Centrifugal slurry pump impeller

Abstract

A centrifugal slurry pump impeller (140) including a back shroud (151) with opposed inner and outer faces (153, 152) and an outer peripheral edge (157), the back shroud (151) including a nose (147) projecting from the inner face (153) at a central axis X, the inner and outer faces (153, 152) being generally perpendicular to the central axis X, and the nose (147) facing an inlet region (148) of the impeller (140) for receiving slurry flow when in use; a front shroud (150) with opposed inner and outer faces (155, 154) and an outer peripheral edge (156), wherein the front shroud (150) includes a central opening having an inner circumferential edge (135) defining the inlet region (148) of the impeller (140), and the inner and outer faces (155, 154) being generally perpendicular to the central axis X, wherein the top surface (180) extending toward the leading edge (171) of each pumping vane (143) extends radially beyond the inner circumferential edge (135) in the direction of the central axis X.

Description

[0001] CENTRIFUGAL SLURRY PUMP IMPELLER

[0002] Technical Field

[0003] This disclosure relates in general to a slurry pump impeller for use in centrifugal slurry pumps. More particularly, to pumps for handling abrasive materials in the form of oil sands. Hydro transport is a process used in the oil sands industry consisting of long pipelines and large centrifugal slurry pumps which work to breakdown the lumps of oil sands before reaching a main extraction plant. An oil sands slurry has particular behavioral characteristics owing to the bitumen content, as well as the large rocks which are present in the slurry. The bitumen acts as a lubricant within the slurry while also increasing viscosity and providing that erosive wear from fine particles on the centrifugal pump parts is reduced compared to other typical abrasive minerals slurries with 2.6 SG or higher and particles larger than 5mm. The primary cause of erosion is the impact of these larger particles. Impact erosion can cause significant damage to the vanes on the impeller of the centrifugal slurry pumps.

[0004] The present disclosure seeks to provide an impeller with improved resistance to impact wear which finds specific application in the oil sands and iron ore mining industries.

[0005] Summary

[0006] According to one aspect there is provided a centrifugal slurry pump impeller including: a back shroud with opposed inner and outer faces and an outer peripheral edge, the back shroud including a nose projecting from the inner face at a central axis, the nose facing an inlet region of the impeller for receiving slurry flow when in use; and a plurality of pumping vanes extending from the inner main face of the back shroud, the pumping vanes being disposed in spaced apart relation, each pumping vane including opposed main side faces, a leading edge in a region of the central axis and a trailing edge in a region of the outer peripheral edge of the back shroud with a passageway between adjacent pumping vanes, wherein the plurality of pumping vanes extend in a direction towards the central axis into the inlet region wherein a top surface of each pumping vane extending towards the leading edge is located in the inlet region of the impeller.

[0007] In some examples, the top surface of each pumping vane located in the inlet region of the impeller is in a plane parallel to the inner face of the back shroud at the location of the passageways.

[0008] In some examples, the top surface of each pumping vane is in a plane which is generally perpendicular to the central axis.

[0009] In some examples, the leading edge of each pumping vane meets the inner face of the back shroud at a leading edge root, the leading edge extending from the leading edge root to the top surface at the leading edge in a direction away from the inner face of the back shroud, wherein the leading edge root is located closer to the central axis than the top surface at the leading edge. In one form, the leading edge root is located on a side of the impeller nose.

[0010] In some examples, the inlet region corresponds to an area defined by the circumference of an inlet passage leading to the impeller when in use.

[0011] In some examples, there is provided a suction inlet arrangement for a centrifugal slurry pump, wherein the suction inlet arrangement includes the impeller described above and a front side liner in fluid communication with the impeller for introducing slurry to the pump. The front side liner includes an annular wall having an outer surface that faces in a direction toward the impeller and an inner peripheral edge defining an inlet passage that aligns with the inlet region of the impeller.

[0012] In one example, the pumping vanes extend radially into the inlet passage of the front side liner.

[0013] In one example, the top surface of each pumping vane at the leading edge is coplanar with the outer surface of the front side liner.

[0014] In another aspect, there is provided a centrifugal slurry pump impeller including a back shroud with opposed inner and outer faces and an outer peripheral edge, the back shroud including a nose projecting from the inner face at a central axis, the inner and outer faces being generally perpendicular to the central axis, and the nose facing an inlet region of the impeller for receiving slurry flow when in use; and a front shroud with opposed inner and outer faces and an outer peripheral edge wherein the front shroud includes a central opening having an inner circumferential edge defining the inlet region of the impeller, and the inner an outer faces being generally perpendicular to the central axis, wherein the plurality of pumping vanes extends between the inner faces of the back shroud and the front shroud, wherein the top surface of each pumping vane at the leading edge extends radially beyond the inner circumferential edge in the direction of the central axis.

