JP7488120B2 - Cavitation suppression device and centrifugal pump - Google Patents

Description

The present invention relates to a device for suppressing the occurrence of cavitation inside a pump. The present invention also relates to a centrifugal pump equipped with such a cavitation suppression device.

A centrifugal pump is a fluid machine for transporting liquid (e.g., water) and includes a rotating shaft to which an impeller is fixed, and a casing that forms a flow path for introducing liquid into the impeller inlet and redirecting the liquid from the impeller outlet in the outlet direction. A centrifugal pump pressurizes the liquid within the casing by rotating the impeller within the casing, and expels the pressurized liquid from a discharge port to the outside.

In a centrifugal pump, a tongue portion for guiding the flow of liquid to the impeller may be provided near the inlet of the impeller (near the outlet of the suction flow passage). Such a tongue portion may have, for example, a plate-like shape, and protrude from the inner surface of the casing toward the inside of the impeller in the radial direction (see Patent Document 1). Liquid sucked into the pump is sucked into the inlet of the impeller while swirling. When the liquid approaches the inlet of the impeller, it collides with the tongue portion, causing the flow direction to be changed toward the inlet of the impeller. As a result, the liquid is smoothly guided to the impeller.

Japanese Patent Application Laid-Open No. 8-109893

When the liquid collides with the tongue, the liquid slows down around the tongue, causing the flow rate of the liquid entering the impeller inlet to become uneven. In conventional centrifugal pumps, this uneven flow rate of the liquid can cause cavitation at the tip of the tongue or turbulence in the flow of the liquid. This cavitation can cause noise while the pump is running and damage to the impeller, and is one of the factors that reduce pump performance. Furthermore, turbulence in the flow of the liquid can cause cavitation and reduce pump performance.

The present invention aims to provide a cavitation suppression device that can guide liquid to an impeller, form a uniform flow of the liquid, and suppress the occurrence of cavitation. Another aim of the present invention is to provide a centrifugal pump equipped with such a cavitation suppression device.

In one aspect, a cavitation suppression device is provided that is fixed to the inner surface of a suction volute of a volute pump that includes a rotating shaft, an impeller fixed to the rotating shaft, and a casing that houses the impeller, and that includes a tongue that protrudes from the inner surface of the suction volute toward the inside of the impeller in the radial direction, and the tip edge of the tongue is inclined in a direction away from the rotating shaft toward the impeller when viewed from a first direction perpendicular to the rotating shaft, and is inclined in the first direction toward the impeller when viewed from a second direction perpendicular to both the rotating shaft and the first direction.

In one aspect, a volute pump is provided that includes a rotating shaft, an impeller fixed to the rotating shaft, and a casing that houses the impeller, the casing having a suction volute that communicates with a suction port, and a cavitation suppression device on the inner surface of the suction volute, the cavitation suppression device having a tongue that protrudes from the inner surface of the suction volute toward the radial inside of the impeller, the tip edge of the tongue being inclined in a direction away from the rotating shaft toward the impeller when viewed from a first direction perpendicular to the rotating shaft, and being inclined in the first direction toward the impeller when viewed from a second direction perpendicular to both the rotating shaft and the first direction.

In one aspect, the cavitation suppression device is removably attached to an inner surface of the suction volute.
In one embodiment, the volute pump is a double suction volute pump, and the cavitation suppression devices are provided on both sides of the inner surface of the suction volute, sandwiching the impeller.

The tongue portion can form a uniform flow of liquid at the inlet of the impeller and improve the uniformity of the velocity distribution and swirl angle distribution of the liquid at the inlet. As a result, the cavitation suppression device can suppress the occurrence of cavitation and improve pump performance. The cavitation suppression device can also mitigate the flow deceleration phenomenon caused by the tongue portion, reduce pressure loss, and form a more uniform flow of liquid in the impeller, improving pump efficiency.

