Centrifugal impeller and centrifugal pump

Abstract

A centrifugal impeller includes at least one centrifugal vane, and the centrifugal vane has: a negative-pressure surface extending from a center part to an outer circumferential edge of the impeller; a pressure surface positioned away from the negative-pressure surface such that the centrifugal vane has a predetermined thickness, and extending from the center part toward the outer circumferential edge of the impeller; and a second pressure surface connected to the pressure surface and positioned closer to the negative-pressure surface than a virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge, on the outer circumferential edge side of the impeller and inward of the outer circumferential edge.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Japanese Patent Application No. 2025-059572 filed on Mar. 31, 2025, the entire disclosure of which is incorporated herein by reference.BACKGROUND

[0002] The technology disclosed herein relates to a centrifugal impeller and a centrifugal pump.

[0003] Japanese Laid-Open Patent Publication No. 2009-293547 discloses a conventional centrifugal impeller and centrifugal pump. This centrifugal impeller is an impeller used for a so-called vortex pump. The centrifugal impeller has a shroud and a plurality of centrifugal vanes provided to stand on the surface of the shroud. The centrifugal impeller is disposed so as to be retracted from a volute part inside a casing. In the vortex pump, there is a relatively large space between the centrifugal impeller and the inner wall surface of the casing, and foreign matter suctioned into the casing is discharged to the outside directly without passing through the impeller.SUMMARY

[0004] As described above, a vortex pump has a large space in a casing, and thus the pump efficiency thereof is relatively reduced. Thus, there is a demand to increase the pump efficiency of the vortex pump as much as possible.

[0005] Not limited to the vortex pump, there is a requirement to improve the pump efficiency of a centrifugal pump that includes, for example, a non-clogging type impeller. The non-clogging type impeller is an impeller provided with a large space for allowing foreign matter to pass through the impeller. In the case of a closed impeller, the centrifugal impeller has inside an inner channel connecting a suction port and a discharge port of the impeller.

[0006] The technology disclosed herein improves the pump efficiency of a centrifugal pump by devising the shape of the centrifugal impeller.

[0007] The technology disclosed herein is directed to a centrifugal impeller. The centrifugal impeller includes at least one centrifugal vane extending from a center part toward an outer circumferential edge of the impeller, wherein

[0008] the centrifugal vane has:

[0009] a negative-pressure surface extending from the center part to the outer circumferential edge of the impeller;

[0010] a pressure surface positioned away from the negative-pressure surface such that the centrifugal vane has a predetermined thickness, and extending from the center part toward the outer circumferential edge of the impeller; and

[0011] a second pressure surface connected to the pressure surface and positioned closer to the negative-pressure surface than a virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge, on the outer circumferential edge side of the impeller and inward of the outer circumferential edge.

[0012] The centrifugal vane of the centrifugal impeller has a negative-pressure surface and a pressure surface. The negative-pressure surface extends from the center part to the outer circumferential edge of the impeller. The negative-pressure surface extends from the center part while curving outward in the radial direction of the impeller and in the direction opposite to the rotation direction of the impeller.

[0013] The pressure surface extends from the center part toward the outer circumferential edge of the impeller. The negative-pressure surface and the pressure surface are positioned away from each other, whereby the centrifugal vane has a predetermined thickness. The pressure surface also extends from the center part while curving outward in the radial direction of the impeller and in the direction opposite to the rotation direction of the impeller.

[0014] The centrifugal vane has a second pressure surface. The second pressure surface is connected to the pressure surface and positioned on the outer circumferential edge side of the impeller and inward of the outer circumferential edge. The outer circumferential edge side of the impeller may be the outer circumferential edge side relative to the intermediate position of the centrifugal vane extending from the center part to the outer circumferential edge of the impeller.

[0015] The second pressure surface is positioned closer to the negative-pressure surface than the virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge. The vane thickness between the second pressure surface and the negative-pressure surface is thinner than the vane thickness between the pressure surface and negative-pressure surface. The second pressure surface can be formed by cutting a part of the centrifugal vane on the pressure surface side.

[0016] The centrifugal impeller in which the centrifugal vane has the second pressure surface can achieve the effect of improving the flow speed on the outer circumferential edge side of the impeller. This is considered to be because a flow along the second pressure surface is accelerated under the influence of a low pressure on the negative-pressure surface side owing to the thin vane thickness between the second pressure surface and the negative-pressure surface. As a result of the acceleration of the flow along the second pressure surface, the centrifugal impeller is considered to achieve the effect of improving the flow speed on the outer circumferential edge side of the impeller. The improved flow speed increases the flow rate at the centrifugal vane.

[0017] The centrifugal impeller having the second pressure surface enables a reduction in shaft power and an increase in the total head of the centrifugal pump as compared to conventional centrifugal impellers having no second pressure surface, and thus the pump efficiency can be improved.

[0018] In addition, it is considered that since the second pressure surface is positioned offset from the virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge, a vortex is generated around the second pressure surface. The vortex draws a flow tending to separate from the pressure surface toward the pressure surface and the second pressure surface, on the outer circumferential edge side of the impeller. Thus, flow separation is suppressed, and the flow is caused to move along the centrifugal vane, whereby the flow speed is improved.

[0019] The second pressure surface may be positioned between the outer circumferential edge of the impeller and the pressure surface along a direction in which the centrifugal vane extends.

[0020] In a case where the second pressure surface is formed, for example, at a position in contact with the outer circumferential edge of the impeller, the above-described effect of improving the flow speed on the outer circumferential edge side of the impeller is enhanced, leading to an advantage for the improvement in pump efficiency. The second pressure surface is not limited to one that is in contact with the outer circumferential edge of the impeller.

[0021] The second pressure surface may extend from an end of the pressure surface to the outer circumferential edge of the impeller at an angle different from the virtual plane.

[0022] The angle herein refers to an angle of a direction along the pressure surface or the second pressure surface of the centrifugal vane extending from the center part toward the outer circumferential edge.

[0023] The second pressure surface may be a surface extending in a direction of approaching the negative-pressure surface from the end of the pressure surface. The second pressure surface may be formed by cutting a part of the pressure surface of the centrifugal vane on the outer circumferential edge side into a substantially triangular shape when seen with the line of sight made parallel to the rotational axis of the impeller. The vane thickness between the second pressure surface and the negative-pressure surface is relatively thin, whereby the flow speed is improved.

[0024] The second pressure surface may include a first part extending from an end of the pressure surface at an angle different from the virtual plane, and a second part continuous with the first part and extending to the outer circumferential edge of the impeller at an angle different from the first part.

[0025] The angle of the second part may be, for example, equal or substantially equal to that of the virtual plane. If the angle of the second part is equal or substantially equal to that of the virtual plane, the second pressure surface is formed by cutting a part of the pressure surface of the centrifugal vane on the outer circumferential edge side into a substantially parallelogram-shaped when seen with the line of sight made parallel to the rotational axis of the impeller.

[0026] The angle of the second part may be, for example, equal or substantially equal to that of the negative-pressure surface.

[0027] The vane thickness between the second pressure surface and the negative-pressure surface is relatively thin, whereby the flow speed is improved. In addition, it is considered that since a step recessed from the pressure surface is formed on the outer circumferential edge side of the centrifugal vane, vortex generation is facilitated around the second pressure surface. As described above, the vortex draws the flow tending to separate from the pressure surface toward the pressure surface and the second pressure surface, on the outer circumferential edge side of the impeller. The substantial passage area in the centrifugal impeller is enlarged, whereby the flow rate is improved. The above-described shape of the second pressure surface contributes to an increase in passage flow rate at the impeller, in addition to the improvement in flow speed. Thus, the pump efficiency of the centrifugal pump including said centrifugal impeller can be improved.

