Centrifugal pump

Abstract

Provided is a centrifugal pump that suppresses the generation of axial thrust. This centrifugal pump (1) is provided with: a motor (3); a rotating shaft (4); a first impeller (6); a second impeller (7); a first pump chamber (23) that accommodates the first impeller; a second pump chamber (24) accommodating the second impeller; and a central partition wall section (21) which is provided with an insertion hole (21c) through which the rotating shaft is inserted, and which divides the first pump chamber and the second pump chamber. The first impeller is provided with: a first suction port (65) that sucks the processing liquid from the first direction side; and a first shield (62) facing the central partition wall portion. The second impeller is provided with: a second suction port (75) that sucks the processing liquid from the second direction side; and a second shield (72) facing the central partition wall portion. A first space (S11) communicating with the insertion hole is formed between the first impeller and the central partition wall portion. A second space (S21) communicating with the insertion hole is formed between the second impeller and the central partition wall portion. The outer diameter of the second protective cover is larger than that of the first protective cover.

Description

Technical Field

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

[0002] A centrifugal pump includes a motor, a rotating shaft, an impeller, and a casing. The impeller is mounted on a rotating shaft that rotates based on the action of the motor, and rotates along with the rotation of the rotating shaft, thereby sucking in the treatment liquid from one axial side of the rotating shaft, for example, discharging the treatment liquid radially outward from the impeller. The impeller includes a plurality of blades, a front shroud (side plate), and a back shroud (main plate). In the axial direction, the front shroud covers one side of the blades, and the back shroud covers the other side of the blades. A portion of the high-pressure treatment liquid discharged from the impeller also flows between the front shroud and the casing, and between the back shroud and the casing, pushing the front shroud toward the back shroud side, and pushing the back shroud toward the front shroud side. Generally, the pressure area of ​​the back shroud is larger than the pressure area of ​​the front shroud. Therefore, in the axial direction, a force (axial thrust) that pushes the impeller toward one side acts on the impeller.

[0003] Among centrifugal pumps, a multi-stage centrifugal pump is known. In order to improve suction performance and achieve high head, the multi-stage centrifugal pump discharges the treated liquid in sequence through multiple impellers installed on a rotating shaft (for example, refer to Patent Document 1). The above-mentioned axial thrust increases depending on the number of impellers (number of stages). Therefore, in a multi-stage centrifugal pump, the multiple impellers are divided into a front-stage group and a rear-stage group, and the front-stage group is installed on the rotating shaft in a manner that is back-to-back with the rear-stage group. Except for the direction of rotation, the design of the impeller of the front-stage group is the same as the design of the impeller of the rear-stage group, so the axial thrust of the front-stage group is balanced with the axial thrust of the rear-stage group, and the axial thrust of the two is eliminated.

[0004] Prior art literature

[0005] Patent Literature:

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-21766. Summary of the Invention

[0007] Typically, a mechanical seal is installed between the partition wall disposed between the front-stage group and the rear-stage group and the rotating shaft. Therefore, the treatment liquid of the rear-stage group will not flow into the front-stage group. However, when the viscosity of the treatment liquid is low, the lubrication performance of the mechanical seal will be reduced by the treatment liquid, so a structure in which no mechanical seal is used between the partition wall and the rotating shaft can also be adopted. The pressure of the treatment liquid flowing through the rear-stage group is higher than the pressure of the treatment liquid flowing through the front-stage group. Therefore, in this structure, the treatment liquid of the rear-stage group flows into the front-stage group through the gap between the partition wall and the rotating shaft, and through this liquid flow, the axial thrust of the front-stage group is enhanced, while the axial thrust of the rear-stage group is weakened. As a result, an axial thrust toward the suction port side of the front-stage group is generated.

[0008] An object of the present invention is to suppress the generation of axial thrust in a multi-stage centrifugal pump.

[0009] One embodiment of the present invention is a centrifugal pump, wherein the centrifugal pump comprises: a motor; a rotating shaft that rotates based on the drive of the motor; a first impeller that is mounted on the rotating shaft and sucks in and discharges a treatment liquid; a second impeller that is mounted on the rotating shaft and sucks in and discharges the treatment liquid discharged from the first impeller; a first pump chamber that accommodates the first impeller; a second pump chamber that is arranged side by side with the first pump chamber in the axial direction of the rotating shaft and accommodates the second impeller; and a central partition wall portion that has an insertion hole for inserting the rotating shaft and divides the first pump chamber from the second pump chamber, wherein in the axial direction, the direction in which the first impeller is arranged relative to the second impeller is a first direction, and the direction opposite to the first direction is a In the second direction, the first impeller comprises: a first suction port, which faces the first direction and sucks the treatment liquid from the first direction side; and a first shield, which is opposite to the central partition wall portion; the second impeller comprises: a second suction port, which faces the second direction and sucks the treatment liquid discharged from the first impeller from the second direction side; and a second shield, which is opposite to the central partition wall portion, a first space connected to the insertion hole is formed between the first impeller and the central partition wall portion, and a second space connected to the insertion hole is formed between the second impeller and the central partition wall portion, the second space and the first space are connected to each other via the insertion hole, and the outer diameter of the second shield is larger than the outer diameter of the first shield.

[0010] Effects of the Invention

[0011] According to the present invention, generation of axial thrust in a multi-stage centrifugal pump can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic cross-sectional view showing an embodiment of a centrifugal pump according to the present invention.

[0013] Figure 2 yes Figure 1 A partially enlarged cross-sectional view of a centrifugal pump.

[0014] Figure 3 yes Figure 1 A schematic rear view of a central partition wall portion of a centrifugal pump.

[0015] Figure 4 yes Figure 1 A schematic front view of a second impeller of a centrifugal pump.

[0016] Figure 5(a) is a partially enlarged schematic cross-sectional view illustrating the axial thrust in a conventional pump. Figure 5 (b) is a partially enlarged schematic cross-sectional view illustrating the axial thrust in a conventional pump that does not have a mechanical seal.

[0017] Figure 6 It is an explanation Figure 4 The second impeller pair Figure 1 A partially enlarged schematic cross-sectional view of the influence of axial thrust on a centrifugal pump.

[0018] Figure 7 It is an explanation Figure 1 The second fixed throttle of the centrifugal pump is Figure 1 A partially enlarged schematic cross-sectional view of the influence of axial thrust on a centrifugal pump.

[0019] Figure 8 It is an explanation Figure 4 The convex portion of the second impeller is Figure 1 A partially enlarged schematic cross-sectional view of the influence of axial thrust on a centrifugal pump, Figure 8 (a) shows a state where the first axial thrust and the second axial thrust are balanced, Figure 8 (b) shows a state where the first axial thrust is greater than the second axial thrust, Figure 8 (c) shows a state where the first axial thrust is smaller than the second axial thrust.

[0020] Figure 9 It is a partially enlarged schematic cross-sectional view of a centrifugal pump according to a first modified example.

[0021] Figure 10 (a) is a partially enlarged schematic cross-sectional view of a centrifugal pump according to a second modification example. Figure 10 (b) is a partially enlarged schematic cross-sectional view of the centrifugal pump of the third modified example, Figure 10 (c) is a partially enlarged schematic cross-sectional view of the centrifugal pump of the fourth modification.

[0022] Figure 11 It is a partially enlarged schematic cross-sectional view showing a centrifugal pump according to a fifth modification. DETAILED DESCRIPTION

[0023] The following describes an embodiment of a centrifugal pump according to the present invention. In the following description, reference is made to the accompanying drawings as appropriate. Identical components and elements in the accompanying drawings are denoted by the same reference numerals, and duplicate descriptions are omitted. Furthermore, for ease of description, the dimensional proportions of the various elements may be exaggerated and are not limited to the proportions shown in the accompanying drawings.

[0024] centrifugal pumps

[0025] Structure of a centrifugal pump

[0026] Figure 1 It is a schematic cross-sectional view showing an embodiment of a centrifugal pump according to the present invention.

[0027] In this figure, a portion of the housing 2 described later is shown in a schematic cross-sectional view, and the other portions are shown in a simplified manner. This figure schematically shows a cross-sectional view of a centrifugal pump 1 cut in the vertical direction along the axial direction of the rotating shaft 4 described later so as to pass through the axial center of the rotating shaft 4 ( Figure 2 as well as Figures 5 to 11 Same).

[0028] Centrifugal pump 1 draws in and discharges a treatment liquid (liquid transport). Centrifugal pump 1 includes a housing 2, a motor 3, a rotating shaft 4, bearings 51 and 52, a first impeller 6, and a second impeller 7. Specifically, centrifugal pump 1 is a two-stage centrifugal pump having two impellers (first impeller 6 and second impeller 7), and is an example of the centrifugal pump of the present invention.

[0029] The "process liquid" is the liquid processed (transported) by the centrifugal pump 1. In this embodiment, the process liquid is a low-viscosity liquid, for example, a cryogenic liquefied gas (eg, liquefied natural gas, liquid hydrogen, etc.).

[0030] In the following description, the “front direction” is the direction in which the first impeller 6 and the second impeller 7 are located relative to the motor 3, and the “rear direction” is the direction in which the motor 3 is located relative to the first impeller 6 and the second impeller 7. The “axial direction” is the direction along the axial centerline of the rotating shaft 4 (front-rear direction), the “radial direction” is the radial direction of the rotating shaft 4, and the “circumferential direction” is the circumferential direction of the rotating shaft 4. The “upstream side” is the upstream side of the treatment liquid in the liquid flow within the housing 2, and the “downstream side” is the downstream side of the treatment liquid in the liquid flow within the housing 2. The front direction is an example of the first direction in the present invention, and the rear direction is an example of the second direction in the present invention.

[0031] The housing 2 accommodates the motor 3, the rotating shaft 4, bearings 51 and 52, the first impeller 6, and the second impeller 7. The housing 2 includes a first partition wall 20, a central partition wall 21, a second partition wall 22, a first pump chamber 23, a second pump chamber 24, a connecting flow path 25, a discharge flow path 26, a suction pipe 27, a discharge pipe 28, and a motor chamber 29.

[0032] Figure 2 It is a partially enlarged cross-sectional view of the centrifugal pump 1.

[0033] This figure shows a cross section of the upper half of the centrifugal pump 1 with the first impeller 6 and the second impeller 7 as the center. Figure 1 .

[0034] The first partition wall 20 is a partition wall that defines the first pump chamber 23 together with the central partition wall 21. The first partition wall 20 is located forward of the first impeller 6 and is disposed at the front end of the housing 2. The first partition wall 20 includes an inner surface 20a and a first through hole 20b.

