Centrifugal pump

Abstract

To suppress the lowering of pump efficiency while suppressing the flow-in of a backflow generated at an inlet portion of an impeller into the impeller, in a centrifugal pump.SOLUTION: A centrifugal pump 1 comprises: a casing 3 in which a discharge chamber 10 is formed; a rotating shaft 20 rotatably arranged at the casing 3; an impeller 30 having a plurality of feather plates 31 arranged at the discharge chamber 10, fixed to the rotating shaft 20, located coaxially with the rotating shaft 20 at an inlet 35, and extending toward the outside in a radial direction so as to be separated from the rotating shaft 20; and a liner ring 40 arranged between the casing 3 and the impeller 30, and fixed to the casing 3. The liner ring 40 has a circulation face 40 which is aligned with an outer end 31b of the feather plate 31 at the inlet 35 side in an axial direction of the rotating shaft 20, and extends toward the outside in the radial direction, and also comprises a wall 40a adjoining the outer end 31b at the outside in the radial direction, and a backflow circulation groove 39 which is at least partially defined by the wall 40a.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] When the flow rate of the liquid transferred by a centrifugal pump is lower than the designed flow rate, a reverse flow may occur at the inlet portion of the impeller. When a reverse flow occurs, cavitation due to the reverse flow may occur. When cavitation occurs, vibration and noise may be generated, which may prevent the normal operation of the pump.

[0003] Patent Document 1 discloses a centrifugal pump including a reverse flow circulation portion provided on the radially outer side of the front end portion, which is the portion located on the most suction side of the blade. The reverse flow generated at the inlet portion of the impeller can circulate in the reverse flow circulation portion. Therefore, the spread of the reverse flow to the upstream side can be restricted, and the occurrence of cavitation can be suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the centrifugal pump described in Patent Document 1, the liquid pressurized by the front end portion of the blade also flows into the reverse flow circulation portion. In other words, the proportion of the liquid flowing into the inside of the impeller among the liquid pressurized by the front end portion of the blade may decrease, and the pump efficiency may decrease.

[0006] An object of the present invention is to suppress a decrease in pump efficiency while suppressing the reverse flow generated at the inlet portion of the impeller from flowing into the inside of the impeller in a centrifugal pump.

Means for Solving the Problems

[0007] The present invention centrifugal pump (1) comprises a casing having a discharge chamber formed therein, a rotating shaft rotatably disposed in the casing, an impeller disposed in the discharge chamber and fixed to the rotating shaft, the impeller having a plurality of blade plates with an inlet located coaxially with the rotating shaft and extending radially outward away from the rotating shaft, and a liner disposed between the casing and the impeller and fixed to the casing. The liner is aligned with the outer end of the blade plate on the inlet side in the axial direction of the rotating shaft, has a circulation surface extending radially outward, and includes a first wall (40a) adjacent to the outer end and the radially outer side, and a reverse flow circulation groove (39) at least partially defined by the first wall (40a). has the following basic configuration. In the first aspect of the present invention, the lining includes a first connecting flow path that communicates the discharge chamber and the backflow circulation groove (39). provides a centrifugal pump (1).

[0008] According to the present invention, the circulation surface is aligned with the outer end of the blade plate on the inlet side in the axial direction of the rotating shaft and extends radially outward. Therefore, the reverse flow generated near the inlet of the impeller can flow into the reverse flow circulation groove (39) along the circulation surface. Accordingly, the reverse flow generated near the inlet of the impeller can be suppressed from flowing into the interior of the impeller. Further, the outer end of the blade plate on the inlet side is adjacent to the first wall (40a). Therefore, the flow of the liquid radially outward of the rotating shaft near the inlet of the impeller can be suppressed. That is, the liquid near the inlet of the impeller can flow toward the interior of the impeller. Accordingly, a decrease in pump efficiency can be suppressed. Also, in the first aspect, liquid can flow from the relatively high-pressure discharge chamber toward the relatively low-pressure backflow circulation groove (39) through the first connecting flow path. Therefore, a part of the backflow that has flowed into the backflow circulation groove (39) can be pushed away in the direction away from the impeller. Accordingly, it is possible to suppress the backflow that has flowed into the backflow circulation groove (39) from being sucked into the impeller.

