GB2389875A

GB2389875A - Vane pump with a non-circular bore

Info

Publication number: GB2389875A
Application number: GB0214425A
Authority: GB
Inventors: Peter Krukowski; Colin Maynard
Original assignee: BOC Group Ltd
Current assignee: BOC Group Ltd
Priority date: 2002-06-21
Filing date: 2002-06-21
Publication date: 2003-12-24
Also published as: GB0214425D0

Abstract

A rotary pump 100 comprises a stator 104 provided with a bore 106 having a non-circular circumferential wall 108. A rotor 122 is mounted eccentrically in the bore 106, and carries at least one blade 126 that is slidable relative to the rotor, such that an end of the blade remains in contacts with the non-circular bore wall as the rotor rotates. A pumping chamber is formed between the rotor, vane and bore wall when in use, the volume of which can be readily increased. Also provided is a stator for a rotary pump, which has a circumferential non-circular bore wall. This wall is constructed of at least three arcuate portions, one of which has its centre at the axis of rotation of the rotor.

Description

VANE PUMPS AND STATORS THEREFOR

The invention relates to mechanical rotary pumps and in particular to vane pumps.

Figure I is a schematic view showing elements of a prior art vane

5 pump. The pump has a stator 10 having a bore 12. The bore 12 houses an eccentrically mounted rotor 14 that has two radial slots 15(1), 15(2); each slot containing a blade, or vane 16(1), 16(2). The bore 12 is defined by a wall 18 and the space between the wall and the rotor constitutes a pumping chamber P. An inlet port 20 and an outlet port 22 each communicate with the pumping 10 chamber P. As the rotor rotates, the tips of the vanes 16 slide over the bore wall 18 and are maintained in contact with the wall by centrifugal force.

Biasing springs may also be used to ensure that the contact between the vane tips and the wall 18 is maintained when the pump is operating at low rotational speeds.

15 The bore 12 has a circular cross-section, or profile, with a portion 24 of the wall 18 between the inlet and exhaust ports being relieved to accommodate a portion of the rotor. The rotor is positioned relative to this portion 24 of the wall 18 such that there is a small clearance between the two, thus minimising gas leakage between the outlet port side 24E and the inlet 20 port side 241. The portion 24 is known as the duo seal area.

In effect the wall 18 comprises two arcuate portions having different radii. The first portion is the portion 24 that defines the duo seal area and this portion has a radius r having as its centre the axis of rotation of the rotor 14.

( The second portion comprises the remainder of the wall 18 and this has a different radius R having as its centre the longitudinal axis of the bore 12. It will be appreciated that the second portion forms the radially outermost wall of the pumping chamber P. 5 In use, the rotor 14 turns at high speed and the vanes 16(1), 16(2) slide in and out of the slots 15 under the influence of centrifugal forces, the biasing springs (if provided) and the profile of the wall 18. At some point adjacent the inlet port side 24I of the duo seal, the vanes commence a radially outward movement with respect to the rotor axis and at some point, usually 180 from 10 the duo seal, the vanes begin to move radially inwards.

The vanes 16 divide the pumping chamber P into a number of separate variable volume sub-chambers that are successively formed as the vanes sweep around the pumping chamber. In the position of the rotor shown in Figure 1, the vanes divide the pumping chamber P into three sub-chambers: a 15 first forming between the inlet port side 24I of the duo seal and the trailing side of the vane 16(1); a second between the leading side of the vane 16(1) and the trailing side of the vane 16(2); and a third between the leading side of the blade 16(2) and the outlet port side 24E of the duo seal.

As the vanes sweep around the wall 18, successive new sub-chambers 20 form at the inlet port side 241 of the duo seal. These sub-chambers move around the pumping chamber P as the vanes are rotated by the rotor: first increasing in volume so that gas is drawn into the sub-chamber through the inlet port 20; subsequently decreasing in volume so that the gas is

compressed; and finally reaching a position at which the compressed gas is discharged from the sub-chamber through the outlet port 22. The position at which the volume of each sub-chamber ceases to increase and then decreases is determined by the profile of the wall 18.

5 The nominal swept volume of the pumping chamber is the volume of the bore 12, minus the volume of the rotor 14 and the exposed volume of the vanes 16(1), 16(2). To obtain a reasonable vane life, it is usual to limit the maximum radial projection of the vanes to 50% of the blade length; the blade length being measured in the radial direction of the rotor.

