Centrifugal pump

Abstract

To provide a centrifugal pump capable of effectively reducing radial thrust during operation at a partial flow rate.SOLUTION: A centrifugal pump 1 comprises a plurality of balance pipes 11A to 11H, each having a first end part 11a connected to a centrifugal flow path 5 and a second end part 11b connected to an inlet 3b side of an impeller 3. Each balance pipe 11A to 11H blocks communication between the centrifugal flow path 5 and the inlet 3b side when the differential pressure (P1-P2) between a pressure P1 in the centrifugal flow path 5 and a pressure P2 on the inlet 3b side of the impeller 3 is less than a threshold value Pth, and connects the centrifugal flow path 5 and the inlet 3b side when the differential pressure (P1-P2) is equal to or larger than the threshold value Pth.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a centrifugal pump. [Background technology]

[0002] It is known that in a centrifugal pump, when it is operated at a partial flow rate below the rated flow rate, the axial symmetry of the flow at the impeller outlet is lost, the pressure distribution in the volute passage at the impeller outlet becomes uneven, and a radial unbalanced resultant force (radial thrust) acts on the impeller.

[0003] In the volute pump disclosed in Patent Document 1, multiple connecting pipes are provided to connect the volute flow paths to an annular pipe provided on the outside of the volute casing, thereby making the pressure distribution in the volute flow path uniform and reducing radial thrust. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 57-23115 Summary of the Invention [Problem to be solved by the invention]

[0005] In the centrifugal pump disclosed in Patent Document 1, since multiple connecting pipes are connected to a common annular pipe, the pressure distribution cannot be effectively uniformed due to the influence of the pressure gradient. In other words, the centrifugal pump disclosed in Patent Document 1 cannot effectively reduce the radial thrust.

[0006] An object of the present invention is to provide a centrifugal pump that can effectively reduce radial thrust during operation at a partial flow rate. [Means for solving the problem]

[0007] One aspect of the present invention provides a spiral pump comprising: a spiral casing; an impeller having a plurality of blades having an inlet on an inner peripheral side and an outlet on an outer peripheral side and disposed within the spiral casing; a spiral flow path provided within the spiral casing adjacent to the outlet on the outer peripheral side of the impeller; and a plurality of balance pipes each having a first end connected to the spiral flow path and a second end connected to the inlet side, the balance pipes blocking communication between the spiral flow path and the inlet side of the impeller if a pressure difference between the pressure of the spiral flow path and the pressure on the inlet side of the impeller is less than a threshold value, and connecting the spiral flow path and the inlet side of the impeller if a pressure difference between the pressure of the spiral flow path and the pressure on the inlet side of the impeller is equal to or greater than a threshold value.

[0008] The balance pipe blocks communication between the volute passage and the inlet side of the impeller when the pressure difference between the pressure of the volute passage and the pressure of the inlet side of the impeller is less than a threshold value, but connects the volute passage and the inlet side of the impeller when the pressure difference becomes equal to or greater than the threshold value. Therefore, when the volute pump is operated at a partial flow rate, the pressure distribution of the volute passage becomes uneven, causing a pressure increase region, and when the pressure difference becomes equal to or greater than the threshold value, the balance pipe connecting the pressure increase region and the inlet side of the impeller connects the pressure increase region and the inlet side of the impeller. Then, a flow returning from the pressure increase region to the inlet side of the impeller is generated through the balance pipe in a connected state. As a result, the pressure in the pressure increase region decreases, the pressure distribution of the volute passage is made uniform, and the radial thrust is reduced. Since the multiple balance pipes each individually connect the volute passage and the inlet side of the impeller, the flow from the pressure increase region toward the inlet side of the impeller through one balance pipe is not affected by the pressure loss of the other balance pipes. Therefore, the reduction in radial thrust due to the uniform pressure distribution can be effectively achieved.

[0009] In one specific aspect, the present invention includes a plurality of differential pressure control valves that are provided in a plurality of balance pipes, respectively, and that close when the differential pressure between the pressure on the volute flow path side and the pressure on the inlet side of the impeller is less than a threshold value, and that open when the differential pressure between the pressure on the volute flow path side and the pressure on the inlet side of the impeller is equal to or greater than a threshold value.

[0010] In this case, the plurality of balance pipes are disposed evenly in the circumferential direction of the spiral flow passage.

