Mechanical seal for crude oil lifting double-screw pump

Abstract

The utility model provides a mechanical seal for a crude oil lifting double-screw pump, which comprises a shaft sleeve and a sealing seat, a first mounting groove is arranged at one end of an inner cavity of the sealing seat, a mounting boss is arranged outside only one end of the first mounting groove of the shaft sleeve, and a primary sealing unit is assembled between one end of the mounting boss and the first mounting groove; the other end of the sealing seat is connected with a flange seat, a second mounting groove is formed between the flange seat and the sealing seat, a secondary sealing unit is assembled between the other end of the mounting boss and the second mounting groove, a liquid inlet and a liquid outlet are formed in the side wall of the sealing seat, and the pressure of the sealing cavity is higher than that of the medium end; a driving ring is connected to the outer portion of the end, away from the mounting boss, of the shaft sleeve, a plurality of set screws abutting against the rotating shaft are arranged on the side wall of the driving ring in a penetrating mode, and a plurality of limiting blocks clamped to the sealing seat are detachably connected to the peripheral wall of the driving ring. The mechanical seal for the crude oil lifting double-screw pump is stable in sealing performance, long in service life and convenient to install.

Description

TECHNICAL FIELD

[0001] The utility model relates to mechanical seal technical field, specifically, relate to a kind of for crude oil lifting double screw rod pump's mechanical seal. BACKGROUND

[0002] At present, many oil fields use screw rod pump lifting mode to carry out oil production. Lifting screw rod pump oil production is applicable to sand-containing, gas-containing, thick oil exploitation occasion, and has the advantages of power saving, simple structure, high efficiency, low operation cost, less land occupation etc., for the oil well with well depth not more than 1500 meters can be used almost, so screw rod pump oil production device has been actively promoted and widely used in each big oil field.

[0003] Crude oil is generally in saline-alkali land, so the crude oil from the bottom of the earth contains sand, saline-alkali land contains various carbonates, chlorides, sulfates, contains hydrogen sulfide, also 10-15% water, also air (medium will change under 100% gas phase and 100% liquid phase, fluid pressure also changes 0.6-3mpa according to the pressure change of crude oil underground, it is a kind of seal operated in gas-liquid-solid three-phase medium.

[0004] With the development of technology, mechanical seal has become the mainstream seal of screw rod pump, and its sealing performance is stable and widely applicable. However, the conventional single-end mechanical seal still has many defects for the screw rod pump seal structure in such special working conditions of crude oil exploitation. For example, the sealing surface is easy to be worn by sand in crude oil, and the high temperature of sealing surface under high pressure environment can easily cause thermal deformation, not only short service life, but also unstable sealing performance; the parts in sealing mechanism are scattered, and the on-site installation is difficult, and the parts are easy to be missed. SUMMARY

[0005] To overcome at least one defect in the above prior art, the utility model provides a kind of for crude oil lifting double screw rod pump's mechanical seal, and sealing performance is stable, service life is long, and installation is convenient.

[0006] The utility model provides a kind of for crude oil lifting double screw rod pump's mechanical seal: including the shaft sleeve of being sleeved in the outside of rotating shaft, the outside of the shaft sleeve is equipped with sealing seat, and the one end of the shaft sleeve extends to the inner chamber of the sealing seat, first installation groove is arranged in the inner chamber of the sealing seat close to medium end, annular mounting boss is formed in the outside of the one end of the shaft sleeve in the inner chamber of the sealing seat, and one level sealing unit is equipped between the one end of the mounting boss and the first installation groove;The other end of the sealing seat is connected with flange seat, the radial inner end between the flange seat and the sealing seat forms second installation groove, two level sealing unit is equipped between the other end of the mounting boss and the second installation groove, and sealing cavity is formed between one level sealing unit, two level sealing unit and the inner side wall of sealing seat, liquid inlet and liquid outlet respectively connected to the sealing cavity are set on the side wall of the sealing seat, and the sealing cavity pressure is higher than medium end pressure;The outside of the one end of the shaft sleeve away from the mounting boss is connected with driving ring, a plurality of tight set screws with the inner end of rotating shaft abutting fit are penetrated on the side wall of the driving ring, and a plurality of limit blocks distributed along the circumference are detachably connected on the outer peripheral wall of the driving ring, the one end of the limit block is clamped and fitted in the positioning groove, and the outer peripheral wall of the positioning column is formed with positioning groove.

