An extraction centrifuge tube

Abstract

This invention discloses an extraction centrifuge tube, the key technical features of which include a tube body, a plunger, a cap, and a switching valve. The plunger includes a plunger head and a plunger rod fixed to the top of the plunger head. The plunger is inserted into the tube body and can slide along the tube wall. The cap is detachably sealed at the top opening of the tube body, and a plunger hole is formed in the cap, through which the plunger rod passes. At least one liquid outlet is formed on the side of the tube body, with at least one of the outlets located in the upper half of the tube body. A switching valve is installed at each outlet. A through hole is formed on the bottom surface of the tube body, and when the plunger head is at its lowest position, all outlets are higher than the plunger head. This invention can be used as a centrifuge tube when the cap is sealed at the tube body opening. For stratified liquids, the experimenter can adjust the position of the plunger to change the liquid level in the tube body according to experimental needs, allowing the switching valve to release the desired upper or lower layer of liquid.

Description

Technical Field

[0001] This invention relates to the field of extraction centrifugation, and more specifically, to an extraction centrifuge tube. Background Technology

[0002] In the testing of food and agricultural products, extraction is a commonly used liquid separation method. Its principle is based on the difference in solubility or partition coefficient of a substance in two immiscible solvents, allowing the solute to transfer from one solvent to the other. It is a unit operation that uses the different solubilities of components in a solvent to separate a mixture. The operation of separating two immiscible liquids after extraction is called liquid-liquid extraction.

[0003] Traditional extraction methods employ separatory funnels for separation, requiring manual or instrumental agitation for extraction, followed by settling and collection of the upper and lower layers as needed. Traditional extraction methods are prone to severe emulsification during the extraction process, resulting in prolonged separation time and poor separation efficiency. While methods such as heating and salting are often used to accelerate demulsification, these are cumbersome, introduce new impurities, and have unsatisfactory demulsification effects, impacting analytical efficiency. Another solution is centrifugation for demulsification and separation. While this method is highly effective, conventional separatory funnels cannot perform centrifugation. The liquid must be transferred to centrifuge tubes, centrifuged, and then transferred back to the separatory funnel for 2-3 extractions. This process is cumbersome, time-consuming, labor-intensive, and time-consuming, and easily introduces contaminants. Furthermore, for viscous solutions, the high viscosity causes the liquid to adhere to the walls, preventing complete transfer and leading to lower analytical results, poor reproducibility, and significantly impacting analytical efficiency and accuracy.

[0004] In the field of extraction centrifugation, Chinese patent CN201720034991 relates to a portable liquid-liquid extraction tube. This extraction tube can realize the centrifugation operation after machine oscillation extraction. However, after centrifugation, the extraction tube needs to be inverted and allowed to stand and separate again, which takes a long time. Moreover, after separation, the lower liquid can only be collected through the valve at the bottom, while the upper liquid is difficult to collect.

[0005] In addition, Chinese patent CN201922283957 discloses a two-phase aqueous extraction centrifuge tube. The main structure of this extraction centrifuge tube involves inserting a sampling tube into a test tube. The bottom of the sampling tube can slide within the tube. The bottom of the sampling tube is mainly divided into two parts: a permeation plate with multiple through-holes and a sealing plate that opens and closes the through-holes by rotation. The sealing plate is rotated to open the through-holes, and the bottom of the sampling tube is moved down until it reaches the separation position. Then, the sealing plate is rotated to close the through-holes, sealing the upper liquid inside the sampling tube. The sampling tube is then removed, and the upper liquid can be extracted. This structure can collect the upper liquid, but the movement of the sampling tube bottom and the rotation of the sealing plate can easily cause turbidity in the lower liquid.

[0006] There is also Chinese patent CN202023017785, which relates to a high-efficiency extraction centrifuge device. This device fixes a separating funnel inside a centrifuge sleeve to facilitate centrifugation. When collecting the upper and lower layers of liquid, the device works similarly to a traditional separating funnel. First, the lower layer of liquid is collected through the discharge nozzle at the bottom, and then the upper layer of liquid is collected. The collected lower layer of liquid needs to be reintroduced into the separating funnel for the next extraction and centrifugation.

