An ultra-low temperature top-mounted online-maintainable bidirectional check valve

Abstract

The application relates to an ultra-low temperature top-mounted on-line maintenance bidirectional check valve, which comprises symmetric guide rings arranged at two ends of a valve body; a left valve clapper and a right valve clapper are assembled in rotation in the valve body; a spring steel sheet is arranged on an eccentric cam. A shaft sleeve is arranged at the lower end of an extended valve cover, a valve rod passes through the shaft sleeve in the extended valve cover, the lower end of the valve rod is assembled into an eccentric cam assembly, and the valve rod is fixed through a nut lock and a pin shaft. The upper end of the valve rod is sequentially assembled into a valve rod Lip-seal, a packing gasket, packing, a packing pressing sleeve and a packing pressing plate, and is fastened through an inner hexagonal bolt. The top of the valve rod is operated and controlled through a handle and is fixed through a locking nut. The check valve can realize free check during LNG ship unloading, can realize bidirectional flow during the establishment of a cold-keeping cycle of an unloading arm pipeline, and can also realize free check during LNG reloading. The top-mounted check valve is convenient and fast to maintain, simple to maintain and low in cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultra-low temperature check valve for preventing medium backflow in LNG receiving station unloading pipeline, and particularly relates to an ultra-low temperature top-mounted bidirectional check valve capable of being maintained online. BACKGROUND

[0002] In recent years, with the energy system planning, the capacity of LNG receiving stations in China has reached a leading position in the world. The receiving station is mainly used for the functions of receiving, storing and external transmission of liquefied natural gas. Liquefied natural gas has the characteristics of flammability and explosiveness. When warmed and gasified, the volume will expand by more than 600 times. The transportation of LNG by ship has become an important way for China to import natural gas. Therefore, the ultra-low temperature check valve is particularly important in the process of loading and unloading liquefied natural gas.

[0003] In order to prevent the fluid in the downstream pipeline and the storage tank from flowing backward during unloading, an ultra-low temperature check valve needs to be installed on each unloading pipeline. The main functions are as follows: during the unloading process of the LNG ship, the check valve can realize free check and prevent the backflow of LNG medium from causing water hammer impact; when the LNG is reloaded into the ship, the check valve needs to flow in the opposite direction and freely check to realize the LNG reloading function; when the unloading arm pipeline cold cycle is established, the check valve can be controlled by a mechanical mechanism to achieve the function of bidirectional flow and realize the pre-cooling of the unloading arm pipeline.

[0004] At present, the ultra-low temperature check valve on the market adopts the axial operation of the French SNRI company. During the unloading process of the ship, the check valve can realize free check. When the LNG is reloaded into the ship, the check valve is opened by the gear and rack mechanical mechanism to achieve the flow function. Because the reverse check function cannot be realized, two positive and negative check valves must be installed at the same time to realize the function, which increases the length of the pipeline and the cost. Another example is the Chinese patent document CN115388216A, which discloses a controllable bidirectional flow ultra-low temperature swing check valve, which comprises a valve body, a valve seat and a valve cover. A valve disc is arranged in the valve body and cooperates with the valve seat. The valve disc is connected to the valve disc shaft through a rocker. A meshing section and a non-meshing section are arranged on the valve rod. The control mechanism can drive the valve rod to move axially relative to the valve body to make the meshing section of the valve rod mesh with the gear to achieve the active driving position, and the non-meshing section cooperates with the gear to make the valve disc not be controlled by the valve rod to achieve the passive swing check position. This design also cannot realize the reverse check function. The gear and the meshing section are in a low-temperature environment, and nitrogen cannot be effectively purged in this space. The air in the space will condense water and cause icing and jamming or wear, resulting in a high failure rate. The valve cannot be replaced or maintained online, and needs to be repaired after the temperature returns to normal, which is time-consuming and costly.

[0005] For example, a Chinese utility model patent with publication number CN2148233Y provides a bidirectional check valve. Its characteristic is that the valve stem, via a fixed crank and a cantilever connector mounted on the crank, operates a valve disc with left and right sealing surfaces, enabling it to seal against two sealing seats located at the inlet and outlet ends of the material flow channel within the valve body. This swing-type, ambient temperature bidirectional check valve has a horizontal operating rod, which prevents the formation of a vaporization space, and the packing cannot be kept above 0°C, making it unsuitable for use in low-temperature conditions.