[0011] In another specific aspect, the pressure sensor includes a plurality of first pressure sensors arranged adjacent to the first end and each detecting the pressure in the spiral flow path, a second pressure sensor detecting the pressure on the inlet side of the impeller, a plurality of on-off valves respectively provided in the plurality of balance pipes, and a control unit that closes the on-off valve provided in the corresponding balance pipe if a differential pressure between the pressure detected by the first pressure sensor and the pressure detected by the second pressure sensor is less than the threshold value, and opens the on-off valve provided in the corresponding balance pipe if a differential pressure between the pressure detected by the first pressure sensor and the pressure detected by the second pressure sensor is less than the threshold value.

[0012] In this case, the plurality of balance pipes and the first pressure sensor are disposed evenly in the circumferential direction of the spiral flow passage. Effect of the Invention

[0013] The centrifugal pump according to the present invention can effectively reduce the radial thrust when operating at partial flow rates. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic perspective view showing a centrifugal pump according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the centrifugal pump of FIG. 1 taken along a cross section perpendicular to the shaft. [Diagram 3] Schematic cross-sectional view of the centrifugal pump of FIG. 1 at a cross section perpendicular to the shaft when operating at rated flow rate. [Figure 4] FIG. 2 is a schematic cross-sectional view of the centrifugal pump of FIG. 1 in a cross section perpendicular to the shaft when operating at partial flow rate. [Diagram 5] FIG. 4 is a schematic perspective view showing a centrifugal pump according to a second embodiment of the present invention. [Figure 6]FIG. 6 is a schematic cross-sectional view of the centrifugal pump of FIG. 5 taken along a cross section perpendicular to the shaft. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0016] (First embodiment) 1 and 2, a single-suction type centrifugal pump 1 according to an embodiment of the present invention includes a centrifugal casing 2, and an impeller 3 is housed within the centrifugal casing 2. A shaft 4 is mechanically connected to the impeller 3, and the shaft 4 is driven to rotate by a driving mechanism such as a motor (not shown), so that the impeller 3 rotates together with the shaft 4. The impeller 3 includes a plurality of blades 3a, and an inlet 3b and an outlet 3c (which are also the inlet and outlet of the impeller 3 itself) of each blade 3a are located on the inner and outer circumferential sides, respectively.

[0017] A spiral flow passage 5 is provided within the spiral casing 2 so as to adjacently surround the outer periphery of the impeller 3, and therefore adjacent to the outlet 3c of each blade 3b. The spiral casing 2 is provided with a suction port 2a facing the inlet 3b of the impeller 3, and a discharge port 2b continuous with the spiral flow passage 5. A suction side pipe 6 is connected to the suction port 2a, and a discharge side pipe 7 is connected to the discharge port 2b.

[0018] The volute casing 2 includes eight balance pipes 11A to 11H. Each balance pipe 11A to 11H includes a first end 11a attached to the volute casing 2 and fluidly connected to a part or a limited area of ​​the volute passage 5, and a second end 11b attached to the suction side pipe 6 and fluidly connected to the inlet 3b side of the impeller 3. The first ends 11a of the eight balance pipes 11A to 11H are evenly arranged in the circumferential direction of the volute passage 5. Specifically, the first ends 11a of the eight balance pipes 11A to 11H are provided at equal angular intervals (45 degree intervals) around the axis L of the shaft 4. In the following description, when one of the balance pipes 11A to 11H is mentioned and there is no need to specify which of the balance pipes 11A to 11H it is, it may be referred to as the balance pipe 11.

[0019] Between the first end 11a and the second end 11b of each of the balance pipes 11A to 11H, a differential pressure driven self-regulating valve (hereinafter referred to as a self-regulating valve) 12 is provided. The automatic regulating valve 12 does not require power to open or close, and opens and closes automatically by the movement of a valve element biased by a spring or the like in response to the pressure difference between the primary side and the secondary side.

[0020] The self-regulating valve 12 changes its opening and closing state depending on whether the differential pressure (P1-P2) between the pressure P1 on the first end 11a side, i.e., the primary side, i.e., a part or limited area of ​​the spiral flow passage 5 to which the balance piping 11 is fluidly connected, and the pressure P2 on the second end 11b side, i.e., the inlet 3b side of the impeller 3, is greater than or equal to a specified pressure or threshold value Pth.