[0028] The second pressure surface may include a first part extending at an angle equal to the virtual plane and at a position closer to the negative-pressure surface than the virtual plane, and a second part positioned between the first part and the outer circumferential edge of the impeller and extending at an angle equal to the virtual plane and at a position closer to the negative-pressure surface than the first part.

[0029] In addition, the second pressure surface may include a first part extending at an angle equal to that of the negative-pressure surface and at a position closer to the negative-pressure surface than the virtual plane, and a second part positioned between the first part and the outer circumferential edge of the impeller and extending at an angle equal to that of the negative-pressure surface and at a position closer to the negative-pressure surface than the first part.

[0030] The second pressure surface may have a shape of approaching the negative-pressure surface stepwise due to two steps defined by the first part and the second part. This shape is advantageous for the above-described vortex generation around the second pressure surface.

[0031] At least one recess recessed from the pressure surface toward the negative-pressure surface may be formed in a site, in the pressure surface, on the outer circumferential edge side of the impeller.

[0032] The recess formed, in the pressure surface, in the vicinity of the second pressure surface further facilitates vortex generation around the second pressure surface.

[0033] The centrifugal impeller may be an impeller for a vortex pump, in which the centrifugal vane stands on a shroud and which is disposed so as to be retracted from a volute part in a casing so as to ensure a predetermined passage diameter.

[0034] The above-described centrifugal impeller is suitable for improving the pump efficiency of the vortex pump.

[0035] The centrifugal impeller may be a non-clogging type impeller in which the centrifugal vane defines a primary channel connecting a suction port formed at one end and a discharge port formed at a side, and a secondary channel continuous with the primary channel and extending along an outer circumferential surface.

[0036] The above-described centrifugal impeller is suitable for improving the pump efficiency of a pump including the non-clogging type centrifugal impeller.

[0037] The centrifugal pump disclosed herein includes the above-described centrifugal impeller. The centrifugal pump includes the above-described centrifugal impeller, whereby the pump efficiency is improved.BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a sectional view of a centrifugal pump including a centrifugal impeller.

[0039] FIG. 2 is a perspective view of the centrifugal impeller.

[0040] FIG. 3 shows a plan view and a partially enlarged view of the centrifugal impeller.

[0041] FIG. 4 shows performance curves of the centrifugal pump.

[0042] FIG. 5 shows a plan view and a partially enlarged view of a centrifugal impeller according to a modification.

[0043] FIG. 6 shows a plan view and a partially enlarged view of a centrifugal impeller according to a modification.

[0044] FIG. 7 shows a plan view and a partially enlarged view of a centrifugal impeller according to a modification.

[0045] FIG. 8 is a plan view of a centrifugal impeller according to a modification.

[0046] FIG. 9 is a plan view of a centrifugal impeller according to a modification.

[0047] FIG. 10 is a plan view of a centrifugal impeller according to a modification.

[0048] FIG. 11 is a plan view of a centrifugal impeller according to a modification.

[0049] FIG. 12 shows a side view and a sectional view along line A-A of a non-clogging type centrifugal impeller.DETAILED DESCRIPTION OF THE DRAWINGS

[0050] Hereinafter, embodiments of a centrifugal impeller and a centrifugal pump will be described with reference to the drawings. The centrifugal impeller and the centrifugal pump described herein are merely illustrative.Entire Structure of Centrifugal Pump

[0051] FIG. 1 shows a centrifugal pump 1 including a centrifugal impeller 2. The centrifugal pump 1 is a submersible pump for sewage treatment, and is a vortex pump having good foreign matter passing performance.

[0052] The centrifugal pump 1 includes a pump unit 3 having a centrifugal impeller 2, and a motor unit 4 having a motor 41 that drives the centrifugal impeller 2. The pump unit 3 is positioned on the lower side relative to an oil casing 11, and the motor unit 4 is positioned on the upper side relative to the oil casing 11. In the inside of the oil casing 11, a shaft 42 (described later) of the motor 41 is sealed by a mechanical seal 12.

[0053] The motor unit 4 has the motor 41 and a motor casing 43 covering the motor 41. The shaft 42 of the motor 41 extends in the vertical direction.

[0054] The centrifugal impeller 2 of the pump unit 3 is mounted on the lower end of the shaft 42 of the motor 41. The pump unit 3 has a pump casing 31.

[0055] The pump casing 31 is attached to a lower part of the oil casing 11. The centrifugal impeller 2 is disposed in an upper region inside the pump casing 31. A lower region inside the pump casing 31 corresponds to a volute portion 34. The centrifugal impeller 2 is disposed so as to be retracted from the volute portion 34. There is a relatively large space between the centrifugal impeller 2 and the inner wall surface of the pump casing 31.

[0056] A suction port 32 opened downward is formed at a lower part of the pump casing 31. A discharge port 33 protruding sideways is formed at a side part of the pump casing 31. The discharge port 33 is connected to an exhaust pipe.Structure of Centrifugal Impeller

[0057] FIG. 2 is a perspective view of the centrifugal impeller 2. FIG. 3 shows a plan view of the centrifugal impeller 2 as seen with the line of sight made parallel to a rotational axis X of the centrifugal impeller 2. FIG. 2 illustrates the centrifugal impeller 2 in an inverted orientation with respect to the state where the centrifugal impeller 2 is attached to the shaft 42 of the motor 41.

[0058] The centrifugal impeller 2 is a semi-open type impeller, and has a shroud 20 and a centrifugal vane 21. The shroud 20 has a substantially disk-shape. The centrifugal vane 21 stands on the surface of the shroud 20 in the direction of the rotational axis X. The centrifugal impeller 2 in FIG. 3 has six centrifugal vanes 21. The six centrifugal vanes 21 are disposed at an equal interval in the circumferential direction of the shroud 20, thereby forming a vane row of the centrifugal impeller 2.

[0059] A hub 22 is formed at the center of the shroud 20. The hub 22 is fixed at the lower end of the shaft 42 of the motor 41.

[0060] Each centrifugal vane 21 extends outward in the radial direction of the shroud 20 from the hub 22 and in the direction opposite to the rotation direction of the centrifugal impeller 2 so as to form a predetermined curved shape. Leading edges of the respective centrifugal vanes 21 are connected to the hub 22. Trailing edges of the respective centrifugal vanes 21 are positioned at the outer circumferential edge of the shroud 20.

[0061] The centrifugal vane 21 has a negative-pressure surface 23 and a pressure surface 24. The negative-pressure surface 23 extends from the hub 22 to the outer circumferential edge of the shroud 20.

[0062] The pressure surface 24 extends from the hub 22 toward the outer circumferential edge of the shroud 20. The pressure surface 24 is positioned at a predetermined interval from the negative-pressure surface 23. The negative-pressure surface 23 and the pressure surface 24 are positioned away from each other, whereby the centrifugal vane 21 has a predetermined thickness. A vane thickness T1 of the centrifugal vane 21 is approximately constant throughout the centrifugal vane 21 except for a part of the trailing edge (described later) of the centrifugal vane 21.

