Liquid nitrogen pump cold end with unloading device

Abstract

The invention relates to the technical field of liquid nitrogen pumps special for oil fields, in particular to a liquid nitrogen pump cold end with an unloading device, a suction valve cavity is formed in the end, close to a suction valve head, of an inner cylinder sleeve of the cold end in a surrounding mode, a suction valve plate is installed in the suction valve cavity, and a liquid passing through hole axially extending to a liquid passing annular groove is formed in one end of the suction valve head. Axial stepped round holes are formed in the two ends of the suction valve head in a penetrating mode, conducting holes communicated with the liquid passing ring grooves are formed in the large-diameter ends of the stepped round holes, a plurality of elastic unloading plungers are installed in the stepped round holes, the unloading plungers are symmetrically distributed with the axis of the suction valve head as the center, and the liquid passing through holes are evenly distributed between the adjacent stepped round holes. An unloading pipeline is mounted at the unloading outlet, and an unloading valve is mounted on the unloading pipeline; the unloading valve is opened or closed, the original equipment structure is not changed, unloading and loading of the cold end of the liquid nitrogen pump are effectively controlled, normal operation under various displacement working conditions is met, repeated disassembly of the cold end of the liquid nitrogen pump is avoided, and the operation efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of liquid nitrogen pump technology for oilfield special equipment, and in particular to a liquid nitrogen pump cold end with an unloading device. Background Technology

[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 ultra-low temperature environments to achieve high-pressure pumping of liquid nitrogen (liquid oxygen, LNG, liquid hydrogen), and can be used in various specialized exploration and development operations such as nitrogen gas lift, nitrogen displacement, nitrogen fracturing, and mixed-gas acidizing. Reciprocating liquid nitrogen pumps typically have a three- or five-cylinder structure with a fixed-diameter cold end, resulting in a fixed displacement. However, due to the complex operating conditions in oilfields and the wide range of displacement requirements, speed adjustment via the drive unit alone cannot meet the needs of small-displacement operations. How to achieve rapid switching between small and large displacements in a liquid nitrogen pump, making displacement adjustment more convenient and faster, is a pressing technical problem that needs to be solved. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a liquid nitrogen pump cold end with an unloading device that can effectively control the unloading and loading of the cold end of the liquid nitrogen pump without changing the original equipment structure, meet the normal operation of various displacement conditions, avoid repeated disassembly of the cold end, improve the operation efficiency, and at the same time not affect the internal lubrication of the cold end and not cause abnormal wear of the cold end.

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is: a liquid nitrogen pump cold end with an unloading device, comprising a cylindrical cold end outer cylinder liner, an inner cold end cylinder liner, a suction valve head, and a high-pressure discharge head sequentially fitted inside the outer cold end cylinder liner; a cold end piston is movably installed inside the inner cold end cylinder liner; a liquid nitrogen inlet and an unloading outlet are provided on the outer cold end cylinder liner; a suction valve chamber is provided around the end of the inner cold end cylinder liner near the suction valve head; a suction valve plate is installed in the suction valve chamber; a liquid-passing ring groove is recessed inward in the middle of the suction valve head; a liquid-passing through hole extending axially to the liquid-passing ring groove is provided at one end of the suction valve head; axial stepped circular holes are provided through both ends of the suction valve head; a through hole communicating with the liquid-passing ring groove is provided at the large diameter end of the stepped circular hole; an elastic unloading plunger is installed in the stepped circular hole; multiple unloading plungers are symmetrically distributed around the axis of the suction valve head. Liquid passage holes are evenly distributed between adjacent stepped circular holes. The opening positions of the suction valve plate, the liquid passage holes, and the stepped circular holes correspond to each other. A one-way valve chamber is opened at the axis of the suction valve head, and a drain one-way valve is installed in the one-way valve chamber. A drain passage hole connected to the drain one-way valve is opened at the axis of the high-pressure drain head. An unloading channel connecting the stepped circular holes and the unloading outlet is also opened on the high-pressure drain head. An unloading pipe is installed at the unloading outlet, and an unloading valve is installed on the unloading pipe. When the unloading valve is open, the suction valve plate slides freely in the suction valve chamber when the cold end piston is working, and liquid nitrogen is discharged normally. When the unloading valve is closed, the suction valve plate is blocked by the unloading plunger when the cold end piston is working, and cannot slide freely in the suction valve chamber. Liquid nitrogen is not discharged and flows back to its original position, thus achieving unloading of the cold end of liquid nitrogen.

