Vacuum pump and sealing joint

Abstract

A vacuum pump (1) has a first sealing joint (13) comprising first and second annular end portions (13a) and two longitudinal members (13b) connecting the annular end portions (13a), the longitudinal members (13b) being inserted between the two half shells (3, 4) of the vacuum pump (1) in a sealing groove (16) formed in at least one of the two half shells (3, 4), each longitudinal member (13b) further comprises a projection (17), each projection (17) having at least one recess (18), these projections (17) mating with the cross-section of the sealing groove (16) surrounding the at least one recess (18).

Description

Technical Field

[0001] This invention relates to a vacuum pump, particularly comprising a stator having complementary half-shells. The invention also relates to a sealing joint for the vacuum pump, particularly a three-dimensional sealing joint. Background Technology

[0002] Dry vacuum pumps comprise one or more pump stages connected in series, through which the gas to be pumped flows. Among vacuum pumps known in the art, there is a distinction between rotary cam pumps—also known as "Roots" pumps—and claw pumps—also known as "claw pumps." These vacuum pumps are called "dry" because, during operation, the rotors rotate within the stator without any mechanical contact between the rotors or with the stator, thus eliminating the need for lubricating oil in the pump stages.

[0003] However, in certain pumping applications, such as those used in the semiconductor industry, flat panel displays, photovoltaics, and coating processes, the gases used may require vacuum pumps to maintain exceptionally high temperatures, such as on the order of 200°C. This is especially true when the gases used are corrosive—for example, those used during the cleaning phase of a processing chamber—or when these gases include, for example, resin vapors. The combination of high temperatures and corrosive chemicals necessitates the use of high-performance elastomer materials of the high-temperature FKM or high-temperature FFKM type for the static sealing joints of the pump stator components. Furthermore, the design of the sealing joint / sealing groove pair must be conceived in a way that considers the sealing requirements at both low and high temperatures, as well as the inherent thermomechanical properties of these elastomers.

[0004] Multistage vacuum pumps with a sliced ​​architecture—where the stator is formed by an axial assembly of multiple stator elements—solve this problem by using O-rings housed in sealing grooves with rectangular cross-sections, the seals being axially compressed between the stator elements.

[0005] Multistage vacuum pumps with a semi-shell architecture are inherently disadvantageous. In practice, such an architecture requires the use of sealant, splice seals, three-dimensional seals, or a combination of these methods.

[0006] For example, US 6,572,351B2 discloses a vacuum pump structure having a stator composed of half-shells assembled along longitudinal assembly surfaces generally parallel to the rotor axis. The vacuum pump includes a one-piece sealing joint having two annular end portions and two longitudinal members connected to and perpendicular to the annular end portions. The two annular end portions are parallel to each other, and each annular end portion is located between an end member and a half-shell. The longitudinal members are inserted between the half-shells. This one-piece sealing joint provides a seal between the half-shells and a seal between the half-shell and the connected end member to isolate the pump stage from the outside atmosphere.

[0007] However, gas leaks can propagate along the longitudinal components of the three-dimensional joint, and thus from the high-pressure stage through the vacuum pump to the low-pressure stage. These gas leaks can adversely affect pumping performance, both in terms of the achieved ultimate vacuum pressure and the power consumption at that pressure. Summary of the Invention

[0008] One object of the present invention is to overcome at least part of one of the above-mentioned disadvantages, particularly by improving the sealing of the stator components of the semi-shell vacuum pump.

[0009] Therefore, the object of the present invention is a vacuum pump comprising:

[0010] The stator includes at least first and second complementary half-shells and first and second end components, which are assembled together to form at least one pump chamber of the pump stage.

[0011] Two rotor shafts, the two rotor shafts being configured to rotate in the at least one pump chamber;

[0012] A first sealing joint, the first sealing joint comprising:

[0013] The first and second annular end portions are inserted between the respective end members and the half-shell; and

[0014] Two longitudinal members, which connect the annular end portions, are inserted between the two half-shells into a sealing groove formed in at least one of the two half-shells.

[0015] Characterized by the fact that these longitudinal members further include respective protrusions having at least one corresponding recess, the protrusions being adapted to the cross-section of the sealing groove surrounding the at least one recess.