[0063] The centrifugal vane 21 has a second pressure surface 25. The second pressure surface 25 is positioned on the outer circumferential edge side of the centrifugal impeller 2 and inward of the outer circumferential edge of the shroud 20. More specifically, as shown in the enlarged view in FIG. 3, the second pressure surface 25 is positioned between the outer circumferential edge of the shroud 20 and the pressure surface 24 along a direction in which the centrifugal vane 21 extends. For facilitating the understanding, the centrifugal vane 21 is shaded in the enlarged view in FIG. 3.

[0064] The second pressure surface 25 is positioned closer to the negative-pressure surface 23 than a virtual plane 241 (see the broken line in FIG. 3) obtained by continuously extending the pressure surface 24 to the outer circumferential edge.

[0065] More specifically, the second pressure surface 25 has a first part 251 and a second part 252. The first part 251 extends from an end of the pressure surface 24 at an angle different from that of the virtual plane 241 so as to approach the negative-pressure surface 23.

[0066] The second part 252 is continuous with the first part 251 and extends to the outer circumferential edge of the shroud 20. The second part 252 extends at an angle different from that of the first part 251. The second part 252 extends at an angle equal or substantially equal to that of the virtual plane 241. In the second part 252, the negative-pressure surface 23 and the second pressure surface 25 are substantially parallel to each other. A vane thickness T2 between the negative-pressure surface 23 and the second pressure surface 25 is thinner than the vane thickness T1 between the negative-pressure surface 23 and the pressure surface 24.

[0067] The negative-pressure surface 23 and the virtual plane 241 may not necessarily be parallel to each other, and the second part 252 is not limited to one that extends at an angle substantially equal to that of the negative-pressure surface 23 and / or the virtual plane 241.

[0068] The second pressure surface 25 is formed by cutting a part of the pressure surface 24 of the centrifugal vane 21 on the outer circumferential edge side into a substantially parallelogram-shaped when seen with the line of sight made parallel to the rotational axis X of the centrifugal impeller 2. A step recessed from the pressure surface 24 is formed by the second pressure surface 25 on the outer circumferential edge side of the centrifugal vane 21.

[0069] In the enlarged view in FIG. 3, reference numeral 29 denotes the trailing edge of the centrifugal vane 21. The trailing edge 29 is a part along the outer circumferential edge of the shroud 20. Since the trailing edge 29 coincides with the outer circumferential edge of the shroud 20, the trailing edge 29 is not referred to herein as a pressure surface or a second pressure surface.

[0070] The centrifugal impeller 2 in which the centrifugal vane 21 has the second pressure surface 25 can achieve the effect of improving the flow speed on the outer circumferential edge side of the shroud 20. This is considered to be because a flow along the second pressure surface 25 is accelerated under the influence of a low pressure on the negative-pressure surface 23 side owing to the thin vane thickness T2 between the second pressure surface 25 and the negative-pressure surface 23. As a result of the acceleration of the flow, the centrifugal impeller 2 can achieve the effect of improving the flow speed on the outer circumferential edge side of the shroud 20. The improved flow speed increases the flow rate at the centrifugal impeller 2.

[0071] In addition, it is considered that owing to the step on the outer circumferential edge side of the pressure surface 24 of the centrifugal vane 21, a vortex is generated around the second pressure surface 25, as shown in the enlarged view in FIG. 3. The vortex draws the flow tending to separate from the pressure surface 24 (see the outlined, broken line arrow) toward the pressure surface 24 or the second pressure surface 25 (see the outlined, solid line arrow), on the outer circumferential edge side of the centrifugal impeller 2. The substantial passage area between the adjacent centrifugal vane 21 and centrifugal vane 21 of the centrifugal impeller 2 is enlarged, thus contributing to an increase in passage flow rate at the centrifugal impeller 2, in addition to the improvement in flow speed.

[0072] FIG. 4 shows performance curves of the centrifugal pump 1 including the centrifugal impeller 2 in FIG. 3. The solid line in FIG. 4 represents an example in which the centrifugal impeller 2 has the second pressure surface 25. The broken line in FIG. 4 represents a conventional example in which a centrifugal impeller does not have a second pressure surface.

[0073] When the example and the conventional example are compared, the shaft power decreases and the total head increases in the example as compared to the conventional example. The pump efficiency in the example is higher than the pump efficiency in the conventional example. The centrifugal impeller 2 having the second pressure surface 25 can improve the pump efficiency of the centrifugal pump 1.

[0074] The technology disclosed herein is not limited to a configuration in which the second pressure surface 25 is provided to all of the centrifugal vanes 21. The second pressure surface 25 may be provided to some of the centrifugal vanes 21. The centrifugal vanes 21 having the second pressure surfaces 25 may be evenly spaced in the circumferential direction in the centrifugal impeller 2.Modifications

[0075] FIG. 5 shows a centrifugal impeller 2 according to a modification. The centrifugal impeller 2 in FIG. 5 is different in the shape of a second pressure surface 26 from the centrifugal impeller 2 in FIG. 3.

[0076] The second pressure surface 26 extends from the end of the pressure surface 24 to the outer circumferential edge of the shroud at an angle different from that of the virtual plane 241. The second pressure surface 26 is formed by cutting a part of the centrifugal vane 21 on the outer circumferential edge side into a substantially triangular shape when seen with the line of sight made parallel to the rotational axis X of the centrifugal impeller 2.

[0077] In the centrifugal impeller 2 in FIG. 5, the vane thickness between the second pressure surface 26 and the negative-pressure surface 23 is relatively small as well, whereby the flow speed is improved. As a result, a centrifugal pump 1 including the centrifugal impeller 2 in FIG. 5 can improve the pump efficiency as well.

[0078] A centrifugal impeller 2 in FIG. 6 is different in the shape of a second pressure surface 28 from the centrifugal impeller 2 in FIG. 3 or FIG. 5.

[0079] The second pressure surface 28 has a first part 281 and a second part 282. The first part 281 extends at a position closer to the negative-pressure surface 23 than the virtual plane 241 and at an angle equal to that of the virtual plane 241 or the negative-pressure surface 23. The second part 282 is a part positioned between the first part 281 and the outer circumferential edge of the shroud 20 along a direction in which the centrifugal vane 21 extends. The second part 282 extends at a position closer to the negative-pressure surface 23 than the first part 281 and at an angle equal to that of the virtual plane 241 or the negative-pressure surface 23. The second pressure surface 28 has a shape of approaching the negative-pressure surface 23 stepwise due to two steps defined by the first part 281 and the second part 282. The centrifugal impeller 2 having two steps is advantageous for vortex generation around the second pressure surface 28.

[0080] FIG. 7 shows a centrifugal impeller 2 according to another modification. In the centrifugal impeller 2 in FIG. 7, a recess 27 is added as compared to the centrifugal impeller 2 in FIG. 3.

[0081] The recess 27 is formed in the pressure surface 24. In the pressure surface 24, the recess 27 is formed in a site on the outer circumferential edge side of the centrifugal impeller 2, i.e., in a site in the vicinity of the second pressure surface 25. The recess 27 is recessed from the pressure surface 24 toward the negative-pressure surface 23.

[0082] The recess 27 in FIG. 7 has a semicircular shape when seen with the line of sight made parallel to the rotational axis X of the centrifugal impeller 2. The shape of the recess 27 is not limited to a semicircular shape, and may be, for example, a triangular or rectangular shape.

