Wind-assisted thrust device for drilling and inserting pipes for gas extraction in coal mines

Abstract

A wind-assisted boosting device for inserting pipes in gas extraction boreholes in coal mines comprises a jet guide head and a one-way ventilation flower tube, the front end of the one-way ventilation flower tube is plugged and matched with the rear end of the jet guide head and connected as a whole through radially arranged bolt pins; the jet guide head is composed of an ellipsoidal end section at the front, a cylindrical section in the middle and a plug-in straight pipe section at the rear from front to back, and an axial air outlet diversion hole that is transparent from front to back is opened inside the ellipsoidal end section and the cylindrical section along the center line, and a circumferential air outlet structure and a rear air outlet boosting structure are opened inside the cylindrical section, and the air inlets of the axial air outlet diversion hole, the circumferential air outlet structure and the rear air outlet boosting structure are all connected to the rear end of the one-way ventilation flower tube. The present invention is installed at the front end of the sealing tube when in use, and the jet guide head is always at the center line of the borehole under the action of high-pressure wind, and drives the extraction pipe to move in the borehole, ensuring that the extraction pipe is smoothly inserted into the bottom of the borehole, and also ensuring the gas extraction effect.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine gas extraction, and in particular relates to a wind-assisted propelling device for drilling and inserting pipes for gas extraction in coal mines. Background Art

[0002] After the underground extraction drilling construction, in order to ensure the smooth progress of gas extraction, it is necessary to insert a pipe to seal the hole. However, due to the large amount of drill cuttings in the drilling process, especially the amount of drill cuttings in the borehole after drilling in soft coal seams is difficult to be completely discharged, and the amount of accumulated cuttings is large. When the sealing tube is inserted, it is inevitable to encounter accumulated drill cuttings, which hinders the insertion of the sealing tube. Due to the gravity of the drill rod itself and the presence of coal seam gangue, the borehole is not actually a completely straight hole, but has a bend. During the insertion of the sealing tube, the borehole wall is hit at the bend of the borehole, making it difficult to insert the sealing tube to the bottom of the hole, which brings great inconvenience and disadvantages to the subsequent sealing, thereby affecting the sealing effect and the later gas extraction effect, and posing a great hidden danger to the safe production of coal mines. Summary of the invention

[0003] In order to solve the deficiencies in the prior art, the present invention provides a wind-assisted thruster for inserting a pipe in a gas extraction borehole in a coal mine. The wind-assisted thruster is used to assist the sealing pipe in smoothly inserting into the bottom of the borehole after the gas extraction drilling construction in the coal mine, thereby clearing the borehole and providing the required extraction channel for gas extraction after sealing.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions: a wind-assisted booster device for gas extraction drilling and inserting pipes in coal mines, comprising an air jet guide head and a one-way ventilation flower pipe, wherein the front end of the one-way ventilation flower pipe is plug-fitted with the rear end of the air jet guide head and connected as a whole through radially arranged bolt pins;

[0005] The jet guide head is composed of an ellipsoidal end section at the front, a cylindrical section in the middle and a plug-in straight pipe section at the rear from front to back. The center lines of the ellipsoidal end section, the cylindrical section and the plug-in straight pipe section coincide with each other. The rear end diameter of the ellipsoidal end section is equal to the diameter of the cylindrical section, and the diameter of the cylindrical section is larger than the diameter of the plug-in straight pipe section. An axial air outlet diversion hole that is transparent from front to back is provided inside the ellipsoidal end section and the cylindrical section along the center line. A circumferential air outlet structure and a rear air outlet boosting structure are provided inside the cylindrical section. The air inlets of the axial air outlet diversion hole, the circumferential air outlet structure and the rear air outlet boosting structure are all connected to the rear end of the one-way ventilation flower tube.

[0006] The circumferential air outlet structure includes a first annular groove opened forward on the rear end face of the cylindrical section, the first annular groove coincides with the center line of the cylindrical section, the minimum diameter of the first annular groove is larger than the diameter of the axial air outlet diversion hole, and a plurality of radial through holes are opened along the circumferential direction on the inner rear side of the cylindrical section, and the inner ends of the radial through holes are correspondingly connected to the front end portion of the first annular groove.

