JP4512048B2 - Water supply pump - Google Patents

Description

  The present invention relates to a water supply pump applied to water supply equipment such as a combined power plant.

  From the viewpoint of increasing the efficiency of a power plant, a combined power plant combining a gas turbine and a steam turbine has been proposed. In this combined power plant, high-temperature exhaust gas discharged from the gas turbine is sent to the exhaust heat recovery boiler, steam is generated in the exhaust heat recovery boiler using a heating unit, and the generated steam is sent to the steam turbine. This steam turbine is driven. The heating unit provided in the exhaust heat recovery boiler is composed of a plurality of units (for example, high pressure, medium pressure, low pressure), each having a economizer, an evaporator, a superheater, etc. Consists of units of the generated steam in a plurality of stages (for example, high pressure, medium pressure, low pressure).

  Therefore, the steam discharged from the low-pressure turbine in the steam turbine is cooled by the condenser to become condensate, and is sent to the high-pressure superheat system by the condensate pump and the feed water pump, where it is superheated to become high-pressure steam. It is sent to the turbine to work and becomes medium pressure steam. This intermediate pressure steam is superheated by a reheater and sent to an intermediate pressure turbine to work and become low pressure steam. This low-pressure steam is sent to a low-pressure turbine for work. A part of the condensate sent from the condenser to the high pressure superheat system is sent to the intermediate pressure superheat system, where it is superheated and then sent to the reheater together with the medium pressure steam from the high pressure turbine. Further, a part of the condensate sent from the condenser to the high-pressure and medium-pressure superheat system is sent to the low-pressure superheat system, where it is superheated and then sent to the low-pressure turbine together with the low-pressure steam from the medium-pressure turbine.

  In such a complex plant, the condensate from the condenser is sent to the high-pressure superheating system, the medium-pressure superheating system, and the low-pressure superheating system by the condensate pump and the feed water pump. A predetermined amount of condensate is extracted from the middle of the feed water pump sent to the system and sent to the medium pressure superheat system.

  5 is a cross-sectional view of a main part of a conventional water supply pump, and FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. In a conventional water supply pump, as shown in FIGS. 5 and 6, a rotary shaft 002 is supported in a hollow casing 001 so as to be driven to rotate. A water supply passage 004 is formed by mounting an impeller 003 composed of a plurality of blades on the rotating shaft 002, and a diffuser 005 is provided on the inner surface of the casing 001. Then, an intermediate extraction pipe 006 is connected so as to communicate with the middle part of the water supply passage 004 in the casing 001.

  Accordingly, when the rotating shaft 002 is driven to rotate, condensate is sucked into a water supply passage 004 in the casing 001 from a suction port (not shown), and is boosted in the process of flowing through the impeller 003 and then discharged to the diffuser 005. The dynamic pressure of water is converted into static pressure and discharged from the discharge port. At this time, a part of the condensate flowing in the water supply passage 004 is extracted from the intermediate extraction pipe 006.

  As such a water supply pump, there is one described in Patent Document 1 below.

JP 2003-0148165 A

  In the conventional water supply pump described above, a part of the condensate whose pressure has been increased by the impeller 003 while flowing in the water supply passage 004 is extracted from the intermediate extraction pipe 006. This intermediate extraction pipe 006 is provided in the casing 001. Since it is provided asymmetrically with respect to the circumferential direction, there is a problem in that the condensate pressure distribution and flow velocity distribution in the circumferential direction of the water supply passage 004 become non-uniform, and the radial load increases and the water supply performance decreases. . In this case, it is conceivable to provide the intermediate extraction pipe 006 symmetrically with respect to the circumferential direction of the casing 001. However, due to the layout of the water supply pump, there is not enough space for the intermediate extraction pipe 006 to be provided below the piping. Becomes complicated and the equipment cost increases. Moreover, when the discharge amount of the condensate extracted from the intermediate extraction pipe 006 increases, the reverse flow of the condensate in the water supply passage 004 is likely to occur, and the water supply performance is significantly deteriorated.

  This invention solves the subject mentioned above, and aims at providing the feed pump which suppressed the fall of feed water performance irrespective of the intermediate | middle extraction amount.