[0083] The centrifugal impeller 2 in FIG. 7 has four recesses 27 for one centrifugal vane 21. The four recesses 27 are arranged from the center of the pressure surface 24 toward the outer circumferential edge side at an equal interval. The number of the recesses 27 can be set as appropriate.

[0084] The recesses 27 formed, in the pressure surface 24, in the vicinity of the second pressure surface 25 facilitate vortex generation around the second pressure surface 25. A centrifugal pump 1 including the centrifugal impeller 2 in FIG. 7 allows a further improvement in pump efficiency.

[0085] The recesses 27 are not limited to be formed in all of the centrifugal vanes 21 of the centrifugal impeller 2. The recesses 27 may be formed in some of the centrifugal vanes 21.

[0086] In addition, the recesses 27 may be formed in the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 5, or may be formed in the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 6.

[0087] FIG. 8 shows a centrifugal impeller 2 having a different number of the centrifugal vanes 21. The centrifugal impeller 2 may have, for example, four centrifugal vanes 21. Each centrifugal vane 21 has a second pressure surface 25, as with the centrifugal vanes 21 of centrifugal impeller 2 in FIG. 3.

[0088] FIG. 9 shows still another centrifugal impeller 2 having four centrifugal vanes 21. Each centrifugal vane 21 in FIG. 9 has a second pressure surface 26, as with the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 5.

[0089] The centrifugal impeller 2 having four centrifugal vanes 21 may have a second pressure surface 28 including two steps, as with the centrifugal impeller 2 in FIG. 6. In addition, the centrifugal impeller 2 having four centrifugal vanes 21 may have a recess 27, as with the centrifugal impeller 2 in FIG. 7.

[0090] FIG. 10 shows a centrifugal impeller 2 having eight centrifugal vanes 21. Each centrifugal vane 21 in FIG. 10 has a second pressure surface 25, as with the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 3.

[0091] FIG. 11 shows still another centrifugal impeller 2 having eight centrifugal vanes 21. Each centrifugal vane 21 in FIG. 11 has a second pressure surface 26, as with the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 5.

[0092] The centrifugal impeller 2 having eight centrifugal vanes 21 may have a second pressure surface 28 including two steps, as with the centrifugal impeller 2 in FIG. 6. In addition, the centrifugal impeller 2 having eight centrifugal vanes 21 may have a recess 27, as with the centrifugal impeller 2 in FIG. 7.

[0093] FIG. 12 shows a non-clogging type centrifugal impeller 5. The lower view in FIG. 12 is a side view of the centrifugal impeller 5, and the upper view in FIG. 12 is a sectional view along line A-A in the lower view.

[0094] A centrifugal vane 51 of the non-clogging type centrifugal impeller 5 defines a primary channel 52 and a secondary channel 53.

[0095] The primary channel 52 connects a suction port 54 and a discharge port 55 of the centrifugal impeller 5. The suction port 54 is opened downward at the lower end of the centrifugal impeller 5. The discharge port 55 is opened sideways at a side part, of the centrifugal impeller 5, above the flange portion 56.

[0096] The secondary channel 53 is formed in a shape such that an outer circumferential part of the centrifugal impeller 5 is partially cut inwardly. The secondary channel 53 is continuous with the discharge port 55 and extends in the circumferential direction of the centrifugal impeller 5.

[0097] The centrifugal impeller 5 has two centrifugal vanes 51. As shown in the upper view in FIG. 12, the centrifugal vanes 51 extend from the center part toward the outer circumferential edge of the centrifugal impeller 5.

[0098] The centrifugal vanes 51 each have a negative-pressure surface 57. The negative-pressure surface 57 extends from the center part to the outer circumferential edge of the centrifugal impeller 5.

[0099] The centrifugal vane 51 has a pressure surface 58. The pressure surface 58 is positioned away from the negative-pressure surface 57 such that the centrifugal vane 51 has a predetermined thickness, and extends from the center part toward the outer circumferential edge of the centrifugal impeller 5. The vane thickness of the centrifugal vane 51 is not constant.

[0100] The centrifugal vane 51 has a second pressure surface 59. The second pressure surface 59 is positioned between the outer circumferential edge of the centrifugal impeller 5 and the pressure surface 58 along a direction in which the centrifugal vane 51 extends.

[0101] The second pressure surface 59 has a first part 591 and a second part 592. The first part 591 extends from an end of the pressure surface 58 to the outer circumferential edge at an angle different from that of a virtual plane 581 obtained by continuously extending the pressure surface 58, so as to approach the negative-pressure surface 57.

[0102] The second part 592 is continuous with the first part 591 and extends to the outer circumferential edge of the centrifugal impeller 5. The second part 592 extends at an angle different from that of the first part 591. More specifically, the second part 592 extends at an angle equal or substantially equal to that of the negative-pressure surface 57.

[0103] With the centrifugal impeller 5 having the second pressure surface 59, the effect of improving the pump efficiency can be achieved.

[0104] In the non-clogging type centrifugal impeller 5, each centrifugal vane 51 may have the second pressure surface 26 as shown in FIG. 5, or may have the second pressure surface 28 with two steps as shown in FIG. 6. Also, each centrifugal vane 51 may have the recess 27 as shown in FIG. 7.

Examples

Embodiment Construction

[0050]Hereinafter, embodiments of a centrifugal impeller and a centrifugal pump will be described with reference to the drawings. The centrifugal impeller and the centrifugal pump described herein are merely illustrative.

Entire Structure of Centrifugal Pump

[0051]FIG. 1 shows a centrifugal pump 1 including a centrifugal impeller 2. The centrifugal pump 1 is a submersible pump for sewage treatment, and is a vortex pump having good foreign matter passing performance.

[0052]The centrifugal pump 1 includes a pump unit 3 having a centrifugal impeller 2, and a motor unit 4 having a motor 41 that drives the centrifugal impeller 2. The pump unit 3 is positioned on the lower side relative to an oil casing 11, and the motor unit 4 is positioned on the upper side relative to the oil casing 11. In the inside of the oil casing 11, a shaft 42 (described later) of the motor 41 is sealed by a mechanical seal 12.

[0053]The motor unit 4 has the motor 41 and a motor casing 43 covering the motor 41. The s...

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Japanese Patent Application No. 2025-059572 filed on Mar. 31, 2025, the entire disclosure of which is incorporated herein by reference.BACKGROUND

[0002] The technology disclosed herein relates to a centrifugal impeller and a centrifugal pump.

[0003] Japanese Laid-Open Patent Publication No. 2009-293547 discloses a conventional centrifugal impeller and centrifugal pump. This centrifugal impeller is an impeller used for a so-called vortex pump. The centrifugal impeller has a shroud and a plurality of centrifugal vanes provided to stand on the surface of the shroud. The centrifugal impeller is disposed so as to be retracted from a volute part inside a casing. In the vortex pump, there is a relatively large space between the centrifugal impeller and the inner wall surface of the casing, and foreign matter suctioned into the casing is discharged to the outside directly without passing through the impeller.SUMMARY

[0004] As described above, a vortex pump has a large space in a casing, and thus the pump efficiency thereof is relatively reduced. Thus, there is a demand to increase the pump efficiency of the vortex pump as much as possible.

[0005] Not limited to the vortex pump, there is a requirement to improve the pump efficiency of a centrifugal pump that includes, for example, a non-clogging type impeller. The non-clogging type impeller is an impeller provided with a large space for allowing foreign matter to pass through the impeller. In the case of a closed impeller, the centrifugal impeller has inside an inner channel connecting a suction port and a discharge port of the impeller.