[0035] The inner surface 20 a is a curved surface that is recessed toward the front in a substantially truncated cone shape so as to follow the shape of a first front shroud 63 of a first impeller 6 described later.

[0036] When viewed from the axial direction, the first through hole 20b is a through hole that penetrates the central part of the first partition wall portion 20 in the axial direction to form a two-stage cylindrical shape. The first through hole 20b is connected to the first pump chamber 23 and the suction pipe 27. The first through hole 20b has a small diameter portion 20c, a large diameter portion 20d and a segment portion 20e. The inner diameter of the small diameter portion 20c is smaller than the inner diameter of the large diameter portion 20d. In the axial direction, the small diameter portion 20c is arranged adjacent to the large diameter portion 20d in front of the large diameter portion 20d. The segment portion 20e is a surface that is arranged between the small diameter portion 20c and the large diameter portion 20d and is continuous with the small diameter portion 20c and the large diameter portion 20d respectively. When viewed from the axial direction, the segment portion 20e is annular in shape. The small diameter portion 20c functions as a flow channel for introducing the treatment liquid into the first impeller 6.

[0037] The central partition wall 21, together with the first partition wall 20, defines the first pump chamber 23, and together with the second partition wall 22, defines the second pump chamber 24. The central partition wall 21 is positioned behind the first partition wall 20. The central partition wall 21 includes a front surface 21a, a rear surface 21b, a central through hole 21c, and eight recesses 21d. The front surface 21a faces forward, and the rear surface 21b faces backward.

[0038] The central through hole 21c is a through hole that penetrates the central portion of the central partition wall 21 in the axial direction in a cylindrical shape. The rotating shaft 4 is inserted through the central through hole 21c. The central through hole 21c is an example of an insertion hole in the present invention.

[0039] Figure 3 It is a schematic rear view of the central partition wall portion 21 .

[0040] This figure schematically shows the state of the central partition wall portion 21 viewed from the rear. This figure also shows the rotating shaft 4 and the first hub portion 64 described later. In addition, for the convenience of explanation, this figure also shows the second impeller 7 and the convex portion 72c virtually with two-dot chain lines. In the following description, reference is also made to Figure 2 .

[0041] The recess 21d suppresses the swirl component of the treatment liquid flowing through the second back side space S21 described later. A portion of the rear surface 21b of the central partition wall portion 21 is recessed into a rectangle toward the front to form the recess 21d. Circumferentially, eight recesses 21d are arranged at equal angles (45 degrees in this embodiment) on the rear surface 21b. When viewed from the axial direction, the shape of the recess 21d is a rectangle with the long side direction of the recess 21d along the radial direction. When viewed from the axial direction, the inner edge portion (radially inner edge portion) of the recess 21d is arranged at the same position as the outer edge portion of the convex portion 72c of the second impeller 7 described later. When viewed from the axial direction, the outer edge portion (radially outer edge portion) of the recess 21d is arranged at approximately the same position as the middle portion between the inner edge portion and the outer edge portion of the second impeller 7.

[0042] The drawings mainly referred to in this description are Figure 1 and Figure 2 .

[0043] The second partition wall 22 is a partition wall that, together with the central partition wall 21, defines the second pump chamber 24. The second partition wall 22 is located behind the second impeller 7 and is disposed behind the central partition wall 21. The second partition wall 22 includes an inner surface 22a and a second through hole 22b.

[0044] The inner surface 22 a is a curved surface that is recessed rearward in a substantially truncated cone shape so as to follow the shape of a second front shroud 73 of the second impeller 7 described later.

[0045] When viewed from the axial direction, the second through hole 22b is a through hole that penetrates the central portion of the second partition wall portion 22 in the axial direction to form a cylindrical shape. The second through hole 22b is connected to the second pump chamber 24 and the connecting flow channel 25. The second through hole 22b includes a small diameter portion 22c, a large diameter portion 22d, a first section 22e, an insertion portion 22f, and a second section 22g. The inner diameter of the small diameter portion 22c is larger than the inner diameter of the insertion portion 22f and smaller than the inner diameter of the large diameter portion 22d. In the axial direction, the insertion portion 22f is arranged adjacent to the small diameter portion 22c behind the small diameter portion 22c, and the large diameter portion 22d is arranged adjacent to the small diameter portion 22c in front of the small diameter portion 22c. The first section 22e is a surface that is arranged between the small diameter portion 22c and the large diameter portion 22d and is continuous with the small diameter portion 22c and the large diameter portion 22d, respectively. The second segment 22g is located between the insertion portion 22f and the small-diameter portion 22c and is continuous with both the insertion portion 22f and the small-diameter portion 22c. When viewed axially, the first segment 22e and the second segment 22g are annular in shape. The rotating shaft 4 is inserted through the second through-hole 22b, forming a cylindrical space between the small-diameter portion 22c and the rotating shaft 4. This cylindrical space serves as a flow path for the treatment liquid to be introduced to the second impeller 7.

[0046] The first pump chamber 23 houses the first impeller 6. The second pump chamber 24 houses the second impeller 7. Axially, the first pump chamber 23 is arranged side by side with the second pump chamber 24, sandwiching the central partition wall 21, in front of the second pump chamber 24. In other words, the first impeller 6 is arranged axially in front of the second impeller 7.

[0047] The connecting flow path 25 is a flow path that guides the treatment liquid discharged from the first impeller 6 to the space in the small diameter portion 22c. The connecting flow path 25 is formed by, for example, a part of the housing 2 and communicates with the first pump chamber 23 and the space in the small diameter portion 22c. Figure 1 and Figure 2 In FIG. 1 , the connecting flow path 25 is schematically shown by a bold solid arrow.

[0048] The discharge flow path 26 is a flow path that guides the treatment liquid discharged from the second impeller 7 to the discharge pipe 28. The discharge flow path 26 is formed by, for example, a part of the housing 2 and communicates with the second pump chamber 24 and the discharge pipe 28. Figure 1 and Figure 2 In FIG. 1 , the discharge flow channel 26 is schematically shown by a dotted arrow.

[0049] The front end portion of the casing 2 (first partition wall portion 20) extends forward in a cylindrical shape coaxially with the rotating shaft 4, forming a suction pipe 27 for sucking (introducing) the treatment liquid into the first pump chamber 23. In addition, a portion of the casing 2 located radially outward of the second impeller 7 extends in a tangential direction (above) of the second impeller 7 to form a discharge pipe 28 for discharging the treatment liquid from the second pump chamber 24 (discharge flow path 26).

[0050] The rear half of the housing 2 defines a motor chamber 29 that houses the motor 3 and bearings 51 and 52 .

[0051] The motor 3 is a conventional motor having a rotor (not shown) mounted on a rotating shaft 4 and a stator (not shown) that rotates the rotor (not shown). The rotating shaft 4 rotates based on the drive (rotation) of the motor 3 and transmits the rotational power to the first impeller 6 and the second impeller 7. The rotating shaft 4 is cylindrical in shape. The rotating shaft 4 is mounted on the motor 3, and the front portion 4a of the rotating shaft 4 protrudes into the first pump chamber 23 and the second pump chamber 24.

[0052] The bearing 51 is arranged in front of the motor 3 and rotatably supports the rotating shaft 4. The bearing 52 is arranged behind the motor 3 and rotatably supports the rotating shaft 4. The bearings 51 and 52 are, for example, rolling bearings.

[0053] The first impeller 6 draws in and discharges the treatment liquid. The first impeller 6 is mounted on the front portion 4a of the rotating shaft 4 and housed in the first pump chamber 23. Specifically, the first impeller 6 is positioned between the first partition wall 20 and the central partition wall 21. The first impeller 6 is a so-called closed impeller. It includes a plurality of first blades 61, a first rear shroud 62, a first front shroud 63, a first hub 64, a first suction port 65, and a first discharge port 66.

[0054] The first blades 61 rotate circumferentially about the rotation axis 4, guiding the treatment liquid drawn in through the first suction port 65 to the first discharge port 66. Axially, the plurality of first blades 61 extend radially from the center toward the outer edge of the first impeller 6 and curve into a spiral shape. The first blades 61 are positioned between the first rear shield 62 and the first front shield 63.

[0055] The first back shield 62 is a plate (so-called main plate) that covers the rear of the first blade 61. The first back shield 62 is in the shape of an annular plate. When viewed axially, the center portion of the first back shield 62 protrudes forward in a roughly truncated cone shape. The first back shield 62 is opposed to the central partition wall 21. The first back shield 62 has a mounting hole 62a and a rear surface 62b. The first back shield 62 is an example of the first shield in the present invention.

[0056] The mounting hole 62a is a through hole through which the front portion 4a of the rotating shaft 4 is inserted. The mounting hole 62a is arranged in the center portion of the first back shield 62 when viewed in the axial direction, and penetrates the center portion in a cylindrical shape in the axial direction.

[0057] The rear surface 62b is a rearward-facing surface that faces the front surface 21a of the central partition wall 21. An annular plate-shaped space (hereinafter referred to as "first rear-side space S11") is formed between the rear surface 62b and the front surface 21a. The first rear-side space S11 is an example of the first space in the present invention.

[0058] The first front shield 63 is a plate (so-called side plate) that covers the front of the first blade 61. The shape of the first front shield 63 is a roughly annular plate with the inner edge protruding further toward the front than the outer edge. The outer diameter of the first front shield 63 is slightly smaller than the outer diameter of the first back shield 62. The first front shield 63 is arranged on the front side relative to the first back shield 62. The first front shield 63 has a front surface 63a and a cylindrical portion 63b. The first front shield 63 is an example of the third shield in the present invention.

[0059] The front surface 63a faces forward and faces the inner surface 20a of the first partition wall portion 20. A substantially annular space (hereinafter referred to as "first front space S12") is formed between the front surface 63a and the inner surface 20a.

