Magnetic turning plate liquid level meter correction equipment

By designing a calibration device for a magnetic flap level meter, using screw, inner cylinder and piston structure to reset float and magnetic flap column, the false liquid level problem of the liquid level meter when the liquid level changes rapidly is solved, and the accuracy of the liquid level display is improved.

CN119555191AInactive Publication Date: 2025-03-04ZHONGKE BEXI INSTRUMENT (CHANGZHOU) CO LTD
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Patent Information

Application Number
CN202510005991.0
Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
Filing Date
2025-01-03
Publication Date
2025-03-04
Estimated Expiration
Not applicable · inactive patent

AI Technical Summary

Technical Problem

When the material level of the magnetic flip level meter changes rapidly, the magnetic body of the float or the magnetic flip column of the magnetic flip level meter is demagnetized or disordered, and false liquid levels are easily present, which affects the accuracy of the liquid level.

Method used

A magnetic flap level gauge calibration device is designed to seal and open the measuring tube and straight cylinder through the movement of the screw and the inner cylinder. The piston and push-pull rod structures are used to move the float up and down, reset the demagnetized or disordered magnetic flap column to prevent the occurrence of false liquid levels.

Benefits of technology

It effectively solves the problem of false liquid level of the magnetic flip level meter when the liquid level changes rapidly, improves the accuracy of the liquid level display, and realizes the correction of the magnetic flip level meter, extending the service life of the equipment.

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Abstract

The invention relates to the technical field of liquid level meters, in particular to magnetic turning plate liquid level meter correction equipment which comprises a measuring tube, a magnetic turning plate mounted on the outer surface of the measuring tube, a detachable straight tube mounted at the lower end of the measuring tube, an inner tube slidably mounted in the straight tube, a screw mounted at the lower position in the inner tube through a support, and a detachable bottom cover mounted at the lower end of the straight tube. A connecting pipe is installed on the outer surface of the lower end of the straight barrel, a transverse barrel is installed at the end, away from the straight barrel, of the connecting pipe, a barrel cover is installed at the end, away from the connecting pipe, of the transverse barrel, a guide hole is formed in the middle of one face of the barrel cover, and a push-pull rod is inserted in the guide hole; the magnetic turning plate liquid level meter has the following beneficial effects that the magnetic turning column which is demagnetized or disordered is reset, the situation of false liquid level of the magnetic turning plate liquid level meter is prevented, the purpose of correcting the magnetic turning plate liquid level meter is achieved, and the liquid level display accuracy is improved.
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Description

Technical Field

[0001] The invention discloses a magnetic flap liquid level gauge calibration device, belonging to the field of liquid level gauges. Background Art

[0002] The magnetic flap level gauge uses a magnetic float to move up and down with the change of liquid level, driving the magnetic flap on the indicator to flip, thereby displaying the liquid level. That is, the magnet in the float attracts the nearby magnetic flaps, causing them to flip and change from white to red (or other contrasting colors). The number of magnetic flaps after flipping is proportional to the liquid level, thus intuitively displaying the liquid level. Due to the rapid change of material level, the magnetic body of the float in the main pipe of the magnetic flap level gauge or the magnetic flip column of the magnetic flap level gauge loses magnetism or disorder, etc., the magnetic flap level gauge will have a false level, affecting the accuracy of the liquid level. Summary of the invention

[0003] In view of the deficiencies in the prior art, the object of the present invention is to provide a magnetic flap level gauge calibration device to solve the problems raised in the above background technology.

[0004] In order to achieve the above-mentioned purpose, the present invention is realized through the following technical scheme: a magnetic flap liquid level gauge calibration device, comprising a measuring tube, a magnetic flap is installed on the outer surface of the measuring tube, a detachable straight cylinder is installed at the lower end of the measuring tube, an inner cylinder is slidably installed in the straight cylinder, a screw is installed at the lower position of the inner cylinder through a bracket, a detachable bottom cover is installed at the lower end of the straight cylinder, a screw is threadedly connected to the lower surface of the bottom cover through a connecting piece, the lower end of the screw extends to the lower side of the bottom cover and is installed with a handle, a connecting tube is installed on the outer surface of the lower end of the straight cylinder, a transverse cylinder is installed at one end of the connecting tube away from the straight cylinder, a cylinder cover is installed at one end of the transverse cylinder away from the connecting tube, a guide hole is opened in the middle position of one side of the cylinder cover, a push-pull rod is inserted in the guide hole, one end of the push-pull rod extends into the transverse cylinder and is installed with a piston, the piston is slidably installed in the transverse cylinder, and a handle is installed at one end of the push-pull rod away from the piston.

