WO2022096713A2

WO2022096713A2 - Sliding vane pump

Info

Publication number: WO2022096713A2
Application number: PCT/EP2021/080949
Authority: WO
Inventors: Eric Figoni; Christophe DESPESSE
Original assignee: Leybold France Sas
Priority date: 2020-11-09
Filing date: 2021-11-08
Publication date: 2022-05-12
Also published as: GB202100752D0; WO2022096713A3; CN220581100U; DE212021000498U1; KR20230001370U; TW202225558A; JP3244413U; GB2600784A

Abstract

A sliding vane pump, vacuum pump lubricated by such a pump and the vane for a sliding vane pump are disclosed. The sliding vane pump comprises: a rotor rotatably mounted within a stator. The rotor comprises at least one vane slidably mounted within a corresponding at least one cavity, at least one end surface of the vane being configured to abut with an inner wall of the stator. The rotor, stator and at least one vane define a plurality of variable volume pumping chambers for conveying fluid from a fluid inlet to a fluid outlet on rotation of the rotor, the at least one vane separating adjacent pumping chambers. The pump further comprises a channel configured to provide a passage between the adjacent pumping chambers.

Description

SLIDING VANE PUMP

FIELD OF THE INVENTION

The field of the invention relates to sliding vane pumps, the vanes used in such pumps and a vacuum pump lubricated by such a pump.

BACKGROUND

Sliding vane pumps are used for pumping liquids such as oils. They may be used in conjunction with vacuum pumps to lubricate the shaft and drive the inlet valve. Such pumps operate at high rotational speeds and have a variable volume pumping chamber formed by the rotor, sliding vane and stator inner wall. The variable volume pumping chamber sucks the lubricant into the chamber through the inlet and compresses the lubricant as it moves it from the inlet to an outlet of the pump.

In such pump a problem of cavitation within the fluid may arise particularly, where the density of the fluid being pumped and the rotational speed of the rotor is high. Cavitation is a phenomenon in which a rapid change of pressure in a liquid leads to the formation of small vapour-filled cavities in the lower pressure regions. When the pressure in these regions increases, these bubbles collapse and can generate shock waves that are strong close to the bubble, such shock waves cause the pump to vibrate and be noisy.

Chemically resistant lubricants such as PTFE lubricants are increasingly used in vacuum pumps which pump aggressive chemicals from semiconductor chambers. These lubricants have a high density, close to double the density of a mineral oil, and cavitation is an increasing problem with such pumps.

It would be desirable to inhibit cavitation in sliding vane pumps. SUMMARY

A first aspect provides a sliding vane pump, said pump comprising: a rotor rotatably mounted within a stator; said rotor comprising at least one vane slidably mounted within a corresponding at least one cavity, at least one end surface of said vane being configured to abut with an inner wall of said stator; said rotor, stator and at least one vane defining a plurality of variable volume pumping chambers for conveying fluid from a fluid inlet to a fluid outlet on rotation of said rotor, said at least one vane separating adjacent pumping chambers; and a channel configured to provide a passage between said adjacent pumping chambers.

The inventors recognised potential problems associated with sliding vane pumps for pumping fluids such as oil. Such pumps generate lower pressure regions where the pumping chamber is increasing in volume and fluid is sucked into the pumping chamber through the inlet. The pumping chamber then decreases in volume towards the outlet and the fluid is compressed and expelled through the outlet. In some circumstances, such as where the pump is rotating at a high speed and/or the fluid is particularly dense, bubbles may form in the lower pressure regions and this can lead to cavitation where during compression of the fluid the bubbles formed at the lower pressures collapse. Cavitation in a pump leads to excess noise and vibration and is to be avoided where possible. Providing a fluid communication channel between adjacent pumping chambers that allows fluid flow from a higher pressure region in one pumping chamber to a lower pressure region in an adjacent pumping chamber, allows excessive pressure drop in the lower pressure regions to be mitigated and inhibits the formation of bubbles in a simple, inexpensive and robust manner.

Although there may be a technical prejudice against providing a channel that allows fluid communication between pumping chambers as this may reduce pumping efficiency and in effect cause leakage. Where cavitation may be a problem, providing a passage of a controlled predefined, constrained size such that the leakage is controlled to a desired value provides an effective solution to the cavitation problem. A passage either through or around a vane may be a solution that is simple to manufacture and provides a defined channel size that is relatively independent of tolerances in the pump components.

