GB2442738A - Barrier fluid channel protecting seal in vacuum pump. - Google Patents

Abstract

A vacuum pump comprises first and second stator components 210-220 sealingly connected together to define a pumping chamber 230-238. An o-ring sealing element 240-248 is engaged between the stator components and located about the pumping chamber. A fluid channel 250-258 is located in the plane of the sealing element between the sealing element and the pumping chamber. The channel may be fluidly connected to other channels. Means are provided for reducing the partial pressure of fluid entering the fluid channel from the pumping chamber, and for inhibiting flow of fluid from the fluid channel to the pumping chamber. The means may include evacuation of the channel by a separate pump or by connection to a low pressure stage of the pump and dilution with a barrier gas form a source 262 and venting through a pump stage. Protects the seal from corrosive pumped materials and reduces barrier gas requirement.

Description

A SEALING SYSTEM

This invention relates to sealing systems suitable for sealing a swept volume of a vacuum pump.

It is known from W02004/099620 to protect an 0-ring seal located between two stator components of a vacuum pump by using a barrier fluid running through a channel located between the 0-ring seal and an adjacent pumping chamber.

Figure 1 illustrates the sealing system described in W02004/099620.

A stator component 5 that forms part of a stator has a pumping chamber 10 formed therein, within which a rotor component, or more often a complementary pair of rotor components, of a rotor assembly (not shown) is housed. In operation the rotor assembly acts in combination with the stator to convey fluid through the vacuum pump from an inlet thereof to an outlet thereof. An 0-ring sealing element 15 is positioned about the pumping chamber 10 in a groove formed in an axial end surface of the stator ::::. component 5. A fluid channel 20 is machined between the 0-ring groove and e* the pumping chamber 10. The fluid channel 20 is provided with an inlet S...

channel 25 and an outlet channel 30. The outlet channel 30 is in fluid *:::: communication with an interstage port 35 of the pumping chamber 10. *... * S

In operation, a relatively high pressure barrier fluid (having, for example, a pressure in the range from 0.2 to 2 bar) is supplied to inlet channel 25, and is conveyed around fluid channel 20 to outlet channel 30 from where it is conveyed into the pumping chamber 10 of the vacuum pump via interstage port 35.

The system illustrated in Figure 1 is appropriate for use in lower vacuum stages of a multistage vacuum pump comprising a plurality of pumping chambers 10 connected in series. The quantity of barrier fluid being conveyed through fluid channel 20 can be significant (for example, in the range from 10 to 45 slm), and so bulk flow of the barrier gas into the pumping chamber 10 can significantly increase the volume of the fluid conveyed through this location of the vacuum pump. However, as the pressure in the lower vacuum stages of a multistage pump generally approaches atmospheric pressure, introduction of the barrier fluid to this region of the pump, even in substantial volumes, does not significantly affect the pumping capacity of the vacuum pump, which is generally governed by the capacity of the high vacuum inlet stages of the pump.

In the higher vacuum stages of a multistage pump, whilst an 0-ring sealing element 15 is provided between adjacent stator components that define each pumping chamber, no fluid channel surrounds the respective pumping chambers as in the lower vacuum stages discussed above. This is because the pumping conditions in higher vacuum stages, in combination with the composition of fluids being pumped therethrough, tends not to result in deterioration of the sealing elements positioned about the pumping chambers of these higher vacuum stages and so the use of fluid channels 20 to protect the sealing elements was not considered necessary. As a result, these sealing elements are simply replaced during scheduled servicing of the vacuum pump.

Over time, the use of vacuum pumps has developed and now multistage vacuum pumps are often used to evacuate enclosures in which . ?O relatively harsh chemicals are employed and which pass through the pumping *s..

chambers of the vacuum pump during evacuation of the process enclosure.

The chemicals being conveyed through the pumping chambers of the vacuum pump are hereinafter collectively termed the pumped fluid. Chemicals within the pumped fluid can cause significant corrosion of components of the vacuum pump. In some circumstances it may be desirable to avoid condensates of these chemicals from forming in pools within the vacuum pump, and so the stator components may be heated to reduce the temperature differential between the pumped fluid and the stator components.

However, this heating of the stator components may, in turn, cause the corrosive properties of some pumped fluids, for example those in gaseous form, to be more significant.

Whilst the corrosive effects of the pumped fluid are more pronounced in the lower vacuum stages of a multistage pump than in the higher stages, in higher pressure processes these corrosive effects may also be experienced in the higher vacuum stages. In particular, when a cleaning step is carried out within the vacuum pump, substantial volumes of corrosive chemicals may be introduced into all stages of the multistage vacuum pump, which may affect all 0-ring seals. Consequently, it may now be considered desirable to protect the 0-ring sealing elements located about the pumping chambers of the higher vacuum stages of the pump in addition to those located about the pumping chambers of the lower vacuum stages of the pump. However, the addition of barrier fluid into the higher vacuum stages of a pump may be severely detrimental to the overall pumping capacity of the vacuum pump, and may undesirably alter the chemical balance of the composition of the pumped fluid.

Furthermore, in clean processes high purity fluids may be used in the process enclosure and it may be desirable to recover these fluids from the pumped fluid. Consequently, it becomes undesirable for these fluids to become contaminated by the introduction of excessive volumes of barrier fluid within * the vacuum pump. * * S

* The pumped fluid conveyed through the vacuum pump often needs to be treated after it is exhausted from the vacuum pump. In such S...

circumstances an abatement device is located downstream of the vacuum pump. The flow rate of pumped fluid originating from a process may, for example, be around 0.5 to 5 slm, whilst the addition of barrier fluid can S..

increase the overall flow rate of pumped fluid exhausted from a vacuum pump, for example, to 10 to 45 slm. This increased flow rate of gas entering the abatement device can significantly decrease the destruction efficiency of the abatement device, or increase the energy requirement of the abatement device.

According to a first aspect, the present invention provides a vacuum pump comprising: first and second stator components to be sealingly connected together to thereby define a pumping chamber; an 0-ring sealing element engaged between the stator components and located about the pumping chamber; a fluid channel in the plane of the sealing element and located between the sealing element and the pumping chamber; and means for reducing the partial pressure of fluid entering the fluid channel from the pumping chamber, and for inhibiting flow of fluid from the fluid channel to the pumping chamber.

By reducing the partial pressure of any fluid that passes into the fluid channel from the pumping chamber, the corrosive impact of any corrosive component contained therein is also reduced. In complementing this with the inhibition of fluid flow from the fluid channel into the pumping chamber, there is minimal impact on pumping capacity, which, in turn, improves efficiency in terms of cost and power requirements of the vacuum pump and in terms of volumetric foot print in the overall apparatus, as an optimal capacity vacuum pump can be used for any particular process to which it is attached.

The aforementioned means may comprise means for evacuating the : ** fluid channel. The means for evacuating the fluid channel may comprise a second vacuum pump. Alternatively, the vacuum pump may comprise, upstream from the pumping chamber, another pumping chamber, with the *.20 means for evacuating the fluid channel comprising this other pumping chamber.

