CN109984780B

CN109984780B - Sleeve assembly

Info

Publication number: CN109984780B
Application number: CN201711499511.2A
Authority: CN
Inventors: 孙宝峰; 马猛
Original assignee: Jiangsu Fengh Medical Equipment Co Ltd
Current assignee: Jiangsu Fengh Medical Equipment Co Ltd
Priority date: 2017-12-31
Filing date: 2017-12-31
Publication date: 2020-09-11
Anticipated expiration: 2037-12-31
Also published as: CN109984780A

Abstract

The invention discloses a cannula assembly, which comprises a tube body and a fixing part, wherein the tube body and the fixing part are integrally formed or mutually connected, the fixing part is arranged on the outer wall of the tube body, and the fixing part is used for connecting the tube body and a puncture body assembly. The sleeve assembly is used on the coreless puncture outfit, so that the coreless puncture outfit is convenient to use, the preparation cost of the whole puncture outfit is saved, and the packaging cost of the puncture outfit is also saved.

Description

Sleeve assembly

Technical Field

The invention relates to a surgical instrument, in particular to a sleeve assembly, and belongs to the field of medical equipment.

Background

The puncture outfit is used as an indispensable surgical instrument in various minimally invasive surgeries, and has a very large using amount. The traditional puncture outfit comprises a puncture core bar, a puncture sleeve and a sealing component, wherein the puncture sleeve and the sealing component jointly form a channel for the puncture core bar, other surgical instruments and the abdominal cavity of a patient to be inflated; the sealing assembly is arranged in the puncture sleeve and used for avoiding gas injected into the abdominal cavity from leaking out and ensuring stable pneumoperitoneum so as to carry out the operation normally, and the puncture core rod is inserted into the puncture sleeve through the sealing assembly and used for realizing puncture on the abdominal cavity of a patient and driving one end of the puncture sleeve to enter the abdominal cavity of the patient.

In the specific operation process, a doctor generally firstly cuts a small incision on the abdomen of a patient, then aligns the top of the puncture core rod with the small incision to reciprocate and move downwards, and drives one end of the puncture sleeve to enter the abdominal cavity of the patient. After the puncture is finished, the puncture core bar is pulled out of the puncture sleeve, and other procedural instruments can enter and exit from a channel formed by the puncture sleeve.

Due to the existence of the puncture core rod, the manufacturing, packing and transportation costs of the puncture device are increased, the puncture core rod is easy to damage the viscera, and the puncture core rod is discarded after being used, thereby causing waste.

Based on the above situation, on the basis of ensuring the puncture performance of the puncture outfit, the main improvement direction of the existing puncture outfit is to simplify the structure, reduce the cost and improve the performance.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a cannula assembly, which solves the problems that the puncture outfit in the prior art is high in manufacturing cost and packaging cost, and has certain potential safety hazard in puncture operation.

The invention is realized by the following technical scheme: the utility model provides a thimble assembly, includes pipe shaft and fixed part, the pipe shaft with the fixed part is integrated into one piece or interconnect, the fixed part sets up on the outer wall of pipe shaft, the fixed part be used for with the pipe shaft is connected with puncture body subassembly.

Preferably, the two ends of the pipe body are respectively a first end and a second end, the first end is selectively sealed by the sealing assembly, the second end is not closed, and the fixing part is arranged on the pipe wall of the second end of the pipe body.

Further, the fixing portion is disposed on an outer wall of the tube body.

Preferably, the fixing part is a receiving groove.

Preferably, a part of the outer wall of the tube body is recessed towards the inner cavity of the sleeve assembly to form a placing groove, the central axis of the placing groove is parallel to the central axis of the tube body, the bottom of the placing groove forms a notch towards the second end of the tube body, and the top of the placing groove forms an abutting surface with the tube body.

Further, the center axis of the accommodation groove is parallel to or overlaps with the center axis of the placement groove.

Further, the top of the accommodating groove overlaps with the top of the placement groove, and the length of the accommodating groove in the axial direction is smaller than the length of the placement groove in the axial direction.

Preferably, the second end of the pipe body is divided into a first side and a second side along the radial direction, the second side is higher than the first side, and the fixing part is arranged on the pipe wall of the first side.

Further, the second end first side bottom with the bottom on second side links to each other through the transition face, the transition face extends and includes first arc surface and second arc surface in proper order from first side direction second side, the radius of first arc surface is greater than the radius of second arc surface, first arc surface with the centre of a circle of second arc surface all faces the second side of second end.

