CN214944887U

CN214944887U - Oil level gauge for air compressor and air compressor

Info

Publication number: CN214944887U
Application number: CN202120013655.8U
Authority: CN
Inventors: 郭志伟; E·阿夫沙尔; 赵秀英; A·克劳姆利希
Original assignee: Knorr Bremse Nankou Air Supply Unit Beijing Co Ltd
Current assignee: Knorr Bremse Nankou Air Supply Unit Beijing Co Ltd
Priority date: 2021-01-05
Filing date: 2021-01-05
Publication date: 2021-11-30
Anticipated expiration: 2031-01-05

Abstract

The utility model provides an oil level gaugember for air compressor, wherein, the oil level gaugember includes: a housing (1), the housing (1) delimiting a chamber and having an observation window for observing an oil level and a high oil level indicating line (11) and a low oil level indicating line (12), the housing (1) having opposite ends in a longitudinal direction of the observation window; a first pipe (2) connected to the housing (1) at one end of the housing (1); and a second tube (3) connected to the housing (1) at the other end of the housing (1), wherein the first tube (2) and/or the second tube (3) extends along a curved path, and/or the first tube (2) and/or the second tube (3) is extendable along a curved path. An air compressor is also presented. By means of the utility model discloses, can make the shape, the size of the casing of oil level gaugember and the mounted position on the oil tank receive less restriction. In particular, the modification of the oil level gauge can be realized at low cost.

Description

Oil level gauge for air compressor and air compressor

Technical Field

The utility model relates to an oil level gaugember and an air compressor for air compressor.

Background

In air compressors, such as screw compressors, lubrication oil is typically used to lubricate and cool the various components of the air compressor, and whether the oil supply system is normal or not is directly related to the normal operation and service life of the air compressor. If the amount of oil in the air compressor is too low (e.g., due to a failure of the lubrication oil circulation system) and the air compressor continues to operate, the air compressor may eventually fail and fail.

In order to check whether the oil amount of the air compressor is sufficient, it is a common practice that an operator observes through an oil level mirror of the air compressor in an oil amount check state of the air compressor. The oil level mirror is mounted, for example, on a tank body of an oil tank of the air compressor, and is capable of displaying an oil level in the oil tank. There is known an oil level mirror formed substantially in the shape of a bolt. The screw-shaped head is provided with a cavity and a circular window through which the oil level in the cavity can be observed. The high oil level marking line and the low oil level marking line are respectively arranged beside the observation window and are adjacent to the highest point and the lowest point of the observation window. The bolt-shaped screw portion is provided with an external thread and is configured to be able to be fixed to a mounting hole formed on a tank body of the oil tank. When the oil level mirror is mounted on the tank body, the cavity communicates to the inner space of the tank body only through the communication hole extending in the screw portion, so that the oil level in the cavity is the same as the oil level in the tank body.

When the oil amount is checked, the oil level of the lubricating oil is between the high oil level indicating line and the low oil level indicating line of the oil level mirror. However, as the operating conditions of the air compressor change, the oil level in the oil tank may change significantly. The oil level may drop below the low oil level indicator line. In the conventional oil level mirror, when the oil level drops below the low oil level indicating line, there may be a case where the oil level drops below the display range of the oil level mirror, so that the oil level mirror cannot display the oil level. This makes it impossible for an operator to observe the oil level from the oil level mirror, for example, when the air compressor is running under load. In other words, the existing oil level mirror is designed only to display the oil level in the oil tank when an oil level check is performed, without considering other operating conditions of the air compressor. Because the oil level scope that this oil level mirror can show is narrower, consequently, set up the oil gauge on the box additionally. If the oil level exceeds the display range of the oil level mirror, the oil scale needs to be unscrewed for inspection.

This oil level mirror of the prior art is directly fixed to the tank body of the oil tank by a screw portion located behind the cavity, and communicates the cavity to the inner space of the tank body through a communication hole extending in the screw portion. This allows the range of the oil level that the oil level mirror can display to be associated with the communication hole in the screw portion and to be limited by the size of the mounting hole on the tank. Therefore, if the oil level mirror needs to be modified, the cost is high and the flexibility is low.