* In another alternative, the aforementioned means may comprise means S...

*** for diluting fluid entering the fluid channel from the pumping chamber. The diluting means may comprise a source of bamer fluid, and means for conveying barrier fluid from the source to the fluid channel. The source of barrier fluid may comprise a source of purge gas, for example one of nitrogen and argon. The barrier fluid may be supplied at a pressure in the range from to (1 x 106) Pa, more preferably in the range from (1 x 10) to (1 x 106) Pa.

The fluid channel may comprise an outlet channel from which barrier fluid is discharged from the fluid channel. The outlet channel may be configured to convey barrier fluid from the fluid channel to a location isolated from fluid located within the pumping chamber, for example, to a second vacuum pump. Alternatively, the outlet channel may be configured to convey barrier fluid from the fluid channel to a location in fluid communication with an outlet from the pump. For example, the vacuum pump may comprise, downstream from the pumping chamber, another pumping chamber, and the outlet channel may be configured to convey barrier fluid to this other pumping chamber.

In another alternative, the vacuum pump may comprise, upstream from the pumping chamber, another pumping chamber, with this other pumping chamber providing a source of purge gas for the fluid channel.

The vacuum pump may comprise a plurality of said fluid channels, a plurality of pumping chambers upstream from said pumping chamber, and, for each fluid channel, means for conveying fluid from that fluid channel to a respective one of said plurality of pumping chambers.

Any of the aforementioned vacuum pumps may comprise a physical barrier seal located between the fluid channel and the pumping chamber. The physical barrier seal may be a corrosion resistant seal, which may be formed, for example, from polytetrafluoroethylene. S...

According to a second aspect, the present invention provides a vacuum pump comprising: a plurality of stator components sealingly connected together thereby to : define a plurality of interconnected pumping chambers of the vacuum pump; * and, for each pumping chamber: an 0-ring sealing element located about the pumping chamber and engaged between stator components defining that pumping chamber; a fluid channel in the plane of the sealing element and located between the sealing element and the pumping chamber; and means for reducing the partial pressure of fluid entering the fluid channel from the pumping chamber, and for inhibiting flow of fluid from the fluid channel to the pumping chamber.

The fluid channels may be in fluid communication with each other. The aforementioned means may comprise means for diluting fluid entering each fluid channel from its respective pumping chamber, or means for evacuating the fluid channels.

In a third aspect, the present invention provides a vacuum pump comprising: a plurality of stator components sealingly connected together thereby to define a plurality of interconnected pumping chambers of the vacuum pump; a plurality of 0-ring sealing elements each located about a respective pumping chamber and engaged between stator components defining that pumping chamber; a plurality of fluid channels, the fluid channels being in fluid communication with each other, each fluid channel being located in the plane of a respective sealing element and between the sealing element and its respective pumping chamber; and means for evacuating the fluid channels.

::::. By evacuating the fluid channels, the partial pressure of a corrosive *... . component of the pumped fluid can be reduced without the need to introduce any additional, externally sourced barrier fluid into the fluid channels. * * **S.

According to a fourth aspect, the present invention provides a vacuum pump comprising: :::: : a plurality of stator components sealingly connected together thereby to * .. define a plurality of interconnected pumping chambers of the vacuum pump; a plurality of 0-ring sealing elements each located about a respective pumping chamber and engaged between stator components defining that pumping chamber; a plurality of fluid channels, the fluid channels being in fluid communication with each other, each fluid channel being located in the plane of a respective sealing element and between the sealing element and its respective pumping chamber; and means for diluting fluid entering each fluid channel from its respective pumping chamber.

By diluting any fluid that enters the fluid channel from its respective pumping chamber, the partial pressure of any corrosive component of this fluid is thereby reduced, thus reducing the impact on a respective 0-ring sealing element. In coupling this diluting mechanism with the feature of providing the fluid channels in fluid communication with one another, in other words, in series, a single stream of fluid may be conveyed through all of the fluid channels without needing to exhaust the fluid directly into the respective pumping chambers of the vacuum pump. In this way, the volume of diluting fluid used within the vacuum pump can be substantially reduced and the volume of fluid that enters the pumping chambers of the vacuum pump can similarly be minimised.

The diluting means may comprise a source of barrier fluid, and means for conveying barrier fluid from the source to the fluid channels. The source of barrier fluid may comprise a source of purge gas, for example, nitrogen or : ** argon. The barrier fluid may be supplied at a pressure in the range from to (1 x 106) Pa, more preferably in the range from (1 x 1O) to (1 x 106) Pa.

The vacuum pump may comprise an outlet channel from which barrier "20 fluid is discharged from the fluid channels. The outlet channel may be * configured to convey barrier fluid from the fluid channels to a location isolated from fluid located within the pumping chambers or the outlet channel may be ** configured to convey barrier fluid from the fluid channels to a location in fluid communication with an outlet from the pump.

The vacuum pump may comprise, downstream from said pumping chambers, another pumping chamber, and the outlet channel may be configured to convey barrier fluid to this other pumping chamber.

Alternatively, the vacuum pump may comprise, upstream from said pumping chambers, another pumping chamber, and the source of purge gas may comprise this other pumping chamber.

In a fifth aspect, the present invention provides a vacuum pump comprising: a plurality of stator components sealingly connected together thereby to define interconnected first and second pumping chambers of the vacuum pump, the first pumping chamber being located upstream from the second pumping chamber; an 0-ring sealing element located about the second pumping chamber and engaged between stator components defining that pumping chamber; a fluid channel located in the plane of the sealing element and between the sealing element and the second pumping chamber; and means for conveying fluid from the fluid channel to the first pumping chamber.

By conveying fluid from the fluid channel to the first pumping chamber, the pressure within the fluid channel can be reduced to that of the first pumping chamber so that any fluid which passes into the fluid channel from the second pumping chamber is similarly reduced. Consequently the partial pressure of any corrosive component of this fluid is lowered such that its corrosive impact is also reduced. The additional benefit of this aspect of the present invention is that this can be achieved within the existing volumetric *2O footprint of the vacuum pump such that a compact apparatus is achieved.

The vacuum pump may comprise a third pumping chamber located between the first and second pumping chambers, a second fluid channel : located in the plane of the sealing element and between the sealing element * and the first-mentioned fluid channel, and means for conveying fluid from the second fluid channel to the third pumping chamber. The pump may comprise a fourth pumping chamber located between the second and third pumping chambers, a third fluid channel located in the plane of the sealing element and between the sealing element and the second fluid channel, and means for conveying fluid from the third fluid channel to the fourth pumping chamber.

According to a sixth aspect, the present invention provides a vacuum pump comprising: a plurality of stator components sealingly connected together thereby to define interconnected first and second pumping chambers of the vacuum pump, the first pumping chamber being located upstream from the second pumping chamber; an 0-ring sealing element located about the first pumping chamber and engaged between stator components defining that pumping chamber; a fluid channel located in the plane of the sealing element and between the sealing element and the first pumping chamber; a source of barrier fluid; means for conveying barrier fluid from the source to the fluid channel; and means for conveying barrier fluid from the fluid channel to the second pumping chamber.