[0006] To address the aforementioned technical issues, it is essential to research and design a top-mounted check valve that is easy to maintain, allows for bidirectional free backflow, and enables bidirectional flow. Summary of the Invention

[0007] To address the aforementioned technical problems in existing technologies, this invention provides a cryogenic, top-mounted, online-maintainable bidirectional check valve. It is simple to operate, ingeniously structured, and allows for free backflow during LNG vessel unloading; it also enables bidirectional flow when establishing a cold-insulating circulation in the unloading arm pipeline; and it provides the same free backflow function during LNG return loading. The top-mounted design offers convenient and quick maintenance, with simple upkeep and low cost.

[0008] To achieve the above objectives, the present invention adopts the following technical solution.

[0009] The present invention provides a cryogenic top-mounted, online-maintainable bidirectional check valve, comprising a valve body, a left valve disc, an eccentric cam, a right valve disc, a bushing, a cam mounting hole, an extended valve cover, a valve stem, and an eccentric hole; symmetrical guide rings are respectively installed at both ends of the valve body and fixed by threaded rotation; the left and right valve discs are sequentially installed into the guide rings from the upper end of the valve body; a spring steel sheet is provided on the eccentric cam and locked to the eccentric cam by screws, and a fixing plate is provided in the middle; the extended valve cover is installed into the bushing, the valve stem passes through the extended valve cover and the bushing, and the lower end of the valve stem is installed into the eccentric cam assembly and locked by a cap. The valve stem is fixed with a pin to prevent loosening, and the eccentric direction of the eccentric hole is consistent with the arrow direction of the valve stem. The upper end of the valve stem is sequentially fitted with a valve stem lip-seal, packing gasket, packing, packing sleeve, and packing pressure plate, and secured with hexagonal socket bolts. A dustproof ring is provided in the packing sleeve. The valve stem is fitted with a handle, ensuring that the arrow on the handle is consistent with the arrow on the valve stem, and secured with a locking nut. The valve body is fitted with two seals: a middle lip-seal and a metal spiral wound gasket. The assembled extension valve cover is then installed from the upper end of the valve body, with the eccentric cam aligned with the cam mounting hole and inserted, and secured with fasteners.

[0010] Preferably, the valve body has a top-mounted streamlined design.

[0011] In any of the above technical solutions, preferably, the left valve disc and the right valve disc are provided with a guide and a thread, are assembled in rotation in the valve body, and form a fairing design after assembly; the upper end is provided with a cam mounting hole, and the lower end is provided with a pressure balance hole.

[0012] In any of the above technical solutions, preferably, the extended valve cover is integrally extended and is provided with a full-welded drip tray.

[0013] In any of the above technical solutions, preferably, the upper end of the extended valve cover is provided with a left limiting baffle and a right limiting baffle, and limiting locking holes are designed in three directions.

[0014] In any of the above technical solutions, preferably, the handle is cast into shape, the end is processed with a locking hole, and the upper plane is provided with a handle arrow.

[0015] In any of the above technical solutions, preferably, the upper end of the valve rod is provided with a valve rod arrow, facilitating installation and indicating the flow direction state.

[0016] In any of the above technical solutions, preferably, the upper end of the valve rod is provided with three seals of a valve rod Lip-seal, packing, and dustproof ring.

[0017] In any of the above technical solutions, preferably, the valve body and the extended valve cover are provided with two seals of a middle Lip-seal and a metal winding pad.

[0018] In any of the above technical solutions, preferably, the handle arrow and the valve rod arrow are consistent with the medium flow direction, and under the action of the medium flow pressure, the combined left valve disc and right valve disc are pushed to move to the right to the eccentric design of the eccentric cam, and the spring sheet is elastically deformed after being stressed; when the medium flow pressure disappears, the backflow medium and the spring sheet push the left valve disc and the right valve disc to move to the left.

[0019] In any of the above technical solutions, preferably, the handle drives the valve rod and the eccentric cam to rotate 180° clockwise together, is limited by the right limiting baffle, the eccentric cam gradually pushes the combined left valve disc and right valve disc to move to the right along the cam curve, and the combined left valve disc and right valve disc are reset under the elastic force of the spring sheet.

