A pipette

Abstract

The utility model relates to pipette technical field relates to a pipette, including holding part and pipette part, both through thread detachable connection, holding part contains the holding shell of arc holding handle and drive module, the lower pressure lever of drive module is equipped with spring no.

Description

Technical Field

[0001] This utility model relates to the field of pipette technology, and specifically to a pipette. Background Technology

[0002] In scientific research and production scenarios such as biological experiments, chemical analysis, and medical testing, pipettes are the core tools for transferring liquids. Their ease of use, maintenance efficiency, and operational stability directly affect the accuracy of experimental data and work efficiency. The lower part of the pipette (the pipetting section), as the key component that directly supports the pipette tip and performs the aspiration and dispensing actions, has a structural design that is a core factor determining the overall performance of the equipment.

[0003] The lower half of the pipette in the prior art has the following defects: Existing solutions are mostly integrated designs. After long-term use, pipettes require periodic precision calibration, internal cleaning, or component replacement of the pipetting section. However, the integrated structure requires disassembling the entire device, which is complicated and can easily damage related components. Some detachable solutions also require the use of special tools to gradually disassemble them, which greatly reduces the efficiency of calibration and maintenance. At the same time, the cumbersome disassembly process indirectly increases the maintenance cost and downtime of the equipment. Traditional pipette tips often require manual removal, which is not only laborious but also prone to spillage due to uneven force, leading to reagent contamination or experimental data deviation. Some pipette tips with ejection functions have complex designs, requiring manual repositioning after ejection, and are prone to incomplete ejection and jamming, affecting the continuity of operation. In addition, manual contact with the pipette tip may pose a risk of biological contamination, which is detrimental to experimental safety. Utility Model Content

[0004] This invention provides a pipette to address the problems of the prior art.

[0005] The objective of this utility model can be achieved through the following technical solution: A pipette includes a gripping part and a pipetting part, wherein the gripping part and the pipetting part are detachably connected by threads. The gripping part includes a gripping shell and a drive module assembled inside the gripping shell. The gripping shell has an integrally formed arc-shaped gripping handle on its side end and an external thread on its lower outer wall. The drive module includes a pressing rod slidably assembled inside the gripping shell and a spring sleeved on the outside of the pressing rod. The two ends of the spring elastically abut against a limiting step inside the gripping shell and a boss on the pressing rod, respectively. The pipetting part includes a pipetting shell, a piston rod, and a ejection module. The upper inner wall of the pipetting shell is provided with a thread that matches the external thread. The device has a threaded connection and an internal cylindrical cavity for housing the piston rod. The upper end of the piston rod is coaxially fixed with the lower pressure rod, and the lower end is fitted with a seal. The seal is sealed and fitted to the inner wall of the cylindrical cavity of the pipette housing. The lower end of the piston rod and the cylindrical cavity of the pipette housing form a sealed volumetric cavity. The ejection module includes an ejection housing that is slidably sleeved on the outside of the pipette housing and a second spring installed inside the ejection housing. The front end of the ejection housing extends to the outside of the pipette tip connection end of the pipette housing for ejecting the pipette tip. The second spring is sleeved on the outside of the pipette housing, and its two ends are elastically abutted against the inner wall of the ejection housing and the limiting protrusion of the pipette housing, respectively, thereby realizing the automatic return of the ejection housing.

[0006] In a further improvement, the lower end of the piston rod is machined with an installation thread, and a piston ring is threaded onto the installation thread. A sealing ring is embedded in the outer peripheral wall of the piston ring, and the sealing ring is in a sealing fit with the inner wall of the capacity cavity to ensure the airtightness of the capacity cavity.

[0007] In a further improvement, the pipetting shell is a split structure, including a shell one and a shell two. The lower end of the shell one is detachably connected to the upper end of the shell two by a thread. The volumetric cavity is formed inside the shell two, and the piston ring is slidably assembled on the inner wall of the shell two.

