JP7397258B2 - two stage centrifugal pump - Google Patents

Description

The present invention relates to a two-stage centrifugal pump equipped with a thrust balance mechanism.

A two-stage centrifugal pump, which is a form of fluid machinery, has two first and second impellers attached along the axial direction to a rotor shaft that is rotationally driven by a drive source such as an electric motor, and a partition wall inside the pump case. Some pumps are constructed by accommodating the first impeller and the second impeller in two defined pump chambers (for example, see Patent Document 1).

By the way, in general, in a centrifugal pump, the pressure of the handled fluid is low on the axial front side, which is the suction side of the impeller, and the pressure of the handled fluid is high on the centrifugal direction, which is the discharge side of the impeller. Therefore, there is always a pressure difference (suction side < discharge side) between the front side of the impeller, which faces the suction side of the impeller, and the back side of the impeller, which is surrounded by the discharge side of the impeller, while the impeller is rotating. It is known that this pressure difference is a source of thrust force that pushes the impeller toward the suction side. If this thrust force is excessive, problems occur such as wear of the sliding bearing that rotatably supports the impeller via the rotor shaft, resulting in reduced durability.

Therefore, various thrust balance mechanisms have been proposed to reduce the thrust force.

For example, Patent Documents 2 and 3 disclose that a thrust balance chamber is formed between the back side of the back shroud of the impeller and the pump case, and that the thrust balance chamber is formed through a balance hole formed in the back shroud of the impeller. It communicates with the suction side of the impeller (the front side of the back shroud) to reduce the pressure difference that acts between the front and back surfaces of the impeller's back shroud, thereby suppressing the thrust force in the suction direction that acts on the rotor shaft. A thrust balance mechanism has been proposed.

Further, Patent Document 4 proposes a configuration in which a thrust balance disk is attached to the rotor shaft to suppress the thrust force acting on the rotor shaft to a small level.

Patent No. 5599463 Utility Model Publication No. 58-084394 Japanese Patent Application Publication No. 9-042190 Utility Model Publication No. 54-002204

However, the thrust balance mechanisms proposed in Patent Documents 2 and 3 are effective for single-stage centrifugal pumps, but not for multi-stage centrifugal pumps. In other words, in a multistage centrifugal pump, the discharge pressure of the previous stage impeller acts on the front side of the second and subsequent stage impellers, so it is not possible to properly adjust the thrust balance of the entire pump by simply forming a balance hole in the impeller. Have difficulty.

Furthermore, in the configuration proposed in Patent Document 4, a thrust balance disk is attached to the rotor shaft of the multistage centrifugal pump in addition to the plurality of impellers, which complicates the structure and reduces the axial length of the entire multistage centrifugal pump. There is a problem that the length increases and the pump itself becomes larger.

The present invention has been made in view of the above problems, and its purpose is to suppress the thrust force acting on the rotor shaft to a small level and increase the durability of the sliding bearing without complicating or increasing the size of the structure. The objective is to provide a two-stage centrifugal pump that can

In order to achieve the above object, the invention according to claim 1 includes a support shaft, a hollow rotor shaft rotatably held by the support shaft, and a cylindrical rotor shaft fixed to the outer periphery of an end of the rotor shaft. a stator disposed on the outer peripheral side of the rotor to generate a rotating magnetic field for rotating the rotor, a cover member having an inlet, a cylindrical portion having a partition wall, and the inlet. a case member having a bottomed cylindrical portion that opens on the side and houses the rotor, and partitions the rotor and the stator; two first and second impellers are mounted on the rotor shaft in the axial direction; the cover member and the case member are connected and integrated into two openings in the axial direction of the cylindrical portion in two pump chambers defined by the partition wall within the pump case; A two-stage centrifugal pump configured to house the first impeller and the second impeller, the inner part of the front shroud being disposed between the cover member and the front shroud of the first impeller facing thereto. A first labyrinth seal portion located on the periphery is provided, and a second labyrinth seal portion located on the outer periphery of the back shroud is provided between the case member and the back shroud of the second impeller facing thereto. , a first space within the cover member that faces the suction port closer to the axis than the first labyrinth seal; and a second space that faces the bottomed cylindrical part closer to the axis than the second labyrinth seal. A first feature is that a communication path is formed in the rotor shaft to communicate between the first space and the second space.

