Centrifugal pump

Abstract

Provided is a centrifugal pump that suppresses generation of axial thrust. A centrifugal pump (1) of the present invention has a motor (3), a rotating shaft (4), a first impeller (6), a second impeller (7), a first pump chamber (23) that houses the first impeller, a second pump chamber (24) that houses the second impeller, and a central partition wall portion (21) that has a through-hole (21c) through which the rotating shaft is inserted and that divides the first pump chamber and the second pump chamber. The first impeller has a first suction port (65) that sucks a treatment liquid from a first direction side and a first shroud (62) that opposes the central partition wall portion. The second impeller has a second suction port (75) that sucks a treatment liquid from a second direction side and a second shroud (72) that opposes the central partition wall portion. A first space (S11) that communicates with the through-hole is formed between the first impeller and the central partition wall portion. A second space (S21) that communicates with the through-hole is formed between the second impeller and the central partition wall portion. The outer diameter of the second shroud is larger than the outer diameter of the first shroud.

Description

Technical Field

[0001] This invention relates to a centrifugal pump. Background Technology

[0002] A centrifugal pump comprises a motor, a rotating shaft, an impeller, and a casing. The impeller is mounted on the rotating shaft, which rotates based on the motor's operation, and rotates along with the shaft, thereby drawing in process fluid from one axial direction of the rotating shaft and discharging it radially outward from the impeller. The impeller has multiple blades, a front shroud (side plate), and a back shroud (main plate). Axially, the front shroud covers one side of the blades, and the back shroud covers the other side. A portion of the high-pressure process fluid 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 towards the back shroud and vice versa. Typically, the pressure-bearing area of ​​the back shroud is larger than that of the front shroud. Therefore, an axial force (axial thrust) acts on the impeller.

[0003] In centrifugal pumps, a multistage centrifugal pump is known that, in order to improve suction performance and achieve high head, sequentially discharges the treated liquid using multiple impellers mounted on a single rotating shaft (see, for example, Patent Document 1). The axial thrust increases with the number of impellers (stages). Therefore, in a multistage centrifugal pump, the multiple impellers are divided into a pre-stage group and a post-stage group, with the pre-stage group mounted on the rotating shaft back-to-back with the post-stage group. Except for the direction of rotation, the impellers in the pre-stage group and the post-stage group have the same design, thus balancing the axial thrust of the pre-stage group and the post-stage group, and eliminating their axial thrust.

[0004] Existing technical documents

[0005] Patent documents:

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

[0007] Typically, a mechanical seal is installed between the partition wall and the rotating shaft between the pre-stage and post-stage units. Therefore, the processing fluid from the post-stage unit does not flow into the pre-stage unit. However, when the viscosity of the processing fluid is low, the lubricating performance of the mechanical seal decreases due to the fluid. Therefore, a structure without a mechanical seal between the partition wall and the rotating shaft can also be used. The pressure of the processing fluid flowing through the post-stage unit is higher than that flowing through the pre-stage unit. Therefore, in this structure, the processing fluid from the post-stage unit flows into the pre-stage unit through the gap between the partition wall and the rotating shaft. This fluid flow increases the axial thrust of the pre-stage unit and decreases the axial thrust of the post-stage unit. As a result, an axial thrust is generated towards the intake side of the pre-stage unit.

[0008] The purpose of this invention is to suppress the generation of axial thrust in multi-stage centrifugal pumps.

[0009] One aspect of the present invention is a centrifugal pump, comprising: a motor; a rotating shaft that rotates based on the drive of the motor; a first impeller mounted on the rotating shaft for drawing in and discharging a treatment liquid; a second impeller mounted on the rotating shaft for drawing in and discharging the treatment liquid discharged from the first impeller; a first pump chamber housing the first impeller; a second pump chamber arranged axially alongside the first pump chamber on the rotating shaft for housing the second impeller; a central partition wall having a through hole for insertion of the rotating shaft and separating the first pump chamber from the second pump chamber; a first partition wall disposed relative to the first impeller on a first direction side, dividing the first pump chamber together with the central partition wall; and a second partition wall disposed relative to the second impeller on a second direction side, dividing the second pump chamber together with the central partition wall. Axially, the direction in which the first impeller is disposed relative to the second impeller is the first direction, and the direction opposite to the first direction is the second direction. The first impeller includes: a first suction port facing the first direction for drawing in the treatment liquid from the first impeller. The second impeller includes: a first suction port facing the second direction, through which the treatment liquid discharged from the first impeller is drawn in from the second direction; a second shield opposing the central partition wall; and a fourth shield disposed relative to the second shield on the second direction side. The third shield includes a first cylindrical portion constituting the first suction port, and the fourth shield includes a second cylindrical portion constituting the second suction port. A first space communicating with the insertion hole is formed between the first impeller and the central partition wall, and 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 communicate with each other via the insertion hole. The outer diameter of the second shield is larger than the outer diameter of the first shield. A second gap between the portion of the second partition wall opposing the second cylindrical portion and the second cylindrical portion is larger than the first gap between the portion of the first partition wall opposing the first cylindrical portion and the first cylindrical portion.

[0010] Invention Effects

[0011] According to the present invention, the generation of axial thrust in a multi-stage centrifugal pump can be suppressed. Attached Figure Description

[0012] Figure 1This is a schematic cross-sectional view illustrating an embodiment of the centrifugal pump of the present invention.

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

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

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

[0016] Figure 5 (a) is a partially enlarged schematic cross-sectional view illustrating the axial thrust in an existing pump. Figure 5 (b) is a partially enlarged schematic cross-sectional view illustrating the axial thrust in an existing pump without a mechanical seal.

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

[0018] Figure 7 This is an explanation Figure 1 The centrifugal pump has a second fixed throttling port for Figure 1 A partially enlarged schematic cross-sectional view showing the effect of axial thrust in a centrifugal pump.

[0019] Figure 8 This is an explanation Figure 4 The second impeller has a convex part Figure 1 A partially enlarged schematic cross-sectional view illustrating the effect of axial thrust in a centrifugal pump. Figure 8 (a) shows the state in which the first axial thrust and the second axial thrust are in balance. Figure 8 (b) shows the state where the first axial thrust is greater than the second axial thrust. Figure 8 (c) shows the state where the first axial thrust is less than the second axial thrust.

[0020] Figure 9 This is a partially enlarged schematic cross-sectional view of the centrifugal pump of the first variant.

[0021] Figure 10 (a) is a partially enlarged schematic cross-sectional view of the centrifugal pump of the second variation. Figure 10 (b) is a partially enlarged schematic cross-sectional view of the centrifugal pump of the third variation. Figure 10 (c) is a partially enlarged schematic cross-sectional view of the centrifugal pump of the fourth variation.

[0022] Figure 11 This is a partially enlarged schematic cross-sectional view showing the centrifugal pump of the fifth modified example.

[0023] Explanation of reference numerals in the attached figures

[0024] 1: Centrifugal pump

[0025] 20: First partition wall section

[0026] 20d: Large diameter section (the part opposite to the first cylindrical section)

[0027] 20e: Section (the part opposite to the first cylindrical section)

[0028] 21: Central partition wall section

[0029] 21c: Central through hole (insertion hole)

[0030] 21d: concave part

[0031] 22: Second partition wall section

[0032] 22d: Large diameter section (the part opposite to the second cylindrical section)

[0033] 22e: First section (the part opposite to the second cylindrical section)

[0034] 3: Motor

[0035] 4: Rotation axis

[0036] 6: First impeller

[0037] 62: First rear shield (first shield)

[0038] 63: First frontal shield (third shield)

[0039] 63b: Cylindrical section (first cylindrical section)

[0040] 65: First Inlet

[0041] 7: Second impeller

[0042] 72: Second rear shield (second shield)

[0043] 72e: Convex part (variable throttling orifice)

[0044] 73: Second Frontal Shield (Fourth Shield)

[0045] 73b: Cylindrical section (second cylindrical section)

[0046] 75: Second Inlet

[0047] S11: First rear side space (first space)

[0048] S13: First cylinder gap (first clearance)

[0049] S14: First annular gap (first gap)

[0050] S21: Second rear side space (second space)

[0051] S23: Second cylinder gap (second clearance)

[0052] S24: Second annular gap (second gap)

[0053] S3: Cylindrical space (insertion hole)

[0054] RL: Return to the flow path. Detailed Implementation

[0055] The following describes an embodiment of the centrifugal pump of the present invention. In the following description, appropriate reference is made to the accompanying drawings. In the drawings, the same reference numerals are used to denote the same parts and elements, and repeated descriptions are omitted. Furthermore, for ease of explanation, the dimensions of the elements may sometimes be exaggerated, and the scale shown in the drawings is not limited to those shown in the drawings.

[0056] centrifugal pump

[0057] Centrifugal pump structure

[0058] Figure 1 This is a schematic cross-sectional view illustrating an embodiment of the centrifugal pump of the present invention.

[0059] In this figure, a portion of the housing 2, described later, is shown in schematic cross-section, while other parts are shown simplified. The figure schematically shows a cross-section of the centrifugal pump 1 cut vertically along the axial direction of the rotating shaft 4, described later, passing through the center of the rotating shaft 4. Figure 2 as well as Figures 5 to 11 (Same as above).