[0020] In any of the above technical solutions, preferably, the handle drives the valve rod and the eccentric cam to rotate 90° clockwise together, is locked through the limiting locking hole, the eccentric cam gradually pushes the combined left valve disc and right valve disc to move to the middle position along the cam curve, and the two end protrusions of the eccentric cam fix the left and right movement of the combined left valve disc and right valve disc.

[0021] In any of the above technical solutions, preferably, the valve body is designed in an upper-mounted manner, the fastener is loosened, the whole valve cover assembly is pulled out from the cam mounting hole, the left valve disc and the right valve disc eliminate the anti-loosening positioning, are rotated and detached, and are taken out respectively.

[0022] Compared with the prior art, the above technical solutions of the present application have the following beneficial effects:

[0023] 1) Bidirectional free check: the handle is rotated by 180 DEG to drive the eccentric cam to gradually push the valve disc to move along the cam curve to reach the designed limiting point, so that the bidirectional free check can be controlled, the number of valves is reduced, the pipeline length is shortened, and the cost is saved.

[0024] 2) Bidirectional flow function: the handle is rotated by 90 DEG to drive the eccentric cam to gradually push the valve disc to move along the cam curve, and the eccentric cam gradually pushes the combined valve disc to the middle position through the limiting locking hole to achieve the bidirectional flow function and realize the pre-cooling of the unloading arm pipeline.

[0025] 3) Convenient online maintenance: the valve body is designed in an upper-mounted manner, the left valve disc and the right valve disc are assembled and assembled in rotation in the valve body, and the whole valve cover is assembled. If the valve disc sealing surface is worn, it can be quickly replaced. This design is simple and fast, the on-site personnel can quickly replace the spare parts, the valve maintenance time is shortened, and the economic loss is reduced.

[0026] 4) Streamlined design and stable operation: the valve body is designed in a streamlined manner, the left valve disc and the right valve disc are provided with a guide and a thread, and are assembled and assembled in rotation in the valve body. After assembly, a flow cover is formed in a streamlined design, the flow resistance coefficient is small, the boundary layer separation is prevented, and the medium flows smoothly.

[0027] 5) Shock absorption and noise reduction: the eccentric cam is provided with a spring steel sheet, the spring steel sheet is elastically deformed after being stressed, and plays a buffering role to achieve the effects of shock absorption and noise reduction. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0029] Figure 1 It is a preferred embodiment of the stop valve structure diagram of the ultra-low temperature upper-mounted online maintenance bidirectional check valve according to the present application.

[0030] Figure 2 It is a preferred embodiment of the stop valve structure diagram of the ultra-low temperature upper-mounted online maintenance bidirectional check valve according to the present application. Figure 1Partial enlarged view of operating mechanism of the embodiment shown;

[0031] Figure 3 Partial enlarged view of operating mechanism of the embodiment shown; Figure 1 Partial enlarged view of operating mechanism of the embodiment shown;

[0032] Figure 4 Partial enlarged view of operating mechanism of the embodiment shown;

[0033] Figure 5 Partial enlarged view of operating mechanism of the embodiment shown;

[0034] Figure 6 Partial enlarged view of operating mechanism of the embodiment shown;

[0035] Figure 7 Partial enlarged view of operating mechanism of the embodiment shown;

[0036] Figure 8 Partial enlarged view of operating mechanism of the embodiment shown.