In the invention according to claim 2, in addition to the first feature, a third labyrinth seal portion is provided between the front shroud of the second impeller and the partition wall facing thereto, and The second feature is that the third space is formed closer to the axis than the third labyrinth seal portion.

In addition to the second feature, the third feature of the invention is that the partition wall is integrally resin-molded with the cylindrical portion.

The invention according to claim 4 is characterized in that, in addition to any one of the first to third features, a reservoir chamber having an internal volume of 80% or more of the volume of the rotor is configured in the bottomed cylindrical portion. is the fourth feature.

According to the invention described in claim 1, the first space faces the axial front side, which is the suction side, of the first impeller on the preceding stage side, and the second space faces the axial back side of the second impeller on the next stage side. Since the spaces are in communication with each other, the pressures in the first space and the second space are balanced and become approximately equal. On the other hand, the pressure of the liquid increased by the first impeller acts on the third space facing the axial rear side of the first impeller and the axial front side of the second impeller. In this case, the pressure of the pressurized liquid flowing into the third space is higher than the suction pressure acting on the first and second spaces. Therefore, the pressure difference that occurs between the front and rear surfaces of the first impeller during rotation of the same impeller (the front side of the first impeller <the rear side of the first impeller) and the rotation of the same impeller between the front and rear surfaces of the second impeller. The pressure difference (front side of the second impeller>back side of the second impeller) generated in the impeller is balanced. That is, the thrust force acting on the first impeller in the suction direction and the thrust force acting on the second impeller in the anti-suction direction are approximately equal, and the thrust forces acting on the rotor shaft are almost canceled out. Therefore, the load that the sliding bearing receives from the rotor shaft is reduced, the wear of the sliding bearing is suppressed, and the durability of the sliding bearing is increased. Since such effects can be obtained without providing a thrust balance disk on the rotor shaft, the structure of the two-stage centrifugal pump does not become complicated or large.

Moreover, since the first labyrinth seal prevents the fluid sent out from the first impeller from entering the first space, the discharge flow rate of the fluid increases and pump efficiency is improved.

According to the invention set forth in claim 2, in the second impeller, a third labyrinth seal portion is provided between the front shroud of the second impeller and the partition wall facing thereto, so that the front and rear surfaces of the front shroud are Almost the pressure of the third space acts on both. As a result, the thrust forces on the front shroud of the second impeller substantially cancel each other out, so that the thrust force in the direction opposite to the suction port is suppressed to be smaller than when the pressure of the second pump chamber acts on the front surface of the front shroud. Therefore, the thrust force transmitted from the second impeller to the rotor shaft in the opposite direction to the suction port can be calibrated and appropriately balanced with the thrust force transmitted from the first impeller to the rotor shaft in the direction toward the suction port. Therefore, the thrust force in the suction direction acting on the first impeller and the force in the anti-suction direction acting on the second impeller cancel each other out appropriately, and the difference between the two thrust forces acting as a thrust force from the rotor shaft on the sliding bearing is reduced. Minimized as much as possible. As a result, the load that the sliding bearing receives from the rotor shaft is reduced, and wear of the sliding bearing is suppressed.

Furthermore, the second and third labyrinth seals prevent the fluid pressurized by the second impeller from flowing into the second and third spaces, thereby increasing the discharge flow rate of the fluid and improving pump efficiency.

According to the invention set forth in claim 3, the partition wall of the pump case that faces the front shroud of the second impeller and constitutes the third labyrinth seal portion is integrally molded with resin together with the cylindrical portion, which simplifies the structure. Cost reduction can be achieved.

According to the invention set forth in claim 4, the volume of the second space into which relatively high-pressure fluid flows is expanded by the bottomed cylindrical portion that functions as a reservoir chamber, so that the volume of the second space is increased due to load fluctuations of the two-stage centrifugal pump. Fluctuations in the internal pressure of the rotor are suppressed, the pressures of the second space and the first space are appropriately balanced, and the thrust force acting on the rotor shaft is suppressed to a small level.

FIG. 1 is a longitudinal sectional view of a two-stage centrifugal pump according to the present invention. It is a figure which shows the guide vane member of the two-stage centrifugal pump based on this invention, Comprising: (a) is a top view, (b) is a side view, (c) is a bottom view. A schematic sectional view showing the basic configuration of the thrust balance mechanism section of the two-stage centrifugal pump according to the present invention, (b) is a comparison of the thrust force acting on the first impeller and the second impeller of the two-stage centrifugal pump with a conventional one. FIG.

