Vertical centrifugal pump

Abstract

The utility model relates to a vertical centrifugal pump, which is characterized in that a labyrinth sleeve is arranged between an impeller and a mechanical seal, the labyrinth sleeve is of a labyrinth structure comprising a movable sleeve and a fixed sleeve, the movable sleeve and the fixed sleeve are sleeved in a coupling and staggered manner, the movable sleeve is fixed on a main shaft, and the fixed sleeve is fixed on a pump body; the movable sleeve and the fixed sleeve do not make contact with each other, an air cavity is formed in the labyrinth sleeve, and air is stored in the air cavity. The labyrinth type mechanical seal has the advantages that the labyrinth type structure prolongs the service life of the mechanical seal, and the length of the air cavity and the length of the main shaft support do not need to be increased; the oil storage cavity can prevent dry friction heating of the mechanical seal of the vertical centrifugal pump when the mechanical seal runs in liquid-free air, and prevent the mechanical seal from being damaged due to too high temperature; the wind wheel is arranged on the shaft sleeve on the rear side of the mechanical seal, and wind generated by rotation of the wind wheel blows into the oil storage cavity, so that the mechanical seal can effectively run in the air without temperature rise and damage.

Description

Technical Field

[0001] This utility model belongs to the field of centrifugal slurry pump technology, and particularly relates to a vertical centrifugal pump. Background Technology

[0002] Patent No. ZL201820807938.8 discloses a centrifugal slurry pump with an air shaft seal: the centrifugal slurry pump is made into a vertical centrifugal pump, and an air retention chamber is set between the seal and the slurry being transported. The retained air isolates the slurry from contact with the mechanical seal assembly, especially from contact between the slurry and the dynamic and static rings of the mechanical seal. This ensures that the dynamic and static rings of the mechanical seal do not contact the transported slurry, thus allowing the mechanical seal to only contact with air, making the working environment of the mechanical seal clean, thereby ensuring safe operation of the mechanical seal and extending its service life.

[0003] However, for the air retention chamber to achieve its intended effect, it must have a certain height. For example, the air chamber height of a 150mm imported vertical centrifugal pump must reach 150 to 200mm to prevent slurry from splashing onto the pump's mechanical seal. However, increasing the air chamber to 150 to 200mm also necessitates increasing the pump's main shaft to 150 to 200mm. As the main shaft lengthens, its strength and torsional resistance change significantly. Increasing the main shaft's strength requires thickening it, increasing the bearing size, and raising the pump frame, thus increasing the pump's manufacturing cost.

[0004] Furthermore, to prevent air leakage from the mechanical seal, an effective method is to increase the pressure between the working surfaces of the dynamic and stationary rings. However, increasing the pressure introduces another problem: the mechanical seal temperature rises sharply, sometimes reaching 100-130°C. Relying solely on the air-cooling system in this technology is insufficient to effectively cool the heat generated by the dynamic and stationary rings during operation. The localized temperature of the mechanical seal continues to rise and stabilize above 80-90°C. This adverse effect directly impacts the service life of the mechanical seal.

[0005] Therefore, existing technologies still fall short in cooling the air that isolates the slurry from the mechanical seal assembly. Utility Model Content

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a vertical centrifugal pump.

[0007] A vertical centrifugal pump includes a pump body, an impeller, a pump casing, a main shaft, a mechanical seal, a shaft sleeve, a sealing box, a motor, a pump inlet, and a pump outlet. A labyrinth sleeve is provided between the impeller and the mechanical seal. The labyrinth sleeve is a labyrinth-type structure consisting of a moving sleeve and a stationary sleeve. The moving sleeve and the stationary sleeve are coupled and staggered together. The moving sleeve is fixed on the main shaft, and the stationary sleeve is fixed on the pump body. The moving sleeve and the stationary sleeve do not contact each other. An air cavity is formed inside the labyrinth sleeve, and the air cavity contains air.

[0008] As a preferred embodiment: the moving sleeve of the labyrinth sleeve is an inverted L-shaped moving sleeve, and the stationary sleeve of the labyrinth sleeve is a U-shaped stationary sleeve. The inverted L-shaped moving sleeve is fixedly connected to the bushing on the main shaft, and the U-shaped stationary sleeve is fixed on the pump body. The protrusion of the inverted L-shaped moving sleeve is inserted into the concave part in the center of the U-shaped stationary sleeve, and the inverted L-shaped moving sleeve and the U-shaped stationary sleeve do not contact each other and form an N-shaped air cavity.