[0060] Centrifugal pump 1 draws in and discharges the treatment liquid (liquid transport). Centrifugal pump 1 has a housing 2, a motor 3, a rotating shaft 4, bearings 51 and 52, a first impeller 6, and a second impeller 7. That is, centrifugal pump 1 is a two-stage centrifugal pump with two impellers (first impeller 6 and second impeller 7), and is an example of the centrifugal pump in this invention.

[0061] The "processing fluid" is the liquid that is processed (liquid transported) by the centrifugal pump 1. In this embodiment, the processing fluid is a low-viscosity liquid, such as a cryogenic liquefied gas (e.g., liquefied natural gas, liquid hydrogen, etc.).

[0062] In the following description, "forward direction" refers to the direction of the first impeller 6 and the second impeller 7 relative to the motor 3, and "rearward direction" refers to the direction of the motor 3 relative to the first impeller 6 and the second impeller 7. "Axial direction" is the direction along the center line of the rotating shaft 4 (forward and backward direction), "radial direction" is the radial direction of the rotating shaft 4, and "circumferential direction" is the circumferential direction of the rotating shaft 4. "Upstream side" is the upstream side of the liquid flow of the treatment fluid within the housing 2, and "downstream side" is the downstream side of the liquid flow of the treatment fluid within the housing 2. The forward direction is an example of a first direction in this invention, and the rearward direction is an example of a second direction in this invention.

[0063] The housing 2 houses the motor 3, the rotating shaft 4, the 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 channel 25, a discharge flow channel 26, a suction pipe 27, a discharge pipe 28, and a motor chamber 29.

[0064] Figure 2 This is a partially enlarged sectional view of centrifugal pump 1.

[0065] This figure shows a cross-section of the upper half of a centrifugal pump 1 centered on the first impeller 6 and the second impeller 7. Reference is also made appropriately in the following description. Figure 1 .

[0066] The first partition wall 20, together with the central partition wall 21, divides the first pump chamber 23. The first partition wall 20 is located in front of the first impeller 6 and is disposed at the front end of the housing 2. The first partition wall 20 has an inner surface 20a and a first through hole 20b.

[0067] The inner surface 20a is a curved surface that is recessed forward in a generally frustum-shaped manner along the shape of the first front shroud 63 of the first impeller 6, which will be described later.

[0068] Viewed axially, the first through-hole 20b is a cylindrical through-hole that extends axially through the central portion of the first partition wall 20, forming two cylindrical sections. The first through-hole 20b communicates with the first pump chamber 23 and the suction pipe 27. The first through-hole 20b includes a small-diameter portion 20c, a large-diameter portion 20d, and a segment 20e. The inner diameter of the small-diameter portion 20c is smaller than the inner diameter of the large-diameter portion 20d. Axially, the small-diameter portion 20c is positioned adjacent to the large-diameter portion 20d in front of it. The segment 20e is a surface positioned between the small-diameter portion 20c and the large-diameter portion 20d, and is continuous with both the small-diameter portion 20c and the large-diameter portion 20d. Viewed axially, the segment 20e has an annular shape. The small-diameter portion 20c functions as a flow channel for introducing the treatment fluid into the first impeller 6.

[0069] The central partition wall 21, together with the first partition wall 20, divides the first pump chamber 23 and together with the second partition wall 22, divides the second pump chamber 24. The central partition wall 21 is located behind the first partition wall 20. The central partition wall 21 has a front surface 21a, a rear surface 21b, a central through hole 21c, and eight recesses 21d. The front surface 21a is the surface facing forward, and the rear surface 21b is the surface facing backward.

[0070] Viewed axially, the central through-hole 21c is a cylindrical through-hole through which the central portion of the central partition wall 21 is axially extended. The rotating shaft 4 is inserted into the central through-hole 21c. The central through-hole 21c is an example of an insertion through-hole in this invention.

[0071] Figure 3 This is a schematic rear view of the central partition wall 21.

[0072] This figure schematically shows the state of the central partition wall 21 as viewed from the rear. The figure also shows the rotating shaft 4 and the first hub 64, which will be described later. Additionally, for ease of explanation, the second impeller 7 and the protrusion 72c are also virtually shown with double-dotted lines. References will be made as appropriate in the following description. Figure 2 .

[0073] The recess 21d suppresses the swirling components of the processing liquid flowing through the second back side space S21, which will be described later. A portion of the rear surface 21b of the central partition wall 21 is recessed forward into a rectangle to form the recess 21d. In the circumferential direction, eight recesses 21d are arranged at equal angles (45 degrees in this embodiment) on the rear surface 21b. Viewed axially, the shape of the recess 21d is a rectangle with its long side extending radially. Viewed axially, the inner edge (radially inner edge) of the recess 21d is positioned at the same location as the outer edge of the protrusion 72c of the second impeller 7, which will be described later. Viewed axially, the outer edge (radially outer edge) of the recess 21d is positioned approximately at the same location as the middle portion of the inner and outer edges of the second impeller 7.

[0074] The accompanying drawings, which are the main references in this description, are referenced here. Figure 1 and Figure 2 .

[0075] The second partition wall 22, together with the central partition wall 21, divides the second pump chamber 24. The second partition wall 22 is located rearward relative to the second impeller 7 and is disposed behind the central partition wall 21. The second partition wall 22 has an inner surface 22a and a second through hole 22b.

[0076] The inner surface 22a is a curved surface that is recessed rearward in a generally frustum-shaped manner along the shape of the second front cover 73 of the second impeller 7, which will be described later.

[0077] Viewed axially, the second through hole 22b is a three-section cylindrical through hole that penetrates the central portion of the second partition wall 22 along the axial direction. The second through hole 22b communicates with the second pump chamber 24 and the connecting flow channel 25. The second through hole 22b has a small diameter portion 22c, a large diameter portion 22d, a first section portion 22e, a through portion 22f, and a second section portion 22g. The inner diameter of the small diameter portion 22c is larger than the inner diameter of the through portion 22f and smaller than the inner diameter of the large diameter portion 22d. Axially, the through portion 22f is disposed adjacent to the small diameter portion 22c behind it, and the large diameter portion 22d is disposed adjacent to the small diameter portion 22c in front of it. The first section portion 22e is a surface disposed between the small diameter portion 22c and the large diameter portion 22d and is continuous with both the small diameter portion 22c and the large diameter portion 22d. The second segment 22g is a surface disposed between the through portion 22f and the small-diameter portion 22c, and is continuous with both the through portion 22f and the small-diameter portion 22c. 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, and a cylindrical space is formed between the small-diameter portion 22c and the rotating shaft 4. This cylindrical space functions as a flow channel to guide the treatment fluid into the second impeller 7.

[0078] 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 and the second pump chamber 24 are arranged side by side in front of the second pump chamber 24, sandwiching the central partition wall 21. That is, axially, the first impeller 6 is arranged in front of the second impeller 7.

[0079] The connecting channel 25 is a channel that guides the treatment fluid discharged from the first impeller 6 into the space within the small-diameter section 22c. The connecting channel 25 is, for example, formed by a portion of the housing 2 and communicates with both the first pump chamber 23 and the space within the small-diameter section 22c. Figure 1 and Figure 2 In the middle, the connecting flow channel 25 is simply shown with a bold solid line arrow.

[0080] The discharge channel 26 is a channel that guides the treatment fluid discharged by the second impeller 7 to the discharge pipe 28. The discharge channel 26 is, for example, formed by a portion of the housing 2 and communicates with the second pump chamber 24 and the discharge pipe 28. Figure 1 and Figure 2 In the middle, the discharge channel 26 is simply shown with a dashed arrow.

[0081] The front end of the housing 2 (first partition wall 20) extends forward in a cylindrical shape, coaxial with the rotation axis 4, forming a suction pipe 27 for drawing (introducing) the treatment liquid into the first pump chamber 23. Additionally, a portion of the housing 2 located radially outward from the second impeller 7 extends tangentially (above) to the second impeller 7, forming a discharge pipe 28 for discharging the treatment liquid from the second pump chamber 24 (discharge channel 26).

[0082] The rear half of the housing 2 is divided into a motor chamber 29 to accommodate the motor 3 and bearings 51 and 52.

[0083] The motor 3 is a known motor comprising a rotor (not shown) mounted on a rotating shaft 4 and a stator (not shown) for rotating the rotor (not shown). The rotating shaft 4 rotates based on the drive (rotation) of the motor 3 and transmits 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 part 4a of the rotating shaft 4 protrudes into the first pump chamber 23 and the second pump chamber 24.

[0084] Bearing 51 is positioned in front of motor 3 and rotatably supports rotating shaft 4. Bearing 52 is positioned behind motor 3 and rotatably supports rotating shaft 4. Bearings 51 and 52 are, for example, rolling bearings.

[0085] The first impeller 6 draws in and discharges the treatment fluid. The first impeller 6 is mounted on the front part 4a of the rotating shaft 4 and housed within the first pump chamber 23. That is, 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. The first impeller 6 includes multiple first blades 61, a first back cover 62, a first front cover 63, a first hub 64, a first suction port 65, and a first discharge port 66.

[0086] The first blade 61 rotates circumferentially around the rotation axis 4, guiding the treatment liquid drawn in from the first suction port 65 to the first discharge port 66. Viewed axially, multiple first blades 61 extend radially from the center side of the first impeller 6 towards the outer edge, and are curved into a vortex shape. The first blades 61 are positioned between the first back cover 62 and the first front cover 63.

