Centrifugal pump

Abstract

To improve suction performance of a centrifugal pump by reducing a flow rate of a leakage flow in the centrifugal pump.SOLUTION: The centrifugal pump 1 includes a casing 2, a motor 3, a rotary shaft 4, an impeller 5, a pump chamber 21, and a suction pipe 24. The impeller includes a front shroud 52 that is oriented in a first direction. The front shroud includes a first surface 521 and a projecting side 5A projecting from the first surface toward the second direction. The housing includes a first partition wall part 22 arranged opposite to the front shroud. The first partition wall part includes a first facing surface 221 facing the first surface, and a recessed part side 2A recessed in the second direction from the facing surface. A first space S1 is formed between the front shroud and the first partition wall. A part of the convex portion is disposed inside the concave portion. A gap T is formed between the convex portion and the concave portion in the radial direction of the rotary shaft.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In centrifugal pumps, leakage flow is known, in which pumped liquid flows into the gap between the front shroud of the impeller and the housing (hereinafter referred to as the "first space") and flows from the gap between the outer circumferential surface of the impeller's suction port and a liner ring arranged in the housing (hereinafter referred to as the "second space") toward the upstream side of the impeller's suction port (suction pipe). Leakage flow occurs when the pressure of the pumped liquid at the impeller's discharge port is higher than the pressure of the pumped liquid at the impeller's suction port. This leakage flow flows backward relative to the mainstream. The backward flow obstructs part of the mainstream flow. As a result, the suction performance of the centrifugal pump deteriorates. In other words, leakage flow reduces the suction performance of the centrifugal pump.

[0003] Patent Document 1 discloses a configuration in which a labyrinth seal for preventing leakage flow is disposed in the gap between the vicinity of the impeller discharge port and a partition wall facing the impeller. The invention disclosed in Patent Document 1 reduces leakage flow by narrowing the gap in the flow path through the placement of the labyrinth seal. Patent Document 2 also discloses a ring-shaped seal plate extending from either the front shroud or the discharge passage toward the other. The seal plate is disposed so as to protrude in the radial direction of the rotating shaft. In the axial direction of the rotating shaft, the seal plate forms a gap between the seal plate and the discharge passage (housing) or between the seal plate and the front shroud, thereby reducing leakage flow.

[0004] Here, a portion of the pumped fluid discharged from the impeller also flows between the rear shroud and the housing. At this time, the front shroud is pressed toward the rear shroud by a portion of the pumped fluid discharged from the impeller, and the rear shroud is pressed toward the front shroud. In this way, a force (axial thrust force) pushing the impeller from both directions acts on the impeller in the axial direction by a portion of the pumped fluid discharged from the impeller. Therefore, the impeller may move in the axial direction when the pressure distribution in the pump chamber changes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-280694 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-208558 Summary of the Invention [Problem to be solved by the invention]

[0006] In the invention described in Patent Document 1, when the impeller moves in the axial direction, the length of the gap between the vicinity of the impeller's discharge port and the partition wall facing the impeller varies. Also, in the invention described in Patent Document 2, when the impeller moves in the axial direction, the length of the gap between the seal member and the discharge passage (housing) or the length of the gap between the seal member and the front shroud varies. Thus, when the impeller moves in the axial direction, the lengths of the respective gaps do not remain constant in the inventions described in Patent Documents 1 and 2. In other words, when the impeller moves in the axial direction, the inventions described in Patent Documents 1 and 2 cannot stably reduce the flow rate of leakage flow.

[0007] An object of the present invention is to reduce the leakage flow rate in a centrifugal pump and improve the suction performance of the centrifugal pump. [Means for solving the problem]

[0008] A centrifugal pump according to one embodiment of the present invention includes a motor, a rotary shaft driven by the motor to rotate, an impeller attached to the rotary shaft to suck in and discharge pumped liquid, a pump chamber accommodating the impeller, a housing defining the pump chamber, and a suction pipe through which the pumped liquid is introduced to the impeller, wherein, in the axial direction of the rotary shaft, a direction in which the impeller is disposed relative to the suction pipe is a first direction, and a direction opposite to the first direction is a second direction, and the impeller has a suction port that sucks in the pumped liquid from the suction pipe and a front shroud facing the first direction, and the front shroud is oriented in the first direction. The shroud has a first surface facing the second direction and at least one convex portion protruding from the first surface in the second direction, the housing has a first partition portion arranged opposite the front shroud, the first partition portion has an opposing surface facing the first surface and a recess recessed from the opposing surface in the second direction, a first space is formed between the front shroud and the first partition portion into which a portion of the handled fluid discharged from the impeller flows, a portion of the convex portion is positioned inside the recess, and a gap is formed between the convex portion and the recess in the radial direction of the rotating shaft. [Effects of the Invention]

[0009] According to the present invention, the centrifugal pump reduces the leakage flow rate to improve the suction performance of the centrifugal pump. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of a centrifugal pump according to an embodiment of the present invention; [Figure 2] FIG. 2 is a partially enlarged cross-sectional view of the centrifugal pump. [Figure 3] FIG. 2 is a perspective view of a first partition wall portion of a housing of the centrifugal pump. [Figure 4] FIG. 2 is a perspective view of an impeller of the centrifugal pump. [Figure 5]FIG. 4 is a partially enlarged cross-sectional view of the protrusion of the impeller, showing the state in which the protrusion is disposed inside the recess of the first partition wall portion. [Figure 6] 10A and 10B are enlarged cross-sectional views of the convex portion, showing the state in which the convex portion has been moved in the axial direction, where (a) shows the state in which the impeller has been moved backward (first direction) from its normal position, (b) shows the state in which the impeller is located in its normal position, and (c) shows the state in which the impeller has been moved forward (second direction) from its normal position. [Figure 7] FIG. 1 is a partially enlarged schematic cross-sectional view of a conventional centrifugal pump, showing the flow of pumped liquid in the conventional centrifugal pump. [Figure 8] 2 is a partially enlarged schematic cross-sectional view of the centrifugal pump of FIG. 1, showing the flow of pumped liquid in the centrifugal pump. FIG. [Figure 9] 1 is a graph comparing the backflow rate of a centrifugal pump according to the present invention with that of a conventional centrifugal pump. [Figure 10] FIG. 4 is a partially enlarged cross-sectional view of a convex portion of a centrifugal pump according to another embodiment of the present invention. [Figure 11] FIG. 10 is a partially enlarged cross-sectional view of a convex portion of a centrifugal pump according to still another embodiment of the present invention. [Figure 12] FIG. 10 is a schematic front view of a front shroud of a centrifugal pump according to still another embodiment of the present invention. [Figure 13] FIG. 13 is a partially enlarged cross-sectional view of the front shroud taken along line AA in FIG. 12. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of a centrifugal pump according to the present invention will be described below. In the following description, reference will be made to the drawings as appropriate. In the drawings, the same members and elements are designated by the same reference numerals, and duplicated descriptions will be omitted. Furthermore, the dimensional proportions of the elements may be exaggerated for the sake of convenience, and are not limited to the proportions shown in the drawings.

[0012] ●Centrifugal pump● ●Configuration of centrifugal pump FIG. 1 is a schematic cross-sectional view of a centrifugal pump according to an embodiment of the present invention. In this figure, a part of the housing 2 (described later) is shown as a schematic cross-sectional view, and other parts are shown in a simplified form. The figure shows a schematic cross-section of the centrifugal pump 1 cut vertically along the axial direction of the rotating shaft 4 (described later) so as to pass through the axial center of the rotating shaft 4.

