WO2007063341A1

WO2007063341A1 - Multi-stage roots vacuum pump

Info

Publication number: WO2007063341A1
Application number: PCT/GB2006/050405
Authority: WO
Inventors: Paul Simon Warbey
Original assignee: Edwards Limited
Priority date: 2005-12-02
Filing date: 2006-11-21
Publication date: 2007-06-07
Also published as: GB0524649D0; TW200730728A

Abstract

A multi-stage Roots vacuum pump comprises a plurality of stator slices. Each stator slice comprises a pumping chamber for receiving intermeshing Roots rotor components. The pump further comprises a channel arrangement (122) for conveying fluid between the pumping chambers . The channel arrangement comprises a plurality of first channels (132,142) each formed in a surface of a respective stator slice and extending about the pumping chamber of that stator slice, and a plurality of second channels (144) , each extending through a respective stator slice, for transferring fluid between the first channels.

Description

MULTI-STAGE ROOTS VACUUM PUMP

The present invention relates to a vacuum pump, and in particular a vacuum pump comprising a Roots rotor mechanism.

A known type of large capacity multi-stage Roots vacuum pump, for example having a capacity of approximately 400m³/hr or higher, comprises a plurality of interconnected pumping chambers. Each pumping chamber houses a respective pair of contra-rotating, cooperating, Roots rotors, each rotor being mounted on a respective drive shaft. In use, the drive shafts serve to rotate the Roots rotors, which act in combination with the stator to transport fluid through the vacuum pump.

It is known to form the stator of such a vacuum pump from a plurality of stator slices. A pumping chamber is formed in each respective stator slice, which are assembled together along the drive shafts.

Such a vacuum pump is illustrated in Figures 1 and 2. The vacuum pump 10 comprises a plurality of stator slices 12, 14, 16, 18, 20, each defining a respective pumping chamber 22, 24, 26, 28, 30. The pumping chambers are interconnected by transfer channels 32, each transfer channel being located within a respective stator slice. Each pumping chamber houses a pair of lobed Roots rotors 34 to define a respective stage of the vacuum pump. The rotors 34 are mounted on respective drive shafts (not shown), which in use are rotated in the directions indicated in Figure 1. This causes fluid to pumped through each pumping chamber from an inlet region 36 of that chamber to an outlet region 38 of that pumping chamber.

The rotors of each stage act to transport fluid through the pumping chambers in a common direction, in this example from an upper (as illustrated) region of the pump 10 to a lower region of the pump 10. It is, therefore, necessary to configure the transfer channels 32 to provide a path along which the fluid from an outlet region 38 of one pumping chamber can be transported to the inlet region 36 of the adjacent pumping chamber. In the example illustrated in Figure 2, each transfer channel 32 has, in cross-section, an "S" - shape to enable the pumped fluid to be transported through the pump 10. This necessitates that these transfer channels 32 are formed using a complex coring, casting technique.

There are a number of disadvantages associated with a coring casting technique. Firstly, the costs associated with cored castings are very high. Secondly, the technique involves a multiple stage and therefore complex manufacturing process, and the transfer channels, once formed, can be hard to clean thoroughly after the casting process. Consequently, residue from the cores may be conveyed into other regions of the pump (such as the gear box) during operation, causing deterioration of conditions in those regions. Furthermore, the space available for providing these transfer channels is limited and the conductance of these channels is therefore compromised. Indeed, from Figure 2 it can be seen that provision of an S-shaped transfer channel 32 within a respective stator slice results in the assembled vacuum pump 10 having a considerable overall length.

It is therefore desirable to provide a multi-stage Roots vacuum pump that does not require the complex coring techniques described above and which, in comparison to pumps manufactured using a complex coring technique, is not only relatively simple to manufacture but also is relatively more compact in length.