[0060] The inner edge of the first front shroud 63 extends forward in a cylindrical shape, coaxially with the rotating shaft 4, forming a cylindrical portion 63b that functions as the first suction port 65. In other words, the first front shroud 63 includes the cylindrical portion 63b that functions as the first suction port 65. In the first impeller 6, the cylindrical portion 63b faces forward and is positioned within the large-diameter portion 20d of the first partition wall 20. The cylindrical portion 63b is an example of the first cylindrical portion in the present invention. The large-diameter portion 20d and the cylindrical portion 63b face each other radially. A cylindrical gap (hereinafter referred to as the "first cylindrical gap S13") is formed between the large-diameter portion 20d and the cylindrical portion 63b. The radial length of the first cylindrical gap S13 (the distance between the large-diameter portion 20d and the cylindrical portion 63b) is such that the cylindrical portion 63b does not abut the large-diameter portion 20d during normal operation of the centrifugal pump 1 and is set to the same length as that of the impeller of a conventional centrifugal pump. In the axial direction, the segment 20e is opposed to the cylindrical portion 63b. A ring-shaped gap (hereinafter referred to as the "first annular gap S14") is formed between the segment 20e and the cylindrical portion 63b. The axial length of the first annular gap S14 (the distance between the segment 20e and the cylindrical portion 63b) is such that the cylindrical portion 63b does not abut the segment 20e during normal operation of the centrifugal pump 1, and is set to the same length as that set for the impeller of a typical centrifugal pump. The first cylindrical gap S13 and the first annular gap S14 constitute the first fixed throttle, which will be described later. The large-diameter portion 20d and the segment 20e are an example of the portion opposing the first cylindrical portion in the present invention.

[0061] The first front side space S12 communicates with the space located radially outside the first impeller 6 and the first cylindrical gap S13. The first annular gap S14 communicates with the first cylindrical gap S13 and the space in the small diameter portion 20c.

[0062] The inner edge of the first rear shield 62 extends cylindrically rearward, coaxially with the rotating shaft 4, forming a first boss portion 64. The front portion 4a of the rotating shaft 4 is inserted through the first boss portion 64. By securing the first boss portion 64 to the front portion 4a of the rotating shaft 4, the first impeller 6 is attached to the front portion 4a. At this point, the first suction port 65 faces forward. The first boss portion 64 covers a portion of the front portion 4a of the rotating shaft 4 and is positioned within the central through-hole 21c.

[0063] The outer edges of the first blades 61 , the first back shroud 62 , and the first front shroud 63 form a first discharge port 66 for discharging the treatment liquid flowing through the flow path in the first impeller 6 .

[0064] The second impeller 7 draws in and discharges the treatment liquid discharged from the first impeller 6. The second impeller 7 is attached to the front portion 4a of the rotating shaft 4 and is housed in the second pump chamber 24. Specifically, the second impeller 7 is positioned between the central partition wall 21 and the second partition wall 22. The second impeller 7 is a so-called closed impeller. It includes a plurality of second blades 71, a second rear shroud 72, a second front shroud 73, a second hub 74, a second suction port 75, and a second discharge port 76.

[0065] The specific speed set by the second pump section P2 composed of the second impeller 7 and the second pump chamber 24 is smaller than the specific speed set by the first pump section P1 composed of the first impeller 6 and the first pump chamber 23. With this structure, in the centrifugal pump 1, high suction performance (discharge flow) is obtained by the first pump section P1, and high head is obtained by the second pump section P2. In addition, generally speaking, the outer diameter (diameter) of the impeller becomes smaller as the specific speed becomes larger. Therefore, the outer diameter (diameter) of the second impeller 7 is larger than the outer diameter (diameter) of the first impeller 6. The values ​​of these specific speeds are appropriately set according to, for example, the design of the centrifugal pump 1 (for example, discharge flow, head, etc.).

[0066] The second blades 71 rotate circumferentially about the rotation axis 4, directing the treatment liquid drawn in through the second suction port 75 to the second discharge port 76. Axially, the plurality of second blades 71 extend radially from the center toward the outer edge of the second impeller 7 and curve into a spiral shape. The second blades 71 are positioned between the second rear shield 72 and the second front shield 73.

[0067] The second back shield 72 is a plate (so-called main plate) that covers the front of the second blades 71 (toward the back side of the second impeller 7). The second back shield 72 is in the shape of an annular plate. When viewed from the axial direction, the center portion of the second back shield 72 protrudes rearward in a truncated cone shape. The second back shield 72 is opposite to the central partition wall portion 21. The second back shield 72 has a mounting hole 72a, a front surface 72b, and a protrusion 72c. The second back shield 72 is an example of the second shield in the present invention.

[0068] The outer diameter (diameter) of the second back shield 72 is larger than the outer diameter (diameter) of the first back shield 62. The outer diameters of the first back shield 62 and the second back shield 72 are set, for example, so that when the first impeller 6 and the second impeller 7 (that is, the centrifugal pump 1) discharge the treatment liquid (at the highest efficiency point), the first axial thrust and the second axial thrust, which will be described later, are approximately balanced.

[0069] The mounting hole 72a is a through hole through which the front portion 4a of the rotating shaft 4 is inserted. The mounting hole 72a is arranged in the center portion of the second back shield 72 when viewed in the axial direction, and penetrates the center portion in a cylindrical shape in the axial direction.

[0070] The front surface 72b is a surface facing forward and faces the rear surface 21b of the central partition wall portion 21. An annular plate-shaped gap (hereinafter referred to as the "second back side space S21") is formed between the front surface 72b and the rear surface 21b. The second back side space S21 is an example of the second space in the present invention.

[0071] Figure 4 It is a schematic front view of the second impeller 7.

[0072] This figure schematically shows the state of the second impeller 7 viewed from the front. In the following description, reference is also made to Figure 2 .

[0073] The convex portion 72c functions as a variable throttle port described later. A portion of the front surface 72b of the second back shield 72 protrudes forward in an annular plate shape in a manner coaxial with the rotating shaft 4, constituting the convex portion 72c. That is, when viewed from the axial direction, the convex portion 72c is in an annular plate shape that is concentric with the rotating shaft 4. In the radial direction, the convex portion 72c is arranged at a position close to the inner side (close to the inner edge) of the second back shield 72. The front surface 72d of the convex portion 72c is a plane parallel to the rear surface 21b of the central partition wall portion 21. In the axial direction, the interval between the convex portion 72c and the rear surface 21b of the central partition wall portion 21 is narrower than the interval between the front surface 72b excluding the convex portion 72c and the rear surface 21b of the central partition wall portion 21. The convex portion 72c is an example of a protrusion (variable throttle port) in the present invention.

[0074] The drawings mainly referred to in this description are Figure 1 and Figure 2 .

[0075] The second front shroud 73 is a plate (so-called side plate) that covers the rear of the second blade 71 (toward the front side in the second impeller 7). The shape of the second front shroud 73 is a roughly annular plate with the inner edge protruding further toward the rear than the outer edge. The outer diameter of the second front shroud 73 is slightly smaller than the outer diameter of the second back shroud 72. The second front shroud 73 is arranged on the rear side relative to the second back shroud 72. The second front shroud 73 has a rear surface 73a and a cylindrical portion 73b. The second front shroud 73 is an example of the fourth shroud in the present invention.

[0076] The rear surface 73a faces rearward and faces the inner surface 22a of the second partition wall portion 22. A substantially annular space (hereinafter referred to as "second front space S22") is formed between the rear surface 73a and the inner surface 22a.

[0077] The inner edge of the second front shield 73 extends rearward in a cylindrical shape in a coaxial manner with the rotating shaft 4, forming a cylindrical portion 73b that functions as the second suction port 75. In other words, the second front shield 73 has a cylindrical portion 73b that functions as the second suction port 75. In the second impeller 7, the cylindrical portion 73b faces rearward and is arranged in the large diameter portion 22d of the second partition wall portion 22. The cylindrical portion 73b is an example of the second cylindrical portion in the present invention. In the radial direction, the cylindrical portion 73b is opposite to the large diameter portion 22d. A cylindrical gap (hereinafter referred to as the "second cylindrical gap S23") is formed between the large diameter portion 22d and the cylindrical portion 73b. The radial length of the second cylindrical gap S23 (the gap between the large-diameter portion 22d and the cylindrical portion 73b) is such that the cylindrical portion 73b does not abut the large-diameter portion 22d during normal operation of the centrifugal pump 1. This gap is set to be longer than the length specified for the impeller of a typical centrifugal pump. In other words, the radial length of the second cylindrical gap S23 is longer than the length of the first cylindrical gap S13. Axially, the cylindrical portion 73b faces the first segment 22e. An annular gap (hereinafter referred to as the "second annular gap S24") is formed between the first segment 22e and the cylindrical portion 73b. The axial length of the second annular gap S24 (the gap between the first segment 22e and the cylindrical portion 73b) is such that the cylindrical portion 73b does not abut the first segment 22e during normal operation of the centrifugal pump 1. This gap is set to be longer than the length specified for the impeller of a typical centrifugal pump. That is, in the axial direction, the length of the second annular gap S24 is longer than the length of the first annular gap S14.

[0078] The second front side space S22 communicates with the space radially outside the second impeller 7 and the second cylindrical gap S23. The second annular gap S24 communicates with the second front side space S22 and the space in the small diameter portion 22c.

[0079] The inner edge of the second back shield 72 extends forward in a cylindrical shape, coaxial with the rotating shaft 4, forming a second boss 74. The front portion 4a of the rotating shaft 4 is inserted through the second boss 74. By securing the second boss 74 to the front portion 4a of the rotating shaft 4, the second impeller 7 is attached to the front portion 4a. At this time, the second suction port 75 faces rearward. The second boss 74 covers a portion of the front portion 4a of the rotating shaft 4 and is positioned within the central through-hole 21c. The second boss 74 abuts the first boss 64, forming a cylindrical space (hereinafter referred to as "cylindrical space S3") between the central through-hole 21c and the first and second bosses 64 and 74. The cylindrical space S3 communicates with the first back-side space S11 and the second back-side space S21. That is, the first back-side space S11 and the second back-side space S21 communicate with each other via the cylindrical space S3 (central through-hole 21c).

[0080] As described above, this is a two-stage centrifugal pump in which the first impeller 6 and the second impeller 7 are mounted on a single rotating shaft 4, facing away from each other with a central partition wall 21 interposed therebetween. The first pump chamber 23 and the second pump chamber 24 are separated by the central partition wall 21 and communicate with each other via the cylindrical space S3. In other words, there is no shaft seal structure, such as a mechanical seal, between the first and second pump chambers 23, 24.

[0081] Centrifugal pump operation

[0082] Next, the operation of the centrifugal pump 1 will be described. Figure 1 and Figure 2 .