[0009] The liner may include a second wall extending in a direction away from the impeller in the axial direction from the tip of the first wall, and a third wall extending radially inward from the tip of the second wall, and the reverse flow circulation groove may be defined by the first wall, the second wall, and the third wall.

[0010] According to the above configuration, the reverse flow that has flowed into the reverse flow circulation groove can circulate in the reverse flow circulation groove. Therefore, it is possible to suppress the reverse flow that has flowed into the reverse flow circulation groove from flowing out of the reverse flow circulation groove and being sucked into the impeller.

[0011] The third wall may extend from the tip of the second wall toward the impeller side in the radial direction and in the axial direction.

[0012] According to the above configuration, the reverse flow that has flowed into the reverse flow circulation groove can be less likely to flow out of the reverse flow circulation groove by flowing along the third wall. Therefore, it is possible to suppress the reverse flow that has flowed into the reverse flow circulation groove from flowing out of the reverse flow circulation groove and being sucked into the impeller.

[0013] The lining has an opposing portion that is axially spaced apart from the impeller, and a gap that allows the flow of liquid is formed between the outer peripheral portion of the inlet and the opposing portion. The opposing portion may be formed with a high-pressure portion that is a tubular groove having a widened cross-sectional area in a direction intersecting the flow direction of the liquid.

[0014] According to the above configuration, liquid can flow from the relatively high-pressure discharge chamber toward the inlet of the relatively low-pressure impeller through the gap. Therefore, the pressure difference inside the impeller in the radial direction of the rotating shaft can be reduced. Accordingly, the occurrence of cavitation can be suppressed. Also, due to the high-pressure portion, a wide portion and a narrow portion of the cross-sectional area of the gap are formed in the gap. Therefore, the flow of the liquid is decelerated by the wide portion of the cross-sectional area of the gap, and the pressure is increased to effectively eliminate cavitation.

[0015] The high-pressure portion may include a first expansion chamber and a second expansion chamber that is axially spaced apart from the first expansion chamber on the downstream side in the flow direction of the liquid.

[0016] According to the above configuration, since the first expansion chamber and the second expansion chamber are provided, the pressure can be increased in two stages. Therefore, the cavitation elimination effect can be enhanced.

[0017] The lining may include a second connecting flow path that communicates the first expansion chamber and the backflow circulation groove (39).

[0018] According to the above configuration, liquid can flow from the first expansion chamber, which is relatively high-pressure compared to the second expansion chamber, toward the backflow circulation groove (39) through the second connecting flow path. That is, the liquid can flow relatively quickly from the first expansion chamber toward the backflow circulation groove (39). Therefore, a part of the backflow that has flowed into the backflow circulation groove (39) is pushed far away in the direction away from the impeller. Accordingly, it is possible to suppress the backflow that has flowed into the backflow circulation groove (39) from being sucked into the impeller.

[0019] The liner may include a third connecting flow path that connects the second expansion chamber and the backflow circulation groove (39).

[0020] According to the above configuration, liquid can flow from the second expansion chamber, which is relatively at a lower pressure than the first expansion chamber, toward the backflow circulation groove (39) via the third connecting flow path. That is, the flow rate of the liquid flowing from the second expansion chamber toward the backflow circulation groove (39) can be relatively reduced. Therefore, the leakage loss of the pump can be reduced and the efficiency can be improved.

