Lubricant recovery system

Abstract

The invention relates to a lubricant recovery system. A lubricant recovery system for a vacuum pump includes a reservoir for storing a lubricant. A supply line is connected to the reservoir, wherein the supply line is connectable to the vacuum pump to supply the lubricant to the vacuum pump. Further, a return line is connected to the reservoir to return the lubricant-air mixture from the vacuum pump to the reservoir through the return line. An air filter is disposed inside the reservoir to separate lubricant from air, where the filter is connected to a purge line connectable to a low pressure region of the vacuum pump such that lubricant separated from the lubricant-air mixture by the air filter is drawn into the vacuum pump via the purge line. According to the invention, a valve is provided in the purge line to selectively separate the air filter from the vacuum pump.

Description

Technical Field

[0001] This case is a divisional application, the parent application number is 202180034371.X, the application date is March 10, 2021, and the invention name is "Lubricant Recovery System". The present invention relates to a lubricant recovery system for a vacuum pump, and in particular to a lubricant recovery system for an oil-sealed vacuum pump. In addition, the present invention relates to a vacuum system having such a lubricant recovery system. Background Art

[0002] A vacuum pump, and in particular an oil-sealed vacuum pump according to the prior art, is connected to an oil or lubricant supply line that supplies oil from a reservoir to the vacuum pump. During the suction process, the lubricant or oil mixes with the air conveyed by the vacuum pump and any other gaseous medium. The air-lubricant mixture is then returned to the reservoir via a return line connected to the vacuum pump. In the reservoir, the oil is collected at the bottom of the reservoir, from which the supply line feeds. However, a certain amount of oil remains in the air above the oil level in the reservoir. This oil- or lubricant-air mixture is sucked through an air filter, where the lubricant is separated from the air. Due to the pressure difference between the low pressure or vacuum in the low-pressure area of ​​the vacuum pump, the lubricant collected by the air filter is sucked into the vacuum pump via a purge line and is thus recycled into the lubricant cycle of the vacuum system.

[0003] Thus, purging of oil or lubricant from the oil / lubricant-air mixture is performed by the pressure difference between the reservoir and the pump, wherein typically the reservoir tank is at atmospheric pressure or even higher, and the low pressure area of ​​the vacuum pump is below atmospheric pressure, i.e. a vacuum.

[0004] In the following the term lubricant is used for any kind of lubricant or oil necessary or used for the operation of the vacuum pump.

[0005] Under certain operating conditions of the vacuum pump, in particular in the case of variable speed drives (VSD) involving different rotational speeds, the lubricant entrainment for the purge line is not constant, because under some operating conditions of the vacuum pump less air is mixed into the lubricant, i.e. less lubricant can be separated by the air filter. This leads to the fact that there is not enough lubricant to completely fill the purge line and therefore air will enter the purge line. Through the purge line, this air enters the vacuum pump and reduces the suction speed and the pump performance, so that the ultimate pressure of the vacuum pump increases. Therein, the lubricant entrainment is the amount of lubricant carried by the air and is the amount of lubricant separated by the air filter and available for purging back to the vacuum pump. Summary of the invention

[0006] An object of the present invention is to provide a lubricant recovery system capable of maintaining the performance of a vacuum pump.

[0007] The problem given above is solved by a lubricant recovery system as claimed in claim 1 and a vacuum system as claimed in claim 10 .

[0008] The lubricant recovery system for a vacuum pump according to the present invention includes a reservoir for storing lubricants. A supply line is connected to the reservoir, wherein the supply line can be connected to a vacuum pump to supply lubricants to the vacuum pump for operation. In addition, a return line is connected to the reservoir to return a lubricant-air mixture from the vacuum pump to the reservoir. The lubricant returned by the return line is usually collected at the bottom of the reservoir. However, above the lubricant level, a lubricant-air mixture is generated. According to the present invention, an air filter is arranged in the reservoir to separate the lubricant from the air, wherein the filter is connected to a purge line. The purge line is connected to a low-pressure area of ​​the vacuum, so that due to the pressure difference between the pressure inside the reservoir, which is usually at atmospheric pressure, and the low-pressure area of ​​the vacuum pump, which is at a lower pressure (i.e., under vacuum), the lubricant separated from the lubricant-air mixture by the filter is sucked into the vacuum pump through the purge line. In addition, a valve is arranged in the purge line to selectively separate the filter from the vacuum pump. Therefore, it is possible to prevent air from the reservoir from entering the vacuum pump and reducing the pump performance of the vacuum pump.