[0013] The centrifugal pump 1 sucks in and discharges (transports) a pumped liquid. The centrifugal pump 1 includes a housing 2, a motor 3, a rotating shaft 4, and an impeller 5. The centrifugal pump 1 is an example of the centrifugal pump defined in the present invention.

[0014] The "handled liquid" is a liquid that is handled (transported) by the centrifugal pump 1. In this embodiment, the handled liquid is, for example, a liquefied gas (for example, liquefied natural gas, liquid hydrogen, etc.).

[0015] In the following description, "rear" refers to the direction in which the motor 3 is located relative to the impeller 5, and "forward" refers to the direction in which the impeller 5 is located relative to the motor 3. The rear is an example of the first direction in the present invention. That is, the "first direction" is the direction in which the motor 3 (the impeller 5 relative to the suction pipe 24 described below) is located relative to the impeller 5. The forward is an example of the second direction in the present invention. That is, the "second direction" is the direction opposite to the first direction.

[0016] In the following description, the "axial direction" refers to the direction along the axial centerline of the rotating shaft 4 (front-to-back direction), the "radial direction" refers to the radial direction of the rotating shaft 4, and the "circumferential direction" refers to the circumferential direction of the rotating shaft 4. The "upstream side" refers to the upstream side in the flow of the treated fluid within the casing 2, and the "downstream side" refers to the downstream side in the flow of the treated fluid within the casing 2.

[0017] The housing 2 accommodates the motor 3, the rotary shaft 4, and the impeller 5. The housing 2 includes a pump chamber 21, a first partition wall portion 22, a second partition wall portion 23, a suction pipe 24, and a discharge pipe 25.

[0018] 2 is a partially enlarged cross-sectional view of the centrifugal pump 1. The figure shows a cross section of the upper half of the centrifugal pump 1 with the impeller 5 at the center. Fig. 3 is a perspective view of the first partition wall portion 22. In the following description, Fig. 1 will be referred to as appropriate together with Figs. 2 and 3.

[0019] The pump chamber 21 accommodates the impeller 5. The pump chamber 21 is partitioned by a first partition wall portion 22 and a second partition wall portion 23.

[0020] The first partition wall portion 22 is a partition wall that partitions the pump chamber 21 together with the second partition wall portion 23. The first partition wall portion 22 is disposed in front of the impeller 5, at the front end portion of the housing 2. The first partition wall portion 22 includes a first opposing surface 221, a recess 2A, and a first through-hole 222.

[0021] The first opposing surface 221 is a surface of the first partition wall portion 22 that faces rearward. The shape of the first opposing surface 221 is a curved surface that is recessed forward in a substantially truncated cone shape. The first opposing surface 221 is disposed in front of the impeller 5 and faces the impeller 5. The first opposing surface 221 is an example of the opposing surface defined in the present invention.

[0022] The radially central portion of the first opposing surface 221 is cylindrically recessed forward so as to be concentric with the rotation shaft 4, forming a recess 2A. That is, when viewed in the axial direction, the recess 2A is a cylindrical groove recessed forward from the first opposing surface 221. When viewed in the axial direction, the shape of the recess 2A is a ring shape concentric with the axis. The cross-sectional shape of the recess 2A along the radial direction is rectangular. The recess 2A has a first recess side surface 2t, a second recess side surface 2u, and a bottom surface 2v.

[0023] The first recess side surface 2t is a surface of the recess 2A that faces radially inward. The shape of the first recess side surface 2t is cylindrical and concentric with the rotation axis 4. The first recess side surface 2t is a surface parallel to the axial direction.

[0024] The second recess side surface 2u is a surface of the recess 2A that faces radially outward. The second recess side surface 2u has a cylindrical shape that is concentric with the rotation axis 4. The second recess side surface 2u is a surface parallel to the axial direction. In other words, the second recess side surface 2u is a parallel surface that is parallel to the first recess side surface 2t. The inner diameter of the second recess side surface 2u is smaller than the inner diameter of the first recess side surface 2t.

[0025] The bottom surface 2v is the surface of the recess 2A facing rearward. When viewed in the axial direction, the bottom surface 2v has a ring shape. In the radial direction, the bottom surface 2v is disposed between the first recess side surface 2t and the second recess side surface 2u.

[0026] As viewed in the axial direction, the first through hole 222 is a cylindrical through hole that axially penetrates the center of the first partition wall portion 22. The first through hole 222 communicates with the pump chamber 21 and the suction pipe 24.

[0027] The second partition wall portion 23 is a partition wall that, together with the first partition wall portion 22, defines the pump chamber 21. The second partition wall portion 23 is disposed between the motor 3 and the impeller 5, and separates the motor 3 from the impeller 5. The second partition wall portion 23 defines a motor chamber that houses the motor 3. The second partition wall portion 23 includes a second opposing surface 231 and a second through-hole 232.

[0028] The second opposing surface 231 is a surface of the second partition wall portion 23 that faces forward. The second opposing surface 231 is disposed behind the impeller 5 and faces the impeller 5.

[0029] When viewed in the axial direction, the second through hole 232 is a cylindrical through hole that axially passes through the center of the second partition wall portion 23. The rotary shaft 4 is inserted through the second through hole 232.

[0030] The front end of the first partition wall portion 22 extends cylindrically forward so as to be concentric with the rotary shaft 4, and forms a suction pipe 24 that draws (introduces) the pumped liquid into the pump chamber 21. A suction port 54 of the impeller 5, which will be described later, is disposed at the rear of the suction pipe 24.

[0031] The liner ring R protects the suction pipe 24. The liner ring R is disposed on the inner peripheral surface of the rear end portion of the suction pipe 24 (the rear opening of the suction pipe 24). The liner ring R has a cylindrical shape.

[0032] A portion of the housing 2 located radially outward from the impeller 5 extends in the tangential direction (upward) of the impeller 5 to form a discharge pipe 25 that discharges the pumped liquid from the pump chamber 21. A discharge port 56 of the impeller 5 is disposed in the pump chamber 21 on the upstream side of the discharge pipe 25.

[0033] The motor 3 is driven at a predetermined drive voltage and drive frequency to rotate the rotary shaft 4 and the impeller 5. The motor 3 is a known motor that includes a rotor (not shown) attached to the rotary shaft 4 and a stator (not shown) that rotates the rotor.

[0034] The rotating shaft 4 is attached to the motor 3 and rotates when driven by the motor 3. The rotating shaft 4 transmits rotational power to the impeller 5. The rotating shaft 4 has a cylindrical shape. A front portion 4a of the rotating shaft 4 protrudes into the pump chamber 21.

[0035] FIG. 4 is a perspective view of the impeller 5. 5 is a partially enlarged cross-sectional view of a protrusion 5A, which will be described later, showing the state in which the protrusion 5A is disposed inside the recess 2A. In the following description, FIGS. 1 to 3 will be referred to as appropriate, along with FIGS. 4 and 5.

[0036] The impeller 5 sucks in and discharges pumped fluid in response to the rotation of the motor 3. The impeller 5 is attached to the front portion 4a of the rotary shaft 4 and is housed in the pump chamber 21. That is, the impeller 5 is disposed between the first partition wall portion 22 and the second partition wall portion 23. The impeller 5 is a so-called closed-type impeller. The impeller 5 includes a plurality of blades 51, a front shroud 52, a rear shroud 55, an inlet port 54, and a discharge port 56.