By exhausting the barrier fluid to a downstream (and therefore higher pressure) pumping chamber, the introduction of additional fluid has less impact on the pumping capacity of the vacuum pump.

: s*, The aforementioned vacuum pump may be a booster pump.

Features described above in relation to any of the first to sixth aspects of the invention may be equally applied to any of the other aspects, and vice versa.

S..... * S

* The invention is described below in greater detail, by way of example * S..

*:*. only, with reference to the accompanying drawings, in which: Figure 1 illustrates an axial cross section of a known vacuum pump; Figure 2 illustrates an axial cross section of first example of a vacuum pump; Figure 3 illustrates an axial cross section of a second example of a vacuum pump; Figure 4 illustrates an axial cross section of a third example of a vacuum pump; Figure 5 illustrates a longitudinal cross section of a fourth example of a vacuum pump; Figure 6 illustrates a longitudinal cross section of a fifth example of a vacuum pump; Figure 7 illustrates a longitudinal cross section of a sixth example of a vacuum pump; Figure 8 illustrates a longitudinal cross section of a seventh example of a vacuum pump; Figure 9 illustrates a longitudinal cross section of an eighth example of a vacuum pump to; Figure 0 illustrates a close up view of a portion of Figure 9 to show the detail of part of a sealing system for sealing a swept volume of the vacuum pump; and Figure 11 illustrates an additional sealing mechanism for use in the vacuum pump of Figure 8 or Figure 9. 0***

Figure 2 illustrates an axial cross section of a first example of a single stage vacuum pump, such as a single stage booster pump. The vacuum pump comprises a stator component 55 whiàh, in combination with an adjacent stator component (not shown), for example a similar stator component or an end plate, defines a pumping chamber 60 therein. The pumping chamber 60 houses one or more rotors (not shown) that act in combination with the stator component to pump fluid through the vacuum pump from an inlet thereof to an outlet thereof.

The vacuum pump comprises an 0-ring sealing element 65 surrounding the pumping chamber 60, for preventing ingress and egress of fluid between the exterior of the vacuum pump and the pumping chamber 60. In this example, the sealing element 65 is located by a groove formed in an axial surface of the stator component 55. The vacuum pump also comprises a fluid channel 70 provided in the plane of the 0-ring sealing element 65 and located between the pumping chamber 60 and the 0-ring sealing element 65 for protecting the sealing element 65. Walls of the fluid channel 70 are formed in the axial surface of the stator component 55 in combination with a cooperating axial surface of the adjacent stator component which is maintained in close contact (for example within 5 pm or less) with the stator component 55 by bolting the two components together. As a result the fluid channel 70 is substantially isolated from the pumping chamber 60.

The fluid channel 70 is in fluid communication with both an inlet channel 75 and an outlet channel 80. In operation, a barrier fluid (for example, nitrogen, argon or other non-corrosive gas which is inert or compatible with the pumped fluid) is conveyed along the fluid channel 70 from the inlet channel 75 to the outlet channel 80 to prevent any chemical that seeps into the fluid channel 70 from the pumping chamber 60 from contacting the 0-ring sealing element 65. The sealing element is thus protected by the combination of the fluid channel 70, and the barrier fluid conveyed thereto through the inlet channel 75.

In this example, the sealing system comprises an outlet channel 80 for *4r* conveying the barrier fluid away from the fluid channel 70. The outlet channel I...

is not in fluid communication with the pumping chamber 60 as in the known ....20 vacuum pump of Figure 1 but, rather, is in fluid communication with an outer surface of the stator component 55. In this way, whilst a very small quantity of barrier fluid (less than 0.5 slm, for example around 0.1 slm) may leak from the fluid channel 70 between the surfaces of the adjacent stator components and into the pumping chamber 60 during normal operation of the vacuum pump, the majority of the barrier fluid (for example, in the range from 10 to 45 slm) passing around fluid channel 70 and forming the bulk or primary flow of barrier fluid, will be exhausted from the fluid channel 70 through outlet channel 80.

Consequently, bulk flow of fluid between the fluid channel 70 and the pumping chamber 60 is therefore inhibited, with the result that the pressure and pumping capacity of the vacuum pump within the stage housing the sealing system will not be detrimentally affected.

Figure 3 illustrates a second example of a vacuum pump which also comprises a stator component 105 which, in combination with another stator component of the vacuum pump, for example an end plate or a component similar to stator component 105, defines a pumping chamber 110. The vacuum pump comprises an 0-ring sealing element 115 surrounding the pumping chamber 110 and located in a groove formed within an axial surface of the stator component 105. The vacuum pump also comprises a fluid channel 120 formed within the axial surface of the stator component 105 and surrounding the pumping chamber 110 for protecting the sealing element 115.

The fluid channel 120 is located between the pumping chamber 110 and the 0-ring sealing element 115. The stator components are provided in close contact with one another, for example having a gap of less than 5 pm, such that flow of fluid therebetween is inhibited. Similar to the first example, the fluid channel 120 is in fluid communication with an inlet channel 125 for conveying barrier fluid to the fluid channel. However, in contrast to the first example no outlet channel is in fluid communication with fluid channel 120.

Consequently, whilst in operation a barrier fluid enters the fluid channel 120 * ** through the inlet channel 125, the barrier fluid is not exhausted therefrom and ::::: will simply collect in the fluid channel 120. Barrier fluid is supplied to fluid channel 120 from a barrier fluid source at a pressure in the range from 100 to (1 x 106) Pa, preferably in the range from (1 x 10) to (1 x 106) Pa. Once the fluid channel 120 is filled with barrier fluid, the barrier fluid in the fluid channel equalises with the source such that supply thereof is effectively terminated. S. S

* No particular flow path is provided between the fluid channel 120 and the : 25 pumping chamber 110 and so barrier fluid will not, therefore, be encouraged to pass into the pumping chamber and avoidance of a bulk flow of barrier fluid into the pumping chamber 110 is therefore achieved. As a result, a reservoir of barrier fluid at a pressure preferably in the range from (1 x I 0) to (1 x 106) Pa is maintained within the fluid channel 120.

Depending on the particular pressures of the source of barrier fluid and that of the pumped fluid, some seepage of pumped fluid (for example, around 0.1 slm) from the pumping chamber 110 into the fluid channel 120 may occur.

In such circumstances, the sealing element 115 will be protected by the dilution of this pumped fluid by the reservoir of barrier fluid. Conversely, some small quantity of barrier fluid may leak from the fluid channel 120 into the pumping chamber. However, as in the previous example, this leakage or secondary flow will be minimal (for example around 0.1 slm) and the volume of barrier fluid in fluid channel 120 will be topped up from the source of barrier fluid through inlet channel 125.