  In order to achieve the above object, a water supply pump according to a first aspect of the present invention has a rotating shaft rotatably supported in a hollow casing, and a plurality of impellers are mounted on the rotating shaft along the axial direction. The water supply passage is formed along the axial direction of the rotary shaft with respect to the impeller, and the suction port communicating with one end portion of the water supply passage is provided in the casing, while the other end portion of the water supply passage is provided. In the water supply pump provided with the discharge port that communicates, an intermediate discharge chamber partitioned from the water supply passage is formed between the plurality of impellers in the casing, and the intermediate discharge chamber is connected to the water supply passage through the communication hole. And an intermediate extraction pipe connected to the intermediate discharge chamber.

  In the water supply pump according to a second aspect of the present invention, the intermediate discharge chamber includes a pair of donut-shaped first and second partitions disposed between the plurality of impellers at a predetermined interval, and the rotating shaft. A ring-shaped third partition wall disposed at a predetermined interval on the outer peripheral side and connected to the inner peripheral portion of the first partition wall and the second partition wall; A plurality of the communication holes are provided.

  The water supply pump according to a third aspect of the invention is characterized in that the intermediate discharge pipe is disposed in an upper part of the casing.

  The water supply pump according to a fourth aspect of the invention is characterized in that a diffuser is provided on the outer peripheral side of the water supply passage so as to face the downstream side in the water supply direction of the impeller.

  According to the water supply pump of the first aspect of the invention, the rotary shaft is rotatably supported in the hollow casing, and a plurality of impellers are mounted on the rotary shaft along the axial direction. A water supply passage is formed along the axial direction of the rotation shaft, and a suction port that communicates with one end of the water supply passage is provided in the casing, while a discharge port that communicates with the other end of the water supply passage is provided, and a plurality of impellers in the casing An intermediate discharge chamber is formed by partitioning from the water supply passage, and the intermediate discharge chamber is connected to the water supply passage through the communication hole, and the intermediate extraction pipe is connected to the intermediate discharge chamber. Is rotated, the fluid is sucked into the water supply passage from the suction port, and the pressure is increased in the process of flowing through the impeller and discharged from the discharge port. However, a part of the fluid flowing in the water supply passage passes through the communication hole to the intermediate discharge chamber. And extracted from the intermediate extraction pipe Therefore, the extraction of the fluid into the intermediate discharge chamber does not adversely affect the pressure and flow velocity of the fluid flowing in the water supply passage, and a sufficient extraction amount can be secured, while the water supply performance is improved. The decrease can be suppressed.

  According to the water supply pump of the invention of claim 2, the intermediate discharge chamber has a pair of donut-shaped first and second partition walls arranged at a predetermined interval between the plurality of impellers, and the outer periphery of the rotating shaft. And a ring-shaped third partition wall disposed at a predetermined interval on the side and connected to the inner peripheral portion of the first partition wall and the second partition wall, and a plurality of communication holes are formed at equal intervals in the circumferential direction on the third partition wall. Since it is provided, the intermediate discharge chamber can be properly configured by dividing from the water supply passage, and the water supply passage can be flowed by providing communication holes that communicate the water supply passage and the intermediate discharge chamber at equal intervals in the circumferential direction. The pressure and flow rate of the fluid to be performed are not uneven, and the performance degradation can be reliably suppressed.

  According to the water supply pump of the invention of claim 3, since the intermediate discharge pipe is disposed at the upper part of the casing, a sufficient extraction amount can be ensured without changing the overall layout, and the water supply performance is deteriorated. Can be suppressed.

  According to the water supply pump of the invention of claim 4, since the diffuser is provided on the outer peripheral side of the water supply passage so as to oppose the downstream side in the water supply direction of the impeller, the dynamic pressure of the fluid boosted by the impeller is statically reduced by the diffuser. By converting the pressure, the fluid can be discharged from the discharge port in an appropriate state.

  Exemplary embodiments of a water supply pump according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a cross-sectional view of a main part showing a water supply pump according to one embodiment of the present invention, FIG. 2 is a cross-sectional view taken along II-II in FIG. 1, and FIG. FIG. 4 is a schematic configuration diagram of a complex plant to which the feed water pump of this embodiment is applied.