[0007] As can be seen from the aforementioned patents, most commercially available extraction centrifuges only involve the collection of either the upper or lower liquid layer, preventing researchers from freely separating the upper and lower liquid layers according to their experimental needs. Therefore, designing an extraction centrifuge that allows researchers to freely separate the upper and lower liquid layers based on their experimental requirements is a pressing issue that needs to be addressed in the field of extraction centrifugation. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide an extraction centrifuge tube. This tube, with its body and plunger forming a piston structure, has a switching valve on the side wall for liquid extraction. When the switching valve is closed and the tube opening is sealed with the cap, the tube can be centrifuged. After centrifugation and demulsification, the experimenter can adjust the plunger position to change the liquid level, facilitating the extraction of either the upper or lower layer of liquid from the tube via the switching valve.

[0009] To achieve the above objectives, the present invention provides the following technical solution: an extraction centrifuge tube, characterized in that it comprises a tube body, a plunger, a tube cap, and a switch valve. The plunger includes a plunger head and a plunger rod fixed to the top of the plunger head. The plunger is inserted into the tube body and can slide along the tube wall. The tube cap is detachably sealed at the top opening of the tube body. A plunger hole is opened on the tube cap, and the plunger rod passes through the plunger hole. At least one liquid outlet hole is opened on the side of the tube body, and at least one of the liquid outlet holes is located in the upper half of the tube body. A switch valve is installed at each liquid outlet hole. A through hole is opened on the bottom surface of the tube body. When the plunger head is at its lowest position, all liquid outlet holes are higher than the plunger head.

[0010] By adopting the above technical solution, the present invention can be used as a centrifuge tube when the tube cap is sealed at the tube opening; for the layered liquid after centrifugation and demulsification, the experimenter can choose to move the plunger head to different heights through the plunger rod according to the experimental needs, thereby changing the liquid height, so that the experimenter can easily take out the upper or lower layer of liquid in the tube from the switch valve.

[0011] The present invention is further configured such that multiple liquid outlet holes are provided, and the multiple liquid outlet holes are located at different heights.

[0012] By adopting the above technical solution, researchers can directly extract liquid from different height areas inside the tube through liquid outlets at different heights, reducing the need to move the plunger and making liquid extraction more convenient.

[0013] The invention is further configured to include a guide tube, one for each switch valve; the top end of each guide tube is connected to its corresponding liquid outlet, and the bottom end is inclined to the side away from the corresponding liquid outlet and connected to its corresponding switch valve.

[0014] By adopting the above technical solution, the bottom end of the guide tube is inclined away from the axis of the tube body, which is conducive to guiding the liquid out of the tube body.

[0015] The present invention is further configured such that: the switching valve includes a valve body and a piston; the valve body is fixed at the bottom end of the guide tube; a vertical cavity is opened in the valve body; the guide tube communicates with the cavity; the piston is embedded in the cavity; a solvent channel is opened inside the piston; the channel outlet is located at the bottom of the piston and communicates with the outside; the channel inlet is located on the side of the piston; the piston is rotatably connected to the valve body; the piston rotation axis is vertical; the channel inlet and the bottom end of the guide tube are at the same height.

[0016] By adopting the above technical solution, when taking liquid, the user only needs to rotate the piston to connect the channel inlet with the guide tube, so that the liquid in the guide tube can leave the piston through the solvent channel; after taking liquid, the user only needs to rotate the piston to make the channel inlet and the guide tube offset, so that the switch valve can be closed; at this time, the channel inlet is in contact with the inner side wall of the cavity, and the bottom end of the guide tube is in contact with the side wall of the piston, so that the liquid in the guide tube cannot enter the solvent channel.

[0017] The present invention is further configured such that the top diameter of the cavity is larger than the bottom diameter, and the piston is embedded in the cavity from the top of the cavity.

[0018] By adopting the above technical solution, the present invention limits the piston to leave the cavity only from the top of the cavity through the cavity wall, and the piston can be embedded in the cavity under the action of gravity, which facilitates the installation of the piston; since the extraction of liquid requires oscillation, such a structure can also reduce the possibility of the piston sliding out of the cavity during oscillation.

