JP7261142B2 - pump - Google Patents

Description

The present invention relates to pumps.

Conventionally, a pump is known in which an outer trumpet portion, an inner trumpet portion inside the trumpet portion, and an axial center trumpet portion further inside thereof are provided at the lower end of a pumping pipe, and vortex prevention ribs are formed on the outer surface of the axial center trumpet portion. (See Patent Document 1, for example).

Although the conventional pump can effectively prevent the generation of underwater vortices generated in the fluid, further improvement is required to prevent the generation of air entrainment vortices. That is, since it is placed in the fluid of the suction tank and used, a high water level portion and a low water level portion are generated around it. On the other hand, water absorption by the pump is performed uniformly from the surroundings. For this reason, there is a risk that an air entrainment vortex will be generated in a portion where the water level is low.

Japanese Patent No. 5345123

An object of the present invention is to provide a pump that can effectively suppress the generation of not only underwater vortices but also air entrainment vortices.

As a means for solving the above problems, the present invention includes a hollow cylindrical pump body having a bell mouth on one end side, and a main shaft disposed in the pump body and having an impeller on one end side. The bell mouth includes an outer bell mouth portion connected to the pump body and an inner bell mouth portion disposed inside the outer bell mouth portion, wherein one end opening of the outer bell mouth portion and the inner side bell mouth portion are arranged. A first suction port is formed between the bell mouth portion and one end opening portion, a second suction port is formed by the one end opening portion of the inner bell mouth portion, and the outer bell mouth portion has an outer suction port, The inner bell-mouth portion has an inner suction port at a position corresponding to the outer suction port, and provides a pump provided with a communication passage that communicates the outer suction port and the inner suction port.

According to this configuration, it is possible to reduce the generation of underwater vortices by the first suction port and the second suction port. Further, the fluid can be sucked through the communicating passage not only from the first suction port and the second suction port, but also from the outer suction port of the outer bell mouth portion. Therefore, by locating the outer suction port at a location where the water level is high around the bell mouth, it is possible to suppress variations in the water level from other locations and reduce the occurrence of air intake vortices.

Preferably, the bell mouth is arranged in the fluid, and the outer suction port has a first outer suction port that opens upstream in the flow direction of the fluid.

According to this configuration, the bell mouth blocks the flow of the fluid and absorbs water from the first outer suction port that opens on the upstream side in the flow direction where the water level tends to rise. water level difference can be suppressed.

Further, the outer suction port includes a second outer suction port that opens downstream in the flow direction of the fluid , and the inner suction port includes a first inner suction port corresponding to the first outer suction port and the second outer suction port. a second inner suction port corresponding to the outer suction port, wherein the second inner suction port is formed closer to the second suction port than the first inner suction port; It is preferable to have a first communication passage that communicates the suction port and the first inner suction port, and a second communication passage that communicates the second outer suction port and the second inner suction port.

According to this configuration, the flow rate in the second communication path can be made smaller than that in the first communication path. That is, it is possible to increase the flow rate of water sucked from the first outer suction port to lower the water level in the vicinity thereof, and reduce the flow rate of suction from the second outer suction port to suppress the decrease in the water level in the vicinity thereof.

It is preferable that the outer bell mouth portion and the inner bell mouth portion are connected by a rectifying plate, and the rectifying plate is formed in a hollow shape to function as the communication path.

According to this configuration, the straightening plate for suppressing the swirl flow can also be used as the communication passage, so the configuration can be simplified.

It is preferable that the shape of the current plate is displaced from the outer bell mouth portion toward the inner bell mouth portion in the rotational direction of the impeller.

According to this configuration, the flow of the fluid can be made smooth by aligning the shape of the rectifying plate along the rotation direction of the impeller.

It is preferable that the bell mouth is arranged in a downstream area in the flow direction in the suction tank, and the outer suction port opens toward the upstream side in the flow direction.