  In the complex plant to which the feed water pump of the present embodiment is applied, as shown in FIG. 4, the gas turbine 11 includes a compressor 12, a combustor 13, and a turbine 14. The steam turbine 15 is configured by connecting a high-pressure turbine 16, an intermediate-pressure turbine 17, and a low-pressure turbine 18 to one shaft. The compressor 12 of the gas turbine 11 is provided with an intake line 19, while the turbine 14 is provided with an exhaust line 20, and exhaust gas discharged from the gas turbine 11 through the exhaust line 20 is sent to the exhaust heat recovery boiler 21. be able to.

  The exhaust heat recovery boiler 21 includes a low pressure unit 22, an intermediate pressure unit 23, a high pressure unit 24, and a reheater 25. In the exhaust heat recovery boiler 21, the exhaust gas from the gas turbine 11 is transferred upward, so that heat is recovered in the order of the high pressure unit 24, the intermediate pressure unit 23, and the low pressure unit 22 to generate steam. Steam is sent to the steam turbine 15 for driving, and the generator 26 can be operated.

  In the exhaust heat recovery boiler 21, the low pressure unit 22 includes a low pressure economizer 27, a low pressure evaporator 28, and a low pressure superheater 29. That is, the feed water heated by the low-pressure economizer 27 is sent to the low-pressure evaporator 28 via the first low-pressure feed water channel 30, and is heated here to generate low-pressure steam. The low-pressure steam generated in the low-pressure evaporator 28 is sent to the low-pressure superheater 29 via the second low-pressure feed water channel 31 and is heated there.

  The intermediate pressure unit 23 includes an intermediate pressure economizer 32, an intermediate pressure evaporator 33, and an intermediate pressure superheater 34. That is, the feed water heated by the intermediate pressure economizer 32 is sent to the intermediate pressure evaporator 33 via the first intermediate pressure feed water channel 35, where it is heated to generate intermediate pressure steam. The intermediate-pressure steam generated in the intermediate-pressure evaporator 33 is sent to the intermediate-pressure superheater 34 through the second intermediate-pressure feed water channel 36 and is heated there.

  Furthermore, the high pressure unit 24 includes a high pressure economizer 37, a high pressure evaporator 38, and a high pressure superheater 39. That is, the feed water heated by the high-pressure economizer 37 is sent to the high-pressure evaporator 38 via the first high-pressure feed water channel 40, where it is heated to generate high-pressure steam. The high-pressure steam generated in the high-pressure evaporator 38 is sent to the high-pressure superheater 39 through the second high-pressure feed water channel 41 and is heated there.

  A high-pressure steam supply line 42 for supplying the high-pressure steam from the high-pressure superheater 39 to the high-pressure turbine 16 is provided, and an intermediate-pressure steam recovery line 43 for returning the intermediate-pressure steam discharged from the high-pressure turbine 16 to the reheater 29 is provided. Is provided. Further, an intermediate pressure steam supply line 44 for supplying the intermediate pressure steam generated in the intermediate pressure superheater 34 to the intermediate pressure steam recovery line 43 is provided. On the other hand, an intermediate pressure steam supply line 45 for supplying the intermediate pressure steam superheated by the reheater to the intermediate pressure turbine 17 is provided, and a low pressure for supplying the intermediate pressure steam discharged from the intermediate pressure turbine 17 to the low pressure turbine 18. A steam transfer line 46 is provided. A low-pressure steam supply line 47 that supplies low-pressure steam generated in the low-pressure superheater 29 to the low-pressure steam transfer line 46 is provided.

  A condenser 48 that condenses the steam discharged from the low-pressure turbine 18 is provided with a cooling water circulation line 49 that is cooled by seawater. The condenser 48 is provided with a condensate recovery line 50 that returns the condensed condensate to the exhaust heat recovery boiler 21. The condensate recovery line 50 includes a condensate pump 51 and a deaerator 52. Is provided. The downstream end of the condensate recovery line 50 is connected to the high-pressure economizer 37 via a water supply pump 53 and a high-pressure water supply line 54, and has an intermediate pressure via an intermediate-pressure water supply line 55 branched from the water supply pump 53. The economizer 32 is connected. The downstream end of the condensate recovery line 50 is connected to the low-pressure economizer 27 via a branched low-pressure water supply line 56.