[0007] The rear air outlet boost structure includes a second annular groove opened forward on the rear end face of the cylindrical section, the second annular groove coincides with the center line of the cylindrical section, the minimum diameter of the second annular groove is greater than the maximum diameter of the first annular groove, the length of the first annular groove in the axial direction is greater than the length of the second annular groove in the axial direction, and a plurality of L-shaped through holes are opened along the circumferential direction on the inner front side of the cylindrical section, one section of the L-shaped through hole is arranged along the radial direction of the cylindrical section and the inner end of the section is correspondingly connected to the second annular groove, and the other section of the L-shaped through hole is parallel to the center line of the cylindrical section and the rear end opening of the section is located on the front end face of the cylindrical section outside the outer circumference of the plug-in straight pipe section.

[0008] A plurality of mounting grooves are provided on the outer ring of the first annular groove inside the cylindrical section, a limit valve is slidably provided inside each mounting groove, and the outer end of the limit valve is connected to the bottom of the mounting groove through a coil spring.

[0009] A plurality of air holes are provided on the one-way ventilation flower tube, and a connecting pipe joint for connecting a sealing pipe is integrally provided on the coaxial line at the rear end of the one-way ventilation flower tube, and the rear part of the plug-in straight pipe section is plugged into the front end of the one-way ventilation flower tube and connected as a whole through the bolt pin; a one-way barrier plastic sheet is provided on the inner wall of the one-way ventilation flower tube at each air hole, and the rear side of each one-way barrier plastic sheet is adhered to the inner wall of the one-way ventilation flower tube at the rear side of the air hole, and the curvature of the one-way barrier plastic sheet is consistent with the curvature of the inner wall of the one-way ventilation flower tube.

[0010] By adopting the above technical scheme, when the present invention is used, after drilling a hole in the coal mine, the plug-in straight pipe section at the rear end of the jet guide head is inserted into the front end of the one-way ventilation flower tube, and a bolt pin is used to radially insert the pin hole corresponding to the plug-in straight pipe section and the one-way ventilation flower tube, and the plug-in straight pipe section is used to seal with a sealant. Then the connecting pipe joint at the rear end of the one-way ventilation flower tube is inserted into the sealing pipe, and the bolt pin is used to insert and fix it radially. Then the entire booster device is inserted into the drilled hole, and a high-pressure air duct is connected to the rear end of the sealing pipe, the valve of the high-pressure air duct is opened, and the wind force is adjusted. The high-pressure air enters the jet guide head through the sealing pipe and the one-way ventilation flower tube. Since the wind direction of the high-pressure air is from back to front in the one-way ventilation flower tube, under the action of the high-pressure air, the one-way barrier plastic sheet pasted on the inner wall of the one-way ventilation flower tube blocks the air hole, and the high-pressure air enters the axial air outlet diversion hole, the first annular groove of the circumferential air outlet structure, and the rear air outlet booster structure at the front end of the plug-in straight pipe section of the jet guide head. Inside the second annular groove, the high-pressure wind blown forward through the axial air outlet diversion hole will blow away the coal slag deposited in the borehole. At the same time, the high-pressure wind through the first annular groove enters the radial through hole forward and sprays outward from several radial through holes, so that the booster end head hovers on the center line of the borehole. At the same time, the high-pressure wind through the second annular groove enters the L-shaped through hole forward and sprays backward from the outlet of the L-shaped through hole. The high-pressure airflow forms a reverse jet flow. The auxiliary operator pushes the sealing pipe forward slightly to make the jet guide head move deep into the borehole until it reaches the bottom of the front end of the borehole. Then close the valve of the high-pressure air pipe and start grouting and sealing the borehole at the orifice of the borehole. After the grouting and sealing is completed, the gas extraction operation is carried out. The outer tube of the sealing tube is connected to the extraction tube. During the gas extraction process, negative pressure is formed inside the one-way ventilation tube, and the one-way barrier plastic sheet at the air holes on the one-way ventilation tube is opened. The air holes on the one-way ventilation tube, the axial air outlet diversion holes at the end of the jet guide head, the circumferential air outlet structure and the rear air outlet booster structure can all be used as gas discharge holes, so that the gas enters the extraction system from the one-way ventilation tube, the sealing tube and the extraction tube.

