JP6948198B2 - Centrifugal pump - Google Patents

Description

The present invention relates to a centrifugal pump, particularly to a centrifugal pump provided with a single-stage impeller or a multi-stage impeller.

The centrifugal pump applies centrifugal force to the liquid by rotating the impeller and boosts the liquid. Most of the boosted liquid flows into the impeller of the next stage or is discharged from the discharge port, but a part of the boosted liquid flows into the back side of the main plate and the back side of the shroud of the impeller. Since there is a difference in the area where the impeller receives the pressure of the liquid between the back side of the main plate of the impeller and the back side of the shroud, an axial thrust that pushes the impeller toward the suction side is generated.

Since the impeller receives such axial thrust, the rotating shaft to which the impeller is fixed is supported by a high thrust bearing capable of receiving a large axial thrust, or by an additional thrust bearing. .. However, axial thrust accelerates bearing wear and shortens bearing life. In particular, in a multi-stage centrifugal pump, a large axial thrust is generated, so that the life of the bearing tends to be shortened.

Therefore, some techniques for reducing the axial thrust have been conventionally proposed. For example, there is a technique of providing a plurality of balance holes on the main plate of an impeller. The liquid that has flowed into the back side of the main plate of the impeller flows into the impeller through the balance hole. As a result, the pressure of the liquid acting on the main plate of the impeller is reduced, and the axial thrust is reduced.

Japanese Unexamined Patent Publication No. 2000-9081

However, since the balance hole returns a part of the liquid boosted by the impeller to the suction side, the pump efficiency is lowered. Therefore, in order to reduce the axial thrust without lowering the pump efficiency, a double liner structure as shown in FIG. 8 may be adopted. This double liner structure includes a first liner ring 104 arranged around the liquid inlet 101 of the impeller 100, and a second liner ring 105 arranged on the back surface side (main plate side) of the impeller 100. The first liner ring 104 is arranged through a minute gap with the liquid inlet 101 formed in the shroud 110 of the impeller 100, and the second liner ring 105 is formed in the main plate (discharge side plate member) 111 of the impeller 100. It is arranged via a minute gap with the ring portion 112 formed. The balance hole 115 is formed in the main plate 111, and is located inside the second liner ring 105 in the radial direction.

The second liner ring 105 arranged at such a position can reduce the amount of the liquid boosted by the impeller 100 reaching the balance hole 115. As a result, the amount of liquid returning into the impeller 100 through the balance hole 115 can be reduced.

However, since the second liner ring 105 gradually wears with the operating time of the pump, it is necessary to replace the second liner ring 105 regularly. Further, in the multi-stage centrifugal pump, since the return blade 120 is arranged on the discharge side of each impeller 100, there may be no space large enough to arrange the second liner ring 105.

Therefore, an object of the present invention is to provide a centrifugal pump capable of reducing the axial thrust with a simple configuration without lowering the pump efficiency.

One aspect of the present invention is a centrifuge including a rotating shaft, an impeller fixed to the rotating shaft, a casing accommodating the impeller, and a liner ring arranged around a liquid inlet of the impeller. A pump, the impeller has a main plate fixed to the rotating shaft, a shroud having the liquid inlet and facing the main plate, and a plurality of blades arranged between the main plate and the shroud. A balance hole is formed in the main plate, and when the impeller is viewed from its suction side, the balance hole is located radially inside the liquid inlet, and the main plate is provided. A plurality of trim edges recessed inward in the radial direction are formed on the outer peripheral portion of the wing, and the outer portion of the wing is located between two adjacent two of the plurality of trim edges. The pump is a single liner type centrifugal pump having the liner ring only on the shroud side of the impeller.

A preferred embodiment of the present invention is characterized in that the diameter of the main plate is the same as or smaller than the diameter of the shroud.
A preferred embodiment of the present invention is characterized in that a plurality of the impellers are provided, and the plurality of impellers are fixed to the rotating shaft.
In a preferred embodiment of the present invention, the main plate has a through hole through which the rotating shaft penetrates, and the through hole has a shape different from the cross-sectional shape of the rotating shaft. A plurality of gaps are formed with the outer surface of the rotating shaft, and the balance hole is characterized in that it is composed of at least one of the plurality of gaps.
In a preferred embodiment of the present invention, the rotating shaft has splines on its surface, the main plate has a plurality of keyways having a shape in which the splines are engaged, and the balance hole is formed by the balance hole. It is characterized in that it is composed of a part of the plurality of keyways.
A preferred embodiment of the present invention is characterized in that each of the impeller and the casing is an assembly of a pressed metal plate.

