JP6137963B2 - pump - Google Patents

Description

  The present invention relates to a pump having an impeller.

  Conventionally, pumps, such as a mixed flow pump or an axial flow pump, are known as a pump which has an impeller (for example, refer to patent documents 1). This pump is provided with a shaft power reduction device that reduces shaft power when the pump is started. The shaft power reduction device includes a bypass pipe that connects the discharge port and the suction port of the pump, a bypass valve that opens and closes the bypass pipe, and a bypass valve that opens the bypass valve when the pressure of the pump discharge port becomes higher than a predetermined pressure. And an opening / closing mechanism. Here, when starting the pump, since the pump is normally started from a state where the discharge port of the pump is closed, the shaft power at the start of the pump is larger than the shaft power at the rated operation. For this reason, the shaft power reduction device opens the bypass valve when the pump discharge pressure becomes higher than a predetermined pressure when starting the pump, and distributes fluid from the discharge port of the pump to the suction port via the bypass pipe. As a result, the increase in shaft power is reduced.

  Similarly, a self-control bypass valve is known as a means for reducing shaft power in the vicinity of when the pump is shut off (see, for example, Patent Document 2). This self-control bypass valve is connected to the pump discharge pipe and opens as the pressure in the pump discharge pipe increases, thereby bypassing the fluid from the pump discharge pipe to the pump inlet side.

JP-A-6-330883 Japanese Patent Laid-Open No. 7-259783

  As described above, in Patent Document 1 and Patent Document 2, when the discharge flow rate Q discharged from the pump discharge port is close to zero, the pressure at the pump discharge port is predetermined in order to reduce the shaft power of the pump. When the pressure becomes higher than the pressure, the bypass valve is opened, and the fluid is circulated from the discharge port of the pump to the suction port via the bypass pipe.

  By the way, in the design stage of the pump, the QH characteristic indicating the characteristics of the discharge flow rate Q and the head H is designed so as to be within the range of the predetermined QH characteristic. However, the QH characteristics of the actual pump, in particular, when the pump is closed, that is, when the discharge flow rate Q is close to zero, the head H may be larger than the design time. As the head H increases, the shaft power of the pump also increases. In this case, a large load may be applied to the pipe connected to the discharge port of the pump.

  Then, this invention makes it a subject to provide the pump which can suppress the increase in the head at the time of a deadline.

  The pump of the present invention includes a casing in which an internal flow path extending from a suction port to a discharge port is formed, and an impeller that is housed in the casing, takes in fluid from the suction port, and sends the fluid toward the discharge port. The front of the impeller so that the pressure in the internal flow path on the discharge side with respect to the front edge of the impeller is equal to or lower than a predetermined pressure when the valve provided in the pipe connected to the discharge port is closed. A pressure reducing mechanism for releasing the fluid flowing through the internal flow path on the discharge side from the edge.

  According to this configuration, when the valve is closed, the pressure reducing mechanism causes the pressure on the discharge side from the front edge of the impeller so that the pressure in the internal flow path on the discharge side from the front edge of the impeller is equal to or lower than a predetermined pressure. The fluid in the internal flow path can be released. For this reason, even if the head rises at the time of closing of the valve, the pressure on the discharge side with respect to the front edge of the impeller can be reduced, so that the head can be reduced. From the above, the pressure applied to the pipe connected to the discharge port can be reduced to a predetermined pressure or less, and the load on the pipe can be reduced. Here, the predetermined pressure is, for example, a design limit pressure related to the discharge pressure of the pump. In addition, when the valve is closed, it is a state near the fully closed state including the fully closed valve. Specifically, when the valve is fully closed from the open state, when the valve is kept in the fully closed state, This is when the valve is opened from the fully closed state.

  In this case, the pressure reducing mechanism has a three-way valve as the valve provided in the pipe and a bypass pipe connected to the three-way valve, and the three-way valve While interposing the communication between the upstream pipe and the downstream pipe in the fluid flow direction, the upstream pipe and the bypass pipe are preferably communicated.