10 It is possible to increase the swept volume of the pumping chamber by increasing the bore diameter. However, this results in excessive vane projection and a consequent reduction in vane life. Alternatively, the swept volume can be increased by increasing the length of the bore, rotor and vanes.

However, this results in a larger pump and can affect the interchangeability of l S the components used in making a range of pumps.

The invention provides a rotary pump comprising a stator provided with a bore having a circumferential wall, a rotor eccentrically mounted in said bore and at least one blade carried by said rotor and slideable relative thereto such that an end thereof can remain substantially in contact with said 20 circumferential wall when, in use, the rotor rotates, said rotor and a portion of said circumferential wall defining a pumping chamber therebetween and said portion of said circumferential wall having a noncircular profile.

The invention also includes a rotary pump comprising a stator provided with a bore having a circumferential wall, a rotor eccentrically mounted in said bore and at least one blade carried in a slot in said rotor such than an end of said blade projects from the slot so that it can contact said wall, 5 the or each blade being slideable in its slot such that, in use, as said rotor rotates the said end thereof can remain substantially in contact with said wall, the stator having an inlet and an outlet to allow fluid being pumped to pass into and out of said bore by rotation of the or each said blade, and said circumferential wall comprising at least three arcuate portions whereby said 10 circumferential wall is noncircular.

The invention also includes a method of providing a stator for a rotary pump, which stator has a bore in which a rotor is to be housed and an inlet port and an outlet port in flow communication with said bore, said method comprising forming a circumferential wall that defines said bore such that 15 said wall comprises at least three contiguous arcuate portions each defined by a radius, wherein the respective radii defining the arcuate portions adjoining each said arcuate portions are different to the radius defining the said arcuate portion. The invention also includes a stator for a rotary pump, said stator 20 having a bore in which a rotor is to be housed an inlet to permit a fluid being pumped to enter said bore and an outlet to permit pumped fluid to leave the bore, said bore being defined by wall comprising at least three arcuate

segments, said arcuate segments being joined end-to-end whereby said bore is non-circular. In order that the invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described with 5 reference to the drawings, in which: Figure I is a schematic view of a prior art vane pump;

Figure 2 is a schematic view of a vane pump according to the invention; and Figure 3 is an enlargement of a portion of Figure 3.

10 Referring to Figure 2' a single-stage vane pump 100 comprises a casing 102 housing a stator 104. The stator has a bore 106 defined by a circumferential wall 108. The stator has an inlet port I I O and art outlet port 112, both communicating with the bore 106 The inlet port 110 is connected to a pump inlet 114 by suitable ducting indicated generally by dashed line 15 116. Similarly, the outlet port 112 is connected to pump exhaust 118 by suitable ducting indicated generally by dashed line 120. A motor (not shown) is provided intemally, or extemally, of the casing 110 for driving a rotor 122 that is housed in the bore 106. The motor will nominally be a 2 or 4-pole ac motor operating at 50 or 60 cycles (Hz). Direct or indirect drive can be used, 20 as can a mechanical or electronic control to provide variable speed operation.

Means for lubricating the pump, filters and non-retum valves may be provided in the usual way, as required. Since these aspects of pump design

( are well known to those skilled in the art, they will not be described in any detail herein.

The rotor 122 is eccentrically mounted in the bore 106 and the space between the bore wall 108 and the rotor constitutes a pumping chamber P. 5 The rotor is connected with the motor so as to be rotatable about its axis of rotation O. The rotor 122 defines two opposed radially extending slots 124, each containing a blade, or vane 126. The vanes 126 are able to slide back and-forth in their slots 124 in the radial direction of the rotor. Although not shown, as is known in the art, compression springs may be provided at the 10 radially inner ends of the slots 124 between the vanes 126 for biasing the vanes radially outwardly of the rotor.

As best seen in Figure 3, the bore wall 108 is non-circular and instead comprises a series of segments (arcuate portions) that combine to define a cylinder having a non-circular circumference.

15 In the embodiment, the bore wall 108 comprises eight segments. The first segment defines a duo seal area 130 and has a radius R1 having as its centre, the axis of rotation O of the rotor 122. The second segment 132 extends from a point adjacent the inlet port side 1301 of the duo seal area 130 to a point 134 and has a radius R2 having as its centre, the longitudinal axis of 20 the bore 106. The radius R2 is selected such so that there is a progressively increasing clearance between the rotor and the bore wall 108 towards the point 134. The third segment 136 extends from the point 134 to a point 138.