[0005] As a preferred technical solution, the unloading plunger is a stepped cylinder, the small diameter end of the unloading plunger has the same diameter as the small diameter end of the stepped circular hole, the length of the small diameter end of the unloading plunger is greater than the length of the small diameter end of the stepped circular hole, the length of the large diameter end of the unloading plunger is less than the length of the large diameter end of the stepped circular hole, and a plunger spring cavity is formed at the center of the large diameter end of the unloading plunger, and an unloading plunger spring is installed in the plunger spring cavity.

[0006] As a preferred technical solution, a stepped groove is formed on the outer periphery of the intake valve plate, and a valve plate spring is fitted on the stepped groove. One end of the valve plate spring abuts against the inner cylinder liner of the cold end, and the other end of the valve plate spring abuts against the stepped groove.

[0007] As a preferred technical solution, the drain check valve has a check valve spring groove at one end near the high-pressure drain head, and a check valve reset spring is installed in the check valve spring groove. The length of the drain check valve is less than the length of the check valve cavity.

[0008] As a preferred technical solution, the cold end outer cylinder liner is provided with an inner cylinder liner cavity, a valve head cavity and a drain head cavity in sequence. The cold end inner cylinder liner is interference-fitted into the inner cylinder liner cavity. The suction valve head is installed in the valve head cavity. The liquid-passing ring groove and the cavity wall of the valve head cavity form a liquid-containing space. The high-pressure drain head is installed in the drain head cavity.

[0009] As a preferred technical solution, the unloading channel is an axial circular hole opened at one end of the high-pressure drain head near the stepped circular hole, and a radial circular hole is opened vertically connected to the axial circular hole. The radial circular hole extends through the outer wall of the high-pressure drain head into the drain head cavity.

[0010] As a preferred technical solution, a drain head plug for sealing the high-pressure drain head is installed in the internal thread of the drain head cavity, a wedge-shaped sealing ring is installed between the high-pressure drain head and the cold end outer cylinder liner, and a pressure ring for pressing the wedge-shaped sealing ring is installed between the drain head plug and the high-pressure drain head.

[0011] As a preferred technical solution, the unloading outlet is a radial circular channel extending from the outer wall of the cold end outer cylinder liner toward the axis, and the radial circular channel extends into the drain head cavity to form an axial circular channel, the outlet of the axial circular channel being connected to the radial circular hole.

[0012] As a preferred technical solution, the drain head plug is provided with a plurality of axial threaded holes, the axial threaded holes are used to install clamping bolts, and the clamping bolts are used to fix the pressure ring on the high-pressure drain head.

[0013] As a preferred technical solution, three stepped circular holes are evenly distributed, and three unloading plungers are installed accordingly.

