A well wash valve

Abstract

The utility model belongs to the method or device technical field of flushing wellbore, concretely relates to a kind of well flushing valve, including valve body and the upper joint and lower joint connected in the both ends of valve body, the center of valve body has flow passage, and there are several liquid outlet holes of communicating flow passage on valve body along its circumferential distribution, spring is loaded in flow passage for the valve core for isolating or communicating liquid outlet hole and flow passage, valve core includes valve rod and the pressure cap of detachable connection on valve rod, valve rod has the sealing end for sealing flow passage, and valve core further includes the sealing ring for sealing liquid outlet hole, and it is clamped between sealing end and pressure cap;Lower joint is equipped with the breathing passage for communicating the flow passage of valve body and the outside of valve body.The double sealing structure of flow passage sealing and liquid outlet hole sealing, and cooperate with the push of spring, enhance the reliability of valve core to flow passage and liquid outlet hole sealing, avoid well fluid leakage or impurity in well enters flow passage;Breathing passage can be set to balance the flow passage of lower part of valve core and the pressure of outside of valve body, eliminate dead space resistance in valve core movement.

Description

Technical Field

[0001] This utility model belongs to the technical field of methods or devices for flushing wells, and specifically relates to a well-washing valve. Background Technology

[0002] During oil extraction, as the ambient temperature and formation properties change, dissolved wax in the crude oil begins to precipitate and accumulate on the production tubing and sucker rod, causing sucker rod lag, well sticking, and other phenomena, affecting normal oil well production. Therefore, wax removal and prevention in oil wells is an essential measure in oilfield production operations. However, in practical applications, commonly used wax removal and prevention technologies have the following main problems: 1) Mechanical wax removal has a short effective period; for example, automatic cleaners, solid wax inhibitors, and temperature-controlled well-washing valves all have an effective period of less than one year; 2) Hot washing wax removal has a long working time, low efficiency, and cannot completely solve the problem of oil layer contamination after hot washing, resulting in a long drainage period, slow oil well production recovery, and even reduced production, significantly impacting oil well output; 3) Wax removal and prevention technologies have limitations in well selection, especially for wells with integral water-blocking tubing strings or leaking casings, where normal wax removal and prevention measures cannot be taken.

[0003] To address the aforementioned issues, the hollow sucker rod hot washing process establishes a positive circulation system within the wellbore tubing. A heat carrier (hot water, hot oil) or chemical agent is continuously or intermittently injected into the wellbore through the inner cavity of the hollow sucker rod. The heat carrier or chemical agent then exits through a one-way water-injection valve at the bottom of the hollow sucker rod, exiting through the annular space between the sucker rod and tubing. This circulation process increases the wellbore temperature, reduces crude oil viscosity, and eliminates wax deposits in the wellbore, thus maintaining normal well production. This method is characterized by its ability to perform well washing operations as needed without shutting down the well; its simple process; high thermal efficiency; low fluid consumption; low cost; and the fact that the washing fluid is not extracted through a deep well pump, thus not reducing the production rate. Furthermore, because the washing fluid does not come into contact with the oil reservoir, it avoids damage to the reservoir.

[0004] In the hot washing process of hollow sucker rods, a well-washing valve is required to establish a circulation channel. For example, Chinese invention patent application CN119860159A, published on April 22, 2025, discloses a hollow rod well-washing single-flow valve, which includes a valve seat and an inner valve seat (i.e., upper connector) and a connecting seat (i.e., lower connector) threaded to both ends of the valve seat. An inner valve ball seat (i.e., valve core) is movably inserted into the valve seat. A centralizing spring is provided on the connecting seat. A spring is sleeved on the outside of the centralizing spring. One end of the spring abuts against the inside of the inner valve ball seat, and the other end abuts against the connecting seat. The valve seat has multiple outlets arranged in a ring array. The inner valve ball seat includes a hemispherical sealing end and a circular tube connected to the sealing end. The outer wall of the circular tube is pressed and fitted against the inner wall of the valve seat. A sealing ring is movably inserted into the sealing end of the inner valve ball seat. In the initial state, under the action of the spring force, the inner valve ball seat closes the liquid outlet and isolates it from the internal liquid cavity of the valve seat; during use, when the inlet water pressure overcomes the force of the spring, the inner valve ball seat moves to open the liquid outlet, so that the liquid outlet and the internal liquid cavity of the valve seat are connected. In this design, the inner valve ball seat is pressed and fitted with the valve seat through a circular tube, causing the cavity formed by the inner valve ball seat, the valve seat, and the centralizing spring rod to a certain extent to become a "dead cavity." This increases the resistance to movement of the inner valve ball seat during the opening of the outlet, resulting in delayed response, delayed opening, or even inability to open. To avoid this phenomenon, there must be a certain gap between the inner valve ball seat and the valve seat. After well washing stops, the waxy well fluid will seep back into the valve seat from the outlet through this gap and condense on the surface of the inner valve ball seat to form a wax film, increasing the frictional resistance between the inner valve ball seat and the valve seat. At the same time, impurities in the well fluid will deposit in this gap, increasing the movement resistance of the inner valve ball seat, causing the inner valve ball seat to get stuck and unable to fully open or close the outlet. Utility Model Content