[0009] As a preferred embodiment: the moving sleeve of the labyrinth sleeve is an L-shaped moving sleeve, and the stationary sleeve of the labyrinth sleeve is an inverted L-shaped stationary sleeve. The L-shaped moving sleeve is fixedly connected to the bushing on the main shaft, and the inverted L-shaped stationary sleeve is fixed on the pump body. The collar of the L-shaped moving sleeve is fitted between the collar of the inverted L-shaped stationary sleeve and the pump body. The L-shaped moving sleeve and the inverted L-shaped stationary sleeve do not contact each other, thereby forming an S-shaped air cavity between the main shaft and the pump body.

[0010] Preferably, a number of radial protrusions are provided on the back of the impeller or an auxiliary impeller is provided on the back of the impeller. The radial protrusions or the auxiliary impeller are used to depressurize the air inside the labyrinth sleeve.

[0011] As a preferred embodiment, an oil storage chamber is provided on the outer periphery of the mechanical seal, and the oil storage chamber contains grease.

[0012] As a preferred embodiment, a fan is provided on the bushing on the rear side of the mechanical seal, with the fan rotating in the direction directly opposite the oil storage chamber.

[0013] As a preferred option, a sand settling chamber is provided at the pump inlet, and a sand discharge port is provided on the sand settling chamber.

[0014] As a preferred option, the stationary sleeve is made of polyethylene with a molecular weight of 5 million, and the moving sleeve is made of silicon carbide.

[0015] Preferably, the pump casing and impeller are made of at least one of metal, plastic, ceramic, resin and mineral; metals include stainless steel and high chromium alloys.

[0016] Another type of vertical centrifugal pump includes a pump body, impeller, pump casing, main shaft, mechanical seal, shaft sleeve, sealing box, motor, pump inlet, and pump outlet; a pressure reducing plate is provided on the main shaft between the back of the impeller and the shaft sleeve; pressure reducing wheel ribs are provided on the cross-section of one end of the pressure reducing plate, and the pressure reducing wheel ribs are several radial protrusions; a pressure reducing pad is provided at the end of the pressure reducing wheel ribs and is fixed to the pump body, the pressure reducing pad is opposite to the pressure reducing wheel ribs but does not contact them, and there is a gap of 0.5mm to 2mm between the pressure reducing pad and the pressure reducing plate; the gap formed between the pressure reducing plate and the pressure reducing pad.

[0017] The beneficial effects of this utility model are:

[0018] This invention designs a vertical centrifugal slurry pump with a good sealing effect, which does not require lengthening or thickening of the main shaft, has an air gap between the mechanical seal and the conveyed slurry.

[0019] On the one hand, this utility model features a labyrinth sleeve with a labyrinth structure between the impeller and the mechanical seal, which lengthens the air passage between the pump chamber and the mechanical seal. When the pump is working, the air is squeezed into the labyrinth structure by the fluid in the pump chamber. Due to the sealing effect of the mechanical seal, the air in the labyrinth structure will not be discharged outside the pump. Due to gravity, the fluid being transported in the labyrinth structure sinks to the bottom, while the air in the labyrinth structure floats to the top. Under the isolation effect of the labyrinth structure, the air cannot enter the pump chamber and is carried away by the fluid, nor can it enter the mechanical seal and be discharged outside the pump chamber. The air can only accumulate in the labyrinth structure, isolating the contact between the transported fluid and the mechanical seal, so that the dynamic and stationary rings of the mechanical seal do not come into contact with the slurry and are protected from the scouring and corrosion of the transported slurry. The labyrinth structure extends the service life of the mechanical seal and does not require increasing the length of the air chamber and the main shaft support.

[0020] On the other hand, this utility model has a pressure reducing plate on the main shaft between the back of the impeller and the bushing. A pressure reducing wheel rib is provided on the cross-section of one end of the pressure reducing plate. A pressure reducing pad is provided at the end of the pressure reducing wheel rib, which is fixed on the pump body and is opposite to the pressure reducing wheel rib. There is a gap between the pressure reducing pad and the pressure reducing plate. Therefore, the air is squeezed into the gap by the fluid in the pump chamber. Due to the sealing of the mechanical seal, the air in the gap will not be discharged outside the pump. The air in the gap isolates the contact between the conveying fluid and the mechanical seal, so that the dynamic ring and stationary ring of the mechanical seal do not contact the slurry and are protected from the scouring and corrosion of the conveyed slurry. In addition, since the pressure reducing wheel rib is a number of radial protrusions, the strength of the pressure reducing plate is increased, so that the vertical centrifugal pump can disperse the impact force of the high solid content slurry and convey the high solid content slurry. The setting of the pressure reducing pad allows the force on the pressure reducing plate to be transmitted to the pressure reducing pad when the pressure reducing plate deforms and contacts the pressure reducing pad, further reducing the deformation range of the pressure reducing plate.