  According to this configuration, when the valve is closed, the three-way valve is operated to close the communication between the upstream pipe and the downstream pipe with the three-way valve interposed therebetween, while the upstream pipe and the bypass pipe are closed. Can communicate with each other. For this reason, since the fluid discharged from the discharge port is guided to the bypass pipe, the pressure on the downstream side of the front edge of the impeller can be reduced, and the head can be reduced. The bypass pipe is preferably arranged so that the fluid discharged from the bypass pipe is again sucked from the suction port.

  In this case, the pressure reducing mechanism is formed inside the impeller, and communicates the internal flow path on the discharge side with respect to the front edge of the impeller and the internal flow path on the suction side of the impeller. Preferably, the internal bypass passage includes a bypass passage and an internal bypass valve provided in the internal bypass passage, and the internal bypass valve opens the internal bypass passage when the deadline is reached.

  According to this configuration, the internal bypass flow path can be opened by operating the internal bypass valve when the valve is closed. For this reason, the fluid which distribute | circulates the internal flow path of the discharge side rather than the front edge of an impeller is guided to the internal flow path of the suction side of an impeller via an internal bypass flow path. As a result, the fluid flowing through the internal flow path circulates between the internal flow path on the discharge side of the impeller and the internal flow path on the suction side of the impeller by the internal bypass flow path. The pressure on the downstream side of the edge can be reduced, and the head can be efficiently reduced.

  In this case, the decompression mechanism is provided outside the casing, and communicates with the internal flow path on the discharge side of the front edge of the impeller, and an external bypass valve provided in the external bypass pipe It is preferable that the external bypass valve releases the external bypass pipe when the deadline is reached.

  According to this configuration, the external bypass pipe can be opened by operating the external bypass valve when the valve is closed. For this reason, since the fluid that flows through the internal flow path on the discharge side from the front edge of the impeller is guided by the external bypass pipe, the pressure on the downstream side of the front edge of the impeller can be reduced. The head can be reduced. The external bypass pipe is preferably arranged such that the fluid discharged from the external bypass pipe is again sucked from the suction port.

FIG. 1 is a cross-sectional structure diagram of a mixed flow pump according to a first embodiment. FIG. 2 is a schematic diagram around the mixed flow pump according to the first embodiment. FIG. 3 is a QH characteristic diagram of the mixed flow pump according to the first embodiment. FIG. 4 is an enlarged view around the impeller of the mixed flow pump according to the second embodiment. FIG. 5 is a schematic diagram of a mixed flow pump according to the third embodiment.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.

  FIG. 1 is a cross-sectional structure diagram of a mixed flow pump according to a first embodiment. FIG. 2 is a schematic diagram around the mixed flow pump according to the first embodiment. FIG. 3 is a QH characteristic diagram of the mixed flow pump according to the first embodiment. The pump 1 according to the first embodiment is a pump 1 having an impeller 25, for example, a vertical shaft type diffuser mixed flow pump (hereinafter referred to as a mixed flow pump) 1 shown in FIG. The mixed flow pump 1 rotates the impeller 25 so that the fluid (for example, water) sucked from the suction port 17 on the lower side in the vertical direction is horizontally supplied from the discharge port 18 on the upper side in the vertical direction. It is what is discharged. In the first embodiment, the pump 1 is described as applied to the mixed flow pump 1, but is not limited to this configuration. That is, if it is the pump 1 which has the impeller 25, you may apply not only to a mixed flow pump but pumps, such as an axial flow pump.

  As shown in FIG. 1, the mixed flow pump 1 includes an outer cylinder casing (casing) 4 and an inner cylinder hub 5 provided inside the center of the outer cylinder casing 4. The outer casing 4 is formed with a suction port 17 and a discharge port 18, the suction port 17 is formed on the upstream side in the lower part of the figure, and the discharge port 18 is formed on the downstream side in the upper part of the figure. The inner cylinder hub 5 is connected and fixed to the outer cylinder casing 4 by a stay (not shown), and an internal flow path 8 through which fluid flows is formed between the outer cylinder casing 4 and the inner cylinder hub 5. The internal flow path 8 is formed from the upstream suction port 17 to the downstream discharge port 18.

  The outer casing 4 is arranged in order from the upstream side (suction side) to the suction bell mouth 10, the impeller casing 11 connected to the downstream side (discharge side) of the suction bell mouth 10, and the downstream side of the impeller casing 11. The shroud 12 is connected, the pumping pipe 13 is connected to the downstream side of the shroud 12, and the bent pipe 14 is connected to the downstream side of the pumping pipe 13.