[0019] The present invention is further configured such that: the solvent channel is T-shaped, and the two channel openings above the solvent channel are both channel inlets.

[0020] By adopting the above technical solution, the present invention sets the solvent channel to a T-shape, which is simple in structure and easy to process; moreover, the T-shaped channel structure allows the solvent channel to have two channel inlets, so that the experimenter can control the opening and closing of the switch valve with a small rotation degree, making it easier to realize the opening and closing control of the switch valve.

[0021] The present invention is further configured such that: the cross-section of the tube is crescent-shaped, both liquid outlets are located in the recess of the crescent shape, and both switch valves are located in the cylindrical area surrounded by the outer arc wall of the crescent shape.

[0022] By adopting the above technical solution, the present invention achieves a size consistent with ordinary test tubes, facilitating placement in conventional vortex shakers and centrifuges for oscillation and centrifugation processes. The present invention is further configured such that: the tube body has vertically marked graduations, and the top surface of the plunger head is horizontal.

[0023] By adopting the above technical solution, it is easy for experimental personnel to intuitively read the volume of the extracted liquid.

[0024] The invention is further configured to include a sealing ring, which is embedded in the wall of the plunger bore and fits tightly against the plunger rod.

[0025] By adopting the above technical solution, the sealing ring can seal the gap between the plunger hole wall and the plunger rod, so as to prevent the liquid in the tube from flowing out from the gap between the plunger hole wall and the plunger rod during the oscillation process.

[0026] The invention is further configured to include two limiting rings and a retaining ring, the retaining ring being fixed to the inner wall of the tube cap, and the two limiting rings being fitted onto the tube body and fixedly connected to the tube body; the tube cap is a shell, and when the tube cap is fitted onto the top of the tube body, the retaining ring is embedded between the two limiting rings.

[0027] By adopting the above technical solution, the present invention uses the elastic deformation of the retaining ring itself to embed the retaining ring between the two limiting rings, and fixes the pipe cap to the pipe body by the snapping of the retaining ring with the two limiting rings.

[0028] In summary, the present invention has the following advantages compared to the prior art:

[0029] 1. When the cap is sealed at the opening of the tube body, the present invention can be used as a centrifuge tube. For the stratified liquid after centrifugation and demulsification, the experimenter can choose to take out the required liquid from any of the switch valves according to the experimental needs. Alternatively, the liquid height in the tube body can be changed by adjusting the position of the plunger, so that the desired upper or lower liquid can flow out from the switch valve.

[0030] 2. The experimenter can intuitively read the volume of liquid taken out according to the scale on the tube, so as to put in or take out a certain volume of liquid as needed for the experiment.

[0031] 3. This invention corresponds to the size of ordinary test tubes and can be placed in conventional vortex shakers and centrifuges for shaking and centrifugation processes. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure of the embodiment;

[0033] Figure 2 for Figure 1 Full sectional view;

[0034] Figure 3 for Figure 2 Enlarged view of region A in the middle;

[0035] Figure 4 This is a cross-sectional view illustrating the pipe structure in the embodiment;

[0036] Figure 5 for Figure 4 Enlarged view of region B in the middle;

[0037] Figure 6 This is a schematic diagram of the piston and handle in the embodiment;

[0038] Figure 7 This is a partial cross-sectional view of the solvent channel in the embodiment;

[0039] Figure 8 This is a cross-sectional view showing the installation position of the retaining ring in the embodiment;

[0040] Figure 9 This is a schematic diagram illustrating the plunger ring in the embodiment.

[0041] In the diagram: 1. Tube body; 11. Through hole; 12. Liquid outlet hole; 2. Plunger; 21. Plunger head; 22. Plunger rod; 3. Tube cap; 31. Plunger hole; 4. Switch valve; 41. Valve body; 411. Cavity; 42. Piston; 421. Solvent channel; 43. Handle; 5. Limiting ring; 6. Snap ring; 7. Guide tube; 8. Sealing ring; 9. Plunger ring. Detailed Implementation

[0042] The technical solution of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the invention.