[0008] In a further improvement, an annular positioning ring is integrally formed on the side of the piston rod near the piston ring. The outer diameter of the positioning ring is larger than the outer diameter of the piston rod. When the piston rod returns to its original position, the upper end of the positioning ring can abut against the inner wall step of the pipetting housing to limit the maximum return displacement of the piston rod.

[0009] In a further improvement, the piston rod is made of engineering plastic, and its lower end is integrally injection molded with a stainless steel capacity rod. A sealing post is provided at the lower end of the stainless steel capacity rod. The outer peripheral wall of the sealing post is sealed and abutted against the inner wall of the pipette shell, together forming a sealed structure of the capacity cavity.

[0010] In a further improvement, a pressure column is provided at the lower end of the stainless steel capacity rod. The pressure column is located above the sealing column, and a limiting ring is fixed on the inner wall of the pipetting shell at the position corresponding to the pressure column. The upper end of the pressure column can abut against the limiting ring to limit the maximum downward displacement of the sealing column.

[0011] In a further improvement, the piston rod is a segmented structure, including a piston rod one fixedly connected to the lower end of the pressure rod and a piston rod two coaxially connected to the lower end of the piston rod. An elastic sealing module is assembled inside the pipetting housing. The elastic sealing module includes a sealing ring two, a limiting ring, and a spring three. The sealing ring two is embedded in the pipetting housing, and its outer peripheral wall is sealed and tightly abutted against the inner wall of the pipetting housing. The limiting ring is pressed against the upper end of the sealing ring two. One end of the spring three abuts against the limiting ring, and the other end abuts against a protrusion inside the pipetting housing. The piston rod two slides through the inner ring of the sealing ring two, and its outer outer wall is sealed and fitted against the inner ring of the sealing ring two.

[0012] Compared with the prior art, the present invention has the following beneficial effects: During assembly, the upper end of the piston rod of the pipette part is aligned with the lower pressure rod of the gripping part. The pipette housing is rotated to engage and lock the internal and external threads until the upper end of the pipette housing and the lower end of the gripping housing are tightly fitted together, completing the assembly. No special tools are required throughout the process, making the operation simple and efficient. When the pipette needs to be calibrated, maintained, or the pipette part needs to be replaced, the pipette housing is rotated in the opposite direction to separate the internal and external threads, allowing the pipette part to be quickly removed from the gripping part. After disassembly, the pipette part can be calibrated, cleaned, or replaced separately, avoiding the cumbersome process of disassembling the entire unit, thus reducing maintenance costs. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present utility model; Figure 2 This is a cross-sectional view of the gripping part of this utility model; Figure 3 This is a cross-sectional view of the pipetting section of Embodiment 1 of this utility model; Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the present invention; Figure 5 This is a cross-sectional view of the pipetting section of Embodiment 2 of this utility model; Figure 6 This is a schematic diagram of the structure of Embodiment 3 of the present invention; Figure 7 This is a cross-sectional view of the pipetting section in Embodiment 3 of this utility model.

[0014] In the diagram, 1. Grip part; 11. Grip shell; 111. Arc-shaped grip handle; 112. External connecting thread; 12. Drive module; 121. Pressing rod; 122. Spring 1; 2. Pipette part; 21. Pipette shell; 211. Internal connecting thread; 212. Shell 1; 213. Shell 2; 22. Piston rod; 221. Mounting thread part; 222. Piston ring; 223. Sealing ring 1; 2221. Annular positioning ring; 23. Unloading module; 231. Unloading shell; 232. Spring 2; 24. Capacity cavity; 31. Stainless steel capacity rod; 311. Sealing column; 312. Pressing column; 51. Piston rod 1; 52. Piston rod 2; 53. Elastic sealing module; 531. Sealing ring 2; 532. Limiting ring; 533. Spring 3. Detailed Implementation

[0015] In the description of this utility model, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", 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 this utility model 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 this utility model.