[0014] Due to the adoption of the above technical solution, the cold end of the liquid nitrogen pump with unloading device includes a cylindrical cold end outer cylinder liner. Inside the cold end outer cylinder liner, a cold end inner cylinder liner, a suction valve head, and a high-pressure discharge head are sequentially installed. A cold end piston is movably installed inside the cold end inner cylinder liner. A liquid nitrogen inlet and an unloading outlet are provided on the cold end outer cylinder liner. A suction valve chamber is formed around the end of the cold end inner cylinder liner near the suction valve head. A suction valve plate is installed inside the suction valve chamber. A liquid-passing ring groove is recessed inward in the middle of the suction valve head. A liquid-passing through hole extending axially to the liquid-passing ring groove is provided at one end of the suction valve head. A shaft is formed through both ends of the suction valve head. The device features a stepped circular hole with a through-hole at its large-diameter end connecting to a liquid ring groove. An elastic unloading plunger is installed within the stepped circular hole, with multiple plungers symmetrically distributed around the axis of the suction valve head. Liquid passage holes are evenly distributed between adjacent stepped circular holes. The suction valve plate corresponds to the opening positions of the liquid passage holes and the stepped circular holes. A one-way valve chamber is located at the axis of the suction valve head, housing a drain one-way valve. A drain through-hole connected to the drain one-way valve is located at the axis of the high-pressure drain head. The high-pressure drain head also has an unloading channel connecting the stepped circular hole and the unloading outlet. An unloading pipe is installed at the unloading outlet, and an unloading valve is installed on the unloading pipe. When the unloading valve is open, liquid nitrogen enters the liquid space inside the cold end through the suction valve head. At this time, the suction pressure should be greater than the external storage tank pressure at the other end of the unloading plunger. At this time, the suction pressure holds the unloading plunger in a certain position, overcoming the elastic force of the unloading plunger spring, allowing the suction valve plate to move freely in the suction valve chamber, thus enabling the liquid nitrogen cold end to work normally. When the unloading valve is closed, liquid nitrogen enters the internal cavity of the cold end through the suction valve head. At this time, the suction pressure acts on the liquid nitrogen through the guide hole on the suction valve head. The unloading plunger is positioned so that the suction pressure is equal at both ends. This allows the unloading plunger spring to push the unloading plunger towards the suction valve plate, which is then held in place by the unloading plunger, preventing contact between the suction valve plate and the suction valve head. In this state, cryogenic liquid nitrogen can still be normally drawn into the cold end inner cylinder liner, but the liquid nitrogen is not discharged; instead, it flows back to its original location to provide cryogenic cooling and lubrication to the entire cold end. Although the cold end piston can still move freely, it can no longer be pressurized in the pump chamber to achieve unloading of the liquid nitrogen cold end. The beneficial effect of this invention is that the cold end inner cylinder liner is installed inside the cold end outer cylinder liner. The cold-end piston reciprocates within the inner cylinder liner of the cold end to compress and pressurize liquid nitrogen. The liquid is discharged from the cold end through a liquid passage in the suction valve head. A one-way valve prevents the high-pressure liquid discharged from the cold end from flowing back. Depending on the application, the unloading valve can be opened or closed without altering the original equipment structure, effectively controlling the unloading and loading of the cold end of the liquid nitrogen pump. This satisfies normal operation under various discharge conditions, avoids repeated disassembly of the cold end, improves operational efficiency, and does not affect the internal lubrication of the cold end, preventing abnormal wear. Attached Figure Description

[0015] The following figures are intended only to illustrate and explain the present invention and do not limit the scope of the invention. Wherein: Figure 1 This is one of the structural schematic diagrams of the cold end of the liquid nitrogen pump with unloading device according to the present invention; Figure 2 This is the second schematic diagram of the structure of the cold end of the liquid nitrogen pump with unloading device according to the present invention; Figure 3 This is a partial cross-sectional view of the structure of the present invention when the unloading valve is in the open state and the cold end piston is pushed. Figure 4 yes Figure 3 A magnified view of a section at point I; Figure 5 This is a partial cross-sectional view of the structure of the present invention when the unloading valve is in the open state and the cold end piston is pulled; Figure 6 yes Figure 5 Enlarged view of a section at point II; Figure 7 This is a partial cross-sectional view of the structure of the present invention when the unloading valve is closed and the cold end piston is pushed. Figure 8 yes Figure 7 Enlarged view of a section at point III; Figure 9 This is a partial cross-sectional view of the structure of the present invention when the unloading valve is closed and the cold end piston is pulled. Figure 10 yes Figure 9 Enlarged view of a section at point IV; Figure 11 This is one of the structural schematic diagrams of the suction valve head of the present invention; Figure 12 This is the second schematic diagram of the structure of the suction valve head of the present invention; Figure 13 yes Figure 12 Sectional view along the middle AA direction; Figure 14 This is a cross-sectional view of the cold-end outer cylinder liner of the present invention; Figure 15 This is a schematic diagram of the unloading plunger of the present invention; Figure 16 This is a schematic diagram of the structure of the suction valve plate of the present invention; Figure 17 This is a schematic diagram of the structure of the present invention after the clamping bolts are installed; Figure 18 This is a partial sectional view of the present invention after the clamping bolts have been installed.