[0087] The first back cover 62 is a plate (so-called main plate) covering the rear of the first blade 61. The first back cover 62 is ring-shaped. Viewed axially, the central portion of the first back cover 62 protrudes forward in a generally frustoconical shape. The first back cover 62 is opposite to the central partition wall portion 21. The first back cover 62 has a mounting hole 62a and a rear surface 62b. The first back cover 62 is an example of the first cover in this invention.

[0088] Mounting hole 62a is a through hole through which the front part 4a of rotating shaft 4 is inserted. Viewed axially, mounting hole 62a is located at the center of the first back cover 62, through which the central part is formed into a cylindrical shape along the axial direction.

[0089] The rear surface 62b is a rearward-facing surface and is opposite to the front surface 21a of the central partition wall 21. An annular 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 this invention.

[0090] The first front shield 63 is a plate (so-called side plate) covering the front of the first blade 61. The first front shield 63 is shaped like a generally annular plate, with its inner edge protruding further forward than its 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 disposed 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 this invention.

[0091] The front surface 63a faces forward and is opposite to the inner surface 20a of the first partition wall portion 20. A generally annular space (hereinafter referred to as "first frontal side space S12") is formed between the front surface 63a and the inner surface 20a.

[0092] The inner edge of the first front cover 63 extends forward in a cylindrical shape, coaxial with the rotation axis 4, forming a cylindrical portion 63b that functions as a first suction port 65. In other words, the first front cover 63 includes a cylindrical portion 63b that functions as a first suction port 65. In the first impeller 6, the cylindrical portion 63b faces forward and is disposed within the large-diameter portion 20d of the first partition wall portion 20. The cylindrical portion 63b is an example of the first cylindrical portion in this invention. In the radial direction, the large-diameter portion 20d is opposite to the cylindrical portion 63b. A cylindrical gap (hereinafter referred to as "first cylindrical gap S13") is formed between the large-diameter portion 20d and the cylindrical portion 63b. In the radial direction, the length of the first cylindrical gap S13 (the interval between the large-diameter portion 20d and the cylindrical portion 63b) is such that the cylindrical portion 63b does not abut against the large-diameter portion 20d during normal operation of the centrifugal pump 1, and is set to be the same as the length set for the impeller of a general centrifugal pump. In the axial direction, the segment 20e is opposite to the cylindrical portion 63b. An annular gap (hereinafter referred to as "first annular gap S14") is formed between the segment 20e and the cylindrical portion 63b. In the axial direction, the length of the first annular gap S14 (the interval between the segment 20e and the cylindrical portion 63b) is such that the cylindrical portion 63b does not abut against 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 throttling orifice, described later. The large-diameter portion 20d and the segment 20e are examples of the portions opposite to the first cylindrical portion in this invention.

[0093] The first frontal 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 within the small diameter portion 20c.

[0094] The inner edge of the first rear cover 62 extends rearward in a cylindrical shape, coaxial with the rotating shaft 4, forming a first hub portion 64. The front portion 4a of the rotating shaft 4 is inserted into the first hub portion 64, and the first impeller 6 is mounted on the front portion 4a by fixing the first hub portion 64 to the front portion 4a of the rotating shaft 4. At this time, the first suction port 65 faces forward. The first hub portion 64 covers a portion of the front portion 4a of the rotating shaft 4 and is disposed within the central through hole 21c.

[0095] The outer edge of the first blade 61, the outer edge of the first back cover 62, and the outer edge of the first front cover 63 form a first outlet 66 for discharging the processing liquid that flows through the flow channel inside the first impeller 6.

[0096] The second impeller 7 draws in and discharges the treatment liquid discharged from the first impeller 6. The second impeller 7 is mounted on the front part 4a of the rotating shaft 4 and housed in the second pump chamber 24. That is, 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. The second impeller 7 includes multiple second blades 71, a second back cover 72, a second front cover 73, a second hub 74, a second suction port 75, and a second discharge port 76.

[0097] The specific speed set for the second pump section P2, which is composed of the second impeller 7 and the second pump chamber 24, is lower than the specific speed set for the first pump section P1, which is composed of the first impeller 6 and the first pump chamber 23. With this structure, the centrifugal pump 1 achieves high suction performance (discharge flow rate) through the first pump section P1 and high head through the second pump section P2. Furthermore, generally speaking, the outer diameter of the impeller decreases as the specific speed increases. Therefore, the outer diameter of the second impeller 7 is larger than the outer diameter of the first impeller 6. These specific speed values ​​are appropriately set, for example, according to the design of the centrifugal pump 1 (e.g., discharge flow rate, head, etc.).

[0098] The second blade 71 rotates circumferentially around the rotation axis 4, guiding the treatment liquid drawn in from the second suction port 75 to the second discharge port 76. Viewed axially, multiple second blades 71 extend radially from the center side of the second impeller 7 towards the outer edge, and are curved into a vortex shape. The second blades 71 are positioned between the second back cover 72 and the second front cover 73.

[0099] The second back cover 72 is a plate (so-called main plate) covering the front of the second blade 71 (in the direction of the back side of the second impeller 7). The second back cover 72 is annular in shape. Viewed axially, the central portion of the second back cover 72 protrudes rearward in a frustoconical shape. The second back cover 72 is opposite to the central partition wall portion 21. The second back cover 72 has a mounting hole 72a, a front surface 72b, and a protrusion 72c. The second back cover 72 is an example of the second cover in this invention.

[0100] The outer diameter of the second back cover 72 is larger than the outer diameter of the first back cover 62. The outer diameters of the first back cover 62 and the second back cover 72 are set, for example, such that when the first impeller 6 and the second impeller 7 (i.e., the centrifugal pump 1) discharge the treatment liquid (at the point of highest efficiency), the first axial thrust and the second axial thrust, as described later, are approximately balanced.

[0101] Mounting hole 72a is a through hole through which the front part 4a of rotating shaft 4 is inserted. Viewed axially, mounting hole 72a is located in the center of the second back cover 72, through which the central part is formed into a cylindrical shape along the axial direction.

[0102] The front surface 72b is the face facing forward and is opposite to the rear surface 21b of the central partition wall 21. An annular space (hereinafter referred to as "second rear side space S21") is formed between the front surface 72b and the rear surface 21b. The second rear side space S21 is an example of the second space in the present invention.

[0103] Figure 4 This is a schematic front view of the second impeller 7.

[0104] This diagram schematically shows the state of the second impeller 7 as viewed from the front. References should also be made appropriately in the following description. Figure 2 .

[0105] The protrusion 72c functions as a variable throttling orifice, as described later. A portion of the front surface 72b of the second back cover 72 protrudes forward in an annular shape, coaxial with the rotation axis 4, forming the protrusion 72c. That is, viewed axially, the protrusion 72c is an annular shape concentric with the rotation axis 4. Radially, the protrusion 72c is positioned near the inner side (near the inner edge) of the second back cover 72. The front surface 72d of the protrusion 72c is a planar shape parallel to the rear surface 21b of the central partition wall 21. Axially, the gap between the protrusion 72c and the rear surface 21b of the central partition wall 21 is narrower than the gap between the front surface 72b (excluding the protrusion 72c) and the rear surface 21b of the central partition wall 21. The protrusion 72c is an example of a protrusion (variable throttling orifice) in this invention.

[0106] The accompanying drawings, which are the main references in this description, are referenced here. Figure 1 and Figure 2 .

[0107] The second front shield 73 is a plate (so-called side plate) covering the rear of the second blade 71 (in the direction of the front side of the second impeller 7). The second front shield 73 is shaped like a generally annular plate, with the inner edge protruding further rearward than the outer edge. The outer diameter of the second front shield 73 is slightly smaller than the outer diameter of the second back shield 72. The second front shield 73 is disposed rearward relative to the second back shield 72. The second front shield 73 has a rear surface 73a and a cylindrical portion 73b. The second front shield 73 is an example of the fourth shield in this invention.

[0108] The rear surface 73a faces rearward and is opposite to the inner surface 22a of the second partition wall 22. A generally annular space (hereinafter referred to as "second frontal side space S22") is formed between the rear surface 73a and the inner surface 22a.

[0109] The inner edge of the second front shield 73 extends rearward in a cylindrical shape, coaxial with the rotation axis 4, forming a cylindrical portion 73b that functions as a second intake port 75. In other words, the second front shield 73 includes a cylindrical portion 73b that functions as a second intake port 75. In the second impeller 7, the cylindrical portion 73b faces rearward and is disposed within the large-diameter portion 22d of the second partition wall portion 22. The cylindrical portion 73b is an example of a second cylindrical portion in this invention. In the radial direction, the cylindrical portion 73b is opposite to the large-diameter portion 22d. A cylindrical gap (hereinafter referred to as "second cylindrical gap S23") is formed between the large-diameter portion 22d and the cylindrical portion 73b. In the radial direction, the length of the second cylindrical gap S23 (the distance between the large diameter portion 22d and the cylindrical portion 73b) is such that the cylindrical portion 73b does not abut against the large diameter portion 22d during normal operation of the centrifugal pump 1, and is set to be longer than the length set for the impeller of a typical centrifugal pump. That is, 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 cylindrical portion 73b is opposite to the first section 22e. An annular gap (hereinafter referred to as "second annular gap S24") is formed between the first section 22e and the cylindrical portion 73b. In the axial direction, the length of the second annular gap S24 (the length between the first section 22e and the cylindrical portion 73b) is such that the cylindrical portion 73b does not abut against the first section 22e during normal operation of the centrifugal pump 1, and is set to be longer than the length set 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.