[0016] The protrusions formed in each longitudinal member of the three-dimensional sealing joint locally fill the sealing groove, which allows for the prevention of gas leakage by interrupting the propagation of any longitudinal gas leakage flow that might occur along the sealing groove of the half-shell. By allowing the edges of the protrusions to deform into the recesses, especially when the vacuum pump is heated to high temperatures, the at least one recess reduces the mechanical stress that might be applied to the protrusions due to the large difference in thermal expansion between the high-performance, high-temperature elastomeric material and the metallic material of the half-shell. This enables uniform compression of the protrusions that is compatible with the thermomechanical properties of the sealing joint.

[0017] The vacuum pump may also include one or more of the following features, which may be used individually or in combination.

[0018] At least one recess may be formed in the flat surface of each protrusion facing the other half of the shell.

[0019] The two recesses can be formed in the opposite plane of each protrusion.

[0020] The at least one recess may have an elongated oval cross-sectional shape.

[0021] For example, the first cross-section of the protrusion at the at least one recess is less than or equal to 90% of the second cross-section of the protrusion outside the at least one protrusion.

[0022] For example, the first cross-section of the protrusion at the at least one recess is greater than or equal to 85% of the second cross-section of the protrusion outside the at least one protrusion.

[0023] The sealing groove can have a rectangular cross-section, and the protrusion can have a complementary shape inscribed in a rectangular parallelepiped.

[0024] The longitudinal member may have transition portions on both sides of the at least one protrusion, these transition portions being located between the columnar strand of the longitudinal member and the protrusion. These transition portions have a gradually increasing cross-section, which increases from the cross-section of the columnar strand towards the cross-section of the protrusion.

[0025] The vacuum pump may include at least one second sealing joint having a shape similar to that of the first sealing joint, the at least first and second sealing joints forming at least two consecutive sealing barriers for the gas.

[0026] The first sealing joint and / or the second sealing joint are made, for example, of a fluoroelastomer or perfluoroelastomer material with high temperature resistance, especially withstanding temperatures greater than 150°C.

[0027] The vacuum pump may include a heating device configured to heat the stator to a temperature greater than 150°C.

[0028] The stator half-shell can form at least two pump stages arranged in series between the suction port and the discharge port of the vacuum pump.

[0029] The present invention also relates to a sealing joint for a vacuum pump as described above, the vacuum pump comprising a stator and two rotor shafts, the stator comprising at least complementary first and second half-shells and first and second end components, the half-shells and end components being assembled together to form at least one pump chamber of a pump stage, the two rotor shafts being configured to rotate within the at least one pump chamber, the sealing joint comprising:

[0030] The first and second annular end portions are inserted between the respective end members and the half-shell; and

[0031] Two longitudinal members, connecting the annular end portions, are inserted between the two half-shells into a sealing groove formed in at least one of the two half-shells.

[0032] Characterized by the fact that these longitudinal members further include respective protrusions having at least one respective recess, the protrusions being adapted to the cross-section of the sealing groove surrounding the at least one recess. Attached Figure Description

[0033] Other advantages and features will become apparent after reading the following description and accompanying drawings of specific, but not limiting, embodiments of the invention, as illustrated in the drawings:

[0034] Figure 1 This is an exploded schematic diagram of the components of an exemplary vacuum pump.

[0035] Figure 2 It is assembled at the assembly surface. Figure 1 A partially enlarged view of the sealing joint in the half-shell of the vacuum pump.

[0036] Figure 3 yes Figure 2 A transverse sectional view of the component in the longitudinal member of the sealing joint at the recess.

[0037] Figure 4 It is a perspective view of the protrusion of the longitudinal member of the sealing joint of the vacuum pump and the transition portion on either side of the protrusion.

[0038] Figure 5 The first cross-section AA and the second cross-section BB of the sealing joint are shown. Figure 4 A partial top view of the protrusion, with cross sections AA and BB located on the protrusion.

[0039] In these figures, the same or similar elements have the same reference numerals.

[0040] Only the elements necessary for understanding the invention are shown. Detailed Implementation

[0041] The following embodiments are examples. Although this specification relates to one or more embodiments, it is not necessarily true that every reference relates to the same embodiment, or that features are applicable only to a single embodiment. Simple features of different embodiments may be combined or interchanged to provide other embodiments without departing from the scope of the invention as defined by the claims.

[0042] A primary vacuum pump (rough vacuum pump) is defined as a positive displacement vacuum pump (positive displacement vacuum pump) that is constructed to draw in, deliver, and then discharge the gas to be pumped at atmospheric pressure via two rotor shafts. The rotor shafts are driven to rotate by the motor of the primary vacuum pump. The primary vacuum pump can be started from atmospheric pressure.