[0016] In the diagram: 1-Cold end outer cylinder liner; 11-Inner cylinder liner cavity; 12-Valve head cavity; 13-Drain head cavity; 14-Liquid nitrogen inlet; 15-Radial circular channel; 16-Axial circular channel; 2-Cold end inner cylinder liner; 21-Suction valve cavity; 22-Suction valve plate; 221-Stepped groove; 23-Valve plate spring; 3-Suction valve head; 31-Liquid ring groove; 32-Liquid through hole; 33-Stepped circular hole; 34-Conducting hole; 35-One-way valve cavity; 3 6-Wedge seal ring; 37-Pressure ring; 4-High-pressure drain head; 41-Drainage through hole; 42-Axial circular hole; 43-Radial circular hole; 5-Cold end piston; 6-Unloading plunger; 61-Plunger spring cavity; 62-Unloading plunger spring; 7-Drainage check valve; 71-Check valve spring groove; 72-Check valve return spring; 8-Unloading pipe; 9-Unloading valve; 10-Drain head plug; 101-Axial threaded hole; 102-Pressure bolt. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the following detailed description, only certain exemplary embodiments of the invention are described by way of illustration. Undoubtedly, those skilled in the art will recognize that various modifications can be made to the described embodiments without departing from the spirit and scope of the invention. Therefore, the drawings and description are illustrative in nature and not intended to limit the scope of the claims.

[0018] like Figures 1 to 18As shown, the cold end of the liquid nitrogen pump with unloading device includes a cylindrical cold end outer cylinder liner 1. Inside the cold end outer cylinder liner 1, a cold end inner cylinder liner 2, a suction valve head 3, and a high-pressure discharge head 4 are sequentially installed. A cold end piston 5 is movably installed inside the cold end inner cylinder liner 2. The cold end piston 5 draws and discharges liquid nitrogen by pushing and pulling inside the cold end inner cylinder liner 2. The cold-end outer cylinder liner 1 is provided with a liquid nitrogen inlet 14 and an unloading outlet. The liquid nitrogen inlet 14 is used for liquid nitrogen to enter the liquid space of the cold end, and the unloading outlet is used to connect to the unloading pipe 8, which in turn connects to the external storage tank. The cold-end inner cylinder liner 2 is provided with a suction valve chamber 21 around one end near the suction valve head 3. A suction valve plate 22 is installed in the suction valve chamber 21 and can slide left and right in the suction valve chamber 21. The middle part of the suction valve head 3 is recessed with a liquid-passing ring groove 31. One end of the suction valve head 3 is provided with a liquid-passing through hole 32 extending axially to the liquid-passing ring groove 31. A stepped circular hole 33 is provided axially through both ends of the suction valve head 3. The large-diameter end of the stepped circular hole 33 is provided with a through hole 34 connecting to the liquid-passing ring groove 31, so that the suction liquid pressure can act on both ends of the unloading plunger 6 when the unloading device is working. The force acting on both ends of the unloading plunger 6 is balanced; an elastic unloading plunger 6 is installed in the stepped circular hole 33. Multiple unloading plungers 6 are symmetrically distributed around the axis of the suction valve head 3. Liquid passage holes 32 are evenly distributed between adjacent stepped circular holes 33. The opening positions of the suction valve plate 22, the liquid passage holes 32, and the stepped circular holes 33 are corresponding. A one-way valve chamber 35 is opened at the axis of the suction valve head 3. A drain one-way valve 7 is installed in the one-way valve chamber 35. A drain through hole 41 connected to the drain one-way valve 7 is opened at the axis of the high-pressure drain head 4. An unloading channel connecting the stepped circular hole 33 and the unloading outlet is also opened on the high-pressure drain head 4. An unloading pipe 8 is installed at the unloading outlet. An unloading valve 9 is installed on the unloading pipe 8. The unloading valve 9 is existing technology and is used to control the unloading or normal operation of the cold end.With unloading valve 9 open, liquid nitrogen enters the liquid storage space inside the cold end through suction valve head 3. At this time, the suction pressure should be greater than the external storage tank pressure at the other end of the unloading plunger 6. This suction pressure holds the unloading plunger 6 in a certain position, overcoming the elastic force of the unloading plunger spring 62, allowing the suction valve plate 22 to move freely within the suction valve chamber 21, thus ensuring normal operation of the liquid nitrogen cold end. With unloading valve 9 closed, liquid nitrogen enters the internal cavity of the cold end through suction valve head 3. At this time, the suction pressure acts on both ends of the unloading plunger 6 through the guide hole 34 on the suction valve head 3, causing... The suction pressure is equal at both ends of the unloading plunger 6, allowing the unloading plunger spring 62 to push the unloading plunger 6 towards the suction valve plate 22. The suction valve plate 22 is held in place by the unloading plunger 6, thus preventing the suction valve plate 22 from contacting the suction valve head 3. In this state, cryogenic liquid nitrogen can still be normally drawn into the cold end inner cylinder liner 2, but the liquid nitrogen is not discharged; instead, it flows back to its original location to provide cryogenic cooling and lubrication for the entire cold end. Although the cold end piston 5 can still move freely, it can no longer be pressurized in the pump chamber to achieve unloading of the liquid nitrogen cold end. The cold end inner cylinder liner 2 is installed inside the cold end outer cylinder liner 1. The cold-end piston 5 reciprocates within the inner cylinder liner 2 of the cold end to compress and pressurize liquid nitrogen. The liquid is discharged from the cold end through the liquid passage 32 inside the suction valve head 3. The discharge check valve 7 prevents the high-pressure liquid discharged from the cold end from flowing back. According to usage requirements, the unloading valve 9 can be opened or closed without changing the original equipment structure, effectively controlling the unloading and loading of the cold end of the liquid nitrogen pump, meeting the normal operation of various discharge conditions, avoiding repeated disassembly of the cold end, improving operating efficiency, and not affecting the internal lubrication of the cold end, thus preventing abnormal wear of the cold end.