  Accordingly, in the gas turbine 11, the air taken into the compressor 12 through the intake line 19 is compressed to become high-temperature and high-pressure compressed air, which is sent to the combustor 13, where the compressed air and fuel The air-fuel mixture is ignited and combusted, and the high-temperature and high-pressure combustion gas generated in the combustor 13 is sent to the turbine 14 to be driven. The exhaust gas discharged from the turbine 14 is sent to the exhaust heat recovery boiler 21 through the exhaust line 20, where steam is generated by the high-temperature and high-pressure exhaust gas.

  That is, the condensate condensed by the condenser 48 is pressurized by the condensate pump 51 and dissolved oxygen is removed by the deaerator 52, and then exhausted through the condensate recovery line 50 by the feed water pump 53. The high pressure unit 24 of the recovery boiler 21 is returned. Then, the high-pressure steam generated by overheating in the high-pressure unit 24 is sent to the high-pressure turbine 16 through the high-pressure steam supply line 42, where it works to become medium-pressure steam. This intermediate pressure steam is sent to the reheater 29 through the intermediate pressure steam recovery line 43, and after being reheated, it is sent to the intermediate pressure turbine 17 through the intermediate pressure steam supply line 45, where it works to produce the low pressure steam. Become. This low-pressure steam is then sent to the low-pressure turbine 18 through the low-pressure steam conveyance line 46, where it works and is returned to the condenser 48.

  Further, the condensate extracted from the feed water pump 53 is returned to the intermediate pressure unit 23 through the intermediate pressure supply water line 55, is overheated by the intermediate pressure unit 23, and then is recovered through the intermediate pressure steam supply line 44. 43. Further, a part of the condensate passing through the condensate recovery line 50 is returned to the low-pressure unit 22 through the low-pressure water supply line 56 and is heated by the low-pressure unit and then supplied to the low-pressure steam transport line 46 through the low-pressure steam supply line 47. Is done.

  As described above, the feed water pump 53 in the complex plant configured as described above pressurizes and supplies the condensate to the high-pressure unit 24, and bleeds the pressurized condensate and supplies it to the intermediate-pressure unit 23. Yes. In this case, if a part of the condensate pressurized by the feed water pump 53 is extracted, the pressure distribution and flow velocity distribution of the condensate become non-uniform in the internal water supply passage, leading to a reduction in water supply performance. Therefore, in this embodiment, an intermediate discharge chamber partitioned from the water supply passage is provided in the water supply pump 53, and air is extracted from the intermediate discharge chamber.

  That is, in the water supply pump 53 of the present embodiment, as shown in FIG. 3, the casing 61 has a hollow shape, the rotation shaft 62 penetrates inside, and is rotatably supported by a pair of bearings 63 and 64. A driving motor (not shown) is drivingly connected to one end of the rotating shaft 62. A plurality of (in this embodiment, six stages) impellers (impellers) 65 are attached to the rotating shaft 62 along the axial direction, so that the rotating shaft 62 extends along the axial direction of the rotating shaft 62. Thus, a water supply passage 66 is formed. A diffuser 67 is provided on the outer peripheral side of the water supply passage 66 so as to face the downstream side of each impeller 65 in the water supply direction. The casing 61 is connected to a water supply pipe (suction port) 68 that communicates with one end of the water supply passage 66, and is connected to a discharge pipe (discharge port) 69 that communicates with the other end of the water supply passage. .

  In the casing 61 of the present embodiment, a plurality of ring members 61a to 61e having a ring shape are fitted to each other, and the ring portions 68a and 69a of the water supply pipe 68 and the discharge pipe 69 are fitted to each end. In the state, it is configured to be fastened by a plurality of fastening bolts 70.

  As shown in FIGS. 1 to 3, intermediate extraction is performed between the first stage impeller 65 and the second stage impeller 65 so as to be sandwiched between ring members 61a and 61b constituting the casing 61. A ring portion 71a of the pipe 71 is disposed. A first partition wall 72 having a donut shape is integrally formed on the inner peripheral portion of the ring member 61a of the casing 61, and a donut shape is formed on the inner peripheral portion of the ring portion 71a of the intermediate extraction pipe 71. The second partition wall 73 is integrally formed with the first partition wall 72 at a predetermined interval. In addition, a third partition wall 74 having a ring shape with a predetermined interval from the outer peripheral surface of the rotation shaft 62 is disposed on the outer periphery side of the rotation shaft 62, and one axial end portion of the third partition wall 74 is the first end portion. While being joined to the inner peripheral portion of the partition wall 72, the other axial end is joined to the inner peripheral portion of the second partition wall 73.