[0021] An oil storage chamber containing grease is provided on the outer periphery of the mechanical seal. This chamber prevents the mechanical seal of the vertical centrifugal pump from generating heat through dry friction when operating in air without liquid. The grease in the oil storage chamber lubricates the friction surfaces of the rotating and stationary rings, reducing the rate of heat generation and preventing damage to the mechanical seal due to excessive temperature. A fan is installed on the bushing behind the mechanical seal. The air generated by the rotation of the fan blows into the oil storage chamber, and the flow of grease in the oil storage chamber conducts the accumulated heat on the rotating and stationary rings. This forms a cooling and lubrication system in which the oil conducts the temperature, the air blows the grease to cool it down, and the grease lubricates the friction pairs of the mechanical seal. This effectively prevents the mechanical seal from overheating and being damaged when operating in air. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of a vertical centrifugal pump.

[0023] Figure 2 A schematic diagram of the structure of a labyrinth sleeve consisting of an inverted L-shaped moving sleeve and a U-shaped stationary sleeve, and an N-shaped air cavity;

[0024] Figure 3 A schematic diagram of the structure of the labyrinth sleeve composed of an inverted L-shaped stationary sleeve and an L-shaped moving sleeve, and the S-shaped air cavity;

[0025] Figure 4 This is a schematic diagram of the pressure-reducing pad and pressure-reducing plate.

[0026] Explanation of reference numerals in the attached drawings: 1. Motor; 2. Main shaft; 3. Mechanical seal; 4. Moving ring; 5. Stationary ring; 6. Pump casing; 7. Impeller; 8. Sand settling chamber; 9. Pump inlet; 10. Pump body; 11. Inverted L-shaped moving sleeve; 12. U-shaped stationary sleeve; 13. Oil storage chamber; 14. N-shaped air chamber; 15. Shaft sleeve; 16. Inverted L-shaped stationary sleeve; 17. L-shaped moving sleeve; 18. S-shaped air chamber; 19. Sealing box; 20. Pump outlet; 21. Radial convex strip; 22. Fan wheel; 23. Pressure reducing plate; 24. Pressure reducing pad; 25. Pressure reducing wheel rib; 26. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that, for those skilled in the art, several modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. Example 1

[0028] like Figure 1 and Figure 2As shown, a vertical centrifugal pump includes a pump body 10, an impeller 7, a pump casing 6, a main shaft 2, a mechanical seal 3, a shaft sleeve 16, a sealing box 20, a motor 1, a pump inlet 9, and a pump outlet 21. A labyrinth sleeve is provided between the impeller 7 and the mechanical seal. The labyrinth sleeve is a labyrinth-type structure comprising a moving sleeve made of silicon carbide and a stationary sleeve made of 5 million molecular weight polyethylene (improving the wear resistance, corrosion resistance, temperature resistance, and service life of the moving and stationary sleeves). The moving and stationary sleeves are coupled and staggered. The labyrinth structure increases the length of the air passage between the pump chamber and the mechanical seal. During pump operation, air is squeezed into the labyrinth structure by the fluid in the pump chamber. The mechanical seal is designed to prevent air from escaping from the pump through the labyrinth structure. Due to gravity, the fluid being pumped sinks to the bottom of the labyrinth structure, while the air floats on top. The labyrinth structure prevents air from entering the pump chamber and being carried away by the fluid, nor from entering the mechanical seal and being expelled from the pump chamber. The air accumulates within the labyrinth structure, isolating the fluid from the mechanical seal and protecting the dynamic and stationary rings from the slurry, thus preventing scouring and corrosion. The labyrinth structure extends the service life of the mechanical seal without requiring an increase in the length of the air chamber and spindle support.