[0011] The outside of the ellipsoidal end section at the front of the jet guide head is a smooth semi-ellipsoidal surface, which can prevent the end from touching the borehole wall and getting stuck after being inserted into the borehole.

[0012] The radial through holes of the circumferential air outlet structure are evenly and symmetrically arranged on the cylindrical section in the middle of the jet guide head. The number depends on the situation. The main function is to spray out air volumes of the same size on the left and right but different sizes up and down, so as to keep the jet guide head always floating on the center line of the drill hole. The air volume of the radial through holes is precisely controlled by the internal limit valve and spiral spring.

[0013] The L-shaped through holes are evenly and symmetrically arranged in the cylindrical section in the middle of the jet guide head. The air volume of each L-shaped through hole is equal. Its function is to eject gas and give a reaction force to the jet guide head. The operator can drive the jet guide head to move deeper into the borehole by slightly pushing the sealing tube forward. The air volume can be adjusted by wind pressure according to actual conditions.

[0014] High-pressure wind is ejected from the front end of the jet guide head along the axial wind outlet diversion hole, which can blow away the coal slag accumulated in front of the drill hole, thereby playing the role of pre-clearing the blocked drill hole.

[0015] The limit valve is a metal cylinder with a smooth appearance, which is connected to the bottom of the installation groove and the limit valve through the two ends of the coil spring. The limit valve located at the upper part of the jet guide head will stretch the coil spring downward out of the installation groove due to the action of gravity, blocking the space of a part of the first installation groove in the upper part, thereby making the radial through hole located at the upper part of the first annular groove have a small air output, while the limit valve located at the lower part of the jet guide head will compress the coil spring under the action of its own gravity, expanding a part of the space through the first installation groove, thereby making the radial through hole in the lower part have a larger air output. The combination of several radial through holes makes the buoyancy of the overall air output basically equal to the gravity of the jet guide head and the front sealing tube, thereby keeping the jet guide head in the center of the drill hole.

[0016] The one-way ventilation flower tube is a section of straight plastic tube. Each air hole on the one-way ventilation flower tube has a one-way barrier sheet with the same curvature as the tube diameter attached to the surface of its internal tube diameter. The function of the entire one-way ventilation flower tube is that the airflow can only enter the tube from the outside through the air holes, and the internal gas cannot be pressed to the outside. When high-pressure gas is passed into the one-way ventilation flower tube, the one-way barrier sheet will cover the air holes under the action of pressure to prevent the airflow from leaking out. In the later gas extraction process, the inside of the one-way ventilation flower tube is under negative pressure, and the one-way barrier sheet rises toward the inside of the one-way ventilation flower tube. Gas can enter the one-way ventilation flower tube through the air holes on the one-way ventilation flower tube, enter the extraction tube and finally reach the extraction system. In the process of pushing the jet guide head forward, due to the presence of the one-way barrier sheet, coal slag can also be prevented from entering the one-way ventilation flower tube, ensuring the normal progress of gas extraction.

[0017] To sum up, the present invention has a scientific principle and a compact structure. It is installed at the front end of the sealing tube when in use. Under the action of high-pressure wind, the special structural design ensures that the jet guide head of the device is always on the center line of the borehole, and drives the extraction tube to move in the borehole, ensuring that the extraction tube is smoothly inserted into the bottom of the borehole and ensuring the gas extraction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the main structure of the jet guide head in the present invention;

[0019] Figure 2 yes Figure 1 Left view of;

[0020] Figure 3 yes Figure 1 Axial cross-sectional view of

[0021] Figure 4 yes Figure 3 Middle AA section view;

[0022] Figure 5 yes Figure 3 Middle BB section view;

[0023] Figure 6 yes Figure 3 Middle CC section view;

[0024] Figure 7 This is a front view of the one-way ventilation flower tube in the present invention;

[0025] Figure 8 yes Figure 7 Axial cross-sectional view of

[0026] Fig. 9 yes Figure 8 Middle DD section view. DETAILED DESCRIPTION

[0027] like Figure 1-Figure 9 As shown, the wind-assisted boosting device for gas extraction drilling and inserting pipes in coal mines of the present invention comprises an air jet guide head and a one-way ventilation flower pipe 17, the front end of the one-way ventilation flower pipe 17 is plug-fitted with the rear end of the air jet guide head and connected as a whole through radially arranged bolt pins;