[0021] If the pressure difference (P1-P2) between the pressure P1 in a part or limited area of ​​the spiral passage 5 and the pressure P2 on the inlet 3b side of the impeller 3 is less than the threshold value Pth, the self-regulating valve 12 maintains a closed state. In other words, if the pressure difference (P1-P2) is less than the threshold value Pth, the balance pipe 11 blocks communication between the part or area to which the first end 11a of the spiral passage 5 is connected and the inlet side 3b of the impeller 3. On the other hand, if the pressure difference (P1-P2) between the pressure P1 in a part or limited area of ​​the spiral passage 5 and the pressure P2 on the inlet 3b side of the impeller 3 is equal to or greater than the threshold value Pth, the self-regulating valve 12 opens. In other words, when the differential pressure (P1-P2) becomes equal to or greater than the threshold value Pth, the balance pipe 11 connects the part or area to which the first end 11a of the spiral passage 5 is connected with the inlet side 3b of the impeller 3, and water (or other liquid) flows from the part or area to which the first end 11a of the spiral passage 5 is connected to the suction side pipe 6.

[0022] Referring to FIG. 3, when operating at a rated flow rate, the flow rate FL of water flowing from the inlet 3b to the outlet 3c of each blade 3a of the impeller 3 is approximately uniform. Therefore, when operating at a rated flow rate, the pressure distribution (conceptually shown by the thickness of the line indicating the path FP) in the circumferential direction of the spiral passage 5, that is, along the water path FP in the spiral passage 5, is approximately uniform, so that radial thrust does not act on the impeller 3, or even if it does, it is sufficiently small. The threshold value Pth of the self-regulating valve 12 is set to be sufficiently larger than the differential pressure (P1-P2) between the pressure P1 in a part or limited area of ​​the spiral passage 5 during operation at the rated flow rate and the pressure P2 on the inlet 3b side of the impeller 3. Therefore, when operating at a rated flow rate, the self-regulating valves 12 of all the balance pipes 11A to 11H are maintained in a closed state. In other words, when operating at the rated flow rate, the provision of balance pipes 11A to 11H does not affect the performance of centrifugal pump 1, and the same maximum pump efficiency can be maintained as when balance pipes 11A to 11H are not provided.

[0023] On the other hand, referring to Fig. 4, when operating at a partial flow rate below the rated flow rate, the flow rate FL of water flowing from the inlet 3b to the outlet 3c of each blade 3a of the impeller 3 becomes non-uniform, and the pressure distribution in the circumferential direction of the spiral passage 5, i.e., along the water path FP in the spiral passage 5, becomes non-uniform. In the example of Fig. 4, a pressure increase area HPA occurs in the area of ​​the spiral passage 5 to which the first end 11a of the balance pipes 11A and 11B is connected, and a pressure decrease area LPA occurs on the circumferential opposite side of the pressure increase area HPA. Since the threshold value Pth of the self-regulating valve 12 is set to be equal to or greater than the above-mentioned differential pressure (P1-P2) in the pressure increase area HPA, the self-regulating valves 12 of the balance pipes 11C-11H among the balance pipes 11A-11H maintain the closed state, but the self-regulating valves 12 of the balance pipes 11A and 11B whose first end 11a is connected to the pressure increase area HPA are switched from the closed state to the open state. When the self-regulating valve 12 is opened, a flow of water is generated from the pressure increase area HPA back to the suction side pipe 6 through the balance pipes 11A and 11B. As a result, the pressure in the pressure increase area HPA is reduced, the pressure distribution in the spiral passage 5 is uniformed, and the radial thrust is reduced. Since the balance pipes 11A to 11H each individually connect the spiral passage 5 to the suction side pipe 6, the flow from the pressure increase area HPA to the suction side pipe 6 through the balance pipe 11A is not affected by pressure loss or the like in the flow from the pressure increase area HPA to the suction side pipe 6 through the balance pipe 11B. This is also true for the flow from the pressure increase area HPA to the suction side pipe 6 through the balance pipe 11B. Therefore, the radial thrust can be effectively reduced by uniforming the pressure distribution. The reduction in radial thrust can reduce vibration of the centrifugal pump 1, extend its life, and simplify its structure. Furthermore, by reducing the radial thrust, it is possible to reduce the size of the shaft 4 and the bearings (not shown) that support it, and to reduce the rigidity and weight of the entire centrifugal pump 1.