[0043] A Roots vacuum pump or Roots compressor (also known as a "Roots blower") is defined as a positive displacement vacuum pump that is constructed to draw in, transport, and then discharge the gas to be pumped via a Roots rotor. The Roots vacuum pump is installed upstream of and in series with a primary vacuum pump. The rotor is driven by two bearings rotated by the motor of the Roots vacuum pump. A Roots vacuum pump comprises one to three pump stages.

[0044] The term "upstream" refers to an element located upstream of another element relative to the flow direction of the gas to be pumped. Conversely, the term "downstream" refers to an element located downstream of another element relative to the flow direction of the gas to be pumped.

[0045] The axial direction is defined as the longitudinal direction of the pump, in which the axis of the rotor shaft extends. The transverse direction is perpendicular to the axial direction. The transverse plane is a plane perpendicular to the longitudinal plane (in this case, it is usually a horizontal plane).

[0046] Figure 1 The components of an example of a so-called dry vacuum pump 1 are shown.

[0047] The vacuum pump 1 includes a stator 2, which includes at least first and second complementary half-shells 3, 4 and first and second end components 5, 6. These half-shells 3, 4 and end components 5, 6 are assembled together to form at least one pump chamber of pump stages T1-T6.

[0048] For example, the stator 2's half-shells 3 and 4 form at least two pump stages T1-T6 arranged in series between the vacuum pump 1's suction port 7 and discharge port 8, for example, between two and ten pump stages (in... Figure 1 (Six in this exemplary instance). Vacuum pump 1 can be a primary vacuum pump ( Figure 1 (or Roots-type vacuum pump)

[0049] The vacuum pump 1 also includes two rotor shafts (not shown) configured to rotate in at least one pumping chamber such that the rotors drive the gas to be pumped between the inlet 7 and the outlet 8.

[0050] The rotor may have convex blades with the same profile, such as "Roots" or "claw" type, or other similar positive displacement vacuum pump principles. The shaft carrying the rotor is driven by a motor (not shown) located at one end, for example, vacuum pump 1.

[0051] Each pumping chamber receives two conjugate rotors, each chamber having its own inlet and outlet. During rotation, the gas drawn in from the inlet is trapped in the volume created by the rotor and stator 2, and then driven by the rotor to the next stage.

[0052] Successive pump stages T1-T6 are connected in series via corresponding interstage channels 9 that connect the outlet of the preceding stage to the inlet of the following stage. The inlet of the first pump stage T1 is connected to the suction port 7. The outlet of the last pump stage is connected to the discharge port 8. The axial dimensions of the rotor and pump chamber (and thus the resulting flow velocities) are, for example, equal or decreasing across the pump stages. Pump stage T1, located on the suction port side 7, receives the rotor with the largest axial dimension and produces the largest flow rate.

[0053] These vacuum pumps are called "dry" because during operation, the rotors rotate inside the stator 2 without any mechanical contact between the rotors or with the stator 2, thus eliminating the need for oil in the pump stage.

[0054] The vacuum pump 1 may include a heating device 11 configured to heat the stator 2 to a temperature greater than 150°C.

[0055] The half-shells 3 and 4 are assembled together along the assembly surface 10. At least one compression chamber and—where appropriate—a transfer channel 9 are partially formed in the first half-shell 3 and partially formed in the second half-shell 4.

[0056] Assembly surface 10 is, for example, a planar assembly surface that passes through the intermediate plane of vacuum pump 1. This planar assembly surface 10, for example, includes the axis of the rotor shaft.

[0057] The first end of the half-shells 3 and 4 is closed by the first end member 5, and the second end of the half-shells 3 and 4 is closed by the second end member 6. Of course, openings are formed in the transverse walls of the partition pump chambers of the half-shells 3 and 4, and—where appropriate—in the end members 5 and 6, for the passage of the rotor shaft.

[0058] The half-shells 3 and 4 and the end members 5 and 6 are assembled together, for example, by complementary engagement of a nose 12 carried by the end members 5 and 6 with a recess formed at the end of the half-shells 3 and 4. The nose 12 protrudes axially. It has, for example, a transversely elongated oval shape and is, for example, solid. The recesses are formed, for example, in the pump chamber of the first pump stage T1 and the pump chamber of the last pump stage.