Fluid simulations have demonstrated that impellers with a main plate with trimmed edges significantly reduce the pressure of the liquid applied to the main plate, without reducing pump efficiency, compared to common impellers. The lower the pressure of the liquid applied to the main plate of the impeller, the lower the axial thrust and the lower the amount of liquid passing through the balance hole. Therefore, according to the present invention, it is possible to reduce the axial thrust without providing the second liner ring shown in FIG. 8 and without lowering the pump efficiency.

It is sectional drawing which shows one Embodiment of a centrifugal pump. It is an enlarged cross-sectional view which shows a part of the centrifugal pump shown in FIG. It is the figure which looked at the impeller from the suction side. It is the figure which looked at the impeller from the discharge side. It is a schematic diagram which shows the distribution of the pressure of the liquid applied to the main plate when the liquid is boosted by the rotation of the impeller shown in FIGS. 3 and 4. It is a schematic diagram which shows the distribution of the pressure of the liquid applied to the main plate when the liquid is boosted by the rotation of the conventional impeller shown in FIG. FIG. 7A is a view of the impeller according to another embodiment as viewed from the discharge side thereof, and FIG. 7B is a cross-sectional view showing another embodiment of the rotating shaft. It is sectional drawing which shows the conventional centrifugal pump of a double liner type.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an embodiment of a centrifugal pump.
The centrifugal pump includes a rotary shaft 1, a plurality of impellers 5 fixed to the rotary shaft 1, and a casing 7 in which the impeller 5 is housed. The rotating shaft 1 is connected to the electric motor 8. When the rotating shaft 1 is rotated by the electric motor 8, the impeller 5 is rotated together with the rotating shaft 1.

The casing 7 includes an inner casing 7A and an outer casing 7B. The inner casing 7A is arranged inside the outer casing 7B, and the outer surface of the inner casing 7A is covered by the outer casing 7B. The suction side opening of the inner casing 7A is connected to the suction port 10, and the discharge side opening of the outer casing 7B is connected to the discharge port 11. A diffuser 15 is arranged around the impeller 5, and a return blade 16 is arranged on the discharge side of the diffuser 15.

As the impeller 5 rotates, the liquid is sucked into the impeller 5 through the suction port 10. Rotating the impeller 5 increases the velocity and pressure of the liquid, and as the liquid passes through the diffuser 15, the velocity energy of the liquid is converted to pressure. The boosted liquid is guided to the next-stage impeller 5 by the return blade 16, and is further boosted by the rotation of the next-stage impeller 5. The liquid leaving the impeller 5 in the final stage flows into the outer casing 7B through the plurality of communication holes 20 formed at the ends of the inner casing 7A. The liquid passes through the flow path 21 formed between the inner surface of the outer casing 7B and the outer surface of the inner casing 7A toward the discharge port 11, and is discharged to the outside of the centrifugal pump through the discharge port 11.

The discharge-side opening end of the casing 7 is closed by the casing cover 9. A mechanical seal 25 is fixed to the casing cover 9 and the rotating shaft 1. The mechanical seal 25 is a shaft seal that seals a gap between the casing cover 9 and the rotating shaft 1. The leakage of the liquid boosted by the rotation of the impeller 5 is prevented by the mechanical seal 25.

In the present embodiment, each of the impeller 5, the inner casing 7A, and the outer casing 7B is an assembly of a pressed metal plate. More specifically, by pressing a metal plate, each part of the impeller 5, the inner casing 7A, and the outer casing 7B is formed, and by assembling these parts, the impeller 5, the inner casing 7A, and the outer casing are assembled. 7B is formed. As the material of the metal plate, the metal is a corrosion-resistant metal such as stainless steel. The centrifugal pump according to the present embodiment is a multi-stage centrifugal pump including a plurality of impellers 5 (four in FIG. 1). In one embodiment, the centrifugal pump may be a single-stage centrifugal pump with one impeller 5.

