DE102013223556A1 - Vacuum pump system and method for operating a vacuum pump system - Google Patents

Abstract

A vacuum pump system has a vacuum pump (10) designed in particular as a screw pump. This serves to evacuate a chamber (16). Upon reaching a desired target pressure in the chamber (16), the vacuum pump system can be operated in a standby mode. For this purpose, an outlet line (22) is connected via a bypass line (24) to an inlet line (30). In standby mode, the inlet valve (18) is closed and a bypass valve (26) is opened, so that medium can be conveyed in a circle by the vacuum pump (10). As a result, the vacuum pump is kept substantially at operating temperature.

Description

The invention relates to a vacuum pump system and a method for operating a vacuum pump system.

Vacuum pumps and vacuum pump systems are often used to evacuate chambers in a short time. This is done using dry compressing vacuum pumps such as screw pumps, claw pumps or multi-stage roots pumps. Possibly. It is also possible to use oil-sealed vacuum pumps, such as rotary vane pumps or barrier vane pumps. Frequently, several pumps are arranged in series and / or parallel to each other in order to pump large volumes of gas in short periods of time.

Typical applications are lock chambers as they are, for example. Provided in coating equipment. The lock chamber must be pumped from atmospheric pressure to a transfer pressure in short periods. This usually takes place in periods of 20 seconds to 120 seconds to a transfer pressure of 0.1 mbar to 10 mbar. Subsequently, a valve which is arranged between the lock chamber and the vacuum pump system can be closed. The valve is closed for an idle time of about one to ten times the pump down time.

Another typical application is large process chambers such as those used for heat treatment or refining of metals. In this application, typical pump down times are 2 min. To 30 min. After the pump down time, the process chamber is at the desired low pressure level. However, it is still necessary to maintain this pressure level to maintain a relatively low gas flow, so that small amounts of gas continue to be pumped out. This is the holding time, which is approximately two to ten times the pumping time.

Both in lock chambers and in correspondingly large process chambers, it is necessary to realize short pump-down times that the vacuum pump system is very large dimensions. During the idling time or during the holding time, however, the high pumping system's high pumping speeds are not necessary. This leads to a high power consumption and thus a high energy consumption.

If, for example, a screw pump is used to evacuate a chamber such as a lock chamber or a process chamber, there is the problem that a gap is provided between the rotor elements of the screw and the housing which, since it is a dry-compressed vacuum pump, is not a lubricant is sealed. The gap width depends in particular on the rotor temperature. Since there is always a backflow of the medium to be pumped through the gap, the optimum delivery rate of the pump is achieved only when the operating temperature and thus at a very small gap. Once a target pressure is achieved in a process chamber, it would be possible to reduce the speed of the pump and thus the pump power or possibly even turn off the pump. However, this has the disadvantage that as soon as the pressure in the process chamber again exceeds the target pressure, the pump must first be brought back to operating temperature before the full pumping power is achieved. This would lead to unacceptable pressure fluctuations in the process chamber. It is necessary that the vacuum pump can be operated directly at full pump power when a setpoint pressure in the process chamber is exceeded, in order to avoid an unwanted increase in the pressure in the process chamber and excessive pressure fluctuations in the process chamber. In lock chambers, the pump must preferably be kept at nominal speed, otherwise they would have to be accelerated only at the end of the idle time. This would extend the pumping time.

The problem that the pump must be kept at operating temperature due to sealing gaps, in order to ensure a maximum flow, there is also with other dry-compressing vacuum pumps, such as claw pumps, Roots pumps udgl.

To reduce the energy consumption of pumps and pump systems during idle or hold time, different approaches are known:
It is possible to use vacuum pumps with a high built-in volume ratio. However, the technically feasible volume ratios are limited by the manufacturing technology, the construction cost and by the requirements for the robustness and tightness of the pumping stages. In particular, this can only be achieved a small reduction in energy consumption. In addition, solutions are required that avoid over-compression during the pumping process to high internal compression.

Furthermore, a combination of backing pumps with the Roots pumps connected in series is known. By this solution, a large volume ratio of the entire pump combination can be achieved. The disadvantage, however, is that the Roots pump at high intake pressures of, for example, about 100 mbar and more provides little support for the backing pump. This is due to the fact that otherwise a very large engine the roots pump would need to be installed. This has the consequence that continue to be very large backing pumps necessary to realize the corresponding pumping times. This leads to a correspondingly high energy consumption.

