Mechanical seal sinking pit pump

Abstract

The present invention provides a mechanical seal sinking pit pump, including a motor and a pit pump assembly. The pump uses a multi-section extended outer support tube to push the pump head deep into the wastewater level in the pit. The pump drives the main shaft to rotate through the motor rotation. The impeller draws liquid from the bottom of the pit into the liquid inlet, and after pressurization, the liquid is pumped into the outlet elbow through the liquid outlet. A lower machine seal is arranged in the inner cavity of the pump cover and the support tube mounting flange. The lower machine seal is sleeved on the shaft sleeve outside the main shaft. An outer support tube is installed outside the main shaft. The cavity between the main shaft and the outer support tube is filled with lubricating medium. The upper end of the main shaft is connected to the bearing box, and the other end of the outlet elbow is connected to the outlet pipe. The design of the lower machine seal of the present invention can reduce the wear of the shaft liner and the main shaft, and extend the service life of the pump; it is suitable for high temperature or ultra-low temperature environment, suitable for conveying unclean, high viscosity, high temperature, easy to pollute and other media, and implements pressure or liquid level protection on the lubricating oil to prevent the leakage of vulnerable parts and cause the pump group to fail. It is suitable for all vertical pit pumps.

Description

Technical Field

[0001] The invention belongs to the technical field of centrifugal pumps, and in particular relates to a mechanical seal sunken vertical pit pump which has a lower mechanical seal added behind an impeller for sealing. Background Art

[0002] Vertical pit pumps are widely used in cleaning wastewater pools in chemical plants, transferring tanked liquids, sewage treatment, etc. The vertical pit pump fixes the pump unit on the installation foundation of the pit through the mounting plate. The pump uses multiple sections of extended support pipes to push the pump head below the wastewater level in the pit. When the pump unit rotates through the motor, the pump drive wheel will draw the liquid from the bottom of the pit to the liquid inlet, and after being pressurized by the drive wheel, the liquid is pumped into the corresponding pipeline through the liquid outlet to achieve the purpose of cleaning sewage.

[0003] Since the pit depths of each factory are different, the insertion depth of the pump support pipe must be designed to be different lengths according to the process requirements to meet the on-site pit depth and customer process requirements. During normal operation, the drive wheel is driven by the motor through the main shaft. The liquid enters the downstream pipeline from the liquid outlet after being pressurized by the drive wheel from the liquid inlet. During the pressurization process, the liquid will move upward along the support pipe due to the pressure. The conventional design is to seal the liquid between the upper support frame and the main shaft to prevent the liquid from spraying out of the pump along the main shaft. Since the main shaft is up to more than 10 meters long, the drive wheel will be impacted by the liquid during work, causing the main shaft to be unstable and swing, causing equipment damage.

[0004] In order to ensure the stability of the main shaft, the usual design is to intermittently add bushing support to ensure the rigidity of the shaft through the bushing. There is a support and grinding relationship between the main shaft and the bushing, so the bushing needs to be lubricated and cooled. There are two main conventional designs:

[0005] 1) Lubricate with the conveyed liquid;

[0006] 2) When the conveyed liquid is not clean, use an external high-pressure cleaning medium to lubricate the shaft liner.

[0007] However, both of the above solutions have defects:

[0008] Disadvantages of lubricating with the delivered liquid: When the liquid delivered by the pump is unclean, contains solid particles or has poor lubricity, the particles will enter between the liner and the main shaft through the flushing pipe, causing wear of the liner or main shaft, and then causing pump failure;

[0009] The disadvantages of lubricating the shaft liner with an external high-pressure cleaning medium: when using an external clean liquid for flushing, the flushing liquid will be mixed into the liquid transported by the pump, which will lead to a large amount of waste of cleaning liquid. Secondly, if the cleaning medium and the conveying liquid are of different properties, it will also cause contamination of the conveying liquid (taking the conveying of waste oil as an example, if flushing is done externally, only diesel or gasoline can be used for flushing, resulting in a lot of waste. If flushing is done with water, the waste oil will be contaminated). Summary of the invention

[0010] The technical problem solved by the present invention is to provide a mechanically sealed sunken pit pump, which solves the problem of wear of the shaft liner or main shaft, which leads to pump failure, waste of a large amount of clean liquid and pollution of the transported liquid, which is encountered when the pit pump is transporting unclean, high-viscosity, high-temperature, easily contaminated media.