[0110] The second frontal side space S22 communicates with the space on the radially outer side of the second impeller 7 and the second cylindrical gap S23. The second annular gap S24 communicates with the second frontal side space S22 and the space inside the small diameter portion 22c.

[0111] The inner edge of the second rear cover 72 extends forward in a cylindrical shape, coaxial with the rotating shaft 4, forming the second hub portion 74. The front part 4a of the rotating shaft 4 is inserted into the second hub portion 74, and the second impeller 7 is mounted on the front part 4a by fixing the second hub portion 74 to the front part 4a of the rotating shaft 4. At this time, the second suction port 75 faces rearward. The second hub portion 74 covers a portion of the front part 4a of the rotating shaft 4 and is disposed in the central through hole 21c. The second hub portion 74 abuts against the first hub portion 64, and a cylindrical space (hereinafter referred to as "cylindrical space S3") is formed between the central through hole 21c and the first hub portion 64 and the second hub portion 74. The cylindrical space S3 communicates with the first rear side space S11 and the second rear side space S21. That is, the first rear side space S11 and the second rear side space S21 are connected to each other through the cylindrical space S3 (central through hole 21c).

[0112] As described above, this is a two-stage centrifugal pump in which the first impeller 6 and the second impeller 7 are mounted back-to-back on a single rotating shaft 4, sandwiched between the central partition wall 21. The first pump chamber 23 and the second pump chamber 24 are separated by the central partition wall 21 and are connected to each other via the cylindrical space S3. That is, no shaft seal structure, such as a mechanical seal, is provided between the first pump chamber 23 and the second pump chamber 24.

[0113] Centrifugal pump operation

[0114] Next, the operation of centrifugal pump 1 will be explained. In the following description, please refer to the relevant references as appropriate. Figure 1 and Figure 2 .

[0115] When centrifugal pump 1 starts operating, motor 3 drives the rotating shaft 4 to rotate. First impeller 6 draws in the treatment liquid introduced into the small diameter section 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 within the small diameter section 22c via connecting channel 25. At this time, a portion of the treatment liquid discharged into the first pump chamber 23 flows into the first back side space S11 and then into the second pump chamber 24 (second back side space S21) via cylindrical space S3. Additionally, another portion of the treatment liquid discharged into the first pump chamber 23 flows back into the space within the small diameter section 20c via the first front side space S12, the first cylindrical gap S13, and the first annular gap S14. This backflow of treatment liquid adversely affects the suction performance of the first impeller 6. Therefore, this 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 throttling sections (first fixed throttling ports) for the liquid flow. The first fixed throttling port (first cylindrical gap S13, first annular gap S14) is an example of the first gap in the present invention.

[0116] The second impeller 7 draws in the treatment fluid delivered to the space within the small diameter section 22c from the rear and discharges it into the second pump chamber 24. The treatment fluid discharged into the second pump chamber 24 is discharged into the discharge pipeline (not shown) via the discharge channel 26 and the discharge pipe 28. At this time, a portion of the treatment fluid discharged into the second pump chamber 24 flows into the second rear side space S21. Here, the pressure of the treatment fluid in the second pump chamber 24 is greater than the pressure of the treatment fluid in the first pump chamber 23. Therefore, the treatment fluid flowing into the second rear side space S21 flows back into the first pump chamber 23 (first rear side space S11) via the cylindrical space S3 in a manner similar to the treatment fluid flowing into the first pump chamber 23. Thus, in the centrifugal pump 1, a flow of treatment fluid is generated from the second pump chamber 24 back to the first pump chamber 23 (hereinafter referred to as "return flow"). The second back side space S21 and the cylindrical space S3 form a flow channel (hereinafter referred to as "return flow channel RL") through which a portion of the treatment liquid in the second pump chamber 24 flows to the first back side space S11 (first pump chamber 23). Additionally, another portion of the treatment liquid discharged into the second pump chamber 24 flows back into the space within the small diameter portion 22c via the second front side space S22, the second cylindrical gap S23, and the second annular gap S24. This return flow of treatment liquid may adversely affect the suction performance of the second impeller 7. Therefore, this flow is primarily 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 throttling sections (second fixed throttling orifices) for this flow. The second fixed throttling orifice is larger than the first fixed throttling orifice. Therefore, the flow rate throttled by the second fixed throttling orifice is less than the flow rate throttled by the first fixed throttling orifice. That is, the flow rate of the treatment fluid flowing through the second fixed throttling orifice is greater than the flow rate of the treatment fluid flowing through the first fixed throttling orifice. The second fixed throttling orifice (second cylindrical gap S23, second annular gap S24) is an example of the second gap in this invention.

[0117] As described below, in centrifugal pump 1, where the processing liquid flows in this manner, an axial thrust, different from that of a conventional two-stage centrifugal pump (hereinafter referred to as "conventional pump"), plays a role. In this specification, the structure of the "conventional pump" is identical to that of centrifugal pump 1, except that the outer diameters of the first impeller (outer diameter of the first back cover) and the second impeller (outer diameter of the second back cover) are the same, and the cylindrical space is sealed by a mechanical seal. That is, the conventional pump is a two-stage centrifugal pump mounted on a single rotating shaft with the first and second impellers facing away from each other. To distinguish centrifugal pump 1 from the conventional pump, in the following description, the same reference numerals as centrifugal pump 1 are supplemented with reference numeral "z" in the reference numerals indicating the structure of the conventional pump.

[0118] "Axial thrust" is the force acting on the rotating shaft 4 (first impeller 6, second impeller 7) in a manner that causes it to move axially. The axial thrust includes: a first axial thrust, which acts to move the rotating shaft 4 forward; and a second axial thrust, which acts to move the rotating shaft 4 backward. The axial thrust is primarily generated by the pressure balance between the front and back sides of the first impeller 6 and the second impeller 7 of the centrifugal pump 1.

[0119] Axial thrust in existing pumps

[0120] Before explaining the axial thrust in centrifugal pump 1, the axial thrust in existing pump 1z and existing pump 1z without mechanical seal Mz will be explained below.

[0121] Figure 5 (a) is a partially enlarged schematic cross-sectional view illustrating the axial thrust in the existing pump 1z. Figure 5 (b) is a partially enlarged schematic cross-sectional view illustrating the axial thrust in an existing pump 1z that does not have a mechanical seal Mz.

[0122] For ease of explanation, only the central partition wall 21z, rotating shaft 4z, first impeller 6z, second impeller 7z, and mechanical seal Mz are shown in this simplified diagram. In diagram (b), a hollow arrow indicates reflux.

[0123] In the following explanation, pressure "P" refers to... f3 "P" indicates the pressure exerted by the first front shield 63z on the first impeller 6z on the processing fluid flowing through the first front side space S12z. r3 "P" indicates the pressure exerted by the first back cover 62z on the first impeller 6z on the processing fluid flowing through the first back side space S11z. f4 "P" indicates the pressure exerted by the second front shroud 73z on the second impeller 7z from the processing fluid flowing through the second front side space S22z. r4 "P" indicates the pressure exerted by the second back cover 72z on the second impeller 7z on the processing fluid flowing through the second back side space S21z. In the first impeller 6z, based on pressure "P" f3 "F" f3 "Action towards the rear, based on pressure" P r3 "F" r3 "Acting forward. Due to pressure "P" f3 "Less than pressure" P r3 Therefore, it is equivalent to the difference between two forces (F). r3 -F f3 The force (first axial thrust) acts forward on the first impeller 6z. Similarly, in the second impeller 7z, the pressure "P" f4 The force formed, Ff4 "Acting forward, pressure" P r4 The force formed, F r4 "Acting backwards. Due to pressure "P" f4 "Less than pressure" P r4 Therefore, it is equivalent to the difference between two forces (F). r4 -F f4 The force (second axial thrust) acts rearward on the second impeller 7z. Figure 5 In the middle, the thin arrow indicates the pressure "P" by its length. f3 “P” r3 “P” f4 “P” r4 The size of the force "F" is indicated by the length of the arrowhead. f3 “F” r3 “F” f4 “F” r4 The size of ".

[0124] like Figure 5 As shown in (a), in the existing pump 1z, the structure of the first impeller 6z is the same as that of the second impeller 7z, except for the direction of rotation. That is, as described above, the outer diameter of the first back cover 62z of the first impeller 6z is the same as the outer diameter of the second back cover 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-bearing area (liquid contact area) of the first front cover 63z is smaller than the pressure-bearing area of ​​the first back cover 62z, and is the same as the pressure-bearing area of ​​the second front cover 73z. In addition, the pressure-bearing area of ​​the first back cover 62z is the same as the pressure-bearing area of ​​the second back cover 72z. In this structure, the pressure "P" f3 "and pressure" P f4 "Same, pressure" P r3 "and pressure" P r4 "Same. As a result, the force F acting on the first back shield 62z" r3 "A force greater than 63z acting on the first frontal shield" F f3 ", and the force "F" acting on the second rear shield 72z r4 "Same. The force F acting on the first frontal shield 63z" f3 "The force F acting on the second frontal shield 73z" f4 "The same. Therefore, it is equivalent to the difference between two forces (F)." r3 -F f3 The force (first axial thrust) acts forward on the first impeller 6z. On the other hand, the difference between the two forces (F) r4 -F f4The force (second axial thrust) acts rearward on the second impeller 7z. 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 reality, the first axial thrust acts on the rotating shaft 4z due to the pressure difference between the processed fluid in the first pump chamber 23z and the processed fluid in the second pump chamber 24z. However, normally, this first axial thrust is absorbed by the bearings. Therefore, in the existing pump 1z, the problematic axial thrust does not act on the rotating shaft 4z.

