Note: Descriptions are shown in the official language in which they were submitted.
CA 02731127 2011-01-17
DESCRIPTION
IMPELLER FOR CENTRIFUGAL PUMP AND PUMP INCLUDING THE SAME
TECHNICAL FIELD
[0001] 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
[0002] 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).
[0003] The centrifugal pump impeller disclosed in Patent Document I 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
[0004] Patent Document 1: Japanese Patent Publication No. 2005-36778
SUMMARY OF THE INVENTION
TECHNICAL PROBLEM
[0005] Such sewage pumps are required to have a high pump head in a low flow
rate
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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.
[0006] 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.
[0007] 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.
[0008] 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
[0009] 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
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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.
[0010] 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.
[0011] 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
[0012] 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
[0013] [FIG. 1] FIG. 1 is a vertical cross-sectional view of a submersible
pump.
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[FIG. 2] FIG. 2 is a perspective view of an impeller.
[FIG. 3] FIG. 3 is a transverse cross-sectional view (a cross-sectional view
taken
along the line 111-II1 in FIG 5) of the impeller.
[FIG. 4] 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] 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] FIG. 6 is graphs of performance curves (pump head coefficient vs.
flow
rate coefficient) of submersible pumps according to an example.
[FIG. 7] FIG. 7 is graphs of performance curves (power coefficient vs. flow
rate
coefficient) of the submersible pumps according to an example.
[FIG. 8] FIG. 8 is graphs of performance curves (pump efficiency vs. flow rate
coefficient) of the submersible pumps according to an example.
DESCRIPTION OF EMBODIMENTS
[0014] 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.
[0015] 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
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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.
[0016] 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.
[0017] 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
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pump may be 100 %.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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
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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.
[0023] As shown in FIG. 2 to FIG. 5, the impeller l l 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
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channel 35 is set comparatively large so as to be a predetermined passage
diameter.
[0024] 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 .
[0025] 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 .
[0026] 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-
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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 1
1 (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.
[0027] 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.
[0028] 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 1 l into a lower portion
in which the inlet
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33 is formed and an upper portion in which the outlet 34 is formed. That is,
the impeller l 1
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.
[0029] 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.
[0030] The centrifugal pump 10 discharges sewage in the following manner. That
is,
when the submersible motor 13 rotates the impeller 11, the impeller I 1 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.
[0031] 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-
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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.
[0032] 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.
[0033] Thus, the impeller I 1 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.
[0034] 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
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example embodiment), thereby achieving a further higher level of the pump head
in a low
flow rate in the centrifugal pump 10.
INDUSTRIAL APPLICABILITY
[0035] 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
[0036] 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
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