[0006] The technology disclosed herein improves the pump efficiency of a centrifugal pump by devising the shape of the centrifugal impeller.

[0007] The technology disclosed herein is directed to a centrifugal impeller. The centrifugal impeller includes at least one centrifugal vane extending from a center part toward an outer circumferential edge of the impeller, wherein

[0008] the centrifugal vane has:

[0009] a negative-pressure surface extending from the center part to the outer circumferential edge of the impeller;

[0010] a pressure surface positioned away from the negative-pressure surface such that the centrifugal vane has a predetermined thickness, and extending from the center part toward the outer circumferential edge of the impeller; and

[0011] a second pressure surface connected to the pressure surface and positioned closer to the negative-pressure surface than a virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge, on the outer circumferential edge side of the impeller and inward of the outer circumferential edge.

[0012] The centrifugal vane of the centrifugal impeller has a negative-pressure surface and a pressure surface. The negative-pressure surface extends from the center part to the outer circumferential edge of the impeller. The negative-pressure surface extends from the center part while curving outward in the radial direction of the impeller and in the direction opposite to the rotation direction of the impeller.

[0013] The pressure surface extends from the center part toward the outer circumferential edge of the impeller. The negative-pressure surface and the pressure surface are positioned away from each other, whereby the centrifugal vane has a predetermined thickness. The pressure surface also extends from the center part while curving outward in the radial direction of the impeller and in the direction opposite to the rotation direction of the impeller.

[0014] The centrifugal vane has a second pressure surface. The second pressure surface is connected to the pressure surface and positioned on the outer circumferential edge side of the impeller and inward of the outer circumferential edge. The outer circumferential edge side of the impeller may be the outer circumferential edge side relative to the intermediate position of the centrifugal vane extending from the center part to the outer circumferential edge of the impeller.

[0015] The second pressure surface is positioned closer to the negative-pressure surface than the virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge. The vane thickness between the second pressure surface and the negative-pressure surface is thinner than the vane thickness between the pressure surface and negative-pressure surface. The second pressure surface can be formed by cutting a part of the centrifugal vane on the pressure surface side.

[0016] The centrifugal impeller in which the centrifugal vane has the second pressure surface can achieve the effect of improving the flow speed on the outer circumferential edge side of the impeller. This is considered to be because a flow along the second pressure surface is accelerated under the influence of a low pressure on the negative-pressure surface side owing to the thin vane thickness between the second pressure surface and the negative-pressure surface. As a result of the acceleration of the flow along the second pressure surface, the centrifugal impeller is considered to achieve the effect of improving the flow speed on the outer circumferential edge side of the impeller. The improved flow speed increases the flow rate at the centrifugal vane.

[0017] The centrifugal impeller having the second pressure surface enables a reduction in shaft power and an increase in the total head of the centrifugal pump as compared to conventional centrifugal impellers having no second pressure surface, and thus the pump efficiency can be improved.

[0018] In addition, it is considered that since the second pressure surface is positioned offset from the virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge, a vortex is generated around the second pressure surface. The vortex draws a flow tending to separate from the pressure surface toward the pressure surface and the second pressure surface, on the outer circumferential edge side of the impeller. Thus, flow separation is suppressed, and the flow is caused to move along the centrifugal vane, whereby the flow speed is improved.

[0019] The second pressure surface may be positioned between the outer circumferential edge of the impeller and the pressure surface along a direction in which the centrifugal vane extends.

[0020] In a case where the second pressure surface is formed, for example, at a position in contact with the outer circumferential edge of the impeller, the above-described effect of improving the flow speed on the outer circumferential edge side of the impeller is enhanced, leading to an advantage for the improvement in pump efficiency. The second pressure surface is not limited to one that is in contact with the outer circumferential edge of the impeller.

[0021] The second pressure surface may extend from an end of the pressure surface to the outer circumferential edge of the impeller at an angle different from the virtual plane.

[0022] The angle herein refers to an angle of a direction along the pressure surface or the second pressure surface of the centrifugal vane extending from the center part toward the outer circumferential edge.

[0023] The second pressure surface may be a surface extending in a direction of approaching the negative-pressure surface from the end of the pressure surface. The second pressure surface may be formed by cutting a part of the pressure surface of the centrifugal vane on the outer circumferential edge side into a substantially triangular shape when seen with the line of sight made parallel to the rotational axis of the impeller. The vane thickness between the second pressure surface and the negative-pressure surface is relatively thin, whereby the flow speed is improved.

[0024] The second pressure surface may include a first part extending from an end of the pressure surface at an angle different from the virtual plane, and a second part continuous with the first part and extending to the outer circumferential edge of the impeller at an angle different from the first part.

[0025] The angle of the second part may be, for example, equal or substantially equal to that of the virtual plane. If the angle of the second part is equal or substantially equal to that of the virtual plane, the second pressure surface is formed by cutting a part of the pressure surface of the centrifugal vane on the outer circumferential edge side into a substantially parallelogram-shaped when seen with the line of sight made parallel to the rotational axis of the impeller.

[0026] The angle of the second part may be, for example, equal or substantially equal to that of the negative-pressure surface.

[0027] The vane thickness between the second pressure surface and the negative-pressure surface is relatively thin, whereby the flow speed is improved. In addition, it is considered that since a step recessed from the pressure surface is formed on the outer circumferential edge side of the centrifugal vane, vortex generation is facilitated around the second pressure surface. As described above, the vortex draws the flow tending to separate from the pressure surface toward the pressure surface and the second pressure surface, on the outer circumferential edge side of the impeller. The substantial passage area in the centrifugal impeller is enlarged, whereby the flow rate is improved. The above-described shape of the second pressure surface contributes to an increase in passage flow rate at the impeller, in addition to the improvement in flow speed. Thus, the pump efficiency of the centrifugal pump including said centrifugal impeller can be improved.

[0028] The second pressure surface may include a first part extending at an angle equal to the virtual plane and at a position closer to the negative-pressure surface than the virtual plane, and a second part positioned between the first part and the outer circumferential edge of the impeller and extending at an angle equal to the virtual plane and at a position closer to the negative-pressure surface than the first part.

[0029] In addition, the second pressure surface may include a first part extending at an angle equal to that of the negative-pressure surface and at a position closer to the negative-pressure surface than the virtual plane, and a second part positioned between the first part and the outer circumferential edge of the impeller and extending at an angle equal to that of the negative-pressure surface and at a position closer to the negative-pressure surface than the first part.

[0030] The second pressure surface may have a shape of approaching the negative-pressure surface stepwise due to two steps defined by the first part and the second part. This shape is advantageous for the above-described vortex generation around the second pressure surface.

[0031] At least one recess recessed from the pressure surface toward the negative-pressure surface may be formed in a site, in the pressure surface, on the outer circumferential edge side of the impeller.

[0032] The recess formed, in the pressure surface, in the vicinity of the second pressure surface further facilitates vortex generation around the second pressure surface.

[0033] The centrifugal impeller may be an impeller for a vortex pump, in which the centrifugal vane stands on a shroud and which is disposed so as to be retracted from a volute part in a casing so as to ensure a predetermined passage diameter.

[0034] The above-described centrifugal impeller is suitable for improving the pump efficiency of the vortex pump.