Embodiments of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a longitudinal sectional view of a two-stage centrifugal pump according to the present invention, and FIG. 2 is a diagram showing a guide vane member of the two-stage centrifugal pump, in which (a) is a plan view, (b) is a side view, and ( c) is a bottom view.

A two-stage centrifugal pump 1 shown in FIG. 1 is a canned motor pump, in which a pump section P arranged vertically (in the axial direction) in FIG. 1 and a motor section M, which is a drive source, are connected along the same central axis. It has an integrated structure, and on its central axis there is a support shaft 6 and a hollow shaft rotatably held by the support shaft 6 for transmitting the rotational power exerted by the motor section M to the pump section P. A rotor shaft 3 is housed therein, and sliding bearings 7 and 8 are interposed between the rotor shaft 3 and the support shaft 6. Note that the two-stage centrifugal pump 1 according to the present embodiment is used in a state in which the pump part P and the motor part M are arranged vertically, that is, in a vertical position, but the pump part P and the motor part M are arranged horizontally. It can also be used in a horizontally placed position.

The pump section P includes a first stage first pump chamber R1 and a second pump chamber R2 formed in the pump case 2, which are arranged vertically in the upper half of the rotor shaft 3. The impeller 4, the second impeller 5 of the second stage, and the guide vane member 10 inserted between the first and second impellers 4 and 5 are respectively accommodated therein. In this embodiment, the pump case 2, the first and second impellers 4 and 5, and the guide vane member 10 are all made of resin.

The pump case 2 is configured by integrally connecting a cylindrical cylindrical portion 21 and a cover member 22 and a case member 23 that respectively cover two upper and lower openings of the cylindrical portion 21 in the axial direction. Here, from the axially intermediate portion of the inner circumferential wall of the cylindrical portion 21, a ring is formed into a disk shape and extends along the cross section of the cylindrical portion 21, while vertically defining the internal space of the cylindrical portion 21. A partition wall 21A is integrally provided, and a first pump chamber R1 and a second pump chamber R2 are defined in the pump case 2 by the partition wall 21A. A cylindrical discharge pipe (not shown) extends tangentially from the outer periphery of the cylindrical portion 21 and communicates with the second pump chamber R2. A circular hole 21a that communicates between the first pump chamber R1 and the second pump chamber R2 is formed on the central axis of the partition wall 21A, and the circular hole 21a communicates between the first pump chamber R1 and the second pump chamber R2. The rotor shaft 3 is inserted through. Further, a guide vane member 10 is placed on the first pump chamber R1 side of the partition wall 21A, and a center hole 10a coaxial with the circular hole 21a is formed in this guide vane member 10. The rotor shaft 3 and the support shaft 6 are inserted through the circular hole 21a, the center hole 10a, the first pump chamber R1, and the second pump chamber R2.

The cover member 22 has a cylindrical suction pipe 22A integrally erected at a portion corresponding to the central axis, and the upper end of the suction pipe 22A opens upward as a suction port 22a. A rectifying cone 22B is integrally formed at the center of the base end of the suction pipe 22A in the cover member 22, and a plurality of (two in the illustrated example) rectifying cones 22B are arranged around the rectifying cone 22B. A plate 22b is formed. The first impeller 4 has its outer periphery surrounded by the guide vane member 10, and is placed in the first pump chamber R1 above the cylindrical portion 21 with its suction side facing the base end of the suction pipe 22A. and is fixed to the rotor shaft 3. Further, the second impeller 5 is housed in the second pump chamber R2 on the lower side of the cylindrical portion 21 with its suction side facing the circular hole 21a on the lower surface side of the partition wall 21A, and is fixed to the rotor shaft 3. has been done.

The case member 23 includes a cup-shaped bottomed cylindrical portion 23A at its center, and a flange portion 23B is integrally formed radially outward from the upper end of the bottomed cylindrical portion 23A. . At the center of the bottom of the bottomed cylindrical portion 23A of the case member 23, a cylindrical boss portion 23a is integrally erected upward. Both ends of the support shaft 6 are fitted into each center of the rectifying cone 22B.