Further, the second side outer wall surface of the second end of the sleeve assembly is an arc surface, the arc surface extends from the vertical pipe wall surface of the sleeve assembly to the second arc surface, the radius of the arc surface is larger than that of the second arc surface, and the circle center of the arc surface faces the first side of the second end. .

Compared with the prior art, the invention has the beneficial effects that: the sleeve assembly is used on the coreless puncture outfit, the puncture core rod is not arranged in the coreless puncture outfit sleeve assembly, the puncture body assembly is arranged on the pipe wall on one side of the sleeve assembly, when the puncture body assembly is in an initial state, the protective shell covers the bottom tip of the puncture rod, and when the puncture body assembly is in a puncture operation state, the protective shell slides to the top of the puncture rod and does not cover the bottom tip of the puncture rod. After the puncture body assembly realizes puncture, surgical instruments such as an anastomat and the like can directly enter through an internal channel formed by the sleeve assembly, and the use is convenient. And the design of the puncture body assembly not only saves the preparation cost of the whole puncture device, but also saves the packaging cost of the whole puncture device because the puncture body assembly does not influence the sealing assembly, and the puncture body assembly does not need to be packaged after being disassembled from the cannula assembly. In addition, the protective shell in the puncture body assembly can slide downwards to enable the puncture body assembly to be in an initial state when puncture is completed, and the protective shell covers the bottom tip of the puncture rod, so that the situation that the tip of the puncture rod is downward due to inertia or the puncture outfit rotates to hurt internal organs in the abdominal cavity of a patient when puncture is completed can be avoided, and the coreless puncture outfit has higher safety operability.

Drawings

FIG. 1 is a schematic diagram of an architecture according to an embodiment of the present invention;

FIG. 2 is an enlarged, fragmentary view of a second end of the coreless penetrator shown in FIG. 1;

FIG. 3 is a schematic view of the second end of a coreless puncture instrument with a protective sheath in an operative position, according to an embodiment of the present invention;

FIG. 4 is a schematic view of a second end of a cannula assembly according to an embodiment of the present invention;

FIG. 5 is a schematic view of the assembly of the penetration rod according to an embodiment of the present invention;

FIG. 6 is a cross-sectional view of the lancet assembly with the protective housing in an initial position according to an embodiment of the present invention;

fig. 7 is a cross-sectional view of the lancet assembly with the protective housing in the operative position according to an embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

As shown in FIG. 1, the present embodiment discloses a coreless puncture instrument, which includes a cannula assembly 1, a sealing assembly 2 and a puncture body assembly 3, the cannula assembly 1 defines a lumen (i.e., a passage for medical instruments during a surgical procedure) including a first end and a second end 12, the first end of the cannula assembly 1 is selectively sealed by the sealing assembly 2, and the first end (not shown) refers to an upper port of the cannula assembly 1, and particularly to a connection portion of the cannula assembly 1 and the sealing assembly 2. The second end 12 of cannula assembly 1 is provided with a piercing body assembly 3. "up" in this embodiment refers to a direction along the central axis of the tube assembly 1 towards the seal assembly 2. "lower" refers to the direction toward the lancet assembly 2 along the central axis of the cannula assembly 1, and the definition of "up" and "down" applies to all components of the coreless lancet of this embodiment. The central axis of the puncture body assembly 3 is parallel to the central axis of the cannula assembly 1, and the puncture body assembly 3 comprises a puncture rod 31 and a protective shell 32, wherein the puncture rod 31 is fixedly arranged on the outer wall of the cannula assembly 1. As shown in FIG. 5, the penetration rod 31 includes a top portion 311 and a bottom portion 312, the bottom portion 312 forming a piercing tip, and the bottom portion 312 of the penetration rod 31 protruding beyond the end face of the second end 12 of the cannula assembly 1. As shown in fig. 2 and 3, the protective shell 32 selectively covers the bottom 312 of the puncture rod 31, and the protective shell 32 is slidably connected to the cannula assembly 1 or the puncture rod 31.

In this embodiment, the puncture body assembly 3 is used to replace a conventional puncture core rod, thereby realizing the puncture function. The piercing body assembly 3 of the present embodiment may be adapted for use with any size cannula assembly 1. The protective shell 32 is slidable along the wall of the cannula assembly 1 and the penetration rod 31 to selectively cover the bottom 312 of the penetration rod 31. As shown in fig. 1 and 2, in the initial state, the protective case 32 of the coreless puncture instrument is in the initial position, covering the bottom 312 of the puncture rod 31. When a doctor uses the coreless puncture outfit of the embodiment, firstly, a small incision is made on the abdomen of a patient, then, the bottom end of the protective shell 32 of the coreless puncture outfit of the embodiment is aligned with the small incision, a downward force is applied to the coreless puncture outfit, the protective shell 32 slides upwards along the tube wall of the cannula assembly 1 under the blocking of the abdominal wall of the patient, as shown in fig. 3, the protective shell 32 is located at an operation position at the moment, namely, the protective shell 32 does not cover the bottom 312 of the puncture rod 31, the bottom 312 of the puncture rod 31 extends out of the protective shell 32 and protrudes out of the end surface of the second end 12 of the cannula assembly 1, and is aligned with the small incision to enter the abdominal cavity of the patient, and the second end 12 of the cannula assembly.