[0016] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0017] The following is a description of the embodiments and appendices. Figures 1-7 The technical solution of this utility model will be further described below. Example 1

[0018] A pipette includes a gripping part 1 and a pipetting part 2, wherein the gripping part 1 and the pipetting part 2 are detachably connected by threads. The gripping part 1 includes a gripping housing 11 and a drive module 12 assembled inside the gripping housing 11. The gripping housing 11 has an arc-shaped grip handle 111 integrally formed on its side end, and the lower outer side wall is provided with a connecting external thread 112. The drive module 12 includes a downward pressure rod 121 slidably assembled inside the gripping housing 11 and a spring 122 sleeved on the outside of the downward pressure rod 121. The two ends of the spring 122 elastically abut against a limiting step inside the gripping housing 11 and a boss of the downward pressure rod 121, respectively. The pipetting part 2 includes a pipetting housing 21, a piston rod 22, and a discharge module 23. The upper inner side wall of the pipetting housing 21 is provided with a connecting external thread 112. The connecting internal thread 211 of the pipette housing 21 has a cylindrical cavity for receiving the piston rod 22. The upper end of the piston rod 22 is coaxially fixed with the lower pressure rod 121 and the lower end is equipped with a seal. The lower end of the piston rod 22 and the cylindrical cavity of the pipette housing 21 enclose a sealed volume cavity 24. The ejection module 23 includes an ejection housing 231 that is slidably sleeved on the outside of the pipette housing 21 and a second spring 232 that is installed in the ejection housing 231. The front end of the ejection housing 231 extends to the outside of the pipette tip connection end of the pipette housing 21 for ejecting the pipette tip. The second spring 232 is sleeved on the outside of the pipette housing 21, and its two ends are elastically abutted against the inner wall of the ejection housing 231 and the limiting protrusion of the pipette housing 21, respectively, so as to realize the automatic return of the ejection housing 231.

[0019] like Figures 1-3 As shown, this utility model includes a gripping part 1 and a pipetting part 2, which are connected by a threaded detachable connection to achieve quick disassembly and assembly; the pipetting part 2 integrates a material ejection module 23, which can efficiently complete the ejection of the pipette tip. The specific structure and connection relationship of each component are as follows: The grip 1 is a handheld operating component for the operator and also provides driving force for pipetting operations. It includes a grip housing 11 and a drive module 12. The grip shell 11 has a hollow cylindrical structure, with an integrally formed arc-shaped grip handle 111 on the outer side wall. The arc design fits the contour of the palm, improving grip comfort and facilitating long-term operation. The lower outer side wall of the grip shell 11 is provided with an external thread 112 for detachable connection with the pipetting part 2. The drive module 12 is assembled inside the grip shell 11 and includes a pressing rod 121 and a spring 122. The pressing rod 121 is slidably assembled along the axis of the grip shell 11, with its upper end extending to the outside of the grip shell 11 for pressing operation, and its lower end extending out of the grip shell 11 and docking with the piston rod 22 of the pipetting part 2. An annular boss is integrally formed on the outer side of the middle part of the pressing rod 121, and an annular limiting step is provided at the corresponding position inside the grip shell 11. The spring 122 is sleeved on the outside of the pressing rod 121, with its two ends elastically abutting against the limiting step and the annular boss, respectively. Under normal conditions, the spring 122 is in a naturally extended state, pushing the pressing rod 121 to maintain the initial position of its upper end extending. The pipetting unit 2 is the core component for performing liquid aspiration and dissipation and pipette tip ejection, including the pipetting housing 21, piston rod 22, and ejection module 23: The pipette housing 21 is a hollow cylindrical structure. The inner wall of the upper end is provided with an internal thread 211, which is adapted to the external thread 112 of the grip part 1. The two can be detached and fixed by screwing the threads together. The pipette housing 21 has a cylindrical cavity inside, which is used to house the piston rod 22 and form a volume cavity 24. The lower end is the pipette tip connection end, and the outer side is provided with anti-slip texture to facilitate the pipette tip to be fitted and fixed.

