DRY VACUUM SCROLL PUMP

Abstract

A dry scroll vacuum pump includes a fixed scroll, a drive shaft having an axis and an eccentric shaft portion, an orbiting scroll connected to the eccentric shaft portion so that during use rotation of the shaft imparts an orbiting motion to the orbiting scroll relative to the fixed scroll for pumping gas between a mechanism inlet and a mechanism outlet of a scroll mechanism comprising the scrolls; an inlet vacuum region for conveying gas from the pump inlet to the mechanism inlet; a cooling flow path formed inside the orbiting scroll for guiding a cooling fluid for cooling the orbiting scroll, the cooling flow path having a fluid inlet; and a sealing arrangement for sealing the fluid inlet from the inlet vacuum region so a cooling fluid can be conveyed across the inlet vacuum region through the sealing arrangement to the fluid inlet.

Description

CROSS-REFERENCE OF RELATED APPLICATION

This application is a Section 371 National Stage Application of International Application No. PCT/GB2016/053528, filed Nov. 10, 2016, which is incorporated by reference in its entirety and published as WO 2017/089745 A1 on Jun. 1, 2017 and which claims priority of British Application No. 1520878.8, filed Nov. 26, 2015.

FIELD

Embodiments relate to a dry vacuum scroll pump and to cooling of the pump.

BACKGROUND

A scroll vacuum pump comprises a pump housing which houses the components of the pump. A fixed scroll is fixed relative to the pump housing. A drive shaft has a concentric shaft portion and an eccentric shaft portion and an orbiting scroll is connected to the eccentric shaft portion so that during use rotation of the shaft imparts an orbiting motion to the orbiting scroll relative to the fixed scroll for pumping fluid between an inlet and an outlet of a scroll mechanism comprising the scrolls.

Gas enters the pumping mechanism through the inlet and is trapped in gas pockets between the scrolls. As the orbiting scroll orbits relative to the fixed scroll these pockets are urged about a spiral or involute path towards a central outlet of the mechanism gradually reducing in size and achieving compression. A by-product of compression and operation of the pumping components is heat energy which may accumulate in the scrolls and a bearing mechanism of the pump degrading performance.

The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.

SUMMARY

The embodiments provide a dry scroll vacuum pump comprising: a pump housing having a housing inlet and a housing outlet; a fixed scroll fixed relative to the pump housing; a drive shaft having an axis and an eccentric shaft portion; an orbiting scroll connected to the eccentric shaft portion so that during use rotation of the shaft imparts an orbiting motion to the orbiting scroll relative to the fixed scroll for pumping gas between a mechanism inlet and a mechanism outlet of a scroll mechanism comprising the scrolls; an inlet vacuum region at inlet pressure within the pump housing for conveying gas from the pump inlet to the mechanism inlet during said orbiting motion; a cooling flow path formed inside the orbiting scroll for guiding flow of a cooling fluid for cooling the orbiting scroll, the cooling flow path having a fluid inlet located in the inlet vacuum region; and a sealing arrangement for sealing the fluid inlet from the inlet vacuum region so that cooling fluid can be conveyed across the inlet vacuum region through the sealing arrangement to the fluid inlet.

Preferably, the cooling fluid is low vacuum and may be at or in the region of atmospheric pressure for example between about 1.5 bar and 0.5 bar and preferably between 1.2 and 1.0 bar. In this arrangement, the atmospheric cooling fluid is conveyed across the inlet vacuum region to the fluid inlet, even though the orbiting scroll is in motion within the inlet vacuum region.

The cooling flow path may have a fluid outlet located in the inlet vacuum region and the sealing arrangement seals the fluid outlet from the inlet vacuum region so that low vacuum cooling fluid can be conveyed across the inlet vacuum region through the sealing arrangement to the fluid outlet.

There is preferably a reverse scroll arrangement wherein the fixed scroll has an opening through which the shaft extends and is connected to the orbiting scroll with the orbiting scroll on an opposing side of the fixed scroll to a drive motor, and the inlet vacuum region is located adjacent the orbiting scroll.

In one example, the sealing arrangement has an inlet seal having a first inlet portion fixed at the fluid inlet of the orbiting scroll, a second inlet portion fixed relative to a pump housing fluid inlet through which cooling fluid is conveyed, and a connecting inlet portion which is flexible to allow relative orbiting motion between the first inlet portion and the second inlet portion during movement of the orbiting scroll in two orthogonal dimensions with respect to the axis.