FIG. 1 is a vertical cross-sectional view showing an embodiment of a volute pump. FIG. 1 is a horizontal cross-sectional view showing one embodiment of a volute pump. FIG. 2 is a view of the volute pump of FIG. 1 with the rotating shaft removed. FIG. 2 is an enlarged view of the cavitation suppression device. 4 is a cross-sectional view taken along line BB in FIG. 3. 4 is a cross-sectional view taken along line CC of FIG. 3. FIG. 2 illustrates velocity vectors of liquid entering an impeller. FIG. 8(a) is a diagram showing the distribution of swirl angles of liquid at the inlet of an impeller of a centrifugal pump equipped with a cavitation suppression device, and FIG. 8(b) is a diagram showing the distribution of swirl angles of liquid at the inlet of an impeller of a centrifugal pump equipped with a conventional tongue portion having a plate-like shape. Figure 9(a) is a diagram showing the liquid velocity distribution at the inlet of an impeller of a centrifugal pump equipped with a cavitation suppression device, and Figure 9(b) is a diagram showing the liquid velocity distribution at the inlet of an impeller of a centrifugal pump equipped with a conventional tongue portion having a plate-like shape.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical cross-sectional view showing an embodiment of a volute pump, and FIG. 2 is a horizontal cross-sectional view showing an embodiment of a volute pump. As shown in FIGS. 1 and 2, the volute pump includes a rotating shaft 1, an impeller 2 fixed to the rotating shaft 1, a casing 3 that houses the impeller 2 and forms a liquid flow path, and a plurality of legs 5 fixed to the casing 3. Only one leg 5 is shown in FIG. 1. As shown in FIG. 1, the impeller 2 is a double-suction type impeller equipped with two inlets 2a and one liquid outlet 2b. The two inlets 2a are located on both sides of the impeller 2 and face in opposite directions. The liquid outlet 2b is located on the outer periphery of the impeller 2. The volute pump of this embodiment is a double-suction volute pump equipped with a double-suction type impeller.

The casing 3 has a spiral shape. The casing 3 has an upper casing 3a and a lower casing 3b that are divided by a horizontal plane passing through the central axis AX of the rotating shaft 1. The multiple legs 5 are connected to the bottom of the lower casing 3b. The lower casing 3b has a liquid suction port 6 and a discharge port 7 that discharges the liquid pressurized by the impeller 2. The suction port 6 and the discharge port 7 face in opposite directions.

As shown in FIG. 1, the rotating shaft 1 is rotatably supported by a number of bearings 10 arranged on both sides of the casing 3. The gap between the rotating shaft 1 and the casing 3 is sealed by a number of shaft seal devices 11. The shaft seal devices 11 are, for example, mechanical seals. The bearings 10 and shaft seal devices 11 are omitted from FIG. 2.

The upper casing 3a and the lower casing 3b have a suction volute 20 that communicates with the suction port 6. The suction volute 20 extends from the suction port 6 to the two inlets 2a of the impeller 2. The upper casing 3a and the lower casing 3b further have a discharge volute 22 that communicates with the discharge port 7. The discharge volute 22 extends from the liquid outlet 2b of the impeller 2 to the discharge port 7.

The rotating shaft 1 is connected to a prime mover (such as an electric motor or an internal combustion engine) not shown. When the prime mover rotates the rotating shaft 1 and the impeller 2, liquid is sucked into the casing 3 through the suction port 6. The liquid flows through the suction volute 20 into the inlet 2a of the impeller 2, and is discharged from the liquid outlet 2b of the impeller 2 to the discharge volute 22 as the impeller 2 rotates. The liquid flows through the discharge volute 22 and is discharged from the discharge port 7.

As shown in FIG. 2, the volute pump further includes two cavitation suppression devices 30 for directing the liquid that has passed through the suction volute 20 to the inlet 2a of the impeller 2. The cavitation suppression devices 30 are provided on the inner surface of the suction volute 20. Specifically, the two cavitation suppression devices 30 are provided at the outlet of the suction volute 20 and are close to the inlet 2a. The two cavitation suppression devices 30 are provided on both sides of the inner surface of the suction volute 20, sandwiching the impeller 2.

3 is a view of the volute pump of FIG. 1 with the rotating shaft 1 removed, FIG. 4 is an enlarged view of the cavitation suppression device 30, FIG. 5 is a cross-sectional view of line B-B in FIG. 3, and FIG. 6 is a cross-sectional view of line C-C in FIG. 3. In FIG. 4, the rotating shaft 1 is omitted. As shown in FIGS. 2 to 6, the cavitation suppression device 30 includes a base 32 that contacts the inner surface of the suction volute 20 and a tongue 34 that protrudes from the inner surface of the suction volute 20 toward the radial inside of the impeller 2. Specifically, the tongue 34 protrudes from the base 32 toward the radial inside of the impeller 2. When the liquid that has passed through the suction volute 20 collides with the tongue 34, the flow direction of the liquid is changed to a direction toward the inlet 2a of the impeller 2. In this embodiment, the base 32 and the tongue 34 are integrally formed.