[0059] The vacuum pump 1 also includes a first sealing joint 13, which is three-dimensional and can be formed as a single piece, i.e., a single unit, or spliced ​​together, i.e., formed by end-to-end mating of multiple flexible sealing joint parts.

[0060] The first sealing joint 13 includes first and second annular end portions 13a inserted between corresponding end members 5, 6 and half-shells 3, 4. The first sealing joint 13 also includes two longitudinal members 13b connecting these annular end portions 13a, the longitudinal members 13b being inserted between half-shells 3, 4.

[0061] The first sealing joint 13 is elastic. It is made, for example, by compression molding or injection molding. The first sealing joint 13 is made, for example, of a fluoropolymer (FKM) or perfluoropolymer (FFKM) material with properties of high temperature resistance, particularly above 150°C.

[0062] At least one annular groove may be formed in at least one nose 12 and / or at least one recess to receive the annular end portion 13a of the sealing connector 13.

[0063] The longitudinal member 13b is inserted into a sealing groove 16 between the two half-shells 3 and 4, the sealing groove being formed in the assembly surface 10 of at least one of the two half-shells 3 and 4, for example, in half-shell 3, in this example, the lower half-shell. For example, two sealing grooves 16 are formed on both sides of the at least one pump chamber in the assembly surface 10 of the first half-shell 3 to receive the corresponding longitudinal member 13b of the first sealing joint 13.

[0064] The first sealing joint 13 (the strands of the longitudinal member 13b and the annular end portion 13a) has, for example, a generally circular cross-section in the uncompressed state.

[0065] As in Figure 2 As can be seen more clearly in the enlarged view, these longitudinal members 13b also include respective protrusions 17, each having at least one recess 18. The protrusions 17 correspond to the cross-section of the sealing groove 16 surrounding the at least one recess 18, especially when cooled, i.e., even when the temperature of the stator 2 is below 150°C. When cooled and in an uncompressed state, the sealing joint 13 further protrudes from the sealing groove 16.

[0066] In each longitudinal member 13b of the three-dimensional sealing joint 13, the protrusion 17 partially fills the sealing groove 16, which allows the gas leakage to be prevented by interrupting the propagation of a potential gas leakage flow that may occur along the sealing groove 16 of the half-shells 3, 4.

[0067] Because the protrusion 17 fills the sealing groove 16 upon cooling, the elastomeric material of the sealing joint 13 is subjected to significant mechanical stress when hot. This effect is exacerbated in certain pumping applications where the gases used may require maintaining the vacuum pump 1 at exceptionally high temperatures, such as approximately 200°C. These high temperatures—combined with corrosive chemicals—necessitate the use of high-performance high-temperature elastomeric materials of the high-temperature FKM or high-temperature FFKM type for the sealing joint, noting that these materials have significantly different coefficients of thermal expansion compared to the metallic materials of the half-shells 3 and 4. This can cause the mechanical properties of the elastomeric material to be locally exceeded in the stressed area of ​​the protrusion 17, leading to irreversible degradation of the sealing joint 13 and ultimately significant creep development, which can result in seal loss when the vacuum pump 1 returns to a cold state, potentially occurring, for example, during maintenance or standby periods of the vacuum pump 1.

[0068] The at least one recess 18 avoids this by allowing the edge of the protrusion 17 to deform into the recess 18, where the material deforms at the point of least resistance, i.e., inward into the recess 18, especially when the vacuum pump 1 is heated to a high temperature. This allows for uniform compression of the protrusion 17 and compatibility with the thermomechanical properties of the sealing joint 13.

[0069] In one exemplary embodiment, the sealing groove 16 has a rectangular cross-section, and the protrusion 17 has a complementary shape inscribed in a rectangular parallelepiped. The length of the protrusion 17 (in the longitudinal direction of the sealing groove 16) is, for example, between 10 mm and 14 mm.

[0070] The protrusion 17 is located, for example, in the middle of the longitudinal member 13b, and in this example, it corresponds to the insertion of the second and third pumping stages T2 and T3. Figure 1 The transverse wall of stator 2 between ).

[0071] At least one recess 18 is formed, for example, in the plane of each protrusion 17 facing the other half of the shell 4. Figure 2 The sealing groove 16 is formed, for example, in the first half-shell 3, while the recess 18 is formed in the flat surface of the protrusion 17 facing the second half-shell 4.

[0072] The recess 18 is formed, for example, in the center of the flat surface of the protrusion 17.

