moving structure to the mounting sleeve, and then to the valve seat. This increases the stability of rotating the mounting sleeve, making it less likely for the moving structure to move back and forth on the valve seat, and allowing the support bar to move stably within the receiving cavity.

[0013] Optionally, the valve seat is provided with a first flange, the mounting plate is provided with a second flange, the first flange is provided with a fastener, the fastener is used to fix the first flange and the second flange relative to each other, and the limiting sleeve is located on the side of the mounting sleeve near the receiving cavity, the limiting sleeve abuts against the first flange.

[0014] By adopting the above technical solution, the limiting sleeve is located on the side of the mounting sleeve close to the receiving cavity, and the limiting sleeve abuts against the first flange, so that the first flange can restrict the movement of the limiting sleeve, thereby allowing the moving block to slide stably in the first moving groove or the second moving hole, so as to realize the stable movement of the moving structure driving the support bar to move in the receiving cavity.

[0015] Optionally, the limiting sleeve is provided with a limiting block, the mounting sleeve is provided with a limiting groove, the limiting groove extends along the circumference of the valve stem, and the limiting block is slidably disposed in the limiting groove.

[0016] By adopting the above technical solution, the limiting block is slidably set in the limiting groove, allowing the mounting sleeve to rotate stably on the valve seat, further increasing the reliability of the mounting sleeve's rotation; and the friction between the limiting block and the wall of the limiting groove restricts the rotation of the mounting sleeve, reducing the possibility of the mounting sleeve rotating arbitrarily.

[0017] Optionally, the elastic element includes an elastic spring and an elastic strip, the elastic strip being disposed between the first moving strip and the second moving strip, and the elastic spring being sleeved on the elastic strip.

[0018] By adopting the above technical solution, the elastic spring is sleeved on the elastic strip, allowing the second moving strip to move towards or away from the first moving strip, so as to facilitate the insertion or removal of the support strip from the receiving cavity.

[0019] Optionally, the elastic strip is a polygonal prism, and the second movable strip has a receiving groove for inserting the elastic strip. A rotating disk is rotatably connected to the second movable strip, and the end of the elastic spring away from the first movable strip is fixedly connected to the rotating disk. When the support strip is in the receiving cavity, the elastic strip is in the receiving groove. When the support strip abuts against the valve seat, the elastic strip is in the receiving groove.

[0020] By adopting the above technical solution, when the support bar is located in the receiving cavity, the operator pulls the second moving bar to allow the elastic bar to disengage from the receiving groove, thereby detaching the valve core supported by the support bar from the receiving cavity. Then, the operator removes the valve core from the support bar. Next, the operator rotates the second moving bar. Since the elastic bar has a polygonal prism structure, it can be inserted into the receiving groove at a different angle, allowing the support bar to be removed from the receiving cavity. This also allows the support bar and connecting bar to abut against the valve seat, enabling them to retract onto the outer surface of the valve seat, reducing the possibility of damage to the support bar and connecting bar, and achieving a retracted state for the support bar and connecting bar.

[0021] Optionally, the support bar is provided with a support block, the valve core is provided with a limiting hole, the valve stem is provided with a limiting member for passing through the limiting hole, the limiting member is used to fix the valve stem and the valve core relatively, and the support block is used to be inserted into the limiting hole.

[0022] By adopting the above technical solution, the support block can be inserted into the limiting hole, which can restrict the valve core from shaking on the support bar, making the connection between the valve core and the support bar more stable and avoiding the situation where the support bar stops moving while the valve core continues to move due to inertia.

[0023] In summary, this application includes at least one of the following beneficial technical effects: First, the operator removes the mounting plate from the valve seat and separates the upper valve stem and valve core. Then, the operator inserts the support bar into the mounting hole and into the receiving cavity using a moving mechanism. Next, the operator separates the valve core and lower valve stem, allowing the support bar to support the valve core. The operator then moves the support bar within the receiving cavity using the moving mechanism, enabling the valve core to move in the direction of medium flow out of the flow channel. Finally, the operator uses the moving mechanism to remove the support bar from the mounting hole, thus separating or installing the valve core and valve seat. This reduces the possibility of accidental collisions between the valve core and valve seat, thereby minimizing the possibility of damage to the valve core or valve seat during disassembly and installation.