  That is, an intermediate discharge chamber 75 defined by the water supply passage 66 is formed between the impeller 65 by the three partition walls 72, 73, and 74. A plurality of communication holes 76 are provided in the third partition wall 74 at equal intervals in the circumferential direction, and the water supply passage 66 and the intermediate discharge chamber 75 are communicated with each other through the plurality of communication holes 76. In addition, the intermediate discharge chamber 75 communicates with the extraction passage 77 of the intermediate extraction pipe 71. In this case, an intermediate discharge pipe 71 is disposed above the casing 61.

  Accordingly, when each impeller 65 rotates together with the rotating shaft 62, the condensate is sucked into the water supply passage 66 in the casing 61 from the suction pipe 68 and is pressurized in the process of flowing through the impeller 65, and then is condensed in each diffuser 67. Is converted into a static pressure and discharged from the discharge pipe 69. At this time, a part of the condensate during the pressure increase flowing in the water supply passage 66 flows into the intermediate discharge chamber 75 through each communication hole 76 and is extracted through the extraction passage 77 of the intermediate extraction pipe 71.

  In this case, the condensate once flows into the intermediate discharge chamber 75 from the water supply passage 66 through each communication hole 76 and then extracted by the intermediate extraction pipe 71, and the pressure of the condensate flowing through the water supply passage 66 is increased. The flow rate hardly fluctuates, and a sufficient amount of extraction is ensured, and a decrease in water supply performance is suppressed.

  Thus, in the water supply pump of this embodiment, the rotary shaft 62 is rotatably supported in the hollow casing 61, and a plurality of impellers 65 are attached to the rotary shaft 62 along the axial direction. A water supply passage 66 is formed along the axial direction of the rotary shaft 62 with respect to the impeller 65, and a suction pipe 68 communicating with one end of the water supply passage 66 is connected to the casing 61, while the other end of the water supply passage 66 is connected to the casing 61. A discharge pipe 69 that communicates is connected, and is partitioned from a water supply passage 66 between a plurality of impellers 65 in the casing 61 to form an intermediate discharge chamber 75, and the intermediate discharge chamber 75 is connected to the water supply passage 66 through a communication hole 76. In addition to communication, an intermediate extraction pipe 71 is connected to the intermediate discharge chamber 75.

  Accordingly, when the impeller 65 rotates together with the rotating shaft 62, the condensed water is sucked into the water supply passage 66 from the suction pipe 68, and is boosted and discharged from the discharge pipe 69 in the process of flowing through the impeller 65. A part of the condensate flowing through the water flows into the intermediate discharge chamber 75 through the communication hole 76 and is extracted from the intermediate extraction pipe 71, and the condensate extracted into the intermediate discharge chamber 75 flows through the water supply passage 66. The pressure and flow velocity are not adversely affected, and a sufficient extraction amount can be ensured, while the water supply performance can be prevented from deteriorating.

  Further, in the water supply pump of the present embodiment, a first partition wall 72 having a donut shape formed on the ring member 61a of the casing 61, a second partition wall 73 having a donut shape formed on the ring portion 71a of the intermediate extraction pipe 71, and An intermediate discharge chamber 75 is formed by a ring-shaped third partition 74 disposed on the outer peripheral side of the rotating shaft 62, and a plurality of communication holes 76 are provided in the third partition 74 at equal intervals in the circumferential direction. Therefore, the intermediate discharge chamber 75 can be appropriately configured by partitioning from the water supply passage 66, and the communication holes 76 communicating the water supply passage 66 and the intermediate discharge chamber 75 are provided at equal intervals in the circumferential direction. The pressure and flow velocity of the fluid flowing through the passage 66 do not become uneven, and the performance degradation can be reliably suppressed.

  Furthermore, in the present embodiment, the intermediate discharge pipe 71 is disposed on the upper portion of the casing 61, so that a sufficient extraction amount can be ensured without changing the overall layout, and a decrease in water supply performance is suppressed. can do. Further, a diffuser 67 is provided on the outer peripheral side of the water supply passage 66 so as to face the downstream side in the water supply direction of the impeller 65. Therefore, the condensate can be discharged from the discharge pipe 69 in an appropriate state by converting the dynamic pressure of the condensate increased by the impeller 65 into a static pressure by the diffuser 67.