[0011] The design principle of the present invention is to add a lower mechanical seal design behind the impeller so that the conveying liquid does not enter the main shaft part, and the main shaft part and the liquid transmission part are kept as two relatively independent parts.

[0012] The technical solution adopted by the present invention is: it includes a motor and a pit pump assembly, the pump uses a multi-section extended outer support pipe to make the pump head penetrate below the wastewater level in the pit, the pump drives the main shaft to rotate through the rotation of the motor, the impeller draws liquid from the bottom of the pit into the liquid inlet, and after pressurization, the liquid is pumped into the outlet elbow through the liquid outlet, the side of the pump body is connected with the outlet elbow, the lower end of the pump body is the liquid inlet, the body inlet ring is installed at the liquid inlet, the pump body is provided with an impeller, the impeller is fixedly installed at the lower end of the main shaft, the upper part of the pump body is connected to the pump cover, the upper part of the pump cover is bolted and connected to the support pipe mounting flange, the pump cover and the support pipe mounting flange The inner cavity is provided with a lower machine seal, the lower machine seal includes a dynamic ring and a static ring, the contact surface of the dynamic ring and the static ring is a sealing surface, the lower machine seal is sleeved on the shaft sleeve outside the main shaft, the outer support tube is installed outside the main shaft, the cavity between the main shaft and the outer support tube is filled with lubricating medium, the upper end of the main shaft is connected to the bearing box, and the other end of the outlet elbow is connected to the outlet pipe. The body ring is used to limit the flow and ensure the efficiency of the pump. If there is no body ring, the high-pressure liquid will flow back from the ring position to the inlet after being pressurized by the impeller, causing the liquid to circulate in the pump.

[0013] Preferably, an intermediate support sleeve is arranged on the outer side of the middle part of the main shaft, a shaft liner is arranged between the main shaft and the intermediate support sleeve, and the main shaft and the shaft liner are connected by a key or the intermediate support sleeve and the shaft liner are fixed by heat fitting.

[0014] The technical effect is to prevent the main shaft from being too long and causing deflection during rotation. When the main shaft and the shaft liner are connected by a key, the main shaft drives the shaft liner to rotate, while the intermediate support tube remains stationary. When the intermediate support sleeve and the shaft liner are hot-fitted and fixed, the main shaft rotates alone, while the shaft liner and the intermediate support tube remain stationary.

[0015] Preferably, an outlet flange is provided at the end of the outlet pipe, the outlet pipe is fixed to the pump mounting plate through an outlet pipe sealing cover, and the bearing box body is fixed to the pump mounting plate through bolts.

[0016] The technical effect is that it is easy to install and fix the pit pump as a whole to the installation foundation on the ground.

[0017] Preferably, the lower mechanical seal isolates and seals the clamping cavity between the pump body and the pump cover from the main shaft, forming an independent lubrication cavity between the main shaft and the outer support tube, so that the shaft liner does not contact the liquid transported in the pump body.

[0018] The technical effect thereof is to prevent the transported liquid from entering into the cavity formed between the main shaft and the outer support tube, thereby causing wear of the wearing parts.

[0019] Preferably, an upper machine seal is installed at the upper end of the main shaft in the bearing box cavity. The upper machine seal is sleeved at the top of the main shaft. The upper machine seal includes an upper machine seal dynamic ring and an upper machine seal static ring. The contact surfaces of the upper machine seal dynamic ring and the upper machine seal static ring are worn for upper sealing. A sealing cavity is formed between the main shaft and the outer support tube between the upper machine seal and the lower machine seal.

[0020] The technical effect is that the combined structure of the upper machine seal and the lower machine seal forms a sealed cavity between the main shaft and the outer support tube between the upper machine seal and the lower machine seal, which is isolated from the external environment. When transporting dangerous liquids, if the lower machine seal is damaged, the upper machine seal plays a role in protecting the environment and personnel safety.

