Cold end structure of ultralow-temperature ultrahigh-pressure pump

Abstract

The invention relates to a cold end structure of an ultralow-temperature ultrahigh-pressure pump, and relates to the field of ultralow-temperature pumping. Comprising an outer cylinder sleeve capable of sucking liquid nitrogen, liquid oxygen, liquid hydrogen or LNG, a piston rod connected to the outer cylinder sleeve in a sliding mode, an inner cylinder sleeve connected between the piston rod and the outer cylinder sleeve in a sleeved mode, an inner core fixedly connected to one end of the outer cylinder sleeve, a liquid drainage one-way valve connected to the inner core in a sliding mode and a liquid drainage connector fixedly connected to one end of the outer cylinder sleeve. The sealing cover is fixedly connected to the other end of the outer cylinder sleeve; the slip is connected with a driving component; the slips are of a semi-cylindrical shell structure, the two ends of the two slips in the axis direction are buckled to the end, extending out of the outer cylinder sleeve, of the piston rod and outside a driving shaft of the driving component, and the two slips do not make contact and are in butt joint through a bolt pair.

Description

Technical Field

[0001] The present invention relates to the technical field of cryogenic pumping technology, and particularly to a cold end structure of a cryogenic and ultra-high pressure pump. Background Art

[0002] The liquid nitrogen (oxygen, LNG, hydrogen) cold end is the core component of a liquid nitrogen (oxygen, LNG, hydrogen) pump. It can extend into a cryogenic environment to achieve high-pressure pumping of liquid nitrogen (liquid oxygen, LNG, liquid hydrogen), and can be used in various special operations for exploration and development such as nitrogen gas lift, nitrogen displacement, nitrogen fracturing, and gas-mixed acidification. Since liquid nitrogen (oxygen, LNG, hydrogen) pumps are special operating equipment, the media they transport have characteristics such as high pressure and low temperature. Therefore, three-cylinder pumps used in oil fields, such as injection pumps and fracturing pumps, are not suitable for transporting cryogenic liquids. In addition, the existing motor-driven reciprocating pumps use inlet valve groups and discharge valve groups, which have a relatively complex structure, many vulnerable parts, and low reliability.

[0003] Therefore, in view of the above deficiencies, a cold end structure of a cryogenic and ultra-high pressure pump needs to be provided. Summary of the Invention

[0004] (I) Technical Problems to be Solved The technical problem to be solved by the present invention is how to improve the reliability of the cryogenic cold end.

[0005] (II) Technical Solutions To solve the above technical problems, the present invention provides a cold end structure of a cryogenic and ultra-high pressure pump, which includes an outer cylinder sleeve capable of sucking liquid nitrogen, liquid oxygen, liquid hydrogen or LNG, a piston rod slidably connected to the outer cylinder sleeve, an inner cylinder sleeve sleeved between the piston rod and the outer cylinder sleeve, an inner core fixedly connected to one end of the outer cylinder sleeve, a discharge check valve slidably connected to the inner core, a discharge joint fixedly connected to one end of the outer cylinder sleeve, a cover fixedly connected to the other end of the outer cylinder sleeve, and a jaw connected to a driving component; the jaw is in a semi-cylindrical shell structure, and both ends of the two jaws in the axial direction are buckled outside one end of the piston rod extending out of the outer cylinder sleeve and the driving shaft of the driving component, and the two jaws do not contact and are butt-jointed through a bolt pair.

[0006] As a further description of the present invention, preferably, a bolt hole is provided in the middle of the jaw, and the bolt pair penetrates into the bolt hole and is located between the driving shaft and the piston rod so that the driving shaft does not contact the piston rod.

[0007] As a further description of the present invention, preferably, the diameter of the part of the piston rod extending into the outer cylinder sleeve is reduced, the inner cylinder sleeve is sleeved outside the reduced-diameter end of the piston rod, and a plurality of overflow grooves are spaced apart on the outer wall surface of the inner cylinder sleeve. The length direction of the overflow grooves is the same as the length direction of the inner cylinder sleeve. One end of the overflow groove close to the inner core is closed and the other end is open. An overflow port is provided on the outer cylinder sleeve at the closed end of the overflow groove, and the overflow port is communicated with the overflow groove.

