JP4730113B2 - Double suction centrifugal pump - Google Patents

Description

  The present invention relates to a double suction centrifugal pump, and is particularly suitable for a double suction centrifugal pump using a symmetrical impeller having two suction ports.

  As the both suction centrifugal pumps, there are known ones mainly composed of a centrifugal pump that pressurizes a fluid by applying a centrifugal force generated by the rotation of an impeller to the fluid.

  A conventional double suction centrifugal pump is shown in FIG. 1 (Prior Art 1). The both suction centrifugal pump 1 includes an impeller 30 in which a partition portion 31, a blade 32 and a side plate 33 are disposed so as to be sucked from both sides in the axial direction and discharged from the outer peripheral surface, and a fluid suction flow into the impeller 30. A pump casing 20 having a suction volute 22 that forms a passage and a discharge volute 21 that forms a discharge passage for fluid from the impeller 30, and an inner peripheral end face of the discharge volute 22 that faces the suction side end of the side plate 33. And a worn wear member 40. The discharge volute 21 is formed wider in the axial direction than the outer peripheral surface of the impeller 30 in order to enlarge the discharge flow path, and the wear ring member 40 is provided in case the impeller 30 and the pump casing 20 are in contact with each other. Is provided. In addition, Non-Patent Document 1 is cited as a document related to this prior art 1.

  As another conventional double suction centrifugal pump, there is one shown in FIG. 2 (Prior Art 2). The both suction centrifugal pump 1 includes an impeller 30 in which a partition portion 31, a blade 32 and a side plate 33 are disposed so as to be sucked from both sides in the axial direction and discharged from the outer peripheral surface, and a fluid suction flow into the impeller 30. A pump casing 20 having a suction volute 22 that forms a passage and a discharge volute 21 that forms a discharge passage for fluid from the impeller 30 is provided. The discharge volute 21 is formed to be wider in the axial direction than the outer peripheral surface of the impeller 30 in order to enlarge the discharge flow path, and is formed to cover the side surface of the impeller 30. Furthermore, in this prior art 2, the wall surface of the suction volute 22 in the vicinity of the inlet of the impeller protrudes into the suction flow path, and the protruding suction flow path wall portion 23 that equalizes the inflow flow into the impeller 30 is formed. . In addition, patent documents 1 are mentioned as literature provided with the pump casing in which the protrusion suction flow path wall part was formed in the spiral pump.

JP-A-57-195899 (FIGS. 7a and 7b) Turbo pump: edited by Turbomachinery Association (p19, Fig. 1.13)

  In order to improve the fluid performance, the pump casing 20 in the prior arts 1 and 2 described above has, for example, a complicated three-dimensional shape in which the cross-sectional shape of the discharge volute 21 continuously changes from the start of volute winding to the discharge port. In many cases, it is generally made of castings.

  For this reason, in the pump casings 20 in the prior arts 1 and 2, other flow paths and the like are used with the casting production accuracy, except that the portion where the wear ring member 40 of the prior art 1 is mounted is machined. It is almost that. In general, the allowable manufacturing error of a casting is about 10 times the allowable error of machining. Therefore, if the gap between the side plate 33 of the impeller 30 and the discharge volute 21 is designed to be narrow, the side plate 33 of the impeller 30 and the discharge volute 21 may come into contact with each other. For this reason, in the prior arts 1 and 2, this gap is designed to have a dimension that has a sufficient margin for the casting tolerance, thereby preventing the side plate 33 of the impeller 30 and the discharge volute 21 from contacting each other during assembly. . That is, the gap between the side plate 33 of the impeller 30 and the discharge volute 21 is designed to be wide.

  However, it has been found that if the gap between the side plate 33 of the impeller 30 and the discharge volute 21 is wide, the performance of the pump is affected. In particular, as shown in FIG. 3, there may be a portion where the total head characteristic curve becomes discontinuous during operation at a low flow rate near the deadline, and the gap between the side plate 33 of the impeller 30 and the discharge volute 21 is unstable. It has been found that performance is affected. This point will be described below with reference to FIGS.