[0005] Specifically, the connecting part includes a pipe sleeve, a pipe sleeve penetrating the bottom cover is installed in the middle position of the lower surface of the bottom cover, a top plate is connected and fixed in the upper position of the pipe sleeve, a threaded hole is opened in the middle position of the upper surface of the top plate, the screw is threadedly connected in the threaded hole, the lower end of the screw extends to the lower side of the pipe sleeve, a baffle plate connected and fixed to the screw is sleeved on the screw, and the baffle plate is slidably installed in the pipe sleeve.

[0006] Specifically, a first flange is installed at the lower end of the measuring tube, a second flange connected and fixed to the straight tube is sleeved at the upper end of the straight tube, and the first flange is connected and fixed to the second flange through a fastener formed by multiple groups of first bolts and first nuts.

[0007] Specifically, a ring is provided between the first flange and the second flange, and a plurality of circular holes are equidistantly provided on one side of the ring in a circular shape, and the first bolts pass through the circular holes. A connecting plate is connected and fixed to the outer surface of the ring, and the end of the connecting plate away from the ring is connected to a vertical plate, and a horizontal cylinder is installed at the lower end of the vertical plate.

[0008] Specifically, two triangular plates are connected and fixed to the upper position of one side surface of the vertical plate, the triangular plates are connected and fixed to the connecting plate, and the vertical plate and the connecting plate are arranged perpendicular to each other.

[0009] Specifically, a pipe joint communicating with the connecting pipe is installed on the outer surface of the connecting pipe, a third flange is installed on one end of the pipe joint away from the connecting pipe, and a blind plate is installed on the third flange through a fastener formed by multiple sets of second bolts and second nuts.

[0010] Specifically, a docking ring connected and fixed to the straight tube is sleeved on the lower end of the straight tube, and the docking ring is connected and fixed to the bottom cover through a fastener formed by a plurality of sets of third bolts and third nuts.

[0011] Specifically, a liquid phase inlet is installed on the outer surface of the lower end of the measuring tube, and a fourth flange is installed on the end of the liquid phase inlet away from the measuring tube. A gas phase inlet is installed on the outer surface of the upper end of the measuring tube, and a fifth flange is installed on the end of the gas phase inlet away from the measuring tube.

[0012] Specifically, a plurality of evenly arranged U-shaped plates are sleeved on the measuring tube, and both ends of the U-shaped plates are connected to the magnetic flaps by screws.

[0013] Specifically, the bracket includes a connecting plate, a connecting plate arranged concentrically with the inner cylinder is provided at the lower position inside the inner cylinder, two support arms are connected and fixed to the outer surface of the connecting plate, one end of the support arm away from the connecting plate is connected and fixed to the inner cylinder, a positioning hole is opened in the middle position of the upper surface of the connecting plate, and the upper end of the screw is installed in the positioning hole.

[0014] Beneficial effects of the present invention: 1. Use the handle to rotate the screw so that the screw drives the inner cylinder to move from the straight cylinder to the measuring tube, so that the inner cylinder blocks the connection between the liquid phase inlet and the measuring tube. At this time, the connection between the connecting tube and the straight cylinder is in an open state. When the inner cylinder moves to the bottom of the straight cylinder, the connection between the connecting tube and the inner cylinder is blocked. At this time, the connection between the liquid phase inlet and the measuring tube is in an open state, and the switching of the blocked part is realized.