[0037] The blades 51 rotate in the circumferential direction around the rotary shaft 4 as the center of rotation, and guide the treated fluid sucked from the suction port 54 to the discharge port 56. When viewed in the axial direction, each of the multiple blades 51 extends radially from the center side to the outer edge side of the impeller 5 and is curved in a spiral shape. The blades 51 are arranged between the front shroud 52 and the rear shroud 55.

[0038] The front shroud 52 is a plate (so-called side plate) that faces forward and covers the front of the blades 51. The front shroud 52 faces the first partition wall portion 22. The front shroud 52 is shaped like a substantially ring plate, with the inner edge being more convex forward than the outer edge. The front shroud 52 includes a first surface 521, a convex portion 5A, and a cylindrical portion 53.

[0039] The first surface 521 is a surface of the front shroud 52 that faces forward. The first surface 521 faces the first opposing surface 221 of the first partition wall portion 22. A substantially ring-shaped space (hereinafter referred to as "first space S1") is formed between the first surface 521 and the first opposing surface 221.

[0040] The first space S1 is a space formed between the first partition wall portion 22 of the housing 2 and the front shroud 52 of the impeller 5. A portion of the pumped fluid discharged from the impeller 5 flows into the first space S1. The first space S1 communicates with a space in the pump chamber 21 that is located radially outward of the impeller 5, and with a second space S2, which will be described later.

[0041] A radially central portion of the first surface 521 protrudes forward in a cylindrical shape concentric with the rotary shaft 4, forming a protrusion 5A. That is, when viewed in the axial direction, the shape of the protrusion 5A is a cylindrical protrusion protruding forward from the front shroud 52. When viewed in the axial direction, the shape of the protrusion 5A is a ring shape concentric with the rotary shaft 4. The cross-sectional shape of the protrusion 5A along the radial direction is rectangular. The protrusion 5A includes a first protrusion side surface 5t, a second protrusion side surface 5u, and a front end surface 5v.

[0042] The first convex portion side surface 5t is a surface of the convex portion 5A facing radially outward. The shape of the first convex portion side surface 5t is cylindrical and concentric with the rotation axis 4. The first convex portion side surface 5t is a surface parallel to the axial direction. The first convex portion side surface 5t faces the first recessed portion side surface 2t of the recessed portion 2A. The first convex portion side surface 5t is a parallel surface parallel to the first recessed portion side surface 2t. The inner diameter of the first convex portion side surface 5t is smaller than the inner diameter of the first recessed portion side surface 2t of the recessed portion 2A.

[0043] The second convex side surface 5u is a surface of the convex portion 5A that faces radially inward. The shape of the second convex side surface 5u is cylindrical and concentric with the rotation axis 4. The second convex side surface 5u is a surface parallel to the axial direction. The second convex side surface 5u faces the second recess side surface 2u. The second convex side surface 5u is a parallel surface parallel to the second recess side surface 2u. The second convex side surface 5u is a parallel surface parallel to the first convex side surface 5t. The inner diameter of the second convex side surface 5u is larger than the inner diameter of the second recess side surface 2u of the recess 2A and smaller than the inner diameter of the first convex side surface 5t.

[0044] The front end surface 5v is the surface of the protrusion 5A facing forward. When viewed in the axial direction, the shape of the front end surface 5v is ring-shaped. In the radial direction, the front end surface 5v is disposed between the first protrusion side surface 5t and the second protrusion side surface 5u. The front end surface 5v faces the bottom surface 2v in the axial direction and is disposed parallel to the bottom surface 2v in the radial direction.

[0045] Here, a part (front half) of the protrusion 5A is disposed inside the recess 2A. The protrusion 5A is disposed away from the recess 2A. The distance of the gap T formed between the protrusion 5A and the recess 2A is shorter (smaller) than the distance (spatial length LS) between the first surface 521 and the first opposing surface 221.

[0046] The gap T has a first gap T1, a second gap T2, and a third gap T3. In the radial direction, the first gap T1 is a gap formed between the first recess side surface 2t and the first protrusion side surface 5t. In the radial direction, the second gap T2 is a gap formed between the second recess side surface 2u and the second protrusion side surface 5u. In the axial direction, the third gap T3 is a gap formed between the bottom surface 2v and the front end surface 5v.

[0047] The space length LS is the length of the first space S1 in the axial direction. That is, the space length LS is the length in the axial direction between the first opposing surface 221 excluding the convex portion 5A and the first surface 521 excluding the concave portion 2A.

[0048] In the following description, reference will be made primarily to FIG. The cylindrical portion 53 functions as a suction port 54 of the impeller 5. The inner edge of the front shroud 52 extends cylindrically forward so as to be concentric with the rotary shaft 4, forming the cylindrical portion 53. In other words, the front shroud 52 has the cylindrical portion 53 that functions as the suction port 54. In the impeller 5, the cylindrical portion 53 faces forward and is disposed within the liner ring R that is disposed in the suction pipe 24. The cylindrical portion 53 faces the liner ring R in the radial direction. A cylindrical gap (hereinafter referred to as the "second space S2") is formed between the cylindrical portion 53 and the liner ring R. The length of the second space S2 in the radial direction (the distance between the outer peripheral surface 53a and the liner ring R) is such that the outer peripheral surface 53a does not come into contact with the liner ring R when the centrifugal pump 1 is operating normally, and is set to be equivalent to the same length set for the impeller 5 of a typical centrifugal pump. The cylindrical portion 53 has an outer circumferential surface 53a.

[0049] The second space S2 is connected to a space in the suction pipe 24, the space being upstream of the suction port 54 of the impeller 5, through which the treated liquid flowing through the first space S1 flows.

[0050] In the radial direction, the outer peripheral surface 53a is the surface facing the liner ring R. The shape of the outer peripheral surface 53a is cylindrical and concentric with the rotation shaft 4. The surface of the outer peripheral surface 53a is formed into a labyrinth structure with a plurality of projections and recesses.

[0051] The suction port 54 sucks the pumped liquid from the suction pipe 24. The suction port 54 is surrounded by a cylindrical portion 53.

[0052] The rear shroud 55 is a plate (so-called main plate) that faces rearward and covers the rear of the blades 51. The rear shroud 55 has a ring-shaped plate shape. The rear shroud 55 includes a second surface 551, a hub portion 552, and mounting holes 55h.

[0053] The second surface 551 is a surface of the rear shroud 55 that faces rearward. The second surface 551 faces the second opposing surface 231 of the second partition wall portion 23. A space having a generally ring-like shape is formed between the second opposing surface 231 and the second surface 551. This space communicates with a space in the pump chamber 21 that is on the outer side in the radial direction of the impeller 5.

[0054] The inner edge of the rear shroud 55 extends cylindrically forward so as to be concentric with the rotary shaft 4, forming a hub portion 552. The hub portion 552 is inserted through the rotary shaft 4 and fixed to the front portion 4a of the rotary shaft 4. As a result, the impeller 5 is attached to the rotary shaft 4.

[0055] The mounting hole 55h is a through-hole through which the rotating shaft 4 is inserted. When viewed in the axial direction, the mounting hole 55h is disposed in the center of the rear shroud 55 and penetrates the center in the axial direction in a cylindrical shape.