[0125] Next, as Figure 5 As shown in (b), in the existing pump 1z without a mechanical seal Mz, the first pump chamber 23z is connected to the second pump chamber 24z via a cylindrical space S3z. In this structure, the pressure of the processing fluid in the second pump chamber 24z is higher than the pressure of the processing fluid in the first pump chamber 23z, thus generating a flow (backflow) of the processing fluid in the second pump chamber 24z into the first pump chamber 23z via the cylindrical space S3z. At this time, in the second back side space S21z, a flow is generated that rotates along the rotation direction of the second impeller 7z and flows from the outer edge of the second back side cover 72z toward the inner edge. Therefore, as Figure 5 As shown by the dashed and solid lines in (b), the pressure "P" of the processing fluid flowing through the second back side space S21z r4 "It becomes lower. On the other hand, in the first back side space S11z, a liquid flow is generated that rotates along the rotation direction of the first impeller 6z and flows from the inner edge side of the first back side shield 62z toward the outer edge side. Therefore, as..." Figure 5 As shown by the dashed and solid lines in (b), the pressure "P" of the processing fluid flowing through the first back side space S11z r3 "It gets higher. Therefore, the force F acting on the first back shield 62z" r3 "Increases, the force acting on the second back shield 72z" F r4 "It becomes smaller. As a result, the first axial thrust acting on the rotating shaft 4z (first impeller 6z, second impeller 7z) is greater than the second axial thrust, and the first axial thrust acts on the rotating shaft 4z. Thus, when the first pump chamber 23z is connected to the second pump chamber 24z via the cylindrical space S3z, the axial thrust in the existing pump 1z is unbalanced, and the axial thrust (first axial thrust) acts on the rotating shaft 4z."

[0126] These axial thrusts increase with the rotational speed of motor 3. Therefore, for example, when conveying a processing fluid requiring high-speed rotation (e.g., a low-viscosity processing fluid), the axial thrust cannot be absorbed by the bearings, requiring a mechanism to counteract the axial thrust (e.g., a balance piston, balance plate, etc.). In this case, not only does the existing pump 1z become larger overall, but the rotating shaft 4z also becomes longer. As a result, it becomes difficult to handle high-speed rotation. Furthermore, when the processing fluid is used to lubricate the bearings, especially if the viscosity of the processing fluid is low, even a slight axial thrust will generate surface pressure on the bearing's sliding surface. As a result, the temperature of the sliding surface rises, and the bearing's lifespan decreases. Therefore, a structure that minimizes axial thrust (ideally, a structure with "0" axial thrust) is needed.

[0127] Axial thrust in centrifugal pumps

[0128] Next, the axial thrust in centrifugal pump 1 is explained as follows. The following explanation also appropriately refers to... Figures 1 to 5 .

[0129] Figure 6 This is a partially enlarged schematic cross-sectional view illustrating the effect of the second impeller 7 on the axial thrust in the centrifugal pump 1.

[0130] In this figure, for ease of explanation, only the central partition wall 21, the rotating shaft 4, the first impeller 6, and the second impeller 7 are shown simplified, while the protrusion 72c is omitted. The hollow arrow in this figure indicates recirculation. Furthermore, in this figure, to easily understand the force acting on the second impeller 7, the second impeller 7 is shown with only the outer diameter of the second back cover 72 being larger than the outer diameter of the first back cover 62, while the outer diameter of the second front cover 73 is the same as the outer diameter of the first front cover 63.

[0131] In the following explanation, pressure "P" refers to... f1 "P" indicates the pressure exerted by the first front shield 63 of the first impeller 6 on the processing fluid flowing through the first front side space S12. r1 "P" indicates the pressure exerted by the first back cover 62 of the first impeller 6 on the processing fluid flowing through the first back side space S11. f2 "P" indicates the pressure exerted by the second front shield 73 of the second impeller 7 on the processing fluid flowing through the second front side space S22. r2 "P" indicates the pressure exerted on the second back cover 72 of the second impeller 7 by the processing fluid flowing through the second back side space S21. Based on pressure "P" f1 "F" f1 "Acting backwards on the first impeller 6, based on pressure "P" r1 "F" r1 "The force acts forward on the first impeller 6. Due to the pressure "P" f1 "Less than pressure" Pr1 Therefore, it is equivalent to the difference between two forces (F). r1 -F f1 The force (first axial thrust) acts forward on the first impeller 6. Similarly, based on the pressure "P f2 "F" f2 "The pressure P acts forward on the second impeller 7." r2 The force formed, F r2 "The force acts backward on the second impeller 7. This is equivalent to the difference between two forces (F)." r2 -F f2 The force (second axial thrust) acts rearward on the second impeller 7. Figure 6 In the middle, the thin arrow indicates the pressure "P" by its length. f1 “P” r1 “P” f2 “P” r2 The size of the force "F" is indicated by the length of the arrowhead. f1 “F” r1 “F” f2 “F” r2 The size of ".

[0132] As described above, the outer diameter of the second back cover 72 is larger than the outer diameter of the first back cover 62. Therefore, as Figure 6 As shown, the pressure-bearing area of ​​the second back cover 72 is larger than that of the first back cover 62. As a result, the force "F" acting on the second impeller 7... r2 "The force F acting on the second impeller 7z of the existing pump 1z" r4 "Increase. Therefore, by designing the outer diameter of the second back cover 72 (i.e., the outer diameter of the second impeller 7) to be larger than the outer diameter of the first back cover 62 (i.e., the outer diameter of the first impeller 6), the second axial thrust (F) acting on the second impeller 7 (rotation shaft 4) is increased." r2 -F f2 The force will be greater than the second axial thrust (F) acting on the second impeller 7z (rotation shaft 4z). r4 -F f4 The axial thrust (first axial thrust) acting on the rotating shaft 4 is larger than that acting on the rotating shaft 4z (the first axial thrust is suppressed). As a result, the first axial thrust (F) acting on the rotating shaft 4 is smaller. r1 -F f1 ) and the second axial thrust (F r2 -F f2 (roughly) balanced.

[0133] Figure 7This is a partially enlarged schematic cross-sectional view illustrating the effect of the second fixed throttling orifice (second cylindrical gap S23 and second annular gap S24) on the axial thrust in centrifugal pump 1.

[0134] In this figure, for ease of explanation, only the first partition wall 20, the central partition wall 21, the second partition wall 22, the rotating shaft 4, the first impeller 6, and the second impeller 7 are shown simplified, while the protrusion 72c is omitted. The hollow arrow in this figure indicates backflow. Furthermore, in this figure, to illustrate only the effect of the second fixed throttling orifice, the second impeller 7 is shown with the same outer diameter as the first impeller 6.

[0135] As described above, radially, the length of the second cylindrical gap S23 is longer than the length of the first cylindrical gap S13. Axially, 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 fluid flowing into the second front side space S22 through the second fixed throttling orifice is less than the flow rate of the treatment fluid flowing into the first front side space S12 through the first fixed throttling orifice. That is, the flow rate of the treatment fluid flowing through the second fixed throttling orifice ( Figure 7 The flow rate of the fluid indicated by the dashed arrow is greater than the flow rate of the treated fluid flowing through the first fixed orifice. Therefore, the pressure "P" experienced by the second front shield 73 from the treated fluid... f2 The pressure is the same when the flow rate of the treated fluid through the second fixed throttle orifice is the same as the flow rate of the treated fluid through the first fixed throttle orifice. Figure 7 (Indicated by dashed lines) is small. As a result, the force acting on the second impeller 7 (second axial thrust) is greater than the force when the flow rate of the processed liquid flowing through the second fixed throttle orifice is the same as the flow rate of the processed liquid flowing through the first fixed throttle orifice. Therefore, by designing the flow rate of the processed liquid flowing through the second fixed throttle orifice to be greater than the flow rate of the processed liquid flowing through the first fixed throttle orifice, the second axial thrust acting on the second impeller 7 (rotation shaft 4) increases, while the axial thrust acting on the rotation shaft 4 (first axial thrust) decreases (is suppressed). Here, normally, if the flow rate of the processed liquid flowing through the first fixed throttle orifice 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 processed liquid flowing through the second fixed throttle orifice increases, the impact on the suction performance of the second impeller 7 is small. Therefore, in this structure, although the performance of the centrifugal pump 1 may deteriorate slightly, the efficiency improvement of the centrifugal pump 1 resulting from the improvement of the axial thrust acting on the rotation shaft 4 is greater than this deterioration.

