Low-temperature slow-closing check valve capable of achieving reverse circulation

Abstract

The low-temperature slow-closing check valve comprises a valve body and a valve cover which are connected together through a bolt, an extending boss is arranged on the side face of the valve body, a valve rod sealing piece is arranged in the extending boss, and the temperature of the valve rod sealing piece is increased through heat exchange between the extending boss and the outside; the sealing part of the valve rod cannot be abraded due to freezing caused by low temperature; a support is arranged at the end of the extending boss, a heavy hammer device and a slowly-closed oil cylinder assembly are arranged in the middle of the support, and when the valve is in a free non-return state, the heavy hammer device can provide certain valve sealing torque to assist the valve to be closed and improve the sealing performance of the valve. The slow-closing oil cylinder assembly is directly connected with the valve rod, when the valve is opened or closed, the valve clack drives the valve rod to rotate, the slow-closing oil cylinder assembly can reduce the operation speed of the valve rod, the damping effect is achieved, direct impact between the valve clack and the valve body is avoided when the valve is opened or closed, and the service life of the valve is prolonged. The check valve is compact in structure, low in noise and easy and convenient to operate.

Description

Technical Field

[0001] The invention belongs to the technical field of globe valves, and particularly relates to a cryogenic slow-closing check valve capable of reverse flow. Background Art

[0002] Check valves need to be installed in the discharge pipelines. The main function is to achieve free check during the unloading process of LNG ships, preventing the reverse flow of LNG medium from causing water hammer impact. However, during inland LNG transportation, reverse loading onto the ship is required. At this time, the pipeline medium flows in the opposite direction to the ship unloading direction, and the check valve needs to be able to flip the valve plate through a mechanical mechanism to achieve full-bore flow through the pipeline. At the same time, when establishing the cold insulation cycle of the discharge arm pipeline, the check valve needs to be able to flip the valve plate through a mechanical mechanism to achieve full-bore flow through the pipeline and realize the pre-cooling of the discharge arm pipeline.

[0003] For example, the Chinese utility model patent with the authorization announcement number CN 221463016 U discloses a cryogenic swing check valve capable of free check, including a valve body, a valve flap, a rocker arm, a valve flap nut, spring pin I, spring pin II, a fork, a hook, a valve stem, cylindrical pin I, cylindrical pin II, etc. The valve flap is fixedly connected to the rocker arm through the valve flap nut, the rocker arm is fixedly connected to the fork through the cylindrical pin, a tension spring is connected between spring pin I and spring pin II, and the valve stem is fixedly connected to the hook through an internal hexagonal screw. This check valve has simple operation and ingenious structure. During the unloading process of LNG ships, this check valve can achieve free check. When the discharge arm pipeline is pre-cooled or LNG is reloaded, the valve flap can be lifted by operating the handwheel to achieve full-bore flow through the pipeline. However, the overall height of this globe valve is relatively high, an independent platform needs to be erected for on-site operation, and there is no damping device for the opening and closing of the valve flap, resulting in relatively large noise during operation.

[0004] For another example, the Chinese patent application for invention with the publication number CN 116379190 A discloses a cryogenic top-mounted online-maintainable two-way check valve of the present invention, which includes symmetric guide rings provided at both ends of the valve body; the left valve flap and the right valve flap are rotationally assembled in the valve body; a spring steel sheet is provided on the eccentric cam. A bushing is provided at the lower end of the extended valve cover, the valve stem passes through the bushing in the extended valve cover, and the lower end of the valve stem is inserted into the eccentric cam assembly and fixed by a union nut and a pin shaft. The upper end of the valve stem is sequentially inserted with a valve stem Lip-seal, a packing gasket, packing, a packing gland, and a packing pressing plate, and fastened by an internal hexagonal bolt. The top of the valve stem is controlled by a handle and fixed by a lock nut. The operation is simple and the structure is ingenious. During the unloading process of the LNG ship, the check valve can achieve free check; during the establishment of the cold insulation cycle of the unloading arm pipeline, it can achieve two-way flow; during the LNG reloading onto the ship, the free check function can also be achieved. The top-mounted type is convenient and fast for maintenance, and the maintenance is simple and the cost is low. However, this check valve uses the cam principle and spring steel sheets to achieve two-way free check. Similarly, there is a lack of a damping device during the closing process of the valve flap, resulting in a relatively large noise problem during operation, and the valve flow resistance is relatively large, which has a greater impact on the pipeline flow rate. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention proposes a cryogenic slow-closing check valve with reverse flow, which reduces the operating speed of the valve stem by setting a weight device and a slow-closing oil cylinder assembly, achieving a damping effect, avoiding direct impact between the valve flap and the valve body when the valve is opened and closed, and extending the service life of the valve.