[0021] A second aspect of the present invention provides a centrifugal pump (1) which, in addition to the above basic configuration, includes a liner having an opposing portion spaced apart from the impeller in the axial direction, a gap allowing the flow of liquid being formed between the outer peripheral portion of the inlet and the opposing portion, a high-pressure portion formed in the opposing portion and consisting of a tubular groove having an enlarged cross-sectional area in a direction intersecting the flow direction of the liquid, the high-pressure portion including a first expansion chamber and a second expansion chamber spaced apart from the first expansion chamber on the downstream side in the flow direction of the liquid, and the liner including a second connecting flow path that connects the first expansion chamber and the backflow circulation groove (39).

[0022] A third aspect of the present invention provides a centrifugal pump (1) which, in addition to the above basic configuration, includes a liner having an opposing portion spaced apart from the impeller in the axial direction, a gap allowing the flow of liquid being formed between the outer peripheral portion of the inlet and the opposing portion, a high-pressure portion formed in the opposing portion and consisting of a tubular groove having an enlarged cross-sectional area in a direction intersecting the flow direction of the liquid, the high-pressure portion including a first expansion chamber and a second expansion chamber spaced apart from the first expansion chamber on the downstream side in the flow direction of the liquid, and the liner including a third connecting flow path that connects the second expansion chamber and the backflow circulation groove (39).

Advantages of the Invention

[0023] According to the centrifugal pump of the present invention, it is possible to suppress a decrease in pump efficiency while suppressing the reverse flow generated at the inlet portion of the impeller from flowing into the inside of the impeller.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0025] (First Embodiment) FIGS. 1 and 2 show an example of the centrifugal pump 1 in the present embodiment. In the present embodiment, the centrifugal pump 1 is a horizontal-axis double-suction centrifugal pump. Further, in the present embodiment, the centrifugal pump 1 discharges the water (liquid) sucked from the suction port 2 from the discharge port 11, and includes a casing 3, a rotating shaft 20, an impeller 30, and a liner 40.

[0026] The casing 3 includes a casing main body 4 and a casing cover 6.

[0027] In the center in the width direction of the casing body 4, a substantially U-shaped lower partition wall 5 is provided. In the center in the width direction of the casing cover 6, a substantially inverted U-shaped upper partition wall 7 is provided so as to be positioned above the lower partition wall 5. By assembling the casing cover 6 to the casing body 4, the lower partition wall 5 and the upper partition wall 7 form an annular body having a mounting hole 8 at the center. In the mounting hole 8, an annular liner 40 made of a material with good slidability, such as stainless steel, cast iron, or bronze, is arranged and fixed to prevent interference with the impeller 30.

[0028] A suction port 2 and a discharge port 11 are formed in the casing body 4. The liquid flow path from the suction port 2 to the discharge port 11 is constituted by a suction chamber 9 and a discharge chamber 10 formed inside the casing 3. The suction chamber 9 is a flow path communicating with the suction port 2 and is formed on both left and right outer sides of the partition walls 5 and 7 inside the casing 3. The discharge chamber 10 is a flow path communicating with the suction chamber 9 through an opening 38 defined by an annular portion 40i of the liner 40 and communicating with the discharge port 11, and is formed inside the partition walls 5 and 7.

[0029] The rotating shaft 20 is rotatably arranged in the casing 3 so as to penetrate the opening 38 of the liner 40 in the axial direction (X direction). Both ends of the rotating shaft 20 protrude outward from the casing 3 in the X direction, are pivotally supported by bearings 22 with respect to the casing 3, and are sealed by a mechanical seal 21. In FIG. 1, a drive machine such as a motor (not shown) is connected to the right end of the rotating shaft 20.

[0030] The impeller 30 is of a double-suction type, is arranged in the discharge chamber 10, and is fixed to the rotating shaft 20. In the present embodiment, the impeller 30 is symmetric with respect to a central axis CL that passes through the center of the impeller 30 in the X direction and the center of the suction port 2. Therefore, in the following description, only the left side with respect to the central axis CL will be described, but the right side has the same configuration.