[0024] The centrifugal pump 1 of this embodiment further has the following advantages and features.

[0025] The centrifugal pump 1 of this embodiment can be realized simply by providing a plurality of balance pipes 11 each equipped with a self-regulating valve 12. In other words, the centrifugal pump 1 of this embodiment can be realized not only by newly designing and manufacturing it, but also by modifying an existing centrifugal pump by providing a plurality of balance pipes 11 each equipped with a self-regulating valve 12.

[0026] As described above, the self-regulating valve 12 operates on the pressure difference between the primary and secondary sides and does not require power to open and close. Therefore, no additional electrical equipment or control circuits are required.

[0027] By adjusting the set pressure or threshold value Pth of the self-regulating valve 12, the centrifugal pump 1 of this embodiment can be realized with the same structure of providing multiple balance pipes 11 equipped with self-regulating valves 12 regardless of the size and specific speed of the centrifugal pump.

[0028] During shut-off operation, for all balance pipes 11A to 11H, the pressure P1 on the volute passage 5 side, which is the primary side of the self-regulating valve 12, rises, and the pressure difference (P1-P2) with respect to the pressure P2 on the suction side pipe 6 side, which is the secondary side, exceeds the threshold value Pth, and the self-regulating valve 12 opens. That is, during shut-off operation, a flow of water is generated that returns from the volute passage 5 to the inlet 3b side of the impeller 3 through the balance pipes 11A to 11H. Therefore, even during shut-off operation, shut-off operation is not performed inside the pump, and excessive radial thrust can be prevented from occurring. In addition, since shut-off operation inside the pump can be avoided even during shut-off operation, the shut-off total head that determines the pressure rating of the discharge side pipe 7 can be reduced, and the pipe thickness of the discharge side pipe 7 can be thinned, thereby achieving cost reduction. This effect is remarkable when the specific speed is large.

[0029] Second embodiment A centrifugal pump 1 according to a second embodiment of the present invention will be described below with reference to Figures 5 and 6. In the following description, the centrifugal pump 1 of this embodiment is similar to that of the first embodiment unless otherwise noted. In Figures 5 and 6, elements that are the same as or similar to those of the first embodiment are denoted by the same reference numerals.

[0030] In the centrifugal pump 1 of this embodiment, each of the balance pipes 11A to 11H is provided with an on / off type solenoid valve 22 instead of the self-regulating valve 12 (see FIG. 1, for example) in the first embodiment. These solenoid valves 22 are of a normally closed type that maintain a closed state unless a valve-opening signal is received from a control unit 25 described later.

[0031] On the wall surface of the volute casing 2 facing the volute flow passage 5, first pressure sensors 23A-23H are provided near the first ends 11a of the balance pipes 11A-11H, respectively. Each of the first pressure sensors 23A-23H detects the pressure of a portion or region to which the corresponding first end 11a of the balance pipes 11A-11H is connected in the volute flow passage 5. For example, the first pressure sensor 23A detects the pressure of a portion or region to which the first end 11a of the balance pipe 11A is connected in the volute flow passage 5. That is, each of the first pressure sensors 23A-23H detects the pressure P1 described in the first embodiment. On the other hand, a second pressure sensor 24 is provided on the inner wall surface of the suction side pipe 6. That is, the second pressure sensor 24 detects the pressure P2 described in the first embodiment.

[0032] The centrifugal pump 1 of this embodiment includes a control unit 25. The control unit 25 receives pressures P1 from the first pressure sensors 23A-23H and pressures P2 from the second pressure sensor 24. The control unit 25 controls the open / close states of the solenoid valves 22 of the balance pipes 11A-11H based on the input pressures P1 and P2. The control unit 25 can be constructed by a storage device such as a ROM or a RAM, and a calculation device such as a CPU. The communication connections between the control unit 25 and the first pressure sensors 23A-23H, the second pressure sensor 24, and the solenoid valves 22 may be wired or wireless.

