JP7461781B2 - Expeller for centrifugal pump and centrifugal pump equipped with same - Google Patents

Description

The present invention relates to a centrifugal pump that transports various liquids (transported fluids) such as fresh water, sludge liquid, pulp liquid, slurry liquid containing fine particles, sand, etc., and in particular to a centrifugal pump that has an expeller that is placed in the space defined between the back surface of the casing and the shaft seal of the rotating shaft.

6, this type of centrifugal pump includes a casing 1 with a suction front surface, an impeller 2 provided within the casing 1, and a shaft 3 for rotating the impeller 2. The impeller 2 has a plurality of blades 4a provided on its front surface and a plurality of rear blades 4b provided on its rear surface (see, for example, Patent Document 1).
A shaft seal device 105 is provided on the back side of the casing 1. In the shaft seal device 105, an expeller 110 (auxiliary impeller) is disposed in a defined space 105a between the back side of the casing 1 and a shaft seal portion 105s of the shaft 3. The expeller 110 is coaxially attached to a position on the back side of the impeller 2 and rotates integrally with the shaft 3.

In the example shown in the figure, the shaft seal device 105 includes a stuffing box 5b formed on the rear side of the expeller 110 so as to surround the outer periphery of the sleeve 6 of the shaft 3. The inner surface of the stuffing box 5b is provided with a shaft seal portion 105s having a plurality of seals 105t made of elastomer or the like.
7, the expeller 110 has a cylindrical boss portion 111 provided at the center, and a disk portion 112 that protrudes radially from the outer circumferential surface of the boss portion 111 and has a smooth surface on its front surface. A plurality of blades 113 are provided on the rear surface of the disk portion 112. Here, in this specification, the suction side of the casing of the impeller and the expeller will be referred to as the "front surface" and the drive side as the "rear surface", respectively.

In this type of centrifugal pump, when the shaft 3 rotates, the sleeve 6, impeller 2, and expeller 110 rotate together. During pump operation, suction pressure acts on the suction side of the casing 1, and pump pressure acts on the outer periphery of the impeller 2 as the blades 4b on the front side of the impeller 2 rotate. In addition, if there is a rear blade 4b on the rear side of the impeller 2, centrifugal force is applied to the liquid around it as the rear blade 4b rotates. This results in a reduction in the pump pressure.

Meanwhile, the expeller 100, which is arranged in the defined space 105a in front of the shaft seal device 105, applies centrifugal force to the liquid at the back of the expeller due to the rotation of its own blades 113, causing a reduction in pressure relative to the pressure at the front of the expeller. Due to this reduction in pressure caused by the expeller 110, an interface between the liquid and air is formed at the back of the expeller 110 during pump operation, thereby preventing or suppressing the movement of the pumped fluid to the shaft seal section 105s side in the stuffing box 105b behind the expeller 110.

JP 2009-115088 A

Here, a swirling flow occurs with the rotation of the expeller 110, and as shown in the image of the flow in Figure 8, the flow of the transported fluid is faster the closer it is to the wall of the disk section 112, and the centrifugal force increases toward the outer periphery of the disk section 112, increasing the radial velocity component of the transported fluid. In the figure, the image of the flow speed of the transported fluid is shown by a triangle shape and the length of the arrow inside it.

Therefore, when the fluid being pumped is a slurry liquid (a muddy liquid containing solid particles), if the outer diameter of the expeller 110 is increased to improve the pressure reduction effect of the expeller 110 in order to improve the sealing performance of the shaft seal device 105, the associated centrifugal force increases, and the amount of particles and solids contained in the slurry liquid that move to the shaft seal section 105s of the stuffing box 105b on the back side of the expeller also increases, resulting in a trade-off problem in that the particles and solids contained in the slurry liquid tend to accumulate in the shaft seal section 105s.

The present invention has been made with a focus on these problems, and aims to provide an expeller for a centrifugal pump, and a centrifugal pump equipped with the same, that can maintain or improve the shaft sealing performance even when the liquid is a slurry liquid, and can reduce the amount of slurry that moves from the outer periphery of the expeller to the shaft seal portion.