In order to ensure the passage space formed by the cannula assembly 1 for facilitating the operation of the surgical instrument, the puncturing body assembly 3 is disposed on the outer wall of the cannula assembly 1.

In one embodiment of the invention, the protective shell 32 is slidably connected to the puncture rod 31. In another embodiment of the present invention, the protective shell 32 is slidably connected to the cannula assembly 1, wherein one way of connecting the cannula assembly 1 is to provide a sliding track on the wall of the cannula assembly 1, and the protective shell 32 is provided in the sliding track, so as to achieve sliding. Of course, the sliding connection is not limited to the above and below, and those skilled in the art will appreciate that other sliding connections may be used without departing from the spirit of the invention.

The coreless puncture outfit of the embodiment adopts the puncture body component 3 to replace the traditional puncture core bar to realize the puncture function, and compared with the traditional puncture outfit, the coreless puncture outfit has simpler structure and lower cost. Meanwhile, the puncture body assembly 3 is directly arranged on the pipe wall of the sleeve assembly 1 and does not need to be inserted through the sealing assembly 2, so that the sealing performance of the sealing assembly 2 is not affected by the puncture body assembly 3 in the embodiment, the puncture body assembly 3 does not need to be disassembled during packaging, the puncture body assembly 1 is packaged after being disassembled, and the packaging space, the packaging cost and the transportation cost of a single puncture device are saved.

When the puncture is completed, since the protective casing 32 enters the abdominal cavity of the patient along with the puncture rod 31, the protective casing 32 is released and is no longer blocked by the abdominal wall, and the protective casing 32 moves downward along the tube wall of the cannula assembly 1 under the action of other external forces and gravity, returns to the initial position from the operating position, and covers the tip of the bottom 312 of the puncture rod 31 again. Therefore, even if some doctors with insufficient experience use the coreless puncture outfit in the present embodiment, the damage to organs in the abdominal cavity caused by downward inertia force when the tip 312 of the puncture rod 31 enters the abdominal cavity or by rotating the coreless puncture outfit during the operation can be effectively avoided, and the coreless puncture outfit in the present embodiment has higher safety and operability.

After the puncture is finished, other operations are not needed to be carried out on the puncture body assembly 3, and the surgical instruments such as an anastomat and tweezers required by the operation can be directly stretched into the abdominal cavity of the patient through the channel formed by the sleeve assembly 1 for the operation, so that the use is convenient. The puncture body assembly 3 in this embodiment is disposed on the outer wall surface of the cannula assembly 1, and the second end 12 of the cannula assembly 1 has an inner diameter substantially the same as the inner diameter of the passage above the cannula assembly 1, so as to facilitate the entry and exit of instruments.

Referring to fig. 1-4, in order to facilitate puncturing, the second end 12 of the cannula assembly 1 is divided into a first side 121 and a second side 122 along a radial direction, the second side 122 is higher than the first side 121, and the puncturing body assembly 3 is disposed on a wall of the first side 121. By "high" it is meant that the second side 122 is at a smaller distance from the first end of the tube assembly 1 than the first side 121 is at the first end of the tube assembly 1, i.e. the bottom end of the second side 122 is above the bottom end of the first side 121 when the tube assembly 1 is in the vertical position.

Specifically, in addition to being connected by the outer peripheral surface, the first side 121 and the second side 122 of the second end 12 of the cannula assembly 1 are also connected by a transition surface 123, the transition surface 123 extends from the first side 121 to the second side 122 and sequentially includes a first circular arc surface 123a and a second circular arc surface 123b, and the radius of the first circular arc surface 123a is larger than that of the second circular arc surface 123 b.

The outer wall surface of second side 122 of second end 12 of sleeve assembly 1 is an arc surface 124, and the arc surface 124 extends from the vertical wall surface of sleeve assembly 1 to second arc surface 123b, and the radius of arc surface 124 is greater than the radius of second arc surface 123 b. The centers of the first arc surface 123a and the second arc surface 123b face the second side 122 of the second end 12, and the center of the arc surface 124 faces the first side 121 of the second end 12. The smooth transition surface 123 and the arc surface 124 facilitate the entry of the second end 12 of the cannula assembly 1, and avoid the damage to the skin of the patient during the puncturing process.

