Patent Description:
Vacuum pumps and in particular oil-sealed vacuum pumps in accordance to the state of the art are connected to an oil or lubricant supply line supplying oil to the vacuum pump from a reservoir. During the pumping process the lubricant or oil is mixed with air any other gaseous medium which is conveyed by the vacuum pump. The air-lubricant mixture is then returned to the reservoir by a return line connected to the vacuum pump. In the reservoir the oil is collected at the bottom of the reservoir wherein the supply line is fed from the bottom of the reservoir. However, a certain amount of oil remains in the air above the oil level in the reservoir. This oil- or lubricant-air mixture is drawn through an air filter where the lubricant is separated from the air. The lubricant collected by the air filter is drawn into the vacuum pump through the scavenge line due to the pressure difference between the low pressure or vacuum in the low-pressure region of the vacuum pump, thereby being recovered into the lubricant cycle of the vacuum system.

Thus, scavenging of the oil or lubricant from the oil/lubricant-air mixture is carried out by the pressure difference between the reservoir and the pump wherein usually the reservoir tank is at atmosphere pressure or even higher and the low-pressure region of the vacuum pump is below atmospheric pressure, i.e. vacuum.

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

Under certain working conditions of the vacuum pump relating in particular to different rotation of speeds in case of a variable speed drive (VSD) the lubricant carryover for the scavenge line is not constant since under some working conditions of the vacuum pump less air is mixed into the lubricant, i.e. a less amount of lubricant can be separated by the air filter. This results in the fact that there is not enough lubricant to fill the scavenge line completely and as a result air will enter the scavenge line. Through the scavenge line this air enters the vacuum pump and reduces the pumping speed and pump performance such that the ultimate pressure of the vacuum pump is increased. Therein, the lubricant carryover is the amount of lubricant that is carried by the air and that is separated by the air filter and available for scavenging back to the vacuum pump.

<CIT> and <CIT> each describe lubricant recovery systems forming the state of the art.

It is an object of the present invention to provide a lubricant recovery system which is able to maintain the performance of the vacuum pump.

The above given problem solved by the lubricant recovery system of claim <NUM> as well as the vacuum system of claim <NUM>.

The lubricant recovery system for a vacuum pump in accordance to the present invention comprises a reservoir to store a lubricant. A supply line is connected to the reservoir wherein the supply line can be connected to the vacuum pump to supply the lubricant to the vacuum pump for operation. Further, a return line is connected to the reservoir to return a lubricant-air mixture from the vacuum pump to the reservoir. Lubricant returned by the return line is usually collected at the bottom of the reservoir. However, above the lubricant level a lubricant-air mixture evolves. In accordance to the present invention an air filter is disposed inside the reservoir to separate the lubricant from the air wherein the filter is connected to a scavenge line. The scavenge line is connected to a low pressure region of the vacuum such that lubricant separated from the lubricant-air mixture by the filter is drawn through the scavenge line into the vacuum pump due to the pressure difference between the pressure inside the reservoir which is usually at atmospheric pressure and the low pressure region of the vacuum pump, which is at lower pressure, i.e. vacuum. Further, a valve is disposed in the scavenge line selectively separate the filter from the vacuum pump. Thus, air from the reservoir can be prevented to enter the vacuum pump and reduce the pump performance of the vacuum pump.

In particular, the valve is closed in working conditions of the vacuum pump in which less lubricant carryover occurs. This usually relates to low pressure, high vacuum conditions. Contrary, the valve is open if there is a considerable amount of lubricant carryover. Therein, the lubricant carryover is the amount of lubricant that is carried by the air in the reservoir and that is separated by the air filter.

In particular, the valve is connected to a control unit. Further, a pressure gauge is 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. Preferably, the low-pressure region of the vacuum pump might refer to the inlet of the vacuum pump. The control unit is configured to control the valve in dependence on the measured pressure. Preferably, if the vacuum pump operates at high pressure close to atmosphere, for example during startup, the valve is controlled to be open since there is sufficient lubricant carryover in the scavenge line to completely fill the scavenge line. If the vacuum pump operates at low-pressure or high vacuum, then the lubricant carryover is reduced and there is no sufficient lubricant collected by the air filter to completely fill the scavenge line. Thus, in order to prevent air from the reservoir to enter into the vacuum pump the valve is controlled to be closed in dependence on the measured pressure.

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

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 an insufficient amount of lubricant is collected by the air filter to completely fill the scavenge line. Thus, by reducing the flow through the scavenge line by the throttle valve it is prevented that air enters the vacuum pump which would reduce the pump performance of the vacuum pump. Preferably, by the throttle valve the reduction of the flow can be controlled continuously in dependence on the measured pressure.

