JPH03290096A - Prerotation type centrifugal pump - Google Patents

Abstract

PURPOSE:To prevent the generation of cavitation, in a pump etc., by suppressing the exfoliation of the water stream in the vicinity of a suction port part by specifying the shape of the suction port part of the title centrifugal pump by making the flow speed distribution and direction change of the water stream in the whole circumferential part of the suction port part so as to be made uniform in each part. CONSTITUTION:The suction port part 14 of a prerotation type centrifugal pump is formed to a shape similar to a bellmouth, and projected toward a casing inner surface 15b opposed to the suction port part 14 from the inner surface 15a of a casing on the periphery, and the inner peripheral surface ranging from the projecting edge 14b of the suction port part 14 to a basic edge 14c is formed to a bulging-out arcuate curved surface 14d which is smoothly continuous. An annular or arcuate groove part 17 is formed between the suction port part 14 and the casing inner surface 15a on the periphery. Accordingly, the flow speed of the water stream F1 lowers before direction change, and direction change is performed gently during turn, and the water stream is sucked into a blade chamber 12, getting over the suction port part 14, and the generation of exfoliation of water stream from the inner peripheral surface at the suction port part 14 is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of the suction port of an impeller chamber in a pre-rotation type centrifugal pump (hereinafter simply referred to as a centrifugal pump).

[Prior Art] As shown in FIG. 7, a centrifugal pump includes a casing l, an impeller 3 provided on a pump shaft 2, etc.
The casing 1 has polyate-shaped suction passages 11, an impeller chamber 12 formed between the terminal ends of these suction passages 11, and a passage between the impeller chamber 12 and the suction passage 11. A volute-shaped discharge channel 13 extends to form a discharge port 13a facing opposite to the suction port 11a of the suction channel 11.
A suction port 14 is formed at the boundary between the impeller chamber 12 and the suction flow path 11, that is, at the inlet opening of the impeller chamber 12. In the case of this centrifugal pump, water sucked in from the direction A perpendicular to the pump shaft 2 as the impeller 3 is rotated becomes a swirling flow in the flow path near the impeller center and approaches the impeller chamber 12. Then, it is sucked into the impeller chamber 12 through the suction port 14 and turned in a direction parallel to the pump shaft 2. In this way, the water flow is turned into a swirling flow and the impeller chamber work 2
The pre-rotation type is called the pre-rotation type, which is the mainstream of today's centrifugal pumps, and its adoption has made it possible to achieve higher performance and faster suction action.

In such a centrifugal pump, conventionally, the impeller chamber 12
The cross-sectional shape of the entire circumference of the suction port 14, which forms the inlet portion of the pump, is as shown in FIG.

That is, the surface of the suction port 14 facing the flow path near the impeller center is a circular arc surface 14a with a radius of curvature r that extends over its entire circumference, and the arc surface 1
End of 4a on the side of suction flow path 11 (starting end of arcuate surface 14a)
The inner surface 15a of the casing around the suction port 14 was almost smoothly continuous with no difference in level by the inclined surface 16 along the water flow direction in the suction flow path 11. In other words,
The conventional suction port 14 has an annular partition wall 17 that partitions a suction flow path 11 formed in the casing 1 and an impeller chamber 12.
The inner peripheral part of the outer peripheral part is made thicker, and the inner end of the thickened inner peripheral part is formed with a circular arc surface 14a having the same radius of curvature r in the entire circumferential direction. Met. At what point on the entire circumference of the suction port 14 is the distance h from the end face of the impeller to the apex of the arcuate surface 14a, and furthermore, the opposing distance from the apex of the arcuate surface 14a to the casing inner surface 15b facing the suction port 14? They were also set the same.

Such a conventional shape of the suction port 14 reduces the resistance against the water flow sucked into the impeller chamber 12, making it difficult for the flow velocity to decrease immediately before the suction port 14. This was adopted based on the idea that the water flow velocity distribution would be approximately uniform throughout the entire circumference of the suction port 14.

[Problem to be solved by the invention 1 However, when we visualized a conventional pre-rotation type double suction centrifugal pump and measured the water flow velocity at each part of the suction port using a pitot tube, we found the following facts. There was found.