[0006] The present invention proposes a cryogenic slow-closing check valve with reverse flow, which includes a valve body and a valve cover. The valve body adopts a top inlet design, and the valve body and the valve cover are connected together by bolts. An extended boss is provided on the side of the valve body, and a valve stem seal is provided inside the extended boss, so as to increase the temperature of the valve stem seal part through heat exchange with the outside through the extended boss, ensuring that the valve stem seal part will not be worn due to icing caused by low temperature; a bracket is provided at the end of the extended boss, and a weight device and a slow-closing oil cylinder assembly are provided in the middle of the bracket. When the valve is in the free check state, the weight device can provide a certain valve sealing torque to assist the valve to close and improve the valve sealing performance; the slow-closing oil cylinder assembly is directly connected to the valve stem. When the valve is opened or closed, the valve flap drives the valve stem to rotate, and the slow-closing oil cylinder assembly can reduce the operating speed of the valve stem, achieving a damping effect, avoiding direct impact between the valve flap and the valve body when the valve is opened and closed, and extending the service life of the valve. The cryogenic slow-closing check valve with reverse flow of the present invention has the characteristics of compact structure, convenient installation and maintenance, low noise, and simple operation. Moreover, it also has fire prevention and anti-static functions, is provided with disc spring seal compensation, and has a long service life.

[0007] Preferably, the weight device includes a weight connected by a lead screw. During operation, the sealing torque can be adjusted by adjusting the screwed length of the lead screw or replacing the weight with a different weight, thereby changing the flow resistance of the valve. An adjusting needle valve is provided on the slow-closing oil cylinder assembly. By adjusting the needle valve, the damping in the slow-closing oil cylinder assembly can be adjusted, so as to control the different operating speeds of the valve stem and achieve the purpose of controlling the opening and closing speeds of the valve.

[0008] In any of the above solutions, preferably, one end of the slow-closing oil cylinder assembly is installed on the extended support of the valve body, and the other end is installed on the weight connecting piece. When the valve is opened or closed, the damping effect is achieved by driving the oil cylinder piston through the valve stem. By adjusting the adjusting needle valve on the slow-closing oil cylinder assembly 7, the magnitude of the damping can be adjusted, thereby controlling the opening and closing speeds of the valve and reducing the operating noise.

[0009] In any of the above solutions, preferably, a double-sealing structure composed of a flexible graphite gasket and a first lip seal ring is adopted between the valve body and the valve cover, which has a good sealing effect and fire safety performance at the same time.

[0010] In any of the above solutions, preferably, a valve cavity is provided in the valve body, a rocker arm and a valve flap are provided in the valve cavity, the rocker arm and the valve flap are connected by a spherical joint provided on the valve flap, which has a certain self-centering effect; the rocker arm and the valve body are connected by a valve stem, the rocker arm can rotate with the valve stem, and the rotation of the valve flap realizes the flow and closing of the valve; hard alloys with different hardnesses are surfacing welded on the sealing surfaces of the valve flap and the valve body, thereby improving the wear resistance of the sealing surface of the valve.