Preferably, the sealing arrangement has an outlet seal having a first outlet portion fixed at the fluid outlet of the orbiting scroll, a second outlet portion fixed relative to a pump housing fluid outlet through which cooling fluid is conveyed, and a connecting outlet portion which is flexible to allow relative orbiting motion between the first outlet portion and the second outlet portion during movement of the orbiting scroll in two orthogonal dimensions with respect to the axis.

The inlet and/or outlet seal may comprise a gaiter seal.

The source of cooling fluid may be configured for conveying cooling fluid through the cooling flow path of the orbiting scroll, and may form part of the scroll pump, or be a separate component from the pump, or a gas line. The flow source may comprise a mechanical fan rotated by the drive shaft. The source of cooling fluid may comprise a pump external to the pump housing for conveying cooling fluid through the cooling flow path. In other arrangements, the source of cooling fluid may be caused by motion of the fluid inlet to convey cooling fluid through the cooling path.

The cooling flow path may be formed by casting within the orbiting scroll during manufacture.

it is preferable that the cooling flow path has a tortuous configuration within the orbiting scroll.

The cooling fluid may be air or water or another fluid, and may be cooled to lower than ambient temperature prior to introduction.

The Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detail Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to he used as an aid in determining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of a dry scroll vacuum pump;

FIG. 2 shows one view of an orbiting scroll of the pump shown in FIG. 1; and

FIG. 3 shows another view of an orbiting scroll of the pump shown in FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, the pump 10 comprises a pump housing 12 and a drive shaft 14 having an eccentric shaft portion 16. The shaft 14 is driven by a motor 18 and the eccentric shaft portion is connected to an orbiting scroll 20 so that during use rotation of the shaft imparts an orbiting motion to the orbiting scroll relative to a fixed scroll 22 for pumping fluid along a fluid flow path between a pump housing inlet 24 and pump housing outlet 26 of the compressor. The fixed scroll is shown generally on the left and the orbiting scroll is shown generally on the right in FIG. 1 (i.e. the fixed scroll plate is on the left and the orbiting scroll plate is on the right as shown whilst the fixed and orbiting scroll walls overlap in the axial direction). In this reverse scroll arrangement, the fixed scroll comprises an opening 28 through which the shaft 14 extends and is connected to the orbiting scroll 20 so that the orbiting scroll is located an opposing side of the fixed scroll to the motor 18. A high, or inlet, vacuum region 30 is located at the inlet 24 and a low vacuum, or outlet, region 32 is located at the outlet 26. The high vacuum region is at inlet pressure. The low vacuum region is at exhaust pressure. In this way, the scroll arrangement is reversed compared to a typical scroll pump in which the orbiting scroll is on the same side of the fixed scroll as the motor.

A first bearing 34 supports the concentric portion of the drive shaft 14 for rotation. The bearing 34 is fixed relative to the housing or as shown the fixed scroll 22. A second bearing 36 connects the eccentric portion 16 of the drive shaft to the orbiting scroll 20 allowing orbiting movement of the orbiting scroll relative to the eccentric portion. A first shaft seal 38 may be provided to resist the passage of lubricant from first bearing 34 towards an interface 40 between the orbiting scroll 20 and the fixed scroll 22 and a second shaft seal 42 resists the passage of lubricant from second bearing 36 to the interface. The shaft seals resist lubricant entering and mixing with the pumped gasses.

A counter-weight 44 balances the weight of the orbiting components of the pump, including the orbiting scroll 20, the second bearing 36 and the eccentric portion 16 of the drive shaft. The orbiting scroll 20 constitutes the majority of the weight of the orbiting components and its centre of mass is located relatively close to the scroll plate of the orbiting scroll. A cap 46 is fixed to a raised seat 48 of the orbiting scroll and seals the low vacuum region, containing the counter-weight and the bearings 34, 36 from the high vacuum region 30.

An anti-rotation device 50 is located in the high vacuum region 30 of the pump and is connected to the orbiting scroll 20 and the housing 12. The anti-rotation device resists rotation of the orbiting scroll but allows orbiting motion of the orbiting scroll. The anti-rotation device is lubricant free and in this example is made from a plastics material, and may be a one-piece polymer component.