[0020] The piston rod 22 is arranged along the axis of the pipetting housing 21, and its upper end is fixed coaxially with the lower pressure rod 121. It rises and falls synchronously with the lower pressure rod 121. A sealing element is embedded at the lower end of the piston rod 22. The sealing element is tightly fitted to the inner wall of the columnar cavity of the pipetting housing 21 to ensure the sealing of the volumetric cavity 24. The pressure inside the volumetric cavity 24 is changed by the rise and fall of the piston rod 22 to realize the intake and discharge of liquid.

[0021] The ejector module 23 is sleeved on the outside of the pipetting housing 21 and includes an ejector housing 231 and a second spring 232. The ejector housing 231 is an annular sleeve structure that can slide along the axis of the pipetting housing 21. Its front end extends inward to form an annular push plate. The inner diameter of the annular push plate is adapted to the outer diameter of the pipetting housing 21's tip connection end and extends to the outside of the tip connection end for contact with the rear end of the tip. The outside of the pipetting housing 21 is provided with an annular limiting protrusion corresponding to the installation position of the ejector housing 231. The second spring 232 is sleeved on the outside of the pipetting housing 21, and its two ends are elastically abutted against the inner wall of the ejector housing 231 and the annular limiting protrusion, respectively. Under normal conditions, the second spring 232 pushes the ejector housing 231 to remain in the initial position away from the tip connection end. After ejection, it can drive the ejector housing 231 to automatically return to its original position.

[0022] During assembly, the upper end of the piston rod 22 of the pipette part 2 is aligned with the lower pressure rod 121 of the gripping part 1. The pipette housing 21 is rotated to engage and lock the internal thread 211 with the external thread 112 until the upper end of the pipette housing 21 and the lower end of the gripping housing 11 are tightly fitted together, thus completing the assembly. No special tools are required throughout the process, making the operation simple and efficient. When the pipette part 2 needs to be periodically calibrated, maintained, or replaced, the pipette housing 21 is rotated in the opposite direction to separate the internal thread 211 from the external thread 112, allowing the pipette part 2 to be quickly removed from the gripping part 1. After disassembly, the pipette part 2 can be calibrated, cleaned, or replaced separately, avoiding the cumbersome process of disassembling the entire integrated structure and reducing maintenance costs.

[0023] Its usage process is as follows: Liquid aspiration operation: Fit the pipette tip connector of the pipette section 2 with the pipette tip and fix it in place. The operator holds the arc-shaped handle 111 and presses down the lower lever 121 to compress the spring 122, which moves the piston rod 22 downward to expel the air in the volumetric cavity 24. Insert the pipette tip into the liquid to be transferred, and slowly release the lower lever 121. The spring 122 returns to its original position and pushes the lower lever 121 and the piston rod 22 upward, creating a negative pressure in the volumetric cavity 24 and drawing the liquid into the pipette tip. Dispensing operation: Move the pipette tip above the target container, press down the pressure rod 121, which will move the piston rod 22 down, squeezing the liquid in the volumetric cavity 24 and dispensing the liquid from the pipette tip to complete the pipetting.

[0024] Material ejection operation: After pipetting, press down on the ejection housing 231 to compress the second spring 232, causing the ejection housing 231 to slide along the pipetting outer shell 21 towards the pipette tip. The annular push plate at its front end abuts against the rear end of the pipette tip and applies a pushing force to push the pipette tip out from the pipette tip connection end. After releasing the ejection housing 231, the second spring 232 resets, causing the ejection housing 231 to automatically return to its initial position, ready for the next operation. This eliminates the need for manual removal of the pipette tip, avoiding reagent contamination or hand injury and improving operational convenience.

[0025] As a further preferred embodiment, the lower end of the piston rod 22 is machined with a mounting thread 221, and a piston ring 222 is threaded onto the mounting thread 221. A sealing ring 223 is embedded in the outer peripheral wall of the piston ring 222, and the sealing ring 223 is sealed and fitted with the inner wall of the capacity cavity 24 to ensure the airtightness of the capacity cavity 24.