Thus, existing oil level mirrors for air compressors still have deficiencies in terms of the range of oil levels that can be displayed, as well as the cost and flexibility of retrofitting.

SUMMERY OF THE UTILITY MODEL

An object of the present invention is to provide an improved oil level indicator for an air compressor to overcome at least one of the above-mentioned drawbacks of the prior art.

According to a first aspect of the present invention, there is provided an oil level gauge for an air compressor, wherein the oil level gauge comprises: a housing that delimits a chamber and has a viewing window for viewing an oil level and a high oil level indicating line and a low oil level indicating line, the housing having opposite ends in a longitudinal direction of the viewing window; a first tube connected to the housing at one end thereof; and a second tube connected to the housing at the other end of the housing, wherein the first tube and/or the second tube extends along a curved path, and/or the first tube and/or the second tube is extendable along a curved path.

According to an exemplary embodiment, the housing is provided with a viewing opening at the viewing window, said viewing opening extending in the longitudinal direction of the viewing window, the at least translucent window panel sealingly closing said viewing opening.

According to an exemplary embodiment, a high oil level indicator line and a low oil level indicator line are arranged next to the viewing opening, wherein the high oil level indicator line is spaced apart from the low oil level indicator line by an indicator distance.

According to an exemplary embodiment, the viewing opening terminates in opposite first and second end points in the longitudinal direction of the viewing window, wherein the high oil level indicator line is closer to the first end point and the high oil level indicator line is spaced from the first end point by a first distance in the longitudinal direction of the viewing window, the low oil level indicator line is closer to the second end point and the low oil level indicator line is spaced from the second end point by a second distance in the longitudinal direction of the viewing window, wherein: the first distance and/or the second distance is large enough to enable the oil level of the oil tank of the air compressor to be displayed through the viewing opening in all normal states of the air compressor; and/or the first distance and/or the second distance is at least 0.8 times the index distance; and/or the second distance is greater than the first distance and/or the index distance.

According to an exemplary embodiment, the housing has an oil drain opening communicating to the chamber, the oil block being detachably arranged at the oil drain opening and being arranged for sealingly closing the oil drain opening.

According to an exemplary embodiment, the oil drain opening is flush with the high oil level indicator line, seen in the longitudinal direction of the viewing window.

According to an exemplary embodiment, the housing comprises a connecting structure adapted to fix the housing to an oil tank of the air compressor, the connecting structure being arranged laterally of the observation window, seen in a longitudinal direction of the observation window; and/or the first tube and/or the second tube are configured as rigid tubes; and/or the inner diameter of the second tube is set to be at least 8 mm; and/or the second tube has an inner diameter greater than the inner diameter of the first tube.

According to an exemplary embodiment, the first tube is connected to a filler plug, which is arranged to be mounted to a filler opening of the fuel tank and has a filler opening, which is arranged to be opened and closed for filling the fuel tank with fuel via the filler opening.

According to an exemplary embodiment, the filler plug includes a plug body and a plug cap, wherein the plug body has a through hole having one end provided to be extendable into or connected to a filler opening when the filler plug is mounted to the filler opening of the fuel tank, and the other end of the through hole forms a filler opening.

According to a second aspect of the present invention, an air compressor is provided, wherein the air compressor comprises an oil level gauge according to the present invention.

The utility model has the advantages of: according to the present invention, since the first pipe and/or the second pipe is provided to extend along a curved path or the first pipe and/or the second pipe is provided to extend along a curved path, the first pipe and/or the second pipe of the oil level gauge can be flexibly connected to different positions of the oil tank, while the shape, size, and mounting position of the housing of the oil level gauge on the oil tank are less restricted, particularly not restricted by the mounting position of the first pipe and/or the second pipe on the oil tank. Thereby, especially a low cost retrofitting of the oil level gauge can be achieved.