[0008] As a further illustration of the present invention, preferably, the dimensions of the inner cylinder liner satisfy: wherein, is the pressure borne by the inner cylinder liner; is the allowable stress of the material; is the outer diameter of the inner cylinder liner; is the inner diameter of the inner cylinder liner; is the total outer margin; is the total inner margin; is the temperature.

[0009] As a further illustration of the present invention, preferably, a plurality of piston rings are inserted on the contact surface between the piston rod and the inner cylinder liner, and the piston rings are in contact with each other in pairs and the outer wall surfaces are in contact with the inner cylinder liner.

[0010] As a further illustration of the present invention, preferably, an expansion ring is inserted between the inner wall surface of the piston ring and the piston rod, and the outer wall surface of the expansion ring is in contact with the inner wall surface of the piston ring to push the piston ring towards the inner cylinder liner.

[0011] As a further illustration of the present invention, preferably, a guide ring is inserted on the piston rod between the piston ring and the inner core, and the guide ring is in interference fit with the inner cylinder liner at normal temperature.

[0012] As a further illustration of the present invention, preferably, a plurality of packing rings are arranged along the axial direction between the piston rod and the outer cylinder liner. The packing rings are conical and the ends with smaller outer diameters all face the inner core. A pressing ring with a tapered groove is inserted between adjacent packing rings, and the pressing ring is in contact with the conical surface of the packing ring and the outer cylinder liner.

[0013] As a further illustration of the present invention, preferably, a circular ring is provided at the end with a larger outer diameter of the packing ring, the outer diameter of the circular ring is equal to the inner diameter of the outer cylinder liner, and the side surface of the pressing ring is in contact with the circular ring.

[0014] As a further illustration of the present invention, preferably, a waterline seal is provided at the connection end between the inner cylinder liner and the inner core, and a waterline seal is adopted on the inner side of the contact surface between the inner core and the liquid discharge joint, and a non-metallic wedge seal is adopted on the outer side.

[0015] (III) Beneficial effects The above technical solutions of the present invention have the following advantages: 1. The cold end assembly designed by the present invention has high adaptability. Due to the use of a slip joint compensator structure design at the connection end, the coaxiality requirement for the cold end and the driving device is reduced, and the piston can automatically achieve active compensation in the radial direction, thereby achieving higher stroke requirements. For ordinary cold ends, the stroke is usually 200 - 300 strokes / min. Since the cold end of the present invention uses a replaceable special material inner cylinder liner, the maximum stroke of the cold end can reach 1000 strokes / min, which is three times that of ordinary cold ends. 2. Through the linkage and cooperation of various components, the cold end of the present invention has a larger displacement. Under the condition of the same cylinder diameter, the liquid discharge volume of a single cold end is 3 - 4 times that of an ordinary cold end. 3. Through the linkage and cooperation of various components, the cold end structure of the present invention has stronger pressure resistance. For ordinary cold ends with the same cylinder diameter, the normal pressure resistance is 35 - 40 MPa, while the maximum pressure resistance of the cold end of the present invention can reach 140 MPa, which is 3 - 4 times the pressure resistance limit of ordinary cold ends. 4. Through the linkage and cooperation of various components, the overall service life of the cold end is longer. Under normal operating conditions, the internal wear-resistant steel sleeve and piston ring can be replaced to extend the overall service life of the cold end, greatly reducing the customer's use cost. 5. The volumetric efficiency of the cold end of the present invention can reach more than 90%. The piston ring and the inner cylinder liner are made of highly wear-resistant materials and are sealed by interference fit, so that the piston ring and the inner cylinder liner are in full contact and jointly bear pressure, resulting in lower leakage and stronger pressure resistance. Description of the Drawings

[0016] Figure 1 is the general assembly sectional view of the present invention; Figure 2 is the slip joint structure diagram of the present invention; Figure 3 is Figure 1 the enlarged view of A in Figure 4 is the packing structure diagram of the present invention; Figure 5 is Figure 1 the enlarged view of B in Figure 6 is the inner cylinder liner structure diagram of the present invention.