[0083] If the centrifugal pump 1 starts to move, the motor 3 is driven and the rotating shaft 4 rotates. The first impeller 6 sucks the treatment liquid introduced into the small-diameter portion 20c from the front and discharges it into the first pump chamber 23. The treatment liquid discharged into the first pump chamber 23 is transported to the space inside the small-diameter portion 22c via the connecting flow channel 25. At this time, a part of the treatment liquid discharged into the first pump chamber 23 flows into the first back side space S11 and flows into the second pump chamber 24 (second back side space S21) via the cylindrical space S3. In addition, another part of the treatment liquid discharged into the first pump chamber 23 flows into (returns to) the space inside the small-diameter portion 20c via the first front side space S12, the first cylindrical gap S13 and the first annular gap S14. The liquid flow returned by this treatment liquid will have an adverse effect on the suction performance of the first impeller 6. Therefore, the liquid flow is mainly throttled through the first cylindrical gap S13 and the first annular gap S14. That is, the first cylindrical gap S13 and the first annular gap S14 function as a throttle portion (first fixed throttle) for the liquid flow. The first fixed throttle (first cylindrical gap S13, first annular gap S14) is an example of the first gap in the present invention.

[0084] The second impeller 7 sucks the treatment liquid delivered to the space within the small diameter portion 22c from the rear and discharges it into the second pump chamber 24. The treatment liquid discharged into the second pump chamber 24 is discharged to the discharge pipeline (not shown) via the discharge flow channel 26 and the discharge pipe 28. At this time, a portion of the treatment liquid discharged into the second pump chamber 24 flows into the second back side space S21. Here, the pressure of the treatment liquid in the second pump chamber 24 is greater than the pressure of the treatment liquid in the first pump chamber 23. Therefore, the treatment liquid flowing into the second back side space S21 flows into the first pump chamber 23 (first back side space S11) via the cylindrical space S3 in a manner that presses back the treatment liquid flowing into the first pump chamber 23. In this way, in the centrifugal pump 1, a liquid flow (hereinafter referred to as "return flow") is generated in which the treatment liquid returns from the second pump chamber 24 to the first pump chamber 23. The second back side space S21 and the cylindrical space S3 constitute a flow channel (hereinafter referred to as the "return flow channel RL") for a portion of the treatment liquid in the second pump chamber 24 to flow to the first back side space S11 (first pump chamber 23). In addition, another portion of the treatment liquid discharged into the second pump chamber 24 flows into (returns to) the space in the small diameter portion 22c via the second front side space S22, the second cylindrical gap S23 and the second annular gap S24. The liquid flow returned by this treatment liquid may have an adverse effect on the suction performance of the second impeller 7. Therefore, the liquid flow is mainly throttled through the second cylindrical gap S23 and the second annular gap S24. That is, the second cylindrical gap S23 and the second annular gap S24 function as a throttling portion (second fixed throttling port) for the liquid flow. The second fixed throttling port is larger than the first fixed throttling port. Therefore, the throttling amount of the flow rate performed by the second fixed throttling port is less than the throttling amount of the flow rate performed by the first fixed throttling port. That is, the flow rate of the treatment liquid flowing through the second fixed throttle is greater than the flow rate of the treatment liquid flowing through the first fixed throttle. The second fixed throttle (the second cylindrical gap S23 and the second annular gap S24) is an example of the second gap in the present invention.

[0085] As described below, in the centrifugal pump 1 in which the process fluid flows in this manner, an axial thrust different from that of the conventional two-stage centrifugal pump (hereinafter referred to as the "conventional pump") is exerted. In this specification, the structure of the "conventional pump" is the same as that of the centrifugal pump 1, except that the outer diameter of the first impeller (the outer diameter of the first back shroud) and the outer diameter of the second impeller (the outer diameter of the second back shroud) are the same and the cylindrical space is sealed with a mechanical seal. In other words, the conventional pump is a two-stage centrifugal pump in which the first impeller and the second impeller are mounted on a single rotating shaft with their backs to each other. In order to distinguish the centrifugal pump 1 from the conventional pump, in the following description, the reference numeral "z" is added to the reference numerals that are the same as those of the centrifugal pump 1 in the structure of the conventional pump.

[0086] "Axial thrust" is the force acting on the rotating shaft 4 (first impeller 6, second impeller 7) to move it in the axial direction. This axial thrust includes a first axial thrust that moves the rotating shaft 4 forward and a second axial thrust that moves the rotating shaft 4 backward. This axial thrust is primarily generated by the pressure balance between the front and rear sides of the first and second impellers 6, 7 of the centrifugal pump 1.

[0087] Axial thrust in existing pumps

[0088] Here, before describing the axial thrust in the centrifugal pump 1 , the axial thrust in the conventional pump 1 z and the conventional pump 1 z not including the mechanical seal Mz will be described below.

[0089] Figure 5 (a) is a partially enlarged schematic cross-sectional view illustrating the axial thrust in the conventional pump 1z. Figure 5 (b) is a partially enlarged schematic cross-sectional view illustrating the axial thrust in a conventional pump 1z that does not include a mechanical seal Mz.

[0090] In this figure, for the sake of convenience, only the central partition wall 21z, the rotating shaft 4z, the first impeller 6z, the second impeller 7z, and the mechanical seal Mz are simplified. In (b) of this figure, the hollow arrows indicate the backflow.

[0091] In the following description, pressure “P f3 " represents the pressure exerted on the first front shield 63z of the first impeller 6z by the treatment liquid flowing through the first front side space S12z. The pressure "P r3 " represents the pressure exerted on the first back side shield 62z of the first impeller 6z by the treatment liquid flowing through the first back side space S11z. The pressure "P f4 " represents the pressure exerted on the second front shield 73z of the second impeller 7z by the treatment liquid flowing through the second front side space S22z. The pressure "P r4 " represents the pressure on the second back shield 72z of the second impeller 7z from the treatment liquid flowing through the second back side space S21z. In the first impeller 6z, based on the pressure "P f3 The force "F f3 ” acts toward the rear, based on the pressure “P r3 The force "F r3 ” acts forward. Due to the pressure “P f3 "less than pressure" P r3 ", so it is equivalent to the difference between the two forces (F r3 -F f3 ) force (first axial thrust) acts forward on the first impeller 6z. Similarly, in the second impeller 7z, the pressure "P f4 The force "Ff4 "Acting forward, the pressure "P r4 The force "F r4 ” acts toward the rear. Due to the pressure “P f4 "less than pressure" P r4 ", so it is equivalent to the difference between the two forces (F r4 -F f4 ) force (second axial thrust) acts on the second impeller 7z toward the rear. Figure 5 In the figure, the thin arrows show the pressure "P f3 "P r3 "P f4 "P r4 ". The thick arrows show the force "F" by the length of the arrow. f3 "F r3 "F f4 "F r4 ” size.

[0092] like Figure 5 As shown in (a), in the existing pump 1z, the structure of the first impeller 6z is the same as the structure of the second impeller 7z except for the direction of rotation. That is, as mentioned above, the outer diameter of the first back shield 62z of the first impeller 6z is the same as the outer diameter of the second back shield 72z of the second impeller 7z. A mechanical seal Mz is installed in the cylindrical space S3z, and the first pump chamber 23z is not connected to the second pump chamber 24z. The pressure area (liquid contact area) of the first front shield 63z is smaller than the pressure area of ​​the first back shield 62z, and is the same as the pressure area of ​​the second front shield 73z. In addition, the pressure area of ​​the first back shield 62z is the same as the pressure area of ​​the second back shield 72z. In this structure, the pressure "P f3 " and pressure "P f4 "Same, pressure "P r3 " and pressure "P r4 ” is the same. As a result, the force “F r3 " is greater than the force "F" acting on the first front shield 63z f3 ”, and the force “F r4 "The same. The force "F f3 ” and the force “F f4 " is the same. Therefore, it is equivalent to the difference between the two forces (F r3 -F f3 ) acts on the first impeller 6z in the forward direction. On the other hand, the difference between the two forces (F r4 -F f4) force (second axial thrust) acts on the second impeller 7z toward the rear. As a result, the first axial thrust and the second axial thrust cancel each other out (axial thrust balance). It should be noted that, in practice, the first axial thrust acts on the rotating shaft 4 due to the pressure difference between the treatment fluid in the first pump chamber 23z and the treatment fluid in the second pump chamber 24z. However, usually, this first axial thrust is absorbed by the bearing. Therefore, in the existing pump 1z, the axial thrust that becomes a problem does not act on the rotating shaft 4z.

[0093] Then, if Figure 5 As shown in (b), in the existing pump 1z that does not have a mechanical seal Mz, the first pump chamber 23z is connected to the second pump chamber 24z via the cylindrical space S3z. In this structure, the pressure of the treatment liquid in the second pump chamber 24z is higher than the pressure of the treatment liquid in the first pump chamber 23z, so a liquid flow (reflux) is generated in which the treatment liquid in the second pump chamber 24z flows into the first pump chamber 23z via the cylindrical space S3z. At this time, in the second back side space S21z, a liquid flow is generated that rotates along the rotation direction of the second impeller 7z and flows from the outer edge side to the inner edge side of the second back side shield 72z. Therefore, as Figure 5 As shown by the dotted and solid lines in (b), the pressure of the treatment liquid flowing through the second back side space S21z is "P r4 On the other hand, in the first back side space S11z, a liquid flow is generated which flows from the inner edge side toward the outer edge side of the first back side shield 62z while swirling along the rotation direction of the first impeller 6z. Therefore, as Figure 5 As shown by the dotted and solid lines in (b), the pressure of the treatment liquid flowing through the first back side space S11z is "P r3 ” becomes higher. Therefore, the force “F r3 " becomes larger, and the force "F" acting on the second back shield 72z r4 ” becomes smaller. As a result, the first axial thrust acting on the rotating shaft 4z (first impeller 6z, second impeller 7z) becomes greater than the second axial thrust, and the first axial thrust acts on the rotating shaft 4z. In this way, when the first pump chamber 23z is connected to the second pump chamber 24z via the cylindrical space S3z, the axial thrust in the conventional pump 1z becomes unbalanced, and the axial thrust (first axial thrust) acts on the rotating shaft 4z.

[0094] These axial thrusts increase as the number of revolutions of the motor 3 increases. Therefore, for example, when transporting a treatment fluid that requires high-speed rotation (for example, a treatment fluid with low viscosity), the axial thrust cannot be absorbed by the bearings, and a mechanism (for example, a balancing piston, a balancing plate, etc.) is required to offset the axial thrust. In this case, not only does the existing pump 1z become larger as a whole, but the rotating shaft 4z also becomes longer. As a result, it becomes difficult to cope with high-speed rotation. In addition, when the treatment fluid is used to lubricate the bearings, especially if the viscosity of the treatment fluid is low, even a slight axial thrust will generate surface pressure on the sliding surface of the bearing. As a result, the temperature of the sliding surface rises and the life of the bearing is reduced. Therefore, it is necessary to avoid structures that generate axial thrust as much as possible (ideally, a structure where the axial thrust is "0").