For example, oil level gauges having different shapes and sizes can be mounted to an existing oil tank without changing the tank body of the oil tank. Also, for example, an oil level gauge capable of displaying different ranges of oil levels may be mounted to an existing oil tank without changing the tank body of the oil tank.

Drawings

The principles, features and advantages of the present invention may be better understood by describing the invention in more detail below with reference to the accompanying drawings. The drawings comprise:

fig. 1 schematically shows a perspective view of an oil level gauge according to an exemplary embodiment of the present invention;

fig. 2 schematically shows a front view of a first half-shell of an oil level gauge according to an exemplary embodiment of the present invention; and

fig. 3 schematically shows an oil level gauge according to an exemplary embodiment of the present invention.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and a plurality of exemplary embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the scope of the invention.

The principles of the present application will be described in detail below with respect to a screw air compressor as an example. However, it should be understood by those skilled in the art that the present application is not limited to screw air compressors, but is applicable to any air compressor that uses lubricating oil.

Screw compressors consist of a pressure vessel, such as an oil tank or oil separator, in which lubricating oil is collected to form an oil sump. Screw compressors are used, for example, in vehicles for generating compressed air, in particular for generating the compressed air required for a brake system. Screw compressors are particularly useful for providing compressed air for braking of railroad trains. The lubricating oil is continuously conveyed out of the oil tank for lubricating and cooling the components of the screw compressor, in particular the moving components.

Fig. 1 schematically shows a perspective view of an oil level gauge according to an exemplary embodiment of the present invention. The oil level gauge includes: a housing 1, the housing 1 defining a chamber and having a viewing window for viewing an oil level, and a high oil level indicating line 11 and a low oil level indicating line 12, the housing 1 having opposite ends in a longitudinal direction of the viewing window; a first pipe 2 connected to the housing 1 at one end of the housing 1; and a second tube 3 connected to the housing 1 at the other end of the housing 1, wherein the first tube 2 and/or the second tube 3 extend along a curved path, and/or the first tube 2 and/or the second tube 3 can extend along a curved path. In this context, the "longitudinal direction" of an object means the direction along which the object has the largest extension.

The oil level gauge may be connected to the oil tank through the first and

second pipes

2 and 3 such that the chamber communicates with the inner space of the oil tank through the first and

second pipes

2 and 3. Thereby, the lubricating oil in the oil tank can flow into the housing 1 through the second pipe 3, and the gas in the oil tank, for example, pressurized air, can flow into the housing 1 through the second pipe 3 so that the oil level in the housing 1 is flush with the oil level in the oil tank. The operator can visually check the oil level in the oil tank through the observation window of the housing 1. Since the first pipe 2 and/or the second pipe 3 are provided to extend along a curved path or the first pipe 2 and/or the second pipe 3 are provided to be extendable along a curved path, the first pipe 2 and/or the second pipe 3 of the oil level gauge can be flexibly connected to the oil tank at different positions, and the shape, size, and mounting position on the oil tank of the housing 1 of the oil level gauge are not necessarily limited by the mounting position of the first pipe 2 and/or the second pipe 3 on the oil tank. Thus, modification of the oil level gauge can be achieved at low cost. For example, different shapes and sizes of fuel level gauges may be fitted to an existing fuel tank without having to change the tank body of the fuel tank.

As described above, in the conventional screw compressor, there is provided an oil level mirror which is directly fixed to the tank of the oil tank by the screw portion located behind the cavity, and communicates the cavity to the inner space of the tank only through the communication hole extending in the screw portion. Therefore, the range of the oil level that the oil level mirror can display is associated with the highest point and the lowest point of the communication hole, and in turn, with the size of the screw portion and the size of the mounting hole on the tank body. For example, when a large display range is required, the distance between the highest point and the lowest point of the communication hole needs to be increased accordingly, the size of the screw portion needs to be increased accordingly, but the mounting hole in the case body cannot be increased accordingly, or the case body needs to be modified to, for example, provide a corresponding new mounting hole for mounting the screw portion. This would require a considerable expenditure of time and money.