Figures 2 and 3 have been described in relation to a single stage vacuum pump, such as a single stage booster pump. However, they could also represent a single stage of a multistage vacuum pump, such as a multistage booster pump or a multistage primary pump. A multistage vacuum pump comprises a plurality of stator components connected together in series to define a plurality of pumping chambers. The remaining figures describe such multistage vacuum pumps in more detail.

A third example of a vacuum pump is illustrated in Figure 4, wherein the equivalent features of the vacuum pump of Figure 3 are identified using the same reference numerals to those used in Figure 3. The vacuum pump illustrated in Figure 4 is a multistage vacuum pump comprising a plurality of :.:::. stator components 105, each defining a respective pumping chamber 110.

.... The plurality of pumping chambers 110, in turn, defines a plurality of pumping stages of the vacuum pump. Each pumping chamber 110 is surrounded by an 0-ring sealing element 115 located between cooperating axial end surfaces * of adjacent stator components 105, to prevent egress of fluid from the * pumping chambers 110 to an exterior of the vacuum pump and to prevent *. ingress of ambient fluid from an exterior of the vacuum pump into the pumping chambers 110 of the vacuum pump.

A fluid channel 120 is formed in an axial surface of each stator component 105, the fluid channel 120 surrounding a respective pumping chamber 110 in order to protect a respective sealing element 115 located between that stator component and an adjacent stator component. Each fluid channel 120 receives barrier fluid from an inlet channel 125'. In this example, and in contrast to the previous examples, the inlet channel 125' of the fluid channel 120 does not communicate with an external surface of the vacuum pump in order to receive barrier fluid. Instead, the inlet channel 125' comprises a bore 126 which is in fluid communication with a fluid channel 120 associated with another stage of the multistage vacuum pump so that barrier fluid is conveyed to fluid channel 120 in series with the fluid channel of the other pumping stage.

Further examples of vacuum pumps in which at least one fluid channel receives barrier fluid from, or exhausts barrier fluid to, another part of the vacuum pump are described below with reference to Figures 5 to 11.

Figure 5 illustrates a multistage vacuum pump 200 comprising a plurality of stator components 210, 212, 214, 216, 218, 220. The outermost stator components 210, 220 are end plates of the vacuum pump 200. Each set of two adjacent stator components define therebetween a pumping chamber 230, 232, 234, 236, 238. The pumping chambers are sealingly connected together in series, for example by bolting the plurality of stator components together, so that in combination the pumping chambers 230-238 define a swept volume of the vacuum pump 200. The vacuum pump 200 comprises a rotor assembly (not shown) having a rotor, or two cooperating rotors, located within each pumping chamber. In operation, the rotor or *..S cooperating rotors act in combination with the pumping chamber to cause fluid to be pumped through the vacuum pump 200 from an inlet thereof to an outlet S...

thereof.

S..... * S

* Each pumping chamber 230-238 is surrounded by an 0-ring sealing : element 240, 242, 244, 246, 248, located between cooperating axial end * . surfaces of adjacent stator components, to prevent egress of fluid from the pumping chambers 230-238 to an exterior of the vacuum pump and to prevent ingress of ambient fluid from an exterior of the vacuum pump into the swept volume of the vacuum pump 200. In order to protect these 0-ringsealing elements from attack by pumped fluid being conveyed through the vacuum pump 200, means are provided for protecting the sealing elements. The sealing elements 240-248 are protected by fluid channels 250, 252, 254, 256, 258 each provided in the plane of a respective 0-ring sealing element 240-248 and located between a respective pumping chamber 230-238 and the 0-ring sealing element. Walls of each fluid channel may be formed in an axial surface of a respective stator component in combination with a cooperating axial surface of another stator component of the vacuum pump. Alternatively, as illustrated here, each fluid channel may be defined by grooves formed in the cooperating axial end surfaces of both of the adjacent stator components.

As illustrated, the fluid channels 250-258 are provided in series with one another, the channels being interconnected via bores 222, 224, 226, 228.

A single inlet channel 260 is provided in fluid communication with a barrier fluid source 262 to permit introduction of a barrier fluid into the series of fluid channels. The source 262 supplies barrier fluid at a pressure, for example, in the range from (1 x 10) to (1 x 106) Pa. In this example, the barrier fluid is introduced into the series of fluid channels towards or at the high vacuum end of the vacuum pump 200, namely that end adjacent to the high vacuum or lowest pressure pumping chamber 230. A single stream of barrier fluid can thus be conveyed through each of the fluid channels in turn to protect each of the 0-ring sealing elements.

The stator components 210-222 are connected together with minimal clearance between their axial surfaces. Whilst they are illustrated in Figure 5 S...

with a gap therebetween, this is for schematic purposes only, as the clearance is very small, for example, less than 5 pm. As a result, the bulk or primary flow of barrier gas (for example in the range from 10 to 45 slm) is conveyed * along the series of fluid channels with minimal leakage or secondary flow of barrier gas (less than 0.5 slm, for example 0.1 slm) from the fluid channels *. 250-254 located towards an inlet of the vacuum pump into their respective pumping chambers 230-234.

An outlet channel 265 is provided for conveying the bulk stream of barrier fluid out from the series of fluid channels 250-258. In this example the barrier fluid is introduced into the pumped fluid at a high pressure region of the vacuum pump, namely a region close to an outlet of the vacuum pump. For example as illustrated in Figure 5 the outlet channel 265 may be in fluid communication with the lowest vacuum pumping chamber 238 adjacent the outlet (not shown) of the vacuum pump, at which location it will have little impact on the pumping capacity of vacuum pump 200.

By providing a single barrier fluid stream which is delivered only into the pumping chamber 238 the volume of fluid used within the vacuum pump is significantly lower than would be used in the conventional arrangement of Figure 1, in which the barrier fluid supplied to each fluid channel is routed directly into the swept volume. Consequently, the pumping capacity is largely unaffected, and significantly lower quantities of consumable barrier fluid are used. In circumstances in which an abatement device is positioned downstream of the vacuum pump 200, this may be configured to accommodate a combination of the pumped fluid conveyed through the vacuum pump 200 and the barrier fluid introduced into the swept volume in the pumping chamber 238.

Figure 6 illustrates a multistage vacuum pump having a very similar configuration to that shown in Figure 5, except that an outlet channel 266 from the series of fluid channels is in direct fluid communication with an exhaust line 270 of the vacuum pump 200, rather than with a pumping chamber 238.

In this way, the bulk of the barrier fluid being conveyed through fluid channels

SS

250-258 bypasses the swept volume entirely so that exhaust of the barrier fluid from the fluid channels has minimal impact on the pumping capacity of * the vacuum pump. Alternatively, if an abatement device is located *..

* downstream of the vacuum pump the outlet channel 266 may be connected to * an exhaust line of the abatement device, so that the abatement device receives only the pumped fluid.

In any of the aforementioned examples, if an abatement device is located downstream of the vacuum pump to treat the pumped fluid exhausted from the vacuum pump, barrier fluid may be sourced, at least partly, from an exhaust line of the abatement device rather than from a source 262 of fresh barrier fluid. Once again, this can significantly reduce or even eliminate the quantity of consumable barrier fluid that is used in a vacuum pumping arrangement including a vacuum pump which implements a sealing system as described in relation to one of the aforementioned examples.