[0011] In any of the above solutions, preferably, the valve stem passes through the extended boss and the bracket assembly and then penetrates the valve body. A bottom cover is provided at the tail end of the valve stem, and the valve stem is sealed with the valve body through the bottom cover. This seal is a double seal formed by a second lip seal ring and a graphite gasket; a dust-proof and waterproof seal ring is provided between the valve stem and the bracket to ensure that the sealed part of the valve stem remains dry and clean, preventing water or impurities from entering the valve stem seal and causing the valve stem to jam during operation; a low-temperature bearing is provided between the valve stem and the bottom cover, and the low-temperature bearing supports the end of the valve stem to reduce the operating friction; the head of the valve stem is sealed with the valve body through the valve stem seal.

[0012] In any of the above solutions, preferably, one end of the valve stem extends into the rocker arm in the valve cavity of the valve body; the other end of the valve stem is connected to the weight device, the manual operation device and the slow-closing oil cylinder assembly. The manual operation device can manually open the check valve through the handwheel operation. When the handwheel is rotated counterclockwise to the limit, the check valve is fully opened and the valve flap cannot move, allowing the pipeline medium to flow reversely; when the handwheel is rotated clockwise to the limit, the check valve is in the free check state, realizing the check function of the pipeline medium.

[0013] Preferably, in any of the above solutions, semi-circular grooves are machined at the end of the valve stem and on the manual operating device. The two are in a semi-engaged state, and the manual opening of the check valve can be realized by operating the handwheel. After the valve is opened, the valve disc is limited in the open position by the limit block on the valve body, and the closing position is limited by the valve stem and the manual operating device; when the movement of the valve disc is completely restricted, the reverse flow of the pipeline medium is realized; after the valve is closed, the valve stem and the manual operating device no longer restrict the rotation of the valve stem, and the valve disc can freely rotate 75 degrees around the valve stem to realize the check function of the pipeline medium.

[0014] Preferably, in any of the above solutions, the valve stem seal includes a third lip seal, a positioning block, a graphite packing set, a sealing ring, a disc spring set, a low-temperature bearing and a sealing ring. The positioning block is used to support the third lip seal and the graphite packing set; two groups of low-temperature O-rings are provided inside and outside the sealing ring, thus forming a triple valve stem seal; the disc spring set is located at the lower end of the sealing ring, providing sealing pre-tightening force and sealing compensation, and increasing the service life; the sealing ring is located between the extension boss and the bracket, used to prevent external water vapor and dust from entering the internal valve stem seal assembly, and keep the inside dry and clean.

[0015] Preferably, in any of the above solutions, a positioning step is provided on the valve stem to prevent the valve stem from flying out; the seals of this check valve are all made of metal or graphite seals, which have good static electricity conduction ability.

[0016] In summary, the reversely flowable low-temperature slow-closing check valve of the present invention has the following advantages: compact structure, convenient installation and maintenance, low noise, and simple operation; by installing the relevant manual operating device through the extension boss provided on the valve body, the height of the valve is greatly reduced, and there is no need to set up an operating platform for the valve seat operation, which is simple to operate; a weight and a slow-closing device are provided on the valve stem, which can effectively reduce the opening and closing operation speeds of the valve while providing sealing pre-tightening, effectively reduce the operating noise, and improve the sealing life of the valve; the seals of this check valve are all made of metal or graphite seals, which have good static electricity conduction ability.

[0017] Explanation of the attached drawing reference numerals

[0018] Valve cover 1, valve body 2, weight device 3, extension boss 4, bracket 5, manual operating device 6, slow-closing oil cylinder assembly 7, rocker arm 8, valve disc 9, valve stem 10, bottom cover 11, valve stem seal 12, flexible graphite gasket 13, first lip seal 14, regulating needle valve 71, second lip seal 111, graphite gasket 112, low-temperature bearing 113, third lip seal 121, positioning block 122, graphite packing set 123, sealing ring 124, disc spring set 125, low-temperature bearing 126, sealing ring 127. Explanation of the attached drawings

[0019] Figure 1Schematic structural diagram of a preferred embodiment of the low-temperature slow-closing check valve with reverse flow according to the present invention.