[0007] Compared with the prior art, the mechanical seal for the crude oil lifting double screw rod pump has the following advantages:

[0008] 1. The mechanical seal structure adopts a packaged design, that is, the overall pre-assembly of each component of the complete sealing device is realized before the mechanical seal is installed into the installation cavity. When the sealing device is installed into the installation cavity of the rotary evaporator, only the complete sealing of the packaged structure needs to be installed into the designed position, and the sealing device is driven and connected to the rotating shaft. Therefore, the installation operation is simple, the technical requirement for installation is low, the working efficiency of workers in assembling the mechanical seal is improved, the damage or failure of the seal caused by installation problems is avoided to the greatest extent, and the maintenance cost and maintenance time of the seal are reduced.

[0009] 2. The double-end mechanical seal is adopted. The two sealing surfaces have higher sealing performance. In the case of leakage of the first main seal, the two level secondary seal can continue to play a sealing role, so as to ensure the stability of the seal. In the sealing structure of the utility model, the two sealing parts share one mounting boss structure during installation, the axial size of the entire sealing structure is effectively shortened, the axial installation space of the seal is saved, and the product competitiveness is improved.

[0010] 3、The sealing seat is provided with a flushing channel, flushing liquid enters from a liquid inlet and is discharged from a liquid outlet, and the circulating flushing liquid can timely take away the friction heat of the two-stage sealing surface, avoids deformation of the sealing ring due to excessive temperature and causes leakage; in addition, the pressure of the sealing cavity is greater than the medium end pressure, so that the grinding surface of the first-stage sealing unit is mainly the liquid film of the flushing liquid, avoids particles in the medium from entering the grinding surface and causing serious wear of the sealing surface, ensures the sealing performance and improves the service life.

[0011] Further, the first-stage sealing unit comprises a driving ring and a driven ring assembly, a first driving ring groove is arranged in the recessed end of the mounting boss, one end of the driving ring is sealingly fitted in the first driving ring groove, the driven ring assembly comprises a driven ring and a driven ring seat, one end of the driven ring seat is slidingly and sealingly fitted in the first mounting groove, the other end of the driven ring seat is provided with a first driven ring groove, one end of the driven ring is sealingly fitted in the first driven ring groove, and the other end of the driven ring abuts against the other end of the driving ring.

[0012] As an improvement, a plurality of first positioning lugs are outwardly protruded on the inner circumferential walls of the first driving ring groove and the first driven ring groove, a plurality of first positioning grooves for matching the first positioning lugs are respectively formed on the outer circumferential walls of the driving ring and the driven ring; a first accommodating groove in the shape of a ring is respectively formed on the bottom walls of the first driving ring groove and the first driven ring groove, a first sealing ring and a ring-shaped block filled with glass fiber PTFE are fitted in the first accommodating groove from the inside to the outside, and the outer wall of the ring-shaped block sealingly cooperates with the tail end of the driving ring or the driven ring.

[0013] Further, the second-stage sealing unit comprises a secondary driving ring and a secondary driven ring assembly, a second driving ring groove is arranged in the recessed other end of the mounting boss, one end of the secondary driving ring is sealingly fitted in the second driving ring groove, the secondary driven ring assembly comprises a secondary driven ring and a secondary driven ring seat, one end of the secondary driven ring seat is slidingly and sealingly fitted in the second mounting groove, the other end of the secondary driven ring seat is provided with a second driven ring groove, one end of the secondary driven ring is sealingly fitted in the second driven ring groove, and the other end of the secondary driven ring abuts against the other end of the secondary driving ring.