[0056] The outer edges of the blades 51, the front shroud 52, and the rear shroud 55 form a discharge port 56 through which the handled fluid flowing through the flow passages in the impeller 5 is discharged. The discharge port 56 discharges the handled fluid sucked into the impeller 5. The discharge port 56 is located on the outer edge of the impeller 5 when viewed in the axial direction. The discharge port 56 opens in the radial direction.

[0057] ●Operation of centrifugal pump Next, a description will be given of the operation of the centrifugal pump 1. In the following description, reference will be made to Figures 1 to 5 as appropriate.

[0058] When the centrifugal pump 1 starts operating, the motor 3 is driven to rotate the rotary shaft 4. The impeller 5 sucks the pumped fluid introduced into the suction pipe 24 from the front and discharges it into the pump chamber 21. The pumped fluid discharged into the pump chamber 21 is sent to the discharge pipe 25. At this time, a portion of the pumped fluid discharged into the pump chamber 21 flows into the first space S1 (the space between the first surface 521 and the first opposing surface 221). In addition, another portion of the pumped fluid discharged into the pump chamber 21 flows into the space between the second opposing surface 231 and the second surface 551.

[0059] The pumped liquid flowing into the first space S1 flows through the first space S1 and into the second space S2 (the space between the liner ring R and the outer circumferential surface 53a of the cylindrical portion 53). The pumped liquid flowing into the second space S2 generates a flow (hereinafter referred to as a "leakage flow") from the second space S2 toward the upstream side of the suction port 54 of the impeller 5 (the suction pipe 24). The leakage flow is a phenomenon that occurs when the pressure of the pumped liquid at the discharge port 56 of the impeller 5 is higher than the pressure of the pumped liquid at the suction port 54 of the impeller 5. The leakage flow that flows from the second space S2 into the suction pipe 24 flows countercurrently with respect to the main flow, which will be described later. This counterflow obstructs part of the flow of the main flow, thereby reducing the suction performance of the centrifugal pump 1. In other words, the leakage flow reduces the suction performance of the centrifugal pump 1.

[0060] The "main flow" is the main flow of the handled liquid flowing inside the suction pipe 24. The main flow is generated by the rotation of the impeller 5. The main flow swirls along the inner circumferential surface of the suction pipe 24 and flows along the axial direction of the suction pipe 24.

[0061] The "backflow" is a flow in the opposite direction to the main flow of the pumped liquid flowing through the suction pipe 24.

[0062] In this embodiment, the centrifugal pump 1 includes a suppression structure for reducing leakage flow. The suppression structure is composed of a recess 2A and a protrusion 5A. As described above, a portion of the protrusion 5A is disposed inside the recess 2A. A gap T is formed between the protrusion 5A and the recess 2A. The gap T is disposed so as to throttle the flow of the pumped fluid in the first space S1. That is, the flow of the pumped fluid in the first space S1 is throttled by the recess 2A and the protrusion 5A (gap T). Therefore, the average flow velocity of the pumped fluid increases in the gap T. As a result, in the first space S1, the pressure of the pumped fluid downstream of the gap T is lower than the pressure of the pumped fluid upstream of the gap T. That is, a pressure difference of the pumped fluid occurs between the upstream and downstream sides of the gap T. Here, in the first space S1, the upstream side is the discharge port 56 side of the impeller 5, and the downstream side is the suction port 54 side of the impeller 5. The second space S2 is disposed downstream of the gap T. The pressure difference is generated mainly by the first gap T1 and the second gap T2 of the gap T. Therefore, the flow rate of the handled liquid is reduced downstream of the first gap T1 and the second gap T2 (second space S2). As a result, the flow rate of the leakage flow (backflow) flowing from the second space S2 toward the upstream side of the suction port 54 of the impeller 5 is reduced.

[0063] ●Relationship between the concave and convex parts due to axial movement of the impeller Next, the relationship between the recessed portion 2A and the protruding portion 5A that accompanies the movement of the impeller 5 in the axial direction will be described.

[0064] 6 is a partially enlarged cross-sectional view of the recessed portion 2A and the protruding portion 5A, showing the state in which the impeller 5 has moved in the axial direction. (a) shows the state in which the impeller 5 has moved rearward from its normal position, (b) shows the state in which the impeller 5 is located in its normal position, and (c) shows the state in which the impeller 5 has moved forward from its normal position. In the following description, FIGS. 1 to 5 will be referred to as well as FIG. 6 as appropriate.

[0065] The "normal position" is the position of the impeller 5 when the pressure of the treated fluid in the first space S1 is balanced in the axial direction with the pressure of the treated fluid in the space between the second opposing surface 231 and the second surface 551. The impeller 5 moves rearward when the pressure of the former increases, and moves forward when the pressure of the latter increases.

[0066] In the centrifugal pump 1 of this embodiment, a portion of the convex portion 5A is disposed inside the concave portion 2A. Therefore, as will be described later, even when the impeller 5 moves in the axial direction, the length of the gap T is unlikely to fluctuate significantly, and the flow rate of leakage flow (backflow) is reduced.

[0067] As described above, the first recess side surface 2t and the first convex side surface 5t each have a cylindrical shape concentric with the rotation shaft 4. The first recess side surface 2t and the first convex side surface 5t are arranged parallel to each other in the axial direction. Therefore, even when the impeller 5 moves in the axial direction, the distance of the first gap T1 is maintained constant. The first recess side surface 2t and the first convex side surface 5t can move parallel to each other in the axial direction within the range of a first length L1 described below while the first recess side surface 2t and the first convex side surface 5t face each other. The first length L1 is set to be longer than the axially movable length of the impeller 5 within the pump chamber 21 (hereinafter referred to as the "second length L2"). As a result, the first gap T1 is always formed even when the impeller 5 moves in the axial direction. At this time, the length of the first gap T1 in the axial direction (i.e., the first length L1) increases or decreases, but the distance of the first gap T1 in the radial direction is maintained constant.

[0068] As described above, the "first length L1" is the length over which the convex portion 5A can move in the axial direction when the surfaces of the concave portion 2A and the convex portion 5A that are parallel to the axial direction (the first concave portion side surface 2t, the first convex portion side surface 5t) face each other. In other words, the first length L1 is the axial length of the region where the surfaces that are parallel to the axial direction (the first concave portion side surface 2t, the first convex portion side surface 5t) face each other.

[0069] As described above, the second recess side surface 2u and the second convex side surface 5u each have a cylindrical shape concentric with the rotation shaft 4. The second recess side surface 2u and the second convex side surface 5u are arranged parallel to each other in the axial direction. Therefore, even when the impeller 5 moves in the axial direction, the distance of the second gap T2 (the distance between the second recess side surface 2u and the second convex side surface 5u) is maintained constant. The second recess side surface 2u and the second convex side surface 5u can move parallel to each other in the axial direction within the range of a third length L3 (described later) while the second recess side surface 2u and the second convex side surface 5u face each other. The third length L1 is set to be longer than the second length L2. As a result, the second gap T2 is always formed even when the impeller 5 moves in the axial direction. At this time, the length of the second gap T2 in the axial direction (i.e., the third length L3) increases or decreases, but the distance of the second gap T2 in the radial direction is maintained constant.