[0073] The two recesses 18 can be formed in the two opposite sides of each protrusion 17 respectively. Figure 3 and 5 The recesses 18 can be identical (in shape and volume). The two recesses 18 are formed, for example, at the top and bottom, i.e., one recess faces the other half of the shell 4, while the other recess 18 is formed in the opposite plane of the protrusion 17.

[0074] The recess 18 can extend in a direction parallel to the sealing groove 16, and the protrusion 17 also extends in that direction.

[0075] The recess 18 has, for example, an elongated longitudinal (or horizontal, i.e., in a plane parallel to the assembly surface 10) cross-section; in other words, it has a shape with a length greater than its width and rounded corners.

[0076] Therefore, thermal expansion will increase the lateral (transverse) dimension of the protrusion 17, which can deform inward due to the central recess 18.

[0077] Figure 5 The first and second cross sections BB and AA of the protrusion 17, which are offset longitudinally along the protrusion 17, are shown.

[0078] The first cross section BB corresponds to the region of the protrusion 17 having at least one recess 18 (two recesses in this example).

[0079] The second cross section AA corresponds to the area of ​​the protrusion 17 that is consistent with the cross section of the sealing groove 16.

[0080] The protrusion 17 has a thickness of, for example, at least 2 mm, and there is no recess on either side of the at least one recess 18 (second cross-section AA).

[0081] For example, the first cross-section BB of the protrusion 17 at the at least one recess 18 is less than or equal to 90% of the second cross-section AA of the protrusion 17 outside the at least one protrusion 18.

[0082] For example, the first cross-section BB of the protrusion 17 at the at least one recess 18 is greater than or equal to 85% of the second cross-section AA of the protrusion 17 outside the at least one protrusion 18.

[0083] These area ratios allow for the promotion of elastic deformation of the protrusion 17 while avoiding plastic deformation.

[0084] In one exemplary embodiment, the area of ​​the first cross-section BB is between 8 mm² and 8 mm². 2 and 11mm 2 Between, the area of ​​the second cross section AA is between 9mm. 2 and 13mm 2 Between. The difference between these cross-sections is, for example, between 0.5 mm. 2 and 3mm 2 between.

[0085] like Figure 2 and 4As shown, the longitudinal member 13b can also include transition portions 19 on both sides of each protrusion 17, these transition portions 19 being located between the columnar strand of the longitudinal member 13b and the protrusion 17. Each of these transition portions 19 has a cross-section that varies along its length. The cross-section of the transition portion 19 is gradually increasing, increasing progressively from the cross-section of the columnar strand to the cross-section of the protrusion 17. These transition portions 19 provide a gradual change in the mechanical stress acting on the protrusion 17, thereby preventing the formation of weak zones.

[0086] Vacuum pump 1 may also include two sealing joints 13 and 20 ( Figure 1 , 2 (and 3), the second sealing joint 20 has a similar shape to the first sealing joint 13.

[0087] Similar to the first sealing joint 13, the second sealing joint 20 is three-dimensional and can be formed as a single piece, i.e., a single unit, or spliced ​​together. It includes first and second annular end portions 20a located between corresponding end members 5, 6 and half-shells 3, 4. The second sealing joint 20 also includes two longitudinal members 20b connecting the annular end portions 20a, the longitudinal members 20b being inserted between the half-shells 3, 4.

[0088] Similar to the first sealing joint 13, the longitudinal members 20b of the second sealing joint 20 may include respective protrusions 17, each having at least one recess 18, the protrusions 17 being aligned with the cross-section of a sealing groove 16 surrounding the at least one recess 18.

[0089] All features of the protrusion 17 and recess 18 of the second sealing joint 20 may be the same as those of the first sealing joint 13.

[0090] The first sealing joint 13 and the second sealing joint 20 are arranged in such a way that the first and at least one second seal 13, 20 form at least two continuous gas sealing barriers.

[0091] The annular end portions 13a and 20a are parallel to each other and perpendicular to the longitudinal members 13b and 20b.

[0092] The multiplication of the sealing barrier ensures a good seal from the outside to the inside and from the inside to the outside, and allows the use of different materials that provide reduced resistance to corrosive gases and / or heat as the distance from the pump chamber increases. In fact, at least one internal first sealing joint 13 is formed of a material that is more corrosion-resistant, abrasion-resistant, and / or heat-resistant than the material of the second sealing joint 20. Therefore, the material of the second sealing joint 20 can be more economical than that of the internal first sealing joint 13, while remaining acceptable in terms of safety. The second sealing joint 20 is made, for example, of a fluorinated elastomer (FKM), while the first sealing joint 13 is made, for example, of a perfluoroelastomer (FFKM).