The object of the invention is to provide a vacuum pump system and a method for operating a vacuum pump system, in which a high particular maximum delivery of the vacuum pump, or the vacuum pump system can be guaranteed in different operating conditions on the one hand and the energy consumption can be reduced can.

The object is achieved according to the invention by a vacuum pump system according to claim 1 or by a method for operating a vacuum pump system according to claim 10.

The vacuum pump system according to the invention has been developed in particular to the fact that even if in a standby mode, the required pressure in the chamber such as a process chamber is already reached, the vacuum pump is maintained at operating temperature and rated speed and then, as soon as the pressure in the process chamber Set pressure exceeds, the vacuum pump can be operated directly again with high pump power. Accordingly, the vacuum pump system according to the invention has been developed for a standby mode in lock chambers, so that on the one hand low Abpumpzeiten realized in the lock chamber and on the other hand, during the idle time energy savings can be realized. Here, the rated speed of the vacuum pump is maintained. For this purpose, the vacuum pump system has one or more vacuum pumps, in particular a dry-compressing vacuum pump such as a screw pump. An inlet of the vacuum pump is connected to a chamber to be evacuated, such as a process chamber or a lock chamber. The outlet of the vacuum pump is connected to an outlet line. This may, for example, be connected to a backing pump.

In the outlet, a preferably mechanical check valve is arranged. By the check valve, which may optionally be designed as a control valve, a backflow of the pumped medium is avoided in the pump chamber of the vacuum pump. According to the invention, the outlet line is connected to the inlet line via a bypass line. In the bypass line, a bypass valve is arranged, which is connected to a control device. This makes it possible to open the bypass valve upon reaching a target pressure in the process chamber or the lock chamber to keep the vacuum pump fully operational with reduced power consumption. In this case, in particular the outlet pressure of the vacuum pump is reduced, wherein the operating temperature of the vacuum pump is at least substantially maintained.

In a particularly preferred embodiment, a switchable inlet valve which is likewise connected to the control device is arranged in the inlet line connected to the inlet of the vacuum pump and the chamber. This has the advantage that when opening the bypass valve, the inlet valve can be closed, so that a complete decoupling of the process or the lock chamber takes place.

If now the pressure in the process chamber exceed a predetermined setpoint, the bypass valve can be closed and the inlet valve can be opened, so that due to the fact that the vacuum pump is substantially at rated speed, immediately again at a high, in particular optimum, delivery rate of the vacuum pump can be promoted. The pressure fluctuations within the process chamber are thus very low and the pumping down times optimally short.

It is likewise possible for the inlet valve not to close completely, so that a small gas flow is always conveyed out of the process chamber at a reduced delivery rate of the at least one vacuum pump.

Accordingly, in the case of a vacuum pump system which serves to evacuate a lock chamber, the inlet valve can be opened again for the next lock operation, so that immediately with high pump volume an evacuation of the lock chamber can take place within the required pump down time.

Furthermore, the vacuum pump system according to the invention has the advantage that in this way considerable energy savings can be achieved. This is particularly advantageous in a standby mode in which the inlet valve (if present) is preferably completely closed and the bypass valve is preferably fully open.

Furthermore, in the case of the vacuum pump system according to the invention, there is the advantage that pressure is equalized between the inlet side and the outlet side of the vacuum pump when the bypass valve is closed. This reduces the pressure in the outlet area of the vacuum pump so that the vacuum pump again achieves a high pumping capacity at very short notice.

The vacuum pump system according to the invention always has at least one vacuum pump on, which is bridgeable by a bypass. Accordingly, a plurality of vacuum pumps can be provided, which can be bridged by a common or multiple bypasses. Furthermore, it is possible that when providing a plurality of vacuum pumps only one or some of the vacuum pumps are bridged over a common and / or over several bypasses. In the following, the invention will be explained with reference to the provision of a vacuum pump.

The bypass line is preferably connected to the inlet line between the inlet valve and the inlet of the vacuum pump. It is also possible to connect the bypass line directly to the inlet of the vacuum pump.

