Pre-pumping filtering structure of roots vacuum pump

Abstract

The utility model belongs to the technical field of Roots vacuum pumps, and particularly relates to a pre-pumping filtering structure of a Roots vacuum pump. Aiming at the defects that a filtering structure in a gas chamber for communicating a lubricating oil chamber and a vacuum chamber of the existing roots vacuum pump is relatively high in processing difficulty and / or relatively low in filtering efficiency, the utility model adopts the following technical scheme that the pre-pumping filtering structure of the roots vacuum pump comprises a filtering chamber and a pre-pumping filtering structure, a filtering device; the first gas path is communicated with the filtering chamber and the lubricating oil chamber; the second gas path is connected with the filtering chamber and the vacuum chamber; wherein the filtering device comprises a filtering assembly, the filtering device further comprises an outer mounting seat and / or an inner mounting seat, the filtering assembly is mounted on the outer mounting seat or the inner mounting seat, the inner mounting seat and the filtering cavity are sealed, and a plurality of vent holes are formed in the inner mounting seat. According to the pre-pumping filtering structure of the roots vacuum pump, a radial hole does not need to be machined in a screw with a small diameter, machining is easier, the filtering area is large, and the filtering efficiency is high.

Description

Technical Field

[0001] This utility model belongs to the field of Roots vacuum pump technology, specifically relating to a pre-evacuation and filtration structure for a Roots vacuum pump. Background Technology

[0002] The shaft of a Roots vacuum pump is supported by bearings at both ends, which are lubricated by splash oil mist. The shaft seal typically uses a piston ring structure. During operation, the pumped medium enters from the inlet, passes through the vacuum chamber of the end cover, and exits from the exhaust port. During vacuuming of a single workpiece and during workpiece replacement, the pressure in the vacuum chamber changes, while the pressure in the lubricating oil chamber remains relatively constant. When the pressure difference between the end cover vacuum chamber and the lubricating oil chamber exceeds a certain range, the piston rings partially fail. The lubricating oil on both sides of the piston rings and the pumped medium will interpenetrate (mainly lubricating oil flowing into the end cover vacuum chamber). Large oil vapor molecules and droplets in the lubricating oil chamber mix with the pumped medium, contaminating it. Simultaneously, the pumped medium seeps into the lubricating oil chamber through the piston rings, causing the lubricating oil to emulsify, lose its lubricating function, and reduce the service life of the Roots pump.

[0003] Chinese invention patent application CN202210372057.9 discloses a pre-evacuation structure for a Roots vacuum pump. The Roots vacuum pump includes a housing with an internal vacuum chamber and a lubricating oil chamber. The pre-evacuation structure includes a pre-evacuation channel and a filter chamber disposed within the housing. One end of the pre-evacuation channel is connected to the upper part of the lubricating oil chamber, and the other end is located on the exhaust side of the low vacuum chamber. A filter assembly is disposed in the filter chamber. The pre-evacuation channel is connected to the filter chamber and passes through the filter assembly.

[0004] The aforementioned pre-evacuation structure of the Roots vacuum pump has the advantages of maintaining a dynamic pressure balance between the vacuum chamber and the lubricating oil chamber, making the oil seal less prone to damage, and preventing the mutual penetration of the pumped medium and the lubricating medium. However, its filter assembly includes filter cotton and filter bolts. The filter chamber has a protruding post, and the pre-evacuation channel includes a second channel penetrating the post. The shank of the filter bolt has a filter channel arranged axially along the shank and a filter through hole arranged radially along the shank. The shank of the filter bolt passes through the filter cotton and is inserted into the post to press and fix the filter cotton onto the post. One end of the second channel is used to connect to the lubricating oil chamber, and the other end is connected to the filter chamber through the filter channel, filter through hole, and filter cotton. It requires machining the axial filter channel and radial filter through hole in the filter bolt, and also requires machining a threaded hole seat in the housing, which is relatively complicated. Furthermore, the size of the filter channel is limited, resulting in low filtration efficiency.