[0014] Further improvement, a plurality of second positioning lugs are outwardly protruded on the inner circumferential walls of the second driving ring groove and the second driven ring groove, a plurality of second positioning grooves for matching the second positioning lugs are respectively formed on the outer circumferential walls of the secondary driving ring and the secondary driven ring; a second accommodating groove in the shape of a ring is respectively formed on the bottom walls of the second driving ring groove and the second driven ring groove, a first sealing ring and a ring-shaped block filled with glass fiber PTFE are fitted in the second accommodating groove from the inside to the outside, and the outer wall of the ring-shaped block sealingly cooperates with the tail end of the secondary driving ring or the secondary driven ring.

[0015] Preferably, the active ring, the main static ring, the secondary active ring and the secondary static ring are of the same structure; and the main static ring seat and the secondary static ring seat are of the same structure.

[0016] Further, the main static ring seat and the first mounting groove bottom wall and the secondary static ring seat and the second mounting groove bottom wall are provided with elastic compensation members; the main static ring seat and the first mounting groove and the secondary static ring seat and the second mounting groove are respectively provided with first and second sealing parts, and the first and second sealing parts are respectively located on the radial outer side of the elastic compensation members.

[0017] Further improved, the first and second sealing parts each include a second sealing ring and a PTFE stop ring distributed in abutment along the axial direction, and the PTFE stop ring is located at one end close to the main static ring seat or the secondary static ring seat.

[0018] Further improved, the sealing seat is provided with a clamping spring on the inner circumferential wall of one end close to the first mounting groove, and the outer wall of the main static ring is provided with a positioning step, when the main static ring assembly is preassembled into the first mounting groove, the clamping spring abuts against the positioning step, so that the main static ring assembly and the sealing seat are preassembled into an integral structure.

[0019] Further improved, the bottom of the first mounting groove and the second mounting groove is provided with an anti-rotation pin, and the main static ring seat and the secondary static ring seat are each provided with an anti-rotation pin groove.

[0020] The above improvements of the utility model will be specifically described in the following specific embodiments, and some of them will become apparent from the description or be understood by implementing the utility model. The purpose and other advantages of the utility model can be achieved and obtained through the structures specifically pointed out in the description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a half sectional view of the mechanical seal for the crude oil lifting double screw pump of the utility model;

[0022] Figure 2 It is a half sectional view of the mechanical seal for the crude oil lifting double screw pump of the utility model; Figure 1 It is a half sectional view of the mechanical seal for the crude oil lifting double screw pump of the utility model;

[0023] Figure 3 It is a half sectional view of the mechanical seal for the crude oil lifting double screw pump of the utility model; Figure 1 It is a half sectional view of the mechanical seal for the crude oil lifting double screw pump of the utility model;

[0024] BRIEF DESCRIPTION OF DRAWINGS

[0025] 1, bushing; 2, sealing seat; 3, first mounting groove; 4, mounting boss; 5, flange seat; 6, second mounting groove; 7, sealing cavity; 8, liquid inlet; 9, liquid outlet; 10, driving ring; 11, set screw; 12, limit block; 13, positioning groove; 14, driving ring; 15, first driving ring groove; 16, driven ring; 17, driven ring seat; 18, first driven ring groove; 19, first positioning lug; 20, first positioning groove; 21, first accommodating groove; 22, first sealing ring; 23, annular stop block; 24, driven driving ring; 25, second driving ring groove; 26, driven driven ring; 27, driven driven ring seat; 28, second driven ring groove; 29, second positioning lug; 30, second positioning groove; 31, second accommodating groove; 32, second sealing ring; 33, PTFE stop ring; 34, snap spring; 35, positioning step; 36, anti-rotation pin; 37, anti-rotation pin groove. DETAILED DESCRIPTION

[0026] Firstly, those skilled in the art should understand that the embodiments are only used to explain the technical principles of the application examples, and are not intended to limit the protection scope of the application examples. Those skilled in the art can make adjustments as needed in order to adapt to specific application occasions.