[0015] 2. Add the same liquid as that in the liquid storage tank into the horizontal cylinder. When the inner cylinder moves to the connection position between the liquid phase inlet and the measuring tube, the structure formed by the handle and the push-pull rod is used to make the piston move back and forth in the horizontal cylinder, so that the liquid level in the measuring tube rises or falls. At this time, the float in the measuring tube moves up and down to reset the demagnetized or disordered magnetic flip column, prevent the magnetic flap level gauge from having a false liquid level, achieve the purpose of calibrating the magnetic flap level gauge, and improve the accuracy of the liquid level display. After the calibration is completed, move the piston to the side away from the connecting tube. At this time, the excess liquid in the measuring tube flows back into the horizontal cylinder, and the inner cylinder is used to block the connection position between the connecting tube and the straight cylinder to prevent the piston from moving arbitrarily in the straight cylinder and affecting the accuracy of the liquid level.

[0016] 3. Make the screw thread connected to the threaded hole on the top plate, and install the top plate on the uppermost side of the pipe sleeve, and then slide the baffle plate installed on the screw into the pipe sleeve. At this time, the connection part between the screw and the threaded hole is in the closed space formed by the baffle plate, the pipe sleeve and the straight tube, preventing small debris from entering the threaded hole at will and affecting the rotation of the screw.

[0017] 4. A ring is arranged between the first flange and the second flange, and the first bolt is passed through the corresponding circular hole and then the first nut is screwed on to limit the position of the ring. At the same time, the assembly of the straight tube and the measuring tube is completed. A structure formed by a connecting plate and a vertical plate is installed between the ring and the horizontal tube to support the horizontal tube and improve the stability of the installation of the horizontal tube. The ring is installed between the first flange and the second flange by using the first nut and the first bolt. There is no need to use other fasteners to limit the position of the ring, thereby reducing the amount of fasteners used. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 It is a structural schematic diagram of a magnetic flap level gauge calibration device of the present invention; Figure 2 It is a stereoscopic diagram of another viewing angle of a magnetic flap level gauge calibration device of the present invention; Figure 3 It is a schematic diagram of the assembly of a straight cylinder, a pipe sleeve, a screw rod and an inner cylinder in a magnetic flap level gauge calibration device of the present invention; Figure 4 It is a schematic diagram of the assembly of an inner cylinder, a top plate, a shielding plate and a screw in a magnetic flap level gauge calibration device of the present invention; Figure 5 It is a schematic diagram of the assembly of a piston, a cylinder cover, a push-pull rod and a horizontal cylinder in a magnetic flap level gauge calibration device of the present invention; Figure 6 It is a schematic diagram of the assembly of a ring, a vertical plate and a horizontal cylinder in a magnetic flap level gauge calibration device of the present invention; In the figure: 1, measuring tube, 2, U-shaped plate, 3, magnetic flap, 4, liquid phase inlet, 5, fourth flange, 6, first flange, 7, second flange, 8, straight cylinder, 9, docking ring, 10, pipe sleeve, 11, screw, 12, handle, 13, connecting pipe, 14, blind plate, 15, horizontal cylinder, 16, cylinder cover, 17, push-pull rod, 18, grip, 19, pipe joint, 20, vertical plate, 21, first bolt, 22, gas phase inlet, 23, fifth flange, 24, first nut, 25, bottom cover, 26, third flange, 27, baffle plate, 28, connecting plate, 29, inner cylinder, 30, top plate, 31, support arm, 32, piston, 33, ring, 34, round hole, 35, connecting plate, 36, triangular plate. DETAILED DESCRIPTION

[0019] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0020] See also Figure 1 and Figure 2 The present invention provides a technical solution: a magnetic flap level gauge calibration device, comprising a measuring tube 1, wherein a liquid phase inlet 4 is installed on the outer surface of the lower end of the measuring tube 1, a fourth flange 5 is installed on the end of the liquid phase inlet 4 away from the measuring tube 1, a gas phase inlet 22 is installed on the outer surface of the upper end of the measuring tube 1, a fifth flange 23 is installed on the end of the gas phase inlet 22 away from the measuring tube 1, a magnetic flap 3 is installed on the outer surface of the measuring tube 1, and a plurality of evenly arranged U-shaped plates 2 are sleeved on the measuring tube 1, so that both ends of the U-shaped plates 2 are connected to the magnetic flap 3 by screws, thereby completing the assembly of the magnetic flap 3 and the measuring tube 1.