According to this configuration, under the condition that the presence of the bellmouth hinders the flow and the water level on the downstream side drops, the amount of water absorption on the upstream side is increased to lower the water level, thereby lowering the water level on the downstream side. difference can be suppressed.

It is preferable that the bell mouth is arranged in a confluence region of flows from two directions in the suction tank, and the outer suction ports are formed at two locations that open upstream in each flow direction.

According to this configuration, even when the water flows into the suction tank from two directions, by opening the outer suction port on the upstream side of each inflow direction, the water surface of the suction tank on the outer periphery of the bell mouth is uneven. It is possible to appropriately prevent water level bias due to the difference.

According to the present invention, since the bell mouth has a double structure consisting of the outer bell mouth portion and the inner bell mouth portion, it is possible to suppress the generation of underwater vortices. In particular, since the water absorption speed is reduced by sucking the fluid also from the outer suction port formed in the outer bell-mouth portion, the effect of suppressing the generation of underwater vortices can be enhanced.

In addition, the water level in the area around the bellmouth where the outer suction port opens can be lowered. Therefore, by arranging the pump so that the outer suction port opens in a region where the water level is high, it is possible to reduce the difference in water level with other regions and suppress the occurrence of air suction vortices.

It is a schematic sectional view of the vertical shaft pump which concerns on this embodiment. FIG. 2 is an enlarged view showing the bell mouth of FIG. 1; 3 is a schematic bottom view of FIG. 2; FIG. FIG. 3 is a cross-sectional view of the straightening plate shown in FIG. 2 ; It is a graph which shows the relationship between the distance from the lower end opening of a bell mouth to the upper end of an inner suction port, and pressure difference, flow volume, and flow velocity. FIG. 4 is a schematic cross-sectional view of a horizontal shaft pump according to another embodiment; It is a schematic plan view of a bell mouth, showing the case where (a) is formed at three places, (b) is at one place, (c) is at two places, and (d) is formed at four places. FIG. 11 is a schematic cross-sectional view of a bell mouth according to another embodiment; FIG. 9 is a schematic bottom view of FIG. 8; FIG. 11 is a schematic cross-sectional view of a bell mouth according to another embodiment; 11 is a schematic bottom view of FIG. 10; FIG. FIG. 11 is a schematic cross-sectional view of a bell mouth according to another embodiment; 13 is a schematic bottom view of FIG. 12; FIG. FIG. 11 is a schematic cross-sectional view of a bell mouth according to another embodiment;

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the following description is essentially merely an example, and is not intended to limit the present invention, its applications, or its uses.

As shown in FIG. 1, a vertical shaft pump 1 according to the present embodiment has a structure in which a main shaft 4 having an impeller 3 at its lower end is arranged in a water pump 2, which is an example of a pump body.

The pumping pipe 2 has a hollow cylindrical shape, and its axis extends along the vertical direction. A discharge elbow 5 is connected to the upper end opening of the pumping pipe 2 . The discharge elbow 5 is bent sideways and its tip is open in the horizontal direction. An impeller housing portion 6 is connected to the lower end opening of the pumping pipe 2 , and a bellmouth 7 is connected to the lower end of the pumping pipe 2 on the same axis as the pumping pipe 2 .

The impeller housing portion 6 has a hollow cylindrical shape, and has an upper end opening connected to a lower end opening of the pumping pipe 2 . The impeller accommodating portion 6 gradually increases radially outward from the upper end opening toward the lower end opening, and then gradually decreases radially inward.

As shown in FIGS. 2 and 3, the bell mouth 7 has a double structure consisting of an outer bell mouth portion 8 and an inner bell mouth portion 9 , which are connected by a plurality of rectifying plates 10 .