In the case of conventional centrifugal pumps, the flow of water inside the casing has become more complicated as the suction performance has improved and the speed has increased, and the water flow inside the casing has become complicated. In the portion X located upstream of the flow path 11, the ideal water flow transition in which the water flow sucked into the impeller chamber 12 reliably contacts the circular arc surface 14a of the suction port 14 and changes direction along it is not performed. For example, when the water flow changes direction as indicated by the arrow in FIG. It was found that this caused erosion that caused vibration and noise, reducing pump performance.

Furthermore, although the conventional centrifugal pump is based on the idea that the water flow velocity distribution at the suction port 14 is almost uniform as described above, as shown in FIG.
From the starting point on the upstream side of the swirling flow to the ending point on the downstream side are Ba and Bb, respectively.

When divided into points Bc and Bd, the flow velocity V actually measured at each point
It has been found that Ba, VBb, VBc, and VBd are not uniform at each part of the entire circumference of the suction port 14. At the same time, the water flow does not swirl sufficiently near point Ba, and
The degree of turning increases as you move away from the point and reach points Bb, Bc, and Bd, and Ba, Bb, Bc,
Since the strength of the swirling flow at each point of Bd is significantly different, Ba, Bb, and Bc.

If the cross-sectional shape of the suction port 14 facing each point of Bd is uniform over the entire circumference as described above, the influence of the cross-sectional shape on the direction change of the water flow will be different at each point. The facts have been revealed.

It has been found that these factors combine to cause the water flow separation phenomenon described above, leading to the occurrence of cavitation and erosion, and a decrease in pump performance.

This invention takes these conventional facts into account and devises an appropriate shape for the suction port, thereby making it possible to make the flow velocity distribution and direction change of the water flow as wide as possible in each part around the entire circumference of the suction port. It is an object of the present invention to provide a centrifugal pump in which separation of water flow near a suction port is less likely to occur, and performance deterioration due to occurrence of cavitation or erosion is less likely to occur.

[Means for Solving the Problems 1] In the centrifugal pump of the present invention, the suction port through which water flows into the impeller is protruded from the inner surface of the casing surrounding the suction port toward the inner surface of the casing opposite to the suction port. The inner circumferential surface from the protruding end to the base end of the part is formed into a smoothly continuous protruding curved surface, and a groove or stepped part is formed between the suction port part and the inner surface of the casing around it. It is something that

[Function 1] According to this configuration, in the portion of the suction port located upstream of the suction flow path (the portion indicated by the symbol X in FIG. The water flow collides with the suction port protruding from the inner surface of the casing at an inflow angle close to a right angle, and the flow velocity of the water flow decreases accordingly.At the same time, the groove between the suction port and the surrounding inner surface of the casing Alternatively, due to the water flow guiding action of the stepped portion, the swirling component of the water flow toward the downstream side of the suction flow path increases, and the water flow swirls around the suction port along the groove or stepped portion and moves around the suction port. It crosses over and gently changes direction parallel to the pump shaft, preventing the water flow from rapidly changing direction. Moreover, since the inner circumferential surface of the suction port is formed into a smoothly continuous protruding curved surface, these effects are synergized to suppress the separation phenomenon of the water flow.

In addition, in the downstream part of the part indicated by the symbol X in Fig. 7, that is, in the part where the water flow flowing through the suction channel in the direction perpendicular to the pump shaft collides with the suction port at a small inflow angle. , since the direction of the water flow is close to the tangential direction of the suction port, the flow velocity does not decrease so much. Therefore, the flow velocity in this portion is relatively close to the flow velocity in the X portion.

The degree of decrease in flow velocity due to collision is smaller in the downstream part of the suction flow path at the suction port, so
The flow velocity over the entire circumference of the suction port is equalized, and accordingly, the direction change of the water flow when passing over the connection port is also equalized over the entire circumference of the connection port.

[Example] Hereinafter, an example of the centrifugal pump according to the present invention will be described in detail.

1 and 2 show the vicinity of the suction port 14 of a Brillo tension type centrifugal pump, and FIG. 1 is a sectional view of a portion corresponding to FIG. 8 already explained. In each of these figures, the same reference numerals represent the same or corresponding parts.