In order to solve the above problems, the centrifugal pump expeller according to one aspect of the present invention is used in a centrifugal pump having a casing in which the axial front surface of a rotating shaft is the suction side and an impeller that rotates with the rotating shaft is housed inside, and is disposed in a defined space between the back surface of the casing and the shaft seal of the rotating shaft, and is characterized in that it comprises a cylindrical boss portion provided coaxially with the rotating shaft, a disk portion that protrudes radially from the outer circumferential surface of the boss portion and has a smooth surface on its front surface, and a plurality of blades provided on the back surface of the disk portion, and the wall surface of the disk portion facing the front surface has one or more annular protrusions that are provided coaxially with the rotating shaft and protrude to the front surface side.

In order to solve the above problem, a centrifugal pump according to one aspect of the present invention is a centrifugal pump comprising a casing with a suction front face, an impeller provided within the casing, a rotating shaft for rotating the impeller, and an expeller arranged coaxially with the rotating shaft and in a space defined between the rear face of the casing and a shaft seal of the rotating shaft, characterized in that the expeller is an expeller for a centrifugal pump according to one aspect of the present invention.

In a centrifugal pump according to one embodiment of the present invention, the wall surface facing the front side of the disk portion of the expeller has one or more annular convex portions arranged coaxially with the rotation axis and protruding toward the front side, so that the annular convex portions regulate the swirling flow that occurs as the expeller rotates, thereby preventing or suppressing the movement of slurry riding on the radial velocity component of the expeller toward the outer periphery of the expeller and even toward the shaft seal portion.
That is, in the centrifugal pump according to one aspect of the present invention, the annular convex portion provided on the front wall surface of the disk portion of the expeller functions as a "slurry return." Therefore, the "slurry return" changes the direction of the swirling flow, thereby reducing the amount of slurry that moves from the outer periphery of the expeller to the rear shaft seal portion. As a result, the seal can have a longer life and wear on the liquid-contacting surface of the shaft seal device can be suppressed.

As described above, the present invention provides an expeller for a centrifugal pump and a centrifugal pump equipped therewith that can maintain or improve shaft sealing performance and reduce the amount of slurry that moves from the outer periphery of the expeller to the shaft seal side, even when the liquid is a slurry liquid.

FIG. 1 is a schematic longitudinal cross-sectional view illustrating an embodiment of a centrifugal pump equipped with an expeller according to an aspect of the present invention, the cross-section being taken along an axis line. 1A to 1C are diagrams illustrating an embodiment of an expeller according to one aspect of the present invention, in which FIG. 1A is a front view, FIG. 1B is a longitudinal sectional view, and FIG. 1C is a rear view. FIG. 2 is an enlarged view of a main part of FIG. 1 . This is a cross-sectional view taken along the line ZZ in FIG. FIG. 2 is an enlarged view of a main part of FIG. 1 . FIG. 1 is a schematic vertical cross-sectional view illustrating an example of a conventional centrifugal pump equipped with an expeller, and shows a cross section along the axis. 1A to 1C are diagrams illustrating an example of a conventional expeller, in which FIG. 1A is a front view, FIG. 1B is a longitudinal sectional view, and FIG. 1C is a rear view. 6A and 6B are diagrams for explaining the flow of the pumped fluid around a conventional expeller, in which FIG. 6A is an enlarged view of the essential parts of the conventional expeller as viewed from the front, and FIG. 6B is an enlarged view of the essential parts of the conventional expeller in FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the drawings are schematic. Therefore, it should be noted that the relationship and ratio between thickness and planar dimensions are different from the actual ones, and the drawings include parts where the relationship and ratio of dimensions are different from each other.
The embodiments described below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the materials, shapes, structures, arrangements, etc. of the components. The same reference numerals are used to denote components that are the same as or correspond to those of the centrifugal pump described above.

As shown in FIG. 1, the centrifugal pump of this embodiment includes a casing 1, an impeller 2 provided within the casing 1, and a shaft 3 that is a rotating shaft for rotating the impeller 2. The impeller 2 has multiple blades 4a on its front surface and multiple rear blades 4b on its rear surface.

The casing 1 has a suction side at its front side in the axial direction of the shaft 3, and a shaft seal device 5 is provided on the back side of the casing 1. The shaft seal device 5 has an expeller 10 disposed in a defined space 5a at the back side of the casing 1, and further has a stuffing box 5b formed on the back side of the expeller 10 so as to surround the outer periphery of a sleeve 6 attached to the shaft 3.
A shaft seal portion 5s having a plurality of seals 5t made of elastomer or the like is disposed on the inner surface of the stuffing box 5b. The shaft seal portion 5s has a plurality of seals 5t, and the lip tip of each seal 5t that protrudes to the inner periphery is in sliding contact with the outer periphery of the shaft 3.