[0005] The purpose of this utility model is to provide a well-washing valve to solve the problem that in the prior art, there is a gap between the valve core and the valve seat of the well-washing valve. After long-term use, impurities or wax in the well fluid will deposit or condense in the gap, increasing the movement resistance of the valve core and easily causing the valve core to jam.

[0006] To achieve the above objectives, the well-washing valve of this utility model adopts the following technical solution: A well-washing valve includes a valve body and an upper connector and a lower connector connected to both ends of the valve body. The valve body has a flow channel at its center, and a plurality of liquid outlet holes communicating with the flow channel are evenly distributed along its circumference on the valve body. A valve core for isolating or connecting the liquid outlet holes and the flow channel is mounted in the flow channel by a spring. The valve core includes a valve stem and a pressure cap detachably connected to the valve stem. The valve stem has a sealing end for sealing the flow channel. The valve core also includes a sealing ring clamped between the sealing end and the pressure cap for sealing the liquid outlet holes. The lower connector has a breather channel communicating with the flow channel of the valve body and the outside of the valve body.

[0007] Furthermore, the valve body flow channel includes a small-diameter section communicating with the upper connector and a large-diameter section communicating with the lower connector, as well as a transition section connecting the small-diameter section and the large-diameter section, the transition section being adapted to the shape of the sealing end.

[0008] Furthermore, both the transition section and the sealing end are tapered structures.

[0009] Furthermore, the sealing ring includes a tapered section for sliding and sealing with the transition section, a through section for closing the liquid outlet, and a reduced diameter section for engaging with the pressure cap.

[0010] Furthermore, an elastic sealing element is provided on the conical surface of the sealing end.

[0011] Furthermore, the sealing ring is an elastic sealing ring.

[0012] Furthermore, the breathing channel includes an axial flow channel extending along the axial direction of the lower connector and a radial flow channel extending radially along the lower connector and communicating with the axial flow channel.

[0013] Furthermore, one end of the spring abuts against the pressure cap, and the other end abuts against the upper end face of the lower connector.

[0014] Furthermore, an anti-rotation structure is provided between the lower connector and the valve body.

[0015] Furthermore, the anti-rotation structure is a screw, and at least two screws are provided and evenly distributed along the circumference of the lower connector.

[0016] The beneficial effects of this utility model are as follows: The well-washing valve provided by this utility model is an improvement on the existing technology. The sealing end of the valve stem directly acts on the flow channel, realizing the overall on / off control of the flow channel. The sealing ring corresponds to the liquid outlet hole on the circumference of the valve body, sealing the liquid outlet hole separately when the valve core is closed. Through the dual sealing structure of the flow channel seal and the liquid outlet hole seal, combined with the spring push, the reliability of the valve core's seal on the flow channel and liquid outlet hole is enhanced, preventing well fluid leakage or downhole impurities from entering the flow channel, reducing the risk of valve core movement obstruction. The valve core has a split structure, so when the sealing ring is worn or the valve stem is damaged, only the corresponding sealing component needs to be replaced, without replacing the entire valve core, reducing maintenance costs. The sealing ring is clamped between the sealing end and the pressure cap, ensuring its stability and adapting to downhole pressure fluctuations, reducing the probability of seal failure. The designed breathing channel balances the pressure between the lower flow channel of the valve core and the external pressure of the valve body, eliminating dead space resistance during valve core movement and ensuring reliable opening and closing actions. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the well-washing valve structure of this utility model; Figure 2 This is a schematic diagram illustrating the application of the well-washing valve of this utility model.