In this embodiment, the suction port 14 through which the water stream flows into the impeller is shaped similar to a bell mouth. That is, the suction port 14 protrudes from the surrounding casing inner surface 15a toward the casing inner surface 15b facing the suction port 14, and the protruding end 14b of the suction port 14
The inner peripheral surface from the base end 14c to the base end 14c is formed into a smoothly continuous overhanging arc-shaped curved surface 14d. Further, an annular or arcuate groove portion 17 is formed between the suction port portion 14 and the casing inner surface 15a surrounding the suction port portion 14. 14e is the outer peripheral surface of the suction port I4. Here, the annular groove 17 is formed when the suction port 14 is annular, and the arcuate groove 17 is formed in the casing 1 as shown in FIG. The formed tongue portion 18 is the suction port portion 1
This is a case where a part of the suction port 14 is removed by the tongue 18 because the suction port 14 protrudes upstream from the opening edge of the opening 4 (toward the front side of the page). Note that this tongue portion 18 has the function of guiding the swirling flow generated around the suction port portion 14 into the interior of the impeller chamber 12 at its most downstream portion.

According to this configuration, in the portion indicated by the symbol X in FIG. The water flow F1 flowing into the groove 1 of the suction port 14
7 and collides with the outer circumferential surface 14e of the suction port 14 to reduce the flow velocity, and then the swirling component of the water flow increases due to the water flow guiding action of the groove 17, and the water flow flows along the suction channel 11 along the groove 17. It flows toward the downstream side, crosses the suction port 14 while turning at a point downstream from the collision point, changes direction gently in a direction parallel to the pump shaft, and is sucked into the impeller chamber 12.

In this way, the flow velocity of the water flow F decreases before changing direction,
Then, while turning, the direction is changed gently, and when the suction port 14 is sucked into the impeller chamber 12, the suction port 14 is sucked into the impeller chamber 12.
The water flow is less likely to separate from the inner peripheral surface. At the stage where the water flow F1 crosses the suction port 14, the water flow F1
A smoothly continuous protruding curved surface 1 of the suction port 14 in the
4d is in a state where it is protruding, and as mentioned above, the flow velocity of the water flow F is slow and the direction change is gradual, making it difficult for the water flow F to separate from the suction port 14. In particular, in the X portion, the suction port 14
Water flow F at a large inflow angle almost perpendicular to the groove 17 of
, even if they collide, a gradual change in direction is achieved due to the accompanying increase in flow velocity and swirling component.

In addition, the part downstream of the X part, that is, the suction flow path 1
The water flow F2.1 is flowing in the direction perpendicular to the pump shaft.
In the portion where F3 collides with the groove 17 of the suction port 14 at a small inflow angle, the direction of the water flows Fz and F3 is close to the tangential direction of the suction port 14, so that the flow velocity does not decrease so much. Therefore, due to the relative relationship with the fact that the flow velocity decreases significantly in the X portion described above, the flow velocity in this downstream portion and the flow velocity in the X portion are equalized. Then, the degree of decrease in flow velocity due to collision is smaller in the portion of the suction port 14 located downstream of the suction flow path 11, so the flow speed in the entire circumferential portion of the suction port 14 is equalized,
Accordingly, the manner in which the water flow changes direction when passing over the connection port is also equalized over the entire circumference of the connection port. This action effectively suppresses the water flow separation phenomenon that occurs with conventional configurations, suppresses cavitation and erosion, and improves pump performance (suction performance, etc.). be.

The suction port portion 14 may be formed in a communication portion between the impeller chamber 12 and the suction flow path 11, that is, in a part of the inlet opening of the impeller chamber 12. In this case, it is formed to include a portion located upstream of the suction flow path 11 at the inlet opening of the impeller chamber 12 (for example, the X portion). This is because, in normal cases, the part where the separation phenomenon of water flow occurs is limited to the vicinity of the above-mentioned X part, so the flow velocity of the water flow F in that X part decreases and the direction changes slowly while swirling. If you push it, the suction port 14
This is because it is possible to effectively suppress the separation phenomenon of water flow throughout the entire area.

When the suction port 14 is formed in a part of the inlet opening of the impeller chamber 12, the suction port 14 shown in FIG.
Gradually and continuously reduce the peak width H, spread width V, and creepage length of the curved surface 14d in 4 from the upstream side to the downstream side of the water flow,
It is desirable that the groove portion 17 of the suction port portion 14 be smoothly continuous with the peripheral edge portion A of the inlet opening. By doing so, the water flow that is encouraged to reduce the flow velocity and gently change direction due to the action of the groove 17 of the suction port 14, and the groove 1
The respective aspects of the swirling flow sucked into the impeller chamber 12 without colliding with or contacting the impeller chamber 12 are equalized over the entire circumference of the inlet opening of the impeller chamber 12, and there are no places where the aspect changes drastically. .