FIG. 2 is an enlarged cross-sectional view showing a part of the centrifugal pump shown in FIG. The impeller 5 includes a main plate (discharge side plate member) 35 fixed to the rotating shaft 1, a shroud (suction side plate member) 37 facing the main plate 35, and a plurality of blades arranged between the main plate 35 and the shroud 37. It has 38 and. The liquid inlet 30 of the impeller 5 is formed in the shroud 37. A plurality of balance holes 40 are formed in the main plate 35. In this embodiment, the balance holes 40 are arranged around the rotation shaft 1 at equal intervals. The main plate 35 has an engaging portion (boss) 45 for engaging the rotating shaft 1 and the impeller 5 at the central portion thereof.

As shown in FIG. 2, a liner ring 31 is arranged around the liquid inlet 30 of the impeller 5 to prevent the liquid boosted by the rotation of the impeller 5 from returning to the suction side. The liner ring 31 is fixed to the inner casing 7A. A minute gap is formed between the liquid inlet 30 of the impeller 5 and the liner ring 31. Unlike the double liner type centrifugal pump shown in FIG. 8, the second liner ring is not provided on the main plate side (rear side) of the impeller 5. Such a type having a liner ring only on the shroud side of the impeller 5 and no liner ring on the main plate side of the impeller 5 is called a single liner type.

FIG. 3 is a view of the impeller 5 as viewed from its suction side, and FIG. 4 is a view of the impeller 5 as viewed from its discharge side. The shroud (suction side plate member) 37 is circular and has a liquid inlet 30 at the center thereof. The main plate (discharge side plate member) 35 has a star shape. The diameter of the main plate 35 is the same as or smaller than the diameter of the shroud 37. A plurality of trim edges 42 recessed inward in the radial direction are formed on the outer peripheral portion of the main plate 35. These trim edges 42 are evenly spaced around the center of the impeller 5. The blades 38 are arranged at equal intervals around the center of the impeller 5, and a liquid flow path is formed between the adjacent blades 38. The outer portion of each wing 38 is located between adjacent trim edges 42.

As shown in FIG. 4, a through hole 48 through which the rotating shaft 1 penetrates is formed in the engaging portion (boss) 45 of the main plate 35. A plurality of balance holes 40 are formed in the main plate 35. The balance holes 40 are arranged at equal intervals around the center of the impeller 5, and each balance hole 40 is located between adjacent blades 38 and 38. In this embodiment, six balance holes 40 are formed. In one embodiment, five or less, or seven or more balance holes 40 may be provided.

The engaging portion 45 has a plurality of key grooves 46 that form a part of the through hole 48. These key grooves 46 are arranged at equal intervals around the center of the impeller 5. Each keyway 46 has a shape that engages with a spline 50 formed on the surface of the rotating shaft 1. The spline 50 is a key extending in the axial direction of the rotating shaft 1. The spline 50 engages the keyway 46, which ensures the transmission of torque from the rotating shaft 1 to the impeller 5.

It has been demonstrated by fluid simulation that the impeller 5 having the star-shaped main plate 35 shown in FIG. 4 can reduce the axial thrust without lowering the pump efficiency. FIG. 5 is a schematic view showing the distribution of the pressure of the liquid applied to the main plate 35 when the liquid is boosted by the rotation of the impeller 5 of the present embodiment. In FIG. 5, the length of the arrow represents the magnitude of pressure. As can be seen from FIG. 5, the pressure of the liquid is applied uniformly over the entire main plate 35.

FIG. 6 is a schematic view showing the distribution of the pressure of the liquid applied to the main plate 111 when the liquid is boosted by the rotation of the conventional impeller 100 shown in FIG. As shown in FIG. 6, the pressure of the liquid applied to the main plate 111 is generally higher than the pressure of the liquid shown in FIG. In addition, the pressure of the liquid is higher at the center than at the outer circumference of the impeller 100.

