Vacuum system with a multi-stage and multi-inlet vacuum pump with a directional element separating pump stages

Abstract

The invention relates to a vacuum system, comprising a vacuum pump, preferably turbomolecular pump, and at least one vacuum chamber, wherein the vacuum pump comprises: at least a first and a second inlet and a common outlet; at least a first and a second pumping stage, each pumping stage comprising at least one rotor element being arranged on a common rotor shaft, wherein the first inlet is connected to an upstream end of the first pumping stage and the second inlet is connected to an upstream end of the second pumping stage; a direction element for preventing a gas flow from a downstream end of the first pumping stage to the second inlet; a conduit having a conduit inlet and a conduit outlet, wherein the conduit inlet is connected to the downstream end of the first pumping stage and the conduit outlet is connected to a location downstream of the second pumping stage; wherein the first inlet and the second inlet of the pump are connected to the same vacuum chamber.

Claims

1. A vacuum system comprising a vacuum pump and at least one vacuum chamber, wherein the vacuum pump comprises: at least a first and a second inlet and a common outlet; at least a first and a second pumping stage, each pumping stage comprising at least one rotor element being arranged on a common rotor shaft, wherein the first inlet is connected to an upstream end of the first pumping stage and the second inlet is connected to an upstream end of the second pumping stage; a direction element for preventing a gas flow from a downstream end of the first pumping stage to the second inlet; a conduit having a conduit inlet and a conduit outlet, wherein the conduit inlet is connected to the downstream end of the first pumping stage and the conduit outlet is connected to a location downstream of the second pumping stage; wherein the first inlet and the second inlet of the pump are connected to the same vacuum chamber; wherein the direction element comprises a static block wall and a blocking wall that is arranged on the rotor shaft, wherein the blocking wall on the rotor shaft and the static blocking wall are arranged in close axial proximity to each other.

2. The vacuum system according to claim 1, wherein both pumping stages define respective gas streams which are separate from each other and flow in parallel mode upstream of the location to which the conduit outlet is connected.

3. The vacuum system according to claim 1, wherein the pump comprises a third pumping stage, wherein the downstream end of the second pumping stage and/or the conduit outlet are connected to an upstream end of the third pumping stage.

4. The vacuum system according to claim 1, wherein the pump comprises a third inlet connected to the upstream end of a third pumping stage, the conduit outlet and/or the downstream end of the second pumping stage, wherein the third inlet is connected to a second vacuum chamber.

5. The vacuum system according to claim 1, wherein the direction element comprises at least one blocking wall.

6. The vacuum system according to claim 5, wherein the blocking wall comprises a disc.

7. The vacuum system according to claim 1, wherein the direction element defines a gap between a rotating part and a static part, the gap having an elongate extension.

8. The vacuum system according to claim 1, wherein the direction element comprises a reverse pumping stage, effecting a gas flow from the second inlet to the conduit inlet and/or to the downstream end of the first pumping stage.

9. The vacuum system according to claim 8, wherein the reverse pumping stage comprises a rotor element which is arranged on the common rotor shaft.

10. The vacuum system according to claim 8, wherein the reverse pumping stage comprises a pumping direction which is opposite a pumping direction of the first and/or second pumping stage.

11. The vacuum system according to claim 1, wherein the conduit inlet and a rotating element arranged on the rotor shaft are arranged such that the conduit inlet is open to a radial end of the rotating element.

12. The vacuum system according to claim 1, wherein the vacuum pump comprises at least two first pumping stages and at least two first inlets corresponding respectively thereto, the downstream ends of all first pumping stages being connected to a location downstream of the second pumping stage and being separated from the second inlet and/or the first inlet of a neighboring first pumping stage.

13. The vacuum system according to claim 1, wherein the vacuum chamber is part of a mass spectrometry and/or chromatography system.

14. A method of using the vacuum pump of claim 1 to evacuate the at least one vacuum chamber, the method comprising the step of: bypassing the second pumping stage and/or the second inlet via the conduit.

