CN113137568A

CN113137568A - Built-in emergency cut-off device for liquefied gas storage tank

Info

Publication number: CN113137568A
Application number: CN202110426692.6A
Authority: CN
Inventors: 郭殿泽; 王文豪; 石剑云; 祝艺洋
Original assignee: Dalian Jiaotong University
Current assignee: Dalian Jiaotong University
Priority date: 2021-04-20
Filing date: 2021-04-20
Publication date: 2021-07-20

Abstract

The invention discloses a built-in emergency cut-off device for a liquefied gas storage tank, relates to the technical field of liquefied gas storage tank safety protection, and particularly relates to a built-in emergency cut-off device for liquefied gas storage tank safety protection. The invention comprises the following steps: the device comprises an exhaust channel, a fluid driving device, an internal valve body, an external opening and closing control valve, a storage tank root connecting pipe and an external stop valve; the external opening and closing control valve is arranged on the bottom tank wall of the liquefied gas storage tank; the built-in valve body is fixedly arranged on an in-tank connector of the connecting pipe at the root part of the storage tank; the outer stop valve (18) is fixedly arranged on the tank outer connector of the storage tank root connecting pipe (17); the bottom end of the exhaust channel is connected with an external opening and closing control valve, and the top end of the exhaust channel is arranged in a gas phase space at the top in the liquefied gas storage tank; the fluid driving device is arranged on the exhaust passage and is connected with the built-in valve body. The technical scheme of the invention solves the problems that the traditional root valve in the prior art is easily influenced by the outside to cause leakage failure, the opening and closing control of the valve is complex and the reliability is poor.

Description

Built-in emergency cut-off device for liquefied gas storage tank

Technical Field

The invention discloses a built-in emergency cut-off device for a liquefied gas storage tank, relates to the technical field of liquefied gas storage tank safety protection, and particularly relates to a built-in emergency cut-off device for liquefied gas storage tank safety protection.

Background

The internal medium of the liquefied gas storage tank has the characteristics of high pressure, flammability, explosiveness and the like, and once leakage occurs, the leakage can not be stopped in time, so that serious accidents such as combustion and explosion are possibly caused.

The root valve of a liquefied gas tank is installed in the root canal and is the last barrier to prevent leakage from the tank, and the importance of the root valve is self-evident. At present, storage tank root valve technology is all more traditional, and the drive mode mostly relies on manpower, hydraulic system, pneumatics or electronic and combination mode, and the valve exists defects such as control loaded down with trivial details, fault rate height, dependence power, and under the accident situation, its own accident hidden danger and inefficient operation process lead to the storage tank emergency function obviously not enough often, lead to the accident scale to enlarge. Reference can be made to the explosion and fire accident of the large-connected 7.16 crude oil pipeline.

In addition, the root valve itself presents a greater risk of leakage. Once the valve is not tightly sealed or is affected by accidental collision, external fire and the like to cause leakage, great pressure is brought to emergency disposal. Reference can be made to the accident of explosion caused by leakage of liquefied gas spherical tank of the gas company of Western' an in 1998.

Through the analysis, the traditional root valve of the current liquefied gas storage tank is easily influenced by the outside world to cause leakage failure, the opening and closing control of the valve is complex, and the reliability is to be improved.

In view of the above problems in the prior art, it is necessary to develop a novel built-in emergency cut-off device for a liquefied gas storage tank to overcome the problems in the prior art.

Disclosure of Invention

According to the technical problems that the traditional valve provided by the prior art is easily affected by the outside to cause leakage failure, the opening and closing control of the valve is complex, and the reliability is poor, the built-in emergency cut-off device for the liquefied gas storage tank is provided. The invention mainly utilizes the fluid driving device and the built-in valve body to drive the external on-off control valve to automatically open and close, thereby realizing automatic and rapid cut-off in emergency and ensuring the safety of the storage tank.

The technical means adopted by the invention are as follows:

a built-in emergency shut-off device for a liquefied gas storage tank comprising: the device comprises an exhaust channel, a fluid driving device, an internal valve body, an external opening and closing control valve, a storage tank root connecting pipe and an external stop valve;

further, an external opening and closing control valve is arranged on the bottom tank wall of the liquefied gas storage tank;

furthermore, the built-in valve body is fixedly arranged on an in-tank interface of the connecting pipe at the root part of the storage tank;

further, the external stop valve is fixedly arranged on an external joint of the connecting pipe at the root part of the storage tank;

further, the bottom end of the exhaust channel is connected with an external opening and closing control valve, and the top end of the exhaust channel is arranged in a gas phase space at the top in the liquefied gas storage tank;

furthermore, the fluid driving device is arranged on the exhaust passage and is connected with the built-in valve body;

further, the external opening and closing control valve controls the opening and closing of the fluid driving device through opening/closing the exhaust channel, so that the internal valve body is driven to move, and the output and the closing of the liquefied gas in the liquefied gas storage tank are realized.