Figure 7 illustrates a multi stage vacuum pump having a similar configuration to that shown in Figures 5 and 6. In this example the outlet channel 267 from the series of fluid channels extends towards a second pump 280. The second pump 280 is separate from the vacuum pump 200.

Consequently, the exhaust of barrier fluid from the series of fluid channels has little, if any, affect on the capacity of the vacuum pump 200. The configuration of the sealing system implemented in the vacuum pump of Figure 7 is particularly useful if one of the barrier fluid and a component of the pumped fluid is to be recovered and re-used, as the flow of barrier fluid is separated from the pumped fluid.

Whilst the sealing system illustrated in Figure 7 is supplied with barrier fluid from a source of barrier fluid 262, this source need not be present. In such circumstances the fluid channels 250-258 are evacuated using the second vacuum pump 280. Thus any pumped fluid that passes into the fluid channels 250-258 from the pumping chambers 230-238 (in the region of 0.1 slm) is drawn out of the fluid channels by the second vacuum pump 280, so that the partial pressure of any corrosive component of the pumped fluid is * ** reduced and therefore minimises the impact on the 0-ring sealing elements 240-248. S... * S S...

In this configuration, the fluid channels 250-258 are evacuated for S...

example to a pressure of approximately 1 mbar or less. As discussed in S.....

* previous examples the minimal clearance (approximately 5 pm) between the adjacent stator components may permit some fluid to pass between the fluid S...

*:*. channels and the swept volume, and vice versa, in the form of a secondary fluid flow path. In this example, in the vicinity of an inlet of the vacuum pump, fluid would be inclined to pass into the highest vacuum pumping chamber 230, in which the pressure is for example 0.1 mbar, from the respective fluid channel where the pressure is for example 1 mbar or less. However, multi-stage vacuum pumps of the type illustrated here are typically sized to at least twice the capacity required to achieve a desired pressure in an enclosure being evacuated and a control valve is positioned between the enclosure and the vacuum pump to control evacuation to the desired pressure (for example 1 mbar). Consequently, the second vacuum pump 280 is sized so as to maintain a pressure in the fluid channels that does not significantly affect the pumping capacity of the high vacuum pumping chamber 230.

Towards the outlet of the vacuum pump, the pressures in the pumping chambers are higher and the direction of the secondary fluid flow path is inclined to be from the pumping chambers into the fluid channels by virtue of the pressure difference therebetween. However, as pumped fluid passes into the fluid channel the pressure of the fluid is rapidly reduced so that the partial pressure of any corrosive component of the pumped fluid is also reduced.

Consequently the impact of the corrosive component of the pumped fluid is minimised not only in the vicinity of the 0-ring sealing element but also within the high vacuum pressure chamber if any of the pumped fluid is conveyed through the series of fluid channels and passes back into the swept volume of the vacuum pump.

Figure 8 illustrates a multistage vacuum pump 300 comprising a plurality of stator components 310, 312, 314, 316, 318, 320. The outermost stator components 310, 320 are end plates of the vacuum pump 300. Each :.:::. set of two adjacent stator components define therebetween a pumping I...

chamber 330, 332, 334, 336, 338. The pumping chambers are sealingly connected together in series, for example by bolting the plurality of stator components together, so that in combination the pumping chambers 330-338 * define a swept volume of the vacuum pump 300. The vacuum pump 300 comprises a rotor assembly (not shown) having a rotor, or two cooperating *. rotors, located within each pumping chamber. In operation, the rotor or cooperating rotors act in combination with the pumping chamber to cause fluid to be pumped through the vacuum pump 300 from an inlet thereof to an outlet thereof.

Each pumping chamber 330-338 is surrounded by an 0-ring sealing element 340, 342, 344, 346, 348, located between cooperating axial end surfaces of adjacent stator components, to prevent egress of fluid from the pumping chambers 330-338 to an exterior of the vacuum pump and to prevent ingress of ambient fluid from an exterior of the vacuum pump into the swept volume of the vacuum pump 300. In order to protect these c-ring sealing elements from attack by pumped fluid being conveyed through the vacuum pump 300, means are provided for protecting the seaUng elements. The sealing elements 346, 348 are protected by fluid channels 356, 358 each provided in the plane of a respective 0-ring sealing element 346, 348 and located between a respective pumping chamber 336, 338 and the 0-ring sealing element. Walls of each fluid channel may be formed in an axial surface of a respective stator component in combination with a cooperating axial surface of another stator component of the vacuum pump. Alternatively, as illustrated here, each fluid channel may be defined by grooves formed in the cooperating axial end surfaces of both of the adjacent stator components.

The fluid channels 356, 358 are provided in series with one another, the channels being interconnected via a bore 328.

The stator components 310-320 are connected together with minimal clearance between their axial surfaces. Whilst they are illustrated in Figure 8 with a gap therebetween, this is for schematic purposes only, as the clearance is very small, for example, less than 5 pm. Small quantities of fluid (for : *** example less than 0.1 slm) may pass through the gap from the swept volume to the vicinity of the 0-ring sealing elements 340-348. In some circumstances, S...

the 0-ring sealing elements 340, 342, 344 which are located about the S...

S.,..' pumping chambers 330, 332, 334 configured to convey the lowest pressure *:" pumped fluid do not require protection from the pumped fluid. Generally, this would be the case where the pressure is sufficiently low in these regions so : that the partial pressure of any corrosive component of the pumped fluid is low * "25 enough to have little impact on the sealing element if they were to come into contact. It may, however, still be desirable to avoid or minimise the use of barrier fluid to save on costs, to avoid contamination of the pumped fluid so that recovery thereof is possible, to avoid any deterioration in the capacity of the vacuum pump (as discussed above) and/or to avoid the need for an oversized abatement device.

The sealing system of Figure 8 therefore comprises an alternative means for protecting sealing elements 346, 348 located in the higher pressure region of the vacuum pump, i.e. the region located towards the outlet. Fluid channels 356, 358 are provided for conveying a barrier fluid, to thereby inhibit pumped fluid from the pumping chambers 336, 338 from coming into contact with the 0-ring sealing elements 346, 348. The fluid channels 356, 358 are formed in an axial surface of at least one of the stator components 316, 318, 320 that define the respective pumping chambers 336, 338. Each respective fluid channel 356, 358 is formed in the plane of its respective 0-ring sealing element 346, 348 and is located between that sealing element 346, 348 and a respective pumping chamber 336, 338.