As shown in FIG. 2, the lower casing 3b has a threaded hole 40. As shown in FIGS. 5 and 6, the base 32 is fixed to the lower casing 3b by a number of bolts 41 screwed into the threaded holes 40. Only one bolt 41 is shown in FIGS. 5 and 6. By fixing the base 32 to the lower casing 3b by the bolts 41, the cavitation suppression device 30 is fixed to the inner surface of the suction volute 20.

As shown in FIG. 2, the tip edge 34a of the tongue portion 34 is inclined toward the impeller 2 and away from the impeller 1 when viewed from a first direction perpendicular to the rotating shaft 1. In this embodiment, the first direction is a downward direction. As shown in FIG. 2, FIG. 5, and FIG. 6, the position of the tip edge 34a moves radially outward from the impeller 2 as it moves toward the impeller 2 in the axial direction of the rotating shaft 1 (the rotating shaft 1 is not shown in FIG. 5 and FIG. 6).

By inclining the tip edge 34a of the tongue 34 toward the impeller 2 and away from the rotating shaft 1 when viewed from a first direction perpendicular to the rotating shaft 1, the collision range between the liquid and the tongue 34 can be reduced in the area close to the inlet 2a, i.e., the area where cavitation and the like are likely to occur. As a result, the occurrence of cavitation and vortexes caused by turbulence in the liquid flow can be suppressed. On the other hand, in the area away from the inlet 2a, i.e., the area where cavitation and the like are unlikely to occur, the collision range between the liquid and the tongue 34 can be sufficiently secured. By securing a sufficient collision range between the liquid and the tongue 34, the liquid can be efficiently swirled and flowed into the impeller 2. As a result, the cavitation suppression device 30 can guide the liquid to the inlet 2a of the impeller 2 while providing the designed swirl and forming a more uniform liquid flow in the impeller, reducing pressure loss due to deceleration and suppressing the occurrence of cavitation and the like.

In this embodiment, a portion of the tip edge 34a of the tongue portion 34 is located inside the inlet 2a of the impeller 2 when viewed in the axial direction of the rotating shaft 1, but in one embodiment, the tip edge 34a may be located outside the inlet 2a of the impeller 2 when viewed in the axial direction of the rotating shaft 1.

As shown in FIG. 3, the tip edge 34a of the tongue portion 34 is further inclined in the first direction toward the impeller 2 when viewed from a second direction perpendicular to both the rotating shaft 1 and the first direction. In this embodiment, the second direction is a direction perpendicular to the longitudinal section of the volute pump shown in FIG. 3. By inclining the tip edge 34a of the tongue portion 34 in the first direction toward the impeller 2 when viewed from the second direction perpendicular to both the rotating shaft 1 and the first direction, the swirling flow from the casing 3 having a spiral shape can be smoothly guided to the inlet 2a. As a result, turbulence in the liquid flow caused by collision between the tongue portion 34 and the liquid can be mitigated.

Therefore, the cavitation suppression device 30 can suppress the occurrence of cavitation, form a uniform flow of liquid at the inlet 2a, and improve the uniformity of the velocity distribution and swirl angle distribution of the liquid at the inlet 2a.

Figure 7 is a diagram showing the velocity vector of the liquid flowing into the impeller 2. Here, the swirl angle of the liquid refers to the angle α between the liquid velocity vector Vt in the circumferential direction and vector V1 when the impeller 2 is rotating in the direction of the arrow shown in Figure 7. Vector Vm in Figure 7 is the liquid velocity vector in the direction of flow into the blades 2d of the impeller 2. Vector V1 is the resultant vector of vectors Vm and Vt, and is a velocity vector that represents the absolute velocity of the liquid as viewed from a stationary coordinate system.

By improving the uniformity of the liquid velocity distribution and swirl angle distribution at the inlet 2a, the angular momentum imparted from the inlet 2a to each blade 2d of the impeller 2 becomes uniform, and by ensuring consistency between the swirl angle of the inlet 2a and the tip angle of the blade 2d, the occurrence of cavitation can be suppressed. As a result, the cavitation suppression device 30 can suppress the occurrence of cavitation and improve pump performance.