[0017] In the figure: 1. Outer cylinder liner; 11. Liquid inlet; 12. Overflow port; 2. Piston rod; 21. Pressure ring; 22. Packing; 23. Piston ring; 24. Expansion ring; 25. Guide ring; 3. Inner cylinder liner; 31. Overflow groove; 4. Inner core; 41. Flow channel; 5. Drain check valve; 6. Drain joint; 7. Cover; 8. Slip joint; 9. Drive shaft. Detailed Embodiments

[0018] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0019] A cold end structure of an ultra-low temperature and ultra-high pressure pump, as Figure 1 shown, includes an outer cylinder sleeve 1, a piston rod 2, an inner cylinder sleeve 3, an inner core 4, a liquid discharge check valve 5, a liquid discharge joint 6, a cover 7 and a chuck 8; one end of the piston rod 2 is slidably connected inside the outer cylinder sleeve 1, and the other end extends outside the outer cylinder sleeve 1. The inner cylinder sleeve 3 is fixedly connected between the outer cylinder sleeve 1 and the piston rod 2. The inner core 4 is fixedly connected inside the outer cylinder sleeve 1. The liquid discharge check valve 5 is slidably connected inside the inner core 4. The liquid discharge joint 6 is fixedly connected to one side of the outer cylinder sleeve 1 close to the inner core 4. The cover 7 is fixedly connected to the side of the outer cylinder sleeve 1 away from the liquid discharge joint 6. The chuck 8 is sleeved outside the piston rod 2 and the driving component.

[0020] As Figure 1 shown, the outer cylinder sleeve 1 is of a columnar structure. There is a liquid inlet 11 on one side of the outer cylinder sleeve 1. The inner core 4 is located inside the outer cylinder sleeve 1 at the liquid inlet 11. A plurality of flow channels 41 are formed on the outer wall surface of the inner core 4. The liquid inlet 11 communicates with the flow channels 41. The flow channels 41 are connected to the inner space inside the outer cylinder sleeve 1 between the piston rod 2 and the inner core 4 through the inner core 4. There is a thread on the outer wall surface of the outer cylinder sleeve 1 close to the extending end of the piston rod 2 and is threadedly connected with a nut. By passing the threaded part of the outer cylinder sleeve 1 into the fixed end of the driving component and locking with the nut, the installation of the outer cylinder sleeve 1 is realized. The output end of the driving component is connected to the piston rod 2 through the chuck 8 to push and pull the piston rod 2. When the piston rod 2 is pulled outwards, a negative pressure environment is formed inside the inner cylinder sleeve 3. At this time, the atmospheric pressure presses the ultra-low temperature liquid nitrogen, liquid oxygen, liquid hydrogen or LNG in the container into the inner cylinder sleeve 3 through the liquid inlet 11 via the flow channels 41, realizing the pumping effect.

[0021] As Figure 1As shown in the figure, a stepped hole is provided in the middle of the inner core 4. One end with a smaller hole diameter is communicated with the moving space of the piston rod 2. The liquid discharge check valve 5 is slidably connected to the end with a larger hole diameter. The liquid discharge joint 6 also abuts against the outside of the end with a larger hole diameter of the inner core 4. A spring is abutted between the liquid discharge check valve 5 and the liquid discharge joint 6. The liquid discharge check valve 5 is pushed towards the end with a smaller hole diameter by the elastic force of the spring to block the small hole. When the driving component pushes the piston rod 2 inwards, the piston rod 2 pushes the ultra-low temperature (-196°C) liquid nitrogen, liquid oxygen, liquid hydrogen or LNG towards the liquid discharge check valve 5. The liquid discharge check valve 5 compresses the spring so that the moving space of the piston rod 2 is communicated with the inner space of the liquid discharge joint 6, and then the ultra-low temperature liquid nitrogen, liquid oxygen, liquid hydrogen or LNG can be pumped out to realize the pumping work. Among them, the end face of the liquid discharge joint 6 is designed with an Autoclave buckle type with a 60° conical surface, and its maximum pressure-bearing capacity can reach 700 MPa. In addition, a waterline seal is provided at the connection end of the inner cylinder sleeve 3 and the inner core 4. The inner side of the joint surface between the inner core 4 and the liquid discharge joint 6 uses a waterline seal, and the outer side uses a non-metallic wedge seal to ensure that the compressed high-pressure medium will not leak during the process of discharging from the outer cylinder sleeve 1.