The third segment has a radius R3 having its centre located at a point 140.

The fourth segment 42 extends from the point 138 to a point 144 and is defined by a radius R4 having its centre at a point 146. The fifth segment 148 extends from the point 144 to a point 150 and has a radius RS having as its centre the axis of rotation O of the rotor. The sixth segment 152 extends from 5 the point 150 to a point 154 and is defined by a radius R6 that has as its centre a point 158. The sixth segment 152 is a mirror image of the fourth segment 142. The seventh segment 160 extends from the point 154 to a point 162 adjacent the upstream edge of the outlet port 112 and has a radius R7 having as its centre a point 164. The seventh segment is a mirror image of the third 10 segment 136. The eighth segment 166 completes the circumference of the bore wall 108 and extends from the point 162 to the exhaust port side 130E of the duo seal area 130. The eighth segment 166 is defined by the radius R2 and is a mirror image of the second segment 132.

The non-circular circumference of the bore wall 108 can be obtained IS by first producing a duo seal area 130 as known in the art. The fifth segment 148 is then generated by sweeping an arc opposite, or 180 , from the duo seal area to suit a pre-selected angle of rotation of the rotor either side of a centre line 168 that extends through the axis of rotation of the rotor and the longitudinal axis of the bore 106. The radius R5 of the arc may be chosen so 20 that the vanes project with their maximum overhang while in contact with the fifth segment 148.

The circumference of the wall 106 is then completed by generating one or more arcs to join the respective ends of the fifth segment 148 to the

duo seal area 130. In the embodiments, there are three arcs defining the three segments 132, 136 and 142 that link the inlet port side 1301 of the duo seal area to the fiRh segment 148. Those arcs are chosen so as to provide a surface configuration or profile, that controls the outward acceleration of the vanes.

5 Similarly, there are three arcs defining the three segments 152, 160 and 166 that link the fifth segment 148 to the outlet port side 1 30E of the duo seal area and these are chosen so as to provide a profile that controls the inward acceleration of the vanes. Controlling the outward acceleration of the vanes is important in ensuring contact between the vane tips and the pumping chamber 10 wall is maintained, otherwise the pump efficiency is reduced. Controlling the inward acceleration of the vanes is important as this minimises the loading on the vane tips and thus minimises tip wear. In the illustrated embodiment, the segments 132, 136 and 142 are mirror images of the segments 152, 160, 166.

However, it will be understood that this is not essential and the arc defining 15 one or more of these segments could be varied in order to produce differing control regimes for the inward and outward acceleration of the vanes.

It will be appreciated that the portion of the bore wall 108 defining the radially outer wall of the pumping chamber is non-circular and is made up of a plurality of arcuate segments. By modifying the pumping chamber so that it 20 has a non-circular outer wall, it is possible to increase the swept volume of a particular configuration of vane pump while retaining all of the original components, the only change being made in the shaping of the bore wall in the stator. In other words, the only change required to any pre-existing pump

design is the selection of a new non-circular profile for the pumping chamber outer wall to provide the desired increase in swept volume. The difference in the volume that can be obtained by providing a non-circular outer wall for the pumping chamber is shown in Figure 2, where the dashed line 190 represents 5 a circular pumping chamber wall corresponding to the wall 18 of the prior art

arrangement shown in Figure 1. In one trial it has been found possible to increase the effective swept volume of a relatively small capacity pump from 1.5 to 1.9 m3h-'.

It will be appreciated that in the embodiment, segments 136, 142, 152 10 and 160 each have their defining radius offset from the plane 168 in which the axis of rotation O of the rotor and the longitudinal axis of the bore are situated. It will also be appreciated that the radii of the segments 136, 142, 152 and 160 are all centred in planes that are perpendicular to the plane 168 and extend parallel to another plane perpendicular to the plane 168 and in 15 which the axis of rotation O of the rotor is situated and that a plane perpendicular to the plane 168 in which the longitudinal axis of the bore is situated is disposed intermediate the perpendicular plane of the axis of rotation O and the perpendicular planes in which the radii of the segments 136, 142, 152 and 160 are centred.

20 It will be understood that while in the embodiment there are three different segments linking each side of the segment 148 that is opposite the duo seal area with the respective sides of the duo seal area, a greater or lesser number of linking segments may be used.

( It will be understood that the non-circular bore 106 can readily be machined using CNC machining apparatus and that used stators could be reconditioned by machining a non-circular bore as described herein.

