IMPELLER FOR CENTRIFUGAL PUMP AND PUMP INCLUDING THE SAME

Abstract

A centrifugal pump impeller 11 includes an impeller body in which an inner channel 35 is formed, and a single centrifugal vane 37 provided in the impeller body so as to have a leading edge at an outlet and a trailing edge at a predetermined point of an outer periphery of the impeller body. The centrifugal vane 37 is designed so that the area of an outer channel 36, which is defined by the centrifugal vane 37, in an angle range of 270° in a peripheral direction from the trailing edge of the centrifugal vane 37 to the total area of the impeller body surrounded by the outer periphery of the impeller body is less than 0.3.

Description

TECHNICAL FIELD

The present disclosure relates to centrifugal pump impellers suitable for conveying, for example, sewage and the like, and centrifugal pumps including such impellers.

BACKGROUND ART

Conventionally, centrifugal pumps have been used for conveying sewage and the like. The centrifugal pumps include, as primary components, impellers and casings. Of the impellers, non-clogging type impellers inside which helical channels are formed have been known as impellers that are hardly clogged with sewage and the like including solid material, such as contaminants, for example (see Patent Document 1, for example).

The centrifugal pump impeller disclosed in Patent Document 1 includes an inner channel extending upward from an inlet formed at the lower surface, and an outer channel defined by a centrifugal vane to turn along the outer peripheral surface and continuing to the inner channel. In this centrifugal pump, the ratio between the passage diameter (the maximum diameter of a ball passable through a channel) and the bore diameter of the pump is set at 100%.

CITATION LIST

Patent Document

• Patent Document 1: Japanese Patent Publication No. 2005-36778

SUMMARY OF THE INVENTION

Technical Problem

Such sewage pumps are required to have a high pump head in a low flow rate region as a pump characteristic in many cases. One of effective strategies for satisfying such a pump characteristic is to increase the outer diameters of the impellers. However, an increases in outer diameter of an impeller increases the required power of the pump. In view of this, the present inventors attempted to increase the outer diameter of an impeller without changing the required power by making the inclination of the head curve (a curve indicating the relationship between a discharge amount and a total pump head) sharp by changing the specification of the impeller, rather than by merely increasing the outer diameter of the impeller.

As a strategy for this, the present inventors considered narrowing the outlet width of an impeller. This can throttle the discharge flow rate to make the inclination of the head curve sharp.

However, narrowing the outlet width of the impeller reduces the passage diameter. As a consequence, it was found that the new disadvantage that the ratio between the passage diameter and the bore diameter of the pump to cannot be maintained at a predetermined value, for example, 100% may occur.

In a centrifugal pump including an impeller including a helical inner channel and an outer channel contributing to its pump head, the techniques disclosed herein are advantageous in increasing the pump head in a low flow rate with its passage diameter maintained at a predetermined value.

Solution to the Problem

Specifically, the present inventors considered a reduction in ratio of the outer channel occupying a transverse cross section of an impeller. This corresponds to a comparatively small amount of fluid being present in the outer channel and discharged from the impeller. For this reason, the discharge flow rate of this impeller is throttled when compared with an impeller having comparatively large ratio of the occupying outer channel under the condition of the same outer diameter. On the other hand, the outlet width (corresponding to the height in axial direction) is not narrowed, thereby maintaining the passage diameter at a predetermined value.

An example centrifugal pump impeller is a centrifugal pump impeller having a predetermined passage diameter, which includes: an impeller body in which a helical inner channel is formed, the inner channel turning about a rotational axis while extending in an axial direction so as to connect an inlet opening in one end surface to an outlet opening in a peripheral surface of the impeller body; and a single centrifugal vane provided in the impeller body so as to have a leading edge at the outlet and a trailing edge at a predetermined point of an outer periphery of the impeller body.

In the centrifugal pump impeller, the centrifugal vane is formed to extend over an angle range of 270° or more in a peripheral direction about the rotational axis as a center, and defines an outer channel recessed from the peripheral surface of the impeller body, the outer channel continuing to the outlet and turning along the peripheral surface of the impeller body, and in a transverse cross section of the outer channel at a center in the axial direction, a ratio of an area of the outer channel in an angle range of 270° in the peripheral direction from the trailing edge of the centrifugal vane to a total area of the impeller body surrounded by the outer periphery of the impeller body, that is,

area ratio=(area of outer channel)/(total area of impeller body)

is less than 0.3.