The one or more sliding vanes are longitudinal elements mounted to slide along a longitudinal axis in a correspondingly shaped cavity within the rotor. This sliding movement allows a variable volume pumping chamber to be produced as the rotor rotates eccentrically within the stator.

Although the channel providing the passage between adjacent pumping chambers may be formed in different ways, in some embodiments said channel is formed in said at least one vane.

In some embodiments, said channel comprises a groove in an end surface of said vane, at least a portion of said end surface abutting said inner stator wall.

One simple and convenient way of providing the channel may be to provide it as a groove in the end surface of the vane.

In some embodiments, said at least one end surface is curved to provide a sealing surface with said inner stator wall.

The groove provides an indent in this sealing surface that forms a channel through that links adjacent pumping chambers and provides a passage between the leading and trailing edges of the vane during operation of the pump.

In other embodiments, said channel comprises a passage within said vane.

An alternative may be to provide the channel is as a passage extending through the vane. As the vane is a sliding vane which extends out of a cavity in the rotor by varying amounts depending on the position of the eccentrically mounted rotor, the passage is configured to be within a portion of the vane that is not obscured by the cavity of the rotor even when the vane is in a recessed as opposed to an extended position.

Alternatively and/or additionally, the channel may comprise a groove in the inner stator wall.

The position of the channel may be in the rotor or stator wall or in both, its actual position is not important provided that a passage allowing some flow between pumping chambers is provided. The amount of flow that is provided depends on the size of the passage. Manufacturing a passage or a groove allows the bypass path between the chambers to be accurately controlled and be relatively independent of other tolerances in the pump. The size of the channel may be selected to provide a desired bypass flow that is sufficient to inhibit cavitation while not unduly impeding the performance of the pump. This will be dependent to some extent both on the density of the fluid to be pumped and the speed of rotation of the pump. Although the channel may be machined in the inner stator wall it may be preferable to provide the channel in the vane as this may be simpler to manufacture.

In some embodiments, both end surfaces of said vane comprise a groove, said grooves forming channels between said pumping chambers.

Although there may be a plurality of individual vanes extending from individual recesses or cavities in the rotor, in some embodiments the vane may extend through the rotor either ends of the vane abutting diametrically opposing surfaces of the inner wall of the stator. The vane slides within the cavity and both ends of the vane comprise a channel in the form of a groove.

In some embodiments, said rotor is mounted to rotate eccentrically within said stator. The centre of rotation of the rotor may be offset with respect to the centre of chamber formed by the inner wall of the stator, such that as it rotates its movement is eccentric with respect to the stator inner wall.

In some embodiments, a cross section of at least a portion of a length of said sliding vane comprises a protruding portion configured to protrude from an outer surface and cooperate with a correspondingly shaped cavity in said rotor to inhibit said vane from twisting about its longitudinal axis.

In order for the vane to provide the channel between the leading and trailing edges during rotation, the vane should be inhibited from twisting or rotating about its longitudinal axis such that the entrances to the channel stay aligned with the pumping chambers that they open into. This may be done by providing a protruding portion configured to cooperate with a correspondingly shaped cavity in the rotor. The protruding portion may extend from the longitudinally extending side surface of the vane and as such prohibits rotation about a longitudinal axis. In some embodiments, where the channel comprises a groove extending in a straight line from a leading to a trailing edge the protruding portion protrudes substantially perpendicularly to the groove.

Although, the pump may be configured to pump a number of fluids, in some embodiments the pump is configured to pump a lubricant.

In some embodiments, the pump is configured to pump a high density lubricant, a density of the lubricant being above 1 .5kg per litre.

Cavitation is a particular problem where a pump is pumping high density fluids and lubricants with a density of more than 1 ,5kg/litre may trigger cavitation in sliding vane pumps such that embodiments are particularly appropriate to such pumps. ln some embodiments, said channel comprises a cross section of between 1 and 2 mm².

The size of the channel required to inhibit cavitation will depend on the density of the fluid being pumped and the speed of rotation of the pump. The channel should be limited in size to avoid too great a drop in pumping efficiency but should be sufficient to allow some pressure relief and inhibit cavitation. In many scenarios a cross section of between 1 and 2 mm² will provide the flow required to inhibit cavitation while not unduly affecting the performance of the pump.