[0035] The centrifugal impeller may be a non-clogging type impeller in which the centrifugal vane defines a primary channel connecting a suction port formed at one end and a discharge port formed at a side, and a secondary channel continuous with the primary channel and extending along an outer circumferential surface.

[0036] The above-described centrifugal impeller is suitable for improving the pump efficiency of a pump including the non-clogging type centrifugal impeller.

[0037] The centrifugal pump disclosed herein includes the above-described centrifugal impeller. The centrifugal pump includes the above-described centrifugal impeller, whereby the pump efficiency is improved.BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a sectional view of a centrifugal pump including a centrifugal impeller.

[0039] FIG. 2 is a perspective view of the centrifugal impeller.

[0040] FIG. 3 shows a plan view and a partially enlarged view of the centrifugal impeller.

[0041] FIG. 4 shows performance curves of the centrifugal pump.

[0042] FIG. 5 shows a plan view and a partially enlarged view of a centrifugal impeller according to a modification.

[0043] FIG. 6 shows a plan view and a partially enlarged view of a centrifugal impeller according to a modification.

[0044] FIG. 7 shows a plan view and a partially enlarged view of a centrifugal impeller according to a modification.

[0045] FIG. 8 is a plan view of a centrifugal impeller according to a modification.

[0046] FIG. 9 is a plan view of a centrifugal impeller according to a modification.

[0047] FIG. 10 is a plan view of a centrifugal impeller according to a modification.

[0048] FIG. 11 is a plan view of a centrifugal impeller according to a modification.

[0049] FIG. 12 shows a side view and a sectional view along line A-A of a non-clogging type centrifugal impeller.DETAILED DESCRIPTION OF THE DRAWINGS

[0050] Hereinafter, embodiments of a centrifugal impeller and a centrifugal pump will be described with reference to the drawings. The centrifugal impeller and the centrifugal pump described herein are merely illustrative.Entire Structure of Centrifugal Pump

[0051] FIG. 1 shows a centrifugal pump 1 including a centrifugal impeller 2. The centrifugal pump 1 is a submersible pump for sewage treatment, and is a vortex pump having good foreign matter passing performance.

[0052] The centrifugal pump 1 includes a pump unit 3 having a centrifugal impeller 2, and a motor unit 4 having a motor 41 that drives the centrifugal impeller 2. The pump unit 3 is positioned on the lower side relative to an oil casing 11, and the motor unit 4 is positioned on the upper side relative to the oil casing 11. In the inside of the oil casing 11, a shaft 42 (described later) of the motor 41 is sealed by a mechanical seal 12.

[0053] The motor unit 4 has the motor 41 and a motor casing 43 covering the motor 41. The shaft 42 of the motor 41 extends in the vertical direction.

[0054] The centrifugal impeller 2 of the pump unit 3 is mounted on the lower end of the shaft 42 of the motor 41. The pump unit 3 has a pump casing 31.

[0055] The pump casing 31 is attached to a lower part of the oil casing 11. The centrifugal impeller 2 is disposed in an upper region inside the pump casing 31. A lower region inside the pump casing 31 corresponds to a volute portion 34. The centrifugal impeller 2 is disposed so as to be retracted from the volute portion 34. There is a relatively large space between the centrifugal impeller 2 and the inner wall surface of the pump casing 31.

[0056] A suction port 32 opened downward is formed at a lower part of the pump casing 31. A discharge port 33 protruding sideways is formed at a side part of the pump casing 31. The discharge port 33 is connected to an exhaust pipe.Structure of Centrifugal Impeller

[0057] FIG. 2 is a perspective view of the centrifugal impeller 2. FIG. 3 shows a plan view of the centrifugal impeller 2 as seen with the line of sight made parallel to a rotational axis X of the centrifugal impeller 2. FIG. 2 illustrates the centrifugal impeller 2 in an inverted orientation with respect to the state where the centrifugal impeller 2 is attached to the shaft 42 of the motor 41.

[0058] The centrifugal impeller 2 is a semi-open type impeller, and has a shroud 20 and a centrifugal vane 21. The shroud 20 has a substantially disk-shape. The centrifugal vane 21 stands on the surface of the shroud 20 in the direction of the rotational axis X. The centrifugal impeller 2 in FIG. 3 has six centrifugal vanes 21. The six centrifugal vanes 21 are disposed at an equal interval in the circumferential direction of the shroud 20, thereby forming a vane row of the centrifugal impeller 2.

[0059] A hub 22 is formed at the center of the shroud 20. The hub 22 is fixed at the lower end of the shaft 42 of the motor 41.

[0060] Each centrifugal vane 21 extends outward in the radial direction of the shroud 20 from the hub 22 and in the direction opposite to the rotation direction of the centrifugal impeller 2 so as to form a predetermined curved shape. Leading edges of the respective centrifugal vanes 21 are connected to the hub 22. Trailing edges of the respective centrifugal vanes 21 are positioned at the outer circumferential edge of the shroud 20.

[0061] The centrifugal vane 21 has a negative-pressure surface 23 and a pressure surface 24. The negative-pressure surface 23 extends from the hub 22 to the outer circumferential edge of the shroud 20.

[0062] The pressure surface 24 extends from the hub 22 toward the outer circumferential edge of the shroud 20. The pressure surface 24 is positioned at a predetermined interval from the negative-pressure surface 23. The negative-pressure surface 23 and the pressure surface 24 are positioned away from each other, whereby the centrifugal vane 21 has a predetermined thickness. A vane thickness T1 of the centrifugal vane 21 is approximately constant throughout the centrifugal vane 21 except for a part of the trailing edge (described later) of the centrifugal vane 21.

[0063] The centrifugal vane 21 has a second pressure surface 25. The second pressure surface 25 is positioned on the outer circumferential edge side of the centrifugal impeller 2 and inward of the outer circumferential edge of the shroud 20. More specifically, as shown in the enlarged view in FIG. 3, the second pressure surface 25 is positioned between the outer circumferential edge of the shroud 20 and the pressure surface 24 along a direction in which the centrifugal vane 21 extends. For facilitating the understanding, the centrifugal vane 21 is shaded in the enlarged view in FIG. 3.

[0064] The second pressure surface 25 is positioned closer to the negative-pressure surface 23 than a virtual plane 241 (see the broken line in FIG. 3) obtained by continuously extending the pressure surface 24 to the outer circumferential edge.

[0065] More specifically, the second pressure surface 25 has a first part 251 and a second part 252. The first part 251 extends from an end of the pressure surface 24 at an angle different from that of the virtual plane 241 so as to approach the negative-pressure surface 23.

[0066] The second part 252 is continuous with the first part 251 and extends to the outer circumferential edge of the shroud 20. The second part 252 extends at an angle different from that of the first part 251. The second part 252 extends at an angle equal or substantially equal to that of the virtual plane 241. In the second part 252, the negative-pressure surface 23 and the second pressure surface 25 are substantially parallel to each other. A vane thickness T2 between the negative-pressure surface 23 and the second pressure surface 25 is thinner than the vane thickness T1 between the negative-pressure surface 23 and the pressure surface 24.

[0067] The negative-pressure surface 23 and the virtual plane 241 may not necessarily be parallel to each other, and the second part 252 is not limited to one that extends at an angle substantially equal to that of the negative-pressure surface 23 and / or the virtual plane 241.