[0018] In the diagram: 1. Upper connector; 2. Valve body; 21. Flow channel; 22. Liquid outlet; 23. Small diameter section; 24. Large diameter section; 25. Transition section; 26. Sealing ring; 3. Lower connector; 31. Screw; 32. Axial flow channel; 33. Radial flow channel; 4. Valve core; 41. Valve stem; 411. Sealing end; 42. Sealing ring; 421. Tapered section; 422. Through section; 423. Reduction section; 43. Pressure cap; 5. Spring; 100. Well washing valve; 200. Hollow sucker rod; 300. Solid sucker rod; 400. Oil pump; 500. Tubing; 600. Hot wash truck; 601. High-pressure hose. Detailed Implementation

[0019] The features and performance of this utility model will be further described in detail below with reference to the embodiments.

[0020] This invention addresses the problem in existing well-washing valves where a gap exists between the valve core and seat. Over long-term use, impurities or wax in the well fluid can deposit or solidify in this gap, increasing the valve core's movement resistance and potentially causing it to jam. The well-washing valve provided by this invention employs a dual-sealing structure—a flow channel seal and an outlet hole seal—along with the push of a spring, to enhance the reliability of the valve core's seal on the flow channel and outlet hole, preventing well fluid leakage or the entry of downhole impurities into the flow channel. Furthermore, the inclusion of a breathing channel reduces the risk of valve core movement obstruction.

[0021] An embodiment of the well-washing valve in this utility model: like Figure 1 As shown, and with reference Figure 2 The well-washing valve 100 includes a valve body 2, and an upper connector 1 and a lower connector 3 connected to both ends of the valve body 2 by threads. The valve body 2 has a flow channel 21 at its center. Several outlet holes 22 that communicate with the flow channel 21 are evenly distributed along the circumference of the valve body 2. A valve core 4 for isolating or connecting the outlet holes 22 and the flow channel 21 is mounted in the flow channel 21 by a spring 5. The spring 5 is mounted between the valve core 4 and the lower connector 3.

[0022] The upper connector 1 is used to connect to the hollow sucker rod 200 and has a through-hole. In other embodiments, the upper connector is integrally formed with the valve body.

[0023] The lower connector 3 is used to connect with the lower solid sucker rod 300, and its two ends are respectively provided with external threads; the lower connector 3 has a boss at the center of the end connected to the valve body 2; the lower connector 3 has a breather channel that connects the flow channel 21 of the valve body 2 to the outside of the valve body 2. When the valve core 4 is compressed by pressure, the liquid in its lower space (i.e., the space between the valve core 4 and the lower connector 3) can be quickly discharged to the outside of the valve body 2 through the breather channel to avoid pressure accumulation; when the well washing is completed and the spring 5 pushes the valve core 4 to reset, the external liquid can be replenished to the lower space of the valve core 4 through the breather channel to avoid the formation of negative pressure that hinders the upward movement of the valve core 4; the breather channel can balance the pressure between the lower flow channel 21 of the valve core 4 and the external pressure of the valve body 2, eliminate the dead space resistance in the movement of the valve core 4, and ensure reliable opening and closing action.

[0024] The breathing channel includes an axial flow channel 32 extending axially along the lower connector 3 and a radial flow channel 33 extending radially along the lower connector 3 and communicating with the axial flow channel 32. It should be understood that the number of radial flow channels 33 can be set to one, two, three, or other suitable numbers, specifically determined according to actual needs; this embodiment does not limit this. When the number of radial flow channels 33 is greater than two, each radial flow channel 33 is evenly distributed around the axial flow channel 32. The axial flow channel 32 allows the fluid generated during the movement of the valve core 4 to be quickly transmitted axially and discharged rapidly to the outside through the radial flow channels 33, thereby eliminating high pressure in the dead cavity and ensuring that the valve core 4 opens without resistance or delay. If multiple radial flow channels 33 simultaneously communicate with the outside, the total cross-sectional area for fluid entry and exit can be increased, accelerating the pressure balance between the lower space of the valve core 4 and the outside.