[0026] Specifically, the piston ring 222 and piston rod 22 are detachably connected by the threaded part 221, which not only facilitates assembly but also allows for the individual replacement of worn piston ring 222 or sealing ring 223 without replacing the entire piston rod 22, thus reducing maintenance costs. The sealing ring 223 is embedded in the outer peripheral wall of the piston ring 222 and seals tightly against the inner wall of the volumetric cavity 24, significantly improving the airtightness of the volumetric cavity 24. This effectively prevents liquid leakage or air pressure leakage during pipetting due to poor sealing, ensuring the accuracy of liquid aspiration and dispensing, and is suitable for experimental and testing scenarios with high requirements for pipetting accuracy.

[0027] As a further preferred embodiment, the pipetting housing 21 has a split structure, including a first housing 212 and a second housing 213. The lower end of the first housing 212 is detachably connected to the upper end of the second housing 213 by a thread. The volumetric cavity 24 is formed inside the second housing 213, and the piston ring 222 is slidably fitted onto the inner wall of the second housing 213.

[0028] Specifically, housing 1 212 and housing 2 213 are detachably connected by threads, further optimizing the advantages of the split design. On the one hand, during assembly, components such as piston rod 22 and piston ring 222 can be pre-installed in housing 2 213 and then docked and fixed with housing 1 212. The disassembly steps are simple, solving the problems of complex assembly and inconvenient maintenance of internal components in traditional integrated pipetting housings. On the other hand, when the inner wall of the volumetric cavity 24 is worn or contaminated, or housing 2 213 is damaged, housing 2 213 can be disassembled and replaced separately without replacing the entire pipetting housing 21. This simplifies the maintenance process and reduces consumable costs. At the same time, the split design of the grip part 1 and the pipetting part 2 enables multi-level split maintenance, further improving ease of use.

[0029] As a further preferred embodiment, an annular positioning ring 2221 is integrally formed on the side of the piston rod 22 near the piston ring 222. The outer diameter of the positioning ring 2221 is larger than the rod diameter of the piston rod 22. When the piston rod 22 returns to its original position, the upper end of the positioning ring 2221 can abut against the inner wall step of the pipetting housing 21 to limit the maximum return displacement of the piston rod 22.

[0030] Specifically, the annular positioning ring 2221 abuts against the step on the inner wall of the pipetting housing 21 to limit the maximum reset displacement of the piston rod 22. This prevents the piston rod 22 from moving excessively upward due to excessive reset force of the spring 122, thereby preventing the piston ring 222 from hardly colliding with the upper end of the volumetric cavity 24 and causing wear on the components, thus extending the service life of the piston ring 222, the sealing ring 223, and the inner wall of the volumetric cavity. At the same time, the positioning ring 2221 ensures that the piston rod 22 is in the same initial position after each reset, ensuring the consistency of the volume of each pipetting operation, improving the repeatability and accuracy of the pipetting operation, and avoiding the impact of piston rod displacement deviation on the accuracy of experimental data. Example 2

[0031] like Figures 4-5 As shown, the difference between Embodiment 2 and Embodiment 1 is that the piston rod 22 is made of engineering plastic, and its lower end is fixedly connected to a stainless steel capacity rod 31 by an integral injection molding process. The lower end of the stainless steel capacity rod 31 is provided with a sealing post 311. The outer peripheral wall of the sealing post 311 is sealed and abutted against the inner wall of the pipetting shell 21, together forming the sealing structure of the capacity cavity 24.

