A LUBRICANT RECOVERY SYSTEM

Abstract

A lubricant recovery system for vacuum pump comprising a reservoir to store lubricant. Supply lines connected to the reservoir wherein the supply line can be connected to the vacuum pump to supply the lubricant to the vacuum pump. Further, a return line is connected to the reservoir to return a lubricant-air mixture from the vacuum pump to the reservoir by the return line. An air filter is disposed inside the reservoir to separate lubricant from the air wherein the filter is connected to a scavenge line which is 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 via the scavenge line into the vacuum pump. In accordance to the present invention a valve is disposed in the scavenge line to selectively separate the air filter from the vacuum pump.

Claims

1. A lubricant recovery system for a vacuum pump, in particular an oil-sealed vacuum pump, comprising: a reservoir to store a lubricant; a supply line connected to the reservoir, wherein the supply line can be connected to the vacuum pump to supply the lubricant to the vacuum pump; a return line connected to the reservoir to return a lubricant-air mixture from the vacuum pump to the reservoir by the return line; an air filter disposed inside the reservoir to separate lubricant from the lubricant-air mixture, wherein the air filter is connected to a scavenge line, wherein the scavenge line is 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 via the scavenge line into the vacuum pump; a valve is disposed in the scavenge line to selectively separate the air filter from the vacuum pump, wherein the valve is connected to a control unit; and a pressure gauge arranged at the low-pressure region of the vacuum pump or inside a vacuum apparatus connected to the vacuum pump in order to measure the pressure inside, wherein the control unit is configured to control the valve in dependence on the measured pressure.

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

3. The lubricant recovery system according to claim 1, characterized in that the valve is a throttle valve and the control unit is configured to reduce the flow through the throttle valve upon decreasing measured pressure.

4. The lubricant recovery system according to claim 1, characterized by a bypass line bypassing the valve in the scavenge line such that low-pressure at the air filter is maintained even with a closed valve.

5. The lubricant recovery system according to claim 4, characterized in that the bypass line has a diameter smaller than the diameter of the scavenge line and/or an orifice is disposed in the bypass line, wherein the orifice has a diameter smaller than the diameter of the scavenge line.

6. The lubricant recovery system according to claim 4, characterized in that a throttle valve is disposed in the bypass line.

7. The lubricant recovery system according to claim 1, characterized in that two or more air filters are disposed in the reservoir, wherein each filter is connected with a scavenge line.

8. The lubricant recovery system according to claim 7, characterized in that at least two and preferably all scavenge lines are fed together, wherein the valve is disposed in the common scavenge line connectable to the vacuum pump and preferably a low-pressure region of the vacuum pump.

9. The lubricant recovery system of claim 7, characterized in that each scavenge line is connected by a bypass line to bypass any valve in each of the scavenge lines.

10. The vacuum system comprising a vacuum pump and a lubricant recovery system according to claim 1.

11. The vacuum system according to claim 10, characterized in that the vacuum pump is an oil-sealed vacuum pump and in particular a screw pump, scroll pump, claw pump, rotary-vane pump.

12. The vacuum system according claim 10, characterized in that the vacuum pump has a first stage and a second stage, wherein in operation the pressure in the first stage is below the pressure in the second stage.

13. The vacuum system according to claim 12, characterized in that the scavenge line and preferably all scavenge lines are connected to the first stage and the bypass line preferably all bypass lines are connected to the second stage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further describing in accordance to the accompanied drawings.

[0029] It is shown:

[0030] FIG. 1 shows first embodiment of the present invention

[0031] FIG. 2 shows a second embodiment of the present invention and

[0032] FIG. 3 shows a comparison between a vacuum pump of the prior art and a vacuum pump accordance with the present invention.