[0027] In the description of the application examples, it should be noted that unless otherwise explicitly specified and limited, the terms "fixed", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meanings of the above terms in the application examples can be understood according to specific circumstances.

[0028] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0029] Reference Figures 1-3 As shown in the drawings, the application example discloses a mechanical seal for a crude oil lifting double screw pump, which comprises a bushing 1 sleeved outside a rotating shaft, and a sealing ring is arranged between one end of the bushing 1 and the outer wall of the rotating shaft, and the other end is in driving connection with the rotating shaft.

[0030] The outer part of the shaft sleeve 1 is sleeved with a sealing seat 2, and one end of the shaft sleeve 1 extends to the inner cavity of the sealing seat 2, and the other end is exposed to the end face of the sealing seat 2 close to the atmosphere side in the axial direction. In addition, a first mounting groove 3 is arranged in the inner cavity of the sealing seat 2 close to the medium end, and an annular mounting boss 4 is formed on the outer part of one end of the shaft sleeve 1 in the inner cavity of the sealing seat 2. A primary sealing unit is arranged between one end of the mounting boss 4 and the first mounting groove 3. The other end of the mounting boss 4 and the second mounting groove 6 formed between the radially inner end of the flange seat 5 and the sealing seat 2 are fitted with a secondary sealing unit. The primary sealing unit, the secondary sealing unit and the inner side wall of the sealing seat 2 form a sealing cavity 7. The side wall of the sealing seat 2 is provided with a liquid inlet 8 and a liquid outlet 9 which respectively communicate with the sealing cavity 7, and the pressure of the sealing cavity 7 is higher than the pressure of the medium end. When the mechanical seal is assembled and installed in the screw pump, an auxiliary flushing system is also needed. The outlet of the auxiliary flushing system is connected with the liquid inlet 8 of the sealing seat 2, and the liquid outlet 9 on the sealing seat 2 is connected with the inlet of the auxiliary flushing system, so as to realize the circulation of the flushing liquid, ensure that the sealing cavity 7 is filled with the flushing liquid, and the friction heat of the primary sealing unit and the secondary sealing unit can be taken away in time during the circulation of the flushing liquid, so as to avoid the thermal deformation of the sealing ring. The pressure of the sealing cavity 7 is greater than the pressure of the medium end, so that the grinding surface of the primary sealing unit is mainly the liquid film of the flushing liquid, avoiding the particles in the medium from entering the grinding surface and causing serious wear of the sealing surface, and ensuring the sealing performance.

[0031] More specifically, the outer part of the end of the shaft sleeve 1 away from the mounting boss 4 is connected with a driving ring 10, a plurality of tight screws 11 are arranged on the side wall of the driving ring 10 and abut against the shaft, the shaft sleeve 1 is drivingly connected with the shaft through the tight screws 11, and synchronous rotation is realized. In this structure, a plurality of connecting screws are also arranged on the side wall of the driving ring 10, and the inner ends of the plurality of connecting screws abut against the outer wall of the shaft sleeve 1, so as to realize the connection and fixation of the driving ring 10 and the shaft sleeve 1. In this structure, due to the limitation of space size, the size of the tight screw 11 cannot be too large, so the tight screw 11 is made of hard galvanized material, so as to ensure the stable and reliable locking ability at 3mpa.