[0031] The impeller 30 rotates integrally with the rotating shaft 20 to suck external water from the suction port 2 into the suction chamber 9 and discharge it from the discharge port 11 through the discharge chamber 10. The impeller 30 is circular when viewed from the direction in which the rotating shaft 20 extends, and includes a plurality of blade plates 31 extending radially outward and a shroud 32 disposed outside the blade plates 31 in the X direction.

[0032] The blade plate 31 extends from a base end portion 31a located on the rotating shaft 20 side to a tip end portion 31c located radially outside the impeller 30 so as to be away from the rotating shaft 20. Further, the blade plate 31 is substantially rectangular having an outer end 31b at the outermost side in the X direction. A fixing portion 33 for fixing to the rotating shaft 20 is integrally provided at the base end portion 31a of the blade plate 31. A raised portion 34 is formed in the fixing portion 33 to guide the sucked water radially outside the impeller 30.

[0033] The shroud 32 is fixed outside the blade plate 31 in the X direction. The shroud 32 is in the shape of a disk having an outer diameter whose outer peripheral edge coincides with the tip end portion 31c of the blade plate 31. An inlet 35 is formed at the center of the shroud 32 where the base end portion 31a of the blade plate 31 is located, and the inlet 35 and the rotating shaft 20 are coaxially positioned.

[0034] As described above, the lining 40 is disposed between the casing 3 and the impeller 30 and is fixed to the casing 3. In the present embodiment, the lining 40 includes a wall (first wall) 40a, a wall (second wall) 40b, a wall (third wall) 40c, and a backflow circulation groove 39.

[0035] In this embodiment, the annular portion 40i of the lining 40 is adjacent to the outer end 31b of the blade plate 31 in the radially outer direction. Further, the wall 40a extends radially outward from the annular portion 40i. That is, the wall 40a is adjacent to the outer end 31b in the radially outer direction. Further, the wall 40a has a circulation surface 40e on the side opposite to the impeller 30 in the X direction. The circulation surface 40e is aligned with the outer end 31b on the inlet 35 side of the blade plate 31 in the X direction and extends radially outward. That is, the wall 40a is configured to have a thickness from the circulation surface 40e aligned with the outer end 31b in the X direction toward the impeller 30. Preferably, the outer end 31b and the circulation surface 40e are at the same position in the X direction.

[0036] The wall 40b extends in a direction away from the impeller 30 in the X direction from the tip of the wall 40a, that is, the radially outer end portion. Further, the wall 40b has a circulation surface 40f on the radially inner side. The circulation surface 40f is connected to the radially outer end portion of the circulation surface 40e. That is, the circulation surface 40e and the circulation surface 40f are continuous.

[0037] The wall 40c extends radially inward from the tip of the wall 40b, that is, the end portion on the side opposite to the impeller 30 in the X direction. Further, the wall 40c has a circulation surface 40g on the impeller 30 side in the X direction. The circulation surface 40g is connected to the end portion on the side opposite to the impeller 30 in the X direction of the circulation surface 40f. That is, the circulation surface 40f and the circulation surface 40g are continuous. In this embodiment, the wall 40a and the wall 40c, more specifically, the circulation surface 40e and the circulation surface 40g are substantially parallel.

[0038] The backflow circulation groove 39 is defined by the walls 40a to 40c. More specifically, the backflow circulation groove 39 is defined by the circulation surfaces 40e to 40g. The backflow circulation groove 39 only needs to be defined at least in part by the wall 40a, that is, all or part of the walls 40b and 40c may be absent.

[0039] In this embodiment, a gap 41 that allows the flow of water from the discharge chamber 10 toward the suction chamber 9 is formed between the impeller 30 and the casing 3. Specifically, the gap 41 allows the flow of water from the discharge chamber 10 toward the location where water is sucked by the impeller 30 of the suction chamber 9, that is, near the inlet 35 of the impeller 30. In other words, the gap 41 communicates the discharge chamber 10 with the inlet 35 of the impeller 30.