In contrast, the shape and dimensions of the housing 1 and thus of the observation window of the oil level indicator according to the present invention are not necessarily limited by the mounting position of the first tube 2 and/or the second tube 3 on the oil tank. According to the utility model discloses, when needs are remodeled the oil level gaugember, only need to change the extension route of first pipe 2 and/or second pipe 3, can adapt current box. In addition, if it is necessary to change the installation position of the oil level gauge on the tank, for example, to change the installation height, an existing tank can be adapted simply by changing the extending path of the first pipe 2 and/or the second pipe 3.

As shown in fig. 1, the housing 1 is, for example, configured in the form of a strip, in particular in the form of a substantially rectangular parallelepiped. The length of the housing 1 extending in the longitudinal direction is significantly greater than its width perpendicular to the longitudinal direction, for example the length of the housing 1 may be at least 2.5 times, in particular 3 times, the width of the housing 1. It is understood that the housing 1 may be configured in other shapes as well, such as circular, triangular, etc. The housing 1 may delimit a large chamber for receiving lubricating oil, which is advantageous for preventing clogging.

Optionally, the casing 1 comprises, for example, a first half-shell 13 and a second half-shell 14, the first half-shell 13 and the second half-shell 14 being fixed to each other in a sealed manner. For example, the first half-shell 13 may be connected to the second half-shell 14 by screws, with a seal being provided between the first half-shell 13 and the second half-shell 14. The first half-shell 13 and the second half-shell 14 may be made of, for example, aluminum alloy.

The second half-shell 14 may have a first connection opening to which the first pipe 2 is mounted and a second connection opening to which the second pipe 3 is mounted at both ends, respectively. The first tube 2 and/or the second tube 3 may be configured as a rigid tube. In particular, the first tube 2 and/or the second tube 3 may be configured to be able to withstand a pressure of at least 10bar, in particular at least 15 bar. For example, the first tube 2 and/or the second tube 3 may be made of stainless steel. It is understood that the first tube 2 and/or the second tube 3 may also be constructed as hoses, as long as they are able to accommodate the temperature and pressure within the screw compressor.

The housing 1 is provided with an observation opening 15 at the observation window, said observation opening 15 extending in the longitudinal direction of the observation window. A high oil level indicator line 11 and a low oil level indicator line 12 are arranged next to the observation opening 15, wherein the high oil level indicator line 11 is spaced apart from the low oil level indicator line 12 by an indicator distance L₀. The high oil level indicating line 11 and the low oil level indicating line 12 may be provided with corresponding indicators, such as the characters "MAX" and "MIN" shown in the drawings, respectively. An at least translucent window pane sealingly closes said viewing opening 15. Herein, "at least translucent" includes both the case of "translucent" and the case of "transparent". A viewing opening 15 may be provided in the first half-shell 13, the louver being correspondingly attached to the second half-shellA half-shell 13. The window panel is made of a material such as polycarbonate or glass.

Fig. 2 schematically shows a front view of the first half-shell 13 of the oil level gauge according to an exemplary embodiment of the present invention. The viewing opening 15 ends in the longitudinal direction of the viewing window at a first end point 151 and a second end point 152 which are opposite, wherein the high oil level indicator line 11 is closer to the first end point 151 and the high oil level indicator line 11 is spaced apart from the first end point 151 by a first distance L in the longitudinal direction of the viewing window₁The low oil level indicating line 12 is closer to the second end point 152 and the low oil level indicating line 12 is spaced apart from the second end point 152 by a second distance L in the longitudinal direction of the observation window₂. First distance L₁And/or the second distance L₂Large enough to enable the oil level of the oil tank of the screw compressor to be displayed through the viewing opening 15 in all normal conditions of the screw compressor. This enables the operator to observe the oil level at any time. Additionally, an oil gauge is not required to be additionally arranged on the oil tank. The normal state of the air compressor includes an operation state of the air compressor with a normal amount of oil, a stop state, and an oil amount check state.