[0136] Next, as described above, a plurality of recesses 21d are disposed on the rear surface 21b of the central partition wall portion 21. The recesses 21d face the second rear side space S21, and the flow of the processing liquid within the second rear side space S21 is disturbed by the recesses 21d. The flow of the processing liquid within the second rear side space S21 becomes a rotational flow that swirls in the same direction of rotation as the second impeller 7, depending on its rotation. That is, the flow of the processing liquid within the second rear side space S21 contains a large amount of swirling components. A portion of the processing liquid flow near the central partition wall portion 21 flows into the recesses 21d and is obstructed by the sidewalls of the recesses 21d. At this time, the swirling components of the flow flowing into the recesses 21d are suppressed, and the flow changes direction radially inward and axially. Therefore, this flow also disturbs the flow that does not flow into the recesses 21d, and the swirling components of the disturbed flow are also slightly suppressed. As a result, the swirling component of the processing fluid flow within the second back-side space S21 is suppressed. Because the swirling component of the processing fluid is high, the pressure of the processing fluid "P" increases. r2 "The pressure of the treatment fluid decreases, therefore, if the swirling component of the treatment fluid is suppressed, the pressure of the treatment fluid will decrease." r2 "Increase. That is, by suppressing the swirling component of the processing liquid in the second back side space S21, the force (second axial thrust) acting on the second impeller 7 increases, and the axial thrust (first axial thrust) acting on the rotating shaft 4 decreases (is suppressed)."

[0137] As described above, the centrifugal pump 1 includes: a structure that suppresses axial thrust (first axial thrust) through the outer diameter of the second back cover (hereinafter referred to as the "first suppression structure"); a structure that suppresses axial thrust (first axial thrust) through the second fixed throttling orifice (hereinafter referred to as the "second suppression structure"); and a structure that suppresses axial thrust (first axial thrust) through 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.

[0138] Figure 8 This is a partially enlarged schematic cross-sectional view illustrating the effect of the protrusion 72c on the axial thrust in the centrifugal pump 1. Figure 8 (a) shows the state in which the first axial thrust and the second axial thrust are in balance. Figure 8 (b) shows the state where the first axial thrust is greater than the second axial thrust. Figure 8 Figure (c) shows the state where the first axial thrust is less than the second axial thrust. In this figure, for ease of explanation, only the central partition wall 21, the rotating shaft 4, and the second impeller 7 are shown in a simplified manner.

[0139] like Figure 8As shown in (a), when the first axial thrust and the second axial thrust are balanced, the rotating shaft 4 (first impeller 6, second impeller 7) is positioned in a predetermined position axially. At this time, a gap S4 with a spacing of "L1" is formed between the protrusion 72c and the rear surface 21b of the central partition wall 21. The processing liquid in the second back side space S21 flows from the outer edge side of the second impeller 7 toward the inner edge side while its flow rate is throbbing in the gap S4.

[0140] Next, as 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 axially, and the gap S4 narrows to "L2". At this time, the throttling flow rate of the treatment fluid formed by the protrusion 72c increases. Therefore, in the second back side space S21, the pressure "P" of the treatment fluid upstream (radially outward) of the protrusion 72c increases. r2 "It gets bigger. In addition, the flow rate of the processing fluid through the cylindrical space S3 decreases, and the pressure of the processing fluid in the first back side space S11 increases." r1 "It becomes smaller. As a result, the force F acting on the second impeller 7" r2 "The force F increases, acting on the first impeller 6" r1 "As it shrinks, the first axial thrust and the second axial thrust eventually become balanced. Thus, as the convex portion 72c moves forward along the rotating shaft 4 (first impeller 6, second impeller 7), a portion of the second back side space S21 (i.e., a portion of the return flow channel RL) narrows, balancing the axial thrusts (first axial thrust and second axial thrust) acting on the rotating shaft 4."

[0141] On the contrary, such as 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 rearward in the axial direction, and the gap S4 widens to "L3". At this time, the throttling flow rate of the treatment fluid formed by the protrusion 72c decreases. Therefore, in the second front side space S22, the pressure "P" of the treatment fluid upstream of the protrusion 72c is lower. r2 "It gets smaller. Additionally, the flow rate of the processing fluid through the cylindrical space S3 increases, and the pressure of the processing fluid in the first back side space S11 decreases." r1 "It gets bigger. As a result, the force F acting on the second impeller 7..." r2 "The force F acting on the first impeller 6 decreases." r1"As it grows larger, the first axial thrust and the second axial thrust eventually become balanced. Thus, as the convex portion 72c moves rearward along the rotating shaft 4 (first impeller 6, second impeller 7), a portion of the second back side space S21 (i.e., a portion of the return flow channel RL) widens, balancing the axial thrust acting on the rotating shaft 4."

[0142] Thus, the protrusion 72c functions as a variable throttle orifice, which adjusts the flow rate of the treatment fluid 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).

[0143] As described above, the second back-side space S21 is an annular plate-shaped space. Therefore, the cross-sectional area (transverse cross-sectional area of ​​the flow channel) of the second back-side space S21 along the circumferential cut surface decreases as the cut surface approaches the inner edge of the second back-side shield 72. That is, as the cut surface approaches the inner edge of the second back-side shield 72, the throttling flow rate of the variable throttling orifice relative to the axial movement of the protrusion 72c increases. Therefore, if the protrusion 72c is positioned close to the inner edge of the second back-side shield 72, even if the axial movement of the protrusion 72c is small, the pressure "P" of the processing fluid upstream of the protrusion 72c will increase. r2 The amount of change will also increase.

[0144] Thus, the centrifugal pump 1 is designed to reduce the force "F" acting on the second impeller 7 through the first to the third suppression structures. r2 "The axial thrust increases. Therefore, by designing the first to third suppression structures to completely balance the first and second axial thrusts acting on the rotating shaft 4, even if the processing fluid 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 this embodiment, the balance between the first and second axial thrusts acting on the rotating shaft 4 is roughly adjusted (coarse adjustment) by the first suppression structure, and further adjusted (fine adjustment) by the second and third suppression structures. In addition, even if the axial thrust acts on the rotating shaft 4, the axial thrust will be suppressed to a slight force by the first to third suppression structures, so the axial thrust can be easily and automatically adjusted by the variable throttle orifice."

[0145] Summarize

[0146] According to the embodiment described above, the centrifugal pump 1 includes a central partition wall 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 21 has a central through hole 21c through which the rotating shaft 4 is inserted. The first pump chamber 23 is separated from the second pump chamber 24 by the central partition wall 21 and is arranged side-by-side with the second pump chamber 24 in front of 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 rearward. A first back side space S11 is formed between the first impeller 6 and the central partition wall 21, and a second back side space S21 is formed between the second impeller 7 and the central partition wall 21. The first back side space S11 communicates with the second back side space S21 via a cylindrical space S3. The outer diameter of the second back cover 72 is larger than the outer diameter of the first back cover 62. According to this structure, the pressure-bearing area of ​​the second back cover 72 is increased, thereby increasing the force "F" acting on the second impeller 7. r2 "Increase. Therefore, even if the processing fluid 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 cover 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."

[0147] Furthermore, according to the embodiment described above, the specific speed set in the first pump section P1, which is composed of the first impeller 6 and the first pump chamber 23, is greater than the specific speed set in the second pump section P2, which is composed of the second impeller 7 and the second pump chamber 24. Generally, as the specific speed increases, the opening on the suction side between the impeller blades becomes larger, and the outer diameter of the impeller becomes smaller. Therefore, according to this structure, the suction performance (discharge flow rate) formed by the first pump section P1 is improved, and the head formed by the second pump section P2 is improved, thus improving the performance of the centrifugal pump 1. In addition, the outer diameter of the second back cover 72 is necessarily larger than the outer diameter of the first back cover 62. As a result, 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 is suppressed.

[0148] Furthermore, 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 throttling port) is larger (longer) than the size (length) of the first cylindrical gap S13 and the first annular gap S14 (first fixed throttling port). According to this structure, the pressure "P" received by the second front shield 73 from the processed liquid... f2 The pressure "P" is the pressure when the flow rate of the treated fluid through the second fixed throttle orifice is the same as the flow rate of the treated fluid through the first fixed throttle orifice. f2 "Small. As a result, the force (second axial thrust) acting on the second impeller 7 is greater than the force (second axial thrust) when the flow rate of the treated liquid through the second fixed throttle orifice is the same as the flow rate of the treated liquid through the first fixed throttle orifice. Therefore, even if the treated 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 further suppressed."

[0149] Furthermore, according to the embodiment described above, the central partition wall 21 has eight recesses 21d. The recesses 21d face the second rear side space S21 and are configured to suppress swirling components of the processing liquid flowing through the second rear side space S21. According to this structure, the pressure "P" of the processing liquid... r2 "As the second axial thrust acting on the second impeller 7 (rotating shaft 4) increases, the axial thrust acting on the rotating shaft 4 (first axial thrust) is further suppressed."

[0150] Furthermore, according to the embodiment described above, the outer diameters of the first back cover 62 and the second back cover 72 are, for example, set such that when the first impeller 6 and the second impeller 7 discharge the treatment liquid, the first axial thrust and the second axial thrust acting on the rotating shaft 4 are balanced. With this structure, the axial thrust acting on the rotating shaft 4 is suppressed to a minimum.

[0151] Furthermore, according to the embodiment described above, the second back cover 72 of the second impeller 7 includes a protrusion 72c. The protrusion 72c functions as a variable throttle orifice, which narrows a portion of the second back side space S21 (a portion of the return flow channel RL) as the rotation shaft 4 moves forward and widens as the rotation shaft 4 moves rearward. With this structure, even if an axial thrust is applied to the rotation shaft 4, the axial thrust is suppressed to a slight force by the first to third suppression structures, thus the axial thrust can be easily and automatically adjusted via the variable throttle orifice.

[0152] Furthermore, according to the embodiment described above, the variable throttle orifice is formed by a protrusion 72c that protrudes forward in an annular shape from the second back cover 72. With this structure, the variable throttle orifice can be formed using a simple structure in which a portion of the second back cover 72 protrudes forward.