  Normally, the flow inside the discharge volute 21 near the design point of the both suction centrifugal pumps 1 is as shown in FIG. That is, the fluid flowing out from the outlet of the impeller 30 flows into the discharge volute 21 along the rotation direction of the impeller 30 and finally flows out from the discharge port of the discharge volute 21. In this process, the fluid flow is decelerated and a part of the kinetic energy is converted to pressure energy. At this time, if there is a large disturbance in the fluid flow, a loss occurs and it is converted into effective pressure energy. I can't. Therefore, the design of the discharge volute shape is designed so that there is no such large flow disturbance. This design is usually made under flow conditions near the design point.

  However, it has been found that the state of fluid flow in other flow ranges is significantly different from the design point. In particular, when the flow of the fluid inside the discharge volute 21 in a low flow rate region close to the shut-off operation is seen, when the gap between the side plate 33 of the impeller 30 and the discharge casing 21 is wide, FIG. As shown, the flow of the fluid once directed to the outer flow path 12 divided by the discharge pipe 11 or the volute partition plate 10 changes its direction at the winding start portion 9 of the discharge volute 21 and the tip end portion of the volute partition plate 10. As shown in FIG. 5 (b), it turned out that it flowed again into the inner flow path 13 divided by the volute winding start portion 9 and the volute partition plate 10 through the wide gap.

  In the fluid flow of the discharge volute 21 in such a low flow rate region, the flow velocity in the outer flow path 12 and the discharge pipe 11 divided by the volute partition plate 10 becomes extremely small, and the pressure increases. Therefore, the flow exiting the impeller 30 is bent to the pressure increase and cannot flow into the discharge pipe 11 or the outer flow path 12, and passes through the gap between the side plate 33 of the impeller 30 and the discharge casing 21. The turn is continued for a while so as to be caught near the exit of the impeller 30.

  Therefore, in such a fluid flow situation, the fluid flow exiting the impeller 30 cannot be sufficiently decelerated by the discharge volute 21 and the turbulence becomes large, so that the pressure cannot be effectively recovered and a large loss occurs. . Moreover, such a flow of fluid suddenly occurs relatively discontinuously near the low flow rate when the flow rates of the two suction centrifugal pumps 1 are continuously changed. As a result, the flow rate-total head characteristic curve of both suction centrifugal pumps 1 becomes discontinuous in the low flow rate region as shown in FIG. 3, resulting in destabilizing performance that is detrimental to the operation control of the pump. . This unstable performance could be a major obstacle to stable unit control operation at the pump station.

  Further, when the pump casing 20 is made of a casting, the gap width between the impeller 30 and the discharge volute 21 is almost different on the left and right with respect to the symmetry axis of the cross section of both suction spiral pumps due to an allowable manufacturing error of the casting. It is. In this case, in the narrower one, the swirl flow accompanying the rotation of the impeller 30 becomes faster than in the wider one, and the pressure decreases as compared with the larger one. Collapses. Originally, it is a double suction centrifugal pump that has one of the merits that axial thrust hardly occurs by making it a symmetrical shape, but it is necessary to design the bearing in consideration of the axial thrust generated by this The bearing cannot be reduced in size, and therefore the pump cannot be reduced in size.

  Further, the projecting suction flow passage wall 23 provided in the vicinity of the impeller entrance of the suction volute 22 in the prior art 2 is effective in improving the cavitation performance at the design point flow rate, but causes the following problems in the low flow rate region. There was a case.

  That is, when the flow of the impeller 30 flows backward to the inlet side, particularly when the suction pressure is reduced, the reverse flow accompanied by cavitation hits the protruding suction flow channel wall 23 as shown in FIG. The pump casing 20 is often made of cast iron or the like, where erosion due to cavitation occurs, paint is peeled off, erosion also occurs from that part, and the vicinity thereof is destroyed by repetition such as erosion due to cavitation again. In some cases, there was a serious problem in the reliability of the pump.

  An object of the present invention is to provide a double-suction centrifugal pump that suppresses unstable performance and axial thrust generation in a low flow rate region and enables stable operation and downsizing of a bearing.

  In order to achieve the above-described object, the present invention provides an impeller having partition portions, blades, and side plates disposed so as to be sucked from both sides in the axial direction and discharged from the outer peripheral surface, and a fluid suction flow into the impeller. A pump casing having a suction volute that forms a passage and a discharge volute that forms a discharge passage for fluid from the impeller, and a wear ring attached to the inner peripheral end face of the discharge volute facing the suction side end of the side plate A suction volute pump in which the discharge volute is formed wider in the axial direction than the outer peripheral surface of the impeller, and the wear ring member is mounted on the inner peripheral end surface of the discharge volute. And a closing portion that extends from the mounting portion to the discharge side end portion of the side plate and closes the gap between the discharge side end portion of the side plate and the inner side surface of the discharge volute. In the door.