During the puncturing process of the puncturing rod 31, the cannula assembly 1 is driven by the puncturing rod 31 to enter the abdominal cavity of the patient along the transition surface 123. The second side 122 of the second end 12 of the cannula assembly 1 is high relative to the first side 121 and the transition surface 123 extending from the first side 121 to the second side 122 is of a steep first and then flat form to facilitate the concentration of downward forces on the penetration rod 31 and the first side 121 of the second end 12 of the cannula assembly 1 during penetration. When transition surface 123 of cannula assembly 1 completely enters the interior of the abdominal cavity of the patient, cannula assembly 1 continues to enter the abdominal cavity along second side 122 outer wall arc surface 124 of second end 12, and due to the shape of transition surface 123 and second side 122 outer wall upper arc surface 124, second end 12 of cannula assembly 1 enters the abdominal cavity of the patient, the resistance of the abdominal wall to the puncture device is gradually increased at first, and then the resistance is reduced and kept stable, which is beneficial for the control of the puncture operation by the doctor in the operation.

As shown in fig. 4, the outer wall of the second end 12 of the cannula assembly 1 is recessed toward the inner lumen of the cannula assembly 1 to form a placement groove 125, an abutment surface (not shown) is formed on the side of the placement groove 125 away from the end surface of the second end 12, the other end of the placement groove 125 is opened toward the second end 12 of the cannula assembly 1, the puncture rod 31 is placed in the placement groove 125, and the tip 311 of the puncture rod 31 abuts against the abutment surface. The puncture rod 31, the placement groove 125 and the central axis of the cannula assembly 1 are axially aligned.

The shape of the placement groove 125 is preferably configured as a circular arc to facilitate accommodation of the puncture rod 31. In the process of realizing puncture, a downward force is applied to the coreless puncture outfit, the puncture rod 31 enters the abdominal cavity of the patient downwards, and the abutting surface abuts against the top 311 of the puncture rod 31 to prevent the puncture rod from moving towards the first end of the sleeve assembly 1.

Referring to fig. 2 and 4 to 7, in order to further prevent the puncture rod 31 from undesired movement during the puncturing process, especially from moving toward the first end of the cannula assembly 1, the puncture rod 31 sequentially comprises a first rod 31a and a second rod 31b along the direction from the top 311 toward the bottom 312, the outer diameter of the first rod 31a is smaller than the outer diameter of the second rod 31b, a receiving groove 126 with a closed upper end is formed on the wall surface of the first side 121 of the second end 12 of the cannula assembly 1, the outer diameter of the first rod 31a is smaller than the inner diameter of the receiving groove 126, the first rod 31a is disposed in the receiving groove 126, the outer diameter of the second rod 31b is larger than the inner diameter of the receiving groove 126, and the upper end surface of the second rod 31b abuts against the lower end surface of the receiving. The receiving slot 126 provides a secure connection of the puncture rod 31 to the cannula assembly 1, preventing the puncture rod 31 from moving during the puncturing procedure, and allowing forces to be concentrated at the puncturing tip at the base 312 of the puncture rod 31.

With reference to fig. 5 to 7, the puncture rod 31 of the present embodiment further includes a third rod 31c, and the first rod 31a, the second rod 31b and the third rod 31c are sequentially connected to each other, wherein an outer diameter of the third rod 31c is smaller than an outer diameter of the second rod 31b, and a first step 313 is formed at a connection portion of the second rod 31b and the third rod 31 c. The protective casing 32 in this embodiment is a hollow cylinder, and is sleeved outside the puncture rod 31, and the protective casing 32 sequentially includes a first protective section 32a and a second protective section 32b along a direction from the top 311 to the bottom 312 of the puncture rod 31, where the inner diameter of the first protective section 32a is slightly larger than the outer diameter of the second rod 31b, at least a portion of the second rod 31b is accommodated in the first protective section 32a, the inner diameter of the second protective section 32b is slightly larger than the outer diameter of the third rod 31c, a portion of the third rod 31c is accommodated in the second protective section 32b, the inner diameter of the second protective section 32b is smaller than the inner diameter of the first protective section 32a, a connecting portion between the second protective section 32b and the first protective section 32a forms a second step 321, the second step 321 is located below the first step 313, and an elastic element 33 is clamped between the first step 313 and the second step 321.

Specifically, the elastic element 33 is a spring, and the spring is disposed around the third rod 31 c. Of course, it is well known to those skilled in the art that the elastic element 33 may also take other forms of elements or other arrangements without departing from the spirit of the present invention, as long as elastic deformation is achieved between the first step 313 and the second step 321.