[0025] An anti-rotation structure is provided between the lower connector 3 and the valve body 2. Specifically, the anti-rotation structure is a screw 31. The lower connector 3 has a threaded through hole, and the valve body 2 has a threaded blind hole. The screw 31 passes through the threaded through hole and connects with the threaded blind hole to achieve an anti-rotation connection between the valve body 2 and the lower connector 3. It should be understood that the number of screws 31 can be set to 1, 2, 3, or other suitable numbers, which can be reasonably set according to needs. This embodiment does not limit this. When the number of screws 31 is greater than 2, each screw 31 is evenly distributed along the circumference of the lower connector 3. In other embodiments, the anti-rotation structure can be a pin. The anti-rotation structure prevents relative rotation between the lower connector 3 and the valve body 2, ensuring that the connection between the lower connector 3 and the valve body 2 remains stable and avoiding the risk of downhole disengagement. When there are two or more anti-rotation structures, the evenly distributed circumferential arrangement can ensure the circumferential force balance between the lower connector 3 and the valve body 2, improving the reliability of the anti-rotation.

[0026] The valve body 2 has a hollow tubular structure, with a central cavity forming a flow channel 21 through which the well-washing fluid passes. The flow channel 21 includes a small-diameter section 23 connected to the upper connector 1 and a large-diameter section 24 connected to the lower connector 3, as well as a transition section 25 connecting the small-diameter section 23 and the large-diameter section 24. The outlet hole 22 is located in the large-diameter section 24 and close to the transition section 25. The gradual change in the flow channel 21 of the valve body 2 makes the flow of the well-washing fluid smoother.

[0027] The valve core 4 includes a valve stem 41 and a pressure cap 43 detachably connected to the valve stem 41. The valve stem 41 has a sealing end 411 that seals the flow channel 21 of the valve body 2. The valve core 4 also includes a sealing ring 42 that is clamped between the sealing end 411 and the pressure cap 43 and is used to seal the liquid outlet hole 22. The pressure cap 43 is threadedly connected to the valve stem 41. The sealing end 411 of the valve stem 41 directly acts on the flow channel 21, realizing the overall on / off control of the flow channel 21. The sealing ring 42 corresponds to the liquid outlet 22 around the valve body 2. When the valve core 4 is closed, it seals the liquid outlet 22 separately. Through the double sealing structure of the flow channel 21 sealing and the liquid outlet 22 sealing, and with the push of the spring 5, the reliability of the valve core 4 sealing the flow channel 21 and the liquid outlet 22 is enhanced, avoiding well fluid leakage or downhole impurities entering the flow channel 21, and reducing the risk of valve core 4 movement being obstructed. The valve core 4 with a split structure can replace only the corresponding parts when the sealing ring 42 is worn or the valve stem 41 is damaged, without replacing the entire valve core 4, thus reducing maintenance costs. The sealing ring 42 is clamped between the sealing end 411 and the pressure cap 43, ensuring its fixed stability, adapting to downhole pressure fluctuations, and reducing the probability of seal failure.

[0028] The shape of the sealing end 411 of the valve stem 41 is adapted to the shape of the transition section 25, both being conical structures. The shape of the sealing end 411 of the valve stem 41 and the transition section 25 of the flow channel 21 of the valve body 2 are adapted to ensure a complete surface seal when they come into contact. When the conical transition section 25 and the conical sealing end 411 are engaged, the sealing contact area is larger, and the contact pressure is evenly distributed along the conical surface. Under the preload of the spring 5, the two can be tightly fitted together, improving the sealing effect. The conical structure of the transition section 25 can guide the axial movement of the valve core 4, ensuring that the valve core 4 moves along the axis of the flow channel 21, avoiding radial offset, and improving the stability of the valve core 4's movement. In other embodiments, the valve stem sealing end is a convex arc surface, and the transition section is a circular arc surface; or, both the valve stem sealing end and the transition section are cylindrical surfaces, in which case the valve stem is a stepped shaft structure.