[0153] Furthermore, according to the embodiment described above, the protrusion 72c is positioned radially near the inner side of the second back cover 72. The cross-sectional area of ​​the second back side space S21 in the circumferential cut surface decreases as the cut surface approaches the inner edge of the second back cover 72. Therefore, according to this structure, even if the axial movement of the protrusion 72c decreases, the pressure "P" of the processing fluid upstream of the protrusion 72c remains constant. r2 The amount of change will also increase. That is, the sensitivity of pressure changes caused by the variable throttle orifice will increase.

[0154] Variations

[0155] Next, focusing on the differences from the previously described embodiment (hereinafter referred to as the "first embodiment"), variations of the centrifugal pump 1 will be described below. In these variations, for ease of explanation, the same reference numerals are used for components identical to those in the first embodiment, as well as components having common functions. Furthermore, in these variations, appropriate reference numerals will be used... Figures 1 to 8 .

[0156] First variation

[0157] Figure 9 This is a partially enlarged schematic cross-sectional view of the centrifugal pump 1A of the first modified example.

[0158] For ease of explanation, only the central partition wall 21, the rotating shaft 4, the first impeller 6, and the second impeller 7 are shown in the figure, while the protrusion 72c is omitted. The hollow arrow in the figure indicates reflux.

[0159] In the centrifugal pump 1A of the first modified example, the shape of the second impeller 7 differs from that of the first embodiment. Specifically, the outer diameter of the second back cover 72 is larger than the outer diameter of the first back cover 62, but the outer diameter of the second front cover 73 of the second impeller 7 is the same as the outer diameter of the first front cover 63. In this structure, only the pressure-bearing area of ​​the second back cover 72 is larger than that of the first back cover 62. Therefore, the force "F" acting on the second impeller 7... r2 "The extent to which the increase in the outer diameter of the second back cover 72 is greater than that in the first embodiment. Therefore, in this modified example, even if the increase in the outer diameter of the second back cover 72 is smaller than that in the first embodiment, the same axial thrust suppression effect can be obtained as in the first embodiment. Furthermore, in this structure, compared to..." Figure 6 The structure shown only shows an increase in the outer diameter of the second rear shroud 72; in the circumferential direction, the second blade 71 also becomes larger. As a result, compared to... Figure 6 The pressure exerted by the second impeller 7 on the treated fluid is greater in the first modification than in the second impeller 7 shown. Therefore, the force (discharge pressure) of the second impeller 7 in the first modification is greater than that of the second impeller 7. Figure 6 The force of the second impeller 7 shown.

[0160] Second to Fourth Modifications

[0161] Figure 10 (a) is a partially enlarged schematic cross-sectional view of the centrifugal pump 1B of the second variation. Figure 10 (b) is a partially enlarged schematic cross-sectional view of the centrifugal pump 1C of the third variation. Figure 10 (c) is a partially enlarged schematic cross-sectional view of the centrifugal pump 1D of the fourth variation.

[0162] In the centrifugal pumps 1B to 1D of the second to fourth modifications, the structure of the variable throttling orifice differs from that of the first embodiment. Specifically, in the centrifugal pump 1B of the second modification, the second back cover 72 does not have a protrusion 72c, while the central partition wall 21 has a 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 throttling orifice in this invention. In the centrifugal pump 1C of the third modification, the central partition wall 21 has a protrusion 21e, and the second back cover 72 also has a protrusion 72c. The protrusions 21e and 72c are positioned opposite each other. Axially, the length of the protrusion 72c is shorter than that of the protrusion 72c in the first embodiment. The protrusions 21e and 72c are examples of a variable throttling orifice in this invention. In the fourth modified centrifugal pump 1D, the second back cover 72 does not have a protrusion 72c, and the rear end of the central through hole 21c is enlarged to form an enlarged diameter portion 21f and a section portion 21g. Additionally, an annular component R is mounted on the rotating shaft 4. Axially, the annular component R is positioned between the second impeller 7 and the section portion 21g, and is opposite to the section portion 21g. The annular component R is an example of a variable throttling orifice in this invention. In these structures, similar to the first embodiment, the partial throttling flow rate of the return flow channel RL changes depending on the forward and backward movement of the rotating shaft 4. Therefore, these structures function as a variable throttling orifice, similar to the first embodiment.

[0163] Fifth variation

[0164] Figure 11 This is a partially enlarged schematic cross-sectional view showing the centrifugal pump 1E of the fifth modified example.

[0165] In the fifth variation of the centrifugal pump 1E, the number of impellers differs from that in the first embodiment. Specifically, the centrifugal pump 1E includes a housing 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. That is, the centrifugal pump 1E is a four-stage centrifugal pump with four impellers (first impeller 6 to fourth impeller 9).

[0166] The housing 2E houses the motor 3, rotating shaft 4, bearings 51 and 52, and first impeller 6 to fourth impeller 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 channel 25, a discharge flow channel 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 positioned in front of the first partition wall 20, and together with the first partition wall 20, divides the space into the third pump chamber 2c, which houses the third impeller 8. The rear partition wall 2b is positioned behind the second partition wall 22, and together with the second partition wall 22, divides the space into the fourth pump chamber 2d, which houses 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 behind the second pump chamber 24. The connecting flow channel 25 is a flow channel that guides the treatment liquid discharged through the first impeller 6 to the fourth impeller 9. The suction pipe 27 is formed in the front partition wall portion 2a, instead of being formed in the first partition wall portion 20.

[0167] 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, but smaller than the outer diameter of the second impeller 7. The third impeller 8 is mounted in front of the first impeller 6 at the front part 4a of the rotating shaft 4. The fourth impeller 9 is mounted behind the second impeller 7 at the front part 4a of the rotating shaft 4. Similar to 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 assembly that draws in the treated liquid from the front, and the fourth impeller 9 and the second impeller 7 constitute a rear-stage assembly that draws in the treated liquid from the rear. In the centrifugal pump 1E, the treated liquid flows in the following order: suction pipe 27, third impeller 8, first impeller 6, connecting channel 25, fourth impeller 9, second impeller 7, discharge channel 26, and discharge pipe 28. In other words, the second impeller 7 draws in and discharges the processing liquid discharged from the first impeller 6 via the connecting channel 25 and the fourth impeller 9.

[0168] In this structure, the pressure difference between the processing fluid in the second pump chamber 24 and the processing fluid in the first pump chamber 23 is approximately twice that of the first embodiment. Therefore, the flow rate of the processing fluid flowing through the return flow channel RL is increased compared to the first embodiment. Consequently, the axial thrust (first axial thrust) acting on the rotating shaft 4 by the processing fluid flowing through the return flow channel RL is greater than the axial thrust in the first embodiment. Under these conditions, the first to third suppression structures and the variable throttle orifice in this invention can also suppress and regulate the axial thrust.

[0169] It should be noted that in this modified example, the structure of the fourth impeller 9 can also be the same as that of the second impeller 7.

[0170] Other implementation methods

[0171] It should be noted that, in the embodiments described above, the centrifugal pump 1, in addition to the first suppression structure, also has a mechanism for applying a force "F" to the second impeller 7. r2 "Other structures (second to third suppression structures) are enlarged. Instead, 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 orifice may be the same as the size (flow rate) of the first fixed throttle orifice. In addition, for example, the central partition wall portion 21 may not have the recess 21d. The structure that is most helpful in suppressing 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 to third suppression structures." In the first suppression structure, the outer diameters of the first back cover 62 and the second back cover 72 are, for example, set such that the first axial thrust and the second axial thrust are balanced when the first impeller 6 and the second impeller 7 (i.e., the centrifugal pump 1) discharge the treated liquid (at the highest efficiency point). That is, for example, when the two-stage centrifugal pump operates under the conditions of a discharge rate of 30 m³ / h, a total head of 65 m, a treated liquid of water (specific gravity: 1, viscosity: 1 cP), and a speed of 3,000 rpm, with the outer diameter of the first impeller 6 being 150 mm and the outer diameter of the second impeller 7 being 158 mm, both the first axial thrust and the second axial thrust are 2,100 N. Here, the return flow rate is set to 10% (3 m³ / h).

[0172] Alternatively, in this invention, the second impeller 7 may not have the protrusion 72c (variable throttling orifice). In this structure, the axial thrust acting on the rotating shaft 4 can also be minimized through the first to third suppression structures.

[0173] Furthermore, in this invention, the central partition wall 21 may also have a protrusion instead of a recess 21d. In this case, the protrusion may have the same size (volume) as the recess 21d.

[0174] Furthermore, in this invention, the number of recesses 21d is not limited to the number in this embodiment. That is, for example, the number of recesses 21d can be "1", or an odd number of "3" or more, or an even number other than "8".

[0175] Furthermore, in this invention, the central partition wall portion 21 may also have a protrusion instead of having some of the recesses 21d among the plurality of recesses 21d. That is, for example, the central partition wall portion 21 may also have four recesses 21d and four protrusions disposed between each recess 21d.

[0176] Furthermore, in this invention, the position of the recess 21d is not limited to the position in this embodiment. That is, for example, in the radial direction, the inner edge of the recess 21d may also be positioned further outward than the protrusion 72c.

[0177] Furthermore, in this invention, the position of the protrusion 72c is not limited to the position in this embodiment. That is, for example, in the radial direction, the protrusion 72c may also be disposed at the central portion or the outer edge portion of the front surface 72b.