Advantages of the Invention

The impeller with this configuration can achieve a high pump head in a low flow rate with the passage diameter maintained at a predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a submersible pump.

FIG. 2 is a perspective view of an impeller.

FIG. 3 is a transverse cross-sectional view (a cross-sectional view taken along the line III-III in FIG. 5) of the impeller.

FIG. 4 is a vertical cross-sectional view (a cross-sectional view taken along the line IV-IV in FIG. 3) of the impeller.

FIG. 5 is a vertical cross-sectional view (a cross-sectional view taken along the line V-V in FIG. 3) of the impeller.

FIG. 6 is graphs of performance curves (pump head coefficient vs. flow rate coefficient) of submersible pumps according to an example.

FIG. 7 is graphs of performance curves (power coefficient vs. flow rate coefficient) of the submersible pumps according to an example.

FIG. 8 is graphs of performance curves (pump efficiency vs. flow rate coefficient) of the submersible pumps according to an example.

DESCRIPTION OF EMBODIMENTS

An example impeller is a centrifugal pump impeller including an impeller body and a single centrifugal vane. In the impeller body, a helical inner channel is formed which turns in the axial direction while extending in the axial direction so as to connect an inlet opening in one end surface to an outlet opening to the peripheral surface of the impeller body. The centrifugal vane is provided in the centrifugal impeller body to have a leading edge located at the outlet and a trailing edge located at a predetermined point of the outer peripheral edge of the impeller body. The impeller has a passage diameter set at a predetermined value.

The centrifugal vane is formed to extend over an angle range of 270° or more in the peripheral direction about the rotational axis as a center. The outer channel, which is recessed from the peripheral surface of the impeller body and is defined by the centrifugal vane, continues to the outlet and turns along the peripheral surface of the impeller body. The centrifugal vane is designed so that, in a transverse cross section of the outer channel at the center in the axial direction, the ratio of the area of the outer channel in the angle range of 270° in the peripheral direction from the trailing edge of the centrifugal vane to the total area of the impeller body surrounded by the outer periphery of the impeller body is less than 0.3.

In this configuration, the centrifugal vane is designed so that, in the predetermined transverse cross section, the ratio of the area of the outer channel in the angle range of 270° in the peripheral direction from the trailing edge of the centrifugal vane to the total area of the impeller body surrounded by the outer periphery of the impeller body (i.e., the area of a circle surrounded by the outer periphery), herein, a value obtained by dividing the area of the outer channel by the total area of the impeller body (hereinafter referred to simply as an area ratio) is less than 0.3. It is noted that the area ratio is larger than 0. That is, the impeller has a comparatively low ratio of the outer channel occupying the transverse cross section. This corresponds to a comparatively small amount of fluid being present in the outer channel and discharged from the impeller. Accordingly, in this impeller, the discharge flow rate is throttled when compared with an impeller having the same outer diameter and a comparatively large area ratio. This makes a centrifugal pump including the impeller with this configuration to have a sharp head curve and to have reduced shaft power. As a consequence, even if the required power of the centrifugal pump is equivalent to that of the conventional one, the impeller body can have an increased outer diameter, thereby increasing the pump head. In other words, a high pump head in a low flow rate can be achieved.

In this configuration, further, the transverse cross-sectional area of the outer channel is reduced, while the outlet width is not narrowed. This can maintain the passage diameter at a predetermined value. As a consequence, the impeller with this configuration can achieve a high pump head in a low flow rate even with the passage diameter maintained at a predetermined value. The ratio between the passage diameter and the bore diameter of the pump may be 100%.

An example centrifugal pump includes the above centrifugal pump impeller, a casing that houses the centrifugal pump impeller, and a motor that drives and rotates the centrifugal pump impeller. As described above, the centrifugal pump can achieve a high pump head in a low flow rate.

Example embodiments of the impeller will be described below with reference to the accompanying drawings. It is noted that the following preferable example embodiments are merely substantial examples. As shown in FIG. 1, the example pump is a submersible pump for sewage disposal. The submersible pump is configured by a centrifugal pump 10, and includes an impeller 11, a casing 12 that covers the impeller 11, and a sealed submersible motor 13 that rotates the impeller 11.

The submersible motor 13 includes a motor 16 including a stator 14 and a rotor 15, and a motor casing 17 that covers the motor 16. A vertically extending drive shaft 18 is provided at the central part of the rotor 15. The drive shaft 18 is rotatably supported by an upper bearing 19 and a lower bearing 20. The lower end of the drive shaft 18 is coupled to the impeller 11. The drive shaft 18 transmits the rotational power of the submersible motor 13 to the impeller 11.