In some embodiments, said channel is sized such that an ultimate pressure achievable by said pump is reduced by between 5 and 15%.

As noted previously, the channel will reduce the ultimate pressure achievable by the pump but will have the advantage of inhibiting cavitation. A channel size selected so that the ultimate pressure achievable by the pump is reduced by a limited amount has been found to provide effective reduction in cavitation while still providing an efficient pump.

In some embodiments there may be a plurality of channels. In some embodiments these may take the form of a plurality of grooves in the end surface of the vane.

In some embodiments the channel forms a substantially straight pathway between the two pumping chambers, while in other embodiments the channel may not be straight.

Having a single channel and having it formed as a straight channel may have the advantage of ease of manufacture. However, there may be embodiments where two or more channels are provided and/or where the channels form a more intricate angled path. ln some embodiments, said pump comprises a lubricant pump for driving a valve and supplying lubricant to a vacuum pump.

Oil pumps for supplying lubricant to vacuum pumps may be mounted on the same shaft as the vacuum pump and thus, their rotational speed is set by the rotational speed of the vacuum pump and may be very high. Furthermore, vacuum pumps are often used for pumping aggressive chemicals and as such the lubricants within these pumps may need to be resistant to such chemicals, such lubricants may have a high density. Thus, problems of cavitation may occur in such pumps for vacuum pumps and embodiments may provide a particularly effective solution to this.

In some embodiments a largest portion of said vane comprises a circular cross section; and at least one further portion of said vane comprises a non-circular cross section.

A second aspect provides a sliding vane pump comprising a rotor rotatably mounted within a stator; said rotor comprising at least one vane slidably mounted within a corresponding at least one cavity; said rotor, stator and at least one vane defining a plurality of variable volume pumping chambers for conveying fluid from a fluid inlet to a fluid outlet on rotation of said rotor, said at least one vane separating adjacent pumping chambers; and a largest portion of said vane having a circular cross section; at least one further portion of said vane having a noncircular cross section.

A circular cross section for the major portion of the vane means that the corresponding portion of the cavity in which the vane slides has a corresponding circular cross section. This leads to easier machining and robust parts.

However, circular cross sections mean that axial rotation or twisting of the vane may occur. The head of the vane has a shape that is required to stay aligned with the stator inner wall to provide an effective seal. Thus, maintaining alignment of the head requires some means to inhibit rotation of the vane. This problem is addressed by providing a portion of the vane with a non-circular cross section which allows rotation of the vane to be impeded. Most of the vane has a circular cross section which allows for easier machining of both the vane and the cavity within the rotor into which it is inserted. Only a portion has a non-circular cross section as inhibiting axial rotation of a portion of the vane will inhibit axial rotation of the whole vane.

In some embodiments, said at least one further portion is at one end of said vane.

In some embodiments, a cross section of an annular recess within said stator configured to receive said sliding vane comprises a non-circular cross section corresponding to said non-circular cross section of said vane.

It may be advantageous for the non-circular portion to be at one end of the vane and in some cases to be the portion of the vane that extends out of the rotor cavity when the rotor is at the position where it is furthest from the stator inner wall. The stator inner wall is provided with an annular recess with a corresponding non-circular cross section and this maintains the vane in a certain alignment and inhibits axial rotation when the vane extends out of the rotor and into the stator.

In some embodiments, said at least one further portion is at both ends of said vane.

Where the vane extends through the rotor it may be advantageous for both ends of the vane to have the non-circular cross section such that at any one time at least one end of the vane will be extending into a correspondingly shaped stator and thus, at any one time at least one end of the vane and thus, the whole vane is impeded from rotation. ln some embodiments, said at least one cavity within said rotor comprises a circular cross section along a length of said cavity.

Where the non-circular cross section portion of the vane is at both ends, then it is the end portions of the vane and the corresponding stator shape which impede axial rotation of the vane and the cavity within the rotor can be circular along its whole length. This makes for easier machining.

In other embodiments, a portion of the cavity within the rotor may have a noncircular cross section a largest portion having a circular cross section.

In some embodiments, said rotor comprises an additional anti-rotation component mounted in a portion of said rotor cavity configured to house said at least one further portion of said vane

In some embodiments, the non-circular cross section portion of the cavity may not be formed within the rotor itself but may be formed by an additional component such as a pin extending across the cavity. In some embodiments the pin may be at one end of the cavity, the pin obscuring a portion of the circular cross section and being located such that it is within the portion of the cavity that houses the non-circular cross section portion of the vane and impedes rotation of the sliding vane. This may be required if the vane does not extend through the rotor and only has one end with a non-circular cross section.