[0024] The operator rotates the mounting sleeve, causing the moving structure to move on the limiting sleeve. This allows the moving block to move along the direction of the first moving groove, and the support bar to slide along the flow channel within the receiving cavity. Then, the operator moves the second moving bar, allowing the moving block to move in the second moving hole, and the support bar to detach from the receiving cavity from the mounting hole, thus separating the valve core from the valve seat. The rotation of the mounting sleeve distributes the force on the moving structure to the mounting sleeve, which in turn distributes the force to the valve seat, increasing the stability of the rotating mounting sleeve and preventing the moving structure from shifting back and forth on the valve seat. This allows the support bar to move stably within the receiving cavity. Attached Figure Description

[0025] Figure 1 This is a structural schematic diagram of an embodiment of this application; Figure 2 It is along Figure 1 A partial sectional view of line AA in the middle; Figure 3 This is an exploded view highlighting the moving structure in the embodiments of this application; Figure 4 This is an exploded view of the limiting component in the embodiments of this application.

[0026] Reference numerals: 1. Valve seat; 11. Upper valve stem; 12. Lower valve stem; 13. Receiving cavity; 131. Flow channel; 132. Mounting hole; 133. Mounting plate; 14. First flange; 141. Second flange; 15. Valve core; 16. Limiting element; 161. Limiting hole; 2. Limiting sleeve; 21. Mounting sleeve; 22. Limiting block; 23. Limiting groove; 24. Moving structure; 241. First moving bar; 242. Elastic element; 243. Second moving bar; 244. Elastic bar; 245. Elastic spring; 246. Rotating disk; 247. Receiving groove; 25. Moving block; 251. First moving groove; 252. Second moving hole; 26. Connecting bar; 261. Support bar; 262. Support block. Detailed Implementation

[0027] The following is in conjunction with the appendix Figures 1-4 This application will be described in further detail.

[0028] This embodiment discloses a four-eccentric C-type ball valve. (Refer to...) Figure 1 A four-eccentric C-type ball valve includes a valve seat 1, a valve core 15, an upper valve stem 11, and a lower valve stem 12. The upper valve stem 11 is rotatably mounted on the valve seat 1, and the lower valve stem 12 is detachably connected to the valve seat 1. The valve core 15 is detachably connected to the upper valve stem 11 and the lower valve stem 12, and the valve core 15 is fixedly connected to the upper valve stem 11 and rotatably connected to the lower valve stem 12.

[0029] Reference Figure 1 The valve seat 1 has a receiving cavity 13 for the valve core 15 to rotate. The valve seat 1 also has a flow channel 131 communicating with the receiving cavity 13 for the medium to pass through. The valve seat 1 has a mounting hole 132 communicating with the receiving cavity 13. A mounting plate 133 is rotatably connected to the valve seat 1 and is used to block the opening of the mounting hole 132.

[0030] Reference Figure 1 A first flange 14 is integrally formed on the valve seat 1, and a second flange 141 is integrally formed on the mounting plate 133. The first flange 14 and the second flange 141 are installed and fixed by multiple bolts. When the mounting plate 133 blocks the mounting hole 132, the first flange 14 aligns with the second flange 141, thereby fixing the mounting plate 133 to the valve seat 1.

[0031] Reference Figure 2 A limiting sleeve 2 is fitted on the valve seat 1. The limiting sleeve 2 surrounds the end of the valve seat 1 near the upper valve stem 11. The surface of the limiting sleeve 2 away from the ground is coplanar with the surface of the first flange 14 away from the ground. An mounting sleeve 21 is fitted on the valve seat 1. The mounting sleeve 21 is rotatably connected to the end of the valve seat 1 near the upper valve stem 11, and the mounting sleeve 21 is located on the side of the limiting sleeve 2 away from the ground.

[0032] Reference Figure 2 A limiting block 22 is fixedly connected to the surface of the limiting sleeve 2 near the mounting sleeve 21. The limiting block 22 is annular and extends circumferentially along the end of the valve seat 1 near the upper valve stem 11. A limiting groove 23 is formed on the surface of the mounting sleeve 21 near the limiting sleeve 2, allowing the limiting block 22 to slide. The limiting groove 23 extends circumferentially along the end of the valve seat 1 near the upper valve stem 11 and is annular. When the limiting block 22 is located within the limiting groove 23, the limiting sleeve 2 is used to prevent accidental rotation of the mounting sleeve 21.

[0033] Reference Figure 2 and Figure 3A movable structure 24 is fixedly connected to the outer surface of the mounting sleeve 21. The movable structure 24 includes a first movable strip 241, an elastic element 242, and a second movable strip 243. The elastic element 242 is located between the first movable strip 241 and the second movable strip 243. The first movable strip 241 is fixedly connected to the outer surface of the mounting sleeve 21. The elastic element 242 includes an elastic strip 244 and an elastic spring 245. The elastic strip 244 is sleeved on the elastic strip 245. One end of the elastic strip 244 is fixedly connected to the end face of the first movable strip 241, and the other end of the elastic strip 244 is fixedly connected to a rotating disk 246. The rotating disk 246 is rotatably connected to the end face of the second movable strip 243 near the first movable strip 241.