[0040] The gap 41 is formed between the outer peripheral portion 36 of the inlet 35 and the outer peripheral portion (opposing portion) 40h of the opening 38 of the lining 40. The opening 38 of the lining 40 and the inlet 35 are formed concentrically and with substantially the same diameter, and are arranged at an interval defined in the X direction. In other words, the outer peripheral portion 40h is positioned at an interval from the impeller 30 in the X direction.

[0041] In order to more effectively eliminate cavitation on the base end portion 31a side of the impeller 30, a high-pressure portion 43 is formed in the gap 41. The high-pressure portion 43 includes expansion chambers 44, 45. The expansion chambers 44, 45 are formed by annularly notching (cutting) the outer peripheral portion 40h of the lining 40. Also, the expansion chambers 44, 45 are formed in the order of the expansion chamber 44 and the expansion chamber 45 in the water flow direction from the discharge chamber 10 toward the inlet 35 (from the outside to the inside in the radial direction of the impeller 30).

[0042] The expansion chambers 44, 45 widen the cross-sectional area of the gap 41 in the X direction that intersects the water flow direction (the flow direction of the liquid), and are constituted by annular grooves provided in the outer peripheral portion 40h of the lining 40 that constitutes the gap 41. The expansion chamber 44 located on the outer side in the radial direction of the lining 40 (the upstream side in the water flow direction) and the expansion chamber 45 located on the inner side in the radial direction of the lining 40 (the downstream side in the water flow direction) are formed with a defined interval therebetween.

[0043] The thus formed gap 41 has a labyrinth structure with a wide portion and a narrow portion in the cross-sectional area of the gap 41 due to two or more expansion chambers 44, 45. And, the wide portion of the cross-sectional area of the gap 41 can decelerate the flow of water flowing through the gap 41 and increase the pressure.

[0044] According to the present embodiment, the circulation surface 40e extends radially outward from the same position as the outer end 31b on the inlet 35 side of the impeller plate 31 in the axial direction of the rotation shaft 20. Therefore, the reverse flow generated near the inlet 35 of the impeller 30 can flow into the reverse flow circulation groove 39 along the circulation surface 40e. Accordingly, the reverse flow generated near the inlet 35 of the impeller 30 can be suppressed from flowing into the inside of the impeller 30. Further, the outer end 31b on the inlet 35 side of the impeller plate 31 is adjacent to the wall 40a. Therefore, the liquid can be suppressed from flowing radially outward of the rotation shaft 20 near the inlet 35 of the impeller 30. That is, the liquid near the inlet 35 of the impeller 30 can flow toward the inside of the impeller 30. Accordingly, the reduction of the pump efficiency can be suppressed.

[0045] Also, since the lining 40 includes the wall 40b and the wall 40c, the reverse flow that has flowed into the reverse flow circulation groove 39 can circulate in the reverse flow circulation groove 39. Therefore, the reverse flow that has flowed into the reverse flow circulation groove 39 can be suppressed from flowing out of the reverse flow circulation groove 39 and being sucked into the impeller 30.

[0046] Furthermore, through the gap 41, the liquid can flow from the discharge chamber 10, which is relatively high in pressure, toward the inlet 35 of the impeller 30, which is relatively low in pressure. Therefore, the pressure difference between the base end portion 31a and the tip end portion 31c of the impeller plate 31, that is, the pressure difference inside the impeller 30 in the radial direction of the rotation shaft 20 can be reduced. Accordingly, the occurrence of cavitation can be suppressed. Also, due to the high-pressure portion 43, since a wide portion and a narrow portion are formed in the cross-sectional area of the gap 41, the wide portion of the cross-sectional area of the gap 41 can decelerate the flow of the liquid and increase the pressure, thereby effectively eliminating cavitation.