Generally, when the oil amount check is performed, the oil level of the lubricating oil should be between the high oil level indicating line 11 and the low oil level indicating line 12 of the oil level gauge. For example, the oil amount check is performed under the condition that the screw compressor is operated for 5 minutes and then stopped for 5 to 20 minutes, and the oil amount is checked in this time range.

As the operating conditions of the screw compressor change, the oil level in the oil tank may change significantly. In screw compressors for railroad trains, the oil level in the tank varies particularly significantly. For example, when the screw compressor is operated, the lubricating oil is transported out of the oil tank and distributed at various locations of the screw compressor, such as the screw, the pipes, the cooler, etc. This causes the oil level in the tank to drop and is likely to drop below the low level indicator line 12. At this time, the oil level in the oil tank may be, for example, within a range shown by a dotted line in fig. 2.

When the screw compressor is shut down for a long period of time, for example 7-8 hours, the oil level in the oil tank may rise somewhat, but still may be below the low oil level indicator line 12. In this case, the oil level in the oil tank may be in a range shown by a chain line in fig. 2, for example.

Optionally, the first distance L₁And/or the second distance L₂Can be set to at least the marking distance L₀0.8 times, in particular 1 time.

Second distance L₂Can be set to be greater than the first distance L₁. Under various operating conditions of the screw compressor, the oil level in the oil tank is likely to drop below the low oil level designation line 12. This arrangement is advantageous for achieving that the oil level of the oil tank of the screw compressor can be observed through the observation opening 15 in all normal states of the screw compressor.

In particular, the second distance L₂Can be set to be greater than the marking distance L₀For example, it can be set to indicate the distance L₀At least 1.2 times. This is particularly advantageous for achieving that the oil level of the oil tank of the screw compressor, in particular for a screw compressor for a railway train, can be observed through the observation opening 15 in all normal states of the screw compressor.

Optionally, the casing 1 has a drain opening 16 (not visible in the figures, the reference numeral 16 only schematically indicating the position of the drain opening), said drain opening 16 being connected to the chamber, and an oil plug 17 is detachably provided at said drain opening 16 and arranged to be able to sealingly close said drain opening 16. Excess lubricating oil can be drained from the oil tank through the drain port 16. For example, the addition of too much lubricating oil to the screw compressor can be avoided.

The drain opening 16 can in particular be flush with the high oil level indicator line 11 in the longitudinal direction of the viewing window. In other words, the drain opening 16 may be flush with the high oil level indication line 11 as viewed in the vertical direction. Thereby, it is advantageous to control the oil level in the tank below the high oil level indication line 11. For example, the oil block 17 may be opened when oil is added to the oil tank. If too much lubricant is added so that the oil level exceeds the high level indicator line 11, excess lubricant will flow out through the drain opening 16.

Optionally, the casing 1 comprises a projection 18 projecting laterally with respect to the longitudinal direction of the observation window, said projection 18 having a connection structure 181, said connection structure 181 being arranged to enable fixing of the casing 1 to the oil tank of the screw compressor. The connection structure 181 may comprise, for example, (threaded) holes, bolts, spacers, etc. Thereby, the housing 1 of the oil level gauge can be firmly fixed to the screw compressor. Meanwhile, the shape, size, and installation height of the housing 1 of the oil level gauge are not excessively affected by the connection structure 181. In other words, the connection structure 181 of the housing 1 is provided at the side of the observation window, not above or below, which is advantageous in achieving flexible modification of the oil level gauge at low cost.

The first tube 2 is connectable to a filler plug 4, said filler plug 4 being arranged to be mountable to a filler opening of a fuel tank and having a filler opening arranged to be openable and closable for filling the fuel tank with fuel via the filler opening. The filler plug 4 is detachably connectable to a filler opening of a fuel tank, for example, by a screw structure. The filler plug 4 may be part of a fuel level gauge. Alternatively, the filler plug 4 may also be provided as a separate component with respect to the oil level gauge.