[0178] Furthermore, in this invention, the specific speed set by the first pump unit P1 can be the same as the specific speed set by the second pump unit P2, except for the difference caused by the difference between the outer diameter of the first back cover 62 and the outer diameter of the second back cover 72.

[0179] Furthermore, in this invention, the centrifugal pump 1 may have an even number of impellers, and is not limited to two. That is, for example, as shown in the fifth variation, the number of impellers may be "4", or it may be "6" or more.

[0180] Furthermore, in this invention, the processing liquid is not limited to liquefied gas. That is, for example, the processing liquid can also be water.

[0181] Embodiments of the present invention

[0182] Next, referring to the terms and reference numerals described in each embodiment, embodiments of the present invention as understood from the above-described embodiments will be described below.

[0183] A first embodiment of the present invention is a centrifugal pump (e.g., centrifugal pumps 1, 1A to 1E), wherein the centrifugal pump comprises: 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) mounted on the rotating shaft, which draws in and discharges a treatment liquid; a second impeller (e.g., second impeller 7) mounted on the rotating shaft, which draws in and discharges the treatment liquid discharged from the first impeller; a first pump chamber (e.g., first pump chamber 23) that houses the first impeller; a second pump chamber (e.g., second pump chamber 24) arranged axially alongside the first pump chamber on the rotating shaft, which houses the second impeller; and a central partition wall (e.g., central partition wall 21) having an insertion hole (e.g., central through hole 21c) through which the rotating shaft passes, and which separates the first pump chamber from the second pump chamber, wherein the direction in which the first impeller is arranged relative to the second impeller on the axial direction is a first direction (e.g., forward direction), wherein the first impeller... The direction opposite to the first direction is the second direction (e.g., the rear direction). The first impeller includes: a first suction port (e.g., first suction port 65) facing the first direction, which draws the treatment liquid from the first direction side; and a first shield (e.g., first back shield 62) opposite to the central partition wall. The second impeller includes: a second suction port (e.g., second suction port 75) facing the second direction, which draws the treatment liquid discharged from the first impeller from the second direction side; and a second shield (e.g., second back shield 72) opposite to the central partition wall. A first space (e.g., first back side space S11) communicating with the insertion hole is formed between the first impeller and the central partition wall. A second space (e.g., second back side space S21) communicating with the insertion hole is formed between the second impeller and the central partition wall. The second space and the first space communicate with each other via the insertion hole. The outer diameter of the second shield is larger than the outer diameter of the first shield.

[0184] According to this structure, even if the processing fluid 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 is suppressed.

[0185] The second embodiment of the present invention is a centrifugal pump according to the first embodiment, wherein the specific speed of the second pump section (e.g., the second pump section P2) formed by the second impeller and the second pump chamber is less than the specific speed of the first pump section (e.g., the first pump section P1) formed by the first impeller and the first pump chamber.

[0186] According to this structure, the performance of centrifugal pump 1 is improved, and the axial thrust acting on the rotating shaft 4 is suppressed.

[0187] A third embodiment of the present invention is a centrifugal pump according to a first or second embodiment, wherein the centrifugal pump has: a first partition wall portion (e.g., first partition wall portion 20) disposed on the first direction side relative to the first impeller, dividing the first pump chamber together with the central partition wall portion; and a second partition wall portion (e.g., second partition wall portion 22) disposed on the second direction side relative to the second impeller, dividing the second pump chamber together with the central partition wall portion, wherein the first impeller has a third shield (e.g., first front shield 63) disposed on the first direction side relative to the first shield, and the second impeller has a third shield disposed on the second direction side relative to the second shield. The fourth shield (e.g., the second front shield 73), the third shield having a first cylindrical portion (e.g., cylindrical portion 63b) constituting the first intake port, the fourth shield having a second cylindrical portion (e.g., cylindrical portion 73b) constituting the second intake port, the second gap (e.g., second cylindrical gap S23 and second annular gap S24) between the portion of the second partition wall opposite to the second cylindrical portion (e.g., the large diameter portion 22d and the first segment portion 22e) and the second cylindrical portion, is greater than the first gap (e.g., first cylindrical gap S13 and first annular gap S14) between the portion of the first partition wall opposite to the first cylindrical portion (e.g., the large diameter portion 20d and the segment portion 20e) and the first cylindrical portion.

[0188] According to this structure, the axial thrust acting on the rotating shaft 4 is further suppressed.

[0189] 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 has at least one protrusion or recess (e.g., recess 21d) facing the second space and is configured to suppress the swirling components of the treatment liquid flowing through the second space.

[0190] According to this structure, the axial thrust acting on the rotating shaft 4 is further suppressed.

[0191] The 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 such that when the first impeller and the second impeller discharge the treatment liquid, a first axial thrust acting in a manner that moves the rotating shaft toward the first direction is balanced with a second axial thrust acting in a manner that moves the rotating shaft toward the second direction.

[0192] According to this structure, the axial thrust acting on the rotating shaft 4 is suppressed to a minimum.

[0193] The 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 through hole constitute a return flow channel (e.g., 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 throttling orifice (e.g., protrusion 72c) configured to narrow a portion of the return flow channel as the rotation shaft moves toward the first direction, and to widen the portion as the rotation shaft moves toward the second direction.

[0194] According to this structure, the axial thrust can be easily and automatically adjusted through a variable throttle orifice.

[0195] The seventh embodiment of the present invention is a centrifugal pump (e.g., centrifugal pumps 1, 1A to 1C, 1E) according to the sixth embodiment, wherein the variable throttling orifice is composed of a protrusion (e.g., convex portion 72c) protruding from the second protective cover toward the first direction and / or a protrusion (e.g., convex portion 21e) protruding from the central partition wall portion toward the second direction.

[0196] Based on this structure, a variable throttling orifice can be formed using a simple structure.

[0197] 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 rotation axis, and is disposed radially on the rotation axis near the inner edge of the second protective cover, and / or on the radial direction near the inner edge of the central partition wall.

[0198] Based on this structure, the sensitivity to pressure variations caused by the variable throttle orifice is improved.

Claims

1. A centrifugal pump, comprising: Electric motor; A rotating shaft that rotates based on the drive of the motor; The first impeller, which is mounted on the rotating shaft, draws in and discharges the treatment liquid; The second impeller, which is mounted on the rotating shaft, draws in and discharges the treatment liquid discharged from the first impeller; A first pump chamber, which houses the first impeller; The second pump chamber, which is arranged side by side with the first pump chamber in the axial direction of the rotating shaft, accommodates the second impeller; The central partition wall has a through hole for the rotating shaft to pass through, and separates the first pump chamber from the second pump chamber; A first partition wall portion, which is disposed on a first direction side relative to the first impeller, and together with the central partition wall portion, divides the first pump chamber; as well as The second partition wall, which is disposed on the second direction side relative to the second impeller, together with the central partition wall, divides the second pump chamber. In the axial direction, the direction in which the first impeller is arranged relative to the second impeller is the first direction, and the direction on the opposite side of the first direction is the second direction. The first impeller has: A first suction port, which faces the first direction, draws the treatment liquid from the first direction side; The first protective cover is opposite to the central partition wall; as well as A third protective shield is disposed on the first direction side relative to the first protective shield. The second impeller has: The second suction port, which faces the second direction, draws in the treatment liquid discharged from the first impeller from the second direction side; The second protective cover is opposite to the central partition wall. as well as The fourth shield is disposed on the second direction side relative to the second shield. The fourth shield has a second cylindrical portion that forms the second intake port. 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 is connected to the first space via the through hole. The outer diameter of the second protective cover is larger than the outer diameter of the first protective cover. In the centrifugal pump, The third shield has a first cylindrical portion that forms the first inlet. The second gap between the portion of the second partition wall that is opposite to the second cylindrical portion and the second cylindrical portion is greater than the first gap between the portion of the first partition wall that is opposite to the first cylindrical portion and the first cylindrical portion.

2. The centrifugal pump according to claim 1, wherein, The specific speed set for the second pump section, which is composed of the second impeller and the second pump chamber, is less than the specific speed set for the first pump section, which is composed of the first impeller and the first pump chamber.

3. The centrifugal pump according to claim 1, wherein, The central partition wall has at least one protrusion or recess facing the second space, which is configured to suppress the swirling components of the treatment liquid flowing through the second space.

4. The centrifugal pump according to claim 1, wherein, The outer diameters of the first and second shields are set such that, when the first and second impellers discharge the treatment liquid, a first axial thrust acting in a manner that moves the rotating shaft toward the first direction is balanced by a second axial thrust acting in a manner that moves the rotating shaft toward the second direction.

5. The centrifugal pump according to any one of claims 1 to 4, wherein, The second space and the through hole form a return channel for a portion of the treatment liquid discharged through the second impeller to flow back to the first space. The centrifugal pump has a variable orifice configured to narrow a portion of the return flow path as the rotating shaft moves toward the first direction, and to widen a portion of the return flow path as the rotating shaft moves toward the second direction.

6. The centrifugal pump according to claim 5, wherein, The variable throttle orifice is formed by a protrusion protruding from the second shield toward the first direction and / or a protrusion protruding from the central partition wall toward the second direction.

7. The centrifugal pump according to claim 6, wherein, The protrusion is circumferentially ring-shaped along the axis of rotation and is positioned radially near the inner edge of the second shield, and / or radially near the inner edge of the central partition wall.

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