Further, the exhaust passage includes: a main pipe, a branch pipe A and a branch pipe B;

further, the top end of the main pipe is positioned in the gas phase space of the liquefied gas storage tank; the bottom end is connected with the top ends of the branch pipe A and the branch pipe B through a tee;

furthermore, the bottom ends of the branch pipe A and the branch pipe B are fixed on the bottom end wall of the liquefied gas storage tank and are communicated with the outside of the tank.

Furthermore, the branch pipe orifice is preferably selected to be a position which is not easily interfered by adverse factors (such as collision, fire and the like) and is convenient to operate. For tall liquefied gas storage tanks, the manifold orifices may be located at the bottom of the storage tank for ease of operation.

Further, external start-stop control valve includes: open control valve structure and close control valve structure:

further, the opening control valve structure includes: opening the valve, the valve cover seat and the valve cover; the opening valve is arranged on the outer wall of the bottom end of the liquefied gas storage tank and is connected with the branch pipe A; the valve cover seat is arranged on the outer wall of the liquefied gas storage tank outside the opening valve; the valve cover is arranged on the valve cover seat;

further, the close control valve structure includes: a shut-off valve, a valve cap seat and a valve cap; the closing valve is arranged on the outer wall of the bottom end of the liquefied gas storage tank and is connected with the branch pipe B; the valve cover seat is arranged on the outer wall of the liquefied gas storage tank outside the closing valve; the valve cover is arranged on the valve cover seat.

Further, the built-in valve body includes: the central gear, the valve rod, the valve clack, the threaded pore plate, the liquid outlet section and the valve seat are arranged on the valve body;

further, a threaded hole is machined in the center of the threaded hole plate;

furthermore, the liquid outlet section is of a cylindrical structure, and a plurality of liquid outlet channels are uniformly processed on the periphery of the liquid outlet section;

further, a liquid outlet hole is processed in the center of the valve seat;

further, the threaded hole plate, the liquid outlet section and the valve seat are fixedly connected together;

further, the valve seat is fixed with the inner section of the connecting pipe at the root part of the storage tank in a welding mode;

furthermore, the bottom end of the valve rod is fixedly provided with a valve clack, and the top end of the valve rod is provided with a central gear; the central gear is connected with the fluid driving device;

further, the valve rod is in threaded connection with the threaded pore plate through threads in the middle of the rod wall; the valve rod drives the valve clack to move downwards to plug the liquid outlet hole in the valve seat through the axial movement generated by the thread engagement.

Further, the fluid driving device includes: an opening driving device and a closing driving device;

further, the opening drive device includes: a fluid motor A, a transmission shaft A and a gear A; the fluid motor A is arranged on the branch pipe A, the output end of the fluid motor A is connected with the transmission shaft A, and the transmission shaft A is provided with a gear A; the gear A is meshed with the central gear;

further, the closing drive means includes: a fluid motor B, a transmission shaft B and a gear B; the fluid motor B is arranged on the branch pipe B, the output end of the fluid motor B is connected with the transmission shaft B, and the transmission shaft B is provided with a gear B; the gear B is meshed with the central gear;

further, the gear a and the gear B are arranged in parallel on both sides of the sun gear;

further, the rotation directions of the gear a and the gear B are opposite.

Furthermore, the contact surface between the valve clack and the liquid outlet hole of the valve seat is a sealing surface.

Further, in the above setting:

the central gear has the same module and the same tooth form angle with the gears driven by the two fluid motors.

The thread angle, the nominal diameter and the thread pitch of the thread pore plate of the built-in valve body and the valve rod are equal.

The exhaust channel, the connecting pipe at the root part of the storage tank and the tank wall are sealed by welding.

The working process of the invention is as follows:

when the liquefied gas tank is in a normal state, the valve clack of the emergency cut-off device is at the highest position, the medium in the tank is communicated with external equipment through the liquid outlet section, the storage tank root connecting pipe and the external stop valve, the opening valve and the closing valve of the emergency cut-off device are both closed, and the valve cover is screwed firmly on the valve cover seat through threads. Because the opening and closing valves are small in size, are arranged in a safer position, and are protected by the valve covers, the possibility of damage and failure in an accident is far lower than that of other valves.