It is particularly preferred that the vacuum pump system is hermetically sealed. In particular, in standby mode, it is advantageous if the external leakage is as low as possible. It is preferred that the external leakage is less than 10 ^-4 mbar × l / s. If larger leaks occur in standby mode, it would also be possible to close the bypass valve in the short term with the inlet valve closed further, so that the medium is discharged through the outlet line of the check valve. If necessary, the speed of the pump can be increased. The pump can then be operated again in standby mode with the intake valve closed and the bypass valve open. A corresponding control can be carried out with the aid of the control device, which serves in addition to the control of the inlet valve and the bypass valve for controlling the vacuum pump. To determine an excessively high leakage current, it is possible to measure the pressure, for example, in the bypass line. Also, the power consumption of the vacuum pump can be measured, as it also increases with increasing pressure.

Furthermore, it is preferred that the pumps used themselves be very dense. The pumps must be designed in such a way that only small gas leaks occur even at greatly reduced outlet pressures of, for example, 10 mbar to 500 mbar. In particular, no gas / air should penetrate from the outside into the pump.

Furthermore, it is preferable that the speed of the vacuum pump in the standby mode is in the range of 100% to 20% of the rated speed.

Furthermore, it is particularly preferred that a volume of gas Vol ₂₂ between the outlet of the vacuum pump and the check valve is smaller than a volume of gas Vol ₁₄ between the inlet valve and the inlet of the vacuum pump. In particular, a ratio of Vol ₂₂ / Vol _{14 is} less than 1.0, preferably less than 0.2 sought. This makes it possible that when opening the bypass valve, the pressure on the outlet side of the vacuum pump is brought to a sufficiently low level. As a result, a particularly high energy savings can be achieved. The corresponding volumes can be realized, in particular, by using as short lines as possible on the outlet side, in particular with small cross sections, and longer lines on the inlet side, possibly with larger cross sections. It is also possible on the inlet side to provide a buffer container for enlarging the inlet-side volume Vol ₁₄ .

Preferably, the vacuum pump system according to the invention will be operated in such a way that when the inlet valve is closed, the bypass valve is also closed when the pressure p ₂ at the inlet of the vacuum pump exceeds a predetermined limit. This results in a pumping of medium in the direction of the outlet through the check valve 24 ,

In a further preferred operating state of the vacuum pump system according to the invention, when the inlet valve is closed, the bypass valve closes when the power or current consumption of the vacuum pump exceeds a predetermined limit value. As a result, for example, an overloading of the vacuum pump can be avoided.

In a further preferred operating state of the vacuum pump system, in which no inlet valve is disposed in the provided between the chamber and the vacuum pump connecting line, occurs at small gas flows out of the chamber opening of the bypass valve, when a pressure p ₂ at the inlet of the vacuum pump or a Pressure p _in the chamber falls below a predetermined limit. Once again, the bypass valve is closed when a further limit value for the pressure p ₂ or p _{in is} exceeded.

Furthermore, the invention relates to a method for operating a vacuum pump system with lock chamber as described above. Here, the vacuum pump is operated in a standby mode as described above, so that in particular fully closed inlet valve and in particular completely open bypass valve, the vacuum pump operated at reduced outlet pressure and preferably rated speed, and thus optimally prepared for the next pumping, however at a reduced power consumption. The method according to the invention is preferably developed as described above with reference to the vacuum pump system.

The invention will be explained in more detail with reference to a schematic drawings. Show it:

1 a schematic representation of a first preferred embodiment of the invention,

2 a schematic representation of a second preferred embodiment of the invention,

3 a schematic representation of a third preferred embodiment of the invention and

4 a schematic diagram of a pressure curve over time.

That in the 1 Vacuum pump system shown has a screw pump 10 on. An inlet 12 the vacuum pump is via an inlet pipe 14 with a chamber, such as a lock or process chamber 16 connected. The chamber 16 has one above a valve 17 (Valve V ₀ ) closable inlet on. In the inlet pipe 14 is a particular controllable inlet valve 18 (Valve V ₁ ) arranged.

With an outlet 20 the vacuum pump 10 is an outlet pipe 22 connected, in which a check valve 24 is arranged. The outlet pipe 22 can be directly connected to the atmosphere or with an exhaust system with a given system pressure. This system pressure may be higher or lower than the atmospheric pressure.