[0068] The second pressure surface 25 is formed by cutting a part of the pressure surface 24 of the centrifugal vane 21 on the outer circumferential edge side into a substantially parallelogram-shaped when seen with the line of sight made parallel to the rotational axis X of the centrifugal impeller 2. A step recessed from the pressure surface 24 is formed by the second pressure surface 25 on the outer circumferential edge side of the centrifugal vane 21.

[0069] In the enlarged view in FIG. 3, reference numeral 29 denotes the trailing edge of the centrifugal vane 21. The trailing edge 29 is a part along the outer circumferential edge of the shroud 20. Since the trailing edge 29 coincides with the outer circumferential edge of the shroud 20, the trailing edge 29 is not referred to herein as a pressure surface or a second pressure surface.

[0070] The centrifugal impeller 2 in which the centrifugal vane 21 has the second pressure surface 25 can achieve the effect of improving the flow speed on the outer circumferential edge side of the shroud 20. This is considered to be because a flow along the second pressure surface 25 is accelerated under the influence of a low pressure on the negative-pressure surface 23 side owing to the thin vane thickness T2 between the second pressure surface 25 and the negative-pressure surface 23. As a result of the acceleration of the flow, the centrifugal impeller 2 can achieve the effect of improving the flow speed on the outer circumferential edge side of the shroud 20. The improved flow speed increases the flow rate at the centrifugal impeller 2.

[0071] In addition, it is considered that owing to the step on the outer circumferential edge side of the pressure surface 24 of the centrifugal vane 21, a vortex is generated around the second pressure surface 25, as shown in the enlarged view in FIG. 3. The vortex draws the flow tending to separate from the pressure surface 24 (see the outlined, broken line arrow) toward the pressure surface 24 or the second pressure surface 25 (see the outlined, solid line arrow), on the outer circumferential edge side of the centrifugal impeller 2. The substantial passage area between the adjacent centrifugal vane 21 and centrifugal vane 21 of the centrifugal impeller 2 is enlarged, thus contributing to an increase in passage flow rate at the centrifugal impeller 2, in addition to the improvement in flow speed.

[0072] FIG. 4 shows performance curves of the centrifugal pump 1 including the centrifugal impeller 2 in FIG. 3. The solid line in FIG. 4 represents an example in which the centrifugal impeller 2 has the second pressure surface 25. The broken line in FIG. 4 represents a conventional example in which a centrifugal impeller does not have a second pressure surface.

[0073] When the example and the conventional example are compared, the shaft power decreases and the total head increases in the example as compared to the conventional example. The pump efficiency in the example is higher than the pump efficiency in the conventional example. The centrifugal impeller 2 having the second pressure surface 25 can improve the pump efficiency of the centrifugal pump 1.

[0074] The technology disclosed herein is not limited to a configuration in which the second pressure surface 25 is provided to all of the centrifugal vanes 21. The second pressure surface 25 may be provided to some of the centrifugal vanes 21. The centrifugal vanes 21 having the second pressure surfaces 25 may be evenly spaced in the circumferential direction in the centrifugal impeller 2.Modifications

[0075] FIG. 5 shows a centrifugal impeller 2 according to a modification. The centrifugal impeller 2 in FIG. 5 is different in the shape of a second pressure surface 26 from the centrifugal impeller 2 in FIG. 3.

[0076] The second pressure surface 26 extends from the end of the pressure surface 24 to the outer circumferential edge of the shroud at an angle different from that of the virtual plane 241. The second pressure surface 26 is formed by cutting a part of the centrifugal vane 21 on the outer circumferential edge side into a substantially triangular shape when seen with the line of sight made parallel to the rotational axis X of the centrifugal impeller 2.

[0077] In the centrifugal impeller 2 in FIG. 5, the vane thickness between the second pressure surface 26 and the negative-pressure surface 23 is relatively small as well, whereby the flow speed is improved. As a result, a centrifugal pump 1 including the centrifugal impeller 2 in FIG. 5 can improve the pump efficiency as well.

[0078] A centrifugal impeller 2 in FIG. 6 is different in the shape of a second pressure surface 28 from the centrifugal impeller 2 in FIG. 3 or FIG. 5.

[0079] The second pressure surface 28 has a first part 281 and a second part 282. The first part 281 extends at a position closer to the negative-pressure surface 23 than the virtual plane 241 and at an angle equal to that of the virtual plane 241 or the negative-pressure surface 23. The second part 282 is a part positioned between the first part 281 and the outer circumferential edge of the shroud 20 along a direction in which the centrifugal vane 21 extends. The second part 282 extends at a position closer to the negative-pressure surface 23 than the first part 281 and at an angle equal to that of the virtual plane 241 or the negative-pressure surface 23. The second pressure surface 28 has a shape of approaching the negative-pressure surface 23 stepwise due to two steps defined by the first part 281 and the second part 282. The centrifugal impeller 2 having two steps is advantageous for vortex generation around the second pressure surface 28.

[0080] FIG. 7 shows a centrifugal impeller 2 according to another modification. In the centrifugal impeller 2 in FIG. 7, a recess 27 is added as compared to the centrifugal impeller 2 in FIG. 3.

[0081] The recess 27 is formed in the pressure surface 24. In the pressure surface 24, the recess 27 is formed in a site on the outer circumferential edge side of the centrifugal impeller 2, i.e., in a site in the vicinity of the second pressure surface 25. The recess 27 is recessed from the pressure surface 24 toward the negative-pressure surface 23.

[0082] The recess 27 in FIG. 7 has a semicircular shape when seen with the line of sight made parallel to the rotational axis X of the centrifugal impeller 2. The shape of the recess 27 is not limited to a semicircular shape, and may be, for example, a triangular or rectangular shape.

[0083] The centrifugal impeller 2 in FIG. 7 has four recesses 27 for one centrifugal vane 21. The four recesses 27 are arranged from the center of the pressure surface 24 toward the outer circumferential edge side at an equal interval. The number of the recesses 27 can be set as appropriate.

[0084] The recesses 27 formed, in the pressure surface 24, in the vicinity of the second pressure surface 25 facilitate vortex generation around the second pressure surface 25. A centrifugal pump 1 including the centrifugal impeller 2 in FIG. 7 allows a further improvement in pump efficiency.

[0085] The recesses 27 are not limited to be formed in all of the centrifugal vanes 21 of the centrifugal impeller 2. The recesses 27 may be formed in some of the centrifugal vanes 21.

[0086] In addition, the recesses 27 may be formed in the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 5, or may be formed in the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 6.

[0087] FIG. 8 shows a centrifugal impeller 2 having a different number of the centrifugal vanes 21. The centrifugal impeller 2 may have, for example, four centrifugal vanes 21. Each centrifugal vane 21 has a second pressure surface 25, as with the centrifugal vanes 21 of centrifugal impeller 2 in FIG. 3.

[0088] FIG. 9 shows still another centrifugal impeller 2 having four centrifugal vanes 21. Each centrifugal vane 21 in FIG. 9 has a second pressure surface 26, as with the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 5.

[0089] The centrifugal impeller 2 having four centrifugal vanes 21 may have a second pressure surface 28 including two steps, as with the centrifugal impeller 2 in FIG. 6. In addition, the centrifugal impeller 2 having four centrifugal vanes 21 may have a recess 27, as with the centrifugal impeller 2 in FIG. 7.

[0090] FIG. 10 shows a centrifugal impeller 2 having eight centrifugal vanes 21. Each centrifugal vane 21 in FIG. 10 has a second pressure surface 25, as with the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 3.