[0032] Specifically, the piston rod 22 is made of engineering plastic, combining lightweight design with good structural strength. Its lower end is fixedly connected to the stainless steel capacity rod 31 through an integrated injection molding process. Compared with traditional threaded or snap-fit ​​connections, the structure is more stable, avoiding problems such as loosening or falling off during long-term use and improving the reliability of component connections. The design of the stainless steel capacity rod 31 with the sealing column 311 utilizes the wear-resistant and corrosion-resistant properties of stainless steel to extend the service life of the capacity rod. At the same time, the sealing column 311 and the inner wall of the pipetting shell 21 seal tightly, strengthening the airtightness of the capacity cavity 24 and effectively preventing liquid leakage or air pressure loss during pipetting, ensuring pipetting accuracy. Meanwhile, the integrated injection molding process simplifies the assembly process, eliminating the need for additional component docking and fixing, and improving production and assembly efficiency.

[0033] As a further preferred embodiment, the lower end of the stainless steel capacity rod 31 is provided with a pressure column 312. The pressure column 312 is located on the upper side of the sealing column 311, and a limiting ring is fixed on the inner wall of the pipetting shell 21 at the position corresponding to the pressure column 312. The upper end of the pressure column 312 can abut against the limiting ring to limit the maximum downward displacement of the sealing column 311.

[0034] Specifically, the pressure column 312 at the lower end of the stainless steel capacity rod 31 forms a limiting fit with the limiting ring on the inner wall of the pipetting housing 21, which can strictly limit the maximum downward displacement of the sealing column 311. This prevents the sealing column 311 from moving too far downward and colliding hard with the bottom of the capacity cavity 24 due to excessive pressure from the operator or deviation in the reset of the drive module. This prevents the sealing column 311 from wearing out, deforming, or the inner wall of the pipetting housing 21 from being damaged, thus extending the service life of the sealing structure. Example 3

[0035] like Figures 6-7As shown, the difference between Embodiment 3 and Embodiment 1 is that the piston rod 22 has a segmented structure, including a piston rod 51 fixedly connected to the lower end of the lower pressure rod 121 and a piston rod 52 coaxially connected to the lower end of the piston rod 51. An elastic sealing module 53 is assembled inside the pipetting housing 21. The elastic sealing module 53 includes a sealing ring 531, a limiting ring 532, and a spring 533. The sealing ring 531 is embedded in the pipetting housing 21, and its outer peripheral wall is sealed and abutted against the inner wall of the pipetting housing 21. The limiting ring 532 is pressed against the upper end of the sealing ring 531. One end of the spring 533 abuts against the limiting ring 532, and the other end abuts against a protrusion inside the pipetting housing 21. The piston rod 52 slides through the inner ring of the sealing ring 531, and its outer outer wall is sealed and fitted against the inner ring of the sealing ring 531.

[0036] Specifically, the piston rod 22 adopts a segmented structure design, which simplifies the overall assembly process. The piston rod 1 51 can be fixed to the pressing rod 121 of the grip, and the piston rod 2 52 can be adapted and installed to the elastic sealing module 53 before coaxial connection. Compared with the integrated piston rod, there is no need for complicated overall alignment operation. On the other hand, when a section of the piston rod is worn, deformed or damaged, the corresponding section can be disassembled and replaced separately without replacing the entire piston rod assembly. Combined with the separate design of the pipette grip and the pipetting part, the advantages of graded maintenance are further enhanced, and maintenance costs and consumable consumption are greatly reduced. At the same time, the segmented structure makes it easy to replace the adapted piston rod 2 52 according to different pipetting needs, improving the adaptability of the pipette. Spring 3 533 continuously applies downward elastic pressure to sealing ring 2 531 through limiting ring 532, ensuring that the outer peripheral wall of sealing ring 2 531 is always tightly pressed against the inner wall of pipetting housing 21, and the inner ring is sealed against the outer wall of piston rod 2 52, forming a bidirectional elastic sealing structure. This effectively avoids sealing failure caused by wear of sealing components or assembly deviations, significantly reducing the risk of liquid leakage or gas pressure leakage during pipetting. The elastic pressure of spring 3 533 can automatically compensate for normal wear of sealing ring 2 531. Even if sealing ring 2 531 experiences slight wear, the preload of the spring can still maintain the sealing effect, extending the service life of sealing ring 2 531. The preferred embodiments of this utility model have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of this utility model without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of this utility model through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A pipette, characterized in that, It includes a gripping part and a pipetting part, which are detachably connected by threads. The gripping part includes a gripping housing and a drive module assembled inside the gripping housing. The grip shell has an integrally formed arc-shaped grip handle on one side, and the lower outer wall is provided with external threads. The drive module includes a pressure rod slidably mounted inside the gripping housing and a spring sleeved on the outside of the pressure rod. The two ends of the spring elastically abut against a limiting step inside the gripping housing and a boss on the pressure rod, respectively. The pipetting unit includes a pipetting housing, a piston rod, and an ejection module. The upper inner wall of the pipetting housing has an internal thread that mates with the external thread, and an internal cylindrical cavity for housing the piston rod. The upper end of the piston rod is coaxially fixed to the pressure rod, and the lower end is fitted with a seal. The cylindrical cavity of the pipette housing is sealed and fitted to the inner wall. The lower end of the piston rod and the cylindrical cavity of the pipette housing form a closed volumetric cavity. The ejection module includes an ejection shell that is slidably sleeved on the outside of the pipette housing and a second spring assembled inside the ejection shell. The front end of the ejection shell extends to the outside of the pipette tip connection end of the pipette housing for ejecting the pipette tip. The second spring is sleeved on the outside of the pipette housing, and its two ends are elastically abutted against the inner wall of the ejection shell and the limiting protrusion of the pipette housing, respectively, thereby realizing the automatic return of the ejection shell.