[0021] Preferably, a socket-type inner thermal insulation sleeve is installed between the main shaft and the outer support tube. The inner thermal insulation sleeve is multi-section, and O-rings are installed at the connections of adjacent inner thermal insulation sleeves. The inner thermal insulation sleeve divides the space between the main shaft and the outer support tube into a double-layer cavity, namely an inner cavity and an outer cavity. The inner cavity is filled with lubricating medium, which is a lubricating medium cavity, and the outer cavity is an air cavity or a vacuum cavity.

[0022] The technical effect is that the pre-filled lubricating medium is heated or cooled. When the temperature of the transported liquid is too high, the temperature of the pre-filled lubricating medium will be too high, the lubricity will decrease, and cooling is required; if the temperature of the transported liquid is too low, the temperature of the pre-filled lubricating medium will be too low, the fluidity will be poor, and heating and insulation are required. The external air cavity or vacuum cavity plays a further role in thermal insulation and reduces the amount of lubricating medium used.

[0023] Preferably, a liquid level monitoring pipeline and a liquid replenishing port are preset outside the outer support tube.

[0024] The technical effect is that when a single seal structure of the lower machine seal is adopted, the liquid level of the pit pump is controlled. When there is a large fluctuation in the liquid level, it means that the lower machine seal is damaged, and an alarm can be issued in time for timely maintenance.

[0025] Preferably, a sealing pressure detection device is connected to the outside of the sealing cavity formed between the upper machine seal and the lower machine seal to monitor the pressure in the sealing cavity in real time.

[0026] Its technical effect is: when a double seal structure of upper machine seal and lower machine seal is adopted, a sealed cavity is formed between the main shaft and the outer support tube between the upper machine seal and the lower machine seal, and the sealed cavity is pressure-detected, which can monitor in real time and give timely alarm. When the pressure drops rapidly, it indicates that the upper machine seal or the lower machine seal is damaged, thereby extending the service life of the pump.

[0027] Preferably, the sealing surface of the lower mechanical seal is sealed by an external pressurization method. One of the external pressurization methods is to connect external pressure gas or pressure lubricating liquid so that the pressure of the cavity is always higher than the pressure of the conveying liquid. The other is to connect the PLAN53 series solution specified in the API682 standard and connect an air bag or accumulator to stabilize the high pressure in the cavity.

[0028] The technical effect is that the pressure of the lubricating medium at the sealing surface of the lower machine seal is higher than the pressure of the conveyed liquid; at this time, the sealing surface is lubricated by the pre-filled lubricating medium instead of the conveyed unclean liquid, thereby increasing the service life of the lower machine seal.

[0029] Preferably, the sealing surface of the lower machine seal is sealed by an internal pressurization method. One of the internal pressurization methods is to process a reverse pressurization groove on the end face of the dynamic ring. The reverse pressurization groove is a plurality of grooves evenly distributed along the end face and processed on the end face of the dynamic ring according to different working conditions. One end notch of the reverse pressurization groove is located on the side of the dynamic ring so that the lubricating medium can enter the reverse pressurization groove. Another method is to install a pressurization wheel on the side wall of the lower machine seal, and the outer side of the wheel body of the pressurization wheel has a spiral convex strip. One of the internal pressurization methods or a combination of the two can be used.

[0030] Its technical effect is: when the pump rotates clockwise, the reverse boosting groove will press the lubricating medium between the two grinding sealing surfaces, which plays a role in lubricating and cooling the sealing surfaces. Because it is a clean lubricating medium with good lubricity, the sealing surface will not be damaged, thereby protecting the lower machine seal; the boosting wheel will pressurize the normal pressure medium in area B and push it against area A, thereby increasing the local pressure in area A to ensure that the pressure of the sealing lubricating medium in area A is greater than the pressure at the liquid conveying end. The lubricating medium in area A will enter the grinding surface of the lower machine seal to lubricate it, thereby achieving the purpose of protecting the lower machine seal.

[0031] The beneficial effects of the present invention are:

[0032] 1. Reduce the wear of the liner and main shaft and extend the service life of the pump.

[0033] 2. Reduce the waste of lubricating fluid and the pollution of conveying fluid.

[0034] 3. Suitable for high or ultra-low temperature environments, suitable for conveying unclean, high-viscosity, high-temperature, easily contaminated media, and suitable for structural optimization of all vertical pit pumps.