[0029] To enhance the sealing reliability of the flow channel 21, an elastic sealing element is provided on the conical surface of the sealing end 411. Specifically, a groove is provided on the conical surface of the sealing end 411, and the elastic sealing element is embedded in the groove. The elastic sealing element can be made of materials such as fluororubber, nitrile rubber, and nylon, and the specific material should be selected according to the well conditions, well depth, and composition of the well washing fluid. This embodiment does not limit the choice of material. The elastic sealing element can fill the fitting gap between the sealing end 411 of the valve stem 41 and the transition section 25 of the valve body 2 through its own deformation, thereby improving the sealing effect of the valve core 4 on the flow channel 21. At the same time, it reduces the movement resistance of the valve core 4 and buffers the frictional impact when the sealing end 411 of the valve stem 41 and the transition section 25 of the valve body 2 slide relative to each other.

[0030] The sealing ring 42 includes a tapered section 421 for sliding sealing with the transition section 25, a through section 422 for closing the outlet hole 22, and a reduced diameter section 423 for engaging with the pressure cap 43; wherein the taper of the tapered section 421 is adapted to the taper of the transition section 25; the diameter of the through section 422 matches the diameter of the large diameter section 24 of the flow channel 21, and its axial length covers the distribution range of the outlet hole 22; the diameter of the reduced diameter section 423 is smaller than that of the through section 422, and the sealing ring 42 is embedded in the groove or inner hole of the pressure cap 43 through the reduced diameter section 423. The conical section 421 forms a surface contact seal with the transition section 25 of the flow channel 21 of the valve body 2. During the opening or closing of the valve core 4, the conical section 421 slides up and down with the valve stem 41 and maintains a tight fit with the transition section 25, preventing high-pressure liquid in the flow channel 21 from leaking from the gap between the valve core 4 and the valve body 2. When the valve core 4 is closed, the through section 422 can completely seal all the liquid outlet holes 22, forming a radial seal to prevent liquid or impurities in the well from seeping back into the flow channel 21 through the liquid outlet holes 22. When the valve core 4 is open, the through section 422 moves down with the valve stem 41 and leaves the area of ​​the liquid outlet holes 22, ensuring that the well washing fluid is sprayed out of the liquid outlet holes 22 without obstruction. The sealing ring 42 is fixed by the axial clamping force of the pressure cap 43 to prevent it from axially moving or radially shifting under the movement of the valve core 4 or high-pressure impact, ensuring that the conical section 421 and the through section 422 are always in the preset sealing position.

[0031] The sealing ring 42 is an elastic sealing ring. Specifically, the sealing ring 42 is made of materials such as fluororubber, nitrile rubber, and nylon, and the specific material is selected according to the well conditions, well depth, and composition of the well-washing fluid. This embodiment does not limit the selection. Under the pre-tightening action of the pressure cap 43, the elastic sealing ring 42 can achieve pressure self-adaptive compensation through its own deformation, enhance the tightness of the fit with the valve body 2, completely block the leakage channel, and improve the sealing reliability of the sealing ring 42. In other embodiments, the sealing ring is a precision-machined metal part.

[0032] Spring 5 is a cylindrical helical spring. One end of spring 5 abuts against the pressure cap 43 and is sleeved on the end of valve stem 41 away from the sealing end 411. The other end of spring 5 abuts against the upper end face of lower connector 3 and is sleeved on the boss of upper connector 1. Both ends of spring 5 are in contact with pressure cap 43 and the upper end face of lower connector 3, respectively, and are coaxial with the axis of valve core 4. This ensures that the force of spring 5 is applied axially along valve core 4, avoiding uneven wear or sealing failure of valve core 4 due to force offset, improving the reliability of valve core 4 reset, and simplifying the assembly structure.

[0033] During well washing operations, the high-pressure washing fluid pushes the valve core 4 to compress the spring 5, causing the sealing ring 42 to disengage from the outlet hole 22 and the sealing end 411 to disengage from the flow channel 21, thus connecting the flow channel 21 with the outlet hole 22. The inner cavity of the upper connector 1, the flow channel 21 of the valve body 2, and the outlet hole 22 of the valve body 2 together form the well washing channel of the well washing valve 100. After the operation is completed, the spring 5 rebounds and pushes the valve core 4 to reset. The sealing end 411 of the valve core 4 seals the flow channel 21, and the sealing ring 42 seals the outlet hole 22, isolating the outlet hole 22 from the flow channel 21 and resealing the valve core 4.