15. A vacuum system comprising a vacuum pump and at least one vacuum chamber, wherein the vacuum pump comprises: at least a first and a second inlet and a common outlet; at least a first and a second pumping stage, each pumping stage comprising at least one rotor element being arranged on a common, rotor shaft, wherein the first inlet is connected to an upstream end of the first pumping stage and the second inlet is connected to an upstream end of the second pumping stage; a Holweck pumping stage arranged on the common rotor shaft downstream of the at least first and second pumping stages; a direction element for preventing a gas flow from a downstream end of the first pumping stage to the second inlet; a conduit having a conduit inlet and a conduit outlet, wherein the conduit inlet is connected to the downstream end of the first pumping stage and the conduit outlet is connected to a location downstream of the second pumping stage; wherein the first inlet and the second inlet of the pump are connected to the same Vacuum chamber; wherein the direction element comprises a blocking wall which is arranged on the rotor shaft.

16. A method of using the vacuum pump of claim 15 to evacuate the at least one vacuum chamber, the method comprising the step of bypassing the second pumping stage and/or the second inlet via the conduit.

17. A vacuum system, the vacuum comprising a vacuum pump and at least one vacuum chamber, wherein the vacuum pump comprises: at least a first and a second inlet and a common outlet; at least a first and a second pumping stage, each pumping stage comprising at least one rotor element being arranged on a common rotor shaft, wherein the first inlet is connected to an upstream end of the first pumping stage and the second inlet is connected to an upstream end of the second pumping stage; a Holweck pumping stage arranged on the common rotor shaft downstream of the at least first and second pumping stages; a direction element for preventing a gas flow from a downstream end of the first pumping stage to the second inlet; a conduit having a conduit inlet and a conduit outlet, wherein the conduit inlet is connected to the downstream end of the first pumping stage and the conduit outlet is connected to a location downstream of the second pumping stage; wherein the first inlet and the second inlet of the pump are connected to the same vacuum chamber; wherein the direction element comprises a static blocking wall and a blocking wall which is arranged on the rotor shaft.

18. A method of using the vacuum pump of claim 17 to evacuate the at least one vacuum chamber, the method comprising the step of bypassing the second pumping stage and/or the second inlet via the conduit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is described in more detail with reference to some exemplary embodiments, such as shown in the schematic drawings.

(2) FIG. 1 shows a vacuum system according to the invention.

(3) FIG. 2 depicts a vacuum pump with a direction element embodied as a blocking wall according to the invention.

(4) FIG. 3 shows a further vacuum pump with a blocking wall.

(5) FIG. 4 shows another vacuum pump with a blocking wall.

(6) FIG. 5 shows a vacuum pump for a vacuum system in accordance with the invention.

(7) FIG. 6 shows another vacuum system in accordance with the invention having two blocking walls.

(8) FIG. 7 depicts another vacuum system in accordance with the invention comprising a reverse pumping stage.

(9) FIG. 8 shows another vacuum system in accordance with the invention comprising three first pumping stages.

DETAILED DESCRIPTION OF THE INVENTION

(10) In FIG. 1, a vacuum system 10 in accordance with the invention is shown. The vacuum system 10 comprises two vacuum chambers, a first vacuum chamber 12 and a second vacuum chamber 14. The vacuum chambers 12, 14 are connected to respective inlets of a vacuum pump 16.

(11) In particular, the pump comprises a first inlet 18 and a second inlet 20, both connected to the same vacuum chamber, i.e. the first vacuum chamber 12. The vacuum pump 16 further comprises a third inlet 22 connected to the second vacuum chamber 14. The inlets 18, 20, 22 are indicated as respective arrows representing a gas stream during pumping action.

(12) The vacuum pump 16 is, in this example, a turbomolecular and split-flow pump and comprises a first pumping stage 24, a second pumping stage 26, a third pumping stage 28 and a fourth pumping stage 30, wherein each pumping stage comprises at least one rotor element 44, three in this embodiment, arranged on a common rotor shaft 32. The rotor shaft 32 forms a rotor of the pump 16. During operation of the pump 16, the rotor shaft 32 rotates at high speed about its longitudinal axis or rotor axis. The rotor elements 44 rotate together with the rotor shaft 32 and cause a pumping effect from the inlets 18, 20, 22 to the common outlet, in the drawings always from right to left (not true for the direction elements and reverse pumping stages as described below).