When the liquefied gas leakage is caused by the failure of the external stop valve of the liquefied gas storage tank or the failure of the external part of the connecting pipe at the root part of the storage tank due to the damage of external force, the valve cover of the closing valve is unscrewed, and the closing valve is opened. At the moment, the gas phase in the storage tank is communicated with the external atmosphere through the exhaust passage, the fluid motor B and the closing valve, the high-pressure gas pushes the fluid motor B to rotate, and the fluid motor B drives the central gear to rotate through the transmission shaft B and the gear B. The central gear drives the valve rod to rotate, the valve rod is matched with the threads of the threaded hole plate, the valve rod and the valve clack are lowered along with the rotation of the gear, and then the valve clack is pressed against the sealing surface of the valve seat, so that a liquid outlet pipe channel is sealed, and medium is prevented from continuously leaking. After the external leakage was stopped, the shut-off valve was closed and the valve cap was screwed on.

After the root pipeline of the liquefied gas storage tank and the external stop valve are repaired, the opening valve is opened, the gas phase in the storage tank is communicated with the external atmosphere through the exhaust channel, the fluid motor A and the opening valve, the high-pressure gas pushes the fluid motor A to rotate, and the fluid motor A drives the central gear to rotate through the transmission shaft A and the gear A. The central gear drives the valve rod to rotate, the valve rod is matched with the threads of the threaded hole plate, the valve rod and the valve clack rise along with the rotation of the gear, and then the valve clack is separated from the sealing surface of the valve seat, so that the liquid outlet channel is opened, and the interior of the storage tank is recovered to be communicated with the exterior normally.

Compared with the prior art, the invention has the following advantages:

1. the built-in emergency cut-off device for the liquefied gas storage tank is arranged on the liquefied gas storage tank and is in an emergency standby state, when a valve or a pipeline of the storage tank leaks, emergency cut-off from the interior of the storage tank can be realized, continuous leakage of a medium is blocked, and the expansion and upgrading of accidents are prevented;

2. according to the built-in emergency cut-off device for the liquefied gas storage tank, the internal cut-off device does not need any external power, the cut-off valve can be driven only by the pressure of the liquefied gas storage tank, and the valve is convenient to open and close and quick to act;

3. according to the built-in emergency cut-off device for the liquefied gas storage tank, the emergency cut-off valve main body is positioned in the storage tank, the two exposed control valves are small in size and protected by the valve cover, the two control valves are not easily damaged by external force, and the reliability of the built-in emergency cut-off device is greatly higher than that of a common external cut-off valve.

In conclusion, the technical scheme of the invention solves the problems that the traditional root valve in the prior art is easy to leak and lose efficacy due to external influence, the opening and closing control of the valve is complex, and the reliability is poor.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is an enlarged view of portion A of FIG. 1;

fig. 3 is an assembly view of a portion of the valve body of the present invention.

In the figure: 1. the device comprises a liquefied gas storage tank 2, a main pipe 3, a gear A4, a transmission shaft A5, a fluid motor A6, a central gear 7, a fluid motor B8, a transmission shaft B9, a gear B10, a branch pipe A11, a branch pipe B12, a threaded hole plate 13, a valve rod 14, a liquid outlet section 15, a valve flap 16, a valve seat 17, a storage tank root connecting pipe 18, an external stop valve 19, a valve cover seat 20, a valve cover 21, an opening valve 22 and a closing valve.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.

In the description of the present invention, it is to be understood that the orientation or positional relationship indicated by the directional terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal" and "top, bottom", etc., are generally based on the orientation or positional relationship shown in the drawings, and are used for convenience of description and simplicity of description only, and in the absence of any contrary indication, these directional terms are not intended to indicate and imply that the device or element so referred to must have a particular orientation or be constructed and operated in a particular orientation, and therefore should not be considered as limiting the scope of the present invention: the terms "inner and outer" refer to the inner and outer relative to the profile of the respective component itself.

Spatially relative terms, such as "above … …," "above … …," "above … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial relationship to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, devices described as "above" or "on" other devices or configurations would then be oriented "below" or "under" the other devices or configurations. Thus, the exemplary term "above … …" can include both an orientation of "above … …" and "below … …". The device may be otherwise variously oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

It should be noted that the terms "first", "second", and the like are used to define the components, and are only used for convenience of distinguishing the corresponding components, and the terms have no special meanings unless otherwise stated, and therefore, the scope of the present invention should not be construed as being limited.