Furthermore, the outlet pipe 22 via a bypass line 30 with the inlet pipe 14 connected. In the bypass line 30 is a particular electrically switchable bypass valve 26 (Valve V ₂ ) arranged. Furthermore, a control device 28 provided, at least with the starting valve 18 and the bypass valve 26 is connected to control these valves. Furthermore, the control device 28 be connected to a pressure sensor arranged in the process chamber. It is also possible that the control device 28 for controlling the vacuum pump 10 serves.

To evacuate the chamber 16 is the inlet valve 18 opened and the bypass valve 26 closed. The gas to be delivered is thus from the vacuum pump 10 over the inlet pipe 14 sucked in and over the outlet pipe 22 through the check valve 24 dissipated. As soon as a certain target pressure is reached in the chamber, the inlet valve becomes 18 by the control device 28 closed and at the same time or delayed the bypass valve 26 open. In this standby mode, further, the speed of the vacuum pump 10 be reduced, leaving a relatively small amount of gas from a vacuum pump 10 through the bypass line 30 is promoted in a circle. As a result, at low power consumption, the vacuum pump 10 be kept fully operational.

To prevent leaks, the vacuum pump system is hermetically sealed. If slight leaks still occur in standby mode, it might be possible to use the bypass valve at short notice 26 to close a portion of the circulating in standby mode medium through the check valve 24 with possibly increased pump speed dissipate. Subsequently, the bypass valve 26 be opened again, so that in turn a small amount of gas can be conveyed in a circle.

In the 2 and 3 are similar or identical components marked with the same reference numerals.

At the in 2 illustrated embodiment is in the inlet pipe 14 in addition another vacuum pump 32 , For example, a roots pump arranged. The bypass line 30 is connected to a part of the inlet line, which is the two vacuum pumps 10 . 32 combines. Such an arrangement is, for example, useful if it is in the chamber 16 is a process chamber and the inlet valve 18 in standby mode is not completely closed, leaving the process chamber 16 even in standby mode, a small amount of gas is pumped out.

With the in 3 illustrated embodiment is in series with the vacuum pump 10 another vacuum pump 34 , For example, a roots pump arranged. The bypass line 30 bridges the two vacuum pumps 10 . 32 , In particular, the pump power of the overall system can be increased by this pump arrangement.

A typical cycle of, for example, in 1 illustrated vacuum pump system provides 4 represents.

The valve designated V ₀ 17 is for filling the lock chamber 16 open. During this period, the pressure p _in shown as a solid line increases in the chamber 16 on p _out , ie at ambient pressure. At the same time that is with 18 designated valve V ₁ closed, so that at the inlet of the vacuum pump 10 a pressure p ₂ prevails. This one is in 4 shown as a dashed line. When opening the with 18 designated Vetils V ₁ increases first the pressure p ₂ at the pump inlet and also the pressure p ₁ at the pump outlet, which is a dotted line in 4 is shown. Before opening the valve V ₁ , the pressure p ₂ decreases in the short term, as that with 26 designated valve V _{2 is} closed, just before the valve V _{1 is} opened.

During the Abpumpzeit, during which the valve V ₁ open, the valves V _o and V _{2 are} closed, there is an evacuation of the lock chamber 16 to a minimum pressure, then in closing the valve V _1, both the pressure p _in in the lock chamber 16 corresponds, as well as the inlet pressure at the vacuum pump 10 is minimal. Since that as a bypass valve 26 designated valve V _{2 is} closed, prevails in the outlet 22 Ambient pressure.

In the next period, the idle time or the standby mode, shortly after closing the valve V ₁ , the valve V _{2 is} opened. As a result, initially takes place essentially a pressure equalization through the bypass line 30 in the corresponding areas of the lines 14 and 22 instead of. The dashed line pressure p ₂ at the inlet of the vacuum pump 10 thus increases a bit. At the same time it falls in the area of the outlet 20 . 22 prevailing pressure p ₁ (dotted line). Since the pressure drop p ₁ according to the invention should be significantly greater than the pressure increase p ₂ , the volume Vol ₂₂ must be correspondingly greater than the volume Vol ₁₄ . During idle time, these pressures are maintained accordingly. Since the valve V _{1 is} closed, the pressure change in the inlet 14 no effect on the pressure in the lock chamber 16 ,

In the next period, the lock time is opened with the valve V ₁ closed, the valve V ₀ and the cycle begins again.