  The suction bell mouth 10 is formed in a bell mouth shape whose diameter increases toward the suction side, and an upstream end of the suction bell mouth 10 serves as a suction port 17. An impeller casing 11 is connected to the downstream side of the suction bell mouth 10.

  The impeller casing 11 is formed in an inverted frustoconical cylindrical shape. A suction bell mouth 10 is connected to the upstream side of the impeller casing 11, and a shroud 12 is connected to the downstream side of the impeller casing 11.

  The shroud 12 is configured in a substantially cylindrical shape. An impeller casing 11 is connected to the upstream side of the shroud 12, and a pumping pipe 13 is connected to the downstream side of the shroud 12. Although details will be described later, the shroud 12 constitutes a part of the diffuser 30.

  The pumping pipe 13 is configured in a substantially cylindrical shape. A shroud 12 is connected to the upstream side of the pumping pipe 13, and a bent pipe 14 is connected to the downstream side of the pumping pipe 13.

  The bent pipe 14 is configured in a cylindrical shape bent in an arc shape so as to guide the fluid pumped in the vertical direction in the horizontal direction, and the pumped pipe 13 is connected to the upstream side of the bent pipe 14. A discharge port 18 is formed at the downstream end of the bent tube 14.

  And the outer cylinder casing 4 is comprised by fastening the suction bell mouth 10, the impeller casing 11, the shroud 12, the pumping pipe 13, and the bending pipe 14 integrally.

  The inner cylinder hub 5 provided in the outer cylinder casing 4 includes, in order from the upstream side, the impeller side hub 20, the diffuser side hub 21 disposed on the downstream side of the impeller side hub 20, and the diffuser side hub 21. And a pumping pipe side hub 22 arranged on the downstream side.

  The impeller side hub 20 is disposed inside the center of the impeller casing 11 and is formed in a cone shape that tapers toward the suction bell mouth 10 side. Here, the impeller side hub 20 constitutes a part of the impeller 25. That is, the impeller 25 includes the above-described impeller side hub 20 and a plurality of vanes 26 attached to the outer periphery of the impeller side hub 20. The impeller 25 is accommodated in the impeller casing 11. Has been. The plurality of vanes 26 are arranged at equal intervals in the circumferential direction with respect to the impeller-side hub 20, and the impeller-side hub 20 is fixed to a tip end of a main shaft 36 described later. Thus, the impeller 25 is configured to be rotatable with the rotation of the main shaft 36.

  The diffuser-side hub 21 is disposed inside the center of the shroud 12 and is formed in a cylindrical shape. Here, the diffuser-side hub 21 constitutes a part of the diffuser 30. That is, the diffuser 30 includes the shroud 12 that forms part of the internal flow path 8, the diffuser-side hub 21 that is disposed in the center of the shroud 12, and the outer surface of the diffuser-side hub 21. And a plurality of diffuser vanes 31 arranged radially toward the inner peripheral surface of the inner peripheral surface, and converts the dynamic pressure of the fluid sent out from the impeller 25 into a static pressure. The plurality of diffuser vanes 31 have base ends attached to the diffuser-side hub 21 and tip ends attached to the shroud 12 and are arranged at equal intervals in the circumferential direction. Thereby, since the diffuser side hub 21 is fixed to the shroud 12 via the plurality of diffuser vanes 31, the upstream side of the diffuser side hub 21 is configured to allow rotation by the impeller 25. That is, a gap C is formed between the impeller side hub 20 and the diffuser side hub 21.

  The pumping pipe side hub 22 is disposed inside the center on the upstream side of the pumping pipe 13 and is formed in a tapered shape that tapers toward the bent pipe 14 side. The upstream end of the pump-pipe-side hub 22 is connected and fixed to the downstream end of the diffuser-side hub 21.

  The mixed flow pump 1 includes a drive source 35 disposed above the bent tube 14 and a main shaft 36 disposed between the drive source 35 and the impeller 25. As the drive source 35, for example, a motor or the like is used, and the impeller 25 is rotated via the main shaft 36. The main shaft 36 is disposed inside the center of the outer casing 4, and has a base end portion that passes through the bent pipe 14 and is connected to the drive source 35, and a tip end portion that passes through the pumping pipe side hub 22. It passes through the inside of the diffuser-side hub 21 and is connected to the impeller-side hub 20 (impeller 25).