[0047] The configuration of the centrifugal pump 1 according to the following second to seventh embodiments differs from that of the first embodiment in the following points. The other configurations of these embodiments are the same as those of the first embodiment, and the same or similar elements as those of the first embodiment are denoted by the same reference numerals.

[0048] (Second Embodiment) Referring to FIG. 3, in the second embodiment, the liner 40 includes a connecting flow path (second connecting flow path) 47 that fluidly connects the expansion chamber 44 and the reverse circulation groove 39 to the wall 40a. Specifically, the connecting flow path 47 extends annularly along the X direction from the expansion chamber 44 toward the reverse circulation groove 39.

[0049] According to the second embodiment, liquid can flow from the expansion chamber 44, which is relatively at a higher pressure than the expansion chamber 45, toward the reverse circulation groove 39 through the connecting flow path 47. That is, the liquid can flow relatively fast from the expansion chamber 44 toward the reverse circulation groove 39. Therefore, a part of the reverse flow that has flowed into the reverse circulation groove 39 is pushed far away in the direction away from the impeller 30. Accordingly, the reverse flow that has flowed into the reverse circulation groove 39 can be suppressed from being sucked into the impeller 30.

[0050] (Third Embodiment) Referring to FIG. 4, in the third embodiment, the liner 40 includes a connecting flow path (third connecting flow path) 48 that fluidly connects the expansion chamber 45 and the reverse circulation groove 39 to the wall 40a. Specifically, the connecting flow path 48 extends annularly along the X direction from the expansion chamber 45 toward the reverse circulation groove 39.

[0051] According to the third embodiment, liquid can flow from the expansion chamber 45, which is relatively at a lower pressure than the expansion chamber 44, toward the reverse circulation groove 39 through the connecting flow path 48. That is, the flow rate of the liquid flowing from the expansion chamber 45 toward the reverse circulation groove 39 can be relatively reduced. Therefore, the leakage loss of the pump can be reduced and the efficiency can be improved.

[0052] (Fourth Embodiment) Referring to FIG. 5, in the fourth embodiment, the lining 40 includes a connecting flow path (second connecting flow path) 47 that fluidly connects the expansion chamber 44 and the reverse circulation groove 39 to the wall 40a. Specifically, the connecting flow path 47 extends annularly along the X direction from the expansion chamber 44 toward the reverse circulation groove 39.

[0053] Further, the lining 40 includes a connecting flow path (third connecting flow path) 48 that fluidly connects the expansion chamber 45 and the reverse circulation groove 39 to the wall 40a. Specifically, the connecting flow path 48 extends annularly along the X direction from the expansion chamber 45 toward the reverse circulation groove 39.

[0054] According to the fourth embodiment, through the connecting flow path 47, liquid can flow from the expansion chamber 44, which is relatively at a higher pressure than the expansion chamber 45, toward the reverse circulation groove 39. That is, the liquid can flow relatively fast from the expansion chamber 44 toward the reverse circulation groove 39. Therefore, a part of the reverse flow that has flowed into the reverse circulation groove 39 is pushed far away in the direction away from the impeller 30. Accordingly, the reverse flow that has flowed into the reverse circulation groove 39 can be suppressed from being sucked into the impeller 30.

[0055] Also, through the connecting flow path 48, liquid can flow from the expansion chamber 45, which is relatively at a lower pressure than the expansion chamber 44, toward the reverse circulation groove 39. That is, the flow rate of the liquid flowing from the expansion chamber 45 toward the reverse circulation groove 39 can be relatively reduced. Therefore, the leakage loss of the pump can be reduced and the efficiency can be improved.

[0056] (Fifth Embodiment) Referring to FIG. 6, in the fifth embodiment, the lining 40 includes a connecting flow path (first connecting flow path) 46 that fluidly and directly connects the discharge chamber 10 and the reverse circulation groove 39 to the wall 40a. Specifically, the connecting flow path 46 extends annularly at an angle with respect to the X direction from the discharge chamber 10 toward the reverse circulation groove 39.