[0028] The jet guide head is composed of, from front to back, an ellipsoidal end section 2 at the front, a cylindrical section 1 in the middle, and a plug-in straight pipe section 4 at the rear. The center lines of the ellipsoidal end section 2, the cylindrical section 1, and the plug-in straight pipe section 4 coincide with each other. The rear end diameter of the ellipsoidal end section 2 is equal to the diameter of the cylindrical section 1, and the diameter of the cylindrical section 1 is larger than the diameter of the plug-in straight pipe section 4. An axial air outlet diversion hole 13 that is transparent from front to back is provided inside the ellipsoidal end section 2 and the cylindrical section 1 along the center line. A circumferential air outlet structure and a rear air outlet boosting structure are provided inside the cylindrical section 1. The air inlets of the axial air outlet diversion hole 13, the circumferential air outlet structure, and the rear air outlet boosting structure are all connected to the rear end of the one-way ventilation flower tube 17.

[0029] The circumferential air outlet structure includes a first annular groove 12 opened forward on the rear end face of the cylindrical segment 1, the first annular groove 12 coincides with the center line of the cylindrical segment 1, the minimum diameter of the first annular groove 12 is larger than the diameter of the axial air outlet diversion hole 13, and a plurality of radial through holes 3 are opened along the circumferential direction on the inner rear side of the cylindrical segment 1, and the inner ends of the radial through holes 3 are correspondingly connected to the front end portion of the first annular groove 12.

[0030] The rear air outlet boost structure includes a second annular groove 11 opened forward on the rear end face of the cylindrical section 1, the second annular groove 11 coincides with the center line of the cylindrical section 1, the minimum diameter of the second annular groove 11 is greater than the maximum diameter of the first annular groove 12, the length of the first annular groove 12 in the axial direction is greater than the length of the second annular groove 11 in the axial direction, and a plurality of L-shaped through holes 6 are opened along the circumferential direction on the inner front side of the cylindrical section 1, one section of the L-shaped through hole 6 is arranged along the radial direction of the cylindrical section 1 and the inner end of the section is correspondingly connected to the second annular groove 11, and the other section of the L-shaped through hole 6 is parallel to the center line of the cylindrical section 1 and the rear end opening of the section is located on the front end face of the cylindrical section 1 outside the outer circumference of the plug-in straight pipe section 4.

[0031] A plurality of mounting grooves 10 are provided on the outer ring of the first annular groove 12 inside the cylindrical section 1 , and a limit valve 8 is slidably provided inside each mounting groove 10 . The outer end of the limit valve 8 is connected to the bottom of the mounting groove 10 via a coil spring 9 .

[0032] A plurality of air holes 15 are provided on the one-way ventilation flower tube 17, and a connecting pipe joint 18 for connecting a sealing pipe is integrally provided on the coaxial line at the rear end of the one-way ventilation flower tube 17, and the rear part of the plug-in straight pipe section 4 is plugged into the front end of the one-way ventilation flower tube 17 and connected as a whole through the bolt pin; a one-way barrier plastic sheet 14 is provided on the inner wall of the one-way ventilation flower tube 17 at each air hole 15, and the rear side of each one-way barrier plastic sheet 14 is adhered to the inner wall of the one-way ventilation flower tube 17 on the rear side of the air hole 15, and the curvature of the one-way barrier plastic sheet 14 is consistent with the curvature of the inner wall of the one-way ventilation flower tube 17.