[0034] Reference Figure 3 The elastic strip 244 is an octagonal prism, but in other embodiments it can be other polygonal prism structures. The second movable strip 243 has a receiving groove 247 on its end face near the first movable strip 241 for the elastic strip 244 to be inserted. The receiving groove 247 is a groove adapted to the elastic strip 244, and its cross-section is octagonal, that is, the elastic strip 244 is located in the receiving groove 247, and the second movable strip 243 cannot rotate.

[0035] Reference Figure 1 and Figure 3 A moving block 25 is fixedly connected to the surface of the second moving strip 243 near the limiting sleeve 2. The surface of the limiting sleeve 2 near the mounting sleeve 21 is provided with a first moving groove 251 and a second moving hole 252. The first moving groove 251 extends along the length direction of the flow channel 131, and the second moving hole 252 extends along the direction from the receiving cavity 13 to the mounting hole 132 to the outer surface of the limiting sleeve 2, and the second moving hole 252 penetrates to the outer surface of the second flange 141.

[0036] Reference Figure 1 and Figure 3 When the moving block 25 is located in the first moving groove 251, the support bar 261 can move along the direction of the flow channel 131. When the moving block 25 is located in the second moving hole 252, the support bar 261 can disengage from the valve seat 1 from the receiving cavity 13 toward the mounting hole 132.

[0037] Reference Figure 2 A connecting strip 26 is fixedly connected to the surface of the second moving strip 243, and the connecting strip 26 extends vertically. A support strip 261 is fixedly connected to the surface of the connecting strip 26, and the support strip 261 extends along the length of the second moving strip 243. The second moving strip 243, the connecting strip 26, and the support strip 261 form a C-shaped arrangement.

[0038] Reference Figure 2 and Figure 4A support block 262 is fixedly connected to the surface of the support bar 261 facing the second moving bar 243. The support block 262 has elastic deformation capability. A limiting member 16 is provided on the upper valve stem 11, and a limiting hole 161 is provided on the valve core 15 for the limiting member 16 to pass through. The limiting member 16 passes through the limiting hole 161 and is inserted into the upper valve stem 11, thereby fixing the valve core 15 and the upper valve stem 11 relatively. When the valve core 15 and the upper valve stem 11 are separated, the valve core 15 remains fixed in the valve seat 1 because it is still in a fixed state with the lower valve stem 12. This allows the support bar 261 to abut against the valve core 15, and the support block 262 to be inserted into the corresponding limiting hole 161, thereby fixing the support bar 261 and the valve core 15 relatively.

[0039] Reference Figure 1 , Figure 2 and Figure 3 The staff opened the mounting plate 133 and then rotated the second moving bar 243 to allow the support bar 261 to pass smoothly through the mounting hole 132 and be inserted into the receiving cavity 13, so that the support bar 261 could support the valve core 15. Then, the operator rotates the mounting sleeve 21, causing the mounting sleeve 21 to slide the support bar 261 within the receiving cavity 13 via the moving structure 24. The moving block 25 moves within the first moving groove 251, ensuring that the valve core 15 is completely located within the receiving cavity 13. Afterward, the operator pulls the second moving bar 243, causing the moving block 25 to move within the second moving hole 252. This allows the second moving bar 243 to move the support bar 261 via the connecting bar 26, thus disengaging the support bar 261 from the receiving cavity 13 and allowing the valve core 15 to be removed from the valve seat 1. Finally, the worker pulls the second moving bar 243, allowing the elastic bar 244 to disengage from the receiving groove 247. Then, the worker rotates the second moving bar 243, causing the connecting bar 26 to rotate from a vertical state to a horizontal state. After that, the elastic bar 244 is inserted into the receiving groove 247. At this time, the support bar 261 can abut against the outer surface of the mounting sleeve 21 and the outer surface of the valve seat 1, so that the connecting bar 26 and the support bar 261 are in a retracted state. The worker can then rotate the mounting plate 133 to seal the mounting hole 132.

[0040] The implementation principle of a four-eccentric C-type ball valve in this application embodiment is as follows: First, the operator rotates the mounting sleeve 21, causing the mounting sleeve 21 to slide the support bar 261 in the receiving cavity 13 via the moving structure 24. The moving block 25 moves in the first moving groove 251, so that the valve core 15 is completely located in the receiving cavity 13. Then, the operator pulls the second moving bar 243, and the moving block 25 moves in the second moving hole 252, so that the second moving bar 243 drives the support bar 261 to move via the connecting bar 26, so that the support bar 261 is disengaged from the receiving cavity 13, allowing the valve core 15 to be removed from the valve seat 1.