[0035] 4. The special reverse boost groove design on the machine cover and the local boost wheel boost design enable the machine seal to be boosted and self-lubricated under normal pressure.

[0036] 5. Implement pressure or liquid level protection on the lubricating oil to prevent leakage of wearing parts and cause failure of the pump unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the overall structure of a mechanical seal sunken pit pump;

[0038] Figure 2 It is a schematic diagram of the overall structure of a mechanical seal sunken pit pump with an internal insulation sleeve;

[0039] Figure 3 It is a schematic diagram of the structure of the inner insulation sleeve;

[0040] Figure 4 It is a schematic diagram of the structure of the liquid level monitoring and liquid filling port of a single sealed pit pump;

[0041] Figure 5 It is a schematic diagram of the supercharger wheel structure;

[0042] Figure 6 It is a schematic diagram of the structure of the dynamic and static rings of the mechanical seal;

[0043] Figure 7 This is a schematic diagram of the structure of the grinding surface of the moving ring;

[0044] Figure 8 for Figure 1 Schematic diagram of the CC cross-section structure.

[0045] Figure markings: 1-outlet elbow, 2-pump body, 3-body mouth ring, 4-impeller, 5-shaft sleeve, 6-pump cover, 7-lower machine seal, 8-support tube mounting flange, 9-outer support tube, 10-main shaft, 11-intermediate support sleeve, 12-shaft liner, 13-upper machine seal, 14-cooling chamber sealing ring, 15-bearing box, 16-outlet flange, 17-pump mounting plate, 18-outlet pipe sealing cover, 19-inner insulation sleeve, 20-O-ring, 21-outlet pipe, 22-packing seal assembly, 23-liquid level monitoring pipeline, 24-liquid filling port, 25-boosting wheel, 71-moving ring, 72-static ring, 711-reverse boosting groove. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] because Figure 1 , Figure 2 and Figure 5 All of them are schematic diagrams of the central cross-section structure. In order to more clearly and intuitively express how the output liquid enters the outlet elbow 1 from the pump body 2, as shown in FIG. Figure 8 Shown Figure 1 The CC cross-sectional structure diagram is the cross-sectional structure of the joint part of the pump body 2 and the outlet elbow 1. The pump body 2 and the outlet elbow 1 are not connected at the center of the cross section of the pump body 2, and the connecting channel is designed eccentrically.

[0048] Embodiment 1: Single-unit sealed single-chamber pit pump.

[0049] The present invention includes a motor and a pit pump assembly. The pump head is pushed below the wastewater level in the pit through a multi-section extended outer support pipe 9. The pump drives the main shaft 10 to rotate through the rotation of the motor. The impeller 4 draws liquid from the bottom of the pit into the liquid inlet, and after pressurization, the liquid is pumped into the outlet elbow 1 through the liquid outlet. The side of the pump body 2 is connected to the outlet elbow. The lower end of the pump body 2 is the liquid inlet, and a body inlet ring 3 is installed at the liquid inlet. The pump body 2 is provided with an impeller 4 inside. The impeller 4 is fixedly installed at the lower end of the main shaft 10. The upper part of the pump body 2 is connected to a pump cover 6. The upper part of the pump cover 6 is fixedly connected to the support pipe mounting flange 8 by bolts. A lower machine seal 7 is arranged in the inner cavity of the pump cover 6 and the support pipe mounting flange 8. The lower machine seal 7 includes a dynamic ring 71 and a static ring 71. The contact surface between the dynamic ring 71 and the static ring 72 is a sealing surface. The lower machine seal 7 is sleeved on the main shaft 10. On the outer sleeve 5, an outer support tube 9 is installed outside the main shaft 10 above the support tube mounting flange 8. The outer support tube 9 is a multi-section type fixedly connected to each other by bolts. The outer support tube 9 at the bottom is fixedly connected to the support tube mounting flange 8 by bolts. The outer support tube 9 at the top is fixedly connected to the fixing structure of the upper bearing box 15 base by bolts. The cavity between the main shaft 10 and the outer support tube 9 is filled with lubricating medium. The upper end of the main shaft 10 is connected to the bearing box 15. An intermediate support sleeve 11 is arranged outside the middle of the main shaft 10. A shaft liner 12 is arranged between the main shaft 10 and the intermediate support sleeve 11. The other end of the outlet elbow 1 is connected to the outlet pipe 21. The connection between the outlet elbow 1 and the outlet pipe 21 is sealed. The form of installing a packing seal assembly 22 can be adopted, or other sealing structures can be adopted. The end of the outlet pipe 21 is equipped with an outlet flange 16. The outlet pipe 21 is fixed to the pump mounting plate 17 through the outlet pipe sealing cover 18. The bearing box 15 box body is fixed to the pump mounting plate 17 by bolts. A cooling chamber sealing ring 14 is installed at the structural connection of each part of the bearing box 15 for sealing.