[0033] When the present invention is used, after drilling a hole in a coal mine, the plug-in straight pipe section 4 at the rear end of the air jet guide head is inserted into the front end of the one-way ventilation flower tube 17, and a bolt pin is inserted radially into the pin hole 5 corresponding to the plug-in straight pipe section 4 and the one-way ventilation flower tube 17, and sealed with a sealant. Then, the connecting pipe joint 18 at the rear end of the one-way ventilation flower tube 17 is inserted into the sealing pipe and fixed with a bolt pin in the radial direction. Then the whole booster device is inserted into the drilled hole, a high-pressure air duct is connected to the rear end of the sealing tube, the valve of the high-pressure air duct is opened, and the wind force is adjusted, and the high-pressure air enters the inside of the jet guide head through the sealing tube and the one-way ventilation flower tube 17. Since the wind direction of the high-pressure air is from back to front in the one-way ventilation flower tube 17, under the action of the high-pressure air, the one-way barrier plastic sheet 14 pasted on the inner wall of the one-way ventilation flower tube 17 blocks the air hole 15, and the high-pressure air enters the axial air outlet diversion hole 13, the first annular groove 12 of the circumferential air outlet structure, and the rear air outlet booster structure at the front end of the plug-in straight pipe section 4 of the jet guide head. Inside the second annular groove 11, the high-pressure wind blown forward through the axial air outlet diversion hole 13 will blow away the coal slag deposited in the borehole, and at the same time, the high-pressure wind through the first annular groove 12 enters the radial through hole 3 forward, and is sprayed outward from a number of radial through holes 3, so that the booster end is suspended on the center line of the borehole, and at the same time, the high-pressure wind through the second annular groove 11 enters the L-shaped through hole 6 forward, and the high-pressure wind is sprayed backward from the outlet of the L-shaped through hole 6. The high-pressure airflow forms a reverse jet flow, and the auxiliary operator slightly pushes the sealing pipe forward to make the jet guide head move to the deep part of the borehole until it reaches the bottom of the front end of the borehole. Then close the valve of the high-pressure air pipe, and start grouting and sealing the borehole at the orifice of the borehole. After the grouting and sealing is completed, the gas extraction operation is carried out, and the outer tube of the sealing tube is connected to the extraction tube. During the gas extraction process, a negative pressure is formed inside the one-way ventilation tube 17, and the one-way barrier plastic sheet 14 at the air hole 15 on the one-way ventilation tube 17 is opened. The air hole 15 on the one-way ventilation tube 17, the axial air outlet diversion hole 13 at the end of the jet guide head, the circumferential air outlet structure and the rear air outlet booster structure can all be used as gas discharge holes, so that the gas enters the extraction system from the one-way ventilation tube 17, the sealing tube and the extraction tube.

[0034] The outside of the ellipsoidal end section 2 at the front of the jet guide head is a smooth semi-ellipsoidal surface, which can prevent the end from touching the borehole wall and getting stuck after being inserted into the borehole.

[0035] The radial through holes 3 of the circumferential air outlet structure are evenly and symmetrically arranged on the cylindrical section 1 in the middle of the jet guide head. The number depends on the situation. The main function is to spray out air volumes of the same size on the left and right but different sizes up and down, so as to keep the jet guide head always floating on the center line of the drill hole. The air volume control of the radial through holes 3 is precisely controlled by the internal limit valve 8 and spiral spring 9.

[0036] The L-shaped through holes 6 are evenly and symmetrically arranged in the cylindrical section 1 in the middle of the jet guide head. The air volume of each L-shaped through hole 6 is equal. Its function is to eject gas and give a reaction force to the jet guide head. The operator can drive the jet guide head to move deeper into the borehole by slightly pushing the sealing tube forward. The air volume can be adjusted by wind pressure according to actual conditions.

[0037] The high-pressure wind is ejected from the front end of the jet guide head along the axial wind outlet diversion hole 13, which can blow away the coal slag accumulated in the front of the drill hole, thereby playing the role of pre-clearing the blocked drill hole.

[0038] The limit valve 8 is a metal cylinder with a smooth appearance, which is connected to the bottom of the installation groove 10 and the limit valve 8 through the two ends of the coil spring 9. The limit valve 8 located at the upper part of the jet guide head will stretch the coil spring 9 downward out of the installation groove 10 due to the action of gravity, blocking the space of the upper part of the first installation groove 10, thereby making the radial through hole 3 located at the upper part of the first annular groove 12 have a small air output. The limit valve 8 located at the lower part of the jet guide head will compress the coil spring 9 under the action of its own gravity, expanding the space through a part of the first installation groove 10, thereby making the lower radial through hole 3 have a larger air output. The combination of several radial through holes 3 makes the buoyancy of the overall air output basically equal to the gravity of the jet guide head and the front sealing tube, thereby keeping the jet guide head in the center of the drilling hole.