It will be understood that althougth the embodiment has only two 5 vanes, additional vanes and slots therefor in the rotor can be provided if desired as is known in the art.

It will be appreciated that the invention is equally applicable to lubricated and dry running vane pumps.

It will also be appreciated that the invention is equally applicable to 10 single-stage and multi-stage pumps.

It will be understood that the invention is particularly applicable to mechanical rotary vacuum pumps.

Claims

it CLAIMS

1. A rotary pump comprising a stator provided with a bore having a circumferential wall, a rotor eccentrically mounted in said bore and at least one blade carried by said rotor and slideable relative thereto such that an end 5 thereof can remain substantially in contact with said circumferential wall when, in use, the rotor rotates, said rotor and a portion of said circumferential wall defining a pumping chamber therebetween and said portion of said circumferential wall having a noncircular profile.

2. A pump as claimed in claim 1, wherein said stator includes an 10 inlet and an outlet for said pumping chamber and said portion of said circumferential wall has opposite ends interconnected by an arcuate segment configured to co-operate with said rotor to define a seal area between said inlet and said outlet.

3. A pump as claimed in claim I or 2, wherein said rotor has an 15 axis of rotation and said portion of said circumferential wall includes an arcuate segment defined by a radius having its centre at said axis of rotation.

4. A pump as claimed in claim 1, 2 or 3, wherein said rotor has an axis of rotation, said bore has a longitudinal axis and said portion of said circumferential wall includes at least one arcuate segment defined by a radius 20 having its centre offset from a first plane in which said axis of rotation and said longitudinal axis are situated.

5. A pump as claimed in claim 4, wherein said centre of said at least one arcuate segment is situated in a second plane that extends parallel to

( lL a third plane that is perpendicular to said first plane and in which said axis of rotation is situated and wherein a fourth plane that is parallel to said second and third planes and in which said longitudinal axis is situated is disposed int;rrnediate said second and third planes.

5

6. A rotary pump comprising a stator provided with a bore having a circumferential wall, a rotor eccentrically mounted in said bore and at least one blade carried in a slot in said rotor such than an end of said blade projects from the slot so that it can contact said wall, the or each blade being slideable in its slot such that, in use, as said rotor rotates the said end thereof can 10 remain substantially in contact with said wall, the stator having an inlet and an outlet to allow fluid being pumped to pass into and out of said bore by rotation of the or each said blade, and said circumferential wall comprising at least three arcuate portions whereby said circumferential wall is non-circular.

7. A pump as claimed in claim 6, wherein a first said arcuate 15 portion is adapted to co-operate with said rotor to define a seal area between said inlet and outlet.

8. A pump as claimed in claim 7, wherein a second said arcuate portion is disposed opposite said first said arcuate portion, said second arcuate portion being arranged such that the or each said blade reaches a position of 20 maximum projection from its slot when substantially in contact with said second arcuate portion.

9. A pump as claimed in claim 8, wherein each side of said second arcuate portion is connected with a respective side of said first arcuate

Vb portion by a respective arcuate portion, said respective arcuate portions being arranged as a mirror image of one another.

10. A method of providing a stator for a rotary pump, which stator has a bore in which a rotor is to be housed and an inlet port and an outlet port 5 in flow communication with said bore, said method comprising forming a circumferential wall that defines said bore such that said wall comprises at least three contiguous arcuate portions each defined by a radius, wherein the respective radii defining the arcuate portions adjoining each said arcuate portions are different to the radius defining the said arcuate portion.

10

11. A method as claimed in claim 10, comprising forming said wall with a said arcuate portion extending between said inlet port and said outlet port and having a radius corresponding substantially to a radius of a rotor to be housed in said bore.

12. A method as claimed in claim 10 or 11, comprising forming 15 said wall with at least four arcuate portions.

13. A method as claimed in claims 10, 1 1 or 12, comprising forming said wall with two mutually opposed arcuate portions and linking adjacent sides of said mutually opposed arcuate portions by respective linking portions each consisting of at least one further arcuate portion.

20

14. A method as claimed in claim 13, wherein said at least one further arcuate portions are equal and opposite one another.

I S. A stator for a rotary pump, said stator having a bore in which a rotor is to be housed, an inlet to permit a fluid being pumped to enter said

bore and an outlet to permit pumped fluid to leave the bore, said bore being defined by wall comprising at least three arcuate segments, said arcuate segments being joined end-to-end whereby said bore is noncircular.