[0095] Axial thrust in centrifugal pumps

[0096] Next, the axial thrust in the centrifugal pump 1 is described below. Figures 1 to 5 .

[0097] Figure 6 It is a partially enlarged schematic cross-sectional view for explaining the influence of the second impeller 7 on the axial thrust in the centrifugal pump 1 .

[0098] For ease of explanation, this figure schematically illustrates only the central partition wall 21, the rotating shaft 4, the first impeller 6, and the second impeller 7, omitting the convex portion 72c. The hollow arrows in this figure indicate backflow. Furthermore, to facilitate understanding of the forces acting on the second impeller 7, this figure illustrates the second impeller 7 as if only the outer diameter of the second back shroud 72 is larger than that of the first back shroud 62, while the outer diameter of the second front shroud 73 is the same as that of the first front shroud 63.

[0099] In the following description, pressure “P f1 " represents the pressure exerted on the first front shield 63 of the first impeller 6 by the treatment liquid flowing through the first front side space S12. The pressure "P r1 " represents the pressure exerted on the first back side shield 62 of the first impeller 6 by the treatment liquid flowing through the first back side space S11. The pressure "P f2 " represents the pressure exerted on the second front shield 73 of the second impeller 7 by the treatment liquid flowing through the second front side space S22. The pressure "P r2 " represents the pressure on the second back side shield 72 of the second impeller 7 from the treatment liquid flowing through the second back side space S21. Based on the pressure "P f1 The force "F f1 " acts on the first impeller 6 toward the rear, based on the pressure "P r1 The force "F r1 ” acts on the first impeller 6 toward the front. Due to the pressure “P f1 "less than pressure" Pr1 ", so it is equivalent to the difference between the two forces (F r1 -F f1 ) acts on the first impeller 6 toward the front. Similarly, based on the pressure "P f2 The force "F f2 ” acts on the second impeller 7 toward the front, the pressure “P r2 The force "F r2 " acts on the second impeller 7 towards the rear. It is equivalent to the difference between the two forces (F r2 -F f2 ) force (second axial thrust) acts on the second impeller 7 toward the rear. Figure 6 In the figure, the thin arrows show the pressure "P f1 "P r1 "P f2 "P r2 ". The thick arrows show the force "F" by the length of the arrow. f1 "F r1 "F f2 "F r2 ” size.

[0100] As described above, the outer diameter of the second back shield 72 is larger than the outer diameter of the first back shield 62. Figure 6 As shown, the pressure area of ​​the second back shroud 72 is larger than the pressure area of ​​the first back shroud 62. As a result, the force "F r2 "The force "F" acting on the second impeller 7z of the existing pump 1z r4 Therefore, by designing the outer diameter of the second back shroud 72 (that is, the outer diameter of the second impeller 7) to be larger than the outer diameter of the first back shroud 62 (that is, the outer diameter of the first impeller 6), the second axial thrust (F r2 -F f2 ) will be greater than the second axial thrust (F r4 -F f4 ) is larger, the axial thrust (first axial thrust) acting on the rotating shaft 4 is smaller (suppressed) than the axial thrust (first axial thrust) acting on the rotating shaft 4z. As a result, the first axial thrust (F r1 -F f1 ) and the second axial thrust (F r2 -F f2 (roughly) balanced.

[0101] Figure 7It is a partially enlarged schematic cross-sectional view illustrating the influence of the second fixed throttle (the second cylindrical gap S23 and the second annular gap S24 ) on the axial thrust in the centrifugal pump 1 .

[0102] For ease of explanation, this figure schematically illustrates only the first partition wall 20, central partition wall 21, second partition wall 22, rotating shaft 4, first impeller 6, and second impeller 7, omitting the convex portion 72c. The hollow arrows in this figure indicate backflow. Furthermore, in this figure, to illustrate only the effect of the second fixed throttle, the second impeller 7 is shown with its outer diameter being the same as that of the first impeller 6.

[0103] As described above, in the radial direction, the length of the second cylindrical gap S23 is longer than the length of the first cylindrical gap S13. In the axial direction, the length of the second annular gap S24 is longer than the length of the first annular gap S14. In this structure, the flow rate of the treatment liquid flowing into the second front side space S22 through the second fixed throttle opening is less than the flow rate of the treatment liquid flowing into the first front side space S12 through the first fixed throttle opening. That is, the flow rate of the treatment liquid flowing through the second fixed throttle opening ( Figure 7 The flow rate of the liquid shown by the dotted arrow is greater than the flow rate of the treatment liquid flowing through the first fixed throttle. Therefore, the pressure "P f2 ”, which is greater than the pressure when the flow rate of the treatment liquid passing through the second fixed throttle is the same as the flow rate of the treatment liquid passing through the first fixed throttle ( Figure 7 (indicated by a dotted line in the figure) is smaller. As a result, the force acting on the second impeller 7 (the second axial thrust) is greater than the force when the flow rate of the treatment liquid flowing through the second fixed throttle is the same as the flow rate of the treatment liquid flowing through the first fixed throttle. Therefore, by designing the flow rate of the treatment liquid flowing through the second fixed throttle to be greater than the flow rate of the treatment liquid flowing through the first fixed throttle, the second axial thrust acting on the second impeller 7 (rotating shaft 4) becomes larger, and the axial thrust (the first axial thrust) acting on the rotating shaft 4 becomes smaller (suppressed). Here, generally, if the flow rate of the treatment liquid flowing through the first fixed throttle increases, the suction performance of the first impeller 6 deteriorates and the efficiency of the centrifugal pump 1 deteriorates. On the other hand, even if the flow rate of the treatment liquid flowing through the second fixed throttle increases, the effect on the suction performance of the second impeller 7 is small. Therefore, in this structure, although the performance of the centrifugal pump 1 may be slightly deteriorated, the improvement in the efficiency of the centrifugal pump 1 brought about by the improvement in the axial thrust acting on the rotating shaft 4 is greater than the deterioration.

[0104] Next, as described above, a plurality of recesses 21d are provided on the rear surface 21b of the central partition wall portion 21. The recesses 21d face the second back side space S21, and the flow of the treatment liquid in the second back side space S21 is disturbed by the recesses 21d. The flow of the treatment liquid in the second back side space S21 becomes a rotational flow that rotates in the same direction of rotation as the second impeller 7 according to the rotation of the second impeller 7. That is, the flow of the treatment liquid in the second back side space S21 contains a large amount of swirl components. In the flow of the treatment liquid in the second back side space S21, part of the flow close to the central partition wall portion 21 flows into the recess 21d and is obstructed by the side wall of the recess 21d. At this time, the swirl component of the flow flowing into the recess 21d is suppressed, and the flow changes direction toward the radial inner side and the axial side. Therefore, the flow also interferes with the flow that has not flowed into the recess 21d, and the swirl component of the disturbed flow is also slightly suppressed. As a result, the swirl component of the process liquid flow in the second back side space S21 is suppressed. Since the swirl component of the process liquid is large, the pressure "P r2 " is reduced, so if the swirl component of the treatment liquid is suppressed, the pressure of the treatment liquid "P r2 That is, by suppressing the swirl component of the treatment liquid in the second back side space S21, the force acting on the second impeller 7 (the second axial thrust) becomes larger, and the axial thrust acting on the rotating shaft 4 (the first axial thrust) becomes smaller (is suppressed).

[0105] As described above, the centrifugal pump 1 includes: a structure for suppressing the axial thrust (first axial thrust) by the outer diameter of the second back shroud (hereinafter referred to as the "first suppression structure"); a structure for suppressing the axial thrust (first axial thrust) by the second fixed throttle (hereinafter referred to as the "second suppression structure"); and a structure for suppressing the axial thrust (first axial thrust) by the recess 21d (hereinafter referred to as the "third suppression structure"). In the centrifugal pump 1, the first to third suppression structures are combined to balance the axial thrust acting on the rotating shaft 4.

[0106] Figure 8 1 is a partially enlarged schematic cross-sectional view illustrating the effect of the convex portion 72c on the axial thrust in the centrifugal pump 1. Figure 8 (a) shows a state where the first axial thrust and the second axial thrust are balanced, Figure 8 (b) shows a state where the first axial thrust is greater than the second axial thrust, Figure 8 (c) shows a state where the first axial thrust is smaller than the second axial thrust. In this figure, for the sake of convenience, only the central partition wall portion 21, the rotary shaft 4, and the second impeller 7 are shown in simplified form.

[0107] like Figure 8As shown in (a), with the first and second axial thrusts balanced, the rotating shaft 4 (first impeller 6, second impeller 7) is positioned in the predetermined axial position. At this point, a gap S4 with a spacing "L1" is formed axially between the protrusion 72c and the rear surface 21b of the central partition wall 21. The process liquid within the second rear side space S21 flows while swirling from the outer edge of the second impeller 7 toward the inner edge, with its flow rate being throttled in the gap S4.

[0108] Then, if Figure 8 As shown in (b), when the first axial thrust is greater than the second axial thrust, the rotating shaft 4 (first impeller 6, second impeller 7) moves forward in the axial direction, and the interval of the gap S4 becomes narrower and becomes "L2". At this time, the throttling amount of the treatment liquid formed by the protrusion 72c becomes larger. Therefore, in the second back side space S21, the pressure "P r2 "Becomes larger. In addition, the flow rate of the processing liquid flowing through the cylindrical space S3 is reduced, and the pressure of the processing liquid in the first back side space S11 is "P r1 ” becomes smaller. As a result, the force “F r2 " becomes larger, and the force "F" acting on the first impeller 6 r1 " becomes smaller, and eventually, the first axial thrust and the second axial thrust become balanced. In this way, as the rotating shaft 4 (the first impeller 6 and the second impeller 7) moves forward, the convex portion 72c narrows a portion of the second back side space S21 (that is, a portion of the return flow path RL), thereby balancing the axial thrusts (the first axial thrust and the second axial thrust) acting on the rotating shaft 4.