Figure 8(a) is a diagram showing the distribution of the swirl angle of the liquid at the inlet 2a of the impeller 2 of a volute pump equipped with a cavitation suppression device 30, and Figure 8(b) is a diagram showing the distribution of the swirl angle of the liquid at the inlet 100a of the impeller 100 of a volute pump equipped with a conventional tongue having a plate-like shape. The impeller 2 and the impeller 100 have the same structure. Figures 8(a) and 8(b) show the results of a fluid analysis simulation. As shown in Figures 8(a) and 8(b), the simulation results show that the volute pump equipped with the cavitation suppression device 30 can improve the uniformity of the distribution of the swirl angle of the liquid at the inlet 2a of the impeller 2 compared to the conventional volute pump.

Figure 9(a) is a diagram showing the liquid velocity distribution at the inlet 2a of the impeller 2 of a centrifugal pump equipped with a cavitation suppression device 30, and Figure 9(b) is a diagram showing the liquid velocity distribution at the inlet 100a of the impeller 100 of a centrifugal pump equipped with a conventional tongue having a plate-like shape. Figures 9(a) and 9(b) show the results of a fluid analysis simulation. As shown in Figures 9(a) and 9(b), the simulation results show that a centrifugal pump equipped with a cavitation suppression device 30 can improve the uniformity of the liquid velocity distribution at the inlet 2a of the impeller 2 compared to a conventional centrifugal pump.

The cavitation suppression device 30 of this embodiment is removably attached to the inner surface of the suction volute 20. The detachable configuration of the cavitation suppression device 30 facilitates the adaptation to design changes of the tongue portion 34 and the maintenance of the cavitation suppression device 30. In one embodiment, the cavitation suppression device 30 may be formed integrally with the suction volute 20.

The volute pump of this embodiment is a double-suction volute pump equipped with a double-suction impeller, but the cavitation suppression device 30 of this embodiment can also be applied to a single-suction volute pump. In one embodiment, the cavitation suppression device 30 of this embodiment can also be applied to a volute pump whose rotating shaft 1 extends vertically.

The above-described embodiments have been described for the purpose of enabling a person having ordinary knowledge in the technical field to which the present invention pertains to practice the present invention. Various modifications of the above-described embodiments would naturally be possible for a person skilled in the art, and the technical ideas of the present invention may also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical ideas defined by the scope of the claims.

REFERENCE SIGNS LIST 1 Rotating shaft 2 Impeller 3 Casing 5 Foot 6 Suction port 7 Discharge port 10 Bearing 11 Shaft seal device 20 Suction volute 22 Discharge volute 30 Cavitation suppression device 32 Base 34 Tongue 34a Tip edge 40 Screw hole 41 Bolt

Claims (4)

A cavitation suppression device fixed to an inner surface of a suction volute of a centrifugal pump including a rotating shaft, an impeller fixed to the rotating shaft, and a casing that houses the impeller,
a tongue portion protruding from an inner surface side of the suction volute toward a radially inner side of the impeller,
a tip edge of the tongue portion is inclined in a direction away from the rotation shaft toward the impeller when viewed from a first direction perpendicular to the rotation shaft, and is inclined in the first direction toward the impeller when viewed from a second direction perpendicular to both the rotation shaft and the first direction ,
A cavitation suppression device , wherein the tip edge is located outside the inlet of the impeller when viewed in the axial direction of the rotating shaft . A rotation axis;
An impeller fixed to the rotating shaft;
A casing that houses the impeller is provided.
The casing has a suction volute communicating with a suction port,
A cavitation suppression device is provided on the inner surface of the suction volute,
The cavitation suppression device includes a tongue portion protruding from an inner surface side of the suction volute toward a radially inner side of the impeller,
a tip edge of the tongue portion is inclined in a direction away from the rotation shaft toward the impeller when viewed from a first direction perpendicular to the rotation shaft, and is inclined in the first direction toward the impeller when viewed from a second direction perpendicular to both the rotation shaft and the first direction ,
A centrifugal pump , wherein the tip edge is located outside the inlet of the impeller when viewed in the axial direction of the rotating shaft . The volute pump of claim 2, wherein the cavitation suppression device is removably attached to the inner surface of the suction volute. The volute pump is a double suction volute pump,
4. The volute pump according to claim 2, wherein the cavitation suppression devices are provided on both sides of the inner surface of the suction volute, with the impeller in between.

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