2. A pipette according to claim 1, characterized in that, The lower end of the piston rod is machined with an installation thread, and a piston ring is threaded onto the installation thread. A sealing ring is embedded in the outer peripheral wall of the piston ring, and the sealing ring is sealed and fitted to the inner wall of the capacity cavity to ensure the airtightness of the capacity cavity.

3. A pipette according to claim 2, characterized in that, The pipetting shell has a split structure, including a shell one and a shell two. The lower end of the shell one is detachably connected to the upper end of the shell two by threads. The volumetric cavity is formed inside the shell two, and the piston ring is slidably assembled on the inner wall of the shell two.

4. A pipette according to claim 2 or 3, characterized in that, The piston rod has an integrally formed annular positioning ring on the side near the piston ring. The outer diameter of the positioning ring is larger than the outer diameter of the piston rod. When the piston rod returns to its original position, the upper end of the positioning ring can abut against the inner wall step of the pipetting shell to limit the maximum return displacement of the piston rod.

5. A pipette according to claim 1, characterized in that, The piston rod is made of engineering plastic, and its lower end is integrally injection molded with a stainless steel capacity rod. The lower end of the stainless steel capacity rod is provided with a sealing post. The outer peripheral wall of the sealing post is sealed and abutted against the inner wall of the pipette shell, together forming the sealing structure of the capacity cavity.

6. A pipette according to claim 5, characterized in that, The lower end of the stainless steel capacity rod is provided with a pressure column, which is located above the sealing column. A limiting ring is fixed on the inner wall of the pipetting shell at the position corresponding to the pressure column. The upper end of the pressure column can abut against the limiting ring to limit the maximum downward displacement of the sealing column.

7. A pipette according to claim 1, characterized in that, The piston rod has a segmented structure, including a piston rod one fixedly connected to the lower end of the lower pressure rod and a piston rod two coaxially connected to the lower end of the piston rod. The pipetting housing is equipped with an elastic sealing module, which includes a sealing ring two, a limiting ring and a spring three. The sealing ring two is embedded in the pipetting housing, and its outer peripheral wall is sealed and abutted against the inner wall of the pipetting housing. The limiting ring is pressed against the upper end of the sealing ring two. One end of the spring three abuts against the limiting ring, and the other end abuts against a protrusion inside the pipetting housing. The piston rod two slides through the inner ring of the sealing ring two, and its outer outer wall is sealed and fitted against the inner ring of the sealing ring two.

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