[0009] In particular, under operating conditions of the vacuum pump where less lubricant carryover occurs, the valve is closed. This typically involves low pressure, high vacuum conditions. Conversely, if there is a significant amount of lubricant carryover, the valve is open. Wherein the lubricant carryover is the amount of lubricant carried by the air in the reservoir and separated by the air filter.

[0010] In particular, the valve is connected to the control unit. In addition, a pressure gauge is arranged in a low-pressure area of ​​the vacuum pump or inside a vacuum device connected to the vacuum pump so as to measure the pressure inside. Preferably, the low-pressure area of ​​the vacuum pump may refer to the inlet of the vacuum pump. The control unit is configured to control the valve according to the measured pressure. Preferably, if the vacuum pump is operated at a high pressure close to the atmosphere, such as during startup, the valve is controlled to be open because there is sufficient lubricant entrainment in the purge line to completely fill the purge line. If the vacuum pump is operated at a low pressure or a high vacuum, the lubricant entrainment is reduced and not enough lubricant is collected by the air filter to completely fill the purge line. Therefore, in order to prevent air from entering the vacuum pump from the reservoir, the valve is controlled to be closed according to the measured pressure.

[0011] In particular, the control unit is configured to close the valve if the measured pressure is below a threshold value.Preferably, the threshold value is predetermined and depends on the vacuum pump type or the configuration of the lubricant recovery system, such as for example the size of the purge line.

[0012] In particular, the valve is a throttle valve and the control unit is configured to reduce the flow through the throttle valve in dependence on the measured pressure. Thus, by reducing the flow through the throttle valve, it is avoided that the amount of lubricant collected by the air filter is insufficient to completely fill the purge line. Thus, by reducing the flow through the purge line by the throttle valve, air is prevented from entering the vacuum pump, which would reduce the pump performance of the vacuum pump. Preferably, by means of the throttle valve, the reduction of the flow can be continuously controlled in dependence on the measured pressure.

[0013] In particular, a bypass line bypassing the valve is adopted in the purge line so that even if the valve is closed, the low pressure provided by the vacuum pump is maintained at the air filter. Therefore, even if the vacuum pump is operated under such a condition that the valve is closed, the functionality of the air filter is maintained by maintaining the low pressure at the air filter via the bypass line so that lubricant is sucked into the vacuum pump from the air filter. Therefore, even if the valve is closed, the remaining amount of oil carryover is effectively filtered by the air filter in the lubricant recovery system and purged to the vacuum pump.

[0014] In particular, the bypass line has a diameter that is smaller than the diameter of the purge line to provide a reduced flow through the bypass line compared to the flow through the purge line. Additionally, or alternatively, an orifice is provided in the bypass line, wherein the orifice has a diameter that is smaller than the diameter of the purge line to reduce the flow accordingly. Thus, the diameter of the bypass line or the orifice itself, or a combination of both, acts as a throttle to reduce the flow from the air filter through the purge line to the vacuum pump even in the presence of less lubricant carryover, to ensure that the purge line is completely filled with lubricant.

[0015] In particular, a throttle valve is arranged in the bypass in order to control the throttling effect provided in the bypass line preferably continuously by means of a control unit as a function of the measured pressure.

[0016] In particular, two or more air filters are arranged in the reservoir, wherein each filter is connected to a purge line.

[0017] Particularly, at least two and preferably all purge lines are fed together to a common purge line, wherein the valve is arranged in the common purge line connected to the vacuum pump. However, each purge line may also have its own valve and be connected to different positions of the low pressure region of the vacuum pump.

[0018] In particular, each purge line is connected by a bypass line so as to bypass any valve in each of these purge lines. Therefore, even if there are two or more air filters, even if the valve of each purge line is closed, the operation of the air filter can also be maintained.

[0019] In particular, the purge line may be connected to a first stage of the vacuum pump and the bypass line may be connected to a second stage of the vacuum pump, wherein in operation, a lower pressure is present in the first stage than in the second stage of the vacuum pump. Due to the lower pressure present in the second stage, the pressure difference between the reservoir and the second stage is reduced. Therefore, if the valve is closed due to the reduced pressure difference, the flow through the purge line is reduced, and thus even in the presence of a smaller lubricant carryover, there is sufficient lubricant to completely fill the purge line to prevent air from entering the vacuum pump and reducing the pump efficiency of the vacuum pump.

[0020] Furthermore, the present invention relates to a vacuum system comprising a vacuum pump and a lubricant recovery system as described above.