The present invention provides a multi-stage Roots vacuum pump comprising a plurality of stator slices, each stator slice comprising a pumping chamber for receiving intermeshing Roots rotor components, and a channel arrangement for conveying fluid between the pumping chambers, the channel arrangement comprising a plurality of first channels each formed in a surface of a respective stator slice and extending about the pumping chamber of that stator slice, and a plurality of second channels, each extending through a respective stator slice, for transferring fluid between the first channels. By forming part of the channel arrangement in the surfaces of the stator slices so that it extends about the pumping chambers, complex coring techniques in a casting process used to fabricate the stator slices can be avoided, thus eliminating problems associated therewith. In contrast, a simpler casting process can be used to form a basic component which can be subsequently machined. All of the machining operations may be carried out from one side of the component, which can lead to a relatively simple manufacturing process that, in turn, can lead to improved geometrical tolerances of the finished stator slice, faster manufacturing times and enhanced reliability in the manufacturing process.

Furthermore, by forming part of the channel arrangement in the surfaces of the stator slices there is an increased freedom of selection of magnitude of the channel arrangement. In other words, the capacity of the channel arrangement can be improved over that which might be achieved through a cored casting technique. This freedom of selection permits a larger capacity channel arrangement to be readily formed in the stator slices close to an inlet portion of the vacuum pump to enable the pump to function more effectively at pressures approaching atmospheric conditions, as may be encountered in load lock applications.

An additional, significant benefit in configuring the channel arrangement in this way is that the thickness of each stator slice can be significantly reduced. In other words, an increased cumulative volume of the pumping chambers, commonly referred to as the swept volume, can be achieved in a pump having the same shaft length, leading to a greater capacity pump.

Alternatively, a shorter shaft may be provided such that dynamic characteristics of the shaft are modified. Most notably, a higher natural frequency would be achieved. Thus the shaft may be rotated faster before a resonant frequency of the shaft is experienced, increasing the capacity of the pump yet further. - A -

Other benefits associated with providing a compact pump are: achieving a lower footprint to enable less end-user processing area to be occupied by vacuum pumping equipment; requiring less material to form the pump and so the basic cost of the material is lower; and having less material to machine and so the cost of machining is lower.

Each second channel is preferably located at respective different position relative to the pumping chamber of its stator slice. By locating the second channel of one stator slice at a different position to that of a subsequent stator slice, direct transfer of fluid between the second channels of adjacent stator slices may be inhibited.

Each of the first channels preferably defines a locus about the pumping chamber of its stator slice. The loci of successive stator slices may be coincident with one another, at least in part, when viewed along a longitudinal axis of the pump. The second channel of one stator slice is preferably at a different position along the locus of the first channel of that stator slice in comparison to the second channel of an adjacent stator slice.

The first channels may have respective different shapes.

The position of the second channel of one stator slice may be closer to the exhaust region of the pumping chamber of that stator slice than that of the immediately preceding (that is, upstream) stator slice. The first channel may be closed by an opposing surface of an adjacent stator slice, or by an end plate depending on its relative position within the pump.

A sealing system may be provided for inhibiting fluid transfer between the pumping chambers and an exterior of the stator slices. The sealing system may be provided between adjacent stator slices and may comprise a plurality of sealing elements each surrounding a respective pumping chamber. These sealing elements may be provided by o-ring seals to provide continuous seals about the pumping chambers. Each first channel may be configured to convey fluid from a second channel to an inlet portion of the pumping chamber of its stator slice. Alternatively, or additionally, each first channel may be configured to convey fluid from an outlet portion of the pumping chamber of its stator slice to a second channel. Each second channel may be configured to convey fluid through its respective stator slice to the first channel of its stator slice. Alternatively, each second channel may be configured to convey fluid through its respective stator slice from the first channel of its stator slice. Each second channel preferably extends substantially orthogonally between opposing surfaces of its stator slice.

The pump may comprise thermal control means for controlling the temperature of the stator slices.

Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 illustrates an axial cross-sectional view of a pumping chamber of a conventional, multi-stage vacuum pump;

Figure 2 illustrates a sectional view through line X-X' of Figure 1 ;

Figure 3 illustrates a sectional view of a first embodiment of a multi-stage vacuum pump;

Figures 4(a) to 4(e) each illustrate an axial view of a respective stator slice of the pump represented in Figure 3; and

Figures 5(a) to 5(e) each illustrate an axial view of a respective stator slice of a second embodiment of a multi-stage vacuum pump.

Figure 3 illustrates a first embodiment of a multi-stage vacuum pump 100 comprising, in this embodiment, five pumping stages. The pump 100 comprises a plurality of stator slices 102, 104, 106, 108, 110 connected together in series, for example by bolting the stator slices together. Each stator slice 102, 104, 106, 108, 1 10 comprises a respective pumping chamber 1 12, 1 14, 116, 1 18, 120. The pumping chambers are interconnected by a channel arrangement, indicated generally at 122 in Figure 3 and described in more detail below, for conveying fluid between the chambers. The channel arrangement 122 comprises a plurality of first channels, each first channel being formed in a surface of a respective stator slice and extending about the pumping chamber of that stator slice, and a plurality of second channels for transferring fluid between the first channels.

One or more of the pumping chambers may be surrounded by a respective o-ring sealing element 124 located between cooperating axial end surfaces of adjacent stator slices to prevent egress of fluid from the pumping chambers to an exterior of the vacuum pump 100, and to prevent ingress of ambient fluid from an exterior of the vacuum pump 100 into the pumping chambers. One such sealing element 124 is illustrated in Figure 3 between stator slices 106 and 108.

The vacuum pump 100 comprises a rotor assembly (not shown in Figure 3) having two cooperating Roots rotors located within each pumping chamber. In operation, the cooperating rotors act in combination with the pumping chamber to cause fluid to be pumped through the vacuum pump 100 from an inlet 126 (illustrated in Figure 4(a)) thereof to an outlet 128 (illustrated in Figure 4(e)) thereof.

The rotors 129 are illustrated in Figures 4(a) to 4(e). Whilst the illustrated rotors 129 have two lobes, three or more lobes may be provided on each rotor 129.

Figure 4(a) illustrates an axial view of surface 130 of stator slice 102; Figure 3 is a cross-sectional view along line Y-Y of Figure 4(a). Pumping chamber 1 12 is formed in the surface 130 of the stator slice 102 which, when the vacuum pump 100 is assembled, is brought into contact with an opposing, substantially planar surface 131 of adjacent stator slice 104. The pumping chamber 1 12 receives fluid to be pumped from the pump inlet 126. A first channel 132 of the channel arrangement 122 is formed in the surface 130 of stator slice 102 and extends about the pumping chamber 1 12. The first channel 132 is in fluid communication with an outlet portion 134 of the pumping chamber 1 12 to receive fluid exhausted from the pumping chamber 1 12.

Figure 4(b) illustrates an axial view of surface 140 of stator slice 104. Pumping chamber 114 is formed in the surface 140 of the stator slice 104 which, when the vacuum pump 100 is assembled, is brought into contact with an opposing, substantially planar surface 141 of adjacent stator slice 106. The stator slice 104 comprises a first channel 142 formed in the surface 140 of stator slice 104 and extending about the pumping chamber 1 14 on both sides thereof. The stator slice 104 further comprises two second channels 144 extending through the stator slice 104, preferably substantially orthogonally between the surfaces 131 , 140 of the stator slice 104, at locations incident with the channel outlets 139.

In operation, the fluid to be pumped enters the pump 100 through inlet 126 and is urged by the rotation of the Roots rotors 129 through the pumping chamber 1 12 to the outlet portion 134. The fluid then passes along the first channel 132 around the outside of the pumping chamber 112. In this embodiment, the first channel 132 extends about the pumping chamber 1 12 in two opposing directions (in this embodiment both clockwise and anticlockwise) which effectively splits the fluid exhausted from the pumping chamber 112 into two portions, with one portion being conveyed to one side of the pumping chamber 1 12 and the other portion being conveyed to the other side of the pumping chamber 1 12. The fluid remains within the first channel 132 until it reaches the outlets 136 from those channels 132. At these locations the fluid is directed into the second channels 144 of the immediately adjacent stator slice 104, and passes through the thickness of the stator slice 104 into the first channel 142 formed in the surface 140 of stator slice 104.