(13) The first, second and third pumping stages 24, 26 and 28 are turbomolecular pumping stages indicated as three vertical lines each representing a pair of turbo-molecular rotor and stator elements. In this embodiment, each of the pumping stages 24, 26, and 28 comprises three such pairs of turbomolecular rotor and stator elements. However, other numbers and arrangements of turbomolecular rotor and stator elements are possible.

(14) The fourth pumping stage is a molecular drag pumping stage and, in particular, a Holweck pumping stage.

(15) All pumping stages 24, 26, 28 and 30 effect a pumping action in the same direction, which is parallel to the rotor shaft 32, in FIG. 1 from right to left. All gas coming from the vacuum chambers 12 and 14 is pumped to a common outlet, which is not shown but is located downstream of the fourth pumping stage.

(16) The vacuum pump 16 further comprises a direction element, embodied here as a blocking wall 34. The blocking wall 34 prevents gas from flowing from a downstream and of the first pumping stage 24 to the second inlet 20 and an upstream end of the second pumping stage 26.

(17) There is further provided a conduit 36 having a conduit inlet 38 connected to the downstream end of the first pumping stage 24 and a conduit outlet 40 connected to a location downstream the second pumping stage 26, and, in the present case, connected to an upstream end of the third pumping stage 28.

(18) The conduit 36 bypasses the inlet 20 and the second pumping stage 26. It may, for example, be formed in a housing of the vacuum pump, a separate block, and/or a tube or hose.

(19) As can be seen in FIG. 1, the first and second pumping stages 24 and 26 are essentially arranged in parallel mode, wherein respective gas streams through the first and second pumping stages 24 and 26 are united at the location downstream the second pumping stage 26 to which the conduit outlet 40 is connected. In the present case, the same location is connected to the third inlet 22 and the upstream end of the third pumping stage 28.

(20) As will be understood, the pressure in the second vacuum chamber 14 will be higher than the pressure in the first vacuum chamber 12. The vacuum chambers 12 and 14 may be connected to each other by means of a small orifice allowing a limited gas stream from the second vacuum chamber 14 to the first vacuum chamber 12.

(21) In FIG. 2, a vacuum pump 16 in accordance with the invention is depicted schematically and in part. The vacuum pump 16 comprises a housing 42, in which a rotor is arranged, the rotor comprising a rotor shaft 32 and at least one pair of turbo rotor and stator elements 44. The rotor further comprises at least one second pumping stage, not shown here. The housing 42 defines a first inlet 18 and a second inlet 20. A downstream end of the first pumping stage 24 is essentially sealed from the inlet 20 by means of a blocking wall 34. The blocking wall 34 surrounds the rotor 32, although in FIG. 2 only an upper half of the blocking wall 34 is shown.

(22) The blocking wall 34 is a static blocking wall as it is fixed to the housing 42. It comprises an axial bore, through which the rotor shaft 32 extends. Between the rotor shaft 32 and the blocking wall 34 there is provided a radial gap 46 circumferentially extending about the rotor shaft 32. The radial gap 46 provides for a radial clearance for allowing radial deflection of the rotor shaft 32, as can occur during pumping operation. Essentially, the radial gap 46 corresponds to the maximum radial deflection of the rotor shaft 32 including security tolerances.

(23) However, FIG. 2 is not to scale and the radial gap 46 is small, for example in the domain of some tenth of a millimeter. Thus, the radial gap provides a rather high resistance for the gas to flow from the downstream end of the first pumping stage 24 to the second inlet 20.

(24) The conduit 36, not shown in FIG. 2, preferably comprises a resistance, which is much lower than the resistance of the radial gap. Thus, the conduit 36 preferably comprises a high conductance, whereas the radial gap 46 preferably comprises a low conductance.

(25) Another embodiment is depicted in schematic FIG. 3. In this embodiment, the direction element also comprises a blocking wall 34 fixed to the housing 42, in particular to an inner surface thereof. The direction element further comprises a sleeve 48 defining the radial gap 46 and providing for an elongate axial extension thereof. This elongate axial extension of the radial gap 46 provides for a long sealing length and, thus, for an advantageous sealing and direction effect.