2, the expeller 10 of this embodiment has a cylindrical boss portion 11 provided at the center coaxially with the shaft 3, and a disk portion 12 that protrudes radially from the outer circumferential surface of the boss portion 11 and has a smooth surface on its front surface. A plurality of blades 13 are provided on the rear surface of the disk portion 12.
Furthermore, the expeller 10 of this embodiment is provided with an annular convex portion 14, which is arranged coaxially with the shaft 3 and protrudes axially forward, on the front wall surface of the disk portion 12. This annular convex portion 14 functions as a "slurry return" as described later.

As long as it is arranged coaxially with the shaft 3, the radial formation position of the annular convex portion 14 is not particularly limited, but in an example of this embodiment, as a suitable shape for the annular convex portion 14 as a "slurry return", as shown in Figure 3, the annular convex portion 14 is formed at the position of the outer peripheral end of the front wall surface of the disk portion 12, and the outer diameter surface of the annular convex portion 14 is flush with the outer diameter surface of the disk portion 12 of the expeller 10 (φd1 = φD).
In addition, the axial height H and radial thickness W of the annular convex portion 14 are not particularly limited, but as a suitable shape for the annular convex portion 14 as a “slurry return,” in FIG. 3 , it is preferable that the axial height H of the annular convex portion 14 be 1 mm or more (H≧1 mm).

However, the axial height H of the annular projection 14 is effective in providing a slurry returning function even if it has even a small protrusion with respect to the end face of the disk portion 12 .
Moreover, it is preferable that the axial gap C between the tip of the annular protrusion 14 and the opposing surface of the inner wall of the casing 1 is larger than the impeller clearance L (C>L). The impeller clearance L is the axial gap between the liquid-contacting surface on the front side of the casing 1 and the leading edge of the main blade 3 of the impeller 2.

Next, the operation and effects of the centrifugal pump of this embodiment will be described.
1, when the shaft 3 rotates, the impeller 2, the expeller 10, and the sleeve 6 rotate together. By rotating the impeller 2, the pumped fluid is pressurized, and the pumped fluid can be transferred from the suction side 1in to the discharge side 1out of the casing 1.
In addition, the expeller 10 rotates with the rotation of the shaft 3, reducing the pressure on the back side of the impeller 2 and preventing the pumped fluid from leaking to the outside through the shaft seal portion 5s in the stuffing box 5b.

In other words, when the impeller 2 pressurizes and transports the fluid being transported, in the shaft seal device 5, the rotation of the expeller 10 arranged in the defined space 5a on the front side of the shaft seal device 5 reduces the back pressure, thereby preventing the fluid being transported from leaking to the outside through the shaft seal section 5s.
Here, a swirling flow of the fluid being pumped occurs in conjunction with the rotation of the expeller 10. As described above, the closer this swirling flow is to the wall surface of the disk portion 12, the faster it flows. Also, as it goes toward the outer periphery of the disk portion 12, the greater the centrifugal force becomes, and the radial velocity component increases.
Therefore, if the liquid is a slurry liquid (a muddy liquid containing solid particles), there is a risk that the slurry will be carried by the radial velocity component and pass over the outer periphery of the expeller 10, reaching the rear shaft seal section 5s, making it easier for the particles and solids contained in the slurry liquid to accumulate in the shaft seal section 5s.

In contrast, the expeller 10 of this embodiment has a circular annular protrusion 14 on the front wall surface of the disk portion 12 so as to protrude axially forward and coaxially with the shaft 3, and this annular protrusion 14 functions as a "slurry return."
5, the "slurry return" by the annular convex portion 14 changes the direction of the swirling flow, thereby reducing the amount of slurry that moves from the outer periphery of the disk portion 12 to the shaft seal portion 5s of the shaft seal device 5. As an effect of the "slurry return", the life of the seal 5t can be extended, and wear on the liquid-contacting surface of the shaft seal device 5 can be suppressed.

In particular, according to this embodiment, an annular protrusion 14 that protrudes axially forward and is coaxial with the shaft 3 is provided on the front wall surface of the disk portion 12 of the expeller 10 to function as a "slurry return." The "slurry return" function of this annular protrusion 14 changes the direction of the swirling flow, thereby reducing the amount of slurry that rides on the radial velocity component and exceeds the outer periphery of the expeller 10, and further reduces the amount of slurry that moves toward the seal side.