Incidentally, the suction port is formed around the entire circumference of the inlet opening of the impeller chamber, and the width of the peak, the width of the spread, and the creepage length of the curved surface of the suction port are gradually and continuously formed from the upstream side of the water flow toward the downstream side. A comparison experiment was conducted under normal conditions to compare the suction performance of an embodiment in which the groove of the suction port smoothly disappears into the periphery of the inlet opening and the conventional example shown in FIG. 8.
In the conventional example, the suction performance NPSH (rq) was 8.1 m, and in the example, it was 7.1 m, which is approximately 1 m lower than the conventional example.
Improved by 111.

The suction performance of the conventional example is also quite high, and it is not easy to further improve this by 1 m.

In the embodiment described above, the groove 17 is formed between the suction port 14 and the inner surface of the casing around it, and the outer peripheral surface 14e of the suction port 14 is parallel or almost parallel to the curved surface 14d of the inner peripheral surface. I explained what was formed,
The same effect can be achieved even if the groove portion 17 is formed into a rectangular groove shape as shown in FIG.

Furthermore, the suction port 14 is not formed with a groove as shown in FIG.
A stepped portion 14f parallel to the pump shaft (not shown) may be formed between the casing inner surface 15a and the surrounding casing inner surface 15a. This can also effectively prevent the separation phenomenon of the water flow due to substantially the same effect as described above.

In the above embodiment, the suction port 14 was explained as having an integral structure with the casing 1, but the impeller chamber 12
Of course, the bottom of the tank may be used as a suction ring attached to the inlet opening of the tank.

[Effects of the Invention 1] As detailed above, according to the present invention, in a centrifugal pump, the flow velocity and direction change when the water flow flowing through the suction channel of the casing crosses over the suction port and is sucked into the impeller chamber. The aspect is relatively equalized over the entire circumference of the suction port, and the inner circumferential surface of the suction port is formed into an overhanging arcuate surface, so that the connection port that occurs in conventional configurations is reduced. This has the effect that separation of water flow in the vicinity is less likely to occur, which leads to suppressing the occurrence of cavitation and erosion, which helps improve pump performance. Moreover, it has the advantage that it is extremely easy to implement since it is sufficient to simply improve the shape of the suction port.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional side view of the vicinity of the suction port showing an embodiment of the centrifugal pump according to the present invention, FIG. 2 is a longitudinal sectional front view of the vicinity of the suction port as seen in the axial direction of the pump shaft, and FIG. 3 4 is an enlarged vertical sectional side view of the main part of FIG. 1, and FIG. 5 is an enlarged longitudinal sectional side view of the main part showing another modification of the suction port. , Fig. 6 is an enlarged longitudinal sectional side view of the main part showing still another modification of the suction port, Fig. 7 is a longitudinal sectional front view showing the general configuration of a general centrifugal pump, and Fig. 8 is a longitudinal sectional view of a conventional centrifugal pump. FIG. 3 is a longitudinal side view of the vicinity of the suction port. DESCRIPTION OF SYMBOLS 1... Casing, 2... Pump shaft, 3... Impeller, 12... Impeller chamber, 14... Suction port part, 14b
...Protruding end of the suction port, 14c...Base end of the suction port, 14d...Curved surface, 4e...Groove-shaped surface, 14f...
- Straight surface, 15a...Inner surface of the casing around the suction port, 15b...Inner surface of the casing facing the suction port, Fl+Fz, h...Water flow.

Claims (1)

[Scope of Claims] 1. It has an impeller, a pump shaft to which the impeller is fixed, and a casing that covers these, and by the rotational drive of the impeller, suction is caused in the casing from a direction perpendicular to the pump shaft. In a pre-rotation type centrifugal pump in which water is diverted in a direction parallel to the pump shaft at a suction port near the impeller center and flows into the impeller chamber, the suction port allows water to flow into the impeller chamber. The inner surface of the casing protrudes from the surrounding inner surface of the casing toward the inner surface of the casing facing the suction port, and the inner circumferential surface from the protruding end of the suction port to the base end is formed into a smoothly continuous overhang-like curved surface. A pre-rotation type centrifugal pump characterized in that a groove or a stepped portion is formed between the suction port and the inner surface of the casing surrounding the suction port.