In contrast to the aforementioned sealing systems, the sealing system for sealing the swept volume shown in Figure 8 is not configured to receive barrier fluid from a separate source of barrier fluid. Instead, the barrier fluid is a very low pressure fluid generated by evacuating the fluid channels. The evacuation of the fluid channels is achieved by connecting the fluid channels 356, 358 surrounding the pumping chambers 336, 338 to a lower pressure pumping chamber, in this example the pumping chamber 330 located adjacent to the inlet of the vacuum pump 300. However, any pumping : *** chamber located upstream from pumping chamber 336, for example pumping chamber 332 or pumping chamber 334, could be connected to the fluid channels 356,358. The fluid channel 356 is connected to the pumping chamber 330 by duct 380 extending from the pumping chamber 330 to the fluid channel 356 through or around stator components 314, 316. In this way, the pressure of the fluid within duct 380, and consequently that in fluid : chambers 356, 358, equalises with the fluid within pumping chamber 330 by * 25 conveying fluid thereto to result in the presence of a barrier fluid within the fluid channels 356, 358 that has a lower pressure than that of the pumped fluid within the pumping chambers 336, 338.

By virtue of the reduced pressure in the fluid channels 356, 358, the pressure of any pumped fluid that does leak from the swept volume into the fluid channels 356, 358 is rapidly reduced. Consequently, the partial pressure of any corrosive component of the pumped fluid is similarly reduced, so that the corrosive impact of the corrosive component of the pumped fluid on the o-ring sealing elements 346, 348 is correspondingly reduced. No additional, externally sourced barrier fluid is introduced to the vacuum pump of Figure 8 and therefore the overall pumping capacity is not detrimentally affected.

Whilst the pumping capacity of the vacuum pump may accommodate a minimal return path of fluid from the low vacuum pumping chamber 338 to the high vacuum pumping chamber 330 it may be desirable to reduce the amount of pumped fluid being conveyed from a higher pressure region of the vacuum pump to a lower pressure region of the vacuum pump, especially in the vicinity of the inlet of the vacuum pump 300, to further reduce any impact on pumping capacity of the vacuum pump or corrosion if particularly harsh components are included in the composition of the pumped fluid.

Figures 9 and 10 illustrate a more sophisticated version of the sealing system described in relation to Figure 8. A multistage vacuum pump 400 is illustrated comprising a plurality of stator components 410, 412, 414, 416, 418, 420. The outermost stator components 410, 420 are end plates of the vacuum pump 400. Each set of two adjacent stator components define therebetween a pumping chamber 430, 432, 434, 436, 438. The pumping chambers are sealingly connected together in series, for example by bolting **.* the plurality of stator components together, so that in combination the pumping chambers 430-438 define a swept volume of the vacuum pump 400.

The vacuum pump 400 comprises a rotor assembly (not shown) having a rotor, * or two cooperating rotors, located within each pumping chamber. In operation, * the rotor or cooperating rotors act in combination with the pumping chamber to cause fluid to be pumped through the vacuum pump 400 from an inlet thereof to an outlet thereof.

Each pumping chamber 430-438 is surrounded by an 0-ring sealing element 440, 442, 444, 446, 448, located between cooperating axial end surfaces of adjacent stator components, to prevent egress of fluid from the pumping chambers 430-438 to an exterior of the vacuum pump 400 and to prevent ingress of ambient fluid from an exterior of the vacuum pump into the swept volume of the vacuum pump 400.

The stator components 410-420 are connected together with minimal clearance between their axial surfaces. Whilst they are illustrated in Figure 9 with a gap therebetween, this is for schematic purposes only, as the clearance is very small, for example, less than 5 pm. Small quantities of fluid (for example less than 0.1 slm) may pass through the gap from the swept volume to the vicinity of the 0-ring sealing elements 440-448. In some circumstances, the 0-ring sealing elements 440, 442, 444, 446 which are located about the pumping chambers 430, 432, 434, 446 towards the inlet of the vacuum pump 400 and configured to convey the lowest pressure pumped fluid do not require protection from the pumped fluid. Generally, this would be the case where the pressure is sufficiently low in these regions so that the partial pressure of any corrosive component of the pumped fluid is low enough to have little impact on the sealing element if they were to come into contact. It may, however, still be desirable to avoid or minimise the use of barrier fluid to save on costs, to avoid contamination of the pumped fluid so that recovery thereof is possible, to avoid any deterioration in the capacity of the vacuum pump (as discussed above) and/or to avoid the need for an oversized abatement device.

: ** The pumping chamber 430, located adjacent an inlet (not shown) of the vacuum pump, is configured to convey low pressure (for example 0.1 mbar) * S..

fluid in operation and, for the purpose of this description, will hereinafter be *5S* referred to as the first pumping chamber. The pumping chamber 438, located adjacent to an outlet (not shown) of the vacuum pump, is configured to convey higher pressure (for example 1 bar) fluid and will hereinafter be referred to as S... . . . . the fifth pumping chamber. The intermediate pumping chambers, configured S *.:25 to convey fluids at sequentially increasing pressures (between 0.1 mbar to 1 bar) will hereinafter be referred to as the second pumping chamber 432, the third pumping chamber 434 and the fourth pumping chamber 436 respectively.

The vacuum pump of the current example comprises means for protecting the 0-ring sealing element 448 surrounding the fifth pumping chamber 438 only. Figure 10 illustrates part of the sealing system i greater detail.

The sealing system comprises a plurality of fluid channels 492, 494, 496 each surrounding the fifth pumping chamber 438, the fluid channels being arranged in parallel between the fifth pumping chamber 438 and the 0-ring sealing element 448. Each fluid channel is formed in an axial surface of one of the stator components 418, 420 which define the fifth pumping chamber 438. In practice, each fluid channel could be part formed in each stator component 418, 420. Whilst a gap is illustrated between the two stator components 418, 420, this is for clarity only and the cooperating axial surfaces of the two stator components are provided in close contact with one another (for example within less than 5 pm). The sealing system comprises a plurality of ducts, similar to duct 380 in the example shown in Figure 8. In this example a series of three ducts 482, 484, 486 are used, each duct extending between a respective different pumping chamber 430, 432, 434 of the vacuum pump 400 and a respective fluid channel 492, 494,496.

A first fluid channel 492, located adjacent the 0-ring sealing element 448 is in fluid communication with the first pumping chamber 430 via a first duct 482. A second fluid channel 494, located between the first fluid * *. channel 492 and the fifth pumping chamber 438, is in fluid communication with the second pumping chamber 432 via a second duct 484. A third fluid **20 channel 496, located adjacent the fifth pumping chamber 438, is in fluid communication with the third pumping chamber via a third duct 486. *

* As in the example illustrated in Figure 8, the fluid channels 492, 494, *, 496 of this more complex sealing system are configured so that a barrier fluid *:*. to be accommodated therein is a very low pressure fluid generated by evacuating the fluid channels. The evacuation of the fluid channels is achieved by virtue of the connections of each respective channel with a lower pressure pumping chamber. Since the first fluid channel 492 is in fluid communication with the first pumping chamber 430, via duct 482, the pressure within the first fluid channel 492 equalises with the pressure in the first pumping chamber 430 by conveying fluid from the first fluid channel to the first pumping chamber. Similarly, the second fluid channel 494 reaches equilibrium with the second pumping chamber 432 and the third fluid channel 496 reaches pressure equilibrium with the third pumping chamber 434. In this way, a graded means for protecting the sealing element 448 is provided such that any pumped fluid that seeps into the fluid channels 496, 494, 492 experiences a series of barrier fluids each having a lower pressure than that found in the previous fluid channel.