[0020] Figure 2 In the low-temperature slow-closing check valve with reverse flow according to the present invention Figure 1 Front view of the shown preferred embodiment.

[0021] Figure 3 In the low-temperature slow-closing check valve with reverse flow according to the present invention Figure 1 Schematic diagram of the internal structure of the valve body in the shown preferred embodiment.

[0022] Figure 4 In the low-temperature slow-closing check valve with reverse flow according to the present invention Figure 1 Top view of the shown preferred embodiment.

[0023] Figure 5 In the low-temperature slow-closing check valve with reverse flow according to the present invention Figure 4 Schematic diagram of the structure of the valve stem seal in the shown preferred embodiment.

[0024] Figure 6 In the low-temperature slow-closing check valve with reverse flow according to the present invention Figure 1 Connection diagram of the valve stem and the manual operating device in the free check state of the shown preferred embodiment. Detailed implementation manners

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0026] As Figure 1 、 Figure 2As shown in the figure, a low-temperature slow-closing check valve with reverse flow is provided, which includes a valve body 2 and a valve cover 1. The valve body 2 adopts a top inlet design. The valve body 2 and the valve cover 1 are connected together by bolts. An extended boss 4 is provided on the side of the valve body 2, and a valve stem seal 12 is provided inside the extended boss 4, so as to increase the temperature of the valve stem seal 12 part through heat exchange between the extended boss 4 and the outside world, ensuring that the valve stem seal 12 part will not be worn due to icing caused by low temperature; a bracket 5 is provided at the end of the extended boss 4, and a weight device 3 and a slow-closing oil cylinder assembly 7 are provided in the middle part of the bracket 5. When the valve is in the free check state, the weight device 3 can provide a certain valve sealing torque to assist the valve to close and improve the valve sealing performance; the slow-closing oil cylinder assembly 7 is directly connected to the valve stem 10. When the valve is opened or closed, the valve flap 9 drives the valve stem 10 to rotate. The slow-closing oil cylinder assembly 7 can reduce the rotation speed of the valve stem and play a damping effect, avoiding direct impact between the valve flap 9 and the valve body 2 when the valve is opened and closed, and extending the service life of the valve. The low-temperature slow-closing check valve with reverse flow of the present invention has the characteristics of compact structure, convenient installation and maintenance, low noise, and simple operation. Moreover, it also has fire prevention and anti-static functions, is provided with disc spring seal compensation, and has a long service life.

[0027] When discharging the ship, the valve needs to be in the free check state. Rotate the handwheel of the manual operating device 6 clockwise to the limit. The manual operating device 6 no longer restricts the rotation of the valve stem 10. The valve flap 9 rotates under its own gravity and the gravity of the weight of the weight device 3 to fit the sealing surface of the valve body 2. When the medium flows forward, the valve flap 9 is pushed under the action of the medium force, and the medium flows downstream. When the medium flows backward, it is automatically closed under the action of the reverse medium force, the gravity of the valve flap 9 itself, and the weight gravity, realizing reverse sealing.

[0028] When loading the ship in reverse, the valve needs to be in the fully open state. Rotate the handwheel of the manual operating device 6 counterclockwise to the limit. The valve stem 10 drives the valve flap 9 to rotate upward. The valve is fully opened, and the valve flap 9 is limited at the position of the limit block of the valve body 2. At the same time, the manual operating device 6 restricts the clockwise rotation of the valve stem 10, resulting in that the valve stem 10 and the valve flap 9 can no longer rotate, realizing the full opening and positioning of the valve, and the medium can flow freely.

[0029] When the valve is in the free check state, the flow of the medium needs to overcome the gravity of the valve flap 9 itself and the weight gravity. The distance between the weight and the valve stem 10 can be adjusted according to the size of the medium pressure, or a weight with a suitable weight can be replaced, reducing the flow resistance of the valve while ensuring the sealing pre-tightening.

[0030] For the parts that often load and unload the ship in reverse, the manual operating device 6 can be replaced with a pneumatic or electric device, which can meet the requirements of the low-temperature slow-closing check valve with reverse flow of the present invention without additional valve modification.