Further, between the rectifying cone 22B of the cover member 22 and the upper sliding bearing 7, a thrust washer 9 is held by a support shaft 6 so as not to rotate together with the thrust washer 9.

The motor unit M, which is a drive source, includes a motor case 11 connected from below the case member 23, and this motor case 11 has a cylindrical outer shell 11A and a lower opening of the outer shell 11A. It is configured by vertically connecting and integrating a bottomed cylindrical cover member 11B that covers from below. Here, the outer shell portion 11A is fluid-tightly connected to the lower surface of the flange portion 23B of the case member 23 via the ring-shaped seal member 12. Further, the upper end surface of the cover member 11B is fluid-tightly connected to the lower side of the outer shell portion 11A via a ring-shaped seal member 13.

The motor section M includes a cylindrical rotor 14 fixed to the lower half of the rotor shaft 3 and a stator 15 disposed opposite to the rotor 14 via the bottomed cylindrical section 23A of the case member 23. . Here, the rotor 14 is housed inside a bottomed cylindrical portion 23A provided in the case member 23 of the pump case 2, and is fixed to the outer periphery of the lower end portion of the rotor shaft 3. Note that the rotor 14 is composed of a permanent magnet.

The stator 15 has a three-phase coil 18 wound around a stator core 16 via an insulator 17, and the stator core 16 includes a yoke 16a formed in a cylindrical shape, for example, and an inner circumference of the yoke 16a. It integrally includes T-shaped teeth 16b that protrude radially inward from a plurality of locations equally spaced in the circumferential direction.

The insulator 17 covers the stator core 16 while exposing the inner peripheral side tip portions of the teeth 16b to face the outside of the bottomed cylindrical portion 23A. On the other hand, in this embodiment, the outer shell part 11A of the motor case 11 is molded from an electrically insulating resin material into which the insulator 17 is inserted, so that the stator 15 is at least partially surrounded by the outer shell part 11A. rare and fixed. Note that the three-phase coils 18 are electrically connected to control circuits formed on a control board 19, which will be described later.

Incidentally, a support leg 11a integrally extends from the lower surface of the outer shell 11A of the motor case 11 toward the inside of the cover member 11B. A control board 19 for controlling the support leg 11a is engaged with and supported by a snap-fit claw 11a1 formed at the lower end of the support leg 11a.

Next, details of the configuration of the guide vane member 10 will be explained below based on FIG. 2.

As described above, the center hole 10a is formed in the center of the guide vane member 10 placed on the first pump chamber R1 side of the partition wall 21A, and the rotor shaft 3 is inserted through the center hole 10a. ing. As shown in FIG. 2(a), six diffuser vanes (blade rows) 31 each having a triangular shape in a plan view are arranged on the outer circumferential portion of the upper surface of the guide vane member 10 in a posture facing the rotating circumferential surface of the first impeller 4. are integrally protruded at equal angular pitches (60 degree intervals) in the circumferential direction, and between two circumferentially adjacent diffuser vanes 31, the passage area gradually increases outward in the radial direction. Groove-shaped diffuser passages 32 are respectively formed that curve in the circumferential direction (rotation direction of the first impeller). That is, six diffuser passages 32, the same number as the diffuser vanes 31, are arranged at equal angular pitches (60 degree intervals in this embodiment) in the circumferential direction on the outer peripheral part of the upper surface of the guide vane member 10, and the outer peripheral ends of the six diffuser passages 32 are arranged on the upper surface of the guide vane member. The groove bottom of each diffuser passage 32 is divided into a shape that approaches the inner wall surface of the cylindrical portion 21 asymptotically as shown as a circumscribed circle C of It is formed in the shape of a helical winding with a lower height (the bottom of the groove approaches the partition wall 21A).

On the other hand, on the lower surface of the guide vane member 10 facing the partition wall 21A, as shown in FIG. (Blade rows) 33 are integrally protruded at equal angular pitches (60 degree intervals) in the circumferential direction. Six return passages 34, the same number as the number of return guide vanes 33, are defined between two return guide vanes 33 adjacent to each other in the circumferential direction.

Here, each of the six diffuser passages 32 and the return passage 34 communicate (communicate) in the first pump chamber R1, and the outer circumferential end of each return passage 34 intersects the diffuser passage 32 with the diffuser vane. 31 is partitioned to have a rectangular inlet 34a that opens downward, and an outlet 32a that is the outer peripheral end of each diffuser passage 32 opens adjacent to the inlet 34a of each return passage 34. ing. Therefore, each diffuser passage 32 and each return passage 34 communicate with each other via the outlet 32a and the inlet 34a.