DETAILED DESCRIPTION

[0033] In the first embodiment a reservoir 10 is connected to a vacuum pump 12 by a supply line 14 supplying a lubricant to the vacuum pump 12 and in particular to the bearings 16 of the vacuum pump 12. During the pump process the lubricant is mixed with air or any other gaseous medium conveyed by the vacuum pump 12. This lubricant-air mixture is returned by a return line 18 to the reservoir 10. The lubricant is then collected at the bottom 20 of the reservoir 10. Above the lubricant level 22 an oil-air mixture 24 is still present. Further, inside the reservoir 10 an air filter 26 is disposed wherein the lubricant-air mixture is drawn through the air filter 26 and the lubricant is separated from the air. The lubricant-air mixture is filtered by the air filter 26 by a pressure difference between the vacuum pump 12 usually operating at pressures below atmosphere, i.e. vacuum, and the pressure inside the reservoir 10, usually atmospheric pressure or even above. Thus, a scavenge line 28 is provided between the filter 26 and a low-pressure region 30 of the vacuum pump 12. Thus, lubricant separated by the air filter 26 is returned by the scavenge line 28 to the vacuum pump 12 and then recycled into the normal cycle of the lubricant.

[0034] However, there are operating situations of the vacuum pump where there is less lubricant carryover, i.e. only a little amount of lubricant is present above the lubricant level 22 in the reservoir 10. Thus, if further operated there is not enough lubricant anymore to completely fill the scavenge line 28. As a consequence, air from the reservoir 10 might enter the low-pressure region 30 of the vacuum pump 12 counteracting the generation of the vacuum pump 12 and thereby reducing the pump performance or the lowest achievable pressure of the vacuum pump 12. In order to avoid these circumstances, a valve 32 is disposed in the scavenge line 28 in order to separate the air filter 26 from the low-pressure region 30 of the vacuum pump 12. As a consequence, no air can enter into the low-pressure region 30 of the vacuum pump 12 anymore if the valve 32 is closed increasing or at least maintaining the pump performance of the vacuum pump 12. However, if the valve 32 is closed no lubricant is scavenged from the lubricant-air mixture in the reservoir 10 by the air filter 26 anymore since the vacuum of the low-pressure region 30 is not provided to the air filter 26 anymore. Thus, a bypass line 34 is used bypassing the valve 32. In the bypass line 34 an orifice 36 is present in order to reduce the flow through the scavenge line 28. Hence, in the case of a closed valve 32 and due to the reduced flow through the scavenge line 28, no air from the reservoir 10 can enter into the low-pressure region 30 of the vacuum pump 12. Thus, the performance of the vacuum pump 12 is maintained efficiently.

[0035] In the second embodiment shown in FIG. 2 same or similar elements are indicated with identical reference signs. However, in the following only the differences between the first embodiment and the second embodiment are described.

[0036] In the second embodiment the vacuum pump 12 comprises a first stage 38 and a second stage 40 wherein the pressure in the first stage 38 is below the pressure of the second stage 40. The scavenge line 28 is connected to the first stage 38 of the vacuum pump 12. The bypass line 34 is bypassing the valve 32 and connected with the second stage 40 of the vacuum pump 12. Thus, under conditions when the valve 32 is closed no air can be drawn into the first stage 38 of the vacuum pump 12 anymore. However, since the bypass line 34 is connected to the second stage 40 of the vacuum pump 12, a reduced pressure difference between the second stage 40 of the vacuum pump 12 and the reservoir 10 is present compared to the situation of an open valve 32 connecting the air filter 26 to the first stage 38 of the vacuum pump 12. Due to the reduced pressure difference the flow through the scavenge line 28 is reduced accordingly in order to make sure that there is always sufficient lubricant to completely fill the scavenge line 28 and thereby prevent air to enter into the vacuum pump 12. In addition, an orifice 36 or throttle is employed in the bypass line 34 to further reduce the flow through the bypass line 34.

[0037] FIG. 3 shows a comparison between a vacuum system according to the prior art by line 50 compared to the vacuum system of the first embodiment by line 52. At the y-axis of the graph the pumping speed in m.sup.3/h is shown over the inlet pressure in mbar. In the prior art for low-pressures the lubricant carryover is reduced. Thus, the scavenge line in the prior art vacuum systems cannot be completely filled anymore. Air from the reservoir enters into the vacuum pump resulting I a shifted ultimate pressure of the vacuum pump. In the embodiment of the present invention the flow is reduced in the scavenge line such that there is under every operational condition sufficient lubricant to completely fill the scavenge line. As a consequence and in accordance with the present invention, no air can enter into the vacuum pump 12. Thus, the ultimate pressure of the vacuum pump is lower compared to the prior art while the pumping speed is always above that of the prior art.

[0038] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0039] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.