In some embodiments, said non-circular cross section is smaller than said circular cross section.

It may be advantageous if the non-circular cross section of the vane is smaller than the circular cross section as this allows it to be machined from a circular cross section portion. Furthermore, it can fit within a circular cross section cavity within the rotor with only a small portion of the cavity having the corresponding non-circular portion to impede rotation. This allows the cavity to be simply machined and an additional anti rotation component such as a pin to be added to the machined cavity.

In some embodiments, said at least one further portion comprises at least one recessed section machined from an outer surface of said vane.

As noted previously where the non-circular cross section is smaller than the circular cross section then the non-circular cross section can be machined from the outer surface to form a recessed section.

In some embodiments, said at least one recessed section comprises a flat axially extending surface.

A flat axially extending surface can be used to inhibit axial rotation and is easy to machine. In this regard, the corresponding flat surface of the recess or cavity that the vane extends into may be within the rotor or where the recessed section is at one or both ends of the vane then the correspondingly shaped recess into which the end of the vane extends will be within the stator of the pump. This may be easier to machine than machining a shape into a cavity in the rotor.

A third aspect provides a vacuum pump comprising a sliding vane pump according to a first or second aspect, for supplying lubricant to said vacuum pump.

A fourth aspect provides a vane for a sliding vane pump according to a first aspect, said vane being configured to be slidably mounted within a corresponding cavity in a rotor and to extend from said cavity such that at least one end surface of said vane abuts an inner stator wall and thereby separates adjacent pumping chambers when mounted in said rotor in said pump; said vane comprising a channel configured to provide a passage between said adjacent pumping chambers when said vane is mounted within said pump. In some embodiments, said channel comprises a groove in said at least one end surface

In other embodiments, said channel comprises a passage extending from a leading to a trailing edge of said vane, when said vane is mounted in said rotor.

A fifth aspect provides a vane for a sliding vane pump according to a second aspect, said vane being configured to have a substantially circular cross section for a larger portion of a length of said vane and a non-circular cross section for a smaller portion of a length of said vane, said vane being configured to be slidably mounted within a correspondingly shaped cavity in a rotor and to extend from said cavity such that at least one end surface of said vane abuts an inner stator wall and thereby separates adjacent pumping chambers when mounted in said rotor in said pump.

In some embodiments, said vane comprising a channel configured to provide a passage between said adjacent pumping chambers when said vane is mounted within said pump.

In some embodiments, said at least one channel is in at least one of said end surfaces.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figure 1 shows a section through a sliding vane pump according to an embodiment;

Figure 2 shows an end view of a pump according to an embodiment;

Figure 3 shows the stator or cylinder of a pump according to an embodiment;

Figure 4 shows the sliding vane and the sliding vane mounted within the rotor;

Figure 5 shows the cylinder of the pump mounted on the rotor;

Figure 6 shows two vanes according to different embodiments;

Figure 7 shows sectional views through a pump according to an embodiment with the rotor in different positions; and

Figure 8 schematically shows the sliding vane pump as an oil pump within a vacuum pump.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided.

Figure 1 shows a section through a sliding vane pump. In this pump there is a rotor 40 mounted to rotate eccentrically within a stator 50. The rotor 40 has a sliding vane 10 mounted within it, the sliding vane 10 being configured to contact the inner walls of the stator 50 and to slide within the rotor as it rotates. Pumping chambers are formed between the sliding vane, the inner wall of the stator and the outer wall of the rotor. Rotation of the rotor pushes oil from an inlet 30 towards an outlet 20 on anticlockwise rotation of rotor 40.