[0005] Furthermore, the second channel of the filter chamber in the aforementioned patent application is vertically arranged, making it easy for dust and other impurities to fall into the second channel. Summary of the Invention

[0006] This invention addresses the shortcomings of existing Roots vacuum pumps, such as the high difficulty in manufacturing the filter structure in the gas chamber connecting the lubricating oil chamber and the vacuum chamber, and / or the low filtration efficiency. It provides a pre-evacuation filter structure for Roots vacuum pumps, reducing manufacturing difficulty and / or improving filtration efficiency.

[0007] To achieve the above objectives, this utility model adopts the following technical solution: a pre-evacuation filtration structure for a Roots vacuum pump, wherein the Roots vacuum pump has a lubricating oil chamber, a vacuum chamber, and an oil seal, and the pre-evacuation filtration structure for the Roots vacuum pump includes:

[0008] Filter chamber;

[0009] The filtration device is located in the filtration chamber;

[0010] The first air passage connects the filter chamber and the lubricating oil chamber;

[0011] The second gas path connects the filter chamber and the vacuum chamber;

[0012] The filter device includes a filter assembly, and also includes an outer mounting base and / or an inner mounting base. The filter assembly is mounted on the outer mounting base or the inner mounting base. The inner mounting base is sealed to the filter chamber, and multiple vent holes are provided on the inner mounting base.

[0013] The pre-evacuation filtration structure of this Roots vacuum pump comprises a filter chamber, a first gas path, and a second gas path. These two gas paths form a pre-evacuation passage connecting the vacuum chamber and the lubricating oil chamber, reducing the pressure difference between them. This ensures the pressure difference is less than the sealing pressure range of the oil seal, preventing mutual penetration between the lubricating oil and the pumped medium at the oil seal. The filtration device prevents lubricating oil from flowing from the lubricating oil chamber into the vacuum chamber, and also prevents the pumped medium from entering the lubricating oil chamber. When the filtration device includes an inner mounting base with multiple vent holes, compared to the existing screw-venting structure, it eliminates the need to machine radial holes in small-diameter screws, making processing easier, resulting in a larger filtration area and higher filtration efficiency. When the filtration device includes an outer mounting base but not an inner mounting base, the filter assembly can directly connect to the filter chamber, resulting in a larger filtration area and eliminating the need to machine radial holes in small-diameter screws, further simplifying processing. Before a Roots vacuum pump starts operating, a backing vacuum pump is usually turned on to evacuate the gas. While the backing vacuum pump is evacuating the vacuum chamber inside the housing, it also evacuates the lubricating oil chamber through a pre-evacuation channel. This keeps the gas pressure in the vacuum chamber and the gas pressure in the lubricating oil chamber basically the same, achieving dynamic balance. This reduces the pressure difference on both sides of the oil seal, reduces axial force, reduces friction, and improves the service life of the oil seal. It also weakens the role of the oil seal, thereby improving the service life of the Roots vacuum pump. The filter assembly in the filter chamber plays a filtering role, allowing small molecule media to pass through while preventing large molecule oil vapors and droplets from passing through. When the pressure in the Roots pump vacuum chamber fluctuates, and the pressure at the vacuum pump outlet is lower than the pressure in the lubricating oil chamber, the filter assembly filters the large molecule oil vapors and droplets in the lubricating oil chamber to prevent them from being drawn away and to prevent them from mixing with the pumped medium, thus ensuring product quality. When the pressure at the vacuum pump outlet is higher than the pressure in the lubricating oil chamber, the pumped medium flows in the opposite direction to the lubricating oil chamber through the pre-pumping channel. The filter assembly filters the pumped medium, turning it into small, non-condensable gases before it enters the lubricating oil chamber, preventing the lubricating oil from emulsifying, failing, or being damaged, and keeping the lubricating oil clean and durable.

[0014] As an improvement, the filter device includes an inner mounting base with threaded holes and multiple vent holes surrounding the threaded holes. The filter assembly is mounted on the inner mounting base by filter screws.

[0015] As an improvement, the filter chamber has a stepped cavity, with an inner mounting seat abutting against the middle wall of the stepped cavity.

[0016] As an improvement, the inner mounting seat is T-shaped, with the large-diameter section of the inner mounting seat abutting the middle wall of the stepped cavity, and an O-ring provided on the small-diameter section of the inner mounting seat, which seals the inner mounting seat and the filter chamber.

[0017] Alternatively, the internal mounting base can be flat.