A flow source of cooling fluid in the form of a mechanical fan 52 is mounted to the drive shaft 14 for rotation when the drive shaft is driven by the motor 18. Rotation of the fan causes flow of cooling fluid (typically ambient air) over the fixed scroll for cooling the fixed scroll. However, in a reverse scroll arrangement the orbiting scroll is on a distal side of the fixed scroll and therefore not physically exposed to coolant. Also the orbiting scroll is located in the high vacuum, or inlet, region 30 which means that there is less gas available for the convection of heat energy away from the orbiting scroll.

The amount of heat produced correlates with the amount of gas which is pumped. Therefore if throughput is increased more gas is compressed and greater energy is lost in the form of heat, particularly at higher pressures closer to atmosphere if the pump is used for roughing. A roughing pump may for example have an inlet pressure of between about 500 mbar and 1 mbar and exhaust pressure at or around atmosphere. A roughing pump may be used for example in the food packaging industry or for paper handling. However, the invention can also be used in lower pressure regimes (less than 1 mbar e.g. 10-2 and 10-3 mbar) for example for scientific instruments, since there is a trend to increase gas throughput in such instruments thereby contributing to increased heat production.

Purely as examples a low throughput for pumping may be 500 to 1000 sccm (standard cubic centimetres per minute) and a high throughput may be greater than 50 slm (standard litres per minute).

Increased pump operating temperatures are not desirable since amongst other things they decrease an operative life of the pump, cause an increased requirement for maintenance and potentially result in failure. The bearing mechanism is a key component of the pump and increased heat deteriorates the mechanism. For example, a 10° C. rise in temperature reduces the life of grease (lubricant) in the bearings by half (by around 50%). Increased temperature causes expansion of bearing components (and scroll members) reducing the fit between components decreasing pumping efficiency and potentially causing contact between moving surfaces. Additionally, tip seal wear increases with increased temperature. The production of tip seal dust causes contamination of clean pumped environments. Tip seal dust is a particular problem in scientific instruments and silicon wafer processing and also in food packaging.

In dry pumping no lubricant is used in the pumping chamber of the scroll mechanism along the flow path for pumping. It is used outside the pumping chamber in the bearing mechanism. Lubricant in the chamber would in a lubricated pump provide a sealing function in addition to lubricating the interface between the scrolls, however it is a source of contamination and additional expense. Dry pumping is preferable in many circumstances, such as for pumping a clean environment or production of comestible products. One disadvantage to dry pumping is that the circulation of lubricant removes heat from a pumping mechanism, and therefore a dry pump is more susceptible to overheating.

As briefly explained above, the problem of scroll member heating is particularly acute in a reverse scroll vacuum pump where the orbiting scroll is located in the vacuum region of the pump. Notwithstanding, the invention has applicability to normal scroll arrangements. The reverse configuration has certain advantages over a normal scroll, including that it is more compact (e.g. axially shorter) and does not require a “bellows” fixed to the orbiting scroll. A bellows acts as a seal for sealing an atmospheric and lubricated region of the pump from a vacuum region and also resists rotation of the orbiting scroll. The provision of bellows increases both axial length and radial width of the pump.

As indicated above the orbiting scroll is at least partially enveloped in low pressure gas and therefore heat is not easily dissipated from the scroll. Instead an atmospheric gas or liquid is required as a cooling agent. A difficulty arises in exposing the orbiting scroll to an atmospheric fluid because it is located in the vacuum region and additional because it is not stationary.

In the present invention a cooling flow path for coolant is formed in the body (principally in the plate) of the orbiting scroll for receiving a cooling agent. The cooling agent is a fluid at or around atmosphere or ambient pressure or a small amount above atmosphere or ambient (e.g. between about 1.5 bar and 0.5 bar, or preferably between about 1.0 and 1.2 bar sufficient to cause flow along the cooling flow path). The cooling agent, or fluid, may be ambient air or a liquid such as water. The cooling agent may be pre-cooled or at ambient temperature, but in either case below the temperature of the orbiting scroll to cause heat exchange from the orbiting scroll to the cooling fluid.

Reference is now made to FIG. 2 which shows a scroll mechanism 60 and cooling arrangement 62 in more detail. FIG. 2 is a simplified representation for explanatory purposes only and omits components of the pump such as the bearing mechanism, cap and anti-rotation device.