[0021] See also Figure 1 and Figure 2 A detachable straight cylinder 8 is installed at the lower end of the measuring tube 1, wherein a first flange 6 is installed at the lower end of the measuring tube 1, and a second flange 7 connected and fixed to the straight cylinder 8 is sleeved on the upper end of the straight cylinder 8, so that the first flange 6 is connected and fixed to the second flange 7 through a fastener formed by multiple groups of first bolts 21 and first nuts 24, which is convenient for disassembly and assembly of the straight cylinder 8 and the measuring tube 1.

[0022] See also Figure 3 and Figure 4An inner cylinder 29 is slidably installed in the straight cylinder 8, and a screw 11 is installed at the lower position of the inner cylinder 29 through a bracket. The bracket includes a connecting disk 28. A connecting disk 28 arranged concentrically with the inner cylinder 29 is provided at the lower position of the inner cylinder 29. Two support arms 31 are connected and fixed to the outer surface of the connecting disk 28. One end of the support arm 31 away from the connecting disk 28 is connected and fixed to the inner cylinder 29. A positioning hole is opened in the middle position of the upper surface of the connecting disk 28, so that the upper end of the screw 11 is installed in the positioning hole, thereby increasing the connection range between the screw 11 and the connecting disk 28. The bracket formed by the support arm 31 and the connecting disk 28 facilitates the liquid to flow through the inner cylinder 29.

[0023] See also Figure 1-Figure 3 A detachable bottom cover 25 is installed at the lower end of the straight cylinder 8, wherein a docking ring 9 connected and fixed to the straight cylinder 8 is sleeved at the lower end of the straight cylinder 8, so that the docking ring 9 is connected and fixed to the bottom cover 25 through a fastener formed by multiple sets of third bolts and third nuts, which facilitates the disassembly and assembly of the bottom cover 25 and the straight cylinder 8.

[0024] See also Figure 1-Figure 4 A pipe sleeve 10 that penetrates the bottom cover 25 is installed in the middle position of the lower surface of the bottom cover 25, and a top plate 30 is connected and fixed to the upper position of the pipe sleeve 10. A threaded hole is opened in the middle position of the upper surface of the top plate 30, and the screw 11 is threadedly connected in the threaded hole. The lower end of the screw 11 extends to the lower side of the pipe sleeve 10, and a shielding plate 27 connected and fixed to the screw 11 is sleeved on the screw 11. The shielding plate 27 is slidably installed in the pipe sleeve 10, so that the screw 11 is threadedly connected to the threaded hole on the top plate 30, and the top plate 30 is installed at the uppermost side of the pipe sleeve 10, and then the shielding plate 27 installed on the screw 11 is slidably installed in the pipe sleeve 10, At this time, the connection part of the screw 11 and the threaded hole is in the closed space formed by the shielding plate 27, the pipe sleeve 10 and the straight tube 8, Preventing small debris from arbitrarily entering the threaded hole and affecting the rotation of the screw 11.

[0025] See also Figure 1-Figure 4 The lower end of the screw rod 11 extends to the lower side of the bottom cover 25 and is provided with a handle 12. The screw rod 11 is rotated by the handle 12 so that the screw rod 11 drives the inner cylinder 29 to move from the straight cylinder 8 to the measuring tube 1, so that the inner cylinder 29 blocks the connection between the liquid phase inlet 4 and the measuring tube 1. At this time, the connection between the connecting tube 13 and the straight cylinder 8 is in an open state. When the inner cylinder 29 moves to the bottom of the straight cylinder 8, the connection between the connecting tube 13 and the inner cylinder 29 is blocked. At this time, the connection between the liquid phase inlet 4 and the measuring tube 1 is in an open state, so that the switching of the blocking part is realized.