[0032] In another aspect, in the embodiment, a plurality of limiting blocks 12 are detachably connected to the outer peripheral wall of the driving ring 10 in the circumferential direction, a positioning column is formed on the outer end of the flange seat 5 away from the sealing seat 2, a positioning groove 13 is formed on the outer peripheral wall of the positioning column, and one end of each limiting block 12 is clamped and fitted in the positioning groove 13, so as to make the sealing seat 2, the flange seat 5, the primary sealing unit, the secondary sealing unit, and the shaft sleeve 1 into an integrated structure. When installed, the entire mechanical seal is installed as a whole structure, which is convenient and fast, and can also avoid the risk of missing parts due to too many parts during on-site assembly. In addition, it should be noted that the positioning block in this structure is used for positioning during assembly, and also plays a role in positioning the working height. When the entire mechanical seal is installed on the screw pump according to the set position, it needs to be disassembled, otherwise it will affect the normal operation of the mechanical seal.

[0033] In addition, in the above structure, the flange seat 5 and the sealing seat 2 are detachably connected in the axial direction by screws, and a corresponding sealing ring is arranged at the end face connection between the flange seat 5 and the sealing seat 2 to avoid leakage. In addition, the inner diameter end of the flange plate exceeds the inner wall of the sealing seat 2 close to the atmospheric side, thereby forming a second installation groove 6.

[0034] In the embodiment, the primary sealing unit includes a driving ring 14 and a primary static ring assembly. A first driving ring groove 15 is arranged in the inner recess of one end of the mounting boss 4, and one end of the driving ring 14 is sealingly fitted in the first driving ring groove 15. The primary static ring assembly includes a primary static ring 16 and a primary static ring seat 17. The primary static ring seat 17 is slidably and sealingly fitted in the first installation groove 3 in the axial direction, and the other end of the primary static ring seat 17 is provided with a first static ring groove 18. One end of the primary static ring 16 is sealingly fitted in the first static ring groove 18, and the other end of the primary static ring 16 is in abutment with the other end of the driving ring 14 in the circumferential direction.

[0035] More specifically, in the above structure, a plurality of first positioning lugs 19 are formed on the outer convex walls of the inner circumferential walls of the first dynamic ring groove 15 and the first static ring groove 18, and a plurality of first positioning grooves 20 are formed on the outer circumferential walls of the main dynamic ring 14 and the main static ring 16, respectively, for matching the first positioning lugs 19; preferably, the first positioning lugs 19 and the first positioning grooves 20 are each divided into four along the circumference, so as to ensure stable operation of the primary sealing unit under high torque. More importantly, annular first accommodating grooves 21 are formed on the bottom walls of the first dynamic ring groove 15 and the first static ring groove 18, respectively, and a first sealing ring 22 and an annular stop block 23 filled with glass fiber PTFE are fitted from the inside to the outside of the first accommodating groove 21, and the outer wall of the annular stop block 23 is in sealing cooperation with the tail end of the main dynamic ring 14 or the main static ring 16. After the annular stop block 23 is set, a small space is left between the main dynamic ring 14, the main static ring 16 and the bottom of the corresponding first dynamic ring groove 15 and first static ring groove 18, i.e. the sealing ring does not directly contact the metal seat, so that the grinding process of the end face of the metal seat can be omitted, which not only reduces the processing cost, but also avoids leakage caused by the assembly of the end face grinding.

[0036] Similarly, in the present embodiment, the secondary sealing unit includes a secondary dynamic ring 24 and a secondary static ring assembly, the other end of the mounting boss 4 is recessed to form a second dynamic ring groove 25, one end of the secondary dynamic ring 24 is sealingly fitted in the second dynamic ring groove 25, the secondary static ring assembly includes a secondary static ring 26 and a secondary static ring seat 27, one end of the secondary static ring seat 27 is slidingly and sealingly fitted in the second mounting groove 6 along the axial direction, the other end of the secondary static ring seat 27 is provided with a second static ring groove 28, one end of the secondary static ring 26 is sealingly fitted in the second static ring groove 28, and the other end of the secondary static ring 26 abuts against the other end of the secondary dynamic ring 24. Moreover, a plurality of second positioning lugs 29 are formed on the inner circumferential walls of the second dynamic ring groove 25 and the second static ring groove 28, and a plurality of second positioning grooves 30 are formed on the outer circumferential walls of the secondary dynamic ring 24 and the secondary static ring 26, respectively, for matching the second positioning lugs 29; in this structure, the second positioning lugs 29 and the second positioning grooves 30 are also divided into four along the circumference. Annular second accommodating grooves 31 are formed on the bottom walls of the second dynamic ring groove 25 and the second static ring groove 28, respectively, and the second accommodating groove 31 is also fitted from the inside to the outside with the first sealing ring 22 and the annular stop block 23 filled with glass fiber PTFE, and the outer wall of the annular stop block 23 is in sealing cooperation with the tail end of the secondary dynamic ring 24 or the secondary static ring 26.