By the way, the two-stage centrifugal pump 1 according to the present embodiment is equipped with a thrust balance mechanism for reducing the thrust force acting on the rotor shaft 3. The configuration of this thrust balance mechanism will be explained below based on FIGS. 1 and 3.

A ring-shaped first labyrinth seal L1 is provided between the inner circumferential portion of the front shroud 4a of the first impeller 4 on the front stage side and the inner surface of the cover member 22 opposing this, and the ring-shaped first labyrinth seal portion L1 In this case, a first space S1 is formed on the rotor shaft 3 side (axis center side) with respect to the first labyrinth seal portion L1.

Further, a ring-shaped second labyrinth seal portion L2 is provided between the outer peripheral portion of the back shroud 5b of the second impeller 5 on the next stage side and the flange portion 23B of the case member 23 facing thereto. In the pump case 2, a second space S2 is formed on the back side of the second impeller 5 on the rotor shaft 3 side (axis center side) with respect to the second labyrinth seal portion L2. Here, the second space S2 includes the bottomed cylindrical portion 23A of the case member 23, the second impeller 5 whose upper opening is substantially covered via the second labyrinth seal portion L2, and the bottomed cylindrical portion 23A. A cylindrical space surrounded by the rotor 14 housed on the bottom side of the section 23A, and in this embodiment, serves as a reservoir chamber having an internal volume that is at least 80% or more of the volume of the rotor 14. It is configured.

Further, a ring-shaped third labyrinth seal portion L3 is provided between the outer peripheral portion of the front shroud 5a of the second impeller 5 and the partition wall 21A facing thereto. Here, the third labyrinth seal portion L3 includes an aperture piece L3a that is annular in an axial view and protrudes from the front shroud 5a toward the partition wall 21A, and an aperture that is recessed in the partition wall 21A and surrounds the circumferential surface of the aperture change L3a. A third space S3 is formed within the pump case 2 on the rotor shaft 3 side (axial center side) with respect to the third labyrinth seal portion L3.

In the present embodiment, as shown in FIG. 1, a communication path 3a extends in the axial direction (vertical direction) of the rotor shaft 3 between the circumferential surface of the rotor shaft 3, the first impeller 4, and the second impeller 5. The upper end of this communication passage 3a opens into the first space S1, and the lower end of the communication passage 3a communicates with the second space S2. Therefore, the first space S1 and the second space S2 communicate with each other via the communication path 3a.

Thus, the thrust balance mechanism includes a first labyrinth seal L1 and a first space S1 formed inside it, a second labyrinth seal L2 and a second space S2 formed inside it, and a third labyrinth seal. It includes a portion L3 and a third space S3 formed inside the portion L3, and is configured by communicating the first space S1 and the second space S2 through a communication path 3a formed in the rotor shaft 3.

Next, the operation of the two-stage centrifugal pump 1 configured as described above will be explained.

Under the control of energization to each three-phase coil 18 of the stator 15, the rotor 14 and the rotor shaft 3 holding the rotor 14 are driven to rotate at a desired speed about the support shaft 6 by the magnetic field generated by the stator 15. Ru.

In the pump section P, a first impeller 4 and a second impeller 5 attached to the rotor shaft 3 rotate in a first pump chamber R1 and a second pump chamber R2 inside the pump case 2, respectively. Then, due to the rotation of the first impeller 4, negative pressure is generated in the suction pipe 22A formed in the cover member 22 of the pump case 2, and the handled liquid (cooling water) is drawn by this negative pressure and flows in the direction of the arrow in FIG. As shown in Figure 2, the air is sucked into the suction pipe 22A from the suction port 22a of the suction pipe 22A. The liquid sucked into the suction pipe 22A flows downward within the suction pipe 22A and is sucked into the first impeller 4 in the first stage.