The outer bell mouth portion 8 has a hollow tubular shape and gradually widens radially outward from the upper end opening toward the lower end opening. An upper end opening of the outer bell mouth portion 8 is connected to a lower end opening of the impeller housing portion 6 . The outer bell mouth portion 8 is formed with an outer suction port 11 that communicates between the outer surface and the inner surface. The outer suction port 11 is formed at three locations, a first outer suction port 11a and, with this first outer suction port 11a as a reference, rotating clockwise and counterclockwise about the axis indicated by the dashed line in FIG. It is composed of a second outer suction port 11b and a third outer suction port 11c arranged at positions rotated by 90° in the circumferential direction.

The inner bellmouth portion 9 has a hollow cylindrical shape, with an upper half portion 9a extending vertically with the same diameter, and a lower half portion 9b gradually widening radially outward toward the lower end opening. The inner bell mouth portion 9 is formed with an inner suction port 12 that communicates between the outer surface and the inner surface. The inner suction port 12 is composed of a first inner suction port 12a, a second inner suction port 12b, and a third inner suction port 12c, which are respectively formed at positions corresponding to the first outer suction port to the third outer suction port. there is The first inner suction port 12a is formed in the upper half portion 9a of the inner bell mouth portion 9, and the second inner suction port 12b and the third inner suction port 12c are formed in the lower half portion 9b.

The current plate 10 is hollow and connects the outer bell mouth portion 8 and the inner bell mouth portion 9 . The cross-sectional shape of each current plate 10 is as shown in FIG. That is, it gradually curves downward from the arc portion at the upper end to reach the arc portion at the lower end. Each rectifying plate 10 is formed in a spiral shape, that is, gradually inclined in one direction in the circumferential direction from the lower end opening of the bell mouth 7 toward the upper end opening. The direction in which each current plate 10 is inclined matches the rotation direction of the impeller 3, which will be described later. In this embodiment, the outer bell mouth portion 8 and the inner bell mouth portion 9 are connected by four current plates 10 . A space between the outer bell mouth portion 8 and the inner bell mouth portion 9 is circumferentially divided into four equal parts by the current plate 10 to form four swirl restricting flow paths 13 . The internal spaces of three of the four rectifying plates 10 form communication passages 14 that communicate the outer suction port 11 of the outer bell mouth portion 8 and the inner suction port 12 of the inner bell mouth portion 9 . The internal space of the first straightening plate 10a that communicates the first outer suction port 11a and the first inner suction port 12a communicates the first communication passage 14a, the second outer suction port 11b and the second inner suction port 12b. The internal space of the plate 10b is the second communication path 14b, and the internal space of the third straightening plate 10c that communicates the third outer suction port 11c and the third inner suction port 12c is the third communication path 14c.

The inner bell mouth portion 9 protrudes downward from the lower end opening of the outer bell mouth portion 8 except for the upper portion. A first suction port 15 is located between the lower end opening of the outer bell mouth portion 8 and the lower end opening of the inner bell mouth portion 9 . A lower end opening of the inner bell mouth portion 9 is the second suction port 16 . The three outer suction ports 11 are the third suction ports 17 .

The main shaft 4 is arranged on the axis of the pumping pipe 2 . The upper portion of the main shaft 4 passes through the discharge elbow 5 and is rotatably supported by a bearing portion 18 attached to the discharge elbow 5 so that a rotational force is applied from a driving means such as a motor (not shown). . An impeller 3 is attached to the lower portion of the main shaft 4 and arranged in an impeller housing portion 6 . When the main shaft 4 is rotated by the driving means, the impeller 3 is rotated, and the water in the suction tank 20 is sucked into the water discharge pipe 2 through the first suction port 15, the second suction port 16 and the third suction port 17. and are being transported to other locations. A mixing chamber 19 is formed between the impeller 3 and the bell mouth 7 so that the water flowing through the center hole 9c of the inner bell mouth portion 9 and the water flowing through the swirling restricting flow path 13 are mixed. It's becoming

The vertical shaft pump 1 constructed as described above is used with its lower portion installed in the fluid in the water suction tank 20 . In the example of FIGS. 2 and 3, the water suction trough 20 is designed so that water flows in from the left side and ends at the right wall. The vertical shaft pump 1 is installed so that the first outer suction port 11a opens toward the upstream side in the water flow direction in the vicinity of the right wall (downstream region), which is the end point in the water flow direction. Therefore, the second outer suction port 11b and the third outer suction port 11c are opened on both sides of the intermediate position in the flow direction.