[0039] The one-way ventilation flower tube 17 is a straight plastic tube section, and each air hole 15 on the one-way ventilation flower tube 17 has a one-way barrier sheet with the same curvature as the tube diameter attached to its inner diameter surface. The function of the entire one-way ventilation flower tube 17 is that the airflow can only enter the flower tube from the outside through the air hole 15, and the internal gas cannot be pressed to the outside. When high-pressure gas is introduced into the one-way ventilation tube 17, the one-way barrier sheet will cover the air hole 15 under the action of pressure to prevent airflow from leaking out. In the later gas extraction process, the inside of the one-way ventilation tube 17 is under negative pressure, and the one-way barrier sheet rises toward the inside of the one-way ventilation tube 17. Gas can enter the one-way ventilation tube 17 through the air hole 15 on the one-way ventilation tube 17, enter the extraction pipe and finally reach the extraction system. In the process of pushing the jet guide head forward, due to the presence of the one-way barrier sheet, coal slag can also be prevented from entering the one-way ventilation tube 17, thereby ensuring the normal progress of gas extraction.

[0040] This embodiment does not impose any formal limitation on the shape, material, structure, etc. of the present invention. Any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A wind-assisted device for drilling and inserting pipes for gas extraction in coal mines, characterized in that: It comprises an air jet guide head and a one-way ventilation flower tube, wherein the front end of the one-way ventilation flower tube is plug-fitted with the rear end of the air jet guide head and connected as a whole through radially arranged bolt pins; The jet guide head is composed of an ellipsoid end section at the front, a cylindrical section in the middle and a plug-in straight pipe section at the rear from front to back. The center lines of the ellipsoid end section, the cylindrical section and the plug-in straight pipe section coincide with each other. The rear end diameter of the ellipsoid end section is equal to the diameter of the cylindrical section. The diameter of the cylindrical section is larger than the diameter of the plug-in straight pipe section. An axial air outlet diversion hole that is transparent from front to back is opened inside the ellipsoid end section and the cylindrical section along the center line. A circumferential air outlet structure and a rear air outlet boosting structure are opened inside the cylindrical section. The air inlets of the axial air outlet diversion hole, the circumferential air outlet structure and the rear air outlet boosting structure are all connected to the rear end of the one-way ventilation flower tube. The circumferential air outlet structure includes a first annular groove opened forwardly on the rear end surface of the cylindrical segment, the first annular groove coincides with the center line of the cylindrical segment, the minimum diameter of the first annular groove is greater than the diameter of the axial air outlet diversion hole, and a plurality of radial through holes are opened along the circumferential direction on the inner rear side of the cylindrical segment, and the inner ends of the radial through holes are correspondingly connected to the front end of the first annular groove; A plurality of air holes are provided on the one-way ventilation flower tube, and a connecting pipe joint for connecting the sealing pipe is integrally provided on the coaxial line at the rear end of the one-way ventilation flower tube, and the rear part of the plug-in straight pipe section is plugged into the front end of the one-way ventilation flower tube and connected as a whole through the bolt pin; a one-way barrier plastic sheet is provided on the inner wall of the one-way ventilation flower tube at each air hole, and the rear side of each one-way barrier plastic sheet is adhered to the inner wall of the one-way ventilation flower tube at the rear side of the air hole, and the curvature of the one-way barrier plastic sheet is consistent with the curvature of the inner wall of the one-way ventilation flower tube; The rear air outlet boost structure includes a second annular groove opened forward on the rear end face of the cylindrical section, the second annular groove coincides with the center line of the cylindrical section, the minimum diameter of the second annular groove is greater than the maximum diameter of the first annular groove, the length of the first annular groove in the axial direction is greater than the length of the second annular groove in the axial direction, and a plurality of L-shaped through holes are opened along the circumferential direction on the inner front side of the cylindrical section, one section of the L-shaped through hole is arranged along the radial direction of the cylindrical section and the inner end of the section is correspondingly connected to the second annular groove, and the other section of the L-shaped through hole is parallel to the center line of the cylindrical section and the rear end opening of the section is located on the front end face of the cylindrical section outside the outer circumference of the plug-in straight pipe section.

2. The wind-assisted booster device for drilling and inserting pipes for gas extraction in coal mines according to claim 1 is characterized in that: A plurality of mounting grooves are provided on the outer ring of the first annular groove inside the cylindrical section, a limit valve is slidably provided inside each mounting groove, and the outer end of the limit valve is connected to the bottom of the mounting groove through a coil spring.

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