[0015] In some examples, the top surface of each pumping vane at the leading edge is in a plane which is parallel to the inner and outer faces of the front shroud. Preferable, the inner and outer faces of the front shroud are generally perpendicular to the central axis.

[0016] In some examples, the top surface of each pumping vane at the leading edge is coplanar with the outer face of the front shroud where it meets the inner circumferential edge. In some examples, the top surface of each pumping vane at the leading edge extends into the inlet region in the direction of the central axis, a length which corresponds to at least 8% of the diameter of the inlet region. In one form, the top surface of each pumping vane at the leading edge extends into the inlet region in the direction of the central axis a length which corresponds to at least 10% of the diameter of the inlet region. In a further form, the top surface of each pumping vane at the leading edge extends into the inlet region in the direction of the central axis a length which corresponds to at least 15% of the diameter of the inlet region.

[0017] In some examples, the top surface of each pumping vane at the leading edge extends into the inlet region in the direction of the central axis a length which corresponds to a maximum of 40% of the diameter of the inlet region.

[0018] In some examples the top surface of the leading edge of the pumping vane extends axially away from the front shroud and beyond the front shroud such that the top surface of the leading edge lies in a plane spaced apart from the outer surface of the front shroud.

[0019] In some examples, the top surface extending toward the leading edge includes a material different from the pumping vane.

[0020] In some examples, the impeller is part of an inlet suction arrangement which includes the impeller and a front side liner. The front side liner includes an annular wall having an outer surface that faces in a direction toward the impeller and an inner peripheral edge defining an inlet passage that aligns with the inlet region of the impeller. The outer face of the front side liner being adjacent the outer face of the front shroud of the impeller. The top surface of each pumping vane extending toward the leading edge extends radially beyond the inner circumferential edge of the impeller and axially away from the impeller and into the inlet passage of the front side liner.

[0021] In one example, the impeller has a width measured from the outer face of the back shroud to the outer face of the front shroud, and the top surface of each pumping vane extends into the inlet passage of the front side liner up to the width of the impeller.

[0022] In another example, the top surface of each pumping vane extends into the inlet passage of the front side liner up to half the width of the impeller.

[0023] Description of the Figures

[0024] The accompanying drawings facilitate an understanding of the various embodiments. Figure 1 is a partial cross-sectional side elevation view of a centrifugal slurry pump including a typical closed slurry pump impeller;

[0025] Figure 2A is one example of an impeller according to the present disclosure; Figure 2 is a partial cross-sectional side elevation view of a centrifugal slurry pump including the slurry impeller shown in Figure 2A; Figure 3 is a view of the slurry pump impeller of Figure 2A as seen if looking through the pump inlet;

[0026] Figure 4 is view of a semi-open slurry pump impeller as seen if looking through the pump inlet in accordance with another example of the present disclosure;

[0027] Figure 5 is a perspective view of the semi-open slurry pump impeller of Figure 4; Figure 6 is a perspective view of a closed slurry pump impeller according to another example of the present disclosure;

[0028] Figure 7 is a partial cross-sectional side elevation view of a centrifugal slurry pump including the slurry impeller shown in Figure 6; and

[0029] Figure 8 is a perspective view of a semi-open slurry pump impeller with a similar embodiment to Figure 6.

[0030] Detailed Description

[0031] Figure 1 shows part of a centrifugal slurry pump 10 including a typical closed impeller 40. The impeller 40 is positioned within a main liner 12 and is mounted or operatively connected to a drive shaft (not shown) which is adapted to rotate about a rotation axis X-X, or central axis. The rotation of the impeller 40 causes slurry (or solid-liquid mixture) being pumped to pass through an inlet 28 into a pumping chamber 42 and then out of the pump 10 via a discharge outlet 29.

[0032] The impeller 40 includes a hub 41 from which a plurality of circumferentially spaced pumping vanes 43 extends. A nose portion 47 extends forwardly from the hub 41 towards the inlet 28. The impeller 40 is in the form of a 'closed' impeller and further includes a front shroud 50 and a back shroud 51, the vanes 43 being disposed and extending therebetween and an impeller inlet region 48.