[0026] See also Figure 1-Figure 6A connecting tube 13 is installed on the outer surface of the lower end of the straight cylinder 8, and a horizontal cylinder 15 is installed on the end of the connecting tube 13 away from the straight cylinder 8. A cylinder cover 16 is installed on the end of the horizontal cylinder 15 away from the connecting tube 13. A guide hole is opened in the middle of one side of the cylinder cover 16, and a push-pull rod 17 is inserted in the guide hole. One end of the push-pull rod 17 extends into the horizontal cylinder 15 and is installed with a piston 32. The piston 32 is slidably installed in the horizontal cylinder 15. A handle 18 is installed on the end of the push-pull rod 17 away from the piston 32. The same liquid as the liquid in the liquid storage tank is added to the horizontal cylinder 15. When the inner cylinder 29 moves to the connection position between the liquid phase inlet 4 and the measuring tube 1, the handle 18 and the push-pull rod 17 are used to The formed structure enables the piston 32 to reciprocate in the horizontal cylinder 15, so that the liquid level in the measuring tube 1 rises or falls. At this time, the float in the measuring tube 1 moves up and down to reset the demagnetized or disordered magnetic flip column, prevent the magnetic flap 3 liquid level gauge from having a false liquid level, achieve the purpose of calibrating the magnetic flap 3 liquid level gauge, and improve the accuracy of the liquid level display. After the calibration is completed, the piston 32 is moved to the side away from the connecting tube 13. At this time, the excess liquid in the measuring tube 1 flows back into the horizontal cylinder 15, and the inner cylinder 29 is used to seal the connecting portion between the connecting tube 13 and the straight cylinder 8 to prevent the piston 32 from moving arbitrarily in the straight cylinder 8 and affecting the accuracy of the liquid level.

[0027] See also Figure 1 and Figure 6 A live ring 33 is provided between the first flange 6 and the second flange 7. A plurality of circular holes 34 are provided in an annular shape and are equidistantly arranged on one side of the live ring 33. The first bolt 21 passes through the circular hole 34. A connecting plate 35 is connected and fixed to the outer surface of the live ring 33. The end of the connecting plate 35 away from the live ring 33 is connected to the vertical plate 20. A horizontal cylinder 15 is installed at the lower end of the vertical plate 20. Two triangular plates 36 are connected and fixed to the upper position of one side surface of the vertical plate 20. The triangular plates 36 are connected and fixed to the connecting plate 35. The vertical plate 20 and the connecting plate 35 are arranged perpendicular to each other. The triangular plates 36 improve the mechanical strength of the connection between the connecting plate 35 and the vertical plate 20. A live ring 33 is arranged between the first flange 6 and the second flange 7, and the first bolt 21 is passed through the corresponding circular hole 34 and then the first nut 24 is screwed on to complete the restriction of the position of the live ring 33. At the same time, the assembly of the straight cylinder 8 and the measuring tube 1 is completed. The structure formed by the connecting plate 35 and the vertical plate 20 is installed between the live ring 33 and the horizontal cylinder 15 to support the horizontal cylinder 15 and improve the stability of the installation of the horizontal cylinder 15. The live ring 33 is installed between the first flange 6 and the second flange 7 by using the first nut 24 and the first bolt 21. There is no need to use other fasteners to limit the position of the live ring 33, thereby reducing the use of fasteners.

[0028] See also Figure 1 , Figure 2 , Figure 5 and Figure 6A pipe joint 19 communicating with the connecting pipe 13 is installed on the outer surface of the connecting pipe 13, and a third flange 26 is installed at one end of the pipe joint 19 away from the connecting pipe 13. The third flange 26 is installed with a blind plate 14 through a fastener formed by multiple groups of second bolts and second nuts. After removing the blind plate 14, it is convenient to discharge the liquid mixed with impurities in the horizontal cylinder 15.

[0029] Although this specification is described according to implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A magnetic flap level gauge calibration device, comprising a measuring tube (1), characterized in that: The outer surface of the measuring tube (1) is mounted with a magnetic flap (3); the lower end of the measuring tube (1) is mounted with a detachable straight tube (8); an inner tube (29) is slidably mounted in the straight tube (8); a screw (11) is mounted at the lower position of the inner tube (29) via a bracket; a detachable bottom cover (25) is mounted at the lower end of the straight tube (8); the lower surface of the bottom cover (25) is threadedly connected with the screw (11) via a connecting piece; the lower end of the screw (11) extends to the lower side of the bottom cover (25) and is mounted with a handle (12); the outer surface of the lower end of the straight tube (8) is mounted with a handle (12) A connecting tube (13) is provided, and a transverse tube (15) is installed at one end of the connecting tube (13) away from the straight tube (8), and a tube cover (16) is installed at one end of the transverse tube (15) away from the connecting tube (13). A guide hole is opened in the middle of one side of the tube cover (16), and a push-pull rod (17) is inserted in the guide hole. One end of the push-pull rod (17) extends into the transverse tube (15) and is installed with a piston (32). The piston (32) is slidably installed in the transverse tube (15), and a handle (18) is installed at one end of the push-pull rod (17) away from the piston (32).