(26) At least one of the opposing surfaces defining the radial gap 46, i.e. at least one of the sleeve 48 and the rotor shaft 32, may comprise an active pump structure, such as a molecular drag pump structure and/or Holweck structure. A gas stream 50 effected by such a pump structure is indicated as an arrow representing a resulting gas stream and leading from the first inlet 20 to the downstream end of the first pumping stage 24. Thus, the pumping direction of the pump structure is directed opposite the one of the first pumping stage 24. Hence, the pump structure acts as a reverse pumping stage.

(27) Such a pump structure may also be implemented at an inner surface of the blocking wall 34 facing the rotor 32 as shown in FIG. 2 and/or opposing surfaces between blocking wall 52 and housing 42, as will be described in more detail with respect to FIG. 4.

(28) In FIG. 4, a further embodiment is shown, wherein the direction element comprises a blocking wall 52, which is arranged on the rotor shaft 32. Thus, the blocking wall 52 rotates together with the rotor shaft 32 and the rotor elements 44 of the respective pumping stages. In this embodiment, a radial gap 54 is defined between the blocking wall 52 and a static element of the pump 16, i.e. the housing 42. The radial gap 54 may, as well, comprise an elongate axial extension and/or a pump structure at least at one of its opposing surfaces, i.e. at least at the inner surface of the housing 42 or the outer surface of the blocking wall 52.

(29) FIG. 5 is a more complete depiction of the embodiment of FIG. 2 with respect to the interior of the pump 16. Also, a conduit 36 is indicated as a corresponding arrow representing a gas stream from the downstream end of the first pumping stage 24 to a location downstream the second pumping stage 26. As can be seen here more clearly, the blocking wall 34 surrounds the rotor shaft 32, wherein the rotor shaft 32 extends through an axial bore of the blocking wall 34.

(30) In FIG. 6, there is shown another vacuum system 10 having a plurality of vacuum chambers, namely a first vacuum chamber 12, a second vacuum chamber 14 and a third vacuum chamber 56. The vacuum chambers are connected to associated inlets of a vacuum pump 16. In particular, the first vacuum chamber 12 is connected to first and second inlets 18, 20, the second vacuum chamber 14 is connected to a third inlet 22, and the third vacuum chamber 56 is connected to a fourth inlet 58 of the vacuum pump 16.

(31) The vacuum pump 16 comprises four pumping stages 24, 26, 28, 30 each connected to and associated with a respective inlet 18, 20, 22, 58 and each effecting a pumping action from the respective inlet towards the common outlet (not shown), as indicated by the arrows extending through the pump 16.

(32) During operation of the vacuum system 10, there will develop different pressure levels, i.e. different vacuum levels, in the vacuum chambers 12, 14, and 56, as their respective inlets are connected to successive pumping stages. The first and second inlets 18, 20 are connected to equally ranking pumping stages 24 and 26, as regards inlet pressure. The third inlet 22 is connected to the third pumping stage 28, which succeeds—i.e. is arranged downstream of—the first and second pumping stages 24, 26. Thus, the pressure at the third inlet 22 is generally higher. Similarly, the fourth inlet 58 is connected to the fourth pumping stage 30, which succeeds the third pumping stage 28. Thus, the pressure at the fourth inlet 58 is higher than at the third inlet 22.

(33) The chambers 12, 14, 56 are connected to the neighboring ones by means of two orifices 60, 62 of different sizes, as indicated by the arrows of different sizes extending therethrough and representing a gas stream. The orifices 60, 62 are small in relation to the pumping speed of the respective pumping stages, such that different vacuum levels still develop in the respective chambers 12, 14, 56.

(34) There are a couple of further optional refinements to point out. The pump 16 comprises a static blocking wall 34. It is generally difficult to completely seal the blocking wall 34 to the rotor shaft 32 since the shaft 32 is spinning and needs some clearance for shock and vibration. The blocking wall 34 may be made in two halves to facilitate installation and these halves have to seal together at least in a molecular flow sense. A snout and/or sleeve can be added, which wraps around the shaft 32 as long as an appropriate clearance can be maintained. An optional improvement to reduce the leakage through the blocking wall 34 is to add an additional blocking wall 52, which is arranged on the rotor shaft 32 and in close axial proximity to the static blocking wall 34. The rotor blocking wall 52 is embodied as a spinning flat plate attached to the shaft 32.