[0070] As described above, the "third length L3" is the length over which the convex portion 5A can move in the axial direction when the axially parallel surfaces (the second concave portion side surface 2u and the second convex portion side surface 5u) of the concave portion 2A and the convex portion 5A face each other. In other words, the third length L3 is the axial length of the region where the axially parallel surfaces (the second concave portion side surface 2u and the second convex portion side surface 5u) face each other.

[0071] In the radial direction, the bottom surface 2v is disposed parallel to the front end surface 5v. At the second length L2, even when the impeller 5 moves forward (in the second direction) to its maximum extent, the bottom surface 2v does not come into contact with the front end surface 5v in the axial direction. In other words, the convex portion 5A does not come into contact with the concave portion 2A in the axial direction. Therefore, even when the impeller 5 moves in the axial direction, the third gap T3 is always formed. In this case, the length of the third gap T3 in the axial direction increases or decreases, but the length of the third gap T3 in the radial direction is kept constant.

[0072] In this way, even when the impeller 5 moves in the axial direction, the first gap T1, the second gap T2, and the third gap T3 (gap T) are always formed. Furthermore, the sum of the lengths of the first gap T1, the second gap T2, and the third gap T3 in the radial direction (the length of the gap T; i.e., the length of the throttled flow path) increases or decreases depending on the increases or decreases in the first length L1 and the third length L3, but does not fluctuate significantly. Therefore, even when the impeller 5 moves in the axial direction, the pressure of the treated fluid on the downstream side in the first space S1 is reduced relative to the pressure of the treated fluid on the upstream side. As a result, the flow rate of leakage flow (backflow) is stably reduced.

[0073] Generally, a similarity relationship holds true for the flow of the pumped liquid inside the centrifugal pump 1. Therefore, for example, the lengths of the first gap T1 and the second gap T2 in the radial direction are set to optimal lengths based on the size of the centrifugal pump 1. In this embodiment, the lengths of the first gap T1 and the second gap T2 in the radial direction are set to, for example, 1.5 mm to 0.15 mm based on the size of the centrifugal pump 1. Note that these numerical values ​​are merely examples, and the lengths of the first gap T1 and the second gap T2 in the radial direction are not limited to the same numerical value. The minimum value of the length of the third gap T3 in the axial direction is set to be greater than the lengths of the first gap T1 and the second gap T2 in the radial direction.

[0074] ●Comparison with conventional centrifugal pumps Next, a comparison between the centrifugal pump 1 and a conventional centrifugal pump (hereinafter referred to as the "conventional pump") will be described below.

[0075] FIG. 7 is a partially enlarged schematic cross-sectional view of a conventional pump, showing the flow of pumped liquid in the conventional pump. The figure shows the upstream side of the suction port of the impeller. The arrows in the figure indicate the flow of pumped liquid. The figure also shows the blocked area OA with a two-dot chain line. In the following description, FIGS. 1 to 6 will be referred to as appropriate, along with FIG. 7.

[0076] The "blocked area OA" is an area where the main flow is disturbed (the flow is blocked) by a backflow due to leakage flow. That is, a backflow occurs in the blocked area OA.

[0077] Figure 8 is a partially enlarged schematic cross-sectional view of the centrifugal pump 1, showing the flow of the pumped liquid in the centrifugal pump 1. Arrows in the figure indicate the flow of the pumped liquid. In the following description, Figures 1 to 7 will be referred to as appropriate, along with Figure 8.

[0078] The figure shows that the occlusion area OA of the centrifugal pump 1 is narrower than that of a conventional pump. The figure also shows that, because part of the convex portion 5A is located inside the concave portion 2A, the flow rate of the treated fluid downstream of the concave portion 2A and the convex portion 5A is reduced relative to the flow rate of the treated fluid upstream of the concave portion 2A and the convex portion 5A. The figure also shows that, because the flow rate of the treated fluid downstream is reduced, the flow rate of leakage flow (backflow) is reduced.

[0079] FIG. 9 is a graph comparing the backflow rate of the centrifugal pump 1 with that of a conventional pump.

[0080] In this graph, the horizontal axis represents the centrifugal pump 1 and the conventional pump. The vertical axis represents the backflow rate (kg / s) of the pumped liquid (leakage flow). This graph shows the results of fluid analysis measured under the same operating environment. In this embodiment, the pumped liquid is water. The temperature of the water is set to 25°C. The density of water is 997 kg / m 3 The dynamic viscosity of water is 0.0008899 kg / (m·s). The flow rate of water is 48.75 m 3 / h. The inlet condition is static pressure, and the outlet condition is set as mass flow rate.

[0081] As shown in Figure 9, the backflow rate of approximately 1.5 kg / s was measured for the conventional pump, while the backflow rate of approximately 0.7 kg / s was measured for the centrifugal pump 1. In this way, the backflow rate of the centrifugal pump 1 is half that of the conventional pump.

[0082] Summary (1) According to the embodiment described above, the centrifugal pump 1 includes a housing 2, a motor 3, a rotating shaft 4, an impeller 5, a pump chamber 21, and a suction pipe 24. The impeller 5 includes a front shroud 52 and a suction port 54. The front shroud 52 includes a first surface 521 and a protruding portion 5A. The housing 2 includes a first partition 22. The first partition 22 includes a first opposing surface 221 and a recessed portion 2A. A first space S1 is formed between the first partition 22 and the front shroud 52, into which a portion of the pumped fluid discharged from the impeller 5 flows. A portion of the protruding portion 5A is disposed within the recessed portion 2A. A gap T is formed between the recessed portion 2A and the protruding portion 5A in the radial direction of the rotating shaft 4. According to this configuration, the gap T is disposed so as to throttle the flow of the pumped fluid in the first space S1. Therefore, the average flow velocity of the pumped fluid increases through the gap T. As a result, in the first space S1, the pressure of the treated fluid downstream of the gap T is lower than the pressure of the treated fluid upstream of the gap T. In this way, a pressure difference of the treated fluid occurs between the upstream and downstream sides of the gap T in the first space S1. Therefore, on the downstream side of the gap T (second space S2), the flow rate of the backflow in the first space S1 is reduced. As a result, the flow rate of the leakage flow (backflow) flowing from the second space S2 toward the upstream side of the suction port 54 of the impeller 5 is reduced.

[0083] Furthermore, according to the embodiment described above, when viewed in the axial direction, the shape of the convex portion 5A is a ring shape that is concentric with the axis of the rotating shaft 4. With this configuration, a gap T is formed between the concave portion 2A and the convex portion 5A over the entire circumference in the circumferential direction.

[0084] Furthermore, according to the embodiment described above, the protrusion 5A has a first protrusion side surface 5t and a second protrusion side surface 5u. The recess 2A has a first recess side surface 2t facing the first protrusion side surface 5t and a second recess side surface 2u facing the second protrusion side surface 5u. In the axial direction, the first protrusion side surface 5t and the first recess side surface 2t, and the second protrusion side surface 5u and the second recess side surface 2u are parallel surfaces that are parallel to each other. With this configuration, even if the impeller 5 moves in the axial direction, the size of the first gap T1 in the radial direction does not change, and the size of the second gap T2 in the radial direction does not change either.