Claims (16)

Vacuum pump system with a vacuum pump ( 10 ), in particular a dry-compressing vacuum pump such as a screw pump, one via an inlet line ( 14 ) with an inlet ( 12 ) of the vacuum pump ( 10 ) connected chamber ( 16 ), one in one with an outlet ( 20 ) of the vacuum pump ( 10 ) connected outlet pipe ( 22 ) arranged check valve ( 24 ), one with the outlet ( 22 ) and the inlet pipe ( 14 ) connected bypass line ( 30 ), one in the bypass line ( 30 ) arranged switchable bypass valve ( 26 ), and one with the bypass valve ( 26 ) ( 28 ). Vacuum pump system according to claim 1, characterized in that the control device ( 28 ) in a standby mode, the bypass valve ( 26 ) opens to the vacuum pump ( 10 ) fully operational at reduced power consumption. Vacuum pump system according to claim 1 or 2, characterized by a in the inlet line ( 14 ) arranged switchable inlet valve ( 18 ). Vacuum pump system according to claim 1 to 3, characterized in that the control device ( 28 ) with the inlet valve ( 14 ) and in the standby mode the control device ( 28 ) the inlet valve ( 18 ) at least partially, preferably completely closes. Vacuum pump system according to one of claims 1-4, characterized in that the bypass line ( 30 ) between the inlet valve ( 18 ) and the inlet ( 12 ) of the vacuum pump ( 10 ) with the inlet line ( 14 ) connected is. Vacuum pump system according to one of claims 1-5, characterized in that the bypass line ( 30 ) between the check valve ( 24 ) and the outlet ( 20 ) of the vacuum pump with the outlet line ( 22 ) connected is. Vacuum pump system according to one of claims 1 to 6, characterized in that the speed in the standby mode is in the range of 20 to 100% of the rated speed. Vacuum pump system according to one of claims 1 to 7, characterized in that the vacuum pump system is hermetically sealed. Vacuum pump system according to one of claims 1 to 8, characterized in that in series with the vacuum pump ( 10 ) at least one further vacuum pump ( 32 . 34 ) is arranged. Vacuum pump system according to claim 9, characterized in that the bypass line ( 30 ) with a connecting line between the vacuum pump ( 10 ) and the further vacuum pump ( 32 ) connected is. Vacuum pump system according to one of claims 1 to 10, characterized in that a volume of gas Vol ₂₂ between the outlet of the vacuum pump ( 10 ) and the check valve ( 24 ) is less than a volume of gas Vol ₁₄ between the inlet valve ( 18 ) and the inlet ( 12 ) of the vacuum pump ( 1 ), wherein the volume ratio Vol ₂₂ / Vol _{14 is} preferably less than 1.0 and more preferably less than 0.2. Method according to one of claims 1-11, wherein the inlet valve ( 18 ) upon reaching a setpoint pressure in the process chamber ( 16 ) is closed. Method according to one of claims 1-12, wherein when the setpoint pressure in the process chamber is exceeded, the inlet valve ( 18 ) is opened. Method according to one of claims 3-13, wherein the bypass valve ( 26 ) with closed inlet valve ( 18 ) is closed when the pressure p ₂ at the inlet ( 12 ) of the vacuum pump ( 10 ) exceeds a predetermined limit. Method according to one of claims 3-14, wherein the bypass valve ( 26 ) with closed inlet valve ( 18 ) is closed when a power or current consumption of the vacuum pump ( 10 ) exceeds a predetermined limit. Method according to Claim 1 or 2, in which, if no inlet valve ( 18 ) is provided, with small gas flows from the chamber ( 16 ) the bypass valve ( 26 ) is opened when a pressure p ₂ at the inlet of the vacuum pump ( 10 ) or a pressure p _in in the chamber ( 16 ) falls below a predetermined limit and the bypass valve ( 26 ) is closed again when a further limit value of the pressure p ₂ or the pressure p _{in is} exceeded.

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