The casing 12 includes inside thereof a volute casing 26 that covers the impeller 11. The volute casing 26 is defined by a side wall 12a curved in a semispherical shape when viewed in vertical cross section. The width of the volute casing 26 in the axial direction (width in the vertical direction in FIG. 1, i.e., height in the axial direction) is substantially equal to the width (height in the axial direction) of an outlet 34 of the impeller 11, which will be described later.

At the lower end of the casing 12, a downwardly protruding suction portion 21 is formed integrally. In the suction portion 21, a downwardly opening suction port 22 is formed. The suction port 22 communicates with an inlet 33 of the impeller 11, which will be described later. On the other hand, a laterally protruding discharge portion 23 is integrally formed at the side part of the casing 12. The discharge portion 23 communicates with the volute casing 26, and forms a laterally opening discharge port 24. The flow path diameter of the discharge portion 23 increases as it goes downstream in the present example embodiment, but is not limited thereto and may be set constant. The diameter of the inlet (connection port to the volute casing 26) of the discharge portion 23 is substantially equal to the diameter of the outlet 34 of the impeller 11, which will be described later. That is, the discharge portion 23 is set to have the same passage diameter as an inner channel 35 of the impeller 11, and the ratio between the passage diameter and the bore diameter of this pump is set at 100%. In this pump, the minimum bore diameter of the discharge portion 23 corresponds to the bore diameter of the pump. It is noted that the passage diameter of the discharge portion 23 may be equal to or larger than that of the inner channel 35.

As shown in FIG. 2 to FIG. 5, the impeller 11 forms a substantially cylindrical shape including an upper end surface, a lower end surface, and a peripheral surface therebetween. It is noted that the cross hatched region in FIG. 3 does not indicates a cross section, but indicates an outer channel 36, which will be described later. The lower end surface of the impeller 11 forms the inlet 33 opening downward. The peripheral surface forms the outlet 34 opening laterally. The impeller 11 includes thereinside the inner channel 35 turning about the rotational axis and extending in the axial direction. The inner channel 35 connects the inlet 33 to the outlet 34. Accordingly, the level of the center of the flow path of the inner channel 35 changes in the axial direction. As shown in FIG. 3, the outlet 34 opens in the direction that the inner channel 35 extends. The inner channel 35 including the inlet 33 and the outlet 34 is configured to have a passage diameter set according to the pipe diameter on the upstream side of the centrifugal pump 10. Here, the diameter of the inner channel 35 is set comparatively large so as to be a predetermined passage diameter.

In the outer peripheral surface of the impeller 11, the outer channel 36 recessed inward in the radial direction is formed. The outer channel 36 is not a flow path extending in the axial direction, and the center of its flow path is located on a plane orthogonal to the rotational axis of the impeller 11. As shown in FIG. 3, the outer channel 36 continues to the downstream end of the inner channel 35 at the outlet 34. The outer channel 36 turns over the length of one half or larger of the periphery of the impeller 11. Specifically, the downstream end of the outer channel 36 extends to the vicinity of the outlet 34, thereby allowing the outer channel 36 to extend in an angle range of 270° in the peripheral direction about the rotational axis as a center. It is noted that the length of the outer channel 36 may be appropriately set in a range equal to or larger than 270° and smaller than 360°.

The outer channel 36 is defined by a vane 37. The vane 37 is a so-called radial flow vane (centrifugal vane). This centrifugal vane 37 increases the pressure of water in the outer channel 36, and discharges the water to the outer peripheral side (radially outward). Here, the centrifugal vane 37 not only defines the outer channel 36 but also defines the inner channel 35 by its inside surface. The centrifugal vane 37 is formed to extend over an angle range of 270° or more in the peripheral direction about the rotational axis as a center. Particularly, in the present example embodiment, it is formed to extend in an angle range of 270°, thereby allowing the outer channel 36 to extend in an angle range of 270°, as described above. Further, the outlet angle of the centrifugal vane 37 is set comparatively small in the present example embodiment. Specifically, the outlet angle is set at approximately 10°.