[0085] Furthermore, according to the embodiment described above, the first convex portion side surface 5t and the first recessed portion side surface 2t are parallel surfaces parallel to each other in the axial direction. The first length L1, over which the first convex portion side surface 5t and the first recessed portion side surface 2t can move in parallel when they face each other, is longer than the second length L2, over which the impeller 5 can move in the axial direction within the pump chamber 21. The third length L3, over which the second convex portion side surface 5u and the second recessed portion side surface 2u can move in parallel when they face each other in the axial direction, is longer than the second length L2. According to this configuration, the first gap T1 and the second gap T2 are always formed when the impeller 5 moves in the axial direction. In other words, the convex portion 5A is always positioned inside the recessed portion 2A. Therefore, even when the impeller 5 moves in the axial direction, the flow rate of leakage flow (backflow) is stably reduced.

[0086] Furthermore, according to the embodiment described above, within the forward movement range of impeller 5 (in the second direction), until impeller 5 moves forward to its maximum extent, convex portion 5A does not come into contact with concave portion 2A in the axial direction. With this configuration, even when impeller 5 moves forward to its maximum extent, third gap T3 is always formed (not closed). In other words, gap T is always formed (not closed).

[0087] Furthermore, according to the embodiment described above, the length of the gap T in the radial direction is shorter (smaller) than the length of the first space S1 in the axial direction. With this configuration, the flow of the pumped liquid in the first space S1 is reliably throttled in the gap T. Therefore, the flow velocity of the pumped liquid increases in the gap T. As a result, the pressure of the pumped liquid downstream of the gap T is lower than the pressure of the pumped liquid upstream of the gap T. Therefore, the flow rate of the pumped liquid downstream of the gap T, i.e., the flow rate of the backflow, is reduced.

[0088] Furthermore, according to the embodiment described above, the cross-sectional shape of the protrusion 5A along the radial direction is rectangular. This configuration simplifies the structure of the protrusion 5A. This makes it easy to design and form the protrusion 5A. Similarly, it makes it easy to design and form the recess 2A.

[0089] ●Variations● Next, modifications of the centrifugal pump 1 will be described below, focusing on differences from the previously described embodiment (hereinafter referred to as the "first embodiment"). In the following modifications, for ease of explanation, the same components as in the first embodiment and components having the same functions as in the first embodiment are denoted by the same reference numerals. In the following modifications, reference will be made as appropriate to FIGS. 1 to 9.

[0090] First modified example FIG. 10 is a partially enlarged cross-sectional view of a centrifugal pump 1B according to a first modified example.

[0091] A centrifugal pump 1B according to the first modification differs from the first embodiment only in the shapes of the recessed portion 2B and the protruding portion 5B.

[0092] The shape of the bottom surface 2w is a semi-elliptical shape that is convex toward the front in a cross-sectional view. That is, the bottom surface 2w is a curved surface that is convex toward the front. The shape of the front end surface 5w is a semi-elliptical shape that is convex toward the front in a cross-sectional view. That is, the front end surface 5w is a curved surface that is convex toward the front. In the axial direction, the front end surface 5w faces the bottom surface 2w and is arranged parallel to the bottom surface 2w. In this configuration, the configurations of the first gap T1 and the second gap T2 are the same as in the first embodiment. Therefore, in the centrifugal pump 1B, the flow rate of leakage flow (backflow) is reduced, similar to the centrifugal pump 1.

[0093] In the present invention, the shapes of the bottom surface 2w and the front end surface 5w are not limited to the first modified example, as long as the front end surface 5w and the bottom surface 2w face each other and are arranged parallel to each other.

[0094] Second modified example FIG. 11 is a partially enlarged cross-sectional view of a convex portion in a centrifugal pump 1C according to a second modification.

[0095] A centrifugal pump 1C according to the second modification differs from the first embodiment only in the shapes of a recessed portion 2C and a protruding portion 5C.

[0096] The recess 2C has a first recess side surface 2t, a second recess side surface 2x, and a bottom surface 2v. The protrusion 5C has a first protrusion side surface 5t and a second protrusion side surface 5x.

[0097] The second recess side surface 2x is an inclined surface of the recess 2C that faces radially outward. In cross-sectional view, the front end of the second recess side surface 2x is located radially outward from the rear end. In other words, the second recess side surface 2x is an inclined surface that slopes downward from the front to the rear. In the axial direction, the length of the bottom surface 2w is shorter than in the first embodiment. The cross-sectional shape of the recess 2C along the radial direction is approximately triangular.

[0098] The second convex side surface 5x is an inclined surface of the convex portion 5C that faces radially inward. In a cross-sectional view, the front end of the second convex side surface 5x is located radially outward from the rear end. In other words, the second convex side surface 5x is an inclined surface that slopes downward from the front to the rear. The front end of the second convex side surface 5x is continuous with the front end of the first convex side surface 5t. The cross-sectional shape of the convex portion 5C along the radial direction is approximately triangular. The second convex side surface 5x faces the second recess side surface 2x. The second convex side surface 5x is a parallel surface that is parallel to the second recess side surface 2x.

[0099] In this configuration, the configuration of the first gap T1 is the same as in the first embodiment. On the other hand, the third gap T3 is almost nonexistent. Furthermore, the length of the gap (third gap T3) between the second convex portion side surface 5x and the second concave portion side surface 2x in the axial direction varies when the impeller 5 moves in the axial direction. Therefore, the effect of reducing the flow rate of leakage flow (backflow) is less than in the first embodiment. However, the flow rate of leakage flow is reduced mainly by the first gap T1.

[0100] In the second modified example, the first recess side surface 2t and the first protrusion side surface 5t may be inclined surfaces instead of the second recess side surface 2x and the second protrusion side surface 5x. In this case, the first recess side surface 2t and the first protrusion side surface 5t are parallel surfaces that are parallel to each other.

[0101] In the second modified example, the shape of the second recess side surface 2x and the shape of the second protrusion side surface 5x are not limited to an inclined surface. For example, the shape of the second recess side surface 2x and the shape of the second protrusion side surface 5x may be a curved surface that is convex forward and downward.

[0102] Third variant FIG. 12 is a schematic front view of a front shroud 52 of a centrifugal pump 1D according to a third modified example. FIG. 13 is a partially enlarged cross-sectional view of the front shroud 52 taken along line AA in FIG.

[0103] A centrifugal pump 1D according to the third modification differs from that of the first embodiment in the number of recesses and protrusions. The centrifugal pump 1D includes three recesses 2D, 2E, and 2F and three protrusions 5D, 5E, and 5F.

[0104] In the axial view, a portion of the first opposing surface 221 is cylindrically recessed forward so as to be triple concentric with the rotation shaft 4, forming three recesses 2D, 2E, and 2F. That is, in the axial view, the recesses 2D, 2E, and 2F are each cylindrical grooves recessed forward from the first opposing surface 221. In the axial view, the shape of each of the recesses 2D, 2E, and 2F is a ring shape concentric with the rotation shaft 4. The cross-sectional shape of each of the recesses 2D, 2E, and 2F along the radial direction is rectangular. In the first opposing surface 221, the recess 2D, recess 2E, and recess 3F are arranged in this order from the outside to the inside in the radial direction, spaced apart from one another. The shapes of the recesses 2D, 2E, and 2F are similar to each other.