[0037] In the above structure, preferably, the primary sealing unit and the secondary sealing unit are completely identical in structure and can be replaced with each other, specifically, the structures of the driving ring 14, the driving static ring 16, the driven ring 24 and the driven static ring 26 are all identical, and the structures of the driving static ring seat 17 and the driven static ring seat 27 are also identical. In addition, the driving ring 14, the driving static ring 16, the driven ring 24 and the driven static ring 26 are all made of hard alloy material, which ensures small deformation under high-pressure operation condition and strong resistance to sand particles in crude oil. The four sealing rings are of common size, which facilitates installation and does not need to be specially distinguished, and also facilitates later inventory management. In this structure, the driving ring 14, the driving static ring 16, the driven ring 24 and the driven static ring 26 are all movable along the axial direction and are not fixed, which avoids stress deformation of the sealing rings due to different expansion coefficients between different materials after assembly under high temperature and high pressure, thereby affecting the sealing performance.

[0038] In another aspect, in the embodiment, the elastic compensation members are arranged between the driving static ring seat 17 and the bottom wall of the first installation groove 3 and between the driven static ring seat 27 and the bottom wall of the second installation groove 6. The first sealing part and the second sealing part are respectively arranged between the driving static ring seat 17 and the first installation groove 3 and between the driven static ring seat 27 and the second installation groove 6, and the first sealing part and the second sealing part are respectively located on the radial outer side of the corresponding elastic compensation member. In this structure, the primary sealing unit and the secondary sealing unit are both static ring compensation type structures, which can avoid the influence of the rotation of the rotating shaft on the elastic compensation force and ensure stable sealing performance. On the other hand, the elastic compensation members are sealed through the corresponding sealing parts, i.e., do not contact the crude oil medium, thereby avoiding corrosion.

[0039] More specifically, the elastic compensation members in the above structure all include a plurality of small springs which are uniformly distributed in the circumferential direction. In order to further improve the stability of the elastic compensation performance, a plurality of spring holes for accommodating the small springs are formed in the bottom of the first installation groove 3 and the bottom of the second installation groove 6, which ensures the stability of the small springs during compression and prevents tilting, thereby ensuring stable and reliable compensation performance.

[0040] In addition, the first sealing part and the second sealing part in the above structure both include the second sealing ring 32 and the PTFE stop ring 33 which are arranged in abutment along the axial direction, and the PTFE stop ring 33 is located at one end close to the driving static ring seat 17 or the driven static ring seat 27. The PTFE is used to prevent the sealing ring from being extruded under high pressure, thereby ensuring stable sealing performance. In this structure, the O-ring groove of the first sealing part and the second sealing part is bidirectional pressure bearing design, and the medium pressure changes between 0.6-3mpa. The bidirectional pressure bearing design ensures that the sealing does not leak when the medium pressure is higher than the internal pressure of the sealing.