When the main shaft 4 is rotated by a driving means (not shown), the impeller 3 rotates integrally with the main shaft 4, and surrounding water is sucked through the first suction port 15, the second suction port 16 and the third suction port 17. be

Water on the lower side of the first suction port 15 is sucked into the center hole 9 c of the inner bell mouth portion 9 . From the second suction port 16, the water on the outer peripheral side of the area sucked from the first suction port 15 is sucked into the swirling restriction flow path 13 and flows while being restricted from swirling. A lower end opening of the bellmouth 7 is divided into a first suction port 15 and a second suction port 16, and flows through the center hole 9c and the swirl restriction flow path 13, respectively. As a result, a swirling flow is less likely to occur within the bellmouth 7, and an underwater vortex can be prevented from occurring on the suction side.

Water around the outer bell mouth portion 8 is sucked into the communication passage 14 from the third suction port 17 and joins the water flowing through the center hole 9 c of the inner bell mouth portion 9 . By forming the third suction port 17, the total value of the opening area of the suction ports at the bell mouth 7 can be increased. Therefore, the speed of water absorption from the first suction port 15 and the second suction port 16 can be suppressed without reducing the amount of water absorbed by the bell mouth 7 as a whole. This point is also effective in preventing the generation of underwater vortices. The water flowing through the center hole 9c of the inner bell mouth portion 9 and the swirling restricting flow path 13 is merged in the mixing chamber 19, then ascends the water pump 2 and is transported to another location.

By the way, there is the following relationship between the distance Z from the lower end position of the inner bell mouth portion 9 to the upper end position of the inner suction port 12 and the flow rate.

As shown in the graph of FIG. 5, the larger the distance Z, in other words, the closer the position of the inner suction port 12 to the impeller 3, the faster the flow velocity V sucked by the inner suction port 12 and the outer suction port. The pressure difference ΔH between 11 and the inner suction port 12 increases, and the flow rate q sucked from the outer suction port 11 increases.

As shown in FIG. 3 , the position of the first inner suction port 12 a is the upper half portion 9 a of the inner bell mouth portion 9 . On the other hand, the positions of the second inner suction port 12b and the third inner suction port 12c are the lower half portion 9b of the inner bell mouth portion 9. As shown in FIG. That is, the first inner suction port 12a is located above the second inner suction port 12b and the third inner suction port 12c, and the distance Z is large. Therefore, compared to the second communication passage 14b from the second outer suction port 11b to the second inner suction port 12b and the third communication passage 14c from the third outer suction port 11c to the third inner suction port 12c, the The flow rate in the first communication passage 14a from the outer suction port 11a to the first inner suction port 12a increases. That is, the amount of water absorbed from the first outer suction port 11a can be increased, and the amount of water absorbed from the second outer suction port 11b and the third outer suction port 11c can be suppressed.

In FIG. 3, the two-dot chain line virtually shows the water absorption distribution around the bell mouth 7 . Since the first outer suction port 11a is opened on the upstream side, and the second outer suction port 11b and the third outer suction port 11c are opened on both sides, the water absorption amount on the upstream side spreads to both sides as a whole. are increasing.

As shown in FIG. 8, the fluid flow in the suction tank 20 is interrupted by the bell mouth 7 of the vertical shaft pump 1, so the water level on the downstream side is lower than on the upstream side. In particular, when the distance between the bellmouth 7 and both side walls of the water suction tank 20 is narrow, the water level difference between the upstream side and the downstream side tends to increase further. Therefore, if water is uniformly absorbed from the periphery of the bell mouth 7, an air intake vortex is likely to occur on the downstream side where the water level is low. When an air-sucking vortex is generated, air is sucked into the pumping pipe 2, causing cavitation.