[0105] When viewed in the axial direction, a portion of the first surface 521 protrudes forward in a cylindrical shape that is triple-concentric with the rotation shaft 4, forming three protrusions 5D, 5E, and 5F. That is, when viewed in the axial direction, the three protrusions 5D, 5E, and 5F each have a cylindrical convex shape that protrudes forward from the first surface 521. When viewed in the axial direction, the protrusions 5D, 5E, and 5F each have a ring shape that is concentric with the rotation shaft 4. In other words, each of the protrusions 5D, 5E, and 5F has an arc-shaped portion that is concentric with the axis of the rotation shaft 4. The protrusions 5D, 5E, and 5F each have the same radius of curvature and are arranged on a concentric circle with the axis. The cross-sectional shape of each of the protrusions 5D, 5E, and 5F along the radial direction is rectangular. On the first surface 521, the protrusions 5D, 5E, and 5F are arranged in this order from the outside to the inside in the radial direction, spaced apart from one another. The shapes of the protrusions 5D, 5E, and 5F are similar to each other. The recess 2D corresponds to the protrusion 5D, the recess 2E corresponds to the protrusion 5E, and the recess 2F corresponds to the protrusion 5F.

[0106] In this configuration, three gaps T are formed in the first space S1. As a result, the flow rate of leakage flow (backflow) is reduced compared to the first embodiment.

[0107] In the third modified example, the number of recesses 2D, 2E, 2F and protrusions 5D, 5E, 5F is not limited to 3. That is, for example, the number of recesses 2D, 2E, 2F and protrusions 5D, 5E, 5F may be 2 or 4 or more.

[0108] In addition, in the third modified example, the recesses 2D, 2E, and 2F are arranged separately from each other, but the recesses 2D, 2E, and 2F may be formed as one. Even if the recesses 2D, 2E, and 2F are formed as one, the total length of the gap T increases. Therefore, the flow rate of the leakage flow (backflow) is reduced.

[0109] Summary (2) According to the third modified example described above, the front shroud 52 includes a plurality of protrusions 5D, 5E, and 5F. The plurality of protrusions 5D, 5E, and 5F are arranged concentrically about the axis and spaced apart from one another. With this configuration, the pumped fluid on the upstream side of each gap T flows through each gap T to the downstream side of each gap T. That is, the length of the gap T that throttles the first space S1 increases. Therefore, the pressure difference between the pressure of the pumped fluid on the upstream side of all the gaps T and the pressure of the pumped fluid on the downstream side of all the gaps T becomes even larger. As a result, the flow rate of leakage flow is reduced compared to the first embodiment.

[0110] Furthermore, according to the third modified example described above, the first partition wall portion 22 has a plurality of recesses 2D, 2E, and 2F corresponding to the plurality of protrusions 5D, 5E, and 5F, respectively. With this configuration, the pumped fluid on the upstream side of each gap T flows through each gap T to the downstream side of each gap. That is, the length of the gap T that restricts the first space S1 is further increased. Therefore, the pressure difference between the pressure of the pumped fluid on the upstream side of all the gaps T and the pressure of the pumped fluid on the downstream side of all the gaps T is further increased. As a result, the flow rate of the leakage flow is further reduced.

[0111] Furthermore, according to the second modified example described above, the cross-sectional shape of the protrusion 5C along the radial direction is triangular. With this configuration, the protrusion 5C has at least one parallel surface parallel to the recess 2C in the axial direction. Therefore, the flow of the treated fluid in the first space S1 is constricted by the recess 2C and the protrusion 5C (gap T). As a result, the flow rate of the leakage flow is reduced.

[0112] Other embodiments In the present invention, the shape of the convex portion 5A does not have to be a ring shape concentric with the axis of the rotating shaft 4. That is, for example, when viewed in the axial direction, the shape of the convex portion 5A does not have to be a continuous circle such as a ring shape. That is, for example, when viewed in the axial direction, the shape of the convex portion 5A may be an arc shape (parallel surface) concentric with the axis of the rotating shaft 4, and the multiple convex portions 5A may have the same radius of curvature and may be arranged on a circle concentric with the axis (for example, multiple arc shapes). That is, the shape of the convex portion 5A functions as the gap T by satisfying the above-mentioned conditions. The shape of the convex portion can be designed based on the above-mentioned arrangement conditions.

[0113] In the present invention, the recessed portion 2A may be disposed on the impeller 5, and the protruding portion 5A may be disposed on the housing 2.

[0114] Furthermore, in the present invention, the number of impellers 5 included in the centrifugal pump 1 is not limited to one. That is, for example, the number of impellers 5 may be two or more. In this case, the protrusion 5A may be disposed on the impeller 5 disposed most upstream.

[0115] Furthermore, in the above-described embodiment, the pumped liquid is not limited to liquefied gas, but may be water, for example.

[0116] ●Embodiments of the present invention● Next, the embodiments of the present invention that can be understood from the above-described embodiments will be described below, using the terms and symbols described in the respective embodiments.

[0117] A first embodiment of the present invention includes a motor (e.g., motor 3), a rotating shaft (e.g., rotating shaft 4) that rotates by driving the motor, an impeller (e.g., impeller 5) that is attached to the rotating shaft and sucks and discharges treated fluid, a pump chamber (e.g., pump chamber 21) in which the impeller is accommodated, a housing (e.g., housing 2) that partitions the pump chamber, and a suction pipe (e.g., suction pipe 24) that introduces the treated fluid to the impeller. In the axial direction of the rotating shaft, a direction in which the impeller is arranged with respect to the suction pipe is a first direction, and a direction opposite to the first direction is a second direction. The impeller includes a suction port (e.g., suction port 54) that sucks the treated fluid from the suction pipe and a front shroud (e.g., front shroud 52) that is oriented in the first direction. the front shroud has a first surface (e.g., first surface 521) facing the second direction and at least one protrusion (e.g., protrusion 5A) protruding from the first surface in the second direction, the housing has a first partition wall portion (e.g., first partition wall portion 22) arranged opposite the front shroud, the first partition wall portion having an opposing surface (e.g., first opposing surface 221) opposing the first surface and a recess (e.g., recess 2A) recessed from the opposing surface in the second direction, a first space (e.g., first space S1) into which a portion of the handled fluid discharged from the impeller flows is formed between the front shroud and the first partition wall portion, a portion of the protrusion is disposed inside the recess, and a gap (e.g., gap T) is formed between the protrusion and the recess in the radial direction of the rotating shaft. According to this configuration, the centrifugal pump of the present invention reduces the flow rate of leakage flow and improves the suction performance of the centrifugal pump.

[0118] A second embodiment of the present invention is the centrifugal pump according to the first embodiment, wherein the shape of the convex portion is a ring shape concentric with the axis of the rotating shaft when viewed in the axial direction. According to this configuration, a gap T is formed between the recessed portion 2A and the protruding portion 5A over the entire circumference in the circumferential direction.

[0119] A third embodiment of the present invention is a centrifugal pump in the second embodiment, wherein the convex portion has a first convex portion side surface (e.g., first convex portion side surface 5t) facing outward in the radial direction and a second convex portion side surface (e.g., second convex portion side surface 5u) facing inward in the radial direction, the concave portion has a first concave portion side surface (e.g., first concave portion side surface 2t) facing the first convex portion side surface and a second concave portion side surface (e.g., second concave portion side surface 2u) facing the second convex portion side surface, and in the axial direction, the first convex portion side surface and the first concave portion side surface, and the second convex portion side surface and the second concave portion side surface are parallel planes. According to this configuration, even if the impeller moves axially, the first gap between the first convex portion side surface and the first concave portion side surface in the radial direction does not change, and the second gap between the second convex portion side surface and the second concave portion side surface in the radial direction does not change.