[0037] The figure shows: valve body 1, left valve disc 2, eccentric cam 3, cap 4, pressure balance hole 5, pin shaft 6, right valve disc 7, guide ring 8, shaft sleeve 9, cam mounting hole 10, lip-seal 11, metal winding gasket 12, fastener 13, extended valve cover 14, valve stem 15, drip tray 16, valve stem lip-seal 17, packing gasket 18, packing 19, dustproof ring 20, packing press sleeve 21, packing press plate 22, fastening assembly 23, handle 24, locking nut 25, locking hole 26, left limit stop 27, handle arrow 28, limit locking hole 29, valve stem arrow 30, right limit stop 31, eccentric hole 32, spring steel sheet 33, fixed plate 35, screw 36, medium flow direction 37, backflow medium 38. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0039] It should be noted that in the description of the present application, it should be understood that the terms "upper end", "lower end", "vertical", "horizontal", "top", "bottom", "left", "right" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0040] In view of the problems in the prior art, the present application provides a check valve which is convenient to maintain, can realize bidirectional free check and bidirectional flow. Figures 1-4 As shown in the figure, the valve body 1 is designed in a streamlined manner, has a small flow resistance coefficient, and is provided with symmetrical guide rings 8 at both ends, the guide rings 8 are triangular support structures to facilitate medium flow; the left valve disc 2 and the right valve disc 7 are provided with guides and threads, and are assembled in rotation in the valve body 1, and after assembly, a flow guide cover streamlined design is formed, the flow resistance coefficient is small, the boundary layer separation is prevented, the medium flows smoothly, the upper end is provided with a cam mounting hole 10, and the lower end is provided with a pressure balance hole 5; the eccentric cam 3 is provided with a spring steel sheet 33, is locked on the eccentric cam by a screw 36, and is provided with a fixed plate 35 in the middle, and the medium flow is damped and silenced in the process, and the free check closing is stable. The extension valve cover 14 is provided with a full-welded drip tray 16 in a whole extension structure, reduces the leakage points, and keeps the packing above 0℃ in a low-temperature environment; the extension valve cover 14 is provided with a shaft sleeve 9 at the lower end and a packing pad 18 at the upper end, and the valve rod 15 can maintain the perpendicularity. The valve rod 15 is integrally forged, passes through the shaft sleeve 9 in the extension valve cover 14, is assembled into the eccentric cam 3 assembly at the lower end of the valve rod 15, is locked by a nut 4 and is fixed by a pin shaft 6 to prevent loosening, the valve rod 15 is provided with a valve rod arrow 30 at the upper end to facilitate installation and indicate the flow direction state, and the valve rod 15 is installed with the eccentric cam 3 to keep the eccentric hole 32 consistent with the direction of the valve rod arrow 30. The valve rod 15 is provided with three seals of a valve rod Lip-seal 17, a packing 19 and a dustproof ring 20 at the upper end, and is provided with a packing pressing sleeve 21 and a packing pressing plate 22 structure, and in the super-low-temperature working condition, the pre-tightening force and secondary pre-tightening can be adjusted by a fastening assembly 23, and the fastening assembly 23 is composed of a disc spring and an internal hexagon. The top of the valve rod 15 is operated and controlled by a handle 24, the handle 24 is connected with the valve rod 15 to keep the handle arrow 28 consistent with the valve rod arrow 30, and is fixed by a locking nut 25. The valve body 1 and the extension valve cover 14 are provided with two seals of a middle Lip-seal 11 and a metal winding pad 12, and are fastened by a fastener 13.

[0041] As Figure 1As shown, the valve body 1, left valve disc 2, eccentric cam 3, right valve disc 7, guide ring 8, extended valve cover 14, valve stem 15, and drip tray 16 described in this embodiment can be made of austenitic stainless steel, and the sealing surface is made of cobalt-based alloy through welding. The left valve disc 2 and right valve disc 7 can also be made of high-strength aerospace aluminum. The valve seat can also be converted into an online replaceable movable valve seat.

[0042] like Figures 1 to 8 As shown, the valve body of this embodiment features a streamlined, top-mounted design with a low flow resistance coefficient. Symmetrical guide rings are located at both ends of the valve body, and these guide rings have a triangular support structure to facilitate media flow. The left and right valve discs are equipped with guides and threads, and are rotated and assembled within the valve body to form a streamlined flow guide design, resulting in a low flow resistance coefficient, preventing separation of the edge media layer, and ensuring smooth media flow. A cam mounting hole is located at the upper end, and a pressure balance hole is located at the lower end. A spring steel sheet is mounted on the eccentric cam and locked to it with screws. A fixing plate is located in the middle to reduce vibration and noise during media flow, and to increase free check and smooth closure. The extended valve cover has an overall extended structure and a fully welded drip tray to reduce leakage points and maintain the packing temperature above 0°C in low-temperature environments. A bushing is located at the lower end of the extended valve cover, and a packing pad is located at the upper end to maintain the verticality of the valve stem. The valve stem is an integral forged structure, passing through a bushing in the extended valve cover. The lower end of the valve stem is fitted into an eccentric cam assembly, secured by a locking nut and pin to prevent loosening. An arrowhead is located at the upper end of the valve stem for easy installation and flow direction indication. When installing the valve stem and eccentric cam, the eccentric hole should be aligned with the arrowhead direction. The upper end of the valve stem features a triple seal: a valve stem lip-seal, packing, and a dust seal. It also includes a packing sleeve and packing plate structure. In cryogenic conditions, the preload and secondary preload can be adjusted via a fastening assembly consisting of a disc spring and an internal hexagonal socket. The valve stem is operated via a handle at the top. The handle is connected to the valve stem, ensuring the handle arrow aligns with the valve stem arrow, and is secured with a locking nut. The valve body and extended valve cover have two seals: a central lip-seal and a spiral wound gasket, secured with fasteners.