[0029] The moving sleeve of the labyrinth sleeve is an inverted L-shaped moving sleeve 12, and the stationary sleeve of the labyrinth sleeve is a U-shaped stationary sleeve 13. The inverted L-shaped moving sleeve 12 is fixedly connected to the bushing 16 on the main shaft 2, and the U-shaped stationary sleeve 13 is fixed on the pump body 10 (the U-shaped stationary sleeve 13 is located between the end of the pump casing 6 and the sealing box 20). The protrusion of the inverted L-shaped moving sleeve 12 is inserted into the recess in the center of the U-shaped stationary sleeve 13, and the inverted L-shaped moving sleeve 12 and the U-shaped stationary sleeve 13 do not contact each other (no friction is generated when the pump is working) and form an N-shaped air cavity 15. An air cavity is formed inside the labyrinth sleeve, and air is stored in the air cavity. After the U-shaped stationary sleeve and the inverted L-shaped moving sleeve are coupled and misaligned, the space for air storage in the pump shaft seal becomes longer, which is beneficial to isolate the contact between the conveyed material and the mechanical seal moving ring and stationary ring.

[0030] Several radial ridges 22 are provided on the back of the impeller 7. These ridges reduce the air pressure inside the labyrinth sleeve, ensuring the mechanical seal operates under low or negative pressure conditions and preventing the conveyed slurry from entering the dynamic and stationary rings through the labyrinth sleeve, thus ensuring the safe operation of the mechanical seal. An oil storage chamber 14 is provided on the outer periphery of the mechanical seal 3. This chamber contains grease, preventing the mechanical seal from generating heat through dry friction in air without liquid. The grease in the oil storage chamber lubricates the friction surfaces of the dynamic and stationary rings, reducing the rate of heat generation and preventing damage to the mechanical seal due to overheating. The shaft sleeve 1 is located on the rear side of the mechanical seal. The pump 6 is equipped with a fan 23, which rotates in the direction of the oil storage chamber 14. The air generated by the rotation of the fan 23 blows into the oil storage chamber, and the grease in the oil storage chamber conducts the accumulated temperature on the moving ring and stationary ring, forming a cooling and lubrication system in which the oil conducts the temperature, the air blows the grease to cool it down, and the grease lubricates the friction pair of the mechanical seal. This effectively prevents the mechanical seal from overheating and being damaged when it operates in the air. A sand settling chamber 8 is set at the pump inlet 9, and a sand discharge port 11 is set on the sand settling chamber 8. The sand settling chamber can prevent the slurry from settling and jamming the impeller when the vertical centrifugal pump stops conveying slurry, thus affecting the normal restart.

[0031] The pump casing 6 and impeller 7 are made of stainless steel. Example 2

[0032] like Figure 1 and Figure 3 As shown, a vertical centrifugal pump includes a pump body 10, an impeller 7, a pump casing 6, a main shaft 2, a mechanical seal 3, a shaft sleeve 16, a sealing box 20, a motor 1, a pump inlet 9, and a pump outlet 21. A labyrinth sleeve is provided between the impeller 7 and the mechanical seal. The labyrinth sleeve is a labyrinth-type structure comprising a moving sleeve made of silicon carbide and a stationary sleeve made of 5 million molecular weight polyethylene (improving the wear resistance, corrosion resistance, temperature resistance, and service life of the moving and stationary sleeves). The moving and stationary sleeves are coupled and staggered. The labyrinth structure increases the length of the air passage between the pump chamber and the mechanical seal. During pump operation, air is squeezed into the labyrinth structure by the fluid in the pump chamber. The mechanical seal is designed to prevent air from escaping from the pump through the labyrinth structure. Due to gravity, the fluid being pumped sinks to the bottom of the labyrinth structure, while the air floats on top. The labyrinth structure prevents air from entering the pump chamber and being carried away by the fluid, nor from entering the mechanical seal and being expelled from the pump chamber. The air accumulates within the labyrinth structure, isolating the fluid from the mechanical seal and protecting the dynamic and stationary rings from the slurry, thus preventing scouring and corrosion. The labyrinth structure extends the service life of the mechanical seal without requiring an increase in the length of the air chamber and spindle support.

[0033] The moving sleeve of the labyrinth sleeve is an L-shaped moving sleeve 18, and the stationary sleeve of the labyrinth sleeve is an inverted L-shaped stationary sleeve 17. The L-shaped moving sleeve 18 is fixedly connected to the bushing 16 on the main shaft 2, and the inverted L-shaped stationary sleeve 17 is fixed on the pump body 10. The collar of the L-shaped moving sleeve 18 is fitted between the collar of the inverted L-shaped stationary sleeve 17 and the pump body 10. The L-shaped moving sleeve 18 and the inverted L-shaped stationary sleeve 17 do not contact each other (no friction is generated when the pump is working). As a result, an S-shaped air cavity 19 is formed between the main shaft 2 and the pump body 10. The air cavity contains air, and the space for air storage in the pump shaft seal becomes longer, which is beneficial to isolate the contact between the conveyed material and the mechanical seal moving ring and stationary ring.