[0019] like Figure 15 As shown, the unloading plunger 6 is a stepped cylinder. The small-diameter end of the unloading plunger 6 has the same diameter as the small-diameter end of the stepped circular hole 33, and the length of the small-diameter end of the unloading plunger 6 is greater than the length of the small-diameter end of the stepped circular hole 33. The large-diameter end of the unloading plunger 6 has a diameter slightly smaller than the diameter of the large-diameter end of the stepped circular hole 33, allowing liquid nitrogen to flow through. The length of the large-diameter end of the unloading plunger 6 is less than the length of the large-diameter end of the stepped circular hole 33. A plunger spring cavity 61 is formed at the center of the large-diameter end of the unloading plunger 6, and an unloading plunger spring 62 is installed inside the plunger spring cavity 61. A sealing groove is also formed on the outer circumference of the large-diameter end of the unloading plunger 6 for installing a sealing ring. The unloading plunger spring 62 is installed in the plunger spring cavity 61 at the end of the unloading plunger 6 and is used to push the unloading plunger 6 to slide left and right.

[0020] like Figure 16As shown, a stepped groove 221 is formed on the outer periphery of the suction valve plate 22. A valve plate spring 23 is fitted on the stepped groove 221. One end of the valve plate spring 23 abuts against the inner cylinder liner 2 of the cold end, and the other end of the valve plate spring 23 abuts against the stepped groove 221. When the unloading valve 9 is open and the unloading plunger 6 does not extend out of the stepped circular hole 33, the valve plate spring 23 is used to ensure that the suction valve plate 22 moves stably back and forth in the suction valve cavity 21 when the cold end is working normally.

[0021] like Figure 4 As shown, the drain check valve 7 has a check valve spring groove 71 at one end near the high-pressure drain head 4. A check valve return spring 72 is installed in the check valve spring groove 71. The length of the drain check valve 7 is less than the length of the check valve cavity 35. The check valve return spring 72 is used to reset the drain check valve 7. The fact that the length of the drain check valve 7 is less than the length of the check valve cavity 35 allows the drain check valve 7 to overcome the elastic force of the check valve return spring 72 and create a gap between itself and the suction valve head 3 when pushing the cold end piston 5, allowing liquid nitrogen to pass through.