[0022] Combined with Figure 1 、 Figure 6 , the piston rod 2 is a solid cylindrical rod, and the diameter of the part of the piston rod 2 extending into the outer cylinder sleeve 1 is reduced. The inner cylinder sleeve 3 is a T-shaped cylindrical structure made of high wear-resistant stainless steel. The part with a smaller outer diameter of the inner cylinder sleeve 3 is sleeved outside the end with a reduced diameter of the piston rod 2, and the end with a larger outer diameter of the inner cylinder sleeve 3 is clamped between the outer cylinder sleeve 1 and the inner core 4. A plurality of overflow grooves 31 are spaced apart on the outer wall surface of the part with a smaller outer diameter of the inner cylinder sleeve 3. The length direction of the overflow grooves 31 is the same as the length direction of the inner cylinder sleeve 3. One end of the overflow grooves 31 close to the inner core 4 extends to the end with a larger outer diameter of the inner cylinder sleeve 3 and then is grooved radially, so that one end of the overflow grooves 31 close to the inner core 4 is closed. The other end of the overflow grooves 31 extends out of the inner cylinder sleeve 3 to be open. An overflow port 12 is provided on the outer cylinder sleeve 1 at the closed end of the overflow grooves 31, and the overflow port 12 is communicated with the overflow grooves 31. The liquid compressed and leaked in the inner cylinder sleeve 3 is discharged from the cold end through the overflow port 12 on the outer cylinder sleeve 1 through the overflow grooves 31, thereby avoiding the damage to the cold end caused by cavitation. In addition, the sealing method of interference fit between the inner cylinder sleeve 3 and the wall surface of the piston rod 2 enables the piston ring 23 to be in full contact with the inner cylinder sleeve 3 and thus be able to bear pressure together, and at the same time is not affected by cold shrinkage in the ultra-low temperature environment, resulting in lower leakage and stronger pressure resistance.

[0023] Among them, the size of the inner cylinder sleeve 3 meets: Among them, is the pressure borne by the inner cylinder sleeve 3; is the allowable stress of the material; is the outer diameter of the inner cylinder liner 3; is the inner diameter of the inner cylinder liner 3; is the total outer margin; is the total inner margin; is the temperature.

[0024] Through reasonable design, the inner cylinder liner 3 can bear a pressure of 140 MPa.

[0025] Combined with Figure 1 , Figure 3 and Figure 4 , the gland 7 is located at one end of the piston rod 2 extending out of the outer cylinder liner 1. There are multiple layers of packing 22 arranged along the axial direction between the piston rod 2 and the outer cylinder liner 1. The packing 22 is made of composite low-temperature resistant PTFE material. The packing 22 is conical and the small-diameter end of each packing faces the inner core 4. A pressure ring 21 with a tapered groove is inserted between adjacent packings 22. The pressure ring 21 is made of metal and abuts against the conical surface of the packing 22 and the outer cylinder liner 1. A ring is provided at the large-diameter end of the packing 22, and the outer diameter of the ring is equal to the inner diameter of the outer cylinder liner 1. The side surface of the pressure ring 21 abuts against the ring, and the ring on the outermost packing 22 abuts against the gland 7 to ensure that the packing 22 is always located inside the outer cylinder liner 1.

[0026] Through the above settings, the packing 22 forms a conical seal under the pre-tightening force of the pressure ring 21. When the piston rod 2 is moving inward, the high-pressure pumping liquid will overflow to the packing 22 through the gap of the inner cylinder liner 3. At this time, the pressure of the overflow liquid will act on the inverted conical sealing cone surface. Under the dual action of the pre-tightening force of the pressure ring 21 and the assisting pressure of the overflow liquid, the inverted conical packing 22 is in close contact with the piston rod 2, so as to ensure excellent sealing effect at the packing 22 when the piston rod 2 is in the state of compressing the liquid. At the same time, when the piston rod 2 is in the outward state, the inverted conical packing 22 can also scrape off the low-temperature liquid on the surface of the piston rod 2, ensuring that the low-temperature liquid will not be taken out of the outer cylinder liner 1 by the piston rod 2, killing two birds with one stone.