Although in this embodiment, only a single vane is shown that extends across the diameter of the rotor, in other embodiments, there may be two or more vanes mounted within correspondingly shaped recesses at different positions in the rotor, the vanes being biased to extend from their recesses and contact the inner stator wall. The vanes, rotor and inner stator wall forming pumping chambers. In this embodiment there are anti-rotational components in the form of pins 41 that extend across a portion of the circular cross section at either end of the cavity in the rotor that houses the vane. The vane 10 has recesses, in the otherwise circular cross section, in portions at either end. These recesses slide against the pins such that the pins inhibit axial rotation of the vanes. In other embodiments such as that shown in Figures 3 and 4, the cross sectional shape of the stator that receives the vane matches the non-circular shape of the ends of the vane and this is sufficient to inhibit rotation of the vane without the requirement for additional non-rotational components such as pins 41 . However, in embodiments where the vane does not extend through the stator (not shown), then anti-rotational components within the rotor cavity itself, or changes to the shape of the rotor cavity will be required to inhibit rotation when the rotor is in the position where the vane does not extend out of the cavity (the position of the left hand side of the vane in this Figure).

Figure 2 shows an end view of the pump of Figure 1 and shows an exhaust pipe leading to the exhaust outlet 20 and an inlet machined aperture leading to the inlet 30. There is also a pressure limiter 60 shown. In this embodiment the sliding vane pump is a lubricant pump for supplying lubricant to a vacuum pump. The pressure limiter 60 controls the pressure of the lubricant supplied to the vacuum pump. In this embodiment the rotor of the sliding vane pump is mounted on the same shaft as the vacuum pump rotor and thus, rotates at the same high speed. The temperature of the pump will rise during operation and will affect the viscosity of the lubricant and the pressure of lubricant supplied to the vacuum pump. The pressure limiter 60 acts to control the supply of lubricant to the vacuum pump.

Some components of the sliding vane pump are shown in Figures 3 and 4. Figure 3 shows the stator or cylinder of the pump 50, the stator has an annular recess or groove with a sealing surface 52 and an anti-rotational surface 53 that is configured to correspond to the truncated circular cross sectional shape of the end portion of the vanes shown in Figure 4. These corresponding non-circular shapes inhibit the vane from rotating axially. The main portion of the vane has a circular cross section that corresponds to the cross section of the cylindrical cavity that extends through the rotor.

Figure 4 shows rotor 40 with sliding vane 10. The sliding vane is shown separately to the rotor and mounted within it. The vane on the left hand side has a circular cross section for most of its length with a recessed end portion that mates with a similarly shaped surface 52 in the stator 50 of Figure 3, thereby impeding the vane from rotating about its longitudinal axis. In the right hand figure there is a side portion that protrudes from a longitudinal side surface of the sliding vane and which when mounted within a correspondingly shaped cavity in the rotor further impedes the vane from twisting or rotating about its longitudinal axis.

Figure 5 shows the pump cylinder or stator 50 mounted on the rotor. It also shows the shaft 42 on which the rotor is mounted.

Figure 6 shows the end surface 8 of vane 10 in more detail. The left hand upper figure of Figure 6 shows a vane of an embodiment of the second aspect where the end surface 8 forms a sealing surface for sealing with the inner wall 52 of the stator isolating the pumping chambers from each other. The sealing surface is curved to correspond to the curved inner wall 52 (see Figure 3) of the pumping cylinder or stator 50. There is a recess in one side towards the end which renders the cross section non-circular. This corresponds to the non-circular cross section of the pumping cylinder in the stator and these corresponding non- circular cross sections impede the vane 12 from rotating about its longitudinal axis.

The upper right hand figure shows a similar embodiment where there is a channel 12 within the end surface 8 of the vane 10 which channel provides a passage between adjacent pumping chambers that are separated by the vane and allows passage of fluid from a lower pressure region on one side of the vane to a higher pressure region on the other side of the vane, which fluid flow may inhibit the formation of bubbles in the lower pressure region. The channel 12 is arranged such that it provides a path between the leading and the trailing edges of the vane in operation of the pump and provides a bypass passage between the adjacent pumping chambers. It should be noted that forming the channel 12 on the end surface of the vane is easy to manufacture, inexpensive and robust. An alternative may be to have a passage having a cylindrical form extending through a portion of the vane that extends from the recess or cavity in the rotor in substantially all positions of the rotor. Alternatively, the channel 12 may be formed as a groove on the inner stator wall rather than on the sliding vane itself.

The lower figure in Figure 6 shows example dimensions of this particular embodiment. In this example, the channel in the form of a groove has a width of 1 mm and a depth of 1 ,4mm. The overall width of the vane is 4.9mm and its length is 40mm. The length of the vane corresponds to the distance between opposing surfaces 52 of pumping cylinder 50 in this embodiment where the vane extends through the rotor.