[0091] FIG. 11 shows still another centrifugal impeller 2 having eight centrifugal vanes 21. Each centrifugal vane 21 in FIG. 11 has a second pressure surface 26, as with the centrifugal vanes 21 of the centrifugal impeller 2 in FIG. 5.

[0092] The centrifugal impeller 2 having eight centrifugal vanes 21 may have a second pressure surface 28 including two steps, as with the centrifugal impeller 2 in FIG. 6. In addition, the centrifugal impeller 2 having eight centrifugal vanes 21 may have a recess 27, as with the centrifugal impeller 2 in FIG. 7.

[0093] FIG. 12 shows a non-clogging type centrifugal impeller 5. The lower view in FIG. 12 is a side view of the centrifugal impeller 5, and the upper view in FIG. 12 is a sectional view along line A-A in the lower view.

[0094] A centrifugal vane 51 of the non-clogging type centrifugal impeller 5 defines a primary channel 52 and a secondary channel 53.

[0095] The primary channel 52 connects a suction port 54 and a discharge port 55 of the centrifugal impeller 5. The suction port 54 is opened downward at the lower end of the centrifugal impeller 5. The discharge port 55 is opened sideways at a side part, of the centrifugal impeller 5, above the flange portion 56.

[0096] The secondary channel 53 is formed in a shape such that an outer circumferential part of the centrifugal impeller 5 is partially cut inwardly. The secondary channel 53 is continuous with the discharge port 55 and extends in the circumferential direction of the centrifugal impeller 5.

[0097] The centrifugal impeller 5 has two centrifugal vanes 51. As shown in the upper view in FIG. 12, the centrifugal vanes 51 extend from the center part toward the outer circumferential edge of the centrifugal impeller 5.

[0098] The centrifugal vanes 51 each have a negative-pressure surface 57. The negative-pressure surface 57 extends from the center part to the outer circumferential edge of the centrifugal impeller 5.

[0099] The centrifugal vane 51 has a pressure surface 58. The pressure surface 58 is positioned away from the negative-pressure surface 57 such that the centrifugal vane 51 has a predetermined thickness, and extends from the center part toward the outer circumferential edge of the centrifugal impeller 5. The vane thickness of the centrifugal vane 51 is not constant.

[0100] The centrifugal vane 51 has a second pressure surface 59. The second pressure surface 59 is positioned between the outer circumferential edge of the centrifugal impeller 5 and the pressure surface 58 along a direction in which the centrifugal vane 51 extends.

[0101] The second pressure surface 59 has a first part 591 and a second part 592. The first part 591 extends from an end of the pressure surface 58 to the outer circumferential edge at an angle different from that of a virtual plane 581 obtained by continuously extending the pressure surface 58, so as to approach the negative-pressure surface 57.

[0102] The second part 592 is continuous with the first part 591 and extends to the outer circumferential edge of the centrifugal impeller 5. The second part 592 extends at an angle different from that of the first part 591. More specifically, the second part 592 extends at an angle equal or substantially equal to that of the negative-pressure surface 57.

[0103] With the centrifugal impeller 5 having the second pressure surface 59, the effect of improving the pump efficiency can be achieved.

[0104] In the non-clogging type centrifugal impeller 5, each centrifugal vane 51 may have the second pressure surface 26 as shown in FIG. 5, or may have the second pressure surface 28 with two steps as shown in FIG. 6. Also, each centrifugal vane 51 may have the recess 27 as shown in FIG. 7.

Examples

Embodiment Construction

[0050]Hereinafter, embodiments of a centrifugal impeller and a centrifugal pump will be described with reference to the drawings. The centrifugal impeller and the centrifugal pump described herein are merely illustrative.

Entire Structure of Centrifugal Pump

[0051]FIG. 1 shows a centrifugal pump 1 including a centrifugal impeller 2. The centrifugal pump 1 is a submersible pump for sewage treatment, and is a vortex pump having good foreign matter passing performance.

[0052]The centrifugal pump 1 includes a pump unit 3 having a centrifugal impeller 2, and a motor unit 4 having a motor 41 that drives the centrifugal impeller 2. The pump unit 3 is positioned on the lower side relative to an oil casing 11, and the motor unit 4 is positioned on the upper side relative to the oil casing 11. In the inside of the oil casing 11, a shaft 42 (described later) of the motor 41 is sealed by a mechanical seal 12.

[0053]The motor unit 4 has the motor 41 and a motor casing 43 covering the motor 41. The s...

Claims

1. A centrifugal impeller comprising at least one centrifugal vane extending from a center part toward an outer circumferential edge of the impeller, whereinthe centrifugal vane has:a negative-pressure surface extending from the center part to the outer circumferential edge of the impeller;a pressure surface positioned away from the negative-pressure surface such that the centrifugal vane has a predetermined thickness, and extending from the center part toward the outer circumferential edge of the impeller; anda second pressure surface connected to the pressure surface and positioned closer to the negative-pressure surface than a virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge, on the outer circumferential edge side of the impeller and inward of the outer circumferential edge.

2. The centrifugal impeller according to claim 1, whereinthe second pressure surface is positioned between the outer circumferential edge of the impeller and the pressure surface along a direction in which the centrifugal vane extends.

3. The centrifugal impeller according to claim 2, whereinthe second pressure surface extends from an end of the pressure surface to the outer circumferential edge of the impeller at an angle different from that of the virtual plane.

4. The centrifugal impeller according to claim 2, whereinthe second pressure surface includes a first part extending from an end of the pressure surface at an angle different from that of the virtual plane, and a second part continuous with the first part and extending to the outer circumferential edge of the impeller at an angle different from that of the first part.

5. The centrifugal impeller according to claim 2, whereinthe second pressure surface includes a first part extending at an angle equal to that of the virtual plane and at a position closer to the negative-pressure surface than the virtual plane, and a second part positioned between the first part and the outer circumferential edge of the impeller and extending at an angle equal to that of the virtual plane and at a position closer to the negative-pressure surface than the first part.

6. The centrifugal impeller according to claim 2, whereinat least one recess recessed from the pressure surface toward the negative-pressure surface is formed in a site, in the pressure surface, on the outer circumferential edge side of the impeller.

7. The centrifugal impeller according to claim 1, whereinthe impeller is for a vortex pump, in which the centrifugal vane stands on a shroud and is disposed so as to be retracted from a volute part in a casing so as to ensure a predetermined passage diameter.

8. The centrifugal impeller according to claim 1, whereinthe impeller is a non-clogging type impeller in which the centrifugal vane defines a primary channel connecting a suction port formed at one end and a discharge port formed at a side, and a secondary channel continuous with the primary channel and extending along an outer circumferential surface.

9. A centrifugal pump comprising a centrifugal impeller, whereinthe centrifugal impeller has at least one centrifugal vane extending from a center part toward an outer circumferential edge of the centrifugal impeller, andthe centrifugal vane has:a negative-pressure surface extending from the center part to the outer circumferential edge of the impeller;a pressure surface positioned away from the negative-pressure surface such that the centrifugal vane has a predetermined thickness, and extending from the center part toward the outer circumferential edge of the impeller; anda second pressure surface connected to the pressure surface and positioned closer to the negative-pressure surface than a virtual plane obtained by continuously extending the pressure surface to the outer circumferential edge, on the outer circumferential edge side of the impeller and inward of the outer circumferential edge.

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