[0057] According to the fifth embodiment, liquid can flow from the discharge chamber 10, which is relatively at a high pressure, toward the backflow circulation groove 39, which is relatively at a low pressure, through the connection flow path 46. Therefore, a part of the backflow that has flowed into the backflow circulation groove 39 can be pushed away in a direction away from the impeller 30. Accordingly, it is possible to suppress the backflow that has flowed into the backflow circulation groove 39 from being sucked into the impeller 30.

[0058] (Sixth Embodiment) Referring to FIG. 7, in the sixth embodiment, the wall 40c of the lining 40 extends from the tip of the wall 40b toward the inside in the radial direction and toward the impeller 30 side in the X direction. In other words, the tip of the wall 40c is inclined toward the wall 40a.

[0059] According to the sixth embodiment, the backflow that has flowed into the backflow circulation groove 39 can be less likely to flow out of the backflow circulation groove 39 by flowing along the wall 40c. Therefore, it is possible to suppress the backflow that has flowed into the backflow circulation groove 39 from flowing out of the backflow circulation groove 39 and being sucked into the impeller 30.

[0060] (Seventh Embodiment) Referring to FIG. 8, in the seventh embodiment, the lining 40 includes a discharge flow path 49 that fluidly connects the backflow circulation groove 39 and the suction chamber 9 between the wall 40b and the wall 40c. Specifically, one end 49a of the discharge flow path 49 is located at the connection portion between the circulation surfaces 40f and 40g, and the other end 49b is located on the outer surface 40j, which is the surface of the lining 40 that is farthest from the impeller 30 in the X direction. Further, the other end 49b is located outside the one end 49a in the radial direction. That is, the discharge flow path 49 extends annularly from the backflow circulation groove 39 toward the outside in the radial direction and away from the impeller 30 in the X direction.

[0061] In the seventh embodiment, the backflow that has flowed into the backflow circulation groove 39 flows out into the suction chamber 9 through the discharge flow path 49. Therefore, the backflow can be kept away from the impeller 30, and it is possible to suppress the backflow from being sucked into the impeller 30.

Explanation of Reference Numerals

[0062] 1 Centrifugal pump 2 Suction port 3 Casing 4 Casing body 5 Lower partition wall 6 Casing cover 7 Upper partition wall 8 Mounting hole 9 Suction chamber 10 Discharge chamber 11 Discharge port 20 Rotating shaft 21 Mechanical seal 22 Bearing 30 Impeller 31 Blade plate 31a Base end 31b Outer end 31c Tip end 32 Shroud 33 Fixing part 34 Protrusion 35 Inlet 36 Outer peripheral part 38 Opening 39 Backflow circulation groove 40 Lining 40a Wall (first wall) 40b Wall (second wall) 40c Wall (third wall) 40e, 40f, 40g Circulation surface 40h Outer peripheral part (opposing part) 40i Annular part 40j Outer surface 41 Gap 42 Inlet 43 High-pressure part 44 Expansion chamber (first expansion chamber) 45 Expansion chamber (second expansion chamber) 46 Connecting flow path (first connecting flow path) 47 Connecting flow path (second connecting flow path) 48 Connecting flow path (third connecting flow path) 49 Discharge flow path 49a One end 49b The other end CL Central axis

Claims

1. A casing having a discharge chamber formed therein, a rotating shaft rotatably disposed in the casing, an impeller disposed in the discharge chamber and fixed to the rotating shaft, having a plurality of blade plates with an inlet located coaxially with the rotating shaft and extending radially outward away from the rotating shaft, a liner disposed between the casing and the impeller and fixed to the casing and comprising: The liner is aligned with the outer end of the blade plate on the inlet side in the axial direction of the rotating shaft, has a circulation surface extending radially outward, and a first wall adjacent to the outer end and in the radially outward direction, a backflow circulation groove at least partially defined by the first wall, and a first connecting flow path communicating the discharge chamber and the backflow circulation groove A centrifugal pump.