Figure 7 shows a section through the pump with a rotor in different positions.

The arrow shows the anticlockwise direction of rotation of the rotor. Arrows 72 point to a compression chamber, that is the position of the pumping chamber where the rotation of the rotor decreases the size of the pumping chamber and thereby pushes oil out of the chamber towards and through the outlet 20. Chamber 74 is the lower pressure chamber where the pumping chamber is expanding and oil is pulled from the inlet 30 into the expanding pumping chamber 74. Region 70 is where cavitation may occur as this is a lower pressure region in the expanding chamber. The passage formed by groove 12 in the end surfaces of the vane between adjacent pumping chambers provides a flow route for fluid from the region of higher pressure 72 to the region of lower pressure where cavitation might occur 70. This increases the pressure in the lower pressure region and inhibits cavitation. As can be appreciated this does lead to a slightly less efficient pump and the size of the channel is selected such that cavitation is inhibited but the efficiency of the pump is still maintained to a desired level. This level may be set such that the ultimate pressure that the pump can produce is only reduced by 15% preferably by less than 10%. In this regard the pressure produced by the oil pump may in some embodiments be higher that is generally required and may be controlled by a pressure limiter as is shown in Figure 2, in such a case reducing the ultimate pressure attainable by the pump may not be acceptable.

Figure 8 shows an embodiment where an oil pump 80 is mounted to provide lubrication to and drive the valve of a vacuum pump 90. As can be seen the oil pump is mounted on the shaft 42 of the vacuum pump which is driven by motor 95. The speed of rotation of the rotor of the oil pump is set by the requirements of the vacuum pump. Thus, the rotor may rotate at a very high speed of rotation, typically of the order of 1500 to 1800 rpm. Furthermore, where the vacuum pump is being used to evacuate chemically aggressive products, as may be the case in semiconductor processing, then the oil or lubricant supplied by the pump 80 is selected to be a lubricant that is chemically resistant. Such lubricants may have a high density, one such lubricant having a density of 1 .88 kg per litre. This is more than twice the density of normal mineral oil and the combination of the high pumping speed and the high density of the fluid being pumped increases the chance of cavitation which can cause knocking within the pump. Providing the channel allowing a limited fluid flow between adjacent pumping chambers inhibits cavitation and may improve pump performance.

Although in the embodiments shown, there is a single vane that extends through the rotor, it should be understood that in other embodiments the vane may be formed as two separate vanes extending from opposite sides of the rotor and being spring biased against the inner stator wall. Other embodiments where there are more pumping chambers and more vanes can also be envisaged and may also benefit from a constrained pressure relief channel between adjacent pumping chambers. Embodiments also provide a method of upgrading a pump whereby the vane is replaced with a vane that has a groove or passage allowing a conventional pump to operate at higher speeds and with higher density lubricants while still inhibiting cavitation.

Embodiments also provide a method of servicing a sliding vane pump whereby a worn vane is replaced with a vane that has a groove or passage.

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS

8 end surface of vane

10 vane

12 channel

20 outlet

30 inlet

40 rotor

41 pin

42 shaft

50 stator or pump cylinder

52 annular recess sealing surface in stator

53 anti-rotation surface

60 pressure limiter

70 potential cavitation site behind the head of the vane

72 compressed pumping chamber

74 reduced pressure pumping chamber

80 oil pump

90 vacuum pump

95 motor

Claims

1 . A sliding vane pump, said pump comprising: a rotor rotatably mounted within a stator; said rotor comprising at least one vane slidably mounted within a corresponding at least one cavity, at least one end surface of said vane being configured to abut with an inner wall of said stator; said rotor, stator and at least one vane defining a plurality of variable volume pumping chambers for conveying fluid from a fluid inlet to a fluid outlet on rotation of said rotor, said at least one vane separating adjacent pumping chambers; and a channel configured to provide a passage between said adjacent pumping chambers.

2. A sliding vane pump according to claim 1 , wherein said channel is formed in said at least one vane.

3. A sliding vane pump according to claim 2, wherein said channel comprises a groove in an end surface of said vane, at least a portion of said end surface abutting said inner stator wall.

4. A sliding vane pump according to claim 2, wherein said channel comprises a passage within said vane.

5. A sliding vane according to any preceding claim, said at least one end surface being curved to correspond to and provide a sealing surface with said inner stator wall.