In the centrifugal vane 37, its leading edge is located at a point comparatively outward in the radial direction, thereby comparatively reducing the aforementioned transverse cross-sectional area of the outer channel 36. Specifically, in the transverse cross section of the outer channel 36 at the center in the axial direction, the ratio of the transverse cross-sectional area of the outer channel 36 (the area of the cross hatched region in FIG. 3) to the total area of the impeller surrounded by the outer periphery of the impeller 11 (the area of the circle in FIG. 3), that is, a value (area ratio) obtained by dividing the area of the outer channel 36 by the total area of the impeller is set to be less than 0.3. In the impeller 11, since the cross-sectional area of the outer channel 36 is set comparatively small in this way, the amount of fluid present in the outer channel 36 is reduced. This throttles the discharge flow rate of the impeller 11, thereby making the inclination of the head curve sharp and reducing the shaft power, as will be described later. It is noted that, in place of change in position of the leading edge, the design function for defining and configuring the outer channel 36 may be appropriately changed to change the shape of the outer channel 36, thereby setting the area ratio to be less than 0.3.

Here, in this impeller 11, the design function for defining and configuring the inner channel 35 is different from that for defining and configuring the outer channel 36. For this reason, usually, the outer channel 36 does not smoothly continue to the inner channel 35 in the vicinity of the outlet 34 of the inner channel 35. However, in the present example embodiment, an arc is formed in the vicinity of the end part of the centrifugal vane 37 (the vicinity indicated by reference character 100 in FIG. 3) to smoothly connect the outer channel 36 to the inner channel 35. Accordingly, in the impeller 11, the leading edge of the centrifugal vane 37 is hard to be apparent. It is noted that, in the impeller 11 shown in FIG. 3, the point where the vertically extending dashed line in FIG. 3 is intersected with the outer surface of the centrifugal vane 37 corresponds to the leading edge of the centrifugal vane 37.

In the impeller 11, a first flange 38 protruding laterally over the entire periphery is formed at a part upper than the outer channel 36. Similarly, a second flange 39 protruding laterally over the entire periphery is formed at a part lower than the outer channel 36. The second flange 39 transversely partitions the impeller 11 into a lower portion in which the inlet 33 is formed and an upper portion in which the outlet 34 is formed. That is, the impeller 11 is a closed type impeller in which the inlet 33 and the outlet 34 are partitioned by the second flange 39. Here, in this impeller 11, the distance between the first flange 38 and the second flange 39 is set equal to the width of the outlet 34 (height in the axial direction), as shown in FIG. 4, for example.

It is noted that a boss portion 31 is formed at the central part of the upper end surface of the impeller 11, and a mounting hole 32 is formed in the boss portion 31 for receiving the tip end of the drive shaft 18.

The centrifugal pump 10 discharges sewage in the following manner. That is, when the submersible motor 13 rotates the impeller 11, the impeller 11 sucks sewage upward from the inlet 33 on its lower side. The sucked sewage passes through the inner channel 35 of the impeller 11, and reaches the outer channel 36 via the outlet 34. The centrifugal vane 37 discharges the sewage reaching the outer channel 36 to the outer peripheral side. The casing 12 covering the impeller 11 receives the discharged sewage. The sewage flows in the volute casing 26, and then is discharged outside the pump via the discharge port 24.

Examples actually carried out will be described next. FIG. 6 to FIG. 8 indicate performance curves of centrifugal pumps 10 including impellers 11 having different area ratios. FIG. 6 indicates dependencies of pump head coefficients on a flow rate coefficient. FIG. 7 indicates dependencies of power coefficients on the flow rate coefficient. FIG. 8 indicates dependencies of pump efficiencies on the flow rate coefficient. The legend symbols in FIG. 6 to FIG. 8 are common to one another, and are indicated only in FIG. 6. Here, the outer diameter, the width of the outlet 34, the position of the trailing edge of the centrifugal vane 37, and outlet angle) (10°) are the same in the impellers 11. On the other hand, the positions of the leading edges of the centrifugal vanes 37 are differentiated to change the cross-sectional shape of the centrifugal vane 37, thereby varying the cross-sectional area of the outer channel 36, and in turn the aforementioned area ratio. That is, the position of the leading edge of the centrifugal vane 37 is changed outward in the radial direction to relatively reduce the cross-sectional area of the outer channel 36, thereby decreasing the area ratio. Conversely, the position of the leading edge of the centrifugal vane 37 is changed inward in the radial direction to relatively increase the cross-sectional area of the outer channel 36, thereby increasing the area ratio. It is noted that the area ratios of 0.252 and 0.230 correspond to the examples. The area ratios of 0.375 and 0.203 correspond to a conventional example and a comparative example, respectively.