A pump housing inlet 24 is in fluid communication with the high vacuum, or inlet, region 30 into which gas is pumped at low pressure (at any pressure between about 500 mbar and 10⁻³ mbar, or even lower, depending on pumping requirements). The high vacuum region is in fluid communication with an inlet 25 of the scroll mechanism through which low pressure gas is drawn from the high vacuum region and compressed by the scroll mechanism. The pump inlet 24 is not connected directly to the scroll mechanism inlet 25 because the orbiting scroll 22 is not stationary during pumping. In this regard, the drive shaft 14 has a central rotational axis 70. The eccentric portion 16 of the shaft has a central longitudinal line 72 offset from axis 70 by a distance OS. Depending on the size and rating of the scroll pump OS may be between about 10 mm and 50 mm. The orbiting scroll 22, which is connected to the eccentric portion, is driven by the drive shaft to orbit with respect to axis 70 in a plane orthogonal to the axis. As viewed in FIG. 2, the orbiting scroll moves about the axis in two orthogonal dimensions (i.e. upwards and downwards and into and out of the page in the Figure) by an amount equal to OS relative to the axis 70, or by an amount 2OS relative to the pump housing.

The inlet 25 of the scroll mechanism 60 is in fluid communication with a radially outer wrap 27 of the scroll mechanism. Orbiting motion of the orbiting scroll causes fluid to be urged from the outer wrap 27 to a radially inner wrap 29. The inner wrap is in fluid communication with an outlet 31 of the scroll mechanism. The low vacuum, or outlet, region 32 within the pump housing is typically located in fluid communication with the outlet of the scroll mechanism and outlet 26 of the pump housing (see FIG. 1). The low vacuum region 32 is separated and sealed from the high vacuum region 30 by the fixed scroll or the pump housing.

The low pressure pumped gas 64 is shown (represented by an X in a circle) located in the vacuum region 30 and partially enveloping the scroll mechanism 60. As shown in this example, the vacuum region 30 is defined between the pump housing, the outer casing 66 of the orbiting scroll (and the cap 46 not shown in FIG. 2) and the outer casing 68 of the fixed scroll. Since the outer casing, or surface, 66 of the orbiting scroll is located in this high vacuum region heat does not easily dissipate from the orbiting scroll.

A cooling arrangement 62 is provided for cooling the orbiting scroll 22. Since the orbiting scroll is not stationary the cooling arrangement bridges the high vacuum region 30 to accommodate the orbiting motion of the orbiting scroll in order to supply a cooling fluid to a cooling flow path in the orbiting scroll.

In more detail, a cooling flow path 74 is formed inside the orbiting scroll for guiding flow of a low vacuum, or atmospheric, cooling fluid for cooling the orbiting scroll by heat exchange with the orbiting scroll. The flow path may be defined by one or more internal conduits cast into the orbiting scroll during casting, or manufacture, of the orbiting scroll or alternatively may be formed between two parts of the orbiting scroll which are subsequently fastened together and sealed. Other techniques may be used to form the flow path.

The cooling flow path has a fluid inlet 76 and a fluid outlet 78. The fluid inlet and the fluid outlet may be positioned at diametrically opposed parts of the orbiting scroll as shown, or more proximate one another. There may be more than one inlet or more than one outlet, and more than one flow path, depending on cooling requirements. In the FIG. 2 example, cooling fluid 80 (represented by symbol ‘0’) is caused to flow from outside the pump housing 12 through the fluid inlet 76, along the flow path 74 and subsequently through the fluid outlet 78 and outside the pump housing. In this arrangement the cooling fluid may conveniently be ambient air.

The fluid inlet 76 of the orbiting scroll 22 is connected to the pump housing 12 by an inlet seal 82. The inlet seal has a first inlet portion 90 fixed at the fluid inlet of the orbiting scroll and a second inlet portion 92 fixed relative to a port 84 in the pump housing. The inlet seal has an inlet connecting portion 94 which is sufficiently flexible to allow relative motion between the first inlet portion and the second inlet portion during motion of the orbiting scroll two dimensions relative to the axis 70. The fluid outlet 78 of the orbiting scroll is connected to the pump housing 12 by an outlet seal 83. The outlet seal has a first outlet portion 96 fixed at the fluid outlet of the orbiting scroll and a second portion 98 fixed relative to a port 79 in the pump housing. The outlet sealing arrangement also has a connecting portion 100 which is sufficiently flexible to allow relative motion between the first portion and the second portion during motion of the orbiting scroll.