(35) This arrangement provides for an axial gap 64 between the blocking walls 34 and 52, which has a relatively long radial extension and, thus, a relatively long sealing length, which even adds to the sealing length of the radial gaps 46 and 54. As a further benefit, gas molecules in the small axial gap 64 between the surfaces tend to hit the spinning disc, i.e. the blocking wall 52, and are flung outward. This further reduces the leakage from the downstream end of the first pumping stage 24 to the second inlet 20.

(36) In the embodiment of FIG. 6, the conduit inlet 38 and the rotor blocking wall 52 are arranged such that the conduit inlet 38 is open to a radial end of the blocking wall 52. Gas molecules striking the radial end of the blocking wall 52 receive a tangential vector which increases the pumping toward the conduit. Thus, pumping speed is further improved.

(37) Another optional refinement is exposing the radial end at least of the last rotor element of the first pumping stage to the conduit inlet 38, as shown. Normally, trying to pump “from the side” of a rotor has a negligible effect on pumping speed. That is because the molecules are flung back out into the chamber, which is to be evacuated. In the case of the conduit, however, it is aimed for pumping molecules radially and then parallel to the axis and the tangential vector helps instead of hurts. Considering the cosine distribution of molecules leaving a surface, it might be generally advantageous to add an angled surface to the conduit inlet, in particular across from an exposed rotating element, a turbo rotor element in this example, to deflect the molecules down the conduit.

(38) In general, a blocking wall may be essentially designed like rotor or stator elements of turbomolecular pumping stages, except that the blocking wall lacks turbo vanes. In particular, the blocking wall may be fixed to a static element, such as the housing, or to the rotor in a manner known from rotor or stator elements. For example, a static blocking wall may be positioned by means of spacing rings disposed at an inner surface of a housing and between neighboring static elements. A blocking wall arranged on the rotor may be formed as an integral part of a one-piece rotor or may be formed as a disc mounted on a rotor shaft, just like known turbo rotor elements.

(39) In FIG. 7, a further embodiment of a vacuum system is shown as being essentially designed like the one of FIG. 6, except that the pump 16 comprises a reverse pumping stage 66 serving as a direction element and preventing a gas flow from the downstream end of the first pumping stage 24 to the second inlet 20 and the upstream end of the second pumping stage 26.

(40) The reverse pumping stage 66 comprises an opposingly arranged, in particular left-handed, set of rotor and stator elements. It causes a pumping action in an opposite geometrical direction as the first pumping stage 24 and gas streams of the two are united at the conduit inlet 38, as indicated in FIG. 7 by the corresponding arrows.

(41) In this embodiment, the reverse pumping stage comprises three sets of rotor/stator pairs, although other numbers of rotors and stators are possible. The conduit inlet 38 is, in the present case, open to a radial end of a final rotor element of both the first and reverse pumping stages 24, 66.

(42) In an embodiment, each of the first, second and reverse pumping stages 24, 26, and 66 comprises a pumping speed of about 300 L/s. At first glance one might think that 900 L/s could be achieved. However, with the practical limits of the shaft length, the conduit conductance may be limited by the size of the conduit inlet 38. Thus, the additional pumping action of the reverse pumping stage 66, preferably using an extra set of left-handed rotors and stators, might not actually achieve much improvement with respect to resulting pumping speed. However, the direction function of the reverse pumping stage might still be beneficial.

(43) The conduction of the conduit 38 may generally be poor. For example, in the embodiments of FIGS. 6 and 7, the gas must make two 90 degree turns and travel the length of the second inlet and several rotor/stator pairs, and then make an additional two 90 degree turns before hitting the third pumping stage 28. However, if enough compression is provided upstream of the conduit 38, i.e. by the first pumping stage 24, then the throughput is quite sufficient to handle the compressed gas despite what appears to be a low conductance. In fact, the cross-section area of the conduit 38 does not need to be very large compared to the pump cross-section area, because of the compression. In nitrogen and water, two or three rotors may be sufficient for each path depending on implementation, because about two orders of magnitude of compression can be achieved. Often, the first rotor element of a pumping stage is a thicker high pumping speed and low compression rotor element. But higher compression rotor elements might allow just two rotor/stator pairs to be workable. Since achieving the necessary compression in a small number of rotor/stator pairs is difficult in helium and hydrogen, this invention may be difficult to implement in gas chromatography mass spectrometry (abbreviated as GC/MS), requiring more rotor/stator pairs and/or more shaft length. Preliminary analysis suggests that 1.5× pumping speed improvements are possible in LC/MS applications using known current motor, shaft, and bearing technology.