The liquid sucked into the first impeller 4 is given kinetic energy from the rotating first impeller 4 and flows radially outward while being pressurized, and flows from the outer peripheral end of the first impeller 4 to the first pump chamber R1. and leaks out. A diffuser passage 32 defined by a plurality of (six in this embodiment) diffuser vanes 31 formed on the upper surface of the guide vane member 10 in the first pump chamber R1 is indicated by an arrow in FIG. 2(a). As shown, they flow radially outward, and proceed to the outlet ports 32a that open at the outer peripheral ends of each diffuser passage 32. Note that the liquid is decelerated and its pressure is further increased in the process of flowing through each diffuser passage 32, which curves while gradually increasing the passage cross-sectional area toward the outside in the radial direction of the guide vane member 10.

Thus, the liquid flows out from the outflow ports 32a opened at the outer peripheral opening end surface of each diffuser passage 32 from the inflow ports 34a opened adjacent to the outflow ports 32a to the six sections partitioned on the lower surface of the guide vane member 10. The water flows into each return passage 34, respectively.

Thereafter, the liquid that has flowed into each return passage 34 travels inward in the radial direction through each return passage 34, as shown by the arrow in FIG. 2(c), and as shown by the arrow in FIG. Then, it passes through a circular hole 21a formed in the center of the partition wall 21A and is guided to the suction side of the second impeller 5 in the second stage facing the circular hole 21a. The liquid guided to the suction side of the second impeller 5 flows radially outward while being given kinetic energy by the rotation of the second impeller 5, and flows from the outer peripheral end of the second impeller 5 to the second pump. While flowing out into the chamber R2, the pressure is further increased while being decelerated in the process of flowing through the volute portion formed in the second pump chamber S2. The liquid pressurized through the first impeller 4 and the second impeller 5 flows tangentially from the second pump chamber R2 to a discharge pipe (not shown), and is discharged from the discharge pipe to the outside of the pump case 2. Ru.

Next, the operation of the thrust balance mechanism will be explained below with reference to FIG.

As described above, from inside the first space S1 to the back surface of the front shroud 4a (that is, inside the first impeller 4), the liquid before being pressurized, which has been sucked into the suction pipe 22A, exists. In addition, since the first space S1 and the second space S2 communicate with each other via the communication passage 3a formed in the rotor shaft 3, the pressure-increasing air sucked into the suction pipe 22A is also connected to the second space S2. liquid exists.

The liquid accelerated by the first impeller 4 and flowing out into the first pump chamber R1 is introduced into the suction side (third space S3) of the second impeller 5 while being pressurized in the guide vane member 10. A portion of this pressurized liquid also enters the gap (the front surface of the front shroud 4a) located above the front shroud 4a in FIG. 3(a). However, a portion of the pressurized liquid is dammed by the first labyrinth seal portion L1 formed between the inner peripheral portion of the front shroud 4a and the inner surface of the cover member 22 facing thereto. It remains almost at the upper surface of the front shroud 4a.

The liquid introduced into the third space S3 advances from there into the second impeller 5, and is led out to the second pump chamber R2 while being re-accelerated by the second impeller 5. Since it is dammed by the labyrinth seal portion L2 and the third labyrinth seal portion L3, liquid is prevented from entering the gap above the front shroud 5a and below the back shroud 5b from the second pump chamber R2. Therefore, the liquid introduced into the third space S3 almost stays in the gap above the front shroud 5a, and the liquid introduced into the second space S2 almost stays in the gap below the back shroud 5b. do.

Here, in the first impeller 4, the liquid pressure p3 of the third space S3, which is increased in pressure by the guide vane member 10, acts on the front surface (upper surface) of the front shroud 4a, and the back surface of the front shroud 4a (first impeller 4 The liquid pressure p1 before the pressure increase in the first space S1 acts on the inside of the first space S1. Further, the liquid pressure p1 of the first space S1 acts on the front surface (upper surface) of the rear shroud 4b facing the first space S1, and the liquid pressure p1 of the rear shroud 4b acts on the rear surface (lower surface) of the rear shroud 4b facing the third space S3. A liquid pressure p3 of . Here, since the liquid pressure p3 in the third space S3 is higher than the liquid pressure p1 in the first space S1 (p3>p1), in a conventional two-stage centrifugal pump without a thrust balance mechanism, As shown in the left column of b), a relatively large thrust force F1' directed upward (in the direction of the suction port) acts on the first impeller 4 in FIG. On the other hand, in the two-stage centrifugal pump 1 according to the present invention equipped with a thrust balance mechanism, a downward thrust force F1down (in the direction opposite to the suction port) acts on the front shroud 4a in FIG. In FIG. 3, an upward thrust force F1up (in the direction of the suction port) is acting on the shroud 4b. As shown in the right column of FIG. 3(b), a thrust force F1 (<F1') in the direction of the suction port is applied to the first impeller 4 by combining these thrust forces F1up and F1down, which act in opposite directions. do. In other words, in the two-stage centrifugal pump 1 according to the present invention, in the first impeller 4, the thrust force F1' in the suction port direction, which has conventionally been generated on the back surface of the back shroud 4b, is reduced to the first labyrinth seal portion, which is a thrust balance mechanism. It is canceled out by the downward thrust force F1down generated on the front surface of the front shroud 4a to which L1 is added, and is reduced to F1 (<F1').