The first pipe 2 can thus be connected to the filler opening of the tank by means of the filler plug 4, which eliminates the need for a further connection opening in the tank for connecting the first pipe 2. The filler opening is normally located in the upper part of the tank and is not flooded with lubricant, a location which is particularly suitable for mounting the first tube 2 so that the air pressure in the chamber of the oil level indicator is maintained in line with the air pressure in the tank. This is particularly important for the accuracy of the oil level display.

The filler plug 4 includes, for example, a plug main body 41 and a plug cap 42, wherein the plug main body 41 has a through hole 411, one end of the through hole 411 is provided to be able to extend into or connect to a filler opening when the filler plug 4 is mounted to the filler opening of the fuel tank, and the other end of the through hole 411 forms a filler opening. The plug cap 42 may be removably attached to the filler opening by a threaded arrangement. When lubricating oil is required to be added, the oil can be filled into the oil tank through the oil filling opening only by opening the plug cap 42.

The plug body 41 has a lateral opening 412, the lateral opening 412 extending laterally, substantially perpendicularly with respect to the through hole 411, and communicating to the through hole 411. The first tube 2 is connected to the lateral opening 412.

In general, in a screw compressor, the temperature is different in each part. In the operating state of the fuel level gauge, the first pipe 2 is connected to the upper part of the tank, normally at a higher temperature, and the second pipe 3 is connected to the lower part of the tank, normally at a lower temperature. Too low a temperature may cause the oil to cake and become clogged.

In an exemplary embodiment, the inner diameter of the second tube 3 is set to be at least 8 mm. Thus, the oil level gauge can be made adaptable to a low ambient temperature without clogging in the pipe. For example, the oil level gauge is configured to be able to accommodate ambient temperatures of-40 ℃ to +55 ℃.

Alternatively or additionally, the inner diameter of the second tube 3 is larger than the inner diameter of the first tube 2. This is also advantageous in preventing clogging from occurring in the oil level gauge.

Sealing parts can be arranged at the joint between the components of the oil level gauge and the oil tank of the screw compressor according to requirements so as to prevent lubricating oil from leaking.

The components of the oil level gauge are configured to be able to withstand high temperatures of at least 100 ℃, in particular 120 ℃, and pressures of at least 10bar, in particular at least 15 bar.

Although specific embodiments of the invention have been described in detail herein, they have been presented for purposes of illustration only and are not to be construed as limiting the scope of the invention. Various substitutions, alterations, and modifications may be devised without departing from the spirit and scope of the present invention.

List of reference numerals

Housing 1

High oil level indicating line 11

Low oil level indicating line 12

First half-shell 13

Second half-shell 14

Viewing opening 15

First endpoint 151

Second end point 152

Oil drain port 16

Oil block 17

Projection 18

Connection structure 181

First pipe 2

Second pipe 3

Oil filler plug 4

Plug body 41

Through hole 411

Lateral opening 412

Plug 42

Indicating a distance L₀

First distance L₁

Second distance L₂

Claims

1. An oil level gauge for an air compressor, the oil level gauge comprising:

a housing (1), the housing (1) delimiting a chamber and having an observation window for observing an oil level and a high oil level indicating line (11) and a low oil level indicating line (12), the housing (1) having opposite ends in a longitudinal direction of the observation window;

a first pipe (2) connected to the housing (1) at one end of the housing (1); and

a second tube (3) connected to the housing (1) at the other end of the housing (1), wherein,

the first tube (2) and/or the second tube (3) extend along a curved path, and/or the first tube (2) and/or the second tube (3) can extend along a curved path.

2. Oil level indicator according to claim 1, characterized in that the housing (1) is provided with a viewing opening (15) at the viewing window, said viewing opening (15) extending in the longitudinal direction of the viewing window, an at least translucent window plate sealingly closing said viewing opening (15).