2. The liner comprises a second wall extending from the tip of the first wall in a direction away from the impeller in the axial direction, and a third wall extending from the tip of the second wall toward the radially inner side and comprising: The backflow circulation groove is defined by the first wall, the second wall, and the third wall. The centrifugal pump according to claim 1.

3. The third wall extends from the tip of the second wall toward the radially inner side and the impeller side in the axial direction. The centrifugal pump according to claim 2.

4. The liner has an opposing portion spaced apart from the impeller in the axial direction, a gap allowing the flow of liquid is formed between the outer peripheral portion of the inlet and the opposing portion, and a high-pressure portion in the form of an annular groove with an enlarged cross-sectional area in a direction intersecting the flow direction of the liquid is formed in the opposing portion. The centrifugal pump according to any one of claims 1 to 3.

5. The high-pressure portion comprises a first expansion chamber, and a second expansion chamber spaced apart from the first expansion chamber on the downstream side in the flow direction of the liquid The centrifugal pump according to claim 4.

6. The liner comprises a second connecting flow path communicating the first expansion chamber and the backflow circulation groove. The centrifugal pump according to claim 5.

7. The liner comprises a third connecting flow path communicating the second expansion chamber and the backflow circulation groove. The centrifugal pump according to claim 5 or 6.

8. A casing having a discharge chamber formed therein, a rotating shaft rotatably disposed in the casing, An impeller having a plurality of blade plates that are disposed in the discharge chamber and fixed to the rotating shaft, with an inlet located coaxially with the rotating shaft and extending radially outward away from the rotating shaft. A liner that is disposed between the casing and the impeller and fixed to the casing. Comprising: The liner: Is aligned with the outer end of the blade plate on the inlet side in the axial direction of the rotating shaft, has a circulation surface extending radially outward, a first wall adjacent to the outer end and in the radially outer side, A reverse flow circulation groove at least partially defined by the first wall, An opposing portion spaced apart from the impeller in the axial direction. Comprising. A gap allowing the flow of liquid is formed between the outer peripheral portion of the inlet and the opposing portion. In the opposing portion, a high-pressure portion is formed by an annular groove having a widened cross-sectional area in a direction intersecting the flow direction of the liquid. The high-pressure portion includes a first expansion chamber and a second expansion chamber spaced apart from the first expansion chamber on the downstream side in the flow direction of the liquid. The liner includes a second connection passage communicating the first expansion chamber and the reverse flow circulation groove. A centrifugal pump.

9. A casing having a discharge chamber formed therein, A rotating shaft rotatably disposed in the casing, An impeller having a plurality of blade plates that are disposed in the discharge chamber and fixed to the rotating shaft, with an inlet located coaxially with the rotating shaft and extending radially outward away from the rotating shaft. A liner that is disposed between the casing and the impeller and fixed to the casing. Comprising: The liner: Is aligned with the outer end of the blade plate on the inlet side in the axial direction of the rotating shaft, has a circulation surface extending radially outward, a first wall adjacent to the outer end and in the radially outer side, A reverse flow circulation groove at least partially defined by the first wall, An opposing portion spaced apart from the impeller in the axial direction. Comprising. A gap allowing the flow of liquid is formed between the outer peripheral portion of the inlet and the opposing portion. In the opposing portion, a high-pressure portion is formed by an annular groove having a widened cross-sectional area in a direction intersecting the flow direction of the liquid. The high-pressure portion includes a first expansion chamber and a second expansion chamber spaced apart from the first expansion chamber on the downstream side in the flow direction of the liquid. The centrifugal pump, wherein the lining includes a third connecting flow path that communicates the second expansion chamber and the reverse circulation groove.

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