[0109] On the contrary, Figure 8 As shown in (c), when the first axial thrust is less than the second axial thrust, the rotating shaft 4 (first impeller 6, second impeller 7) moves backward in the axial direction, and the interval of the gap S4 becomes wider and becomes "L3". At this time, the throttling amount of the treatment liquid formed by the protrusion 72c becomes smaller. Therefore, in the second front side space S22, the pressure "P r2 " becomes smaller. In addition, the flow rate of the processing liquid flowing through the cylindrical space S3 increases, and the pressure of the processing liquid in the first back side space S11 "F r1 ” becomes larger. As a result, the force “F r2 ” becomes smaller, and the force “F r1" becomes larger, and eventually, the first axial thrust and the second axial thrust become balanced. In this way, the convex portion 72c widens a portion of the second back side space S21 (that is, a portion of the return flow path RL) as the rotating shaft 4 (the first impeller 6 and the second impeller 7) moves rearward, thereby balancing the axial thrust acting on the rotating shaft 4.

[0110] Thus, the convex portion 72 c functions as a variable throttle that adjusts the flow rate of the processing liquid in the second front side space S22 according to the axial thrust acting on the rotating shaft 4 (thereby adjusting the axial thrust acting on the rotating shaft 4 ).

[0111] As described above, the second back side space S21 is a ring-plate-shaped space. Therefore, the cross-sectional area (cross-sectional area of ​​the flow channel) of the second back side space S21 in the circumferential cutting surface becomes smaller as the cutting surface approaches the inner edge of the second back side shield 72. That is, as the cutting surface approaches the inner edge of the second back side shield 72, the throttling amount of the variable throttle port relative to the amount of movement of the convex portion 72c in the axial direction increases. Therefore, if the convex portion 72c is arranged at a position close to the inner edge of the second back side shield 72, even if the amount of movement of the convex portion 72c in the axial direction is small, the pressure "P" of the processing liquid on the upstream side of the convex portion 72c is smaller. r2 The amount of change will also increase.

[0112] Thus, the centrifugal pump 1 is designed to reduce the force "F" acting on the second impeller 7 through the first to third restraining structures. r2 ” becomes larger. Therefore, by designing the first suppression structure to the third suppression structure so that the first axial thrust and the second axial thrust acting on the rotating shaft 4 are completely balanced, even if the processing liquid in the second pump chamber 24 flows into the first pump chamber 23 via the cylindrical space S3 (return flow channel RL), the axial thrust will not act on the rotating shaft 4. Here, in the present embodiment, the balance between the first axial thrust and the second axial thrust acting on the rotating shaft 4 is roughly adjusted (coarse adjustment) by the first suppression adjustment, and auxiliary adjustment (fine adjustment) is performed by the second suppression structure and the third suppression structure. In addition, even if an axial thrust acts on the rotating shaft 4, the axial thrust is suppressed to a slight force by the first suppression structure to the third suppression structure, so that the axial thrust is easily and automatically adjusted by the variable throttle.

[0113] Summarize

[0114] According to the embodiment described above, the centrifugal pump 1 includes a central partition wall portion 21, a first pump chamber 23, a second pump chamber 24, a rotating shaft 4, a first impeller 6, and a second impeller 7. The central partition wall portion 21 includes a central through hole 21c for the rotating shaft 4 to pass through. The first pump chamber 23 is divided from the second pump chamber 24 by the central partition wall portion 21, and is arranged in front of the second pump chamber 24 side by side with the second pump chamber 24. The first suction port 65 of the first impeller 6 faces forward, and the second suction port 75 of the second impeller 7 faces backward. A first back side space S11 is formed between the first impeller 6 and the central partition wall portion 21, and a second back side space S21 is formed between the second impeller 7 and the central partition wall portion 21. The first back side space S11 is connected to the second back side space S21 via the cylindrical space S3. The outer diameter of the second back side shield 72 is larger than the outer diameter of the first back side shield 62. According to this structure, the pressure area of ​​the second back side shield 72 is increased, thereby increasing the force "F" acting on the second impeller 7. r2 ” increases. Therefore, even if the processing liquid in the second pump chamber 24 flows into the first pump chamber 23 via the cylindrical space S3, the axial thrust acting on the rotating shaft 4 will be suppressed. Therefore, by adjusting the outer diameter of the second back shield 72 to balance the axial thrust acting on the rotating shaft 4, the axial thrust acting on the rotating shaft 4 can be suppressed to a minimum.

[0115] In addition, according to the embodiment described above, the specific speed set by the first pump section P1 composed of the first impeller 6 and the first pump chamber 23 is greater than the specific speed set by the second pump section P2 composed of the second impeller 7 and the second pump chamber 24. Generally speaking, as the specific speed increases, the opening on the suction side between the blades of the impeller becomes larger, and the outer diameter of the impeller becomes smaller. Therefore, according to this structure, the suction performance (discharge flow) formed by the first pump section P1 is improved, and the head formed by the second pump section P2 is increased, and the performance of the centrifugal pump 1 is improved. In addition, the outer diameter of the second back shield 72 must be larger than the outer diameter of the first back shield 62. As a result, even if the treated liquid in the second pump chamber 24 flows into the first pump chamber 23 through the cylindrical space S3, the axial thrust acting on the rotating shaft 4 will be suppressed.

[0116] Moreover, according to the embodiment described above, the centrifugal pump 1 includes a first partition wall portion 20 and a second partition wall portion 22. The first impeller 6 includes a first front shield 63 and a cylindrical portion 63b that functions as a first suction port 65. The second impeller 7 includes a second front shield 73 and a cylindrical portion 73b that functions as a second suction port 75. In the first partition wall portion 20, the large diameter portion 20d and the segment portion 20e are opposite to the cylindrical portion 63b. In the second partition wall portion 22, the large diameter portion 22d and the first segment portion 22e are opposite to the cylindrical portion 73b. The size (length) of the second cylindrical gap S23 and the second annular gap S24 (second fixed throttle port) is larger (longer) than the size (length) of the first cylindrical gap S13 and the first annular gap S14 (first fixed throttle port). According to this structure, the pressure "P f2 ”, which is the pressure “P” when the flow rate of the treatment liquid passing through the second fixed throttle is the same as the flow rate of the treatment liquid passing through the first fixed throttle. f2 " is small. As a result, the force acting on the second impeller 7 (the second axial thrust) is greater than the force (the second axial thrust) when the flow rate of the treatment liquid through the second fixed throttle opening is the same as the flow rate of the treatment liquid through the first fixed throttle opening. Therefore, even if the treatment liquid in the second pump chamber 24 flows into the first pump chamber 23 through the cylindrical space S3, the axial thrust acting on the rotating shaft 4 will be further suppressed.

[0117] Furthermore, according to the embodiment described above, the central partition wall portion 21 has eight recesses 21d. The recesses 21d face the second back side space S21 and are configured to suppress the swirl component of the treatment liquid flowing through the second back side space S21. According to this structure, the pressure "P r2 ” becomes larger, the second axial thrust acting on the second impeller 7 (rotating shaft 4) becomes larger, and the axial thrust acting on the rotating shaft 4 (first axial thrust) is further suppressed.

[0118] Furthermore, according to the embodiment described above, the outer diameters of the first back shield 62 and the second back shield 72 are set, for example, so that the first axial thrust and the second axial thrust acting on the rotating shaft 4 are balanced when the first impeller 6 and the second impeller 7 discharge the treatment liquid. With this configuration, the axial thrust acting on the rotating shaft 4 is suppressed to a minimum.

[0119] Furthermore, according to the embodiment described above, the second back shroud 72 of the second impeller 7 includes a convex portion 72c. This convex portion 72c functions as a variable orifice, narrowing a portion of the second back side space S21 (a portion of the return flow path RL) as the rotating shaft 4 moves forward, and widening this portion as the rotating shaft 4 moves rearward. With this structure, even if axial thrust acts on the rotating shaft 4, it is suppressed to a minimal force by the first through third suppression structures, allowing the variable orifice to easily and automatically adjust this axial thrust.

[0120] Furthermore, according to the embodiment described above, the variable throttle orifice is formed by the annular protrusion 72c protruding forward from the second back shield 72. With this configuration, the variable throttle orifice can be formed with a simple structure in which a portion of the second back shield 72 protrudes forward.

[0121] Furthermore, according to the embodiment described above, the convex portion 72c is arranged radially closer to the inner side of the second back shield 72. The cross-sectional area of ​​the second back side space S21 in the cut surface along the circumferential direction decreases as the cut surface approaches the inner edge of the second back shield 72. Therefore, according to this structure, even if the amount of movement of the convex portion 72c in the axial direction decreases, the pressure "P" of the processing liquid on the upstream side of the convex portion 72c remains unchanged. r2 The amount of change in pressure will also increase. In other words, the sensitivity of the variable throttle to pressure changes will increase.

[0122] Modification

[0123] Next, a modified example of the centrifugal pump 1 will be described below, focusing on the differences from the previously described embodiment (hereinafter referred to as the "first embodiment"). In the following modified examples, for the sake of convenience, the same reference numerals as those in the first embodiment are given to the same components and components having common functions as those in the first embodiment. Figures 1 to 8 .

[0124] First Modification

[0125] Figure 9 It is a partially enlarged schematic cross-sectional view of a centrifugal pump 1A according to a first modified example.

[0126] In this figure, for the sake of convenience, only the central partition wall 21, the rotating shaft 4, the first impeller 6, and the second impeller 7 are shown in simplified form, and the projection 72c is omitted. The hollow arrows in this figure indicate backflow.

[0127] In the centrifugal pump 1A of the first modified example, the shape of the second impeller 7 is different from that of the first embodiment. Specifically, the outer diameter of the second back shield 72 is larger than the outer diameter of the first back shield 62, but the outer diameter of the second front shield 73 of the second impeller 7 is the same as the outer diameter of the first front shield 63. In this structure, only the pressure receiving area of ​​the second back shield 72 is larger than the pressure receiving area of ​​the first back shield 62. Therefore, the force "F" acting on the second impeller 7 is larger than that of the first back shield 62. r2 "The degree to which the outer diameter of the second back shield 72 is increased relative to the amount of expansion is greater than that in the first embodiment. Therefore, in this modification, even if the amount of expansion of the outer diameter of the second back shield 72 is smaller than that in the first embodiment, the same axial thrust suppression effect as in the first embodiment can be obtained. In addition, in this structure, compared with the Figure 6 In the structure shown in FIG. 1 , only the outer diameter of the second back shroud 72 is enlarged, and the second blade 71 is also enlarged in the circumferential direction. As a result, compared with Figure 6 The pressure exerted by the second impeller 7 on the treatment liquid is greater than that exerted by the second impeller 7 in the first variant. Therefore, the force (discharge pressure) of the second impeller 7 in the first variant is greater than that of the second impeller 7 in the first variant. Figure 6 The force of the second impeller 7 is shown.