As described above, the amount of water absorbed flowing into each communication passage 14 from each of the outer suction ports 11 opened at three locations around the outer bell mouth portion 8 is determined by the first outer suction port 11a, the second outer suction port 11b, and the second outer suction port 11b. It is made different from the third outer suction port 11c to give directivity to the suction performance. That is, the amount of water absorbed by each suction port 11 is maximized at the first outer suction port 11a and decreased at the second outer suction port 11b and the third outer suction port 11c. As a result, the amount of water absorbed on the upstream side in the flow direction in the water suction tank 20 is increased to lower the water level, while the amount of water absorbed on the downstream side is decreased to prevent the water level from dropping too much. . In other words, it is possible to keep the surrounding water level almost the same by achieving a balance between areas that require water absorption and areas that do not. As a result, it is possible to prevent the occurrence of an air entrainment vortex due to a low water level at a specific location.

According to the vertical shaft pump 1 configured as described above, the following effects can be obtained.
(1) Since the third suction port 17 is formed in addition to the first suction port 15 and the second suction port, the total opening area of the suction ports can be increased to reduce the flow velocity. As a result, together with the double structure of the outer bell mouth portion 8 and the inner bell mouth portion 9, it is possible to effectively suppress the generation of underwater vortices.
(2) By making the amount of water absorbed by each of the outer suction ports 11 constituting the third suction port 17 different, it is possible to suppress the occurrence of a water level difference around the bell mouth 7 . Therefore, it is possible to prevent the occurrence of an air entrainment vortex due to a partial drop in the water level. Further, by preventing the water level from becoming too low in a part of the pump, even if the water level is low as a whole, the pump can be operated in a stable state while preventing the generation of the air suction vortex.

The present invention is not limited to the configurations described in the above embodiments, and various modifications are possible.

In the above-described embodiment, the configuration of the bell mouth 7 has been described as being applied to the vertical shaft pump 1, but it can also be applied to the horizontal shaft pump 21 shown in FIG.
The horizontal shaft pump 21 has a main shaft 24 that has an impeller 23 at one end and extends horizontally in a casing 22 that is an example of a pump body. The casing 22 consists of a suction casing 25 and a discharge casing 26 . The suction casing 25 curves and extends from a first opening 25a that opens vertically downward, and opens a second opening 25b in the horizontal direction. The discharge casing 26 has an axial center indicated by a dashed line in FIG. 6 extending in the horizontal direction, and an opening 26a on one end side is connected to a second opening 25b. The main shaft 24 is arranged along the axis of the discharge casing 26 extending in the horizontal direction. The impeller 23 at one end of the main shaft 24 is arranged within a bearing casing 27 within the discharge casing 26 . The other end of main shaft 24 penetrates discharge casing 26 and is rotatably supported by bearing 28 . The other end of the main shaft 24 is adapted to transmit a rotational force from a driving means (for example, a motor) (not shown). The bell mouth 7 has the same structure as that of the above-described embodiment, and is connected to the first opening 25a of the suction casing 25. As shown in FIG.

In the above embodiment, the current plate 10 is made hollow so that it can be used as the communication passage 14. However, the outer suction port 11 and the inner suction port 12 are connected by a communication passage (not shown) provided separately. can be

In the above-described embodiment, three communication passages 14 are provided to connect the outer suction port 11 and the inner suction port 12, but the following configuration is also possible. 7(a) to (d) are plan views of the bell mouth 7 and schematically show the number and positions of the outer suction ports 11. FIG. FIG. 7(a) shows the position of the outer suction port 11 when the communicating passages 14 described in the above embodiment are provided at three locations, and FIGS. 7(b) to 7(d) are described below. , the positions of the outer suction ports 11 are respectively shown when the communicating passages 14 are provided at one, two, and four locations. By forming the outer suction port 11, the suction flow rate can be increased at any position around the bell mouth 7, and the suction flow rate can be given directivity. The cases of FIGS. 7B to 7D will be described in detail below.