[0043] like Figure 3 As shown, the upper end of the extended valve cover is provided with a left limit baffle and a right limit baffle, and limit locking holes are also designed in three directions; the handle is cast and the end is machined with a locking hole, which can be locked through the locking hole in both bidirectional check and bidirectional flow, or to prevent unauthorized operation.

[0044] like Figure 3 , Figure 5 , Figure 6As shown, the handle arrow and valve stem arrow are aligned with the direction of medium flow. Under the pressure of the medium flow, they can push the combined left and right valve discs to the right to the eccentric design limit of the eccentric cam, allowing medium flow. The spring steel sheet deforms elastically under force, providing a buffering effect and achieving vibration reduction and noise reduction. When the pressure of the medium flow disappears, the backflowing medium and the spring steel sheet push the left and right valve discs to the left, achieving a check valve function and preventing backflow of LNG medium from causing water hammer impact.

[0045] like Figures 1 to 8 As shown, in this embodiment, the handle drives the valve stem and the eccentric cam to rotate 180° clockwise together. Limiting this rotation via the right stop plate, the eccentric cam gradually pushes the combined left and right valve discs to the right along the cam curve. Under the elastic force of the spring steel sheet, the combined left and right valve discs return to their original positions. Figure 7 As shown, it achieves free flow and free backflow. Its working principle is the same as the unloading process, and will not be described further.

[0046] like Figures 1 to 8 As shown, in this embodiment, the handle drives the valve stem and the eccentric cam to rotate 90° clockwise together, and locks them through the limit locking hole. The eccentric cam gradually pushes the combined left and right valve discs along the cam curve to the middle position, as shown. Figure 8 As shown, the two protrusions at both ends of the eccentric cam fix the left and right valve discs of the valve disc assembly to move left and right, achieving bidirectional flow and realizing the pre-cooling of the unloading arm pipeline.

[0047] like Figures 1 to 8 As shown, the valve body, left valve disc, eccentric cam, right valve disc, guide ring, extended valve cover, valve stem, and drip tray described in this embodiment can be made of austenitic stainless steel, and the sealing surface can be made of cobalt-based alloy through welding. The left and right valve discs can also be made of high-strength aerospace aluminum. The valve seat can also be converted into an online replaceable movable valve seat.

[0048] To better understand the above technical solutions, the actual application of the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] Example 1:

[0050] Valve body 1 both ends are respectively equipped with symmetrical guide ring 8, screw rotation fixed; Left valve 2 and right valve 7 are equipped with from valve body 1 upper end in turn into the guide ring; Eccentric cam 3 is equipped with spring steel sheet 33, is locked in eccentric cam by screw 36, is equipped with fixed plate 35 in middle; Extension valve cover 14 is equipped into shaft sleeve 9, valve stem 15 passes through extension valve cover 14 and shaft sleeve 9, valve stem 15 lower end is equipped into eccentric cam 3 combination, is locked and is fixed by pin shaft 6 to prevent loosening, eccentric hole 32 eccentric direction is consistent with the direction of valve stem arrow 30; Valve stem 15 upper end is equipped in turn valve stem Lip-seal 17, packing 18, packing 19, packing pressure sleeve 21, packing pressure plate 22, is fastened by internal hexagon bolt 23, packing pressure sleeve 21 is equipped with dustproof ring 20 in; Valve stem 15 is installed handle 24, keeps handle arrow 28 and valve stem arrow 30 consistent, is fixed by locking nut 25; Valve body 1 is equipped with two seals of middle way Lip-seal 11 and metal winding pad 12, and the assembled extension valve cover is equipped from valve body 1 upper end, is put into by aligning cam mounting hole 9 when being equipped, is fastened by fastener 13.