The orbiting scroll of the scroll pumping mechanism orbits relative to the fixed scroll to form gas pockets between the scroll walls which are gradually compressed during orbiting motion as the pockets are urged from the radially outer inlet of the mechanism towards the central outlet. The orbiting motion causes the orbiting scroll to follow a circular path in a plane orthogonal to the axis of the drive shaft. Therefore the cooling fluid inlet 76 and the cooling fluid outlet 78 of the orbiting scroll move in circular paths relative to housing ports 84 and 79, respectively. This circular movement constitutes movement in two dimensions in the plane orthogonal to the axis 70 (i.e. as shown towards and away from the housing ports, and into and out of the page). The circular movement typically has a radius OS of between about 10-50 mm. The sealing arrangements are therefore required to be compressed and expand by an amount twice OS and to bend in a lateral (axial) dimension by an amount OS. At high pump rotational speeds (e.g. 60 Hz) significant physical stresses and strains are applied to the sealing arrangements 82, 83. The sealing arrangements must accommodate the physical impact of this movement over prolonged durations (e.g. for several weeks of constant use between maintenance operations).

In the example shown in FIG. 2, the sealing arrangements are formed by gasket seals having a pleated configuration. The sealing arrangements are preferably made from a plastics or rubber having material characteristics which tolerate such movement at typical rotational speeds for prolonged periods. It will also be appreciated that it may be desirable to keep the pump as compact as possible and therefore to minimize the spacing between the housing ports 79, 84 and the fluid inlet/outlet 76, 78. In this case, the sealing arrangements are required to expand and contract by many times their own length. For example, if OS is 50 mm and the minimum such spacing is 10 mm, the length of the sealing arrangements would vary from 10 mm to 110 mm. If OS is 10 mm and the minimum such spacing is 10 mm, the length of the sealing arrangements would vary from 10 mm to 30 mm. Clearly other possible dimensions may be used depending pump configuration and intended use and the sealing arrangements are required to accommodate such variation of length from a compacted to expanded length by at least a factor of two or (3 or 11 in the examples given above). A gasket as shown has been found to have a suitable configuration in this regard.

FIG. 3 is a cross-section through the orbiting scroll showing the cooling flow path. The cooling flow path 74 guides cooling fluid 80 from the fluid inlet 76 to the fluid outlet 78 in the orbiting scroll 22. FIG. 3 shows only one example of the flow path, which in this configuration is a single curvilinear flow path between the fluid inlet and fluid outlet.

The configuration of the flow path is preferably such as to pass through a substantial volume of the orbiting scroll in order to exchange heat with as much of the orbiting scroll as is practical. For example if the cross-sectional area through the orbiting scroll is X then the flow path may extend through 50% of X and preferably 75% of X. The flow path may have a path centre which extends in a single plane through the orbiting scroll (e.g. orthogonal to the pump axis 70) or the flow path may extend in more than one plane through the orbiting scroll.

In other arrangements, there is a differential distribution of heat through the orbiting scroll when in use and the flow path is configured so that it can remove more heat from higher temperature parts of the orbiting scroll. In this regard, the flow path may be configured by volume or by cross-sectional area or total cross-sectional area (if there is more than one flow path) such that more cooling fluid is exposed to higher temperature parts of the scroll so that flow is proportional with temperature.

For example, a radially inner part of the orbiting scroll is at higher pressure and a radially outer part is at lower pressure. Since more heat is generated at higher pressures the flow path may be configured to cause more flow per volume of the orbiting scroll (or heat exchange) in the typically hotter radially inner part than the cooler radially outer part, particularly as the radially inner part is proximate the bearings so as to reduce transfer of heat to the lubricant.

The flow path may have a tortuous, labyrinthine, spiral or any other configuration with multiple turns in order to penetrate through an increased amount of the body of the scroll. A turn causes the fluid to change direction of flow and may be a turn through 45 degrees, 90 degrees, 135 degrees, 180 degrees or more, or any angle between. A change of flow direction causes some turbulence for mixing the cooling fluid (i.e. within the flow path, hotter fluid adjacent a scroll surface is mixed with cooler fluid away from the scroll surface) and this mixing increases heat exchange.

Referring again to FIG. 2, the source of cooling fluid 86 is a pump or fan external to the pump housing 12 for conveying cooling fluid through the cooling flow path 74. In an alternative arrangement, a mechanical source of cooling fluid may be driven by drive shaft 14, shown in FIG. 1, for example fan 52. In this latter case, fan 52 may he in fluid communication with an outer sleeve of the housing for conveying cooling fluid along the cooling flow path.