A preferred specific configuration example of the present invention is as follows.
(1) The pump casing is made of a casting, and the wear ring member is made of stainless steel.
(2) The closing portion of the wear ring member is formed of a plate-like portion that extends from a wide gap to a narrow gap with respect to the side plate and then extends to reach the side surface of the discharge volute. thing.
(3) The wear ring member includes a protruding suction channel wall portion that projects from the mounting portion into the suction channel of the suction volute.
(4) The protruding suction channel wall portion has a suction channel surface that is thicker and semicircular than the mounting portion.

  According to the present invention, it is possible to provide a double suction centrifugal pump that suppresses unstable performance and generation of axial thrust in a low flow rate range and enables stable operation and downsizing of the bearing.

  Hereinafter, a plurality of embodiments of the present invention will be described with reference to the drawings. The same reference numerals in the drawings of the embodiments and the drawings of the prior art indicate the same or equivalent.

  The double suction centrifugal pump according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 7 is a longitudinal sectional view of the double suction centrifugal pump 1 of the first embodiment of the present invention, and FIG. 8 is a discharge volute in a flow rate range from the design point flow rate to the low flow rate of the double suction centrifugal pump 1 of the first embodiment. FIG. 9 is a cross-sectional view for explaining the internal flow, and FIG. 9 is a diagram showing the flow rate-head characteristics of the double suction centrifugal pump of the first embodiment.

  As shown in FIG. 7, both suction centrifugal pumps 1 are configured to include an impeller 30, a pump casing 20, a wear ring member 40, a shaft 7, and a bearing 8.

  The impeller 30 is configured by disposing a partition portion 31, blades 32 and side plates 33 so as to be sucked from both sides in the axial direction and discharged from the outer peripheral surface. The partition part 31 is located in the axial center part of the impeller 30, and is formed in the disk shape extended to radial direction outward. A plurality of blades 32 are provided in the circumferential direction on both sides of the impeller 30. The side plate 33 is provided on the side surface of the wing 32 in a conical ring shape.

  The pump casing 20 includes a discharge volute 21 that forms a discharge passage for fluid from the impeller 30 and a suction volute 22 that forms a suction passage for fluid to the impeller 30. The discharge volute 21 is formed wider than the outer peripheral surface of the impeller 30 in the axial direction so as to enlarge the discharge flow path, and is formed so as to cover the side surface of the impeller 30. Two suction volutes 22 are formed on both sides of the discharge volute 21 so as to surround the suction port of the impeller 30.

  The pump casing 20 is made of a casting because the sectional shape of the discharge volute 21 is a complicated three-dimensional shape that continuously changes from the start of winding of the volute to the discharge port. The casting pump casing 20 is used with the casting flow precision other than the portion where the wear ring member 40 is mounted, with the other flow channel shapes and the like being used.

  The wear ring member 40 is configured by integrally including a mounting portion 41 and a closing portion 42, and is made of stainless steel or the like. The mounting portion 41 is a portion that is mounted on the inner peripheral end surface of the discharge volute 22 that faces the suction side end of the side plate 33. The closing portion 42 is a portion that extends from the mounting portion 41 to the discharge end portion side of the side plate 33 and closes the gap between the discharge end portion of the side plate 33 and the inner surface of the discharge volute 21.

  Specifically, the closing portion 42 is formed of a plate-like portion that extends from the wide gap to the narrow gap 5 with respect to the side plate 33 and then extends to reach the side surface of the discharge volute 21. According to this structure, weight reduction can be achieved compared with the case where the suction volute 22 is thickened and the gap with the side plate 33 is narrowed. Further, when the shape of the side plate 33 is different (in other words, when the shape of the wing 32 is different), for example, even when the curvature of the side plate 33 is different, it is absorbed by the wide gap portion of the wear ring member 40 having the same shape. Can respond.

  The shaft 7 passes through the central portion of the partition portion 31 of the impeller 30 and is fixedly attached to the impeller 30, and is supported by brackets 23 provided on both sides of the pump casing 20. The bearing 8 is installed in the bracket 23 so as to rotatably support both end portions of the shaft 7.