2. The magnetic flap level gauge calibration device according to claim 1, characterized in that: The connecting member comprises a pipe sleeve (10), a pipe sleeve (10) penetrating the bottom cover (25) is installed at a middle position of the lower surface of the bottom cover (25), a top plate (30) is connected and fixed at an upper position inside the pipe sleeve (10), a threaded hole is provided at a middle position of the upper surface of the top plate (30), the screw rod (11) is threadedly connected in the threaded hole, the lower end of the screw rod (11) extends to the lower side of the pipe sleeve (10), a shielding plate (27) connected and fixed to the screw rod (11) is sleeved on the screw rod (11), and the shielding plate (27) is slidably installed in the pipe sleeve (10).

3. The magnetic flap level gauge calibration device according to claim 1, characterized in that: A first flange (6) is mounted on the lower end of the measuring tube (1), and a second flange (7) connected and fixed to the straight tube (8) is sleeved on the upper end of the straight tube (8); the first flange (6) is connected and fixed to the second flange (7) via a fastener formed by a plurality of sets of first bolts (21) and first nuts (24).

4. The magnetic flap level gauge calibration device according to claim 3 is characterized in that: A ring (33) is provided between the first flange (6) and the second flange (7), and a plurality of circular holes (34) are provided in an annular shape at equal intervals on one side of the ring (33). The first bolts (21) pass through the circular holes (34). A connecting plate (35) is connected and fixed to the outer surface of the ring (33). One end of the connecting plate (35) away from the ring (33) is connected to the vertical plate (20), and a horizontal cylinder (15) is installed at the lower end of the vertical plate (20).

5. The magnetic flap level gauge calibration device according to claim 4, characterized in that: Two triangular plates (36) are connected and fixed to the upper position of one side surface of the vertical plate (20), and the triangular plates (36) are connected and fixed to the connecting plate (35). The vertical plate (20) and the connecting plate (35) are arranged perpendicular to each other.

6. The magnetic flap level gauge calibration device according to claim 1, characterized in that: A pipe joint (19) communicating with the connecting pipe (13) is mounted on the outer surface of the connecting pipe (13); a third flange (26) is mounted on one end of the pipe joint (19) away from the connecting pipe (13); and a blind plate (14) is mounted on the third flange (26) via a fastener formed by a plurality of sets of second bolts and second nuts.

7. The magnetic flap level gauge calibration device according to claim 1, characterized in that: The lower end of the straight tube (8) is sleeved with a docking ring (9) connected and fixed to the straight tube (8); the docking ring (9) is connected and fixed to the bottom cover (25) via a fastener formed by a plurality of sets of third bolts and third nuts.

8. The magnetic flap level gauge calibration device according to claim 1, characterized in that: A liquid phase inlet (4) is installed on the outer surface of the lower end of the measuring tube (1), and a fourth flange (5) is installed on the end of the liquid phase inlet (4) away from the measuring tube (1). A gas phase inlet (22) is installed on the outer surface of the upper end of the measuring tube (1), and a fifth flange (23) is installed on the end of the gas phase inlet (22) away from the measuring tube (1).

9. The magnetic flap level gauge calibration device according to claim 1, characterized in that: The measuring tube (1) is sleeved with a plurality of evenly arranged U-shaped plates (2), and both ends of the U-shaped plates (2) are connected to the magnetic flaps (3) via screws.

10. The magnetic flap level gauge calibration device according to claim 1, characterized in that: The bracket comprises a connecting plate (28), a connecting plate (28) arranged concentrically with the inner cylinder (29) is provided at a lower position inside the inner cylinder (29), two supporting arms (31) are connected and fixed to the outer surface of the connecting plate (28), one end of the supporting arm (31) away from the connecting plate (28) is connected and fixed to the inner cylinder (29), a positioning hole is provided at a middle position on the upper surface of the connecting plate (28), and the upper end of the screw rod (11) is mounted in the positioning hole.