[0018] As an improvement, the filter chamber is formed by the end cap of the Roots vacuum pump. The end cap includes a cap body and a cover. The cover is fixed to the cap body by cap screws and directly or indirectly abuts against the filter assembly.

[0019] As an improvement, the filter device includes an outer mounting base, a cover abutting against the outer mounting base, the outer mounting base abutting against the filter assembly, and an O-ring provided on the outer mounting base to seal the space between the outer mounting base and the filter chamber.

[0020] As an improvement, the filter device includes an external mounting base with threaded holes, and the filter assembly is mounted on the external mounting base by filter screws.

[0021] As an improvement, the filter chamber is formed by the end cover of the Roots vacuum pump. The end cover includes a cover body and a sealing cover. The sealing cover is fixed to the cover body by cover screws and abuts against the outer mounting seat. The sealing cover and the cover body are sealed. Alternatively, an O-ring is provided on the outer mounting seat, and the O-ring seals the outer mounting seat and the filter chamber.

[0022] As an improvement, the filter chamber has a stepped cavity, and the filter assembly abuts against the middle wall of the stepped cavity.

[0023] As an improvement, the filter assembly includes filter cotton, or the filter assembly includes filter cotton and a filter screen; and / or,

[0024] The angle between the first air passage and the center of the filter chamber is 15° to 45°; and / or,

[0025] The angle between the second air passage and the center of the filter chamber is 15° to 45°.

[0026] The pre-evacuation filtration structure of this Roots vacuum pump has a filter chamber, a first gas path, and a second gas path. These two gas paths form a pre-evacuation passage connecting the vacuum chamber and the lubricating oil chamber, reducing the pressure difference between them. This ensures the pressure difference is less than the sealing pressure range of the oil seal, preventing mutual penetration between the lubricating oil and the pumped medium at the oil seal. The filtration device prevents lubricating oil from flowing out of the vacuum chamber and also prevents the pumped medium from entering the lubricating oil chamber. When the filtration device includes an inner mounting base with multiple vent holes, compared to the existing screw-venting structure, it eliminates the need to machine radial holes on small-diameter screws, making processing easier, resulting in a larger filtration area and higher filtration efficiency. When the filtration device includes an outer mounting base but not an inner mounting base, the filter assembly can directly communicate with the filter chamber, resulting in a larger filtration area and eliminating the need to machine radial holes on small-diameter screws, further simplifying processing. Attached Figure Description

[0027] Figure 1This is a cross-sectional view of the pre-extraction filter structure of Embodiment 1 of this utility model.

[0028] Figure 2 This is a schematic diagram of the lower mounting base of the pre-extraction filter structure according to Embodiment 1 of this utility model.

[0029] Figure 3 This is a cross-sectional view of the pre-extraction filter structure of Embodiment 2 of this utility model.

[0030] Figure 4 This is a schematic diagram of the lower mounting base of the pre-extraction filter structure in Embodiment 2 of this utility model.

[0031] Figure 5 This is a cross-sectional view of the pre-extraction filter structure of Embodiment 3 of this utility model.

[0032] Figure 6 This is a cross-sectional view of the pre-extraction filter structure of Embodiment 4 of this utility model.

[0033] Figure 7 and Figure 8 These are cross-sectional views of the pre-evacuation and filtration structure of the Roots vacuum pump according to Embodiment 4 of this utility model from different angles.

[0034] In the diagram, 01 is the end cap; 02 is the filter device; 03 is the vacuum chamber; 04 is the lubricating oil chamber; and 05 is the oil seal.

[0035] 1. Cover body; 11. Filter chamber; 111. Stepped chamber; 112. Intermediate wall; 12. First air passage; 13. Second air passage;

[0036] 2. Cover;

[0037] 3. Cover screws;

[0038] 4. Filter components;

[0039] 5. Inner mounting base 5; 51. Threaded hole; 52. Vent hole; 53. Large diameter section; 54. Small diameter section; 55. Sealing groove;

[0040] 6. External mounting bracket 6;

[0041] 7. Filter screw;

[0042] 8. O-rings;

[0043] 9. Cushioning pad. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be explained and described below. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0045] See Figures 1 to 8 This utility model discloses a pre-evacuation filtration structure for a Roots vacuum pump. The Roots vacuum pump has a lubricating oil chamber, a vacuum chamber, and an oil seal. The pre-evacuation filtration structure for the Roots vacuum pump includes:

[0046] Filter chamber;

[0047] The filtration device is located in the filtration chamber;

[0048] The first air passage connects the filter chamber and the lubricating oil chamber;

[0049] The second gas path connects the filter chamber and the vacuum chamber;

[0050] The filter device includes a filter assembly and an outer mounting base 6 and / or an inner mounting base 5. The filter assembly is mounted on the outer mounting base 6 or the inner mounting base 5. The inner mounting base 5 is sealed to the filter chamber and has multiple vent holes.