In particular, a bypass line is employed in the scavenge line bypassing the valve such that a low-pressure provided by the vacuum pump is maintained at the air filter even if the valve is closed. Thus, even if the vacuum pump is operated under such conditions in which 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 such that lubricant is drawn from the air filter into the vacuum pump. Thus, 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 scavenged to the vacuum pump.

In particular, the bypass line has a diameter smaller than the diameter of the scavenge line to provide a reduced flow through the bypass line compared to the flow through the scavenge line. Additionally, or alternatively an orifice is disposed in the bypass line wherein the orifice has a diameter smaller than the diameter of the scavenge line to reduce the flow accordingly. Thus, either the diameter itself of the bypass line or the orifice or both in combination works as a throttle to reduce the flow through the scavenge line from the air filter to the vacuum pump even under conditions when there is less lubricant carryover in order to make sure that the scavenge line is completely filled with lubricant.

In particular, the throttle valve is disposed in the bypass in order to continuously control the throttle effect provided in the bypass line preferably by the control unit, in dependence on the measured pressure.

In particular, two or more air filters are disposed in the reservoir wherein each filter is connected with a scavenge line.

In particular, at least two and preferably all scavenge lines are fed together to a common scavenge line wherein the valve is disposed in the common scavenge line connected to the vacuum pump. However, it is also possible that each scavenge line has its own valve and connected to different positions of the low-pressure region of the vacuum pump.

In particular, each scavenge line is connected by a bypass line to bypass any valve in each of the scavenge lines. Thus, even if there are two or more air filters operation of the air filters can be maintained even if the valve of each scavenge lines are closed.

In particular, the scavenge line is connectable to a first stage of the vacuum pump while the bypass line is connectable to a second stage of the vacuum pump wherein in the first stage a lower pressure is present than in the second stage of the vacuum pump under operation. Since in the second stage lower pressure is present, the pressure difference between the reservoir and the second stage is reduced. Thus, flow through the scavenge line is reduced if the valve is closed due to the reduced pressure difference and as a consequence even under conditions when there is less lubricant carryover there is enough lubricant to fill the scavenge line completely to prevent air to enter into the vacuum pump and reduce the pump efficiency of the vacuum pump.

Further, the present invention relates to a vacuum system comprising a vacuum pump and a lubricant recovery system as previously described.

In particular, the vacuum pump has a housing comprising an inlet and an outlet and at least one pump element disposed in the housing and rotated by a motor in order to convey a gaseous medium from the inlet to the outlet of the vacuum pump. Further, the housing comprises a lubricant supply connection connected to a lubricant supply line of the lubricant recovery system. Further, the housing comprises a lubricant return connection connected to the return line of the lubricant recovery system in order to return the lubricant air mixture to the reservoir.

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

In particular, the vacuum pump has a first stage and a stage wherein when in operation the pressure in the first stage is below the pressure in the second stage.

In particular, the scavenge line and preferably all scavenge lines are connected to the first stage while the bypass line and preferably all bypass lines are connected to the second stage in order reduce the pressure difference between the vacuum pump and the reservoir.

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

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

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 <NUM> in the reservoir <NUM>. Thus, if further operated there is not enough lubricant anymore to completely fill the scavenge line <NUM>. As a consequence, air from the reservoir <NUM> might enter the low-pressure region <NUM> of the vacuum pump <NUM> counteracting the generation of the vacuum pump <NUM> and thereby reducing the pump performance or the lowest achievable pressure of the vacuum pump <NUM>. In order to avoid these circumstances, a valve <NUM> is disposed in the scavenge line <NUM> in order to separate the air filter <NUM> from the low-pressure region <NUM> of the vacuum pump <NUM>. As a consequence, no air can enter into the low-pressure region <NUM> of the vacuum pump <NUM> anymore if the valve <NUM> is closed increasing or at least maintaining the pump performance of the vacuum pump <NUM>. However, if the valve <NUM> is closed no lubricant is scavenged from the lubricant-air mixture in the reservoir <NUM> by the air filter <NUM> anymore since the vacuum of the low-pressure region <NUM> is not provided to the air filter <NUM> anymore. Thus, a bypass line <NUM> is used bypassing the valve <NUM>. In the bypass line <NUM> an orifice <NUM> is present in order to reduce the flow through the scavenge line <NUM>. Hence, in the case of a closed valve <NUM> and due to the reduced flow through the scavenge line <NUM>, no air from the reservoir <NUM> can enter into the low-pressure region <NUM> of the vacuum pump <NUM>. Thus, the performance of the vacuum pump <NUM> is maintained efficiently.

In the second embodiment shown in <FIG> 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.

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

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