[0041] In the embodiment, the sealing seat 2 is equipped with a ring-shaped snap spring 34 on the inner circumferential wall near one end of the first mounting groove 3, and the outer wall of the main static ring 16 is provided with a positioning step 35. The snap spring 34 is mainly used for axial positioning when the main static ring assembly is preassembled with the sealing seat 2. Specifically, when the main static ring assembly is preassembled into the first mounting groove 3, the snap spring 34 abuts against the positioning step 35, so that the main static ring assembly and the sealing seat 2 are preassembled into an integrated structure. This facilitates the installation of the shaft sleeve 1 structure and improves the assembly efficiency of the entire mechanical sealing device.

[0042] In addition, the bottom of the first mounting groove 3 and the second mounting groove 6 is provided with an anti-rotation pin 36, and the main static ring seat 17 and the auxiliary static ring seat 27 are provided with an anti-rotation pin groove 37. In order to adapt to high-pressure and high-torque working conditions, the anti-rotation pin has a large diameter to ensure effective anti-rotation capability. Moreover, the anti-rotation pin groove 37 is arranged on the metal seat instead of directly arranged on the sealing ring, so that the strength of the sealing ring is not affected.

[0043] In the description of the present application, the description of the terms "the embodiment", "some embodiments", and the like means that the specific features, mechanisms, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials, or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0044] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed in the present application can be easily thought of by those skilled in the art, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A mechanical seal for a crude oil lift twin screw pump, characterized by: The utility model provides a sealing structure of rotating shaft, including the sleeve (1) of the sleeve of rotating shaft, the outer sleeve (1) is equipped with the sealing seat (2), and one end of sleeve (1) extends to the inner chamber of sealing seat (2), and the inner chamber of sealing seat (2) is provided with first installation groove (3) near medium end, and the outer portion of one end of sleeve (1) is formed with annular installation boss (4) in the inner chamber of sealing seat (2), and one end of installation boss (4) is equipped with primary sealing unit with first installation groove (3), the other end of sealing seat (2) is connected with flange seat (5), and the radial inner end between flange seat (5) and sealing seat (2) forms second installation groove (6), and the other end of installation boss (4) is equipped with secondary sealing unit with second installation groove (6), and the inner side wall between primary sealing unit, secondary sealing unit and sealing seat (2) forms sealing cavity (7), the side wall of sealing seat (2) is provided with liquid inlet (8) and liquid outlet (9) that lead to sealing cavity (7) respectively, and the pressure of sealing cavity (7) is higher than medium end pressure, the outer portion of one end of sleeve (1) is connected with driving ring (10) away from installation boss (4), the side wall of driving ring (10) is provided with multiple tight screws (11) that are in abutting fit with rotating shaft, and the outer circumferential wall of driving ring (10) is detachably connected with multiple limit blocks (12) that are distributed in circumferential direction, and the outer convex of one end of flange seat (5) away from sealing seat (2) is formed with positioning column, the outer circumferential wall of positioning column is formed with positioning groove (13), and one end of each limit block (12) is snap spring matched in positioning groove (13).

2. The mechanical seal for a crude oil lift double screw pump of claim 1, wherein: The primary sealing unit includes driving ring (14) and main static ring assembly, the recessed one end of installation boss (4) is provided with first dynamic ring groove (15), and one end of driving ring (14) is sealingly fitted in first dynamic ring groove (15), the main static ring assembly includes main static ring (16) and main static ring seat (17), one end of main static ring seat (17) is slidably and sealingly fitted in first installation groove (3) along the axial direction, and the other end is provided with first static ring groove (18), one end of main static ring (16) is sealingly fitted in first static ring groove (18), and the other end is in abutting contact with the other end of driving ring (14).

3. The mechanical seal for a crude oil lift double screw pump of claim 2, wherein: The inner circumferential wall of the first dynamic ring groove (15) and the first static ring groove (18) is outwardly convexly formed with a plurality of first positioning lugs (19), and the outer circumferential wall of the main dynamic ring (14) and the main static ring (16) is respectively formed with a plurality of first positioning grooves (20) matched with the first positioning lugs (19); the bottom wall of the first dynamic ring groove (15) and the first static ring groove (18) is respectively provided with an annular first accommodating groove (21), and the first accommodating groove (21) is inwardly and outwardly fitted with a first sealing ring (22) and an annular stop block (23) filled with glass fiber and PTFE, and the outer wall of the annular stop block (23) is in sealing cooperation with the tail end of the main dynamic ring (14) or the main static ring (16).