[0033] The impeller front shroud 50 includes an inner face 55, an outer face 54 and a peripheral edge portion 56. The back shroud 51 includes an inner face 53, an outer face 52 and a peripheral edge portion 57. In this example the pumping vanes 43 extend between the inner faces 55, 53 of the shrouds 50, 51. The front shroud 50 includes an inner circumferential edge 35 which defines the outer circumferential boundary of the impeller inlet region 48. The shrouds 50, 51 are generally circular or disc-shaped when viewed in elevation; that is in the direction of rotation axis X. Another form of impeller is a 'semi-open' impeller which includes a back shroud only. In the case of a semi open impeller, the circumferential boundary of the impeller inlet region 48 is in line with the inner circumference of the inlet 28 of the throatbush, or front side liner 30.

[0034] Figures 2, 2A and 3 show an example of a centrifugal slurry pump impeller 140 in accordance with the present disclosure. The impeller 140 is a "closed" impeller type, which includes a back shroud 151 and a front shroud 150 with pumping vanes 143 located therebetween. The circled area in Figure 2 shows where the pumping vanes 143 extend within the inlet region 148 of the impeller 140. Examples of the present disclosure may equally be in the form of a "semi-open" impeller configuration including a back shroud only as depicted in Figs. 4 and 5.

[0035] The closed impeller 140 includes a back shroud 151 and a front shroud 150 each with opposed inner 153, 155 and outer faces 152, 154. The shrouds 150, 151 each have an outer peripheral edge 157, 156 and a central axis X. The central axis X is in line with the center of the hub 141 on the back shroud 151 , the impeller nose 147 and a centre point of the impeller inlet region 148. The front shroud 150 has an inner circumferential edge 135 defining the inlet region 148 of the impeller 140.

[0036] Figure 3 shows the closed impeller 140 as seen when viewed through the pump inlet region 148. The front shroud 150 includes auxiliary vanes 160 equally spaced around the outer face 154. Auxiliary vanes may or may not be used on either the front or back shroud. A plurality of pumping vanes 143 extends between the inner faces of the back (seen in Figure 2) and front shrouds 150. In this example there are four pumping vanes 143. The number of vanes may be dependent on passage requirements. For example, larger rocks, less vanes. Each pumping vane 143 has an inner side face 108 and an outer side face 107. A passageway 106 is located between each adjacent pumping vane 143. Each passageway 106 includes a blended region located between each of the side faces 107, 108 of the pumping vanes 143. The blended regions act as a transition surface between the surface of the side faces 107, 108 and the inner face 153 of the back shroud 151.

[0037] The plurality of pumping vanes 143 extends in a direction towards the central axis X into the impeller inlet region 148 of the impeller 140 wherein a top surface 180 of each pumping vane 143 extending towards the leading edge 171 is located in the inlet region 148 of the impeller 140. In the closed impeller example of Figs. 2 and 3, the front shroud 150 has an inner circumferential edge 135 defining an outer circumference of the inlet region 148 of the impeller 140 which includes a diameter D graphically depicted in Fig. 3. The top surface 180 at the leading edge 171 of each pumping vane 143 extends beyond the inner circumferential edge 135 of the front shroud 150 along the diameter D of the inlet region 148 of the impeller 140 in the direction of the central axis X.

[0038] The top surface 180 at the leading edge 171 may be located in a plane which is parallel to the inner face 153 of the back shroud 151 at the location of the passageways 106. Further, the top surface 180 at the leading edge 171 of each pumping vane 143 may be in a plane which is generally perpendicular to the central axis X.

[0039] The leading edge 171 of each pumping vane 143 meets the inner face 153 of the back shroud 151 at a leading edge root 181. The leading edge 171 extends from the leading edge root 181 to the top surface 180 at the leading edge 171 in a direction away from the inner face 153 of the back shroud 151. The leading edge root 181 may be located closer to the central axis X than the top surface 180 at the leading edge 171 so that the leading edge 171 extends at an angle away from the central axis X. Alternatively, the leading edge may be straight or inclined toward the central axis, making it suitable for other impeller designs.

[0040] As is best seen in Figure 3, the leading edge root 181 of each pumping vane 143 may be located on a side of the impeller nose 147.