[0050] The lower mechanical seal 7 isolates and seals the clamping cavity between the pump body 2 and the pump cover 6 from the main shaft 10 , and forms an independent lubrication cavity between the main shaft 10 and the outer support tube 9 , so that the shaft liner 12 does not contact the liquid transported in the pump body 2 .

[0051] About condition monitoring and protection design:

[0052] like Figure 4 As shown, the external support tube 9 is preset with a liquid level monitoring pipeline 23 and a liquid replenishing port 24 to control the liquid level of the pit pump. When the liquid level fluctuates greatly, it indicates that the lower machine seal 7 is damaged, and an alarm can be issued in time for timely maintenance.

[0053] There are mainly the following ways to seal the lower machine seal 7:

[0054] The sealing surface of the lower machine seal 7 is sealed by external pressurization. One of the external pressurization methods is to connect external pressure gas or pressure lubricating liquid to make the pressure of the cavity always higher than the pressure of the conveyed liquid. The other is to connect the PLAN53 series solution specified in the API682 standard, and connect the air bag or accumulator to make the cavity stable and high pressure. Make the pressure of the lubricating medium at the sealing surface of the lower machine seal 7 higher than the pressure of the conveyed liquid; at this time, the sealing surface is lubricated by the pre-filled lubricating medium instead of the conveyed unclean liquid, which increases the service life of the lower machine seal 7.

[0055] Another type, the sealing surface of the lower mechanical seal 7 is sealed by internal pressurization, such as Figure 6-7 As shown, one of the internal pressurization methods is to process a reverse pressurization groove 711 on the end face of the dynamic ring 71. The reverse pressurization groove 711 is a plurality of grooves evenly distributed along the end face of the dynamic ring 71 designed according to different working conditions. One end notch of the reverse pressurization groove 711 is located on the side of the dynamic ring so that the lubricating medium can enter the reverse pressurization groove 711. When the pump rotates clockwise, the reverse pressurization groove 711 will press the lubricating medium between the two grinding sealing surfaces, which plays a role in lubricating and cooling the sealing surface. Because it is a clean lubricating medium with good lubricity, the sealing surface will not be damaged, which plays a role in protecting the lower mechanical seal. Figure 5 As shown, the other method is to install a booster wheel 25 on the side wall of the lower machine seal 7, and the outer side of the booster wheel 25 has spiral convex strips. The booster wheel 25 will pressurize the normal pressure medium in area B and push it against area A, so that the local pressure in area A increases to ensure that the pressure of the sealing lubricating medium in area A is greater than the pressure at the end of the conveying liquid. The lubricating medium in area A will enter the lower machine seal to lubricate the grinding surface, thereby protecting the lower machine seal 7. This embodiment can adopt one of the internal boosting methods or a combination of the two.

[0056] Embodiment 2: Double-sealed single-chamber pit pump.

[0057] Based on the structure of the first embodiment, Figure 1 As shown, an upper machine seal 13 is installed in the cavity of the bearing box 15 at the upper end of the main shaft 10. The upper machine seal 13 is sleeved on the top of the main shaft 10. The upper machine seal 13 includes an upper machine seal dynamic ring and an upper machine seal static ring. The contact surfaces of the upper machine seal dynamic ring and the upper machine seal static ring are grinded for upper sealing. A sealed cavity is formed between the main shaft 10 and the outer support tube 9 between the upper machine seal 13 and the lower machine seal 7.