4. The mechanical seal for a crude oil lift double screw pump of claim 3, wherein: The secondary sealing unit comprises a secondary dynamic ring (24) and a secondary static ring assembly, the other end of the mounting boss (4) is recessed to provide a second dynamic ring groove (25), one end of the secondary dynamic ring (24) is sealingly fitted in the second dynamic ring groove (25), the secondary static ring assembly comprises a secondary static ring (26) and a secondary static ring seat (27), one end of the secondary static ring seat (27) is axially slidably and sealingly fitted in the second mounting groove (6), and the other end is provided with a second static ring groove (28), one end of the secondary static ring (26) is sealingly fitted in the second static ring groove (28), and the other end abuts against the other end of the secondary dynamic ring (24).

5. The mechanical seal for a crude oil lift twin screw pump of claim 4, wherein: The inner circumferential wall of the second dynamic ring groove (25) and the second static ring groove (28) is outwardly convexly formed with a plurality of second positioning lugs (29), and the outer circumferential wall of the secondary dynamic ring (24) and the secondary static ring (26) is respectively formed with a plurality of second positioning grooves (30) matched with the second positioning lugs (29); the bottom wall of the second dynamic ring groove (25) and the second static ring groove (28) is respectively provided with an annular second accommodating groove (31), and the second accommodating groove (31) is inwardly and outwardly fitted with a first sealing ring (22) and an annular stop block (23) filled with glass fiber and PTFE, and the outer wall of the annular stop block (23) is in sealing cooperation with the tail end of the secondary dynamic ring (24) or the secondary static ring (26).

6. The mechanical seal for a crude oil lift double screw pump of claim 5, wherein: The main dynamic ring (14), the main static ring (16), the secondary dynamic ring (24) and the secondary static ring (26) are all the same in structure; and the main static ring seat (17) and the secondary static ring seat (27) are the same in structure.

7. The mechanical seal for a crude oil lift twin screw pump of claim 4, wherein: An elastic compensation member is arranged between the main static ring seat (17) and the bottom wall of the first mounting groove (3) and between the secondary static ring seat (27) and the bottom wall of the second mounting groove (6); a first sealing part and a second sealing part are respectively arranged between the main static ring seat (17) and the first mounting groove (3) and between the secondary static ring seat (27) and the second mounting groove (6), and the first sealing part and the second sealing part are respectively located on the radial outer side of the elastic compensation member.

8. The mechanical seal for a crude oil lift twin screw pump of claim 7, wherein: The first sealing part and the second sealing part each comprise a second sealing ring (32) and a PTFE stop ring (33) abuttingly distributed along the axial direction, and the PTFE stop ring (33) is located at one end close to the main static ring seat (17) or the auxiliary static ring seat (27).

9. The mechanical seal for a crude oil lift twin screw pump of claim 7, wherein: An annular snap spring (34) is fitted on the inner circumferential wall of one end of the sealing seat (2) close to the first mounting groove (3), and a positioning step (35) is arranged on the outer wall of the main static ring (16), when the main static ring assembly is preassembled into the first mounting groove (3), the snap spring (34) abuts against the positioning step (35), so that the main static ring assembly and the sealing seat (2) are preassembled into an integral structure.

10. The mechanical seal for a crude oil lift twin screw pump of claim 7, wherein: The bottom of the first mounting groove (3) and the second mounting groove (6) is provided with an anti-rotation pin (36), and the main static ring seat (17) and the auxiliary static ring seat (27) are each provided with an anti-rotation pin groove (37).

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