[0041] The top surface 180 at the leading edge 171 of each pumping vane 143 extends radially into the inlet region 148 of the impeller 140 in the direction of the central axis X a length which corresponds to at least 5% of the diameter D of the inlet region 148 of the impeller 140, preferably at least 8% of the diameter D of the inlet region 148 of the impeller 140, still preferably, at least 10% of the diameter D of the inlet region 148 of the impeller 140, and more preferably at least 15% of the diameter D of the inlet region 148 of the impeller 140. The top surface 180 at the leading edge 171 of each pumping vane 143 may extend into the inlet region 148 of the impeller 140 toward the central axis X a length which corresponds to a maximum of 40% of the diameter D of the inlet region 148.

[0042] The top surface 180 at the leading edge 171 of each pumping vane 143 may be in a plane which is parallel to the inner and outer faces 154, 155 of the front shroud 150 and generally perpendicular to the central axis X. As best seen in Figure 2A, the top surface 180 at the leading edge 171 of each pumping vane 143 may be coplanar to the outer face 154 of the front shroud 150 where it meets the inner circumferential edge 135. Extending the vanes 143 radially to the inlet 135 allows the slow-moving settled bed of larger dense particles to fall between the vanes and limit the impact area to the top surface of the vanes 180 which is travelling at a much lower velocity. The particles will also be imparted energy in the radial direction and have reduced axial momentum limiting wear on the back shroud 151.

[0043] In accordance with another example, a semi-open impeller 240 is shown in Figures 4 and 5. The semi-open impeller 240 includes a back shroud 251 only with an opposed inner 253 and outer face (not shown), an outer peripheral edge 257 and a central axis X. The semi-open impeller 240 includes pumping vanes 243 which extend or project from the inner face 253 of the back shroud 251 with a passageway 206 located between adjacent pumping vanes 243.

[0044] In the case of a semi-open impeller 240 which does not include a front shroud, the outer circumference of the impeller inlet region may be equal, or substantially equal, to the inner circumference of the inlet passage of a front side part, or throatbush (not shown) when the semi-open impeller 240 is part of a centrifugal slurry pump assembly. As best seen in Figure 5, the pumping vanes 243 each include opposed side faces 207, 208, a leading edge 271 in the region of the central axis X, and a trailing edge 270 in the region of the outer peripheral edge 257 of the back shroud 251. The main side faces 207, 208 of the pumping vanes 243 include a pumping or pressure side face 207 and a suction side face 208.

[0045] Figure 6 shows another example of a closed impeller 340 having a back shroud 351 and a front shroud 350. In this example, the pumping vanes 343 extend into the inlet region 348 of the impeller 340 toward the central axis X similar to described above. Additionally, material is added to the leading edge 371 of the pumping vane 343 such that the leading edge 371 extends axially away from the back shroud 351 and beyond the outer face 354 of the front shroud 350 and the top surface 380 of the leading edge 371 is located in a plane forward of the outer face 354 of the front shroud 350. The impeller 340 has a width measured from the outer face 355 of the back shroud 351 and the outer face 354 of the front shroud 350, and the leading edge 371 may be extended a length which corresponds to up to the width of the impeller 340. The additional material combats wear at the leading comer of the top 380 surface of the vane 380 caused by impacts as they rotate into the slow-moving bed of particles approaching the inlet. The additional material may be the same material as the pumping vane 343, or a wear resistant material such as tungsten carbide.

[0046] Figure 7 shows an example of a suction inlet arrangement 500 including the impeller 340 described above and a front side liner, or throatbush 530. The throatbush 530 is annular with an inner peripheral edge 512 defining an inlet passage 516 which substantially aligns with the inlet region 348 of the impeller 340. The pumping vanes 343 extend radially towards the central axis X such that at least the top surface 380 of the leading edge 371 extends into the inlet region 348 of the impeller 340, and axially into the inlet passage 516 of the throatbush 530 such that the top surface 380 of the leading edge 371 is forward of the outer face 354 of the front shroud 350. In use, as the impeller 340 rotates the extended vanes 343 help to mix rocks settled at the bottom of the throatbush 530, disrupting the stratification of solids on the bottom of the suction spool before entering the pump.