  In the present embodiment, the gap between the discharge end portion of the side plate 33 and the inner surface of the discharge volute 21 is closed by the closing portion 42, so that there is no excessive flow into the gap from the discharge flow channel side of the discharge volute 21. It is small enough. As a result, the flow through the gap between the side plate 33 of the impeller 30 and the discharge volute 21 from the discharge flow path side of the discharge volute is substantially blocked, and the flow that keeps turning around the impeller as shown in FIG. It is suppressed. Therefore, the flow exiting the impeller 30 flows through the discharge flow path of the discharge volute 21 as shown in FIG. 8 even in the operation in the low flow rate region, and no excessive loss occurs. As shown in FIG. 9, no unstable part occurs. Of course, since the flow is not hindered at the design point, the head characteristic curve near the design point does not change in an unstable manner.

  Further, another effect in the present embodiment will be described below. As described above, since the pump casing 20 of the both suction centrifugal pump 1 is made of a casting, the gap between the side plate 33 of the impeller 30 and the discharge volute 21 must be widened as it is, and the gap is left and right. Asymmetric. In this case, for example, even at the design point flow rate, the flow swirling the gap between the impeller side plate and the discharge casing by the flow swirled by the rotation of the impeller is different due to the difference in cross-sectional area at that portion due to the difference in gap, The turning speed will be different on the left and right. Therefore, the difference in speed creates a pressure difference between the left and right, and the thrust in the axial direction should not work in a double suction centrifugal pump that is originally symmetrical. It will occur. On the other hand, in this embodiment, since the gap between the discharge end portion of the side plate 33 and the inner surface of the discharge volute 21 is closed by the closing portion 42, such axial thrust does not occur, and the bearing is It can be made smaller than before, and the pump can be made smaller.

  As described above, in this embodiment, the unstable performance at a low flow rate and the deviation of axial thrust generated in the conventional double suction centrifugal pump can be suppressed, stable operation control on the pump can be performed, and the bearing and pump Can be miniaturized.

  Furthermore, in this embodiment, since the gap between the side plate 33 of the impeller 30 and the discharge volute 21 is closed by the wear ring member 40, the pump casing 20 of the both suction centrifugal pump 1 is made of a casting and then the flow passage portion. Processing may not be performed. Therefore, the machining cost of the pump casing 20 can be reduced. In addition to this, a gap can be provided between the wear ring member 40 and the discharge volute 21 in this portion. In this case, the cross-sectional shape of the pump casing 20 may be set to the minimum thickness by ensuring the strength that can withstand the pressure difference between the discharge flow path and the suction flow path, particularly at the boundary between the discharge volute 21 and the suction volute 22. It will be. Therefore, useless wall thickness can be eliminated from the viewpoint of strength, the pump performance can be improved, the weight of the pump casing 20 can be reduced, and the manufacturing cost of the pump can be reduced. Furthermore, by setting it as such a shape, when manufacturing the pump casing 20, the casting flow of a casting can be improved and the defect at the time of casting manufacture can be reduced. Therefore, options for using materials having different properties such as ductite having a relatively poor casting flow are widened, the degree of freedom in designing the pump casing 20 is improved, and a more reliable pump can be designed.

  Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 10 is a cross-sectional view showing a double suction centrifugal pump according to a second embodiment of the present invention. The second embodiment is different from the first embodiment in the points described below, and the other points are basically the same as those in the first embodiment, and thus redundant description is omitted.

  In the second embodiment, the wear ring member 40 includes a protruding suction channel wall 43 that projects from the mounting portion 41 into the suction channel of the suction volute 22. In other words, the wear ring member 40 is mounted in the vicinity of the sliding portion between the impeller 30 and the inner peripheral end surface of the discharge volute 21, and the shape of the wear ring member 40 near the side plate 33 side at the inlet of the impeller on the suction volute side. However, it has a shape protruding in the upstream direction of the impeller inlet. The protruding suction channel wall 43 has a suction channel surface that is thicker than the mounting portion 41 and has a semicircular arc shape.