[0093] Although the accompanying drawings show a vacuum pump 1 with a nose 12 in its end member and complementary recesses in its half-shells 3 and 4, the invention is also applicable to vacuum pumps without a nose or recesses. Sealing joints 13 and 20 can then be compressed between the surface of the end member and the transverse end face of the half-shell 3.

Claims

1. A vacuum pump (1), comprising: The stator (2) includes at least complementary first half-shell (3) and second half-shell (4) as well as first end part (5) and second end part (6), which are assembled together to form at least one pump chamber of pump stage (T1-T6). Two rotor shafts configured to rotate within the at least one pump chamber. The first sealing joint (13) includes: The first and second annular end portions (13a) are inserted between the respective end members (5, 6) and the half-shells (3, 4); and Two longitudinal members (13b) connect the annular end portion (13a), and these longitudinal members (13b) are inserted between the two half-shells (3, 4) into a sealing groove (16) formed in at least one of the two half-shells (3, 4). Characterized in that these longitudinal members (13b) further include a respective protrusion (17) having at least one corresponding recess (18) adapted to the cross-section of the sealing groove (16) surrounding the at least one recess (18).

2. The vacuum pump (1) according to claim 1, characterized in that, At least one recess (18) is formed in the flat surface of each protrusion (17) facing the other half shell (4).

3. The vacuum pump (1) according to any one of the preceding claims, characterized in that, Two recesses (18) are formed in the opposite flat surfaces of each protrusion (17).

4. The vacuum pump (1) according to any one of the preceding claims, characterized in that, The at least one recess (18) has an elongated cross-sectional shape.

5. The vacuum pump (1) according to any one of the preceding claims, characterized in that, The first cross section (BB) of the protrusion (17) at the at least one recess (18) is less than or equal to 90% of the second cross section (AA) of the protrusion (17) outside the at least one protrusion (18).

6. The vacuum pump (1) according to any one of the preceding claims, characterized in that, The first cross section (BB) of the protrusion (17) at the at least one recess (18) is greater than or equal to 85% of the second cross section (AA) of the protrusion (17) outside the at least one protrusion (18).

7. The vacuum pump (1) according to any one of the preceding claims, characterized in that, The sealing groove (16) has a rectangular cross-section, and the protrusion (17) has a complementary shape inscribed in a cuboid.

8. The vacuum pump (1) according to any one of the preceding claims, characterized in that, The vacuum pump includes at least one second sealing joint (20) with a shape similar to the first sealing joint (13), the at least one first and second sealing joints (13, 20) forming at least two successive sealing barriers for the gas.

9. The vacuum pump (1) according to any one of the preceding claims, characterized in that, The first sealing joint (13) and / or the second sealing joint (20) are made of fluorinated elastomer or perfluoroelastomer material with high temperature resistance, especially withstanding temperatures greater than 150°C.

10. The vacuum pump (1) according to any one of the preceding claims, characterized in that, The vacuum pump includes a heating device (11) configured to heat the stator (2) to a temperature greater than 150°C.

11. The vacuum pump (1) according to any one of the preceding claims, characterized in that, The stator (2) half-shells (3, 4) form at least two pump stages (T1-T6) connected in series between the suction port (7) and discharge port (8) of the vacuum pump (1).

12. A sealing joint (13, 20) for a vacuum pump (1) according to any one of the preceding claims, the vacuum pump comprising a stator (2) and two rotor shafts, the stator comprising at least complementary first half-shell (3) and second half-shell (4) and a first end member (5) and a second end member (6), the half-shells (3, 4) and end members (5, 6) being assembled together to form at least one pump chamber of a pump stage (T1-T6), the two rotor shafts being configured to rotate in the at least one pump chamber, the sealing joint (13, 20) comprising: The first and second annular end portions (13a, 20a) are inserted between the respective end members (5, 6) and the half-shells (3, 4); and Two longitudinal members (13b, 20b) connecting the annular end portions (13a, 20a) are inserted between the half-shells (3, 4) into a sealing groove (16) formed in at least one of the two half-shells (3, 4). The longitudinal members (13b, 20b) are characterized in that each of the longitudinal members further includes a respective protrusion (17) having at least one corresponding recess (18) adapted to the cross-section of the sealing groove (16) surrounding the at least one recess (18).

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