[0051] The pre-evacuation filtration structure of the Roots vacuum pump of this utility model embodiment has a filter chamber, a first gas path, and a second gas path. The filter chamber, the first gas path, and the second gas path form a pre-evacuation passage connecting the vacuum chamber and the lubricating oil chamber, reducing the pressure difference between the vacuum chamber and the lubricating oil chamber. This ensures that the pressure difference between the vacuum chamber and the lubricating oil chamber is less than the sealing pressure range of the oil seal, thereby preventing mutual penetration between the lubricating oil and the pumped medium at the oil seal. The filtration device prevents lubricating oil from flowing from the lubricating oil chamber into the vacuum chamber, and also prevents the pumped medium from entering the lubricating oil chamber. When the filtration device includes an inner mounting base 5 with multiple vent holes, compared with the prior art structure using screw venting, there is no need to machine radial holes on the screws with smaller diameters, making processing easier, resulting in a larger filtration area and higher filtration efficiency. When the filtration device includes an outer mounting base 6 but not an inner mounting base 5, the filter assembly can be directly connected to the filter chamber, resulting in a larger filtration area. There is also no need to machine radial holes on the screws with smaller diameters, making processing easier.

[0052] Example 1

[0053] See Figure 1 and Figure 2 According to Embodiment 1 of this utility model, a pre-evacuation filtration structure for a Roots vacuum pump is provided. The Roots vacuum pump has a lubricating oil chamber 04, a vacuum chamber 03, and an oil seal 05. The pre-evacuation filtration structure for the Roots vacuum pump includes:

[0054] Filter chamber 11;

[0055] Filter device 02 is installed in filter chamber 11;

[0056] The first air passage 12 connects the filter chamber 11 and the lubricating oil chamber 04;

[0057] The second gas passage 13 connects the filter chamber 11 and the vacuum chamber 03;

[0058] The filter device 02 includes a filter assembly 4 and an outer mounting base 6 and / or an inner mounting base 5. The filter assembly 4 is mounted on the outer mounting base 6 or the inner mounting base 5. The inner mounting base 5 is sealed to the filter chamber 11. Multiple vent holes 52 are opened on the inner mounting base 5.

[0059] In this embodiment, the filter device 02 includes an inner mounting base 5, on which a threaded hole 51 is formed, and multiple vent holes 52 surround the threaded hole 51. The filter assembly 4 is mounted on the inner mounting base 5 by filter screws 7. The filter screws 7 are capped screws, and a gasket is also provided between the filter screws 7 and the filter assembly 4.

[0060] In this embodiment, the filter chamber 11 has a stepped cavity 111, and the inner mounting seat 5 abuts against the middle wall 112 of the stepped cavity 111.

[0061] In this embodiment, the axis of the filter chamber 11 is vertical, and the radial (or horizontal) cross-section of the filter chamber 11 is circular. In other embodiments, the filter chamber 11 may also be oriented in other ways, and the axis of the filter chamber 11 may be horizontal or at other angles.

[0062] In this embodiment, the inner mounting base 5 is T-shaped and has a large diameter section 53 and a small diameter section 54. The large diameter section 53 of the inner mounting base 5 abuts against the middle wall 112 of the stepped cavity 111. An O-ring 8 is provided on the small diameter section 54 of the inner mounting base 5, and the O-ring 8 seals the inner mounting base 5 with the filter chamber 11.

[0063] In this embodiment, the filter chamber 11 is formed by the end cap 01 of the Roots vacuum pump. The end cap 01 includes a cap body 1 and a cover 2. The cover 2 is fixed to the cap body 1 by a cap screw 3 and indirectly abuts against the filter assembly 4.