[0058] About condition monitoring and protection design:

[0059] A sealing pressure detection device is connected to the outside of the sealing cavity formed between the upper machine seal 13 and the lower machine seal 7 to monitor the pressure in the sealing cavity in real time. When a double-seal structure of the upper machine seal 13 and the lower machine seal 7 is adopted, a sealing cavity is formed between the main shaft 10 and the outer support tube 9 between the upper machine seal 13 and the lower machine seal 7, and the pressure of the sealing cavity is detected, which can be monitored in real time and alarmed in time. When the pressure drops rapidly, it means that the upper machine seal 13 or the lower machine seal 7 is damaged. When the pump is increased outside: a pressure switch or transmitter can be added to the pressure source. When the pressure drops, it means that the sealing surface is leaking. At this time, the pump should be stopped and repaired in time. When the pump is pressurized, a liquid level monitoring can be preset in the sealing cavity pre-filled with lubricating fluid. When the liquid level is abnormal, an alarm is triggered, which means that the lower machine seal 7 is leaking. At this time, the pump should be stopped and repaired in time.

[0060] The sealing form of the lower mechanical seal 7 is the same as that of the first embodiment.

[0061] Embodiment 3: Single-unit sealed double-chamber pit pump.

[0062] Based on the structure of the first embodiment, Figure 2 As shown, a socket-type inner insulation sleeve 19 is installed between the main shaft 10 and the outer support tube 9. The inner insulation sleeve 19 is multi-stage, and O-rings 20 are installed at the connection of adjacent inner insulation sleeves 19 for radial sealing. The inner insulation sleeve 19 divides the space between the main shaft 10 and the outer support tube 9 into a double-layer cavity, namely an inner cavity and an outer cavity. The inner cavity is filled with lubricating medium, which is a lubricating medium cavity, and the outer cavity is an air cavity or a vacuum cavity, which is used to isolate or slow down the temperature transfer to the inner cavity. The inner cavity can use an external cooling and heating cavity or a built-in cooling and heating coil to cool or heat the pre-filled lubricating medium to ensure that the pre-filled lubricating medium always works at the optimal temperature. When the pre-filled lubricating medium is heated or cooled, when the temperature of the transported liquid is too high, the temperature of the pre-filled lubricating medium will be too high, and the lubricity will decrease, so cooling is required; if the temperature of the transported liquid is too low, the temperature of the pre-filled lubricating medium will be too low, and the fluidity will be poor, so heating and insulation are required. The external air cavity or vacuum cavity plays a further role in temperature insulation and reduces the use of lubricating medium.

[0063] The difference from the structure of the first embodiment is that the structure of the intermediate support sleeve 11 is as follows: Figure 3As shown, the upper end of the intermediate support sleeve 11 of this embodiment is processed into a size for socketing with the inner insulation sleeve 19, and an O-ring 20 is installed at the connection between the intermediate support sleeve 11 and the inner insulation sleeve 19.

[0064] Embodiment 4: Double-sealed double-chamber pit pump.

[0065] Based on the structure of the second embodiment and combined with the structure of the third embodiment, the sealed cavity includes an upper mechanical seal 13 and a lower mechanical seal 7 and the sealed cavity is divided into an inner cavity and an outer cavity by the structure of an inner insulation sleeve 19 .

[0066] The above are specific embodiments of the present invention and the technical principles used. Any modifications and equivalent changes based on the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A mechanical seal sinking pit pump, comprising a motor and a pit pump assembly, wherein the pump head is lowered below the wastewater level in the pit through a plurality of extended outer support pipes (9), the pump drives the main shaft (10) to rotate through the motor, and the impeller (4) draws liquid from the bottom of the pit to the liquid inlet, and after being pressurized, the liquid is pumped into the outlet elbow (1) through the liquid outlet, characterized in that: The side of the pump body (2) is connected to the outlet elbow (1); the lower end of the pump body (2) is a liquid inlet, and a body inlet ring (3) is installed at the liquid inlet. An impeller (4) is arranged inside the pump body (2), and the impeller (4) is fixedly installed on the lower end of the main shaft (10). The upper part of the pump body (2) is connected to a pump cover (6), and the upper part of the pump cover (6) is fixedly connected to the support pipe mounting flange (8) by bolts. A lower machine seal (7) is arranged in the inner cavity of the pump cover (6) and the support pipe mounting flange (8), and the lower machine seal (7) includes a dynamic ring (71) and a static ring (72). The contact surface of the dynamic ring (71) and the static ring (72) is a sealing surface. The lower machine seal (7) is sleeved on the shaft sleeve (5) outside the main shaft (10). An outer support tube (9) is installed outside the main shaft (10), and a cavity between the main shaft (10) and the outer support tube (9) is filled with a lubricating medium. The upper end of the main shaft (10) is connected to a bearing box (15), and the other end of the outlet elbow (1) is connected to an outlet pipe (21). A socket-type inner insulation sleeve (19) is installed between the main shaft (10) and the outer support tube (9). The inner insulation sleeve (19) is multi-stage, and an O-ring (20) is installed at the connection between adjacent inner insulation sleeves (19). The inner insulation sleeve (19) divides the space between the main shaft (10) and the outer support tube (9) into a double-layer cavity, namely an inner cavity and an outer cavity. The inner cavity is filled with a lubricating medium and is a lubricating medium cavity, and the outer cavity is an air cavity or a vacuum cavity.