[0034] Several radial ridges 22 are provided on the back of the impeller 7. These ridges reduce the air pressure inside the labyrinth sleeve, ensuring the mechanical seal operates under low or negative pressure conditions and preventing the conveyed slurry from entering the dynamic and stationary rings through the labyrinth sleeve, thus ensuring the safe operation of the mechanical seal. An oil storage chamber 14 is provided on the outer periphery of the mechanical seal 3. This chamber contains grease, preventing the mechanical seal from generating heat through dry friction in air without liquid. The grease in the oil storage chamber lubricates the friction surfaces of the dynamic and stationary rings, reducing the rate of heat generation and preventing damage to the mechanical seal due to overheating. The shaft sleeve 1 is located on the rear side of the mechanical seal. The pump 6 is equipped with a fan 23, which rotates in the direction of the oil storage chamber 14. The air generated by the rotation of the fan 23 blows into the oil storage chamber, and the grease in the oil storage chamber conducts the accumulated temperature on the moving ring and stationary ring, forming a cooling and lubrication system in which the oil conducts the temperature, the air blows the grease to cool it down, and the grease lubricates the friction pair of the mechanical seal. This effectively prevents the mechanical seal from overheating and being damaged when it operates in the air. A sand settling chamber 8 is set at the pump inlet 9, and a sand discharge port 11 is set on the sand settling chamber 8. The sand settling chamber can prevent the slurry from settling and jamming the impeller when the vertical centrifugal pump stops conveying slurry, thus affecting the normal restart.

[0035] The pump casing 6 and impeller 7 are made of plastic. Example 3

[0036] like Figure 4As shown, a vertical centrifugal pump includes a pump body 10, an impeller 7, a pump casing 6, a main shaft 2, a mechanical seal 3, a shaft sleeve 16, a sealing box 20, a motor 1, a pump inlet 9, and a pump outlet 21. Its features include: a pressure-reducing disc 24 is provided on the main shaft 2 between the back of the impeller 7 and the shaft sleeve 16; pressure-reducing wheel ribs 26 are provided on the cross-section of one end of the pressure-reducing disc 24, the pressure-reducing wheel ribs 26 being several radial protrusions; a pressure-reducing pad 25 is provided at the end of the pressure-reducing wheel ribs 26 and fixed to the pump body 10, the pressure-reducing pad 25 being opposite to but not in contact with the pressure-reducing wheel ribs 26, and a 1mm gap existing between the pressure-reducing pad 25 and the pressure-reducing disc 24. Air is squeezed into the gap by the fluid in the pump chamber. Due to the sealing of the mechanical seal, the air in the gap will not be discharged outside the pump. The air in the gap isolates the contact between the conveying fluid and the mechanical seal, so that the dynamic and stationary rings of the mechanical seal do not come into contact with the slurry and are protected from the scouring and corrosion of the conveyed slurry. In addition, since the pressure reducing wheel has several radial protrusions, the strength of the pressure reducing plate is increased, which enables the vertical centrifugal pump to disperse the impact force of the high solids content slurry and convey the high solids content slurry. The setting of the pressure reducing pad allows the force on the pressure reducing plate to be transmitted to the pressure reducing pad when the pressure reducing plate deforms and comes into contact with the pressure reducing pad, further reducing the deformation range of the pressure reducing plate.

[0037] Several radial ridges 22 or auxiliary impellers are provided on the back of the impeller 7. The radial ridges 22 or auxiliary impellers are used to reduce the air pressure inside the labyrinth sleeve, which can ensure that the mechanical seal operates under low pressure or negative pressure conditions and prevent the conveyed slurry from entering the dynamic ring and stationary ring through the labyrinth sleeve, thus ensuring the safe operation of the mechanical seal. An oil storage chamber 14 is provided on the outer periphery of the mechanical seal 3. The oil storage chamber 14 contains grease, which can prevent the mechanical seal of the vertical centrifugal pump from dry friction and heat generation when operating in air without liquid. The grease in the oil storage chamber can lubricate the dynamic ring. The friction surface with the stationary ring reduces the rate of heat generation and prevents the mechanical seal from being damaged due to excessive temperature. A fan wheel 23 is provided on the bushing 16 on the rear side of the mechanical seal. The rotation direction of the fan wheel 23 is directly opposite to the oil storage chamber 14. The air generated by the rotation of the fan wheel 23 blows into the oil storage chamber. The grease in the oil storage chamber conducts the accumulated temperature on the rotating ring and the stationary ring, forming a cooling and lubrication system in which the oil conducts the temperature, the air blows the grease to cool it down, and the grease lubricates the friction pair of the mechanical seal. This effectively prevents the mechanical seal from overheating and being damaged when it operates in the air.