[0047] Figure 8 shows an example of a semi-open impeller 440. In this example, the pumping vanes 443 extend from the inner face 453 of the back shroud 451 to form a central intake opening, or inlet region 448. Each vane 443 includes a leading edge 471 in the region of the central axis X, and a trailing edge 470 in the region of the outer peripheral edge 457 of the back shroud 451. Additional material is added to the leading edge 471 of each pumping vane 443 to build up the leading edge 471 for a length of about 5-25% of the width W defined by the width of the impeller as measured from the back shroud 451 to the top surface 420 of the pumping vane 443 near the trailing edge 470. In this example, the inlet region 448, which is defined by the extended leading edge in both the radial and axial directions, may be smaller than the inner circumference of the inlet passage defined by a front side part, or throatbush (not shown) when the semi-open impeller 440 is part of a centrifugal slurry pump assembly.

[0048] For both closed and semi-open impeller embodiments, the top surface 180, 280, 380, 480 extending towards the leading edge 171, 271, 371 of each pumping vane 143, 243, 343 spans the distance between the pressure side face 107, 207, 307 and the suction side face 108, 208, 308 of each pumping vane 143, 243, 343. For slurry pumps, the thickness of the pumping vanes, i.e. the distance between the pressure side face and the suction side face is substantially greater than the vane thickness found on impellers for other applications, such as for example for clear water applications. Often the thickness of the pumping vanes for slurry pump impellers may be 2-1 / 2 to 6 inches (38-152 mm).

[0049] It was found that the impellers shown in Figs. 2 and 3 and Figs. 4 and 5 displayed reduced wear compared to the impeller design depicted in Fig. 1 when the impellers were used to pump oil sands slurry. In particular, the impellers in accordance with examples of the present disclosure showed significant resistance to impact wear which often results from the large rocks common to oil sands slurry.

[0050] Without wishing to be bound by theory, it is thought that by extending the leading edge of the vane, and in particular the top surface of the pumping vanes at the leading edge, radially into the inlet region of the impeller, the large rocks included in oil sands and iron ore slurry are distributed into the passageways between the pumping vanes at a greatly reduced rotational velocity leading to a significant reduction in impact wear in this region of the impeller. Advantageously, extending the vanes axially into the inlet region may also facilitate mixing the stratified solids that can cause accelerated wear on the front side liner, or throatbush, as they act as a blockage at the bottom of the inlet causing a pressure increase on slurry that is recirculating from the volute between the front face of the impeller and the suction liner face. As this recirculating slurry rotates in the direction of the impeller rotation past the blockage there is a drop in pressure and subsequent increase in velocity. This spike in velocity causes an acceleration in wear. This blockage and spike in velocity may be avoided by creating a more uniform and less localized wear increasing the life of the impeller and front side liner.

[0051] List of Parts

[0052] Pump 10, 100

[0053] Main liner 12

[0054] Rear side liner 14

[0055] Inlet 28, 128

[0056] Discharge outlet 29

[0057] Front side liner, throatbush 30, 230, 330, 530

[0058] Inner circumferential edge of front shroud 35, 135

[0059] Impeller 40, 140, 240, 340, 440

[0060] Hub 41, 141

[0061] Pumping chamber 42

[0062] Pumping vanes 43, 143, 243, 343, 443

[0063] Impeller nose 47, 147, 247

[0064] Impeller inlet region 48, 148, 248, 348

[0065] Front shroud 50, 150, 350

[0066] Back shroud 51, 151, 251, 351, 451

[0067] Outer face of back shroud 52, 152

[0068] Inner face of back shroud 53, 153, 253, 353, 453

[0069] Outer face of front shroud 54, 154

[0070] Inner face of front shroud 55, 155

[0071] Peripheral edge portion of front shroud 56, 156

[0072] Peripheral edge portion of back shroud 57, 157, 257

[0073] Auxiliary vanes 60, 160

[0074] Passageway 106, 206, 306

[0075] Pressure side face 107, 207, 307

[0076] Suction side face 108, 208, 308 Throatbush inner peripheral edge 512

[0077] Throatbush inlet passage 516

[0078] Leading edge 171, 271, 371, 471

[0079] Top surface of pumping vane 180, 280, 380, 480 Leading edge root 181, 281

[0080] Side face 207, 208

[0081] Trailing edge 270

[0082] Diameter of inlet region D

[0083] Width of semi open impeller

Claims

CLAIMS1. A centrifugal slurry pump impeller including: a back shroud with opposed inner and outer faces and an outer peripheral edge, the back shroud including a nose projecting from the inner face at a central axis, the nose facing an inlet region of the impeller for receiving slurry flow when in use; and a plurality of pumping vanes extending from the inner main face of the back shroud, the pumping vanes being disposed in spaced apart relation, each pumping vane including opposed main side faces, a leading edge in a region of the central axis and a trailing edge in a region of the outer peripheral edge of the back shroud with a passageway between adjacent pumping vanes, wherein the plurality of pumping vanes extends in a direction towards the central axis into the inlet region wherein a top surface of each pumping vane extending towards the leading edge is located in the inlet region of the impeller.