This makes it possible to extend the life of the sealing function of the shaft seal portion 5s of the shaft seal device 5 and also suppress wear on the inner wall surfaces of each part of the shaft seal device 5. Such a configuration is preferable in preventing particles and solids contained in the slurry liquid from accumulating on the elastomer seal 5t in the slurry pump.
The centrifugal pump according to the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit and scope of the present invention.

3, the annular protrusions serving as "slurry return" can be provided in multiple stages in a concentric manner spaced apart in the radial direction of the disk portion 12. In other words, the number of annular protrusions 14 is at least one, which functions as a "slurry return", but they may be formed in multiple locations in a concentric manner spaced apart in the radial direction of the expeller.
3, a second annular convex portion 14B may be provided at a position closer to the inner circumference than the end annular convex portion 14. In this case, the outer diameter φD of the expeller may be set as the maximum outer diameter, and a multi-stage structure may be provided in which a plurality of "slurry return holes" are provided on the inside with a diameter smaller than the outer diameter φD of the expeller (in the example shown in the figure, φD>φd1>φd2).

Also, for example, as shown in Figure 4, it is preferable to form baffle plates 1j radially along the diameter direction on the back surface of the casing 1 facing the expeller 10 to suppress the circumferential flow of the swirling flow caused by the expeller 10 (in the example shown in the same figure, eight baffle plates 1j are formed radially).
However, it should be avoided to form a concave or convex shape along the circumferential direction on the back surface of the casing 1, which would result in a labyrinth shape as indicated by the symbol L in dashed lines in Fig. 3. On the other hand, except for the annular convex portion 14 that serves as a "slurry return," it is preferable that the surface of the disk portion 12 facing the back surface of the casing 1 is a flat surface.

In other words, the technical idea of "slurry return" by the annular convex portion 14 is different from the labyrinth mechanism, and it is desirable that the opposing surface of the casing 1 with the annular convex portion 14, which serves as the "slurry return", be shaped so as not to hinder the movement of the slurry returned by the "slurry return" function of the annular convex portion 14 in the inward radial direction.
For this reason, a labyrinth mechanism is not formed by providing a shape such as an annular protrusion or annular groove that restricts the movement of fluid in the radial direction on the back surface of the casing 1. This is because there is a concern that clogging problems may occur due to accumulation of slurry in the labyrinth mechanism.

1 Casing 2 Impeller
3 Shaft (rotating axis)
4a Blade 4b Back blade 5 Shaft seal device 5a Definition space 5b Stuffing box 5s Shaft seal portion 5t Seal 6 Sleeve 10 Expeller 11 Boss portion 12 Disk portion 13 Blade 14 Annular convex portion 14B Second annular convex portion L Impeller clearance W Radial thickness of annular convex portion C Axial gap H Axial height of annular convex portion B Axial thickness of disk portion φd1 Outer diameter of first annular convex portion φd2 Outer diameter of second annular convex portion φD Outer diameter of expeller

Claims (3)

An expeller is used in a centrifugal pump having a casing in which a front surface in the axial direction of a rotating shaft is a suction side and an impeller rotated by the rotating shaft is housed inside the casing, the expeller being disposed in a space defined between a back surface of the casing and a shaft seal portion of the rotating shaft,
a cylindrical boss portion provided coaxially with the rotating shaft, a disk portion protruding radially from an outer circumferential surface of the boss portion and having a smooth surface on its front surface, and a plurality of blades provided on a rear surface of the disk portion,
a wall surface of the disk portion facing the front side, the wall surface having one or more annular protrusions that are provided coaxially with the rotation shaft , axially face the rear surface of the casing in the defined space, and protrude axially toward the front side ;
An expeller for a centrifugal pump, characterized in that at least one of the one or more annular convex portions is formed at the outer peripheral end position of the disk portion, and the outer diameter surface of the annular convex portion is a cylindrical surface that is flush with the outer diameter surface of the disk portion. 2. The centrifugal pump expeller according to claim 1 , wherein the annular protrusions are provided at a plurality of positions spaced apart in a radial direction of the disk portion. A centrifugal pump comprising: a casing having a suction front surface; an impeller provided within the casing; a rotating shaft for rotating the impeller; and an expeller arranged coaxially with the rotating shaft and in a space defined between a rear surface of the casing and a shaft seal of the rotating shaft,
A centrifugal pump comprising the expeller for a centrifugal pump according to claim 1 or 2 as the expeller.

Images