  Here, the operation of the mixed flow pump 1 will be described. The mixed flow pump 1 configured as described above is installed in a pit 38 for storing fluid. At this time, the mixed flow pump 1 is arranged such that the suction port 17 and the impeller 25 are immersed in the fluid of the pit 38. When the driving source 35 is driven to rotate the impeller 25, the rotated impeller 25 sucks fluid from the suction port 17 and sends the sucked fluid toward the discharge port 18 in the vertical direction. As the fluid sent out from the impeller 25 passes through the diffuser 30, the static pressure rises. The fluid whose static pressure has increased passes through the pumping pipe 13 and the bent pipe 14 and is discharged from the discharge port 18 in the horizontal direction.

  Next, a configuration around the mixed flow pump 1 will be described with reference to FIG. The mixed flow pump 1 has a pipe 41 connected to the discharge port 18. The pipe 41 is provided with a three-way valve 42 for opening and closing the flow path of the pipe 41. The three-way valve 42 constitutes a part of a pressure reducing mechanism 51 described later. Here, the equipment including the mixed flow pump 1 is provided with a control unit 44 for controlling the mixed flow pump 1.

  A drive source 35, a three-way valve 42, and a pressure gauge 45 are connected to the control unit 44. The pressure gauge 45 measures the pressure in the internal flow path 8 on the discharge side of the impeller 25. The control unit 44 controls the operation of the mixed flow pump 1, controls the opening and closing of the three-way valve 42 according to the operation state of the mixed flow pump 1, and controls the three-way valve 42 according to the pressure of the pressure gauge 45. Open / close control is performed.

  Here, in the mixed flow pump 1, the flow path of the pipe 41 may be closed (closed) by the three-way valve (valve) 42 during rated operation. That is, the mixed flow pump 1 may perform a rated operation when the flow path of the pipe 41 is closed. In this case, the QH characteristic that is the characteristic of the discharge flow rate Q and the head H of the mixed flow pump 1 is a graph shown in FIG. The deadline is a state in the vicinity of the fully closed state including the valve fully closed (that is, the block of the flow path of the pipe 41 by the three-way valve 42), specifically, when the valve is fully closed from the open state. When the valve is maintained in the fully closed state, the valve is released from the fully closed state.

  In FIG. 3, the horizontal axis represents the discharge flow rate Q, and the vertical axis represents the head H. In FIG. 3, the QH characteristic in the actual performance of the mixed flow pump 1 is L1 (solid line), the QH characteristic in the design performance of the mixed flow pump 1 is L2 (two-dot chain line), and the design limit pressure is P. The design limit pressure P is the limit pressure of the discharge pressure of the mixed flow pump 1 defined in the design. In order to simplify the explanation, FIG. 3 shows the design limit pressure P, but specifically, it is the head H corresponding to the design limit pressure P.

  As shown in FIG. 3, the QH characteristic L2 of the mixed flow pump 1 at the design stage is designed to have a predetermined QH characteristic below the design limit pressure P. On the other hand, the QH characteristic L1 of the actual mixed flow pump 1 may be higher than that at the time of design, particularly at the time of closing, that is, at the time of closing when the discharge flow rate Q is close to zero.

  For this reason, the mixed flow pump 1 is provided with the pressure reduction mechanism 51 which suppresses the raise of the lift H at the time of a deadline. As shown in FIG. 2, the pressure reducing mechanism 51 includes the above three-way valve 42 and a bypass pipe 52 connected to the three-way valve 42.

  One side of the three-way valve 42 provided in the pipe 41 is connected to the upstream side pipe 41a in the fluid flow direction with the three-way valve 42 interposed therebetween, and the other side is connected to the downstream side pipe 41b with the three-way valve 42 interposed therebetween. Is connected, and a bypass pipe 52 is connected to the other one. The three-way valve 42 communicates the upstream pipe 41a and the downstream pipe 41b and closes the bypass pipe 52, and communicates the upstream pipe 41a and the bypass pipe 52 and the downstream pipe 41b. It is possible to switch between the states of closing.