[0031] In this embodiment, an extended boss 4 is provided on the side of the valve body 2, which greatly reduces the height of the previous structure, meets the sealing requirements at normal temperature and low temperature at the same time, has a compact and simple structure, does not require additional tools for installation and disassembly, is easy to operate on site, and has good slow-closing and speed-adjustable functions, which can greatly improve the service life of the valve.

[0032] In this embodiment, the weight device 3 includes a weight connected by a lead screw. During operation, the sealing torque can be adjusted by adjusting the screwing length of the lead screw or replacing the weight with different weights, so as to change the flow resistance of the valve; an adjusting needle valve 71 is provided on the slow-closing oil cylinder assembly 7. By adjusting the needle valve 71, the damping in the slow-closing oil cylinder assembly can be adjusted, so as to control the different operating speeds of the valve stem 10 to achieve the purpose of controlling the opening and closing speed of the valve.

[0033] In this embodiment, one end of the slow-closing oil cylinder assembly 7 is installed on the extended support of the valve body 2, and the other end is installed on the weight connecting piece 3. When the valve is opened or closed, the damping effect is realized by driving the oil cylinder piston through the valve stem 10. By adjusting the adjusting needle valve on the slow-closing oil cylinder assembly 7, the size of the damping can be adjusted, so as to control the opening and closing speed of the valve and reduce the running noise.

[0034] As Figure 3 shown, the internal structure schematic diagram of the valve body in the preferred embodiment of the reversely flowable low-temperature slow-closing check valve according to the present invention Figure 1 is shown.

[0035] In this embodiment, a double-sealing structure composed of a flexible graphite gasket 13 and a first lip seal 14 is adopted between the valve body 2 and the valve cover 1, which has a good sealing effect and at the same time has fire safety performance.

[0036] In this embodiment, a valve cavity is provided in the valve body 2, and a rocker arm 8 and a valve flap 9 are provided in the valve cavity. The rocker arm 8 and the valve flap 9 are connected by a spherical joint provided on the valve flap 9, which has a certain self-centering effect; the rocker arm 8 and the valve body 1 are connected by a valve stem 10, and the rocker arm 8 can rotate with the valve stem 10, and the rotation of the valve flap 9 realizes the flow and closing of the valve; hard alloys with different hardnesses are surfacing welded on the sealing surfaces of the valve flap 9 and the valve body 2, so as to improve the wear resistance of the sealing surface of the valve.

[0037] Refer to Figure 4 shown, the top view of the preferred embodiment of the reversely flowable low-temperature slow-closing check valve according to the present invention Figure 1 is shown.

[0038] In this embodiment, the valve stem 10 passes through the extension boss 4 and the bracket 5 assembly and then penetrates through the valve body 1. A bottom cover 11 is provided at the tail end of the valve stem 10. The valve stem 10 realizes sealing with the valve body 1 through the bottom cover 11, and this seal is a double seal formed by the second lip seal ring 111 and the graphite gasket 112; a dust-proof and waterproof seal ring is provided between the valve stem 10 and the bracket 5 to ensure that the sealed part of the valve stem 10 remains dry and clean, and prevent the valve stem 10 from getting stuck due to water or impurities entering the seal; a low-temperature bearing 113 is provided between the valve stem 10 and the bottom cover 11, and the low-temperature bearing 113 supports the end of the valve stem 10 to reduce operating friction; the head of the valve stem 10 is sealed with the valve body 1 through the valve stem seal 12.

[0039] In this embodiment, one end of the valve stem 10 extends into the rocker arm 8 in the valve cavity of the valve body 2; the other end of the valve stem 10 is connected to the weight device 3, the manual operation device 6 and the slow-closing oil cylinder assembly 7. The manual operation device 6 can realize the manual opening of the check valve through the handwheel operation. When the handwheel is rotated counterclockwise to the limit, the check valve is fully opened, and the valve flap 9 cannot move, allowing the pipeline medium to flow reversely; when the handwheel is rotated clockwise to the limit, the check valve is in the free check state, realizing the check function of the pipeline medium.