  In the above-described embodiment, the casing 61 is fitted with a plurality of ring members 61a to 61e having a ring shape, and the ring portions 68a and 69a of the water supply pipe 68 and the discharge pipe 69 are fitted to each end. The ring portion 71a of the intermediate extraction pipe 71 is disposed between the ring members 61a and 61b. However, the present invention is not limited to this structure. For example, the casing may be integrally formed, and a suction pipe, a discharge pipe, and an intermediate extraction pipe may be connected to the outer periphery of the casing.

  In the embodiment described above, the first partition wall 72 is formed on the ring member 61 a of the casing 61, the second partition wall 73 is formed on the ring portion 71 a of the intermediate extraction pipe 71, and the ring-shaped third partition wall 74 is formed in the first shape. The intermediate discharge chamber 75 is formed by being connected to the first partition wall 72 and the second partition wall 73. However, the structure is not limited to this structure. For example, a cross-section is formed in a U shape on the inner peripheral side of a cylindrical casing. The partition member may be fixed.

  Furthermore, although the arrangement position of the intermediate extraction pipe 71 with respect to the casing 61 is set between the first stage impeller and the second stage impeller, the condensate may be extracted from another part depending on the pressure of the condensed water to be extracted. .

  In this embodiment, the feed water pump of the present invention is applied as the feed water pump 53 of the exhaust heat recovery boiler 21 in the combined plant. However, the present invention is not limited to this field, and any field can be used as long as it is a pump that bleeds during pressure increase. But it is applicable.

  The water supply pump according to the present invention is capable of securing a sufficient amount of extraction without adversely affecting the fluid flowing through the water supply passage regardless of the amount of extraction, and suppressing a decrease in water supply performance. It can also be applied to a water supply pump.

It is principal part sectional drawing showing the feed water pump which concerns on one Example of this invention. It is II-II sectional drawing of FIG. It is a whole block diagram showing the feed pump of a present Example. It is a schematic block diagram of the complex plant to which the feed water pump of the present Example was applied. It is principal part sectional drawing of the conventional water supply pump. It is VI-VI sectional drawing of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Gas turbine 15 Steam turbine 21 Waste heat recovery boiler 22 Low pressure unit 23 Medium pressure unit 24 High pressure unit 25 Reheater 26 Generator 48 Condenser 50 Condensate recovery line 53 Water feed pump 54 High pressure feed water line 55 Medium pressure feed water line 56 Low pressure water supply line 61 Casing 62 Rotating shaft 65 Impeller (impeller)
66 Water supply passage 67 Diffuser 68 Water supply pipe (suction port)
69 Discharge pipe (discharge port)
71 Intermediate extraction pipe 72 First partition 73 Second partition 74 Third partition 75 Intermediate discharge chamber 76 Communication portion

Claims (4)

  A rotating shaft is rotatably supported in a hollow casing, and a plurality of impellers are mounted on the rotating shaft along the axial direction, and a water supply passage is provided along the axial direction of the rotating shaft with respect to the impeller. In the water supply pump in which the suction port that communicates with one end portion of the water supply passage is provided in the casing, and the discharge port that communicates with the other end portion of the water supply passage is provided in the casing, An intermediate discharge chamber partitioned from the water supply passage is formed between the impellers, the intermediate discharge chamber communicates with the water supply passage through a communication hole, and an intermediate extraction pipe is connected to the intermediate discharge chamber. A water supply pump characterized by that.   2. The water supply pump according to claim 1, wherein the intermediate discharge chamber includes a pair of donut-shaped first and second partitions disposed between the plurality of impellers at a predetermined interval, and the rotating shaft. A ring-shaped third partition wall disposed at a predetermined interval on the outer peripheral side and connected to the inner peripheral portion of the first partition wall and the second partition wall; A water supply pump comprising a plurality of the communication holes.   3. The water supply pump according to claim 1, wherein the intermediate discharge pipe is disposed on an upper portion of the casing.   The water supply pump as described in any one of Claim 1 to 3 WHEREIN: The diffuser was provided facing the downstream of the water supply direction in the said impeller on the outer peripheral side of the said water supply channel | path.

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