[0051] In the embodiment of the application, as shown in Figure 3 The extension valve cover 14 upper end is equipped with left limit baffle 27 and right limit baffle 31, and limit locking hole 29 is designed in three directions. The handle 24 is cast into shape, and the end is processed into locking hole 26.

[0052] The principle and specific steps of the ultra-low temperature top-mounted on-line maintainable bidirectional check valve are as follows:

[0053] S1. Free check during LNG ship unloading process: as shown in Figure 3 、 Figure 5 、 Figure 6 The handle arrow 28 and the valve stem arrow 30 are consistent with the medium flow direction 37, and under the action of the medium flow direction 37 pressure, the combined left valve 2 and right valve 7 can be pushed to move to the right to the eccentric design position of the eccentric cam 3, so as to realize medium flow. After the spring steel sheet 33 is stressed, the spring steel sheet 33 is elastically deformed 34, so as to play a buffering role, so as to achieve the effects of shock absorption and noise reduction. When the medium flow direction 37 pressure disappears, the backflow medium 38 and the spring steel sheet 33 push the left valve 2 and the right valve 7 to move to the left, so as to realize the check function and prevent the water hammer impact caused by the backflow of LNG medium.

[0054] S2. Reverse flow and free check during LNG re-shipment: the handle 24 drives the valve stem 15 and the eccentric cam 3 to rotate clockwise by 180°, and the combined left valve 2 and right valve 7 are limited by the right limit baffle 31 and are gradually pushed by the eccentric cam 3 along the cam curve to move to the right. Under the action of the elastic force of the spring steel sheet 33, the combined left valve 2 and right valve 7 are reset as shown in Figure 7As shown, the realization to the flow and free check, and the working principle and unloading process, no longer described.

[0055] S3: unloading arm pipe cold cycle when two-way flow function: the handle 24 with valve stem 15 and eccentric cam 3 together clockwise rotation 90°, through the limiting locking hole 29 locking, eccentric cam 3 along the cam curve gradually push the combined left valve 2, right valve 7 move to the intermediate position, such as Figure 8 As shown, the two ends of eccentric cam 3 convex point fixed valve combination of left valve 2, right valve 7 left and right movement, to achieve the function of two-way flow, realize the unloading arm pipe precooling.

[0056] S4: online maintenance function: the valve body 1 on the design, loosen the fastener 13, extension valve cover 14 assembly can be taken out from the cam mounting hole 10 as a whole, left valve 2 and right valve 7 eliminate anti loose positioning, rotation disassembly, respectively. Can replace the valve, valve body sealing surface repair, increase the service life. Valve body sealing surface can also be designed as a movable seat.

[0057] The above is only the preferred embodiment of the present application, and is not intended to limit the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. An ultra-low temperature top-mounted online-maintainable bidirectional check valve, comprising a valve body (1), a left valve disc (2), an eccentric cam (3), a right valve disc (7), a shaft sleeve (9), a cam mounting hole (10), an extended bonnet (14), a valve stem (15) and an eccentric hole (32), characterized in that: The valve body (1) is equipped with symmetrical guide rings (8) at both ends, which are fixed by screw rotation; the left valve disc (2) and the right valve disc (7) are sequentially equipped with sleeves from the upper end of the valve body (1) into the guide rings, and the connecting ports of the left valve disc (2) and the right valve disc (7) are provided with guide structures and threads; the left valve disc (2) and the right valve disc (7) are rotationally connected to the cam mounting holes (10) to align and spot weld them to prevent loosening; the eccentric cam (3) is provided with spring steel sheets (33) and is locked on the eccentric cam by screws (36), and a fixed plate (35) is arranged in the middle; the extension valve cover (14) is equipped with a shaft sleeve (9), the valve rod (15) passes through the extension valve cover (14) and the shaft sleeve (9), the lower end of the valve rod (15) is equipped with the eccentric cam (3) assembly, and the extension valve cover (14) is locked and fixed by the cap (4) and the pin shaft (6) to prevent loosening, and the eccentric direction of the eccentric hole (32) is consistent with the direction of the valve rod arrow (30); the upper end of the valve rod (15) is sequentially equipped with a valve rod lip-shaped sealing ring (17), a packing pad (18), a packing (19), a packing pressing sleeve (21), and a packing pressing plate (22), which are fastened by an internal hexagonal bolt (23), and the packing pressing sleeve (21) is provided with a dustproof ring (20); the valve rod (15) is provided with a handle (24), the handle arrow (28) is consistent with the valve rod arrow (30), and the handle (24) is fixed by a locking nut (25); the valve body (1) is equipped with two seals of a middle lip-shaped sealing ring (11) and a metal winding pad (12), the assembled extension valve cover is equipped from the upper end of the valve body (1), the eccentric cam (3) is aligned with the cam mounting hole (10) when being put in, and the extension valve cover is fastened by a fastener (13).