As shown in the drawings, the present invention provides a built-in emergency cut-off device for a liquefied gas storage tank, comprising: an exhaust passage, a fluid driving device, an internal valve body, an external opening and closing control valve, a storage tank root connecting pipe 17 and an external stop valve 18; the external opening and closing control valve is arranged on the bottom tank wall of the liquefied gas storage tank 1; the built-in valve body is fixedly arranged on the tank connector of the connecting pipe 17 at the root part of the storage tank; the external stop valve is fixedly arranged on the tank external connector of the connecting pipe 17 at the root part of the storage tank; the bottom end of the exhaust channel is connected with an external opening and closing control valve, and the top end of the exhaust channel is arranged in a gas phase space at the top in the liquefied gas storage tank 1; the fluid driving device is arranged on the exhaust passage and is connected with the built-in valve body; the external opening and closing control valve controls the opening/closing of the fluid driving device through opening/closing the exhaust passage to drive the internal valve body to move, so that the output and the closing of the liquefied gas in the liquefied gas storage tank 1 are realized.

The exhaust passage includes: main pipe 2, branch pipe a10 and branch pipe B11; the top end of the main pipe is positioned in the gas phase space of the liquefied gas storage tank 1; the bottom end is connected with the top ends of the branch pipe A10 and the branch pipe B11 through a tee; the bottom ends of the branch pipe A10 and the branch pipe B11 are fixed on the bottom end wall of the liquefied gas storage tank 1 and are communicated with the outside of the tank.

External start-stop control valve includes: open control valve structure and close control valve structure:

the opening control valve structure includes: an opening valve 21, a valve cover seat 19 and a valve cover 20; the opening valve 21 is arranged on the outer wall of the bottom end of the liquefied gas storage tank 1 and is connected with a branch pipe A10; the valve cover seat 19 is arranged on the outer wall of the liquefied gas storage tank 1 outside the opening valve 21; the valve cover 20 is arranged on the valve cover seat 19;

the close control valve structure includes: a shut-off valve 22, a bonnet seat 19 and a bonnet 20; the closing valve 22 is arranged on the outer wall of the bottom end of the liquefied gas storage tank 1 and is connected with the branch pipe B11; the valve cover seat 19 is arranged on the outer wall of the liquefied gas storage tank 1 outside the closing valve 22; the valve cover 20 is mounted on the valve cover seat 19.

The built-in valve body includes: the valve comprises a central gear 6, a valve rod 13, a valve clack 15, a threaded pore plate 12, a liquid outlet section 14 and a valve seat 16; a threaded hole is processed in the center of the threaded hole plate 12; the liquid outlet section 14 is a cylindrical structure, and a plurality of liquid outlet channels are uniformly processed on the periphery of the liquid outlet section; a liquid outlet hole is processed in the center of the valve seat 16; the threaded orifice plate 12, the liquid outlet section 14 and the valve seat 16 are fixedly connected together; the valve seat 16 is fixed with the inner section of the connecting pipe 17 at the root part of the storage tank in a welding mode; the bottom end of the valve rod 13 is fixedly provided with a valve clack 15, and the top end is provided with a central gear 6; the central gear 6 is connected with a fluid driving device; the valve rod 13 is in threaded connection with the threaded orifice plate 12 through threads in the middle of the rod wall; the valve rod 13 drives the valve clack 15 to move downwards to block the liquid outlet hole in the valve seat 16 through the axial movement generated by the thread engagement.

The fluid driving device includes: an opening driving device and a closing driving device;

the opening drive device includes: fluid motor a5, drive shaft a4, and gear A3; the fluid motor A5 is arranged on the branch pipe A10, the output end of the fluid motor A5 is connected with the transmission shaft A4, and the transmission shaft A4 is provided with a gear A3; gear a3 is in mesh with the sun gear;

the closing drive device includes: fluid motor B7, drive shaft B8, and gear B9; the fluid motor B7 is arranged on the branch pipe B11, the output end of the fluid motor B7 is connected with the transmission shaft B8, and the transmission shaft B8 is provided with a gear B9; gear B9 meshes with the sun gear;

the gear a3 and the gear B9 are arranged in parallel on both sides of the sun gear 6;

the rotation directions of the gear A3 and the gear B9 are opposite.