Any pumped fluid that passes out of the fifth pumping chamber 438 into the third fluid channel 496 experiences a reduction in pressure and a consequential reduction in partial pressure of any corrosive component contained therein. This reduction in partial pressure reduces the corrosive impact of the corrosive component. Any fluid that then passes from the third fluid channel 496 into the second fluid channel 494 experiences a further reduction in pressure and consequential reduction in corrosive impact of any corrosive component contained therein. Similarly any fluid that then passes to the first fluid channel 492 experiences a further reduction in pressure. In other words, each additional level of complexity further protects the 0-ring sealing element 448.

Furthermore, the impact of any fluid being conveyed towards the lower pressure region of the vacuum pump from the fluid channels will also have S..

less impact than in the example illustrated in Figure 8. As discussed above, the graduated pressures experienced by any pumping fluid passing out of the S.,.

fifth pumping chamber 438 serve to gradually reduce the partial pressure of any pumped fluid passing towards the third pumping chamber 434.

: Consequently, if some pumped fluid migrates back from the third fluid channel 496 to the third pumping chamber 434 it has less impact than it would if it was conveyed directly to the first pumping chamber 430, as was the case in the example illustrated in Figure 8. If, subsequently, some pumped fluid migrates back from the second fluid channel 494 to the second pumping chamber 432, the pressure will be lower and so the corrosive impact of a corrosive component of the pumped fluid will be correspondingly reduced. Similarly, if some pumped fluid migrates back from the first fluid channel 492 to the first pumping chamber 430 the partial pressure of the corrosive component will be even lower and, therefore, so will the corrosive impact thereof.

Figure 11 illustrates an additional sealing mechanism for use in the vacuum pump of Figure 8 or Figure 9. Two stator components 518, 520 of a vacuum pump 500 are illustrated, the stator components being arranged axially in series and defining therebetween a pumping chamber 538. An o-ring sealing element 548 surrounds the pumping chamber 538 and is located between the two stator components 518, 520 to prevent ingress of fluid from an exterior of the vacuum pump 500 to the pumping chamber 538 and egress of pumped fluid from the pumping chamber 538 to an exterior of the vacuum pump 500. A fluid channel 558 surrounds the pumping chamber 538 and is located between the 0-ring sealing element 548 and the pumping chamber.

The fluid channel 558 is of the type defined in relation to the examples in Figure 8 and Figure 9 whereby a duct 580 is provided in fluid communication therewith, the duct extending to a pumping chamber configured to convey pumped fluid having a lower pressure than that conveyed through pumping chamber 538. The fluid channel 558 is therefore evacuated during normal operation of the vacuum pump 500. As discussed above, pumped fluid can pass from the pumping chamber 538 into the fluid channel 558 and therefrom along the duct 580 into another pumping chamber. Whilst the pressure of this pumped fluid is reduced upon entry into the fluid channel 558 and therefore *:::*20 the partial pressure of any corrosive component of the pumped fluid is also reduced so that less corrosive impact is experienced when the fluid comes into contact with any surfaces, it is desirable to minimise the quantity of *** js* * pumped fluid that passes from the pumping chamber 538 into the fluid * channel 558 in the first place. ** e * g.

An additional channel may therefore be provided in an axial surface of one or each of the stator components that define the pumping chamber 538.

The additional channel surrounds the pumping chamber 538 and is located between the pumping chamber 538 and the fluid channel 558. A seal 525, for example a seal made of polytetrafluoroethylene (PTFE), is provided in the additional channel. The effective gap between adjacent stator components is consequently reduced below the anticipated 5pm so that passage of pumped fluid through this gap is further reduced. In other words, the seal 525 provides a physical barrier to deflect pumped fluid back into the pumping chamber 538 to further inhibit egress of pumped fluid from the pumping chamber 538 into the fluid channel and subsequently along duct 580 to the other, lower pressure, pumping chamber which serves to evacuate fluid channel 558.

Such a seal 525 may have very corrosion resistant properties. Figure 11 illustrates one example of the cross section of barrier seal that may be used.

The seal shown could be implemented in an alternative orientation such that the back of the seal is pressurised. Alternatively, an entirely different cross section (for example, rectangular or circular) could be used.

The combination of the seal 525 and the fluid channel 558 provides an effective means for protecting the 0-ring sealing element 548 whilst inhibiting any backward contamination of substances from the lower vacuum pumping chamber 538, adjacent to the 0-ring sealing element 548, into a higher vacuum pumping chamber located towards the inlet of the vacuum pump via the duct 580. Whilst the physical barrier is illustrated in relation to the : .5 configurations shown in Figures 8 to 10 the seal 525 could also be implemented in the earlier examples of vacuum pumps. *.S.

Additional benefits of the including the physical barrier seal are a potential volumetric reduction in requirement of barrier fluid in those examples which use such a fluid, as illustrated in Figures 2 to 7, and a reduction in the : 20 level of vacuum that needs to be attained in the fluid channels in the configurations illustrated in Figures 8 to 10.

Multistage vacuum pumps are generally illustrated in the examples, however a single stage booster pump or other vacuum pump could readily use a sealing system of the type described herein.

Whilst the description relates to protection of 0-ring seals which are directly linked to the overall integrity of the stator of the vacuum pump, a similar mechanism can be used to protect any 0-ring seal exposed to a corrosive component of a pumped fluid which is incorporated into a vacuum pumping arrangement. For example, those seals used in any external pipe seals, abatement devices or silencers could be suitably protected by providing them with a fluid channel of one of the types described above, located between the respective 0-ring sealing element and the source of corrosive material. * .. * * S **.* **.* * S S... S... * .

S **S.S * S S. S

S S... S. S

S S S S 55

Claims (41)

1. A vacuum pump comprising: first and second stator components to be sealingly connected together to thereby define a pumping chamber; an 0-ring sealing element engaged between the stator components and located about the pumping chamber; a fluid channel in the plane of the sealing element and located between the sealing element and the pumping chamber; and means for reducing the partial pressure of fluid entering the fluid channel from the pumping chamber, and for inhibiting flow of fluid from the fluid channel to the pumping chamber.

2. A vacuum pump according to Claim 1, wherein said means comprises : * means for evacuating the fluid channel.

3. A vacuum pump according to Claim 2, wherein the means for evacuating the fluid channel comprises a second vacuum pump. S...

4. A vacuum pump according to Claim 2, comprising, upstream from said pumping chamber, another pumping chamber, the means for evacuating the fluid channel comprising said another pumping chamber.

5. A vacuum pump according to Claim 1, wherein said means comprises means for diluting fluid entering the fluid channel from the pumping chamber.

6. A vacuum pump according to Claim 5, wherein the diluting means comprises a source of barrier fluid, and means for conveying barrier fluid from the source to the fluid channel.