[0043] It should be noted that the terms "center", "upper", "lower", "horizontal", "left", "right", "front", "rear", "lateral", "longitudinal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0044] Example

[0045] like Figure 1-3 The diagram shows the basic structure of a preferred embodiment of the present invention. An extraction centrifuge tube includes a tube body 1, a plunger 2, a tube cap 3, and a switching valve 4. The plunger 2 includes a plunger head 21 and a plunger rod 22 fixed to the top of the plunger head 21. The plunger 2 is inserted into the tube body 1 and can slide along the tube wall. The tube cap 3 is detachably sealed at the top opening of the tube body 1. A plunger hole 31 is opened on the tube cap 3, and the plunger rod 22 passes through the plunger hole 31. At least one liquid outlet hole 12 is opened on the side of the tube body 1, and at least one of the liquid outlet holes 12 is located in the upper half of the tube body 1. A switching valve 4 is installed at each liquid outlet hole 12. A through hole 11 is opened on the bottom surface of the tube body 1. When the plunger head 21 is in the lowest position, all liquid outlet holes 12 are higher than the plunger head 21.

[0046] In this embodiment, multiple outlet holes 12 are provided, located at different heights. In another embodiment, two outlet holes 12 are provided, located at the top and bottom of the tube body 1, respectively. When the tube cap 3 is sealed at the opening of the tube body 1, this invention can be used as a centrifuge tube. For the layered liquid after centrifugation and demulsification, the experimenter needs to open the upper valve 4 or the tube cap 3 to balance the air pressure inside and outside the tube body 1. Then, depending on the experimental needs, the experimenter can choose to directly open the lower valve 4 to remove the lower layer of liquid in the tube body 1, or pull up the top of the plunger rod 22 to raise the plunger head 21, which is fixedly connected to the plunger rod 22, thereby raising the liquid in the tube body 1 and taking the upper layer of liquid flowing from the upper valve 4. After the liquid is taken, all valves 4 are closed. During the process of raising the liquid, if there is air inside the tube body 1, the rising liquid will first squeeze the air out of the upper valve 4.

[0047] Specifically, in this embodiment, multiple grooves are provided at the top of the plunger rod 22 to increase friction and facilitate the push and pull of the plunger rod 22 by the experimenter.

[0048] In this embodiment, the tube body 1 has vertically marked graduations, and the top surface of the plunger head 21 is horizontal. This configuration allows the experimenter to intuitively read the volume of liquid taken out, so that the experimenter can put in or take out a certain volume of liquid according to experimental needs.

[0049] In this embodiment, the cross-section of the tube 1 is crescent-shaped, and the two liquid outlet holes 12 are both located in the crescent-shaped depression. The two switch valves 4 are both located in the cylindrical area surrounded by the outer arc wall of the crescent shape, so that this embodiment can be matched with the size of a regular test tube, so that it can be placed in a conventional vortex shaker and centrifuge for shaking and centrifugation.

[0050] like Figure 4-6 As shown, this embodiment also includes a guide tube 7, with one corresponding to each switch valve 4; the top end of each guide tube 7 is connected to its corresponding liquid outlet 12, and the bottom end is inclined to the side away from the corresponding liquid outlet 12 and connected to its corresponding switch valve 4. The bottom end of the guide tube 7 is inclined away from the axis of the tube body 1, which is beneficial for guiding the liquid out of the tube body 1.

[0051] The switching valve 4 includes a valve body 41, a piston 42, and a handle 43. The valve body 41 is fixed to the bottom end of the guide tube 7. A vertical cavity 411 is opened inside the valve body 41, and the guide tube 7 is connected to the cavity 411. The piston 42 is embedded in the cavity 411. A solvent channel 421 is opened inside the piston 42. The channel outlet is located at the bottom of the piston 42 and is connected to the outside. The channel inlet is located on the side of the piston 42. The piston 42 is rotatably connected to the valve body 41, and the rotation axis of the piston 42 is vertical. The handle 43 is fixed to the top of the piston 42 to facilitate the experimenter to rotate the piston 42. The channel inlet is at the same height as the bottom end of the guide tube 7. When taking liquid, the user only needs to rotate the piston 42 to connect the channel inlet with the guide tube 7, allowing the liquid in the guide tube 7 to leave the piston 42 through the solvent channel 421. After taking liquid, the user only needs to rotate the piston 42 to offset the channel inlet from the guide tube 7, thus closing the switch valve 4. At this time, the channel inlet is in contact with the inner wall of the cavity 411, and the bottom end of the guide tube 7 is in contact with the side wall of the piston 42, preventing the liquid in the guide tube 7 from entering the solvent channel 421. In this embodiment, the valve body 41 and the guide tube 7 are integrally formed, and the piston 42 and the handle 43 are integrally formed.