  By adopting such a shape, not only the performance instability and the axial thrust are suppressed as described in the first embodiment, but also a flow rectification effect at the impeller inlet is obtained. . Therefore, it is possible to suppress the occurrence of non-uniform circumferential cavitation generated at the impeller blades at the flow rate near the design point, and as a result, the cavitation performance can be improved. Further, when backflow occurs at the impeller inlet in a low flow rate region, particularly when the suction pressure is low, backflow accompanied by cavitation hits the protruding portion, and erosion due to cavitation bubble collapse is a concern. However, in this fourth embodiment, since a part of the wear ring member 40 forms the protruding suction flow passage wall 43, it is not necessary to change the material of the pump casing 20 to a relatively hard material in particular. By making the material of the wear ring member 40 hard and rust-resistant stainless steel, it becomes possible to suppress the erosion caused by the backflow of the inlet and the occurrence of corrosion. A ring made of another sliding member may be used between the wear ring member 40 and the seal portion of the impeller 30.

  According to the second embodiment, the unstable performance at a low flow rate generated in the conventional double suction centrifugal pump and the deviation of axial thrust can be suppressed, stable operation control on the pump can be performed, and the bearing and Providing a highly reliable double suction centrifugal pump that not only can reduce the size of the pump, but also can suppress pump cavitation performance and cavitation erosion during low suction water level and low flow rate operation. it can.

It is sectional drawing which shows the double suction vortex pump of the prior art 1. FIG. It is sectional drawing which shows the both suction centrifugal pump of the prior art 2. FIG. It is a figure which shows the flow volume-head characteristic of both the suction vortex pumps of prior arts 1 and 2. It is sectional drawing explaining the flow inside a discharge volute in the design point flow volume of the double suction vortex pump of the prior arts 1 and 2. FIG. It is sectional drawing explaining the flow inside a discharge volute in the low flow area of the both suction vortex pumps of prior art 1 and 2. It is sectional drawing explaining the flow of the impeller suction part in the low flow area of the both suction vortex pump of the prior art 2. FIG. It is sectional drawing which shows the double suction vortex pump of 1st Embodiment of this invention. It is sectional drawing explaining the flow inside a discharge volute in the flow volume range from the design point flow volume of the double suction vortex pump of 1st Embodiment of this invention to a low flow volume. It is a figure which shows the flow volume-head characteristic of the both suction vortex pump of 1st Embodiment of this invention. It is sectional drawing which shows the both suction vortex pump of 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Double suction vortex pump, 5 ... Gap, 7 ... Shaft, 8 ... Bearing, 9 ... Winding start part of discharge volute, 10 ... Partition plate of volute, 11 ... Discharge pipe, 12 ... Outer flow path of volute, 13 ... Inner flow path of volute, 20 ... pump casing, 21 ... discharge volute, 22 ... suction volute, 23 ... bracket, 30 ... impeller, 31 ... partition, 32 ... vane, 33 ... side plate, 40 ... wear ring member, 41 ... mounting part, 42 ... closing part.

Claims (5)

An impeller provided with a partition, wings and side plates so as to be sucked from both sides in the axial direction and discharged from the outer peripheral surface;
A pump casing having a suction volute that forms a suction passage for fluid to the impeller and a discharge volute that forms a discharge passage for fluid from the impeller; and
A wear ring member mounted on the inner peripheral end surface of the discharge volute facing the suction side end of the side plate, and
In the double suction centrifugal pump, the discharge volute is formed wider in the axial direction than the outer peripheral surface of the impeller,
The wear ring member includes a mounting portion mounted on an inner peripheral end surface of the discharge volute, a discharge side end portion of the side plate extending from the mounting portion to a discharge side end portion of the side plate, and an inner side surface of the discharge volute. Having a closing part that closes the gap between,
Double suction centrifugal pump characterized by   2. The double suction centrifugal pump according to claim 1, wherein the pump casing is made of a casting and the wear ring member is made of stainless steel.   3. The double suction centrifugal pump according to claim 1, wherein the closed portion of the wear ring member extends so as to have a gap that becomes a narrow gap from a wide gap with respect to the side plate, and then reaches a side surface of the discharge volute. A double suction centrifugal pump, characterized in that it is formed of a plate-like portion extending like this.   The double suction centrifugal pump according to claim 2, wherein the wear ring member includes a projecting suction channel wall portion projecting from the mounting portion into the suction channel of the suction volute. Centrifugal pump. 5. The double suction centrifugal pump according to claim 4, wherein the protruding suction flow channel wall portion has a suction channel surface that is thicker and semicircular than the mounting portion. .

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