[0041] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," "third," and similar terms used in this application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. The terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "comprising" or "including" and similar terms mean that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including" and their equivalents, and do not exclude other elements or objects. "Above," "below," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0042] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the design concept of this application should be included within the protection scope of this application.

Claims

1. A four-eccentric C-type ball valve, comprising a valve seat (1), a valve core (15), an upper valve stem (11), and a lower valve stem (12), wherein the valve seat (1) has a receiving cavity (13), the valve core (15) is detachably connected to the upper valve stem (11) and the lower valve stem (12), the valve core (15) is rotatably connected to the receiving cavity (13), the upper valve stem (11) is rotatably disposed on the valve seat (1), the lower valve stem (12) is disposed on the valve seat (1), the valve seat (1) has a mounting hole (132) communicating with the receiving cavity (13), and a mounting plate (133) for sealing the mounting hole (132) is detachably connected to the valve seat (1), characterized in that: A movable structure (24) is movably disposed on the valve seat (1). A connecting strip (26) is provided on the movable structure (24). A support strip (261) is provided on the connecting strip (26). The support strip (261) and the movable structure (24) are arranged horizontally. The connecting strip (26) is arranged vertically. The support strip (261) is used to support the valve core (15). When the support strip (261) abuts against the valve core (15), the movable structure (24) is used to drive the support strip (261) to move along the direction of the flow channel (131).

2. The four-eccentric C-type ball valve according to claim 1, characterized in that: The movable structure (24) includes a first movable bar (241), an elastic element (242), and a second movable bar (243). The elastic element (242) is disposed between the first movable bar (241) and the second movable bar (243). The connecting bar (26) is disposed on the second movable bar (243). The elastic element (242) is used to drive the second movable bar (243) to move in the direction of the first movable bar (241) so that the support bar (261) can be inserted into the mounting hole (132).

3. A four-eccentric C-type ball valve according to claim 2, characterized in that: A mounting sleeve (21) is rotatably connected to the valve seat (1). The moving structure (24) is set on the mounting sleeve (21). A moving block (25) is provided on the second moving strip (243). A limiting sleeve (2) is fixedly connected to the valve seat (1). A first moving groove (251) for the moving block (25) to be inserted is opened on the limiting sleeve (2). A second moving hole (252) communicating with the first moving groove (251) is opened on the limiting sleeve (2). The second moving hole (252) allows the moving block (25) to pass through. When the moving block (25) slides in the first moving groove (251), the support strip (261) slides in the receiving cavity (13) along the direction of the flow channel (131). When the moving block (25) slides in the second moving hole (252), the support strip (261) can disengage from the receiving cavity (13) from the mounting hole (132).

4. A four-eccentric C-type ball valve according to claim 3, characterized in that: The valve seat (1) is provided with a first flange (14), the mounting plate (133) is provided with a second flange (141), the first flange (14) is provided with a fastener, the fastener is used to fix the first flange (14) and the second flange (141) relative to each other, the limiting sleeve (2) is located on the side of the mounting sleeve (21) close to the receiving cavity (13), and the limiting sleeve (2) abuts against the first flange (14).

5. A four-eccentric C-type ball valve according to claim 4, characterized in that: The limiting sleeve (2) is provided with a limiting block (22), and the mounting sleeve (21) is provided with a limiting groove (23). The limiting groove (23) extends circumferentially along the upper valve stem (11), and the limiting block (22) is slidably disposed in the limiting groove (23).

6. A four-eccentric C-type ball valve according to claim 2, characterized in that: The elastic element (242) includes an elastic spring (245) and an elastic strip (244). The elastic strip (244) is disposed between the first moving strip (241) and the second moving strip (243), and the elastic spring (245) is sleeved on the elastic strip (244).

7. A four-eccentric C-type ball valve according to claim 6, characterized in that: The elastic strip (244) is a polygonal prism. The second movable strip (243) has a receiving groove (247) for the elastic strip (244) to be inserted. A rotating disk (246) is rotatably connected to the second movable strip (243). The end of the elastic spring (245) away from the first movable strip (241) is fixedly connected to the rotating disk (246). When the support strip (261) is located in the receiving cavity (13), the elastic strip (244) is located in the receiving groove (247). When the support strip (261) abuts against the valve seat (1), the elastic strip (244) is located in the receiving groove (247).

8. A four-eccentric C-type ball valve according to claim 7, characterized in that: The support bar (261) is provided with a support block (262), the valve core (15) is provided with a limiting hole (161), the upper valve stem (11) is provided with a limiting member (16) for passing through the limiting hole (161), the limiting member (16) is used to fix the upper valve stem (11) and the valve core (15) relative to each other, and the support block (262) is used to be inserted into the limiting hole (161).

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