7. A vacuum pump according to Claim 6, wherein the source of barrier fluid comprises a source of purge gas.

8. A vacuum pump according to Claim 7, wherein the purge gas comprises one of nitrogen and argon.

9. A vacuum pump according to any of Claims 6 to 8, wherein the barrier fluid is at a pressure in the range from 0.2 to 2 bar.

10. A vacuum pump according to any of Claims 6 to 9, wherein the fluid channel comprises an outlet channel from which barrier fluid is discharged from the fluid channel.

11. A vacuum pump according to Claim 10, wherein the outlet channel is configured to convey barrier fluid from the fluid channel to a location isolated from fluid located within the pumping chamber.

12. A vacuum pump according to Claim 11, wherein the outlet channel is configured to convey barrier fluid to a second vacuum pump.

13. A vacuum pump according to Claim 10, wherein the outlet channel is configured to convey barrier fluid from the fluid channel to a location in fluid : *** communication with an outlet from the pump. S...

14. A vacuum pump according to Claim 13, comprising, downstream from *....

15 said pumping chamber, another pumping chamber, and wherein the outlet S...

channel is configured to convey barrier fluid to said another pumping chamber.

* 15. A vacuum pump according to Claim 6, comprising, upstream from said I. pumping chamber, another pumping chamber, the source of purge gas comprising said another pumping chamber.

16. A vacuum pump according to Claim 1, comprising a plurality of said fluid channels, a plurality of pumping chambers upstream from said pumping chamber, and, for each fluid channel, means for conveying fluid from that fluid channel to a respective one of said plurality of pumping chambers.

17. A vacuum pump according to any preceding claim, comprising a physical barrier seal located between the fluid channel and the pumping chamber.

18. A vacuum pump according to Claim 17, wherein the physical barrier seal is a corrosion resistant seal.

19. A vacuum pump according to Claim 17 or Claim 18, wherein the physical barrier seal is formed from polytetrafluoroethylene.

20. A vacuum pump comprising: a plurality of stator components sealingly connected together thereby to define a plurality of interconnected pumping chambers of the vacuum pump; and, for each pumping chamber: an 0-ring sealing element located about the pumping chamber and engaged between stator components defining that pumping chamber; a fluid channel in the plane of the sealing element and located between the sealing element and the pumping chamber; and means for reducing the partial pressure of fluid entering the fluid channel from the pumping chamber, and for inhibiting flow of fluid from the fluid channel to the pumping chamber.

: *.

21. A vacuum pump according to Claim 20, wherein the fluid channels are *.,15 in fluid communication with each other. *e..

22. A vacuum pump according to Claim 21, wherein said means comprises means for evacuating the fluid channels. * *

*

23. A vacuum pump comprising: 1*S *. : a plurality of stator components sealingly connected together thereby to * "20 define a plurality of interconnected pumping chambers of the vacuum pump; a plurality of 0-ring sealing elements each located about a respective pumping chamber and engaged between stator components defining that pumping chamber; a plurality of fluid channels, the fluid channels being in fluid communication with each other, each fluid channel being located in the plane of a respective sealing element and between the sealing element and its respective pumping chamber; and means for evacuating the fluid channels.

24. A vacuum pump according to Claim 22 or Claim 23, wherein the means for evacuating the fluid channels comprises a second vacuum pump.

25. A vacuum pump according to Claim 22 or Claim 23, comprising, upstream from said pumping chambers, another pumping chamber, the means for evacuating the fluid channels comprising said another pumping chamber.

26. A vacuum pump according to Claim 21, wherein said means comprises means for diluting fluid entering each fluid channel from its respective pumping chamber.

27. A vacuum pump comprising: a plurality of stator components sealingly connected together thereby to define a plurality of interconnected pumping chambers of the vacuum pump; a plurality of 0-ring sealing elements each located about a respective pumping chamber and engaged between stator components defining that pumping chamber; : .. a plurality of fluid channels, the fluid channels being in fluid communication with each other, each fluid channel being located in the plane of a respective sealing element and between the sealing element and its respective pumping chamber; and means for diluting fluid entering each fluid channel from its respective pumping chamber. S...

*:..0

28. A vacuum pump according to Claim 26 or Claim 27, wherein the diluting means comprises a source of barrier fluid, and means for conveying barrier fluid from the source to the fluid channels.

29. A vacuum pump according to Claim 28, wherein the source of barrier fluid comprises a source of purge gas.

30. A vacuum pump according to Claim 29, wherein the purge gas comprises one of nitrogen and argon.

31. A vacuum pump according to any of Claims 28 to 30, wherein the barrier fluid is at a pressure in the range from 0.2 to 2 bar.

32. A vacuum pump according to any of Claims 28 to 31, comprising an outlet channel from which barrier fluid is discharged from the fluid channels.

33. A vacuum pump according to Claim 32, wherein the outlet channel is configured to convey barrier fluid from the fluid channels to a location isolated from fluid located within the pumping chambers.

34. A vacuum pump according to Claim 32, wherein the outlet channel is configured to convey barrier fluid from the fluid channels to a location in fluid communication with an outlet from the pump.

35. A vacuum pump according to Claim 34, comprising, downstream from said pumping chambers, another pumping chamber, and wherein the outlet channel is configured to convey barrier fluid to said another pumping chamber.

36. A vacuum pump according to Claim 28, comprising, upstream from : *** said pumping chambers, another pumping chamber, the source of purge gas comprising said another pumping chamber.

*...15

37. A vacuum pump comprising: a plurality of stator components sealingly connected together thereby to define interconnected first and second pumping chambers of the vacuum *.. pump, the first pumping chamber being located upstream from the second pumping chamber; an 0-ring sealing element located about the second pumping chamber and engaged between stator components defining that pumping chamber; a fluid channel located in the plane of the sealing element and between the sealing element and the second pumping chamber; and means for conveying fluid from the fluid channel to the first pumping chamber.

38. A vacuum pump according to Claim 37, comprising a third pumping chamber located between the first and second pumping chambers, a second fluid channel located in the plane of the sealing element and between the sealing element and the first-mentioned fluid channel, and means for conveying fluid from the second fluid channel to the third pumping chamber.

39. A vacuum pump according to Claim 38, comprising a fourth pumping chamber located between the second and third pumping chambers, a third fluid channel located in the plane of the sealing element and between the sealing element and the second fluid channel, and means for conveying fluid from the third fluid channel to the fourth pumping chamber.

40. A vacuum pump comprising: a plurality of stator components sealingly connected together thereby to define interconnected first and second pumping chambers of the vacuum pump, the first pumping chamber being located upstream from the second pumping chamber; an 0-ring sealing element located about the first pumping chamber and engaged between stator components defining that pumping chamber; a fluid channel located in the plane of the sealing element and between the sealing element and the first pumping chamber; a source of barrier fluid; means for conveying barrier fluid from the source to the fluid channel; and means for conveying barrier fluid from the fluid channel to the second * pumping chamber. I. *

:::: :20

41. A vacuum pump according to any preceding claim, wherein the vacuum * .. pump is a booster pump.