6. A sliding vane pump according to any preceding claim, wherein said channel comprises a groove in said inner stator wall.

7. A sliding vane pump according to any preceding claim, said sliding vane pump comprising a single vane slidably mounted in a cavity extending through said rotor, either end of said vane abutting with said inner wall of said stator.

8. A sliding vane pump according to claim 7 when dependent on claim 3, wherein both end surfaces of said vane comprise said groove.

9. A sliding vane pump according to any preceding claim, wherein said rotor is mounted to rotate eccentrically within said stator.

10. A sliding vane pump according to any preceding claim, a cross section of at least a portion of a length of said sliding vane comprising a protruding portion configured to cooperate with a correspondingly shaped indent in said cavity in said rotor, said protruding portion inhibiting said vane from twisting about its longitudinal axis.

11. A sliding vane pump according to any preceding claim, said pump being configured to pump a lubricant.

12. A sliding vane pump according to claim 11 , said pump being configured to pump a high density lubricant, a density of said lubricant being above 1 .5 Kg/litre.

13. A sliding vane pump according to any preceding claim, said channel comprising a cross section of between 1 and 2 mm².

14. A sliding vane pump according to any preceding claim, said channel being sized such that an ultimate pressure achievable by said pump is reduced by between 5 and 15%.

15. A sliding vane pump according to any preceding claim, wherein a largest portion of said vane comprises a circular cross section; and at least one further portion of said vane comprises a non-circular cross section.

16. A sliding vane pump comprising a rotor rotatably mounted within a stator; said rotor comprising at least one vane slidably mounted within a corresponding at least one cavity; said rotor, stator and at least one vane defining a plurality of variable volume pumping chambers for conveying fluid from a fluid inlet to a fluid outlet on rotation of said rotor, said at least one vane separating adjacent pumping chambers; and a largest portion of said vane having a circular cross section; at least one further portion of said vane having a non-circular cross section.

17. A sliding vane pump according to claim 15 or 16, wherein said at least one further portion is at one end of said vane.

18. A sliding vane pump according to claim 17, wherein said at least one further portion is at both ends of said vane

19. A sliding vane pump according to any one of claims 15 to 18, wherein a cross section of a recess within said stator configured to receive said sliding vane comprises a non-circular cross section corresponding to said non-circular cross section of said vane.

20. A sliding vane pump according to any one of claims 15 to 19, wherein said at least one cavity within said rotor comprises a circular cross section along a length of said cavity.

21 . A sliding vane pump according to any one of claims 15 to 20, wherein said rotor comprises an additional anti-rotation component mounted in a portion of said rotor cavity configured to house said at least one further portion of said vane - 22 -

22. A sliding vane pump according to any one of claims 15 to 21 , wherein said non-circular cross section is smaller than said circular cross section.

23. A sliding vane pump according to any one of claims 15 to 22, wherein said at least one further portion comprises at least one recessed section machined from an outer surface of said vane.

24. A sliding vane pump according to claim 23, wherein said at least one recessed section comprises a flat axially extending surface

25. A sliding vane pump according to any preceding claim, wherein said pump comprises a lubricant pump for driving a valve and supplying lubricant to a vacuum pump.

26. A vacuum pump comprising a sliding vane pump according to any preceding claim for supplying lubricant to said vacuum pump.

27. A vane for a sliding vane pump according to any one of claims 1 to 15, said vane being configured to be slidably mounted within a corresponding cavity in a rotor and to extend from said cavity such that at least one end surface of said vane abuts an inner stator wall and thereby separates adjacent pumping chambers when mounted in said rotor in said pump; said vane comprising a channel configured to provide a passage between said adjacent pumping chambers when said vane is mounted within said pump.

28. A vane according to claim 27, wherein said channel comprises a groove in said at least one end surface of said vane.

29. A vane according to claim 28, wherein said channel comprises a passage extending through said vane. - 23 -

30. A vane for a sliding vane pump according to any one of claims 15 to 24, said vane being configured to have a substantially circular cross section for a larger portion of a length of said vane and a non-circular cross section for a smaller portion of a length of said vane, said vane being configured to be slidably mounted within a correspondingly shaped cavity in a rotor and to extend from said cavity such that at least one end surface of said vane abuts an inner stator wall and thereby separates adjacent pumping chambers when mounted in said rotor in a pump.