8 and 9 are detailed explanations of FIG. 7(b), and the communication path 14 is formed only at one location. In this case, the pump may be installed in the suction tank 20 so that the outer suction port 11 opens toward the upstream side in the flow direction. As a result, it is possible to increase the amount of water absorption on the upstream side in the flow direction, which collides with the bellmouth 7 and tends to stay there, as shown by the distribution of the amount of water absorption indicated by the chain double-dashed line in FIG. Then, it becomes possible to suppress the difference in water level between the upstream side and the downstream side in the flow direction with the bell mouth 7 interposed therebetween. The position of the inner suction port 12 may be set according to the flow rate that remains upstream of the bell mouth 7 . Specifically, when used under high flow conditions, the position of the inner suction port 12 may be set on the upper side, and conversely, when used under low flow conditions, the position of the inner suction port 12 may be set on the lower side. should be set to

10 and 11 are detailed explanations of FIG. 7(c), and the communicating passages 14 are formed at two locations. Each communicating passage 14 is arranged such that the first inner suction port 12a and the second inner suction port 12b are located on the same upper side in the height direction, and the first outer suction port 11a and the second inner suction port 12b are arranged as indicated by the two-dot chain line in FIG. The amount of water absorption of the second outer suction port 11b is increased, and the difference between the amounts of water absorption is prevented. For example, in the case of a suction tank 20 into which water flows in from two different directions, each outer suction port 11 may be opened in each direction of inflow. As a result, it is possible to suppress the increase in the water level on the upstream side in the inflow direction, and to prevent variations in the water level from occurring around the bellmouth 7, which is the confluence area of the fluids .

12 and 13 are detailed explanations of FIG. 7(d), and the communicating passages 14 are formed in four equal parts around the bell mouth 7. As shown in FIG. Moreover, the position of the inner suction port 12 in the height direction is the same. Therefore, the distribution of the amount of water absorption around the bell mouth 7 is a substantially rectangular shape, as indicated by the chain double-dashed line in FIG. . In this case, the installation of the pump in the water suction sump 20 is such that, for example, in the case of the water suction sump 20 inflowing from two opposing directions, two outer suction ports 11 are opened in each inflow direction, and the other two are open. should be opened in a direction orthogonal to this. When the width dimension of the suction tank 20 is large, the water level is high not only on the upstream side in the flow direction, but also on both sides, resulting in a large flow rate. In this case, by opening the outer suction ports 11 at four locations, the water level around the bell mouth 7 can be lowered and the water level can be prevented from varying.

Thus, by changing the circumferential position of the outer suction port 11 and the height direction position of the inner suction port 12, the water level varies around the bell mouth 7 regardless of the difference in the environment in which the pump is installed. can be properly prevented.

The position at which the outer suction port 11 is formed may be determined according to variations in the water level around the bell mouth 7 when the outer suction port 11 is not formed. For example, the outer suction port 11 can be formed at the highest water level. When a plurality of outer suction ports 11 are formed, as a result of forming the first outer suction port 11, if the water level varies in other parts, the second outer suction port 11 is placed at the position with the next highest water level. should be formed. In the case of forming the third and subsequent outer suction ports 11, they may be formed at positions with higher water levels in the same manner. Moreover, although the case where the number of the outer suction ports 11 is 1 to 4 has been described, the number may be 5 or more.

Further, the position where the inner suction port 12 is formed may be determined according to the water level when the outer suction port 11 is not formed. The position of the inner suction port 12 in the height direction may be determined according to how high the water level is relative to a preset reference value. By forming the inner suction port 12 at a higher position corresponding to the outer suction port 11 formed at a higher water level, the water absorption amount can be increased and the water level can be lowered.