[0040] In this embodiment, a positioning step is provided on the valve stem 10 to prevent the safety function of the valve stem 10 from flying out; all the sealing parts of this check valve adopt metal or graphite seals, which have good static electricity conduction ability.

[0041] Next, refer to Figure 5 As shown, in the low-temperature slow-closing check valve that can reverse-flow according to the present invention Figure 4 Schematic diagram of the structure of the valve stem seal in the preferred embodiment shown.

[0042] In this embodiment, the valve stem seal 12 includes a third lip seal ring 121, a positioning block 122, a graphite packing group 123, a sealing ring 124, a disc spring group 125, a low-temperature bearing 126 and a seal ring 127. The positioning block 122 is used to support the third lip seal ring 121 and the graphite packing group 123; two groups of low-temperature O-rings are provided inside and outside the sealing ring 124, thus forming a triple valve stem seal; the disc spring group 125 is located at the lower end of the sealing ring 124, providing sealing pre-tightening force and sealing compensation to increase the service life; the seal ring 127 is located between the extension boss 4 and the bracket 5 (see Figure 4 As shown), used to prevent external water vapor and dust from entering the internal valve stem seal assembly and keep the inside dry and clean.

[0043] Finally, refer to Figure 6 As shown, in the low-temperature slow-closing check valve that can reverse-flow according to the present invention Figure 1 Schematic diagram of the connection between the valve stem and the manual operation device in the free check state in the preferred embodiment shown.

[0044] In this embodiment, semi-circular grooves are machined at the end of the valve stem 10 and on the manual operating device 6, and the two are in a semi-engaged state, enabling manual opening of the check valve by operating the handwheel. After the valve is opened, the valve flap 9 is limited in the open position by the limit block on the valve body 2 and in the closed position by the valve stem 10 and the manual operating device 6; when the movement of the valve flap 9 is completely restricted, reverse flow of the pipeline medium is achieved; after the valve is closed, the valve stem 10 and the manual operating device 6 no longer restrict the rotation of the valve stem 10, and the valve flap 9 can freely rotate 75 degrees around the valve stem 10 to achieve the check function of the pipeline medium.

[0045] It is not difficult for those skilled in the art to understand that the reversely flowable low-temperature slow-closing check valve of the present invention includes any combination of the various parts in this specification. Limited by space and for the sake of conciseness of the specification, these combinations are not introduced in detail one by one here, but after reading this specification, the scope of the present invention constituted by any combination of the various parts formed by this specification is self-evident.

Claims

1. A low-temperature slow-closing check valve capable of reverse flow, comprising a valve body (2) and a valve cover (1), wherein the valve body (2) adopts a top inlet design, and the valve body (2) and the valve cover (1) are connected together by bolts, characterized in that: An extension boss (4) is provided on the side of the valve body (2), and a valve stem seal (12) is provided inside the extension boss (4); a bracket (5) is provided at the end of the extension boss (4), and a weight device (3) and a slow-closing cylinder assembly (7) are provided in the middle of the bracket (5); the slow-closing cylinder assembly (7) is directly connected to the valve stem (10), and when the valve is opened or closed, the valve disc (9) drives the valve stem (10) to rotate.

2. The low-temperature slow-closing check valve capable of reverse flow according to claim 1, characterized in that: The weight device (3) comprises a weight connected by a screw rod. When working, the sealing torque can be adjusted by adjusting the screw rod screwing length or replacing the weight with different weights to change the flow resistance of the valve. The slow closing oil cylinder assembly (7) is provided with an adjusting needle valve (71). By adjusting the needle valve (71), the damping size in the slow closing oil cylinder assembly can be adjusted.

3. The low-temperature slow-closing check valve capable of reverse flow according to claim 1 or 2, characterized in that: One end of the slow-closing oil cylinder assembly (7) is mounted on the extension support of the valve body (2), and the other end is mounted on the heavy hammer connecting piece (3).