[0128] Second to fourth modified examples

[0129] Figure 10 (a) is a partially enlarged schematic cross-sectional view of a centrifugal pump 1B according to a second modified example. Figure 10 (b) is a partially enlarged schematic cross-sectional view of a centrifugal pump 1C according to a third modified example. Figure 10 (c) is a partially enlarged schematic cross-sectional view of a centrifugal pump 1D according to a fourth modification.

[0130] In the centrifugal pumps 1B to 1D of the second to fourth variants, the structure of the variable throttle differs from that of the first embodiment. Specifically, in the centrifugal pump 1B of the second variant, the second back shield 72 does not have the protrusion 72c, and the central partition wall 21 has the protrusion 21e. The protrusion 21e is located near the inner edge of the rear surface 21b of the central partition wall 21 (near the central through-hole 21c). The protrusion 21e is an example of a variable throttle in the present invention. In the centrifugal pump 1C of the third variant, the central partition wall 21 has the protrusion 21e, and the second back shield 72 also has the protrusion 72c. The protrusion 21e and the protrusion 72c are located in positions opposite to each other. In the axial direction, the length of the protrusion 72c is shorter than that of the protrusion 72c in the first embodiment. The protrusions 21e and 72c are an example of a variable throttle in the present invention. In the centrifugal pump 1D of the fourth modified example, the second back shield 72 does not have the protrusion 72c, and the rear end portion of the central through hole 21c is enlarged to form the enlarged diameter portion 21f and the segment portion 21g. In addition, an annular component R is mounted on the rotating shaft 4. In the axial direction, the annular component R is arranged between the second impeller 7 and the segment portion 21g and is opposite to the segment portion 21g. The annular component R is an example of a variable throttle port in the present invention. In these structures, as in the first embodiment, the partial throttling amount of the return flow channel RL changes according to the movement of the rotating shaft 4 in the front-to-back direction. Therefore, these structures function as the same variable throttle port as the first embodiment.

[0131] Fifth Modification

[0132] Figure 11 It is a partially enlarged schematic cross-sectional view showing a centrifugal pump 1E according to a fifth modification.

[0133] The centrifugal pump 1E of the fifth modification differs from the first embodiment in the number of impellers. Specifically, the centrifugal pump 1E includes a casing 2E, a motor 3, a rotating shaft 4, bearings 51 and 52, a first impeller 6, a second impeller 7, a third impeller 8, and a fourth impeller 9. In other words, the centrifugal pump 1 is a four-stage centrifugal pump having four impellers (first impeller 6 to fourth impeller 9).

[0134] The housing 2E houses the motor 3, the rotating shaft 4, bearings 51 and 52, and the first through fourth impellers 6 through 9. The housing 2E includes a first partition wall 20, a central partition wall 21, a second partition wall 22, a first pump chamber 23, a second pump chamber 24, a connecting flow path 25, a discharge flow path 26, a suction pipe 27, a discharge pipe 28, a motor chamber 29, a front partition wall 2a, a rear partition wall 2b, a third pump chamber 2c, and a fourth pump chamber 2d. The front partition wall 2a is located in front of the first partition wall 20 and, together with the first partition wall 20, defines the third pump chamber 2c, which accommodates the third impeller 8. The rear partition wall 2b is located behind the second partition wall 22 and, together with the second partition wall 22, defines the fourth pump chamber 2d, which accommodates the fourth impeller 9. The third pump chamber 2c is arranged side by side with the first pump chamber 23 in front of the first pump chamber 23, and the fourth pump chamber 2d is arranged side by side with the second pump chamber 24 in the rear of the second pump chamber 24. The connecting flow path 25 is a flow path that guides the treatment liquid discharged by the first impeller 6 to the fourth impeller 9. The suction pipe 27 is formed in the front partition wall portion 2a instead of the first partition wall portion 20.

[0135] The structure of the third impeller 8 is the same as that of the first impeller 6. The structure of the fourth impeller 9 is the same as that of the first impeller 6 except for the direction of rotation. That is, the outer diameters of the first impeller 6, the third impeller 8, and the fourth impeller 9 are the same as each other, but smaller than the outer diameter of the second impeller 7. The third impeller 8 is mounted on the front portion 4a of the rotating shaft 4 in front of the first impeller 6. The fourth impeller 9 is mounted on the front portion 4a of the rotating shaft 4 behind the second impeller 7. As in the first embodiment, the first impeller 6 and the second impeller 7 are arranged back to back with the central partition wall 21 sandwiched between them. The third impeller 8 and the first impeller 6 constitute a front-stage group that draws in the treatment liquid from the front, and the fourth impeller 9 and the second impeller 7 constitute a rear-stage group that draws in the treatment liquid from the rear. In the centrifugal pump 1E, the treatment liquid flows in the order of the suction pipe 27, the third impeller 8, the first impeller 6, the connecting flow channel 25, the fourth impeller 9, the second impeller 7, the discharge flow channel 26, and the discharge pipe 28. In other words, the second impeller 7 sucks in and discharges the treatment liquid discharged from the first impeller 6 via the connecting flow path 25 and the fourth impeller 9 .

[0136] In this structure, the pressure difference between the pressure of the treatment liquid in the second pump chamber 24 and the pressure of the treatment liquid in the first pump chamber 23 is about twice the pressure difference in the first embodiment. Therefore, the flow rate of the treatment liquid flowing through the return channel RL increases compared to the flow rate in the first embodiment. Therefore, the axial thrust (first axial thrust) acting on the rotating shaft 4 by the treatment liquid flowing through the return channel RL is greater than the axial thrust in the first embodiment. In the above case, the first to third suppression structures and the variable throttle port in the present invention can also suppress and adjust the axial thrust.

[0137] It should be noted that, in this modified example, the structure of the fourth impeller 9 may also be the same as that of the second impeller 7 .

[0138] Other implementations

[0139] It should be noted that in the embodiment described above, the centrifugal pump 1 has, in addition to the first suppression structure, a structure for reducing the force "F" acting on the second impeller 7. r2 ” becomes larger (second suppression structure to third suppression structure). Instead of this, the centrifugal pump 1 may not have some or all of the other structures. That is, for example, the size (flow rate) of the second fixed throttle port may be the same as the size (flow rate) of the first fixed throttle port. In addition, for example, the central partition wall portion 21 may not have the recess 21d. The structure that is most helpful in suppressing the axial thrust is the first suppression structure. Therefore, as long as the centrifugal pump 1 has the first suppression structure, even if the treatment liquid in the second pump chamber 24 flows into the first pump chamber 23 through the cylindrical space S3, the axial thrust acting on the rotating shaft 4 will be suppressed. Here, the centrifugal pump 1 only has the first suppression structure to the third suppression structure. In the first suppression configuration, the outer diameters of the first and second back shields 62, 72 are set, for example, so that the first and second axial thrusts are balanced when the first and second impellers 6, 7 (i.e., centrifugal pump 1) discharge the process fluid (at its peak efficiency point). For example, when a two-stage centrifugal pump is operating at a discharge rate of 30 m³ / h, a total head of 65 m, water (specific gravity: 1, viscosity: 1 cP) as the process fluid, and a rotational speed of 3,000 rpm, with the outer diameters of the first impeller 6 being 150 mm and the second impeller 7 being 158 mm, the first and second axial thrusts are both 2,100 N. The return flow rate is set at 10% (3 m³ / h).

[0140] In the present invention, the second impeller 7 may not include the convex portion 72c (variable throttle). In this configuration, the axial thrust acting on the rotating shaft 4 can be suppressed to a minimum by the first to third suppression structures.

[0141] Furthermore, in the present invention, the central partition wall portion 21 may include a convex portion instead of the concave portion 21d. In this case, the convex portion has, for example, the same size (volume) as the concave portion 21d.

[0142] In the present invention, the number of recesses 21d is not limited to that of the present embodiment. For example, the number of recesses 21d may be 1, an odd number greater than 3, or an even number other than 8.

[0143] In the present invention, the central partition wall 21 may include convex portions instead of some of the concave portions 21d. That is, for example, the central partition wall 21 may include four concave portions 21d and four convex portions disposed between the concave portions 21d.

[0144] In the present invention, the position of the recess 21d is not limited to that of the present embodiment. That is, for example, the inner edge of the recess 21d may be located radially outside the projection 72c.

[0145] In the present invention, the position of the convex portion 72c is not limited to that of the present embodiment. That is, for example, the convex portion 72c may be arranged at the center or outer edge of the front surface 72b in the radial direction.

[0146] In the present invention, the specific speed set for the first pump unit P1 may be the same as the specific speed set for the second pump unit P2 except for the difference caused by the difference in outer diameter between the first back shield 62 and the second back shield 72 .

[0147] Furthermore, in the present invention, the number of impellers provided in the centrifugal pump 1 can be an even number and is not limited to two. That is, for example, as shown in the fifth modification, the number of impellers may be four, or six or more.

[0148] Furthermore, in the present invention, the processing liquid is not limited to liquefied gas, and may be water, for example.

[0149] Modes for Carrying Out the Invention

[0150] Next, the embodiments of the present invention understood from the above-described embodiments will be described below, citing the terms and reference numerals described in the embodiments.