In a further alternative, a cooling fluid may be caused to flow along the cooling flow path by virtue of the movement of the orbiting scroll, without or with the addition of a further source of cooling fluid. This movement may be sufficient in itself to create flow by the pumping action of the orbiting scroll relative to the pump housing, for example by causing turbulence at the inlet and outlet of the path.

It is an object of the invention to provide pump cooling.

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

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

Claims

1. A dry scroll vacuum pump comprising:

a pump housing having a housing inlet and a housing outlet;

a fixed scroll fixed relative to the pump housing;

a drive shaft having an axis and an eccentric shaft portion;

an orbiting scroll connected to the eccentric shaft portion so that during use rotation of the shaft imparts an orbiting motion to the orbiting scroll relative to the fixed scroll for pumping gas between a mechanism inlet and a mechanism outlet of a scroll mechanism comprising the scrolls;

an inlet vacuum region at inlet pressure within the pump housing for conveying gas from the pump inlet to the mechanism inlet during said orbiting motion;

a cooling flow path formed inside the orbiting scroll for guiding flow of a cooling fluid for cooling the orbiting scroll, the cooling flow path having a fluid inlet located in the inlet vacuum region; and

a sealing arrangement for sealing the fluid inlet from the inlet vacuum region so a cooling fluid can be conveyed across the inlet vacuum region through the sealing arrangement to the fluid inlet.

2. The dry vacuum scroll pump as claimed in claim 1, wherein the cooling flow path has a fluid outlet located in the inlet vacuum region and the sealing arrangement seals the fluid outlet from the inlet vacuum region so that low vacuum cooling fluid can be conveyed across the inlet vacuum region through the sealing arrangement to the fluid outlet.

3. The dry vacuum scroll pump as claimed in claim 1, having a reverse scroll arrangement wherein the fixed scroll has an opening through which the shaft extends and is connected to the orbiting scroll with the orbiting scroll on an opposing side of the fixed scroll to a drive motor, and the inlet vacuum region is located adjacent the orbiting scroll.

4. The dry vacuum scroll pump as claimed in claim 1, wherein the sealing arrangement has an inlet seal having a first inlet portion fixed at the fluid inlet of the orbiting scroll, a second inlet portion fixed relative to a pump housing fluid inlet through which cooling fluid is conveyed, and a connecting inlet portion which is flexible to allow relative orbiting motion between the first inlet portion and the second inlet portion during movement of the orbiting scroll in two orthogonal dimensions with respect to the axis.

5. The dry vacuum scroll pump as claimed in claim 1, wherein the sealing arrangement has an outlet seal having a first outlet portion fixed at the fluid outlet of the orbiting scroll, a second outlet portion fixed relative to a pump housing fluid outlet through which cooling fluid is conveyed, and a connecting outlet portion which is flexible to allow relative orbiting motion between the first outlet portion and the second outlet portion during movement of the orbiting scroll in two orthogonal dimensions with respect to the axis.

6. The dry vacuum scroll pump as claimed in claim 4, wherein the inlet and/or outlet seal comprises a gaiter seal.

7. The dry vacuum scroll pump as claimed in claim 1, comprising a source of cooling fluid configured for conveying cooling fluid through the cooling flow path of the orbiting scroll.

8. The dry vacuum scroll pump as claimed in claim 7, wherein the flow source comprises a mechanical fan rotated by the drive shaft.

9. The dry vacuum scroll pump as claimed in claim 1, wherein the source of cooling fluid comprises a pump external to the pump housing for conveying cooling fluid through the cooling flow path.

10. The dry vacuum scroll pump as claimed in claim 1, wherein the source of cooling fluid is caused by motion of the fluid inlet to convey cooling fluid through the cooling path.

11. The dry vacuum scroll pump as claimed in claim 1, wherein the cooling flow path is formed by casting within the orbiting scroll during manufacture.

12. The dry vacuum scroll pump as claimed in claim 1, wherein the cooling flow path has a tortuous configuration within the orbiting scroll.

13. The dry vacuum scroll pump as claimed in claim 1, wherein the cooling fluid is air or water.

14. The dry vacuum scroll pump as claimed in claim 1, wherein the cooling fluid is at or in the region of atmospheric pressure 1 bar to 0.5 bar and preferably 1.0 to 1.2 bar.

15. (canceled)