4. The low-temperature slow-closing check valve capable of reverse flow according to claim 1, characterized in that: A flexible graphite gasket (13) and a first lip-shaped sealing ring (14) are used between the valve body (2) and the valve cover (1) to form a double sealing structure.

5. The low-temperature slow-closing check valve capable of reverse flow according to claim 1 or 4, characterized in that: A valve cavity is provided in the valve body (2), and a rocker arm (8) and a valve flap (9) are provided in the valve cavity. The rocker arm (8) and the valve flap (9) are connected via a spherical joint provided on the valve flap (9); the rocker arm (8) and the valve body (1) are connected via a valve stem (10), and the rocker arm (8) can rotate along with the valve stem (10). The rotation of the valve flap (9) enables the flow and closing of the valve; and hard alloys of different hardness are welded on the sealing surfaces of the valve flap (9) and the valve body (2).

6. The low-temperature slow-closing check valve capable of reverse flow according to claim 1, characterized in that: The valve stem (10) passes through the extension boss (4) and the bracket (5) assembly and then penetrates the valve body (1). A bottom cover (11) is provided at the rear end of the valve stem (10). The valve stem (10) is sealed with the valve body (1) through the bottom cover (11). The seal is a double seal formed by a second lip seal ring (111) and a graphite gasket (112). A dustproof and waterproof seal ring is provided between the valve stem (10) and the bracket (5). A low-temperature bearing (113) is provided between the valve stem (10) and the bottom cover (11). The low-temperature bearing (113) supports the end of the valve stem (10) to reduce operating friction. The head of the valve stem (10) is sealed with the valve body (1) through a valve stem seal (12).

7. The low-temperature slow-closing check valve capable of reverse flow according to claim 1 or 6, characterized in that: One end of the valve stem (10) extends into the rocker arm (8) in the valve cavity of the valve body (2); the other end of the valve stem (10) is connected to the weight device (3), the manual operating device (6) and the slow-closing cylinder assembly (7); the manual operating device (6) can realize manual opening of the check valve by operating a hand wheel; when the hand wheel rotates counterclockwise to a limit position, the check valve is fully opened, the valve disc (9) cannot move, and the pipeline medium can flow in the reverse direction; when the hand wheel rotates clockwise to a limit position, the check valve is in a free check state, realizing the pipeline medium check function.

8. The low-temperature slow-closing check valve capable of reverse flow according to claim 7, characterized in that: The end of the valve stem (10) and the manual operating device (6) are both processed with semicircular grooves, and the two are in a semi-engaged state. The check valve can be manually opened by a hand wheel operation. After the valve is opened, the valve flap (9) is limited to the open position by the limit block on the valve body (2), and is limited to the closed position by the valve stem (10) and the manual operating device (6); when the movement of the valve flap (9) is completely restricted, the reverse flow of the pipeline medium is achieved; after the valve is closed, the valve stem (10) and the manual operating device (6) no longer restrict the operation of the valve stem (10), and the valve flap (9) can freely rotate 75 degrees around the valve stem (10), thereby achieving the pipeline medium check function.

9. The low-temperature slow-closing check valve capable of reverse flow according to any one of claims 1, 4 or 6, characterized in that: The valve stem seal (12) includes a third lip seal ring (121), a positioning block (122), a graphite packing group (123), a sealing ring (124), a disc spring group (125), a low-temperature bearing (126) and a sealing ring (127). The positioning block (122) is used to support the third lip seal ring (121) and the graphite packing group (123); two groups of low-temperature O-rings are arranged inside and outside the sealing ring (124), thereby forming a triple valve stem seal; the disc spring group (125) is located at the lower end of the sealing ring (124) to provide sealing preload and sealing compensation; the sealing ring (127) is located between the extension boss (4) and the bracket (5).

10. The low-temperature slow-closing check valve capable of reverse flow according to claim 1, characterized in that: A positioning step is provided on the valve stem (10); the sealing elements of the check valve are all metal or graphite seals.

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