2. The centrifugal slurry pump impeller according to claim 1, wherein the top surface of each pumping vane located in the inlet region of the impeller is in a plane parallel to the inner face of the back shroud at the location of the passageways.

3. The centrifugal slurry pump impeller according to claim 1 or claim 2 wherein the top surface of each pumping vane is in a plane which is generally perpendicular to the central axis.

4. The centrifugal slurry pump impeller according to any one of the preceding claims wherein the leading edge of each pumping vane meets the inner face of the backshroud at a leading edge root, the leading edge extending from the leading edge root to the top surface at the leading edge in a direction away from the inner face of the back shroud, wherein the leading edge root is located closer to the central axis than the top surface at the leading edge.

5. A suction inlet arrangement for a centrifugal slurry pump, the suction inlet arrangement including: an impeller according to claim 1 ; and a front side liner in fluid communication with the impeller, wherein the front side liner includes an annular wall having an outer surface that faces in a direction toward the impeller and an inner peripheral edge defining an inlet passage that aligns with the inlet region of the impeller.

6. The suction inlet arrangement according to claim 5, wherein the pumping vanes extend radially into the inlet passage of the front side liner.

7. A centrifugal slurry pump impeller including: a back shroud with opposed inner and outer faces and an outer peripheral edge, the back shroud including a nose projecting from the inner face at a central axis, the inner and outer faces being generally perpendicular to the central axis, and the nose facing an inlet region of the impeller for receiving slurry flow when in use; a front shroud with opposed inner and outer faces and an outer peripheral edge, wherein the front shroud includes a central opening having an inner circumferential edge defining the inlet region of the impeller, and the inner and outer faces being generally perpendicular to the central axis, wherein the top surface extendingtoward the leading edge of each pumping vane extends radially beyond the inner circumferential edge in the direction of the central axis.

8. The centrifugal slurry pump impeller according to claim 7, wherein the top surface of each pumping vane at the leading edge is in a plane which is parallel to the inner and outer faces of the front shroud.

9. The centrifugal slurry pump impeller according to claim 8, wherein the top surface of each pumping vane at the leading edge is coplanar with the outer face of the front shroud where it meets the inner circumferential edge.

10. The centrifugal slurry pump impeller according to claim 7, wherein the top surface of each pumping vane extending toward the leading edge extends radially into the inlet region in the direction of the central axis a length which corresponds to at least 8% of the diameter of the inlet region.

11. The centrifugal slurry pump impeller according to claim 10, wherein the top surface of each pumping vane at the leading edge extends into the inlet region in the direction of the central axis a length which corresponds to at least 15% of the diameter of the inlet region.

12. The centrifugal slurry pump impeller according to claim 11 , wherein the top surface of each pumping vane at the leading edge extends into the inlet region in the direction of the central axis a length which corresponds to a maximum of 40% of the diameter of the inlet region.

13. The centrifugal slurry pump impeller according to claim 7, wherein the top surface extending toward the leading edge of the pumping vane lies in a plane spaced axially away from the back shroud and beyond the outer face of the front shroud.

14. The centrifugal slurry pump impeller according to claim 13, wherein the top surface of the leading edge includes a material different from the pumping vane.

15. A suction inlet arrangement for a centrifugal slurry pump including: the impeller according to claim 7; and a front side liner including an annular wall having an outer surface that faces in a direction toward the impeller and an inner peripheral edge defining an inlet passage that aligns with the inlet region of the impeller, the outer face of the front side liner being adjacent the outer face of the front shroud of the impeller, wherein the top surface of each pumping vane extending toward the leading edge extends radially beyond the inner circumferential edge of the impeller and axially away from the impeller and into the inlet passage of the front side liner.

16. The suction inlet arrangement according to claim 15, wherein the impeller has a width measured from the outer face of the back shroud and the outer face of the front shroud, and the top surface of each pumping vane extending toward the leading edge extends into the inlet passage of the front side liner at a length equal to the width of the impeller.

17. The suction inlet arrangement according to claim 16, wherein the top surface of each pumping vane extending toward the leading edge extends into the inlet passage of the front side liner at a length equal to half the width of the impeller.

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