[0120] A fourth embodiment of the present invention is a centrifugal pump in the third embodiment, wherein, when the first convex side surface and the first recess side surface are parallel surfaces in the axial direction, a first length (e.g., first length L1) along which the first convex side surface and the first recess side surface can move in parallel while facing each other is longer than a second length (e.g., second length L2) along which the impeller can move in the first direction within the pump chamber, and when the second convex side surface and the second recess side surface are parallel surfaces in the axial direction, a third length (e.g., third length L3) along which the second convex side surface and the second recess side surface can move in parallel while facing each other is longer than the second length. According to this configuration, the first gap and the second gap are always formed when the impeller moves in the axial direction, so that the flow rate of the leakage flow (backflow) is stably reduced even when the impeller moves in the axial direction.

[0121] A fifth embodiment of the present invention is a centrifugal pump in the fourth embodiment, wherein within the range of movement of the impeller in the second direction, the convex portion does not abut the concave portion in the axial direction until the impeller moves to its maximum extent in the second direction. According to this configuration, even when the impeller moves to the maximum extent in the second direction, the gap is always formed (not closed).

[0122] A sixth embodiment of the present invention is the centrifugal pump according to the first embodiment, wherein the length of the gap in the radial direction is shorter than the length of the first space in the axial direction. With this configuration, the flow velocity of the pumped fluid increases in the gap, and the pressure of the pumped fluid downstream of the gap becomes lower than the pressure of the pumped fluid upstream of the gap, thereby reducing the flow rate of the pumped fluid downstream of the gap, i.e., the flow rate of the backflow.

[0123] A seventh embodiment of the present invention is a centrifugal pump in the second embodiment, wherein the front shroud has a plurality of the protrusions, each of which is arranged concentrically with the axis and spaced apart from one another. With this configuration, the length of the gaps that restrict the first space is increased, which further increases the pressure difference between the pressure of the pumped fluid upstream of all the gaps and the pressure of the pumped fluid downstream of all the gaps, thereby further reducing the flow rate of leakage flow.

[0124] An eighth embodiment of the present invention is the centrifugal pump according to the seventh embodiment, wherein the first partition portion comprises a plurality of the recesses corresponding to the plurality of the protrusions, respectively. With this configuration, the length of the gaps that restrict the first space is further increased, which further increases the pressure difference between the pressure of the pumped fluid on the upstream side of all the gaps and the pressure of the pumped fluid on the downstream side of all the gaps, thereby further reducing the flow rate of the leakage flow.

[0125] A ninth embodiment of the present invention is the centrifugal pump according to the second embodiment, wherein a cross-sectional shape of the convex portion along the radial direction is rectangular. According to this configuration, the structure of the protrusion is simple, and therefore the design and formation of the protrusion is easy.

[0126] A tenth embodiment of the present invention is the centrifugal pump according to the second embodiment, wherein the cross-sectional shape of the convex portion along the radial direction is triangular. According to this configuration, the convex portion has at least one parallel surface that is parallel to the concave portion in the axial direction, thereby reducing the flow rate of leakage flow.

[0127] An eleventh embodiment of the present invention is a centrifugal pump in the first embodiment, wherein the front shroud has a plurality of the convex portions, and when viewed in the axial direction, the shape of the convex portions is an arc concentric with the axis of the rotating shaft, and each of the convex portions has the same radius of curvature and is arranged on a concentric circle with the axis. According to this configuration, the shape of the convex portion can be designed based on the above-mentioned arrangement conditions. [Explanation of symbols]

[0128] 1. Centrifugal pump 2. Case 21 Pump Room 22 1st bulkhead section 221 First opposing surface 2A Recess 2t First recess side 2u Second recess side 2v bottom 23 Second bulkhead part 231 Second opposing surface 24 Suction pipe 3 motors 4 rotation axes 5 impeller 52 Front shroud 521 Page 1 5A Convex part 5t First convex part side 5u Second protrusion side 5v front end 54 Intake port S1 1st space T-gap LS space length L1 First length L2 Second length L3 Third length

Claims

1. A motor; a rotating shaft that rotates when driven by the motor; an impeller attached to the rotary shaft for sucking in and discharging the pumped fluid; a pump chamber in which the impeller is accommodated; a housing that defines the pump chamber; a suction pipe for introducing the pumped liquid into the impeller; and a first direction in which the impeller is disposed relative to the suction pipe in an axial direction of the rotation shaft, and a second direction in which the impeller is disposed opposite to the first direction, The impeller is a suction port that draws the pumped fluid from the suction pipe; a front shroud oriented in the first direction; With The front shroud comprises: a first surface facing the second direction; at least one protrusion protruding from the first surface in the second direction; With The housing includes: a first partition wall portion disposed opposite the front shroud; With The first partition wall portion is an opposing surface opposing the first surface; a recess recessed from the opposing surface in the second direction; With a first space into which a portion of the pumped fluid discharged from the impeller flows is formed between the front shroud and the first partition wall portion, A part of the protrusion is disposed inside the recess, A gap is formed between the protrusion and the recess in the radial direction of the rotation shaft. Centrifugal pump.

2. When viewed in the axial direction, the shape of the convex portion is a ring shape concentric with the axis of the rotation shaft.

2. The centrifugal pump of claim 1.

3. The convex portion is a first convex portion side surface facing outward in the radial direction; a second protrusion side surface directed inward in the radial direction; With The recessed portion is a first recess side surface facing the first protrusion side surface; a second recess side surface facing the second protrusion side surface; With In the axial direction, the first convex portion side surface and the first recessed portion side surface, and / or the second convex portion side surface and the second recessed portion side surface are parallel surfaces that are parallel to each other.

3. The centrifugal pump according to claim 2.

4. when the first convex portion side surface and the first recessed portion side surface are parallel surfaces parallel to each other in the axial direction, a first length by which the first convex portion side surface and the first recessed portion side surface can move in parallel in a state in which they face each other is longer than a second length by which the impeller can move in the first direction within the pump chamber, When the second convex portion side surface and the second recessed portion side surface are parallel surfaces parallel to each other in the axial direction, a third length by which the second convex portion side surface and the second recessed portion side surface can move in parallel in a state in which they face each other is longer than the second length.

4. The centrifugal pump according to claim 3.

5. Within a movable range of the impeller in the second direction, the convex portion does not abut against the concave portion in the axial direction until the impeller moves to a maximum extent in the second direction.

5. The centrifugal pump according to claim 4.

6. The length of the gap in the radial direction is shorter than the length of the first space in the axial direction.

2. The centrifugal pump of claim 1.

7. The front shroud comprises: A plurality of the protrusions; With The plurality of protrusions are arranged concentrically with the axis and spaced apart from one another.

3. The centrifugal pump according to claim 2.

8. The first partition wall portion is a plurality of recesses corresponding to the plurality of protrusions, respectively; Equipped with 8. The centrifugal pump according to claim 7.

9. The cross-sectional shape of the protrusion along the radial direction is rectangular.

3. The centrifugal pump according to claim 2.

10. A cross-sectional shape of the protrusion along the radial direction is triangular.

3. The centrifugal pump according to claim 2.

11. The front shroud comprises: A plurality of the protrusions; With When viewed in the axial direction, the shape of the convex portion is an arc shape concentric with the axis of the rotation shaft, The convex portions have the same radius of curvature and are arranged on concentric circles around the axis.

2. The centrifugal pump of claim 1.

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