[0034] To ensure a tight seal at the connection between the well-washing valve 100 and the upper hollow sucker rod 200, a sealing ring 26 is provided on the valve body 2 for sealing cooperation with the upper hollow sucker rod 200. Specifically, the sealing ring 26 is positioned corresponding to the mating part of the hollow sucker rod 200, preventing well-washing fluid from leaking to the outside through the connection gap, and simultaneously preventing impurities in the well fluid within the annulus of the sucker rod and tubing 500 from entering the valve body 2. In other embodiments, the sealing ring is located on the upper connector 1. It should be understood that the material and cross-sectional shape of the sealing ring 26 can be reasonably selected according to operating conditions, etc., and this embodiment does not impose any limitations on this.

[0035] like Figure 2 As shown, when the well-washing valve 100 provided by this utility model is in use, the upper end of the well-washing valve 100 is connected to the hollow sucker rod 200 through the upper connector 1, and the lower end is connected to the solid sucker rod 300 through the lower connector 3. It is lowered into the wellbore by the oil pump 400. During the hot washing operation, the wellhead hot washing truck 600 is connected to the hollow sucker rod 200 through the high-pressure hose 601. Under a certain pressure, the hot washing medium is pumped into the hollow sucker rod 200. The high-pressure hot washing medium pushes the valve core 4 to move away from the upper connector 1 and leak out the liquid outlet 22, so that the inner cavity of the upper connector 1, the flow channel 21 of the valve body 2 and the liquid outlet 22, and the annulus between the sucker rod and the tubing 500 are connected to form a circulating well-washing channel. When the well washing is finished, the valve core 4 is pushed back to its original position under the action of the spring 5.

[0036] Finally, it should be noted that the above are merely preferred embodiments of this utility model and are not intended to limit the utility model. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments without creative effort, or make equivalent substitutions for some technical features, or organically combine different specific implementation methods to create the specific implementation methods shown in the accompanying drawings. Of course, those skilled in the art can also create other specific implementation methods not shown in the accompanying drawings. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A well-washing valve, comprising a valve body and an upper connector and a lower connector connected to both ends of the valve body, wherein the valve body has a flow channel at its center, and a plurality of liquid outlet holes communicating with the flow channel are evenly distributed along its circumference on the valve body, and a valve core for isolating or connecting the liquid outlet holes and the flow channel is mounted in the flow channel by a spring, characterized in that: The valve core includes a valve stem and a pressure cap detachably connected to the valve stem. The valve stem has a sealing end for sealing the flow channel. The valve core also includes a sealing ring sandwiched between the sealing end and the pressure cap for sealing the liquid outlet. The lower connector has a breathing channel that connects the valve body flow channel to the outside of the valve body.

2. The well-washing valve according to claim 1, characterized in that: The valve body flow channel includes a small-diameter section communicating with the upper connector and a large-diameter section communicating with the lower connector, as well as a transition section connecting the small-diameter section and the large-diameter section, the transition section being adapted to the shape of the sealing end.

3. The well-washing valve according to claim 2, characterized in that: Both the transition section and the sealing end are tapered structures.

4. The well-washing valve according to claim 3, characterized in that: The sealing ring includes a tapered section for sliding and sealing with the transition section, a through section for closing the liquid outlet, and a reduced diameter section for engaging with the pressure cap.

5. The well-washing valve according to claim 3 or 4, characterized in that: An elastic sealing element is provided on the conical surface of the sealing end.

6. The well-washing valve according to any one of claims 1 to 4, characterized in that: The sealing ring is an elastic sealing ring.

7. The well-washing valve according to any one of claims 1 to 4, characterized in that: The breathing channel includes an axial flow channel extending along the axial direction of the lower connector and a radial flow channel extending radially along the lower connector and communicating with the axial flow channel.

8. The well-washing valve according to any one of claims 1 to 4, characterized in that: One end of the spring abuts against the pressure cap, and the other end abuts against the upper end face of the lower connector.

9. The well-washing valve according to any one of claims 1 to 4, characterized in that: An anti-rotation structure is provided between the lower connector and the valve body.

10. The well-washing valve according to claim 9, characterized in that: The anti-rotation structure is a screw, and at least two screws are provided and evenly distributed along the circumference of the lower connector.

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