The first channel 142 conveys the fluid received from the second channels 144 to the inlet portion 146 of the pumping chamber 114. The fluid is urged by the rotation of the Roots rotors 129 through the pumping chamber 1 14 to the outlet portion 148 of the pumping chamber 1 14. Similar to the first channel 132 of the stator slice 102, the first channel 142 extends about the pumping chamber 1 14 in two opposing directions which splits the fluid exhausted from the pumping chamber 1 14 into two portions, with one portion being conveyed to one side of the pumping chamber 1 14 and the other portion being conveyed to the other side of the pumping chamber 1 14. The fluid remains within the first channel 142 until it reaches the outlets 149 from that channel 142. The portions of the first channel 142 that extend between the outlet portion 148 of the pumping chamber 142 and a respective outlet 149 are shorter than the corresponding portions of the first channel 132 of the stator slice 102.

Figure 4(c) illustrates an axial view of surface 150 of stator slice 106.

Pumping chamber 116 is formed in the surface 150 of the stator slice 106 which, when the vacuum pump 100 is assembled, is brought into contact with an opposing, substantially planar surface 151 of adjacent stator slice 108. Similar to stator slice 104, the stator slice 106 comprises a first channel 152 formed in the surface 150 of stator slice 106 and extending about the pumping chamber 1 16 on both sides thereof. Again similar to stator slice 104, the stator slice 106 further comprises two second channels 154 extending through the stator slice 106, again preferably substantially orthogonally between the surfaces 141 , 150, at locations incident with the channel outlets 149 from the first channel 142 of the stator slice 104.

The second channels 154 receive fluid from the channel outlets 149 of the first channel 142 of the stator slice 104, and convey that fluid through the stator slice 106 to the first channel 152 of the stator slice 106. The first channel 152 conveys the fluid received from the stator slice 104 to the inlet portion 156 of the pumping chamber 1 16. The first channel 152 subsequently receives fluid from the outlet portion 158 of the pumping chamber 1 16, and conveys fluid to the channel outlets 159 from the first channel 152 of the stator slice 106.

The first channel 152 of the stator slice 106 is thus similar to the first channel 142 of the stator slice 104, with the exception that, as illustrated in Figures 4(b) and 4(c) the portions of the first channel 152 that convey fluid from a second channel into a pumping chamber are longer than those of the first channel 142, whilst the portions of the first channel 152 that convey fluid from a pumping chamber to a second channel are shorter than those of the first channel 142. The second channels 154 of the stator slice 106 are thus at different positions relative to the pumping chamber 1 14 of their stator slice 106 in comparison to the second channels 144 of the stator slice 104.

Figure 4(d) illustrates an axial view of surface 160 of stator slice 108. Pumping chamber 118 is formed in the surface 160 of the stator slice 108 which, when the vacuum pump 100 is assembled, is brought into contact with an opposing, substantially planar surface 161 of adjacent stator slice 1 10. Similar to stator slices 104 and 106, the stator slice 108 comprises a first channel 162 formed in the surface 160 of stator slice 108 and extending about the pumping chamber 1 18 on both sides thereof. Again similar to stator slices 104 and 106, the stator slice 108 further comprises two second channels 164 extending through the stator slice 108, preferably substantially orthogonally between the surfaces 151 , 160, at locations incident with the channel outlets 159 from the first channel 152 of the stator slice 106.