[0033] The control unit 25 stores the threshold value Pth described in the first embodiment. For each of the first pressure sensors 23A to 23H, if the differential pressure (P1-P2) is less than the threshold value Pth, the control unit 25 does not output a valve open signal to the corresponding solenoid valve 22 and keeps the corresponding solenoid valve 22 in a closed state, but if the differential pressure (P1-P2) is equal to or greater than the threshold value Pth, the control unit 25 outputs a valve open signal to the corresponding solenoid valve 22 and opens the corresponding solenoid valve 22.

[0034] For example, when the pressure difference (P1-P2) between the two pressure sensors 23A, 23B becomes equal to or greater than the threshold value Pth, the control unit 25 outputs a valve open signal to the solenoid valves 22 of the balance pipes 11A, 11B to open the valves. This causes a water flow to return from the pressure increase area HPA (see FIG. 4) of the spiral passage 5 to the suction side pipe 6 via the balance pipes 11A, 11B. As a result, the pressure in the pressure increase area HPA decreases, the pressure distribution in the spiral passage 5 is made uniform, and the radial thrust is reduced.

[0035] In this embodiment, by changing the value of the threshold value Pth stored in the control unit 25, the threshold value Pth can be adjusted without replacing parts or the like.

[0036] The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0037] For example, the number of balance pipes 11 is not limited to eight as in the embodiment, but may be set within the range of, for example, four to twelve.

[0038] In the embodiment, the second end 11b of the balance pipe 11 is connected to the suction side pipe 6. However, the connection location of the second end 11b is not particularly limited as long as it is on the inlet 3a side of the impeller 3. [Explanation of symbols]

[0039] 1. Centrifugal pump 2. Spiral casing 2a Intake port 2b Outlet 3 Impeller 3a Feather 3b entrance 3c exit 4 Shaft 5. Spiral Channel 6 Suction side piping 7 Discharge side piping 11A~11H Balance piping 11a First end 11b Second end 12 Differential pressure actuated self-regulating valve 22 Solenoid valve 23A~23H First pressure sensor 24 Second pressure sensor 25 Control Unit AX axis FL Water flow rate at each blade 3a Water path in FP vortex channel 5 HPA Pressure Increase Area LPA Pressure Drop Area

Claims

1. A spiral casing; an impeller disposed within the volute casing, the impeller having a plurality of blades each having an inlet on an inner circumferential side and an outlet on an outer circumferential side; a volute passage provided in the volute casing adjacent to the outlet on an outer circumferential side of the impeller; a plurality of balance pipes each having a first end connected to the swirl flow passage and a second end connected to the inlet side, and blocking communication between the swirl flow passage and the inlet side of the impeller when a pressure difference between the pressure in the swirl flow passage and the pressure on the inlet side of the impeller is less than a threshold value, and connecting the swirl flow passage and the inlet side of the impeller when a pressure difference between the pressure in the swirl flow passage and the pressure on the inlet side of the impeller is equal to or greater than a threshold value; The centrifugal pump comprises:

2. 2. The centrifugal pump according to claim 1, further comprising a plurality of differential pressure control valves respectively provided in a plurality of balance pipes, the differential pressure control valves closing when a differential pressure between the pressure on the volute flow path side and the pressure on the inlet side of the impeller is less than a threshold value and opening when a differential pressure between the pressure on the volute flow path side and the pressure on the inlet side of the impeller is equal to or greater than a threshold value.

3. The centrifugal pump according to claim 2 , wherein the plurality of balance pipes are disposed evenly in a circumferential direction of the centrifugal flow passage.

4. a plurality of first pressure sensors disposed adjacent to the first end and configured to respectively detect the pressure in the spiral passage; a second pressure sensor that detects the pressure on the inlet side of the impeller; A plurality of on-off valves are provided in the plurality of balance pipes, respectively; a control unit that closes the on-off valve provided in the corresponding balance pipe when a differential pressure between the pressure detected by the first pressure sensor and the pressure detected by the second pressure sensor is less than the threshold value, and opens the on-off valve provided in the corresponding balance pipe when a differential pressure between the pressure detected by the first pressure sensor and the pressure detected by the second pressure sensor is less than the threshold value; and The centrifugal pump of claim 1 , comprising:

5. The centrifugal pump according to claim 4 , wherein the plurality of balance pipes and the first pressure sensor are disposed uniformly in a circumferential direction of the centrifugal passage.

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