(44) Generally, further inlets could be provided for connection to the first chamber 12. The further inlets preferably may be combined in the conduit or provided with separate conduits. This not only may further increase the pumping speed applied to the first chamber 12 but also makes for a distributed pump which has its pumping speed distributed along a long rectangle area rather than in a large circle. The advantages are significant. First, the pump can be run faster than a conventional turbo pump of the same pumping speed making it more space efficient and cheaper. Secondly, for linear systems such as are common in mass spectrometry, or other physically linear systems, the pump width would then continue to match the manifold. The manifold could enjoy the advantage of the higher pumping speed without having to switch to a more expensive larger manifold. In the case of systems with gas loads distributed along an axis, the inherent limitation of the manifold end-to-end conduction is relieved, because the gas is transported from the various inlets in a compressed form back to the final molecular and then viscous compression stages.

(45) Although both FIGS. 6 and 7 show a third inlet 22 across from the conduit outlet 40, it would also be possible to have the conduit 38 reenter the pump before or after the third inlet 22 depending on the pressure of that third inlet 22. In some systems, there would be no need for this third inlet 22. Similarly, the fourth inlet 58 connected to the fourth pumping stage 30, which is a molecular drag stage in the present embodiment, of the pump 16 might not be needed in some systems. The figures show a single conduit 40. It could be arranged on the same side of the pump 16 as a controller, thus fitting into a volume that is often an empty space in a product. However, multiple parallel conduits are also possible. For example, four parallel conduits, one in each corner, could allow the pump to contain its own conduits within the confines of a rectangular extrusion, which is only a little larger than the rotor diameter.

(46) FIG. 8 shows another vacuum system 10, which generally corresponds to the one shown in FIG. 6 except that the vacuum pump comprises three first pumping stages 24.1, 24.2 and 24.3 and three first inlets 18.1, 18.2 and 18.3 corresponding respectively thereto, i.e. the first inlet 18.1 is connected to the upstream end of the first pumping stage 24.1 and so forth as shown. The downstream ends of all first pumping stages 24.1, 24.2, 24.3 are connected to a location downstream of the second pumping stage 26 by means of a common conduit 36. The downstream ends of each first pumping stage 24.1, 24.2, 24.3 are separated from the second inlet and the first inlet 18.2, 18.3 of a respective neighboring first pumping stage 24 as well as from the upstream ends of stages 26, 24.2 and 24.3 by means of direction elements 34.1, 52.1, 34.2, 52.2, 34.3, 52.3. The first inlets 18 and the second inlet 20 are all connected to the same vacuum chamber 12. The first pumping stages 24 and the second pumping stage 26 operate in parallel mode. Generally, there may be any number of first pumping stages, in particular characterized in that their downstream ends are connected to a location downstream of the second pumping stage and separated from the second inlet or a neighboring first inlet, in particular by means of a direction element, in particular wherein the upstream ends of all first pumping stages are connected to the same vacuum chamber as the upstream end of the second pumping stage.

LIST OF REFERENCE NUMBERS

(47) 10 vacuum system 12 first vacuum chamber 14 second vacuum chamber 16 vacuum pump 18 first inlet 20 second inlet 22 third inlet 24 first pumping stage 26 second pumping stage 28 third pumping stage 30 fourth pumping stage 32 rotor shaft 34 blocking wall 36 conduit 38 conduit inlet 40 conduit outlet 42 housing 44 pair of rotor/stator elements 46 radial gap 48 sleeve 50 gas stream 52 blocking wall 54 radial gap 56 third vacuum chamber 58 fourth inlet 60 orifice 62 orifice 64 axial gap 66 reverse pumping stage