[0064] In this embodiment, the filter device 02 includes an outer mounting base 6, a cover 2 abutting against the outer mounting base 6, the outer mounting base 6 abutting against the filter assembly 4, and an O-ring 8 provided on the outer mounting base 6, which seals the outer mounting base 6 and the filter chamber 11.

[0065] In this embodiment, the filter chamber 11 is formed by the end cover 01 of the Roots vacuum pump. The end cover 01 includes a cover body 1 and a sealing cover 2. The sealing cover 2 is fixed to the cover body 1 by cover screws 3 and abuts against the outer mounting base 6.

[0066] In this embodiment, an O-ring 8 is provided on the outer mounting base 6, which seals the outer mounting base 6 and the filter chamber 11. In other embodiments, the cover 2 is sealed to the cover body 1, and the outer mounting base 6 does not need to be sealed to the filter chamber 11.

[0067] In this embodiment, the filter chamber 11 is formed directly when the cover body 1 of the end cover 01 is formed.

[0068] In this embodiment, the filter device 02 component includes filter cotton. In other embodiments, the filter component 4 includes filter cotton and a filter screen.

[0069] In this embodiment, the angle between the center of the first air passage 12 and the center of the filter chamber 11 is 15° to 45°, and the angle between the second air passage 13 and the center of the filter chamber 11 is 15° to 45°, so as to avoid or reduce dust and impurities from falling into the first air passage 12 and the second air passage 13.

[0070] In this embodiment, the inner mounting base 5 is a single part, and the outer mounting base 6 is an assembly. In other embodiments, the inner mounting base 5 and the outer mounting base 6 can be single parts or assemblies.

[0071] The pre-evacuation filtration structure of the Roots vacuum pump in Embodiment 1 of this utility model has a filter chamber 11, a first air passage 12, and a second air passage 13. The filter chamber 11, the first air passage 12, and the second air passage 13 form a pre-evacuation passage connecting the vacuum chamber 03 and the lubricating oil chamber 04, reducing the pressure difference between the vacuum chamber 03 and the lubricating oil chamber 04. This ensures that the pressure difference between the vacuum chamber 03 and the lubricating oil chamber 04 is less than the sealing pressure range of the oil seal 05, thereby preventing mutual permeation between the lubricating oil and the pumped medium at the oil seal 05. The filter device 02 prevents lubricating oil from flowing out of the vacuum chamber 03 and also prevents the pumped medium from entering the lubricating oil chamber 04. The filter device 02 includes an inner mounting base 5 with multiple vent holes 52. Compared with the prior art's screw-venting structure, it eliminates the need to machine radial holes on small-diameter screws, making processing easier, resulting in a larger filtration area and higher filtration efficiency.

[0072] Example 2

[0073] The difference between Embodiment 2 and Embodiment 1 lies in the inner mounting base 5.

[0074] See Figure 3 and Figure 4In this embodiment, the inner mounting base 5 is flat. The structure of the inner mounting base 5 is simpler, and the O-ring 8 on the inner mounting base 5 is omitted. However, the sealing performance between the inner mounting base 5 and the filter chamber 11 is lower than that in the first embodiment.

[0075] Example 3

[0076] See Figure 5 In this embodiment, the filter device 02 includes an outer mounting base 6 but no inner mounting base 5. The outer mounting base 6 has a threaded hole 51, and the filter assembly 4 is mounted on the outer mounting base 6 by a filter screw 7.

[0077] In this embodiment, the filter chamber 11 has a stepped cavity 111, and the filter assembly 4 abuts against the middle wall 112 of the stepped cavity 111.

[0078] In this embodiment, the filter device 02 includes an outer mounting base 6 but not an inner mounting base 5. The filter assembly 4 is directly connected to the filter chamber 11, resulting in a larger filtration area. It also eliminates the need to machine radial holes in screws with smaller diameters, making the process easier.

[0079] Example 4

[0080] See Figures 6 to 8 The cover 2 is sealed to the cover body 1 by cover screws, and the outer mounting base 6 is sealed to the cover body 1 by cover screws 3 and buffer pads 9. The outer mounting base 6 is a single part, and the filter screw 7 is a stepped screw. The cover 2 restricts the axial movement of the filter screw 7 and the inner mounting base 5. In addition to its sealing function, the buffer pad 9 also prevents the cover 2 from buckling due to the force of the filter screw 7.