[0022] like Figure 14 As shown, the cold-end outer cylinder liner 1 is sequentially provided with an inner cylinder liner cavity 11, a valve head cavity 12, and a drain head cavity 13. The cold-end inner cylinder liner 2 is interference-fitted into the inner cylinder liner cavity 11. The suction valve head 3 is installed in the valve head cavity 12. The liquid-passing ring groove 31 and the cavity wall of the valve head cavity 12 form a liquid-containing space. The high-pressure drain head 4 is installed in the drain head cavity 13. The inner diameters of the inner cylinder liner cavity 11, the valve head cavity 12, and the drain head cavity 13 are different, and are adapted to the dimensions of the components installed inside them.

[0023] like Figure 6 As shown, the unloading channel is an axial circular hole 42 located at one end of the high-pressure drain head 4 near the stepped circular hole 33. A radial circular hole 43 is provided perpendicularly to the axial circular hole 42, extending through the outer wall of the high-pressure drain head 4 into the drain head cavity 13. The unloading channel is used to connect to an external storage tank for pressure relief.

[0024] like Figure 14 As shown, the unloading outlet is a radial circular channel 15 extending from the outer wall of the cold end outer cylinder liner 1 towards the shaft center. The radial circular channel 15 extends into the drain head cavity 13 and forms an axial circular channel 16. The outlet of the axial circular channel 16 is connected to the radial circular hole 43. The unloading outlet is used to connect to an external storage tank for pressure relief.

[0025] like Figure 3 , Figure 5 , Figure 7 and Figure 9As shown, a drain plug 10 for sealing the high-pressure drain head 4 is installed in the internal thread of the drain head cavity 13. A wedge-shaped sealing ring 36 is installed between the high-pressure drain head 4 and the cold end outer cylinder liner 1. The wedge-shaped sealing ring 36 is used to seal the gap between the high-pressure drain head 4 and the cold end outer cylinder liner 1 to prevent leakage. A pressure ring 37 for pressing the wedge-shaped sealing ring 36 is installed between the drain plug 10 and the high-pressure drain head 4. The pressure ring 37 is used to press and fix the wedge-shaped sealing ring 36 onto the high-pressure drain head 4 to prevent it from falling off.

[0026] like Figure 17 and Figure 18 As shown, the drain head plug 10 has several axial threaded holes 101. The axial threaded holes 101 are used to install clamping bolts 102. The clamping bolts 102 are used to press the pressure ring 37 onto the high-pressure drain head 4 to increase the pressure on the pressure ring 37. The end face of the clamping bolt 102 near the pressure ring 37 is flat. The length of the clamping bolt 102 is greater than the length of the axial threaded holes 101.

[0027] like Figure 11 and Figure 12 As shown, there are three stepped circular holes 33 evenly distributed, and three corresponding unloading plungers 6 are installed. Installing three unloading plungers 6 on one cold end is the optimal technical solution. However, other numbers of stepped circular holes 33 can be designed to install unloading plungers 6 as needed, as long as they are evenly distributed circumferentially to ensure the balance of liquid nitrogen flow.

[0028] The workflow of this invention: (1) Normal working mode, unloading valve 9 is open.

[0029] like Figure 5 and Figure 6 As shown, when the cold end piston 5 is pulled outward, liquid nitrogen enters the liquid space formed by the liquid ring groove 31 and the cavity wall of the valve head cavity 12 from the liquid nitrogen inlet 14. At this time, the suction valve plate 22 overcomes the elastic force of the valve plate spring 23 and moves to the left in the suction valve cavity 21. Since the unloading valve 9 is in the open state, the pressure P1 on the left side of the unloading plunger 6 is greater than the pressure P2 on the right side. A part of the liquid nitrogen passes through the guide hole 34 and enters the large diameter end of the stepped circular hole 33. It passes through the axial circular hole 42, the radial circular hole 43, the axial circular channel 16, and the radial circular channel 15 in sequence, and finally enters the external storage tank from the unloading pipe 8.