The contact surface between the valve clack 15 and the liquid outlet hole of the valve seat 16 is a sealing surface.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A built-in emergency cut-off device for a liquefied gas storage tank, the built-in emergency cut-off device comprising: the device comprises an exhaust channel, a fluid driving device, an internal valve body, an external opening and closing control valve, a storage tank root connecting pipe (17) and an external stop valve (18);

the external opening and closing control valve is arranged on the bottom tank wall of the liquefied gas storage tank (1);

the built-in valve body is fixedly arranged on an in-tank interface of the connecting pipe (17) at the root part of the storage tank;

the outer stop valve (18) is fixedly arranged on an outer joint of the root connecting pipe (17) of the storage tank;

the bottom end of the exhaust channel is connected with an external opening and closing control valve, and the top end of the exhaust channel is arranged in a gas phase space at the top in the liquefied gas storage tank (1);

the fluid driving device is arranged on the exhaust passage and is connected with the built-in valve body;

the external opening and closing control valve controls the opening/closing of the fluid driving device through opening/closing the exhaust channel, drives the internal valve body to move, and realizes the output and closing of the liquefied gas in the liquefied gas storage tank (1).

2. A built-in emergency shut off device for a liquefied gas storage tank as claimed in claim 1, wherein the exhaust passage comprises: a main pipe (2), a branch pipe A (10) and a branch pipe B (11);

the top end of the main pipe is positioned in the gas phase space of the liquefied gas storage tank (1); the bottom end is connected with the top ends of the branch pipe A (10) and the branch pipe B (11) through a tee;

the bottom ends of the branch pipe A (10) and the branch pipe B (11) are fixed on the bottom end wall of the liquefied gas storage tank (1) and are communicated with the outside of the tank.

3. An internal emergency shut off device for a liquefied gas storage tank as claimed in claim 1, wherein the external on-off control valve comprises: open control valve structure and close control valve structure:

the opening control valve structure comprises: an opening valve (21), a valve cover seat (19) and a valve cover (20); the opening valve (21) is arranged on the outer wall of the bottom end of the liquefied gas storage tank (1) and is connected with the branch pipe A (10); the valve cover seat (19) is arranged on the outer wall of the liquefied gas storage tank (1) outside the opening valve (21); the valve cover (20) is arranged on the valve cover seat (19);

the closing control valve structure includes: a shut-off valve (22), a valve cover seat (19) and a valve cover (20); the closing valve (22) is arranged on the outer wall of the bottom end of the liquefied gas storage tank (1) and is connected with the branch pipe B (11); the valve cover seat (19) is arranged on the outer wall of the liquefied gas storage tank (1) outside the closing valve (22); the valve cover (20) is arranged on the valve cover seat (19).

4. An internal emergency shutdown device for a liquefied gas storage tank as claimed in claim 1, wherein said internal valve body comprises: the valve comprises a central gear (6), a valve rod (13), a valve clack (15), a threaded pore plate (12), a liquid outlet section (14) and a valve seat (16);

a threaded hole is processed in the center of the threaded hole plate (12);

the liquid outlet section (14) is of a cylindrical structure, and a plurality of liquid outlet channels are uniformly processed on the periphery of the liquid outlet section;

a liquid outlet hole is processed in the center of the valve seat (16);

the threaded pore plate (12), the liquid outlet section (14) and the valve seat (16) are fixedly connected together;

the valve seat (16) is fixed with the inner section of the storage tank root connecting pipe (17) in a welding mode;

the bottom end of the valve rod (13) is fixedly provided with a valve clack (15), and the top end is provided with a central gear (6); the central gear (6) is connected with the fluid driving device;

the valve rod (13) is in threaded connection with the threaded pore plate (12) through threads in the middle of the rod wall; the valve rod (13) drives the valve clack (15) to move downwards to plug the liquid outlet hole on the valve seat (16) through the axial movement generated by the threaded engagement.

5. A built-in emergency shut off device for a liquefied gas storage tank as claimed in claim 4, wherein said fluid driving means comprises: an opening driving device and a closing driving device;

the opening driving device comprises: a fluid motor A (5), a transmission shaft A (4) and a gear A (3); the fluid motor A (5) is arranged on the branch pipe A (10), the output end of the fluid motor A is connected with the transmission shaft A (4), and the transmission shaft A (4) is provided with a gear A (3); the gear A (3) is meshed with the central gear;

the closing driving device comprises: a fluid motor B (7), a drive shaft B (8), and a gear B (9); the fluid motor B (7) is arranged on the branch pipe B (11), the output end of the fluid motor B is connected with the transmission shaft B (8), and the transmission shaft B (8) is provided with a gear B (9); the gear B (9) is meshed with the central gear;

the gear A (3) and the gear B (9) are arranged on two sides of the central gear (6) in parallel;

the rotation directions of the gear A (3) and the gear B (9) are opposite.

6. A built-in emergency cut-off device for a liquefied gas storage tank as claimed in claim 4, wherein the contact surface between the valve flap (15) and the liquid outlet hole of the valve seat (16) is a sealing surface.