[0021] In particular, the vacuum pump has a housing including an inlet and an outlet and at least one pump element which is arranged in the housing and rotated by the motor in order to convey the gaseous medium from the inlet to the outlet of the vacuum pump. In addition, the housing includes a lubricant supply connection connected to a lubricant supply line of a lubricant recovery system. In addition, the housing includes a lubricant return connection which is connected to a return line of the lubricant recovery system in order to return the lubricant-air mixture to the reservoir.

[0022] In particular, the vacuum pump is an oil-sealed vacuum pump and in particular a screw pump, a scroll pump, a claw pump or a rotary vane pump.

[0023] In particular, the vacuum pump has a first stage and a second stage, wherein when in operation the pressure in the first stage is lower than the pressure in the second stage.

[0024] In particular, the purge line and preferably all purge lines are connected to the first stage, while the bypass line and preferably all bypass lines are connected to the second stage in order to reduce the pressure difference between the vacuum pump and the reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is further described with reference to the accompanying drawings.

[0026] It shows: Figure 1 The first embodiment of the present invention is shown Figure 2 A second embodiment of the present invention is shown, and Figure 3A comparison between a prior art vacuum pump and a vacuum pump according to the invention is shown. DETAILED DESCRIPTION

[0027] In the first embodiment, the reservoir 10 is connected to the vacuum pump 12 via a supply line 14, which supplies lubricant to the vacuum pump 12, and in particular to the bearings 16 of the vacuum pump 12. During the suction process, the lubricant is mixed with the air or any other gaseous medium conveyed by the vacuum pump 12. This lubricant-air mixture is returned to the reservoir 10 via a return line 18. The lubricant is then collected at the bottom 20 of the reservoir 10. Above the lubricant level 22, there is still an oil-air mixture 24. In addition, an air filter 26 is provided inside the reservoir 10, wherein the lubricant-air mixture is sucked in through the air filter 26, and the lubricant is separated from the air. The lubricant-air mixture is filtered by the pressure difference between the pressure inside the vacuum pump 12 and the reservoir 10 through the air filter 26, and the vacuum pump is usually operated at a pressure lower than the atmosphere (ie, under vacuum), and the pressure inside the reservoir is usually atmospheric pressure or even higher. Therefore, a purge line 28 is provided between the filter 26 and the low-pressure area 30 of the vacuum pump 12. Thus, the lubricant separated by the air filter 26 is returned to the vacuum pump 12 through the purge line 28 and then recirculated into the normal circulation of the lubricant.

[0028] However, there are operating situations of the vacuum pump in which there is less lubricant carryover, i.e., only a small amount of lubricant is present above the lubricant level 22 in the reservoir 10. Therefore, if further operation is performed, there is no longer enough lubricant to completely fill the purge line 28. As a result, air from the reservoir 10 may enter the low-pressure region 30 of the vacuum pump 12, counteracting the production of the vacuum pump 12 and thereby reducing the pump performance or the minimum achievable pressure of the vacuum pump 12. In order to avoid these situations, a valve 32 is provided in the purge line 28 to separate the air filter 26 from the low-pressure region 30 of the vacuum pump 12. As a result, if the valve 32 is closed, air can no longer enter the low-pressure region 30 of the vacuum pump 12, thereby increasing or at least maintaining the pump performance of the vacuum pump 12. However, if the valve 32 is closed, lubricant is no longer purged from the lubricant-air mixture in the reservoir 10 by the air filter 26, since the vacuum of the low-pressure region 30 is no longer provided to the air filter 26. Therefore, a bypass line 34 is used to bypass the valve 32. In the bypass line 34, an orifice 36 is present in order to reduce the flow through the purge line 28. Thus, with the valve 32 closed and due to the reduced flow through the purge line 28, no air can enter the low pressure region 30 of the vacuum pump 12 from the reservoir 10. Thus, the performance of the vacuum pump 12 is effectively maintained.

[0029] exist Figure 2In the second embodiment shown in FIG. 1 , the same or similar elements are denoted by the same reference numerals. However, in the following, only the differences between the first embodiment and the second embodiment are described.