[0030] like Figure 3 and Figure 4As shown, when the cold end piston 5 is pushed inward, the suction valve plate 22 is pressed tightly against the suction valve head 3 under pressure, completely blocking the small diameter end of the liquid passage 32 and the stepped circular hole 33. The pressure P1 on the left side of the unloading plunger 6 is greater than the pressure P2 on the right side. Under pressure, the discharge check valve 7 overcomes the elastic force of the check valve return spring 72 and moves to the right, creating a gap between the discharge check valve 7 and the suction valve head 3. Liquid nitrogen enters the hole of the discharge check valve 7 through the gap, and then enters the discharge passage 41 and is discharged from the high-pressure discharge head 4.

[0031] (2) Unloading mode, unloading valve 9 is closed.

[0032] like Figure 9 and Figure 10 As shown, when the cold end piston 5 is pulled outward, liquid nitrogen enters from the liquid nitrogen inlet 14 into the liquid space formed by the liquid ring groove 31 and the cavity wall of the valve head cavity 12. At this time, since the unloading valve 9 is in the closed state, the pressure P1 on the left side of the unloading plunger 6 is equal to the pressure P2 on the right side. At this time, the unloading plunger 6 moves to the left under the elastic force of the unloading plunger spring 62, and pushes the suction valve plate 22 against the left side, so that the suction valve plate 22 always maintains a certain gap with the suction valve head 3. A part of the liquid nitrogen passes through the guide hole 34 and enters the large diameter end of the stepped circular hole 33 and no longer flows.

[0033] like Figure 7 and Figure 8 As shown, when the cold end piston 5 is pushed inward, the pressure P1 on the left side of the unloading plunger 6 is equal to the pressure P2 on the right side because the unloading valve 9 is closed. At this time, the unloading plunger 6 moves to the left under the elastic force of the unloading plunger spring 62, and the suction valve plate 22 is pressed against the left side, so that the suction valve plate 22 always maintains a certain gap with the suction valve head 3. At this time, the drain check valve 7 is in a blocked state under the elastic force of the check valve reset spring 72. Liquid nitrogen enters the liquid space formed between the liquid ring groove 31 and the cavity wall of the valve head cavity 12 from the liquid through hole 32, and then returns from the liquid nitrogen inlet 14 to achieve unloading.

[0034] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "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 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 this invention.

[0035] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A liquid nitrogen pump cold end with an unloading device, characterized in that: The device includes a cylindrical cold-end outer cylinder liner (1), a cold-end inner cylinder liner (2), a suction valve head (3), and a high-pressure discharge head (4) sequentially fitted inside the cold-end outer cylinder liner (1). A cold-end piston (5) is movably installed inside the cold-end inner cylinder liner (2). A liquid nitrogen inlet (14) and a unloading outlet are provided on the cold-end outer cylinder liner (1). A suction valve chamber (21) is provided around one end of the cold-end inner cylinder liner (2) near the suction valve head (3). A suction valve plate (22) is installed inside the suction valve chamber (21). A liquid-passing ring groove (31) is recessed inward in the middle of the suction valve head (3). A liquid-passing through hole (32) extending axially to the liquid-passing ring groove (31) is provided at one end of the suction valve head (3). A stepped circular hole (33) is provided axially through both ends of the suction valve head (3). A through hole communicating with the liquid-passing ring groove (31) is provided at the large diameter end of the stepped circular hole (33). 34), an elastic unloading plunger (6) is installed in the stepped circular hole (33). Multiple unloading plungers (6) are symmetrically distributed around the axis of the suction valve head (3). The liquid passage holes (32) are evenly distributed between adjacent stepped circular holes (33). The suction valve plate (22) corresponds to the opening position of the liquid passage holes (32) and the stepped circular holes (33). A single valve plate is opened at the axis of the suction valve head (3). The valve chamber (35) is equipped with a drain check valve (7). The high-pressure drain head (4) has a drain through hole (41) connected to the drain check valve (7) at its axis. The high-pressure drain head (4) also has a unloading channel connecting the stepped circular hole (33) and the unloading outlet. An unloading pipe (8) is installed at the unloading outlet. An unloading valve (9) is installed on the unloading pipe (8). When the unloading valve (9) is open and the cold end piston (5) is working, the suction valve plate (22) slides freely in the suction valve chamber (21) and the liquid nitrogen is discharged normally. When the unloading valve (9) is closed, and the cold end piston (5) is working, the suction valve plate (22) is blocked by the unloading plunger (6) and cannot slide freely in the suction valve chamber (21). Liquid nitrogen is not discharged and flows back to its original position, thus achieving unloading of the cold end of liquid nitrogen.