3. Oil level indicator according to claim 2, characterized in thatA high oil level marking line (11) and a low oil level marking line (12) are arranged beside the observation opening (15), wherein the high oil level marking line (11) and the low oil level marking line (12) are separated by a marking distance (L)₀)。

4. Oil level indicator according to claim 3, characterized in that the viewing opening (15) ends in a longitudinal direction of the viewing window at opposite first (151) and second (152) end points, wherein the high oil level indicator line (11) is closer to the first end point (151) and the high oil level indicator line (11) is spaced from the first end point (151) by a first distance (L) in the longitudinal direction of the viewing window₁) The low-oil-level marking line (12) is closer to the second end point (152) and the low-oil-level marking line (12) is spaced from the second end point (152) by a second distance (L) in the longitudinal direction of the viewing window₂) Wherein:

first distance (L)₁) And/or a second distance (L)₂) Is large enough to enable the oil level of the oil tank of the air compressor to be displayed through the viewing opening (15) in all normal conditions of the air compressor; and/or

First distance (L)₁) And/or a second distance (L)₂) At least the marked distance (L)₀) 0.8 times of; and/or

Second distance (L)₂) Greater than the first distance (L)₁) And/or indicating a distance (L)₀)。

5. Oil level indicator according to any one of claims 1-4, characterized in that the housing (1) has an oil drain opening (16), said oil drain opening (16) being connected to the chamber, an oil plug (17) being detachably arranged at said oil drain opening (16) and being arranged adapted to sealingly close said oil drain opening (16).

6. Oil level indicator according to claim 5, characterized in that the drain opening (16) is flush with the high oil level indicator line (11) seen in the longitudinal direction of the viewing window.

7. Oil level indicator according to any one of claims 1-4, 6,

the housing (1) comprises a connecting structure (181) adapted to fix the housing (1) to an oil tank of the air compressor, said connecting structure (181) being arranged laterally of the observation window, seen in the longitudinal direction of the observation window; and/or

The first pipe (2) and/or the second pipe (3) is/are designed as a rigid pipe; and/or

The inner diameter of the second tube (3) is set to be at least 8 mm; and/or

The inner diameter of the second tube (3) is larger than the inner diameter of the first tube (2).

8. Oil level indicator according to claim 5,

The inner diameter of the second tube (3) is set to be at least 8 mm; and/or

9. Level indicator according to any one of claims 1-4, 6, 8, characterized in that the first tube (2) is connected to a filler plug (4), said filler plug (4) being arranged to be mounted to a filler opening of a fuel tank and having a filler opening arranged to be opened and closed for filling the fuel tank with fuel via the filler opening.

10. Level indicator according to claim 5, characterized in that the first tube (2) is connected to a filler plug (4), said filler plug (4) being arranged to be mounted to a filler opening of a fuel tank and having a filler opening arranged to be opened and closed for filling the fuel tank with fuel via the filler opening.

11. Level indicator according to claim 7, characterized in that the first tube (2) is connected to a filler plug (4), said filler plug (4) being arranged to be mounted to a filler opening of a fuel tank and having a filler opening arranged to be opened and closed for filling the fuel tank with fuel via the filler opening.

12. The fuel level gauge according to claim 9, characterized in that the filler plug (4) comprises a plug body (41) and a plug cover (42), wherein the plug body (41) has a through hole (411), one end of the through hole (411) being provided to be extendable into or connected to a filler opening of the fuel tank when the filler plug (4) is mounted to the filler opening, the other end of the through hole (411) forming a filler opening.

13. The fuel level gauge according to claim 10 or 11, wherein the filler plug (4) comprises a plug main body (41) and a plug cap (42), wherein the plug main body (41) has a through hole (411), one end of the through hole (411) is provided to be extendable into or connected to a filler opening of the fuel tank when the filler plug (4) is mounted to the filler opening, and the other end of the through hole (411) forms a filler opening.

14. An air compressor, characterized in that it comprises an oil level gauge according to any one of claims 1-13.