[0030] In the second embodiment, the vacuum pump 12 includes a first stage 38 and a second stage 40, wherein the pressure in the first stage 38 is lower than the pressure in the second stage 40. The purge line 28 is connected to the first stage 38 of the vacuum pump 12. The bypass line 34 bypasses the valve 32 and is connected to the second stage 40 of the vacuum pump 12. Therefore, under the condition that the valve 32 is closed, air can no longer be sucked into the first stage 38 of the vacuum pump 12. However, since the bypass line 34 is connected to the second stage 40 of the vacuum pump 12, there is a reduced pressure difference between the second stage 40 of the vacuum pump 12 and the reservoir 10 compared to the case where the valve 32 is opened to connect the air filter 26 to the first stage 38 of the vacuum pump 12, and due to the reduced pressure difference, the flow through the purge line 28 is correspondingly reduced to ensure that there is always enough lubricant to completely fill the purge line 28, and thereby prevent air from entering the vacuum pump 12. In addition, an orifice 36 or a throttle valve is adopted in the bypass line 34 to further reduce the flow through the bypass line 34.

[0031] Figure 3 A comparison is shown between a vacuum system according to the prior art, shown by line 50, and a vacuum system of the first embodiment, shown by line 52. At the y-axis of the graph, the vacuum in mbar is shown relative to the inlet pressure in mbar. 3 / h. In the prior art under low pressure conditions, the lubricant carryover is reduced. Therefore, the purge line in the prior art vacuum system can no longer be completely filled. Air from the reservoir enters the vacuum pump, causing the ultimate pressure of the vacuum pump to change. In an embodiment of the present invention, the flow in the purge line is reduced so that there is enough lubricant to completely fill the purge line under each operating condition. As a result, according to the present invention, no air can enter the vacuum pump 12. Therefore, compared with the prior art, the ultimate pressure of the vacuum pump is lower, while the suction speed is always higher than the suction speed of the prior art.

Claims

1. A lubricant recovery system for a vacuum pump, the vacuum pump being particularly an oil-sealed vacuum pump, the lubricant recovery system comprising: a reservoir (10) for storing lubricant; a supply line (14) connected to the reservoir (10), wherein the supply line (14) is connectable to the vacuum pump (12) to supply the lubricant to the vacuum pump (12); a return line (18) connected to the reservoir (10) to return the lubricant-air mixture from the vacuum pump (12) to the reservoir (10) through the return line; an air filter (26) disposed within the reservoir (10) to separate lubricant from the lubricant-air mixture, wherein the air filter (26) is connected to a purge line (28), wherein the purge line (28) is connectable to a low-pressure area (30) of the vacuum pump (12), such that the lubricant separated from the lubricant-air mixture by the air filter (26) is sucked into the vacuum pump (12) via the purge line (28); a valve (32) disposed in the purge line (28) to selectively separate the air filter (26) from the vacuum pump (12), wherein the valve (32) is connected to a control unit; and A pressure gauge is arranged at the low-pressure area (30) of the vacuum pump (12) or inside a vacuum device connected to the vacuum pump (12) so as to measure the internal pressure, wherein the control unit is configured to control the valve (32) according to the measured pressure.

2. The lubricant recovery system according to claim 1, characterized in that: The control unit is configured to close the valve (32) if the measured pressure is below a threshold value.

3. The lubricant recovery system according to claim 1, characterized in that: The valve (32) is a throttle valve, and the control unit is configured to reduce the flow through the throttle valve when the measured pressure decreases.

4. The lubricant recovery system according to any one of claims 1 to 3, characterized in that: A bypass line (34) bypasses the valve (32) in the purge line (28) so that a low pressure at the air filter (26) is maintained even when the valve (32) is closed.

5. The lubricant recovery system according to claim 4, characterized in that: The bypass line (34) has a diameter smaller than the diameter of the purge line (28) and / or an orifice (36) is provided in the bypass line (34), wherein the orifice (36) has a diameter smaller than the diameter of the purge line (28).

6. The lubricant recovery system according to claim 4 or 5, characterized in that: A throttle valve is arranged in the bypass line (34).

7. The lubricant recovery system according to any one of claims 1 to 6, characterized in that: Two or more air filters (26) are arranged in the reservoir (10), wherein each filter (26) is connected to a purge line (28).

8. The lubricant recovery system according to claim 7, characterized in that: At least two and preferably all purge lines (28) are fed together, wherein the valve (32) is arranged in a common purge line connectable to the vacuum pump (12) and preferably connectable to a low pressure region (30) of the vacuum pump (12).

9. The lubricant recovery system according to claim 7 or 8, characterized in that: Each purge line (28) is connected via a bypass line (34) to bypass any valve (32) in each of the purge lines (28).

10. A vacuum system comprising a vacuum pump (12) and a lubricant recovery system according to any one of claims 1 to 9.

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