2. The cold end of the liquid nitrogen pump with an unloading device as described in claim 1, characterized in that: The unloading plunger (6) is a stepped cylinder. The small diameter end of the unloading plunger (6) is equal to the small diameter end of the stepped circular hole (33). The length of the small diameter end of the unloading plunger (6) is greater than the length of the small diameter end of the stepped circular hole (33). The length of the large diameter end of the unloading plunger (6) is less than the length of the large diameter end of the stepped circular hole (33). A plunger spring cavity (61) is provided at the center of the large diameter end of the unloading plunger (6). An unloading plunger spring (62) is installed in the plunger spring cavity (61).

3. The cold end of the liquid nitrogen pump with an unloading device as described in claim 1, characterized in that: The outer periphery of the intake valve plate (22) is provided with a stepped groove (221), and a valve plate spring (23) is fitted on the stepped groove (221). One end of the valve plate spring (23) abuts against the inner cylinder liner (2) of the cold end, and the other end of the valve plate spring (23) abuts against the stepped groove (221).

4. The cold end of the liquid nitrogen pump with an unloading device as described in claim 1, characterized in that: The drain check valve (7) has a check valve spring groove (71) at one end near the high pressure drain head (4), and a check valve reset spring (72) is installed in the check valve spring groove (71). The length of the drain check valve (7) is less than the length of the check valve cavity (35).

5. The cold end of the liquid nitrogen pump with an unloading device as described in claim 1, characterized in that: The cold end outer cylinder liner (1) is provided with an inner cylinder liner cavity (11), a valve head cavity (12) and a drain head cavity (13) in sequence. The cold end inner cylinder liner (2) is installed in the inner cylinder liner cavity (11) with an interference fit. The suction valve head (3) is installed in the valve head cavity (12). The liquid flow ring groove (31) and the cavity wall of the valve head cavity (12) form a liquid-containing space. The high pressure drain head (4) is installed in the drain head cavity (13).

6. The cold end of the liquid nitrogen pump with an unloading device as described in claim 5, characterized in that: The unloading channel is an axial circular hole (42) opened at one end of the high-pressure drain head (4) near the stepped circular hole (33), and a radial circular hole (43) is opened vertically through the axial circular hole (42). The radial circular hole (43) extends through the outer wall of the high-pressure drain head (4) into the drain head cavity (13).

7. The cold end of the liquid nitrogen pump with an unloading device as described in claim 6, characterized in that: The drain head cavity (13) is threaded with a drain head plug (10) for sealing the high pressure drain head (4). A wedge-shaped sealing ring (36) is installed between the high pressure drain head (4) and the cold end outer cylinder liner (1). A pressure ring (37) for pressing the wedge-shaped sealing ring (36) is installed between the drain head plug (10) and the high pressure drain head (4).

8. The cold end of the liquid nitrogen pump with an unloading device as described in claim 7, characterized in that: The unloading outlet is a radial circular channel (15) extending from the outer wall of the cold end outer cylinder liner (1) toward the axis. The radial circular channel (15) extends into the drain head cavity (13) and has an axial circular channel (16). The outlet of the axial circular channel (16) is connected to the radial circular hole (43).

9. The cold end of the liquid nitrogen pump with an unloading device as described in claim 8, characterized in that: The drain head plug (10) has several axial threaded holes (101) for installing clamping bolts (102), which are used to fix the pressure ring (37) on the high pressure drain head (4).

10. The cold end of the liquid nitrogen pump with an unloading device as described in any one of claims 1 to 9, characterized in that: The stepped circular holes (33) are evenly distributed in three places, and the corresponding unloading plungers (6) are installed in three places.

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