On the other hand, in the second impeller 5, in a two-stage centrifugal pump not equipped with a thrust balance mechanism, the volute of the second pump chamber R2 is connected from the outer peripheral end of the second impeller 5 to the back surface of the back shroud 5b of the second impeller 5. The liquid pressure p4 (not shown) that has flowed out into the volute section acts, but as mentioned above, the liquid pressure p4 increased in the volute section is equal to the pressure p2 in the second space S2 and the pressure in the third space S3 before the pressure increase. Since it is even higher than p3 (p4>p3>p2), a relatively large upward thrust force F2' (in the direction of the suction port) acts in Fig. 3, as shown in the left column of Fig. 3(b). On the other hand, in the two-stage centrifugal pump 1 according to the present invention, which is equipped with the second labyrinth seal part L2, the third labyrinth seal part L3, and the communication passage 3a, which are thrust balance mechanisms, the front surface of the front shroud 5a ( The liquid pressure p3 of the third space S3 acts on the rear surface of the front shroud 5a (that is, the inside of the second impeller 5), and the lower surface of the rear shroud 5b (the second impeller 5). The liquid pressure p2 of the second space S2 acts on the outside and lower surface of the second space S2. As described above, since the liquid pressure p3 in the third space S3 increased by the guide vane member 10 is higher than the pressure p2 in the second space S2 before pressure increase (p3>p2), the front surface of the second impeller 5 The thrust force on the shroud 5a is almost canceled out on the front and back surfaces, and a thrust force F2 in the direction opposite to the suction port (downward in FIG. 3) acts on the rear shroud 5b.

Therefore, the contradictory thrust forces F1 and F2 act together on the rotor shaft 3 of the two-stage centrifugal pump 1 according to the present embodiment. In other words, in the two-stage centrifugal pump 1 according to the present invention, in the rotor shaft 3, the thrust force F1 remaining in the first impeller 4 toward the suction port is offset by the downward thrust force F2 generated by the second impeller 5. has been done. Therefore, the load that the sliding bearings 7, 8 receive from the rotor shaft 3 is reduced, the wear of the sliding bearings 7, 8 is suppressed, and the durability of these sliding bearings 7, 8 is increased. Since such effects can be obtained without providing a thrust balance disk on the rotor shaft 3, the structure of the two-stage centrifugal pump 1 does not become complicated or enlarged.

In addition, the first labyrinth seal portion L1 prevents the fluid pressurized by the first impeller 4 from entering the first space S1, and the fluid pressurized by the second impeller 5 is prevented from flowing into the second space S2 and the third space S3. Since the second labyrinth seal portion L2 and the third labyrinth seal portion L3 prevent the liquid from flowing around the liquid, the discharge flow rate of the liquid increases and the pumping efficiency of the two-stage pump 1 is increased.

In the present embodiment, the first space S1 and the second space S2 can be communicated with each other by a simple configuration of just forming the axial communication path 3a in the rotor shaft 3 without requiring any additional parts. Therefore, it is possible to simplify the structure and reduce the cost of the two-stage centrifugal pump 1.

Furthermore, in the two-stage centrifugal pump 1 according to the present embodiment, the volume of the second space S2 into which relatively high-pressure fluid flows is set to be relatively large, and the second space S2 functions as a reservoir chamber. That is, the reservoir chamber, which communicates with the suction port 22a and is set to have a relatively large volume, absorbs the flow of liquid pressurized by the second impeller 5 that leaks beyond the second labyrinth seal portion L2 into the second space S2. Since the associated pressure change is small, fluctuations in the liquid pressure p2 in the second space S2 are suppressed, and the thrust force F2 related to the liquid pressure p2 can be applied smoothly.