2. The mechanical seal sunken pit pump according to claim 1, characterized in that: An intermediate support sleeve (11) is arranged on the outer side of the middle part of the main shaft (10), a shaft liner (12) is arranged between the main shaft (10) and the intermediate support sleeve (11), and the main shaft (10) and the shaft liner (12) are connected by a key or the intermediate support sleeve (11) and the shaft liner (12) are fixed by heat-fitting.

3. The mechanical seal sunken pit pump according to claim 1, characterized in that: The outlet pipe (21) is provided with an outlet flange (16) at the end thereof. The outlet pipe (21) is fixed to the pump mounting plate (17) via an outlet pipe sealing cover (18). The bearing box (15) is fixed to the pump mounting plate (17) via bolts.

4. The mechanical seal sunken pit pump according to claim 2, characterized in that: The lower mechanical seal (7) isolates and seals the clamping cavity between the pump body (2) and the pump cover (6) from the main shaft (10), forming an independent lubrication cavity between the main shaft (10) and the outer support tube (9), so that the shaft liner (12) does not contact the liquid transported in the pump body (2).

5. The mechanical seal sunken pit pump according to claim 1, characterized in that: An upper machine seal (13) is installed at the upper end of the main shaft (10) in the cavity of the bearing box (15). The upper machine seal (13) is sleeved on the top end of the main shaft (10). The upper machine seal (13) comprises an upper machine seal dynamic ring and an upper machine seal static ring. The contact surfaces of the upper machine seal dynamic ring and the upper machine seal static ring are rubbed for upper sealing. A sealing cavity is formed between the main shaft (10) and the outer support tube (9) between the upper machine seal (13) and the lower machine seal (7).

6. The mechanical seal sunken pit pump according to any one of claims 1 to 4, characterized in that: The outer support tube (9) is pre-set with a liquid level monitoring pipeline (23) and a liquid replenishing port (24) outside.

7. The mechanical seal sunken pit pump according to claim 5, characterized in that: The sealing cavity formed between the upper machine seal (13) and the lower machine seal (7) is externally connected to a sealing pressure detection device to monitor the pressure in the sealing cavity in real time.

8. The mechanical seal sunken pit pump according to any one of claims 1 to 5, characterized in that: The sealing surface of the lower mechanical seal (7) is sealed by an external pressurization method. One of the external pressurization methods is to connect external pressure gas or pressure lubricating liquid so that the pressure of the cavity is always higher than the pressure of the conveying liquid.

9. The mechanical seal sunken pit pump according to any one of claims 1 to 5, characterized in that: The sealing surface of the lower machine seal (7) is sealed by an internal pressurization method. One of the internal pressurization methods is to process a reverse pressurization groove (711) on the end face of the dynamic ring (71), wherein the reverse pressurization groove (711) is a plurality of groove bodies evenly distributed along the end face and processed on the end face of the dynamic ring (71) according to different working conditions, and one end notch of the reverse pressurization groove (711) is located on the side face of the dynamic ring (71) so that the lubricating medium can enter the reverse pressurization groove (711). Alternatively, a pressurization wheel (25) is installed on the side wall of the lower machine seal (7), and the outer side of the wheel body of the pressurization wheel (25) has a spiral convex strip.

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