[0027] Combined with Figure 1 , Figure 5, several groups of piston rings 23 are inserted on the contact surface between the piston rod 2 and the inner cylinder sleeve 3. Two piston rings 23 are closely attached within each group of piston rings 23, and the outer wall surface of the piston rings 23 abuts against the inner cylinder sleeve. An expansion ring 24 is inserted between the inner wall surface of the piston rings 23 and the piston rod 2, and the outer wall surface of the expansion ring 24 abuts against the inner wall surface of the piston rings 23. The outer diameter of the expansion ring 24 in the free state is larger than the inner diameter size of the piston rings 23 in the free state. After the piston rings 23 are installed, under the tension of the expansion ring 24, the piston rings 23 are always kept in a contact state with a certain pressure against the inner cylinder sleeve 3. At the same time, when the piston rod 2 moves, cryogenic liquid nitrogen, liquid oxygen, LNG or liquid hydrogen plays a lubricating role on the contact surface, greatly improving the pumping efficiency of the cold end under high-pressure conditions. At the same time, as the piston rings 23 wear, the thickness of the piston rings 23 decreases. Due to the expansion effect of the expansion ring 24, radial compensation is carried out on the piston rings 23, ensuring the maximum utilization rate of the piston rings 23, thereby greatly increasing the service life of the cold end.

[0028] As Figure 1 shown, a non-metallic guide ring 25 is inserted on the piston rod 2 between the piston rings 23 and the inner core 4, and a guide ring 25 is also provided on the other side of the piston rings 23. The guide ring 25 has an interference fit with the inner cylinder sleeve 3 at normal temperature. Setting the guide ring 25 can ensure that when the piston rod 2 makes high-speed reciprocating motion in the inner cylinder sleeve 3, it remains concentric with the inner cylinder sleeve 3, reducing the possibility of metal contact between the piston rod 2 and the inner cylinder sleeve 3, thereby protecting the inner cylinder sleeve 3 and the piston rod 2. In addition, in a cryogenic environment, due to the linear expansion coefficient of the guide ring 25 being smaller than that of the inner cylinder sleeve 3, the fit between the guide ring 25 and the inner cylinder sleeve 3 changes from an interference fit at normal temperature to a near clearance fit. At the same time, cryogenic liquid nitrogen, liquid oxygen, LNG or liquid hydrogen plays a lubricating role in the clearance, greatly increasing the service life of the cold end and the pumping efficiency under high-pressure conditions.

[0029] Combined with Figure 1 , Figure 2, the slip 8 is a semi-cylindrical shell structure. A bolt hole is provided in the middle of the slip. Both ends of the two slips 8 in the axial direction are buckled on one end of the piston rod 2 extending out of the outer cylinder sleeve 1 and the drive shaft 9 of the drive component. The two slips 8 do not contact each other and are butted through a bolt pair. The bolt pair penetrates into the bolt hole and is located between the drive shaft 9 and the piston rod 2 so that the drive shaft 9 does not contact the piston rod 2. The annular groove at the connection between the upper and lower slips 8 and the piston rod 2 adopts a clearance structure design. The traditional cold end is thread-connected to the drive end. Due to the action of the pre-tightening force of the ordinary connector, the coaxiality between the piston rod 2 and the inner cylinder sleeve 3 cannot be guaranteed, so that the piston rod 2 and the inner cylinder sleeve 3 are prone to wear. In the present invention, by using two-piece slips 8 as a compensator, there is a gap with a certain width designed at the connection of the upper and lower slips 8. When the crosshead at the power end pushes the piston rod 2, even if there is a coaxiality deviation between the two, due to the existence of the compensation gap of the compensator, under the action of the guide ring 25 inside the piston rod 2, the piston rod 2 is straightened, avoiding the wear of the piston rod 2 and the inner cylinder sleeve 3 caused when the coaxiality between the piston rod 2 and the inner cylinder sleeve 3 cannot be guaranteed.