The second channels 164 receive fluid from the channel outlets 159 of the first channel 152 of the stator slice 106, and convey that fluid through the stator slice 108 to the first channel 162 of the stator slice 108. The first channel 162 conveys the fluid received from the stator slice 106 to the inlet portion 166 of the pumping chamber 1 18. The first channel 162 subsequently receives fluid from the outlet portion 168 of the pumping chamber 1 18, and conveys fluid to the channel outlets 169 from the first channel 162 of the stator slice 108.

The first channel 162 of the stator slice 108 is thus similar to the first channel 152 of the stator slice 106, with the exception that, as illustrated in Figures 4(c) and 4(d) the portions of the first channel 162 that convey fluid from a second channel into a pumping chamber are longer than those of the first channel 152, whilst the portions of the first channel 162 that convey fluid from a pumping chamber to a second channel are shorter than those of the first channel 152.

Figure 4(e) illustrates an axial view of surface 170 of stator slice 1 10. Pumping chamber 120 is formed in the surface 170 of the stator slice 1 10 which, when the vacuum pump 100 is assembled, is brought into contact with an opposing, substantially planar surface 171 of an end plate 180. The stator slice 1 10 comprises a first channel 172 formed in the surface 170 of stator slice 1 10 and extending about the pumping chamber 120 on both sides thereof. The stator slice 1 10 further comprises two second channels 174 extending through the stator slice 1 10, preferably substantially orthogonally relative to the surfaces 161 , 170, at locations incident with the channel outlets 169 from the first channel 162 of the stator slice 108.

The second channels 174 receive fluid from the channel outlets 169 of the first channel 162 of the stator slice 108, and convey that fluid through the stator slice 1 10 to the first channel 172 of the stator slice 1 10. The first channel 172 conveys the fluid received from the stator slice 108 to the inlet portion 176 of the pumping chamber 120. Fluid exhausted from this pumping chamber 120 is conveyed out from the pump 100 through the outlet 128.

In this embodiment the first channels are each formed along an identical path in relation to their respective stator slice. In other words, they define a locus that reflects the shape of the pumping chamber, but is offset radially therefrom to form a separate fluid channel. The outlets from the first channels are each located on that locus, but progress towards the outlet region of the pumping chamber with each successive stage towards the outlet 128 of the pump 100. Consequently, for each of the stator slices 104, 106, 108 and 110, the second channels of one stator slice are at a different position along the locus of the first channel of that stator slice in comparison to the second channels of an adjacent stator slice. In practice, this similarity in the configuration of the stator slices represents a compact configuration that benefits from requiring a consistent machining pattern. The exact path of the first channels is, however, open to alternative routing and is only subject to the second channels being provided at different locations relative to the pumping chamber of their respective stator slice in such a way that direct transfer of fluid between the second channels, that is, without passing through the pumping chambers, is inhibited.

In this first embodiment each of the first channels has two portions that convey fluid to its respective pumping chamber, and/or two portions that convey fluid away from its respective pumping chamber. However, each of the first channels may have only one such portion. Such an embodiment is illustrated in Figures 5(a) to 5(e), which illustrate alternative configurations for the first channels of each of the stator slices. With reference to Figure 5(a), the first channel 132 extends about the pumping chamber 1 12 in an anticlockwise direction (as viewed) only from the outlet portion 134 of the pumping chamber 1 12 to the (single) channel outlet 136. Consequently, as illustrated in Figure 5(b), the stator slice 104 has a single second channel 144 for receiving the fluid from the first channel 132 of the stator slice 102, and for conveying that fluid through the stator slice 104 to the first channel 142 of the stator slice 104. The first channel 142 conveys fluid to the inlet portion 146 of its pumping chamber 1 14, and then extends in a clockwise direction (as viewed) from the outlet portion 148 of its pumping chamber 1 14 to the channel outlet 149.