In particular, in order to limit the sliding distance of the protective case 32 and prevent the protective case 32 from falling off the puncture rod 31, a kidney-shaped displacement hole 314 is formed in the second rod 31b along the axial direction of the puncture rod 31, the positioning pin 34 passes through the displacement hole 314, the length of the positioning pin 34 along the second rod 31b is greater than the outer diameter of the second rod 31b and less than the outer diameter of the first protective section 32a, and both sides of the positioning pin 34 are fixedly connected to the protective case 32. Of course, the displacement hole 314 may have a rectangular or other elongated shape.

The puncture rod 31 in this embodiment is a three-stage type, and may be integrally formed or separately formed. Similarly, the protective shell 32 in this embodiment is two-segment, and may be integrally formed or separately formed.

As shown in fig. 5 and 6, when the elastic member 33 covers the tip of the bottom 312 of the puncture rod 31 in the initial position, i.e., the spring in this embodiment, is in the natural original state, the positioning pin 34 is located at the bottom of the displacement hole 314. As shown in fig. 7, during puncturing, the protective shell 32 moves towards the top 311 of the puncturing rod 31 under the resistance of the abdominal wall, the positioning pin 34 also moves towards the topmost part of the displacement hole 314 in the kidney-shaped hole, meanwhile, the second step 321 moves upwards, the distance between the first step 313 and the second step 321 is shortened, the spring contracts, the tip end of the bottom 312 of the puncturing rod 31 protrudes out of the protective shell 32, and the axial length of the displacement hole 314 and the stroke of the spring limit the movable distance of the protective shell 32 and prevent the protective shell 32 from moving upwards excessively. When the puncture is completed, the protective shell 32 enters the inside of the abdominal cavity along with the puncture rod 31, the protective shell 32 returns to the initial position under the action of the self gravity and the spring elasticity, the spring also returns to the original natural state, and the positioning pin 34 falls back to the bottommost part 312 of the displacement hole 314.

The distance of the protective shell 32 moving upwards is limited by the positioning pin 34, and meanwhile, the elastic force is added in the displacement process of the protective shell 32, so that when puncture is completed, the protective shell 32 can timely return to the initial position, the top end of the bottom 312 of the puncture rod 31 is coated, and the puncture rod is prevented from damaging visceral organs in the abdominal cavity, therefore, the arrangement mode of the puncture rod 31 and the protective shell 32 further improves the safety of the coreless puncture device in the embodiment.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; may be mechanically coupled, may be electrically coupled or may be in communication with each other; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A cannula assembly is characterized by comprising a cannula body and a fixing part, wherein the cannula body and the fixing part are integrally formed or mutually connected, the fixing part is arranged on the outer wall of the cannula body, and the fixing part is used for connecting the cannula body and a puncture body assembly; the two ends of the pipe body are respectively a first end and a second end, the first end is selectively sealed by a sealing assembly, the second end is not closed, and the fixing part is arranged on the pipe wall of the second end of the pipe body.

2. The ferrule assembly of claim 1, wherein the retention portion is a receiving groove.

3. A cannula assembly as set forth in claim 2, wherein a portion of the outer wall of the shaft is recessed toward the cannula assembly lumen to form a slot having a central axis parallel to the central axis of the shaft, a bottom of the slot forming a notch toward the second end of the shaft, and a top of the slot forming an abutment surface with the shaft.

4. A block of bushings according to claim 3, characterized in that the central axis of the receiving groove is parallel or overlapping with the central axis of the placing groove.

5. The block of bushings of claim 4, wherein the top of the receiving groove overlaps the top of the placement groove, the receiving groove having a length in the axial direction that is less than the length of the placement groove in the axial direction.

6. A block of bushings according to claim 1, characterized in that the second end of the shaft is radially divided into a first side and a second side, the second side being higher than the first side, the anchoring portion being arranged on the wall of the first side.

7. A block of bushings according to claim 6, characterized in that the bottom end of the first side of the second end is connected to the bottom end of the second side by a transition surface extending from the first side to the second side and comprising in sequence a first arc surface and a second arc surface, the radius of the first arc surface being larger than the radius of the second arc surface, the centre of the first arc surface and the centre of the second arc surface both facing the second side of the second end.

8. A block of casing as claimed in claim 7, wherein the second outer sidewall surface of the second end of the casing is a curved surface extending from the vertical wall of the casing to the second arcuate surface, the curved surface having a radius greater than a radius of the second arcuate surface, the center of the curved surface being toward the first side of the second end.