  The bypass pipe 52 has one end connected to the three-way valve 42 and the other end immersed in the fluid of the pit 38. A discharge port 53 is formed at the other end of the bypass pipe 52 and is disposed in the vicinity of the suction port 17 of the mixed flow pump 1. For this reason, the fluid discharged from the discharge port 53 of the bypass pipe 52 is sucked from the suction port 17 of the mixed flow pump 1.

  Next, the operation of the pressure reducing mechanism 51 of the mixed flow pump 1 when the piping 41 is closed will be described. In the following description, as an example of the deadline, the case where the flow path of the pipe 41 is opened after the mixed flow pump 1 is started and the rated operation is performed from the state where the flow path of the pipe 41 is closed will be described. .

  The control unit 44 communicates the upstream pipe 41a and the bypass pipe 52 and closes the downstream pipe 41b so that the three-way valve 42 is closed in the flow path of the pipe 41. 42 is switched. In this state, the control unit 44 drives the drive source 35 to rotate the impeller 25. The mixed flow pump 1 sucks fluid from the suction port 17 and discharges the sucked fluid from the discharge port 18 as the impeller 25 rotates. The fluid discharged from the discharge port 18 flows into the upstream pipe 41 a and then into the three-way valve 42. The fluid flowing into the three-way valve 42 is guided to the bypass pipe 52 from the upstream pipe 41 a via the three-way valve 42. Then, the fluid flows through the bypass pipe 52 and is returned to the pit 38. A part of the fluid returned to the pit 38 is again sucked from the suction port 17 of the mixed flow pump 1. And even if the mixed flow pump 1 reaches the rated operation, that is, even if the rotation of the impeller 25 reaches a predetermined rotational speed, the fluid sucked from the suction port 17 of the mixed flow pump 1 passes through the bypass pipe 52. It circulates and is returned to the pit 38. Therefore, even when the three-way valve 42 closes the flow path of the pipe 41, the discharge flow rate Q shown in FIG. 3 does not become zero, and the predetermined discharge flow rate Q is discharged from the bypass pipe 52. At this time, the opening degree of the three-way valve 42 is set so that the predetermined discharge flow rate Q becomes a discharge flow rate Q lower than the design limit pressure P.

  Then, when the mixed flow pump 1 reaches the rated operation, the control unit 44 communicates the upstream side pipe 41a and the downstream side pipe 41b so that the three-way valve 42 opens the flow path of the pipe 41. In addition, the three-way valve 42 is switched to a state in which the bypass pipe 52 is closed. The mixed flow pump 1 that performs rated operation causes the fluid sucked from the suction port 17 to flow into the three-way valve 42 via the discharge port 18. The fluid flowing into the three-way valve 42 is guided by the three-way valve 42 from the upstream pipe 41a to the downstream pipe 41b. For this reason, the fluid sucked by the mixed flow pump 1 flows through the pipe 41.

  As described above, according to the configuration of the first embodiment, when the deadline is reached, the pressure reducing mechanism 51 causes the blades to reduce the pressure in the internal flow path 8 on the discharge side from the front edge of the impeller 25 to a predetermined pressure or less. The fluid in the internal flow path 8 on the discharge side from the front edge of the vehicle 25 can be released. The front edge of the impeller 25 is an upstream edge of the vane 26. For this reason, even if the lift H rises at the deadline, the pressure on the discharge side relative to the front edge of the impeller 25 can be reduced, and therefore the lift H can be reduced. From the above, the pressure applied to the pipe 41 connected to the discharge port 18 can be set to a predetermined pressure or less, and the load on the pipe 41 can be reduced.

  Further, according to the configuration of the first embodiment, at the time of closing, by operating the three-way valve 42, while blocking the communication between the upstream pipe 41a and the downstream pipe 41b across the three-way valve 42, The upstream pipe 41a and the bypass pipe 52 can be communicated with each other. For this reason, since the fluid discharged from the discharge port 18 is guided to the bypass pipe 52, the pressure on the downstream side of the front edge of the impeller 25 can be reduced, and the head H can be reduced. .