The results indicated in FIG. 6 to FIG. 8 show that a reduction in area ratio from 0.375 to 0.252, to 0.230, then to 0.203 gradually changes the inclination of the head curve in a direction it becomes sharp, and gradually reduces the power coefficient also. However, too small area ratio reduces the shutoff head to reduce the pump efficiency as a whole (see crosses). Accordingly, the examples prove that it is preferable to set the area ratio in a range less than 0.30 and equal to or larger than 0.23 for making the inclination of the head curve sharp and reducing the power coefficient.

Thus, the impeller 11 and the centrifugal pump 10 exemplified herein have a sharp inclination of the head curve and have reduced shaft power by setting the area ratio to be less than 0.3. Accordingly, even if the required power is equivalent to that of the conventional one, the outer diameter of the impeller 11 can be increased to increase the pump head. Thus, a high pump head in a low flow rate can be achieved in the centrifugal pump 10.

In addition, setting the outlet angle of the centrifugal vane 37 to be comparatively small also contributes to making the inclination of the head curve sharp. Thus, the impeller 11 and the centrifugal pump 10 exemplified herein can have a further sharp inclination of the head curve by a combination of setting the aforementioned area ratio to be comparatively small and setting the outlet angle to be comparatively small (approximately 10° in the present example embodiment), thereby achieving a further higher level of the pump head in a low flow rate in the centrifugal pump 10.

INDUSTRIAL APPLICABILITY

As described above, the techniques disclosed herein are useful for centrifugal pumps for conveying fluids, and for example, are useful for sewage treatment pumps for conveying sewage including contaminants and the like.

DESCRIPTION OF REFERENCE CHARACTERS

• • 10 centrifugal pump
  • 11 impeller (impeller body)
  • 12 casing
  • 13 submersible motor (motor)
  • 18 drive shaft (rotational axis)
  • 34 outlet
  • 35 inner channel
  • 36 outer channel
  • 37 centrifugal vane

Claims

1. A centrifugal pump impeller having a predetermined passage diameter, comprising: an impeller body in which a helical inner channel is formed, the inner channel turning about a rotational axis while extending in an axial direction so as to connect an inlet opening in one end surface to an outlet opening in a peripheral surface of the impeller body; anda single centrifugal vane provided in the impeller body so as to have a leading edge at the outlet and a trailing edge at a predetermined point of an outer periphery of the impeller body, whereinthe centrifugal vane is formed to extend over an angle range of 270° or more in a peripheral direction about the rotational axis as a center, and defines an outer channel recessed from the peripheral surface of the impeller body, the outer channel continuing to the outlet and turning along the peripheral surface of the impeller body, andin a transverse cross section of the outer channel at a center in the axial direction, a ratio of an area of the outer channel in an angle range of 270° in the peripheral direction from the trailing edge of the centrifugal vane to a total area of the impeller body surrounded by the outer periphery of the impeller body is less than 0.3.

2. The centrifugal pump impeller of claim 1, wherein a ratio of the passage diameter to a bore diameter of the pump is 100%.

3. A centrifugal pump, comprising: a centrifugal pump impeller;a casing that houses the centrifugal pump impeller; anda motor that drives and rotates the centrifugal pump impeller, whereinthe centrifugal pump impeller has a predetermined passage diameter, and includes an impeller body in which a helical inner channel is formed, the inner channel turning about a rotational axis while extending in an axial direction so as to connect an inlet opening in one end surface to an outlet opening in a peripheral surface of the impeller body, anda single centrifugal vane provided in the impeller body so as to have a leading edge at the outlet and a trailing edge at a predetermined point of an outer periphery of the impeller body,the centrifugal vane is formed to extend over an angle range of 270° or more in a peripheral direction about the rotational axis as a center, and defines an outer channel recessed from the peripheral surface of the impeller body, the outer channel continuing to the outlet and turning along the peripheral surface of the impeller body, andin a transverse cross section of the outer channel at a center in the axial direction, a ratio of an area of the outer channel in an angle range of 270° in the peripheral direction from the trailing edge of the centrifugal vane to a total area of the impeller body surrounded by the outer periphery of the impeller body is less than 0.3.

4. The centrifugal pump of claim 3, wherein a ratio of the passage diameter to a bore diameter of the pump is 100%.