[0151] A first embodiment of the present invention is a centrifugal pump (e.g., centrifugal pumps 1, 1A to 1E), wherein the centrifugal pump includes: a motor (e.g., motor 3); a rotating shaft (e.g., rotating shaft 4) that rotates based on the drive of the motor; a first impeller (e.g., first impeller 6) that is mounted on the rotating shaft and sucks in and discharges the treatment liquid; a second impeller (e.g., second impeller 7) that is mounted on the rotating shaft and sucks in and discharges the treatment liquid discharged from the first impeller; a first pump chamber (e.g., first pump chamber 23) that accommodates the first impeller; a second pump chamber (e.g., second pump chamber 24) that is arranged side by side with the first pump chamber in the axial direction of the rotating shaft and accommodates the second impeller; and a central partition wall portion (e.g., central partition wall portion 21) that has an insertion hole (e.g., central through hole 21c) for inserting the rotating shaft and divides the first pump chamber and the second pump chamber, wherein the direction in the axial direction in which the first impeller is arranged relative to the second impeller is a first direction (e.g., forward direction), and the second impeller is arranged in a direction opposite to the first impeller. The direction opposite to one direction is a second direction (for example, a rear direction), and the first impeller has: a first suction port (for example, a first suction port 65), which faces the first direction and sucks the treatment liquid from the first direction side; and a first shield (for example, a first back shield 62), which is opposite to the central partition wall portion, and the second impeller has: a second suction port (for example, a second suction port 75), which faces the second direction and sucks the treatment liquid discharged from the first impeller from the second direction side; and a second shield (for example, a second back shield 72), which is opposite to the central partition wall portion, a first space (for example, a first back side space S11) connected to the insertion hole is formed between the first impeller and the central partition wall portion, and a second space (for example, a second back side space S21) connected to the insertion hole is formed between the second impeller and the central partition wall portion, the second space and the first space are connected to each other via the insertion hole, and the outer diameter of the second shield is larger than the outer diameter of the first shield.

[0152] According to this structure, even if the processing liquid in the second pump chamber 24 flows into the first pump chamber 23 via the cylindrical space S3 , the axial thrust acting on the rotary shaft 4 is suppressed.

[0153] A second embodiment of the present invention is a centrifugal pump according to the first embodiment, wherein a specific speed set by a second pump section (e.g., second pump section P2) consisting of the second impeller and the second pump chamber is smaller than a specific speed set by a first pump section (e.g., first pump section P1) consisting of the first impeller and the first pump chamber.

[0154] According to this structure, the performance of the centrifugal pump 1 is improved, and the axial thrust acting on the rotating shaft 4 is suppressed.

[0155] A third embodiment of the present invention is a centrifugal pump according to the first embodiment or the second embodiment, wherein the centrifugal pump comprises: a first partition wall portion (for example, the first partition wall portion 20), which is arranged on the first direction side relative to the first impeller and divides the first pump chamber together with the central partition wall portion; and a second partition wall portion (for example, the second partition wall portion 22), which is arranged on the second direction side relative to the second impeller and divides the second pump chamber together with the central partition wall portion, the first impeller includes a third shroud (for example, the first front shroud 63) arranged on the first direction side relative to the first shroud, and the second impeller includes a third shroud (for example, the first front shroud 63) arranged on the second direction side relative to the second shroud. Four guards (for example, the second front guard 73), the third guard having a first cylindrical portion (for example, the cylindrical portion 63b) constituting the first suction port, the fourth guard having a second cylindrical portion (for example, the cylindrical portion 73b) constituting the second suction port, the second gap (for example, the second cylindrical gap S23 and the second annular gap S24) between the portion of the second partition wall portion opposite to the second cylindrical portion (for example, the large diameter portion 22d and the first section portion 22e) and the second cylindrical portion is larger than the first gap (for example, the first cylindrical gap S13 and the first annular gap S14) between the portion of the first partition wall portion opposite to the first cylindrical portion (for example, the large diameter portion 20d and the section portion 20e) and the first cylindrical portion.

[0156] According to this structure, the axial thrust acting on the rotary shaft 4 is further suppressed.

[0157] The fourth embodiment of the present invention is a centrifugal pump according to any one of the first to third embodiments, wherein the central partition wall portion has at least one convex portion or concave portion (for example, concave portion 21d), which faces the second space and is configured to suppress the vortex component of the treatment liquid flowing through the second space.

[0158] According to this structure, the axial thrust acting on the rotary shaft 4 is further suppressed.

[0159] A fifth embodiment of the present invention is a centrifugal pump according to any one of the first to fourth embodiments, wherein the outer diameter of the first shroud and the outer diameter of the second shroud are set so that a first axial thrust acting in a manner to move the rotating shaft toward the first direction and a second axial thrust acting in a manner to move the rotating shaft toward the second direction are balanced when the first impeller and the second impeller discharge the treatment liquid.

[0160] According to this structure, the axial thrust acting on the rotating shaft 4 is suppressed to the minimum.

[0161] A sixth embodiment of the present invention is a centrifugal pump according to any one of the first to fifth embodiments, wherein the second space and the insertion hole constitute a return flow channel (for example, a return flow channel RL) for a portion of the treatment liquid discharged through the second impeller to flow to the first space, and the centrifugal pump has a variable throttle port (for example, a protrusion 72c), which is configured to narrow a portion of the return flow channel as the rotating shaft moves toward the first direction, and widen the portion as the rotating shaft moves toward the second direction.

[0162] According to this structure, the axial thrust is easily and automatically adjusted by the variable throttle.

[0163] The seventh embodiment of the present invention is a centrifugal pump according to the sixth embodiment (for example, centrifugal pumps 1, 1B to 1D), wherein the variable throttle port is composed of a protrusion protruding from the second guard toward the first direction (for example, the protrusion 72c) and / or a protrusion protruding from the central partition wall toward the second direction (for example, the protrusion 21e).

[0164] According to this structure, the variable throttle port can be formed with a simple structure.

[0165] The eighth embodiment of the present invention is a centrifugal pump according to the seventh embodiment, wherein the protrusion is annular along the circumference of the rotating shaft, and is arranged at a position close to the inner edge of the second shroud in the radial direction of the rotating shaft, and / or is arranged at a position close to the inner edge of the central partition wall in the radial direction.

[0166] According to this structure, the sensitivity of the variable throttle to pressure fluctuations is improved.

[0167] Description of Reference Numerals

[0168] 1: Centrifugal pump

[0169] 20: First partition wall

[0170] 20d: Large diameter portion (the portion facing the first cylindrical portion)

[0171] 20e: Segment (the portion facing the first cylindrical portion)

[0172] 21: Central partition wall

[0173] 21c: Central through hole (insertion hole)

[0174] 21d: concave part

[0175] 22: Second partition wall

[0176] 22d: Large diameter portion (portion facing the second cylindrical portion)

[0177] 22e: First section (the portion opposite to the second cylindrical portion)

[0178] 3: Motor

[0179] 4: Rotation axis

[0180] 6: First impeller

[0181] 62: First back shield (first shield)

[0182] 63: First front shield (third shield)

[0183] 63b: cylindrical portion (first cylindrical portion)

[0184] 65: First suction port

[0185] 7: Second impeller

[0186] 72: Second back shield (second shield)

[0187] 72e: convex part (variable throttle)

[0188] 73: Second front shield (fourth shield)

[0189] 73b: cylindrical portion (second cylindrical portion)

[0190] 75: Second suction port

[0191] S11: First back side space (first space)

[0192] S13: First cylinder gap (first gap)

[0193] S14: First annular gap (first gap)

[0194] S21: Second back side space (second space)

[0195] S23: Second cylindrical gap (second gap)

[0196] S24: Second annular gap (second gap)

[0197] S3: Cylindrical space (through hole)

[0198] RL: Return runner.

Claims

1. A centrifugal pump, wherein: The centrifugal pump has: Motor; a rotating shaft that rotates based on the driving of the motor; a first impeller mounted on the rotating shaft to suck in and discharge the treatment liquid; a second impeller mounted on the rotating shaft to suck in and discharge the treatment liquid discharged from the first impeller; a first pump chamber accommodating the first impeller; a second pump chamber, arranged side by side with the first pump chamber in the axial direction of the rotating shaft, and accommodating the second impeller; as well as a central partition wall portion having an insertion hole for inserting the rotating shaft and dividing the first pump chamber from the second pump chamber; In the axial direction, the direction in which the first impeller is arranged relative to the second impeller is a first direction, and the direction opposite to the first direction is a second direction. The first impeller comprises: a first suction port, which faces the first direction and sucks the treatment liquid from the first direction side; and a first shield, which is opposed to the central partition wall portion; The second impeller comprises: a second suction port, which faces the second direction and sucks the treatment liquid discharged from the first impeller from the second direction side; as well as a second shield, which is opposed to the central partition wall portion; A first space communicating with the insertion hole is formed between the first impeller and the central partition wall. A second space communicating with the insertion hole is formed between the second impeller and the central partition wall. The second space and the first space are connected to each other via the insertion hole. The outer diameter of the second shield is greater than the outer diameter of the first shield.

2. The centrifugal pump according to claim 1, wherein The specific speed set for the second pump portion formed by the second impeller and the second pump chamber is lower than the specific speed set for the first pump portion formed by the first impeller and the first pump chamber.

3. The centrifugal pump according to claim 1, wherein The centrifugal pump has: a first partition wall portion disposed on the first direction side relative to the first impeller and partitioning the first pump chamber together with the central partition wall portion; as well as a second partition wall portion, which is arranged on the second direction side relative to the second impeller and defines the second pump chamber together with the central partition wall portion; The first impeller includes a third shroud disposed on the first direction side relative to the first shroud. The second impeller includes a fourth shroud disposed on the second direction side relative to the second shroud. The third hood includes a first cylindrical portion constituting the first suction port. The fourth hood includes a second cylindrical portion constituting the second suction port. A second gap between a portion of the second partition wall portion facing the second cylindrical portion and the second cylindrical portion is larger than a first gap between a portion of the first partition wall portion facing the first cylindrical portion and the first cylindrical portion.

4. The centrifugal pump according to claim 1, wherein The central partition wall portion includes at least one convex portion or concave portion, and the convex portion or concave portion faces the second space and is configured to suppress a swirl component of the treatment liquid flowing through the second space.

5. The centrifugal pump according to claim 1, wherein The outer diameter of the first shroud and the outer diameter of the second shroud are set to balance a first axial thrust acting to move the rotating shaft toward the first direction and a second axial thrust acting to move the rotating shaft toward the second direction when the first impeller and the second impeller discharge the processing liquid.

6. The centrifugal pump according to any one of claims 1 to 5, wherein The second space and the insertion hole constitute a return flow path for a portion of the treatment liquid discharged by the second impeller to flow to the first space. The centrifugal pump includes a variable throttle configured to narrow a portion of the return flow path as the rotating shaft moves toward the first direction, and to widen the portion as the rotating shaft moves toward the second direction.

7. The centrifugal pump according to claim 6, wherein: The variable throttle port is formed of a protrusion protruding from the second shroud toward the first direction and / or a protrusion protruding from the central partition wall toward the second direction.

8. The centrifugal pump according to claim 7, wherein The protrusion is annular along the circumference of the rotating shaft and is arranged near the inner edge of the second shroud in the radial direction of the rotating shaft and / or near the inner edge of the central partition wall in the radial direction.

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