  Moreover, according to the structure of Example 1, since the other edge part of the bypass pipe 52 can be arrange | positioned in the suction inlet 17 vicinity, a part of fluid discharged | emitted from the bypass pipe 52 is again drawn into the suction inlet 17. Can be sucked in from. For this reason, the fluid discharged from the bypass pipe 52 can be circulated between the internal flow path 8 on the discharge side of the impeller 25 and the internal flow path 8 on the suction side of the impeller 25. It can be reduced efficiently.

  Next, a mixed flow pump 80 according to the second embodiment will be described with reference to FIG. FIG. 4 is an enlarged view around the impeller of the mixed flow pump according to the second embodiment. In the second embodiment, only parts different from the first embodiment will be described in order to avoid the description overlapping with the first embodiment. In the mixed flow pump 1 of the first embodiment, the pressure reducing mechanism 51 includes the three-way valve 42 and the bypass pipe 52. However, in the mixed flow pump 80 of the second exemplary embodiment, the pressure reducing mechanism 81 is provided inside the impeller 25. It has been. In the first embodiment, since the pressure reducing mechanism 51 includes the three-way valve 42, the three-way valve 42 is provided in the pipe 41. However, in the second embodiment, the three-way valve 42 provided in the pipe 41 is It is an on-off valve. Hereinafter, the pressure reducing mechanism 81 of the mixed flow pump 80 according to the second embodiment will be described with reference to FIG.

  As shown in FIG. 4, the decompression mechanism 81 includes an internal bypass passage 83 formed inside the impeller 25 and an internal bypass valve 84 provided in the internal bypass passage 83.

  The internal bypass channel 83 is formed extending in the axial direction of the main shaft 36. Note that a plurality of internal bypass channels 83 may be formed at predetermined intervals in the circumferential direction of the main shaft 36. Here, a gap C is formed between the rotating impeller-side hub 20 and the fixed diffuser-side hub 21. One end of the internal bypass channel 83 is connected to the gap C. For this reason, the internal bypass flow path 83 is connected to the discharge-side internal flow path 8 with respect to the impeller 25 through the gap C. The other end of the internal bypass channel 83 is located on the suction side of the discharge-side end of the impeller-side hub 20, that is, the front edge (upstream-side edge) of the vane 26 of the impeller 25. It is connected to the flow path 8. For this reason, the internal bypass flow path 83 communicates the internal flow path 8 on the discharge side of the impeller 25 and the internal flow path 8 on the suction side of the impeller 25.

  The internal bypass valve 84 is an open / close valve, for example, and opens and closes the internal bypass flow path 83. The internal bypass valve 84 is connected to the control unit 44, and the control unit 44 opens and closes the internal bypass valve 84 according to the operating state of the mixed flow pump 80, and also according to the pressure of the pressure gauge 45. The internal bypass valve 84 is opened and closed.

  Next, the operation of the pressure reducing mechanism 81 of the mixed flow pump 80 when the piping 41 is closed will be described. In the following description, as an example of the closing time, a case where the flow path of the pipe 41 is opened after the mixed flow pump 80 is started and the rated operation is performed from the state where the flow path of the pipe 41 is closed will be described. .

  The control unit 44 closes the on-off valve so that the flow path of the pipe 41 is closed. At this time, the internal bypass valve 84 is closed. In this state, the control unit 44 rotates the impeller 25 by driving the drive source 35 and rotating the main shaft 36. As the impeller 25 rotates, the mixed flow pump 80 sucks fluid from the suction port 17 and sends the sucked fluid toward the discharge port 18. At this time, since the pipe 41 is closed by the on-off valve, the pressure in the internal flow path 8 rises. The controller 44 opens the internal bypass valve 84 when the pressure in the internal flow path 8 detected by the pressure gauge 45 becomes higher than a predetermined pressure. Then, the fluid in the internal flow path 8 on the discharge side of the impeller 25 flows through the gap C and flows into the internal bypass flow path 83. The fluid that has flowed into the internal bypass flow path 83 passes through the internal bypass flow path 83 and flows into the internal flow path 8 on the suction side of the impeller 25. That is, the fluid in the internal flow path 8 on the discharge side of the impeller 25 passes through the internal bypass flow path 83 and returns to the internal flow path 8 on the suction side of the impeller 25. For this reason, even if the on-off valve closes the flow path of the pipe 41, the head H shown in FIG. At this time, the pressure reducing mechanism 81 is designed so that the flow rate of the fluid recirculated through the internal bypass flow channel 83 is a flow rate that is lower than the design limit pressure P.