In the above embodiments, an example in which the present invention is applied to a two-stage water pump that uses coolant as the handling liquid has been described, but the present invention also applies to a two-stage water pump that uses cooling liquid as the handling liquid. The same applies to the two-stage centrifugal pump used.

Further, in the embodiment, an example has been described in which the third labyrinth seal portion L3 is formed on the outer peripheral portion of the front shroud 5a of the second impeller 5, but the present invention is not limited to this. For example, the third labyrinth seal portion L3 can be formed at the radially intermediate portion of the front shroud 5a of the second impeller 5, or at the inner peripheral portion of the front shroud 5a. As a result, the magnitude of the thrust force F2 acting in the direction opposite to the suction port can be adjusted, so that the thrust force F1 of the first impeller 4 and the thrust force F2 of the second impeller 5 are appropriately offset, and the sliding bearing The thrust force acting on 7 can be kept as small as possible.

In addition, the application of the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the technical ideas described in the claims, specification, and drawings. Of course.

1 Two-stage centrifugal pump 2 Pump case 21 Cylindrical part 21A Partition wall 22 Cover member 22a Inlet 23 Case member 23A Bottomed cylindrical part (reservoir chamber)
3 Rotor shaft 3a Communication path of rotor shaft 4 First impeller 4a Front shroud of the first impeller 5 Second impeller 5a Front shroud of the second impeller 5b Back shroud of the second impeller 6 Support shaft 10 Guide vane member 14 Rotor 15 Stator L1 First labyrinth seal part L2 Second labyrinth seal part L3 Third labyrinth seal part M Motor part (drive source)
P Pump part R1 First pump chamber R2 Second pump chamber S1 First space S2 Second space S3 Third space

Claims (4)

A support shaft (6),
a hollow rotor shaft (3) rotatably held by the support shaft (6);
a cylindrical rotor (14) fixed to the outer periphery of the end of the rotor shaft (3);
a stator (15) that is disposed on the outer peripheral side of the rotor (14) and generates a rotating magnetic field for rotating the rotor (14);
a cover member (22) having an inlet (22a);
a cylindrical tubular portion (21) having a partition wall (21A);
A case member (23) that partitions the rotor (14) and the stator (15) by having a bottomed cylindrical portion (23A) that opens toward the suction port (22a) and accommodates the rotor (14). ) and
Two first and second impellers (4, 5) are attached to the rotor shaft (3) along the axial direction, and the cover member (22) is attached to the two openings in the axial direction of the cylindrical portion (21). The first impeller (4) is placed in two pump chambers (R1, R2) defined by the partition wall (21A) within a pump case (2) configured by connecting and integrating the case member (23). ) and the second impeller (5), the two-stage centrifugal pump (1) comprising:
A first labyrinth seal portion (L1) located at an inner peripheral portion of the front shroud (4a) between the cover member (22) and the front shroud (4a) of the first impeller (4) facing thereto. In addition to establishing
A second labyrinth seal portion (L2) located on the outer periphery of the back shroud (5b) is provided between the case member (23) and the back shroud (5b) of the second impeller (5) facing thereto. established,
A first space (S1) facing the suction port (22a) on the axial center side of the first labyrinth seal part (L1) in the cover member (22), and a first space (S1) facing the suction port (22a) further than the second labyrinth seal part (L2). a communication passage (S2) forming a second space (S2) facing the bottomed cylindrical portion (23A) on the axis side, and communicating between the first space (S1) and the second space (S2); 3a) is formed on the rotor shaft (3). A third labyrinth seal part (L3) is provided between the front shroud (5a) of the second impeller (5) and the partition wall (21A) facing thereto, and the third labyrinth seal part (L3) is provided in the pump case (2). The two-stage centrifugal pump according to claim 1, characterized in that a third space (S3) is formed closer to the axis than the seal portion (L3). The two-stage centrifugal pump according to claim 2, characterized in that the partition wall (21A) is integrally molded with resin together with the cylindrical portion (21). The two-stage centrifuge according to any one of claims 1 to 3, characterized in that the bottomed cylindrical portion (23A) is configured with a reservoir chamber having an internal volume of 80% or more of the volume of the rotor (14). pump.