[0038] The pump casing 6 and impeller 7 are made of stainless steel.

Claims

1. A vertical centrifugal pump, comprising a pump body (10), an impeller (7), a pump shell (6), a main shaft (2), a mechanical seal (3), a shaft sleeve (16), a seal box (20), a motor (1), a pump suction inlet (9) and a pump outlet (21); the pump body (10) is connected with the pump shell (6), the pump shell (6) is connected with the seal box (20), the main shaft (2) is connected with the impeller (7), the mechanical seal (3) is connected with the shaft sleeve (16), the shaft sleeve (16) is connected with the main shaft (2), the motor (1) is connected with the main shaft (2), the pump suction inlet (9) is connected with the pump body (10), and the pump outlet (21) is connected with the pump body (10); characterized in that: The labyrinth sleeve is of a labyrinth structure comprising a movable sleeve and a fixed sleeve, the movable sleeve and the fixed sleeve are coupled and misaligned, the movable sleeve is fixed on the main shaft (2), and the fixed sleeve is fixed on the pump body (10); the movable sleeve and the fixed sleeve are not in contact with each other, and an air cavity is formed in the labyrinth sleeve, and air is stored in the air cavity.

2. The vertical centrifugal pump of claim 1, wherein: The movable sleeve of the labyrinth sleeve is a reverse L-shaped movable sleeve (12), the fixed sleeve of the labyrinth sleeve is a U-shaped fixed sleeve (13), the reverse L-shaped movable sleeve (12) is fixedly connected with the shaft sleeve (16) on the main shaft (2), and the U-shaped fixed sleeve (13) is fixed on the pump body (10); the convex part of the reverse L-shaped movable sleeve (12) is inserted into the concave part in the center of the U-shaped fixed sleeve (13), and the reverse L-shaped movable sleeve (12) and the U-shaped fixed sleeve (13) are not in contact with each other and form an N-shaped air cavity (15).

3. The vertical centrifugal pump of claim 1, wherein: The movable sleeve of the labyrinth sleeve is an L-shaped movable sleeve (18), the fixed sleeve of the labyrinth sleeve is a reverse L-shaped fixed sleeve (17), the L-shaped movable sleeve (18) is fixedly connected with the shaft sleeve (16) on the main shaft (2), and the reverse L-shaped fixed sleeve (17) is fixed on the pump body (10); the collar of the L-shaped movable sleeve (18) is sleeved between the collar of the reverse L-shaped fixed sleeve (17) and the pump body (10), the L-shaped movable sleeve (18) and the reverse L-shaped fixed sleeve (17) are not in contact with each other, and thus an S-shaped air cavity (19) is formed between the main shaft (2) and the pump body (10).

4. The vertical centrifugal pump of claim 1, wherein: A plurality of radial protrusions (22) are arranged on the back of the impeller (7), or a secondary impeller is arranged on the back of the impeller (7), and the radial protrusions (22) or the secondary impeller are used for reducing the pressure of air in the labyrinth sleeve.

5. The vertical centrifugal pump of claim 1, wherein: An oil storage cavity (14) is arranged on the outer periphery of the mechanical seal (3), and oil is stored in the oil storage cavity (14).

6. The vertical centrifugal pump of claim 5, wherein: A wind wheel (23) is arranged on the shaft sleeve (16) at the rear side of the mechanical seal, and the rotating direction of the wind wheel (23) is opposite to the oil storage cavity (14).

7. The vertical centrifugal pump of claim 1, wherein: A sand settling cavity (8) is arranged at the suction inlet (9) of the pump, and a sand discharge port (11) is arranged on the sand settling cavity (8).

8. The vertical centrifugal pump of claim 1, wherein: The fixed sleeve is made of polyethylene with a molecular weight of 5 million, and the movable sleeve is made of silicon carbide.

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