  Then, when the mixed flow pump 80 reaches the rated operation, the control unit 44 opens the on-off valve provided in the pipe 41 so that the flow path of the pipe 41 is opened. The mixed flow pump 80 that operates at a rated rate discharges the fluid sucked from the suction port 17 to the pipe 41 through the discharge port 18. The fluid discharged to the pipe 41 flows through the pipe 41.

  As described above, according to the configuration of the second embodiment, the internal bypass passage 83 can be opened by operating the internal bypass valve 84 at the time of closing. For this reason, the fluid flowing through the internal flow path 8 on the discharge side from the front edge of the impeller 25 is guided to the internal flow path 8 on the suction side of the impeller 25 via the internal bypass flow path 83. Thus, the fluid flowing through the internal flow path 8 is circulated between the internal flow path 8 on the discharge side of the impeller 25 and the internal flow path 8 on the suction side of the impeller 25 by the internal bypass flow path 83. Thus, the pressure on the downstream side of the front edge of the impeller 25 can be reduced, and the head H can be efficiently reduced.

  In the second embodiment, an on-off valve is applied as the internal bypass valve 84. However, a pressure regulating valve that opens when the pressure becomes higher than a predetermined pressure and closes when the pressure becomes lower than the predetermined pressure may be applied. In this case, since it is not necessary to execute the opening / closing control by the control unit 44 based on the detection result of the pressure gauge 45, the configuration can be simplified.

  Next, a mixed flow pump 90 according to the third embodiment will be described with reference to FIG. FIG. 5 is a schematic diagram of a mixed flow pump according to the third embodiment. In the third embodiment, only parts different from the first and second embodiments will be described in order to avoid overlapping with the first and second embodiments. In the mixed flow pump 80 of the second embodiment, the pressure reducing mechanism 81 is provided inside the impeller 25, but in the mixed flow pump 90 of the third embodiment, the pressure reducing mechanism 91 is provided outside the outer casing 4. Yes. In the third embodiment, as in the second embodiment, the three-way valve 42 of the first embodiment provided in the pipe 41 is an on-off valve. Hereinafter, the pressure reducing mechanism 91 of the mixed flow pump 90 according to the third embodiment will be described with reference to FIG.

  As shown in FIG. 5, the decompression mechanism 91 has an external bypass pipe 93 provided outside the outer cylinder casing, and an external bypass valve 94 provided in the external bypass pipe 93.

  The external bypass pipe 93 is connected to the outer casing 4 so that one end thereof communicates with the internal flow path 8 between the impeller 25 and the diffuser 30. That is, one end of the external bypass pipe 93 is connected to the impeller casing 11 or the shroud 12 between the impeller 25 and the diffuser 30. The external bypass pipe 93 is provided with the other end immersed in the fluid of the pit 38. A discharge port 95 is formed at the other end of the external bypass pipe 93 and is disposed in the vicinity of the suction port 17 of the mixed flow pump 90. For this reason, the fluid discharged from the discharge port 95 of the external bypass pipe 93 is sucked from the suction port 17 of the mixed flow pump 90.

  Next, the operation of the pressure reducing mechanism 91 of the mixed flow pump 90 when the piping 41 is closed will be described. In the following description, as an example of closing, the case where the flow path of the pipe 41 is opened after the mixed flow pump 90 is started and the rated operation is performed from the state where the flow path of the pipe 41 is closed will be described. .