2. The ultra-low temperature top-mount, in-line maintainable, bi-directional check valve of claim 1, wherein: The valve body (1) is designed as an upper-mounted streamline.

3. The ultra-low temperature top-mount, in-line maintainable check valve of claim 1, wherein: The left valve disc (2) and the right valve disc (7) are provided with guides and threads, and are rotationally combined and assembled in the valve body (1), and form a flow cover streamline design after combination; the upper end is provided with a cam mounting hole (10), and the lower end is provided with a pressure balance hole (5).

4. The ultra-low temperature top-mount, in-line maintainable check valve of claim 1, wherein: The extension valve cover (14) has an overall extension structure and is provided with a full-welded drip pan (16).

5. The ultra-low temperature top-mount, in-line maintainable, bi-directional check valve of claim 4, wherein: The upper end of the extension valve cover (14) is provided with a left limiting baffle (27) and a right limiting baffle (31), and limiting locking holes (29) are designed in three directions.

6. The ultra-low temperature top-mount, in-line maintainable check valve of claim 1, wherein: The handle (24) is cast into shape, the end is processed into a locking hole (26), and the upper plane is provided with a handle arrow (28).

7. The ultra-low temperature top-mount, in-line maintainable check valve of claim 1, wherein: The upper end of the valve rod (15) is provided with a valve rod arrow (30), which is convenient for installation and indicating the flow direction.

8. The ultra-low temperature top-mount, in-line maintainable check valve of claim 1, wherein: The upper end of the valve rod (15) is provided with three seals of a valve rod lip-shaped sealing ring (17), a packing (19), and a dustproof ring (20).

9. The ultra-low temperature top-mount, in-line maintainable check valve of claim 1, wherein: The valve body (1) and the extension valve cover (14) are provided with two seals of a middle lip-shaped sealing ring (11) and a metal winding pad (12).

10. The ultra-low temperature top-mounted, in-line maintainable, bi-directional check valve of any of claims 1, 4, 5, 6, further comprising: The handle arrow (28) and valve stem arrow (30) are consistent with the medium flow direction (37), under the action of the pressure of the medium flow direction (37), the combined left valve (2) and right valve (7) are pushed to move to the right to the eccentric design of the eccentric cam (3) to limit, the spring steel sheet (33) is elastically deformed (34) after being stressed; when the pressure of the medium flow direction (37) disappears, the backflow medium (38) and the spring steel sheet (33) push the left valve (2) and the right valve (7) to move to the left.

11. The ultra-low temperature top-mounted, in-line maintainable, bi-directional check valve of any of claims 1, 4, 5, 6, further comprising: The handle (24) drives the valve stem (15) and the eccentric cam (3) to rotate 180° clockwise together, is limited by the right limiting baffle (31), the eccentric cam (3) gradually pushes the combined left valve (2) and right valve (7) to move to the right along the cam curve, under the action of the elastic force of the spring steel sheet (33), the combined left valve (2) and right valve (7) reset.

12. The ultra-low temperature top-mounted, in-line maintainable, bi-directional check valve of any of claims 1, 4, 5, 6, further comprising: The handle (24) drives the valve stem (15) and the eccentric cam (3) to rotate 90° clockwise together, is locked through the limiting locking hole (29), the eccentric cam (3) gradually pushes the combined left valve (2) and right valve (7) to move to the intermediate position along the cam curve, the two end protrusions of the eccentric cam (3) fix the left and right movement of the combined left valve (2) and right valve (7).

13. The ultra-low temperature top-mount, in-line maintainable check valve of claim 1, wherein: The valve body (1) is designed as an upper-mounted type, the fastener (13) is loosened, the extension valve cover (14) assembly is taken out from the cam mounting hole (10) as a whole, the left valve (2) and the right valve (7) eliminate the anti-loose positioning, are rotated and disassembled, and are taken out respectively.

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