[0052] Specifically, the top diameter of cavity 411 is larger than the bottom diameter, and piston 42 is inserted into cavity 411 from the top. Specifically, cavity 411 is vertically divided into three sections: upper, middle, and lower. The diameter of the upper section wall is larger than that of the lower section wall; the middle section wall is an inverted frustum, with its top edge diameter equal to that of the upper section wall and its bottom edge diameter equal to that of the lower section wall; the side of piston 42 fits against all three side walls of cavity 411. The inverted truncated cone surface in the middle section allows the piston 42 to be embedded in the cavity 411 under the action of gravity, facilitating the installation of the piston 42. Since the extraction of liquid requires oscillation, the upper and lower vertical walls can limit the piston 42 to leave the cavity 411 only in a vertically upward direction, reducing the possibility of the piston 42 sliding out of the cavity 411 during oscillation. Moreover, the upper and lower vertical walls can also increase the contact area between the piston 42 and the inner wall of the cavity 411, increasing friction and further reducing the possibility of the piston 42 sliding out of the cavity 411 during oscillation.

[0053] like Figure 7 As shown, the solvent channel 421 is T-shaped. The two upper openings of the solvent channel 421 are both channel inlets, and the lower opening is the channel outlet. The T-shaped solvent channel 421 has a simple structure and is easy to manufacture. Moreover, the T-shaped channel structure gives the solvent channel 421 two channel inlets, allowing the experimenter to control the opening and closing of the switch valve 4 with a small rotation degree, making it easier to achieve the opening and closing control of the switch valve 4.

[0054] like Figure 5 and Figure 8As shown, this embodiment also includes two limiting rings 5 ​​and a retaining ring 6. The retaining ring 6 is fixed to the inner wall of the tube cap 3, and the two limiting rings 5 ​​are fitted onto the tube body 1 and fixedly connected to the tube body 1. The tube cap 3 is a shell, and when the tube cap 3 is fitted onto the top of the tube body 1, the retaining ring 6 is embedded between the two limiting rings 5. In this embodiment, the retaining ring 6 is embedded between the two limiting rings 5 ​​by its own elastic deformation, and the tube cap 3 is fixed to the tube body 1 by the engagement of the retaining ring 6 with the two limiting rings 5. Specifically, the tube body 1 and the two limiting rings 5 ​​are integrally formed.

[0055] This embodiment also includes a sealing ring 8, which is embedded in the wall of the plunger hole 31 and fits tightly against the plunger rod 22, so that the sealing ring 8 can seal the gap between the wall of the plunger hole 31 and the plunger rod 22, so as to prevent the liquid in the tube 1 from flowing out from the gap between the wall of the plunger hole 31 and the plunger rod 22 during the oscillation process.

[0056] like Figure 9 As shown, this embodiment also includes two plunger rings 9, which are fitted onto the plunger head 21 and fixedly connected to it. The two plunger rings 9 are tightly fitted to the inner wall of the tube body 1 to achieve a seal between the plunger head 21 and the inner wall of the tube body 1, preventing liquid from seeping into the space below the plunger head 21 and leaking out from the through hole 11. In this embodiment, the two plunger rings 9 and the plunger head 21 are integrally formed.

[0057] Specifically, the outer side of the tube cap 3 has multiple vertical grooves arranged along the top edge to increase friction and make it easier for the experimenter to pull out the tube cap 3.

[0058] In this embodiment, the bottom surface of the tube body 1 is an arc surface, and the bottom edge of the arc surface smoothly tapers towards the through hole 11. The shape of the plunger head 21 matches the shape of the bottom inner side of the tube body 1, so that when the plunger head 21 moves down, the air below the plunger head 21 is squeezed out of the through hole 11 along the inclined surface.