As can be seen from the comparison of the pressure distributions of FIGS. 5 and 6, in the impeller 5 according to the present embodiment shown in FIG. 5, the pressure of the liquid applied to the entire main plate 35 is low. As a result, the amount of liquid returning into the impeller 5 through the balance hole 40 formed in the main plate 35 is small. Therefore, it is not necessary to provide the second liner ring shown in FIG. On the other hand, in the conventional impeller 100 shown in FIG. 6, a high pressure is applied to the main plate 111. Therefore, in order to reduce the amount of liquid returning into the impeller 100, the second liner ring 105 shown in FIG. 8 is used. It is necessary to provide.

As described above, the impeller 5 according to the present embodiment can reduce the axial thrust without providing the second liner ring 105 shown in FIG. 8 and without lowering the pump efficiency. be.

FIG. 7A is a view of the impeller 5 according to another embodiment as viewed from the discharge side thereof, and FIG. 7B is a cross-sectional view showing another embodiment of the rotating shaft 1. Since the configuration of the present embodiment, which is not particularly described, is the same as that of the embodiment described with reference to FIGS. 2 to 6, the duplicate description thereof will be omitted. In the present embodiment, the through hole 48 has a shape different from the cross-sectional shape of the rotating shaft 1. A plurality of gaps are formed between the through hole 48 and the outer surface of the rotating shaft 1, and the balance hole 40 is composed of at least one of the plurality of gaps. More specifically, at least one of the key grooves 46 formed in the engaging portion (boss) 45 functions as a balance hole 40. That is, the number of key grooves 46 of the engaging portion 45 is larger than the number of splines 50 of the rotating shaft 1 shown in FIG. 7 (b). Therefore, the keyway 46 with which the spline 50 does not engage can function as a balance hole 40. The present invention is not limited to the present embodiment, and the through hole 48 may have a polygonal shape such as a quadrangle or a hexagon different from the cross-sectional shape of the rotating shaft 1. Further, the torque transmission from the rotating shaft 1 to the main plate 35 is not limited to the spline structure, and other mechanisms such as a taper collet may be used.

The above-described embodiment is described for the purpose of enabling a person having ordinary knowledge in the technical field to which the present invention belongs to carry out the present invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is construed in the broadest range according to the technical idea defined by the claims.

1 Rotating shaft 5 Impeller 7 Casing 7A Inner casing 7B Outer casing 8 Electric motor 9 Casing cover 10 Suction port 11 Discharge port 15 Diffuser 16 Return blade 20 Communication hole 21 Flow path 25 Mechanical seal 30 Liquid inlet 31 Liner ring 35 Main plate (Discharge Side plate member)
37 shroud (suction side plate member)
38 Wings 40 Balance holes 42 Trim edges 45 Engagement part (boss)
46 Key groove 48 Through hole 50 Spline

Claims (6)

Rotation axis and
An impeller fixed to the rotating shaft and
A casing that houses the impeller and
A centrifugal pump equipped with a liner ring arranged around the liquid inlet of the impeller.
The impeller
The main plate fixed to the rotating shaft and
A shroud having the liquid inlet and facing the main plate,
With a plurality of wings arranged between the main plate and the shroud,
A balance hole is formed in the main plate.
When the impeller is viewed from its suction side, the balance hole is located radially inside the liquid inlet.
A plurality of trim edges recessed inward in the radial direction are formed on the outer peripheral portion of the main plate, and the outer portion of the wing is located between two adjacent two of the plurality of trim edges.
The centrifugal pump is a single liner type centrifugal pump having the liner ring only on the shroud side of the impeller. The centrifugal pump according to claim 1, wherein the diameter of the main plate is the same as or smaller than the diameter of the shroud. The centrifugal pump according to claim 1 or 2, wherein a plurality of the impellers are provided, and the plurality of impellers are fixed to the rotating shaft. The main plate has a through hole through which the rotation shaft penetrates.
The through hole has a shape different from the cross-sectional shape of the rotating shaft.
A plurality of gaps are formed between the through hole and the outer surface of the rotating shaft.
The centrifugal pump according to any one of claims 1 to 3, wherein the balance hole is composed of at least one of the plurality of gaps. The rotating shaft has a spline on its surface.
The main plate has a plurality of keyways having a shape in which the splines are engaged.
The centrifugal pump according to any one of claims 1 to 3, wherein the balance hole is composed of a part of the plurality of keyways. The centrifugal pump according to any one of claims 1 to 5, wherein each of the impeller and the casing is an assembly of a pressed metal plate.

Images