As illustrated in Figure 5(c), the stator slice 106 has a single second channel 154 for receiving the fluid from the first channel 142 of the stator slice 104, and for conveying that fluid through the stator slice 106 to the first channel 152 of the stator slice 106. As in the first embodiment, the second channel 154 of the stator slice 106 is at different position relative to the pumping chamber 1 16 of its stator slice 106 in comparison to the second channel 144 of the stator slice 104. The first channel 152 conveys fluid to the inlet portion 156 of its pumping chamber 1 16, and then extends in an anticlockwise direction (as viewed) from the outlet portion 158 of its pumping chamber 1 16 to the channel outlet 159. With reference to Figure 5(d), the stator slice 108 also has a single second channel 164 for receiving the fluid from the first channel 152 of the stator slice 106, and for conveying that fluid through the stator slice 108 to the first channel 162 of the stator slice 108. As in the first embodiment, the second channel 164 5 of the stator slice 108 is at different position relative to the pumping chamber 1 18 of its stator slice 108 in comparison to the second channel 154 of the stator slice 106. The first channel 162 conveys fluid to the inlet portion 166 of its pumping chamber 1 18, and then extends in a clockwise direction (as viewed) from the outlet portion 168 of its pumping chamber 1 18 to the channel outlet 169. Finally, o with reference to Figure 5(e), the stator slice 1 10 also has a single second channel 174 for receiving the fluid from the first channel 162 of the stator slice 108, and for conveying that fluid through the stator slice 1 10 to the first channel 172 of the stator slice 1 10. As in the first embodiment, the second channel 174 of the stator slice 1 10 is at different position relative to the pumping chamber 120 5 of its stator slice 1 10 in comparison to the second channel 164 of the stator slice 108. The first channel 172 conveys fluid to the inlet portion 176 of its pumping chamber 120. Fluid exhausted from this pumping chamber 120 is conveyed out from the pump through the outlet 128.

In any of the aforementioned embodiments, cross-sectional dimensions of 0 each of the first and second channels of the channel arrangement may be preselected to accommodate an anticipated fluid flow therethrough during operation of the pump 100.

5

Claims

1 . A multi-stage Roots vacuum pump comprising a plurality of stator slices, each stator slice comprising a pumping chamber for receiving intermeshing Roots rotor components, and a channel arrangement for conveying fluid between the pumping chambers, the channel arrangement comprising a plurality of first channels each formed in a surface of a respective stator slice and extending about the pumping chamber of that stator slice, and a plurality of second channels, each extending through a respective stator slice, for transferring fluid between the first channels.

2. A pump according to Claim 1 , wherein each second channel is located at respective different position relative to the pumping chamber of its stator slice.

3. A pump according to any preceding claim, wherein each first channel defines a locus about the pumping chamber of its stator slice, the loci of the plurality of first channels being, at least in part, coincident, and wherein the second channel of one stator slice is at a different position along the locus of the first channel of that stator slice in comparison to the second channel of an adjacent stator slice.

4. A pump according to any preceding claim, wherein the first channels have respective different shapes.

5. A pump according to any preceding claim, wherein the position of the second channel of one stator slice is closer to the exhaust region of its respective pumping chamber than that of an adjacent stator slice.

6. A pump according to any preceding claim, wherein each first channel is configured to convey fluid from a second channel to an inlet portion of the pumping chamber of its stator slice.

7. A pump according to any preceding claim, wherein each second channel is configured to convey fluid through its respective stator slice to the first channel of that stator slice.

8. A pump according to any preceding claim, wherein each first channel is configured to convey fluid from an outlet portion of the pumping chamber of its stator slice to a second channel.

9. A pump according to any preceding claim, wherein each second channel extends substantially orthogonally between opposing surfaces of its stator slice.

10. A pump according to any preceding claim, wherein the pump comprises a thermal control system for controlling the temperature of the stator slices.

1 1. A pump according to any preceding claim, comprising a sealing system for inhibiting fluid transfer between the pumping chambers and an exterior of the pump.

12. A pump according to Claim 1 1 , wherein the sealing system comprises a plurality of sealing elements each surrounding a respective pumping chamber and located between adjacent stator slices.

13. A pump according to Claim 12, wherein each sealing element comprises an o-ring seal.