[0081] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the content described in the above specific embodiments. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A pre-evacuation filtration structure for a Roots vacuum pump, the Roots vacuum pump having a lubricating oil chamber (04), a vacuum chamber (03), and an oil seal (05), characterized in that: The pre-evacuation filter structure of the Roots vacuum pump includes: Filter chamber (11); A filter device (02) is installed in the filter chamber (11); The first air passage (12) connects the filter chamber (11) and the lubricating oil chamber (04); The second gas path (13) connects the filter chamber (11) and the vacuum chamber (03); The filter device (02) includes a filter assembly (4), and the filter device (02) also includes an outer mounting base (6) and / or an inner mounting base (5). The filter assembly (4) is mounted on the outer mounting base (6) or the inner mounting base (5). The inner mounting base (5) is sealed to the filter chamber (11). Multiple vent holes (52) are opened on the inner mounting base (5).

2. The pre-evacuation and filtration structure of a Roots vacuum pump according to claim 1, characterized in that: The filter device (02) includes an inner mounting base (5), a threaded hole (51) is provided on the inner mounting base (5), and a plurality of vent holes (52) surround the threaded hole (51). The filter assembly (4) is mounted on the inner mounting base (5) by filter screws (7).

3. The pre-evacuation and filtration structure of a Roots vacuum pump according to claim 2, characterized in that: The filter chamber (11) has a stepped cavity (111), and the inner mounting seat (5) abuts against the middle wall (112) of the stepped cavity (111).

4. The pre-evacuation and filtration structure of a Roots vacuum pump according to claim 2, characterized in that: The inner mounting base (5) is T-shaped. The large diameter section (53) of the inner mounting base (5) abuts against the middle wall (112) of the stepped cavity (111). An O-ring (8) is provided on the small diameter section (54) of the inner mounting base (5). The O-ring (8) seals the inner mounting base (5) and the filter chamber (11). Alternatively, the inner mounting base (5) is flat.

5. The pre-evacuation and filtration structure of a Roots vacuum pump according to claim 2, characterized in that: The filter chamber (11) is formed by the end cap (01) of the Roots vacuum pump. The end cap (01) includes a cap body (1) and a cover (2). The cover (2) is fixed to the cap body (1) by a cap screw (3). The cover (2) directly or indirectly abuts against the filter assembly (4).

6. The pre-evacuation and filtration structure of a Roots vacuum pump according to claim 5, characterized in that: The filter device (02) includes an outer mounting base (6), a cover (2) abutting against the outer mounting base (6), the outer mounting base (6) abutting against the filter assembly (4), and an O-ring (8) provided on the outer mounting base (6), which seals the outer mounting base (6) and the filter chamber (11).

7. The pre-evacuation filter structure of a Roots vacuum pump according to claim 1, characterized in that: The filter device (02) includes an outer mounting base (6), on which a threaded hole (51) is provided, and the filter assembly (4) is mounted on the outer mounting base (6) by a filter screw (7).

8. The pre-evacuation filter structure of a Roots vacuum pump according to claim 7, characterized in that: The filter chamber (11) is formed by the end cover (01) of the Roots vacuum pump. The end cover (01) includes a cover body (1) and a cover (2). The cover (2) is fixed to the cover body (1) by cover screws (3). The cover (2) abuts against the outer mounting seat (6). The cover (2) is sealed with the cover body (1). Alternatively, the outer mounting seat (6) is provided with an O-ring (8). The O-ring (8) seals the outer mounting seat (6) and the filter chamber (11).

9. The pre-evacuation filter structure of a Roots vacuum pump according to claim 7, characterized in that: The filter chamber (11) has a stepped cavity (111), and the filter assembly (4) abuts against the intermediate wall (112) of the stepped cavity (111).

10. The pre-evacuation filter structure of a Roots vacuum pump according to claim 1, characterized in that: The filter assembly (02) includes filter cotton, or the filter assembly (4) includes filter cotton and a filter screen; and / or, The angle between the center of the first air passage (12) and the center of the filter chamber (11) is 15° to 45°; and / or, The angle between the center of the second air passage (13) and the center of the filter chamber (11) is 15° to 45°.

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