[0059] Specifically, the plunger rod 22 is a plastic plunger rod, and the plunger head 21 is a rubber plunger head.

[0060] In summary, this embodiment can be used as a centrifuge tube when the cap 3 is sealed at the opening of the tube body 1. For the layered liquid after centrifugation and demulsification, the experimenter can select any of the valves 4 to extract the desired liquid, or adjust the position of the plunger 2 to change the liquid level in the tube body 1, allowing the valve 4 to release the desired upper or lower layer of liquid. Furthermore, the experimenter can visually read the volume of liquid extracted from the tube body 1 using the markings, allowing for the addition or removal of specific volumes of liquid as needed. Finally, this embodiment corresponds to the size of ordinary test tubes and can be placed in conventional vortex shakers and centrifuges for oscillation and centrifugation processes.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An extraction centrifuge tube, characterized in that: The tube includes a tube body (1), a plunger (2), a tube cap (3), and a switch valve (4). The plunger (2) includes a plunger head (21) and a plunger rod (22) fixed to the top of the plunger head (21). The plunger (2) is inserted into the tube body (1) and can slide along the tube wall. The tube cap (3) is detachably sealed at the top of the tube body (1). A plunger hole (31) is opened on the tube cap (3), and the plunger rod (22) passes through the plunger hole (31). The tube body (1) has multiple liquid outlet holes (12) on its side. The multiple liquid outlet holes (12) are located at different heights. At least one of the liquid outlet holes (12) is located in the upper half of the tube body (1). A switch valve (4) is installed at each liquid outlet hole (12). The tube body (1) has a through hole (11) on its bottom surface. When the plunger head (21) is at its lowest position, all liquid outlet holes (12) are higher than the plunger head (21). The switching valve (4) includes a valve body (41) and a piston (42). The valve body (41) is fixed to the bottom end of the guide tube (7). A cavity (411) is vertically penetrating the valve body (41) inside the valve body (41). The guide tube (7) is connected to the cavity (411). The piston (42) is embedded in the cavity (411). A solvent channel (421) is provided inside the piston (42). The channel outlet is located at the bottom of the piston (42) and is connected to the outside. The channel inlet is located on the side of the piston (42). The piston (42) is rotatably connected to the valve body (41). The piston (42) has a vertical rotation axis. The channel inlet is at the same height as the bottom end of the guide tube (7). It also includes a guide tube (7), one for each switch valve (4); the top of each guide tube (7) is connected to its corresponding liquid outlet (12), and the bottom is inclined to the side away from the corresponding liquid outlet (12) and connected to its corresponding switch valve (4).

2. The extraction centrifuge tube according to claim 1, characterized in that: The top diameter of the cavity (411) is larger than the bottom diameter, and the piston (42) is inserted into the cavity (411) from the top.

3. The extraction centrifuge tube according to claim 1, characterized in that: The solvent channel (421) is T-shaped, and the two channel openings above the solvent channel (421) are both channel inlets.

4. An extraction centrifuge tube according to claim 1, characterized in that: The tube body (1) has a crescent-shaped cross-section, all liquid outlets (12) are located in the crescent-shaped depression, and all switch valves (4) are located in the cylindrical area surrounded by the outer arc wall of the crescent shape.

5. An extraction centrifuge tube according to claim 1, characterized in that: The tube body (1) has vertical markings, and the top surface of the plunger head (21) is horizontal.

6. An extraction centrifuge tube according to claim 1, characterized in that: It also includes a sealing ring (8), which is embedded in the wall of the plunger hole (31) and fits tightly against the plunger rod (22).

7. An extraction centrifuge tube according to claim 1, characterized in that: It also includes two limiting rings (5) and a retaining ring (6). The retaining ring (6) is fixed to the inner wall of the tube cap (3). The two limiting rings (5) are fitted onto the tube body (1) and fixedly connected to the tube body (1). The tube cap (3) is a shell. When the tube cap (3) is fitted onto the top of the tube body (1), the retaining ring (6) is embedded between the two limiting rings (5).

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