[0030] In summary, the cold end assembly designed by the present invention has high adaptability. Due to the use of the slip 8 connection compensator structure design at the connection end, the coaxiality requirement for the cold end and the drive device is reduced, and the radial movement compensation of the piston can be automatically realized, and then a higher stroke frequency requirement can be achieved; the stroke frequency of the ordinary cold end is usually 200 - 300 strokes / min. The cold end of the present invention can reach a maximum stroke frequency of 1000 strokes / min because it adopts a replaceable special material inner cylinder sleeve 3, which is 3 times that of the ordinary cold end. Moreover, the interference fit with the piston rod 2 can be approximately combined into one part, and the pressure resistance degree far exceeds that of a single part. And under the action of the packing 22, the piston ring 23 and the guide ring 25, the pressure resistance ability of the cold end structure is stronger. Specifically, for ordinary cold ends with the same cylinder diameter size, the normal pressure resistance is 35 - 40 MPa, while the cold end of the present invention can reach a maximum pressure resistance of 104 MPa in the current actual work, and the theoretical maximum pressure resistance can reach 140 MPa, which is 3 - 4 times the pressure resistance limit of the ordinary cold end. Even if there is an overflow, it can still flow back into the container filled with cryogenic medium through the overflow port 12, avoiding waste and not significantly reducing the structural strength of the inner cylinder sleeve 3 itself.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cold end structure of an ultra-low temperature and ultra-high pressure pump, characterized in that: The invention comprises an outer cylinder sleeve (1) capable of sucking liquid nitrogen, liquid oxygen, liquid hydrogen or LNG, a piston rod (2) slidably connected to the outer cylinder sleeve (1), an inner cylinder sleeve (3) sleeved between the piston rod (2) and the outer cylinder sleeve (1), an inner core (4) fixedly connected to one end of the outer cylinder sleeve (1), a discharge check valve (5) slidably connected to the inner core (4), a discharge joint (6) fixedly connected to one end of the outer cylinder sleeve (1), a sealing cover (7) fixedly connected to the other end of the outer cylinder sleeve (1) and a slip (8) connected to a driving component; the piston rod (2) The diameter of the portion extending into the outer cylinder sleeve (1) is reduced, and the inner cylinder sleeve (3) is sleeved on the outer side of the end of the piston rod (2) with a reduced diameter. A plurality of overflow grooves (31) are arranged at intervals on the outer wall surface of the inner cylinder sleeve (3). The length direction of the overflow grooves (31) is the same as the length direction of the inner cylinder sleeve (3). One end of the overflow groove (31) close to the inner core (4) is closed and the other end is open. An overflow port (12) is provided on the outer cylinder sleeve (1) at the closed end of the overflow groove (31), and the overflow port (12) is communicated with the overflow groove (31).

2. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 1, characterized in that: A bolt hole is provided in the middle of the slip (8), and a bolt pair is inserted into the bolt hole and is located between the drive shaft (9) and the piston rod (2) so that the drive shaft (9) does not contact the piston rod (2).

3. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 1, characterized in that: The slips (8) are of a semi-cylindrical shell structure. The two slips (8) are buckled at both ends in the axial direction of the piston rod (2) extending out of the outer cylinder sleeve (1) and outside the drive shaft (9) of the drive component. The two slips (8) do not contact each other and are butt-jointed by a bolt pair.

4. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 1, characterized in that: The dimensions of the inner cylinder sleeve (3) shall meet the following requirements: in, To bear the pressure on the inner cylinder liner (3); is the allowable stress of the material; is the outer diameter of the inner cylinder sleeve (3); is the inner diameter of the inner cylinder sleeve (3); is the sum of external margins; is the sum of the internal margins; For temperature.

5. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 4, characterized in that: A plurality of piston rings (23) are inserted into the interface between the piston rod (2) and the inner cylinder sleeve (3). The piston rings (23) are fitted in pairs and their outer walls are in contact with the inner cylinder sleeve (3).

6. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 5, characterized in that: An expansion ring (24) is inserted between the inner wall surface of the piston ring (23) and the piston rod (2), and the outer wall surface of the expansion ring (24) abuts against the inner wall surface of the piston ring (23) to push the piston ring (23) toward the inner cylinder sleeve (3).

7. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 1, characterized in that: A guide ring (25) is inserted on the piston rod (2) between the piston ring (23) and the inner core (4), and the guide ring (25) is interference-fitted with the inner cylinder sleeve (3) at room temperature.

8. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 1, characterized in that: A plurality of packings (22) are arranged along the axial direction between the piston rod (2) and the outer cylinder sleeve (1); the packings (22) are conical in shape and the ends with smaller outer diameters are all facing the inner core (4); a pressure ring (21) with a conical groove is inserted between adjacent packings (22); the pressure ring (21) abuts against the conical surface of the packing (22) and the outer cylinder sleeve (1).

9. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 8, characterized in that: A circular ring is provided at the end of the packing (22) with a larger outer diameter. The outer diameter of the circular ring is equal to the inner diameter of the outer cylinder sleeve (1). The side surface of the pressure ring (21) abuts against the circular ring.

10. The cold end structure of the ultra-low temperature and ultra-high pressure pump according to claim 8, characterized in that: A waterline seal is provided at the joint end between the inner cylinder sleeve (3) and the inner core (4); a waterline seal is used on the inner side of the joint surface between the inner core (4) and the drain joint (6), and a non-metallic wedge seal is used on the outer side.

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