  The control unit 44 closes the on-off valve so that the flow path of the pipe 41 is closed. At this time, the external bypass valve 94 is closed. In this state, the control unit 44 rotates the impeller 25 by driving the drive source 35 and rotating the main shaft 36. As the impeller 25 rotates, the mixed flow pump 90 sucks fluid from the suction port 17 and sends the sucked fluid toward the discharge port 18. At this time, since the pipe 41 is closed by the on-off valve, the pressure in the internal flow path 8 rises. The control unit 44 opens the external bypass valve 94 when the pressure in the internal flow path 8 detected by the pressure gauge 45 becomes higher than a predetermined pressure. Then, the fluid in the internal flow path 8 on the discharge side of the impeller 25 flows into the external bypass pipe 93. The fluid flowing into the external bypass pipe 93 flows through the external bypass pipe 93 and is returned to the pit 38. A part of the fluid returned to the pit 38 is sucked again from the suction port 17 of the mixed flow pump 90. Even when the mixed flow pump 90 reaches the rated operation, that is, even if the rotation of the impeller 25 reaches a predetermined number of rotations, the fluid sucked from the suction port 17 of the mixed flow pump 90 is external bypass pipe 93. Is circulated to the pit 38. For this reason, even if the on-off valve closes the flow path of the pipe 41, the head H shown in FIG. At this time, the pressure reducing mechanism 91 is designed so that the flow rate of the fluid recirculated through the internal bypass flow channel 83 is a flow rate lower than the design limit pressure P.

  When the mixed flow pump 90 reaches the rated operation, the control unit 44 opens the on-off valve and opens the pipe 41. The mixed flow pump 90 that operates at a rated rate discharges the fluid sucked from the suction port 17 to the pipe 41 through the discharge port 18. The fluid discharged to the pipe 41 flows through the pipe 41.

  As described above, according to the configuration of the third embodiment, the external bypass pipe 93 can be opened by operating the external bypass valve 94 at the time of closing. For this reason, the fluid flowing through the internal flow path 8 on the discharge side with respect to the front edge of the impeller 25 is guided to the external bypass pipe 93, so that the pressure on the downstream side of the front edge of the impeller 25 is reduced. And the head H can be reduced. Further, according to the configuration of the third embodiment, the pressure reducing mechanism 91 can be handled integrally with the mixed flow pump 90.

  In the third embodiment, one end of the external bypass pipe 93 is connected to the outer casing 4 so as to communicate with the internal flow path 8 between the impeller 25 and the diffuser 30. However, the configuration is limited to this configuration. Not. As shown by the dotted line in FIG. 5, one end of the external bypass pipe 93 may be connected to the bent pipe 14 in the vicinity of the discharge port 18. Even in this configuration, the pressure reducing mechanism 91 can be handled integrally with the mixed flow pump 90.

DESCRIPTION OF SYMBOLS 1 Diagonal flow pump 4 Outer cylinder casing 5 Inner cylinder hub 8 Internal flow path 10 Suction bell mouth 11 Impeller casing 12 Shroud 13 Pumping pipe 14 Bending pipe 17 Suction inlet 18 Discharge outlet 20 Impeller side hub 21 Diffuser side hub 22 Lifting pipe Side hub 25 Impeller 26 Vane 30 Diffuser 31 Diffuser vane 35 Drive source 36 Main shaft 38 Pit 41 Piping 42 Three-way valve 44 Control unit 45 Pressure gauge 51 Pressure reducing mechanism 52 Bypass pipe 53 Discharge port 80 Diagonal flow pump (Example 2)
81 Pressure reducing mechanism (Example 2)
83 Internal bypass flow path (Example 2)
84 Internal bypass valve (Example 2)
90 Mixed flow pump (Example 3)
91 Pressure reducing mechanism (Example 3)
93 External bypass pipe (Example 3)
94 Valve for external bypass (Example 3)
95 Discharge port (Example 3)
C gap

Claims (1)

A casing in which an internal flow path from the suction port to the discharge port is formed;
An impeller that is housed in the casing, takes in fluid from the suction port, and sends out the fluid toward the discharge port;
When the valve provided in the pipe connected to the discharge port is closed, the front edge of the impeller is such that the pressure in the internal flow path on the discharge side from the front edge of the impeller is equal to or lower than a predetermined pressure. A pressure reducing mechanism for releasing the fluid flowing through the internal flow path on the discharge side ,
The decompression mechanism is
An internal bypass flow path formed inside the impeller, communicating the internal flow path on the discharge side with respect to the front edge of the impeller, and the internal flow path on the suction side of the impeller,
An internal bypass valve provided in the internal bypass flow path,
The internal bypass passage opens the internal bypass flow path when the internal bypass valve is closed .

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