Also, the opening area of each outer suction port 11, the total value of the opening areas of the outer suction ports 11, and the like may be taken into consideration. By making the opening area of each outer suction port 11 different, the water absorption speed at each outer suction port 11 can be changed. By reducing the opening area, the water absorption rate can be increased. By also changing the opening area of the corresponding inner suction port 12, the amount of water absorption can also be changed. By increasing the opening area of the outer suction port 11 and correspondingly increasing the opening area of the inner suction port 12, the amount of water absorption can be increased.

Although not particularly mentioned in the above embodiment, the cross-sectional shape of the rectifying plate 10 may be streamlined. That is, the cross section of the rectifying plate 10 may be formed so that the outer surface shape of the cross section from the suction port side to the impeller side forms a streamline shape. According to this, it is possible to smoothen the flow state in the swirling restriction flow path 13 and prevent a decrease in the flow rate of the transport by the pump.

Although not specifically mentioned in the above embodiment, a filter (not shown) may be provided at the inlet of the communication passage 14 . The filter prevents clogging of the outer suction port 11 and the communication passage 14 with dust and the like contained in water.

In the above-described embodiment, the rectifying plate 10 has a hollow structure, but as shown in FIG. good.

1... Vertical shaft pump 2... Pumping pipe (pump body)
DESCRIPTION OF SYMBOLS 3... Impeller 4... Main shaft 5... Discharge elbow 6... Impeller accommodating part 7... Bell mouth 8... Outside bell mouth part 9... Inside bell mouth part 10... Current plate 11... Outside suction port 12... Inside suction port 13... Turning Regulated flow path 14 Communication passage 15 First suction port 16 Second suction port 17 Third suction port 18 Bearing portion 19 Mixing chamber 20 Suction tank 21 Horizontal shaft pump 22 Casing (pump main body)
DESCRIPTION OF SYMBOLS 23... Impeller 24... Main shaft 25... Suction casing 26... Discharge casing 27... Bearing casing 28... Bearing part

Claims (7)

A hollow cylindrical pump body having a bell mouth on one end side, and a main shaft disposed in the pump body and having an impeller on one end side,
The bell mouth is
an outer bell mouth portion connected to the pump body;
an inner bell mouth portion disposed inside the outer bell mouth portion;
with
forming a first suction port between one end opening of the outer bell mouth and one end opening of the inner bell mouth;
one end opening of the inner bell mouth portion constitutes a second suction port,
The outer bell mouth portion has an outer suction port,
The inner bell mouth portion has an inner suction port at a position corresponding to the outer suction port,
A pump comprising a communication passage that communicates the outer suction port and the inner suction port. 2. The pump according to claim 1, wherein said bell mouth is disposed within a fluid, and said outer suction port comprises a first outer suction port that opens upstream in a flow direction of said fluid. Furthermore, the outer suction port includes a second outer suction port that opens downstream in the flow direction of the fluid ,
The inner suction port has a first inner suction port corresponding to the first outer suction port and a second inner suction port corresponding to the second outer suction port, and the second inner suction port is the second inner suction port. 1 is formed on the second suction port side compared to the inner suction port,
The communication passage has a first communication passage that communicates the first outer suction port and the first inner suction port, and a second communication passage that communicates the second outer suction port and the second inner suction port. 3. A pump according to claim 2. The outer bell mouth portion and the inner bell mouth portion are connected by a rectifying plate,
4. The pump according to any one of claims 1 to 3, wherein the current plate is hollow to function as the communication passage. 5. The pump according to claim 4, wherein the rectifying plate is displaced in the direction of rotation of the impeller from the outer bell mouth portion toward the inner bell mouth portion. The pump according to any one of claims 1 to 5, wherein the bell mouth is arranged in a flow direction downstream region in a suction sump, and the outer suction port opens toward the flow direction upstream side. 6. Said bell mouth is arranged in a confluence region of flows from two directions in a suction tank, and said outer suction ports are formed at two locations respectively opening upstream in respective flow directions. The pump according to any one of Claims 1 to 3.

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