JP2014020356A - Suction casing, and vertical shaft pump having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent both development of an underwater vortex in a suction casing and reduction of pump efficiency in a pump arranged in a vertical shaft.SOLUTION: A suction casing 1 of a vertical shaft pump is positioned below a pump arranged in a vertical shaft and formed by concrete to change a flow from a lateral direction to a vertical direction. Then, a center cone with a bottom part fixed to a bottom surface of the suction casing is arranged to oppose a suction port of the pump and a tabular removal protective plate is provided with one end connected to one end of the suction casing in a flow direction and the other end connected to the center cone. The center cone is formed into a cone shape standing erect from the bottom surface of the suction casing with a gradually decreasing radius as going upward. The removal preventive plate has a thickness that is sufficient enough to suppress occurrence of a swirl flow to a downstream of the center cone.

Description

  The present invention relates to a suction casing used for a pump device and a vertical shaft pump provided with the suction casing.

  An example of a conventional suction water tank is described in Patent Document 1. In the closed type pump suction water tank described in this publication, even if the flow velocity near the pump suction port is increased, the horizontal cross-sectional area from the floor surface of the suction water tank toward the pump suction port is prevented so that a submerged vortex does not occur. Is provided so as to face the suction port of the pump. Further, the two flat plates are arranged in a substantially V-shape in a range that is symmetrical with respect to the flow direction and has an opening angle of 30 ° to 100 ° toward the downstream side.

  An example of a conventional suction channel is described in Patent Document 2. The suction channel described in this publication is made of concrete, and a suction port of a vertical shaft pump is disposed in the vicinity of the end portion. The suction port is surrounded by an umbrella-shaped annular bulging portion, and a truncated conical protrusion whose diameter decreases from the bottom surface toward the suction port is disposed below the suction port. Furthermore, a flat partition is provided on the end portion side of the suction channel.

  Further, Patent Document 3 describes that a pump in which a cross-shaped baffle is attached directly below a suction bell mouth arranged downward is suspended from a pump-installed water tank. And the substantially semicircular punching metal-made underwater vortex generation prevention member is arrange | positioned in the area | region which opposes the rear wall of the pump installation water tank directly under the suction bell mouth.

Japanese Patent Laid-Open No. 11-13694 JP-A-6-137299 JP 2004-270479 A

  As described in Patent Document 2, when a suction casing having a concrete structure with an umbrella-shaped annular bulging portion is used, the excavation depth at the time of construction is less than that of a suction tank having a suction bend. Is possible. In recent years, there has been a demand for further cost reduction using this concrete-structured suction casing, reducing the width of the suction flow path and reducing the bottom depth of the machine field, and reducing the amount of excavation in the pump machine field. Reduced. As a result, in order to maintain the suction flow rate of the pump, the flow velocity in the suction casing is increased.

  When the flow velocity in the suction casing is increased, loss in the suction flow path is likely to increase. Also, in order to suppress the generation of the central vortex, many truncated cylindrical protrusions, that is, center cones, are arranged facing the suction port of the pump. A swirl flow is generated by shear flow with the flow. This swirl flow may develop into an underwater vortex with a cavity at the center of the vortex as the flow speed increases. When the developed underwater vortex interferes with the pump impeller, the vibration and noise of the pump increase, and in the worst case, the pump operation is hindered.

  Therefore, in the pump suction water tank described in Patent Document 1, two rectifying plates are provided as an underwater vortex preventing device. However, when the current plate is provided, the area of the flowing water portion is reduced and the flow velocity is increased. Furthermore, since a gap is formed between the wall surface of the suction casing and the partition plate, the flow that wraps around the back side of the rectifying plate is peeled off, or the wrapping flows collide with each other, resulting in flow turbulence. In other words, the rectified flow is made to flow in with the bell mouth shape as the suction shape, and the efficiency is improved, but if the turbulent flow flows into the suction part, the upstream rectified flow is not retained, and the efficiency is reduced. cause.

  In the suction channel device described in Patent Document 2, since the partition bodies are installed on both the upstream side and the downstream side of the suction flow path, the wet edge area increases by the amount of the partition body. Both the increase in friction loss due to the increase in wetted edge area and the increase in flow speed in the suction channel may increase fluid loss. In particular, this publication focuses on improving the efficiency of the pump and does not consider the generation of underwater vortices, so the thickness of the partition is not considered. If the thickness is reduced, the development of the swirling flow around the back side of the center cone is promoted, and there is a risk of developing into a submerged vortex.

  The vortex prevention device for the pump described in Patent Document 3 can prevent the swirling flow from developing into an underwater vortex when passing through the punching metal, and the change of the fixed building can be performed by renewing the pump. It seems to be effective because it is not necessary. However, the friction loss when passing through the punching metal cannot be ignored, and there is a risk that the efficiency of the pump is reduced.

  In any of the above prior arts, attention is focused on either preventing the development of submerged vortices at the pump suction port or improving efficiency. However, it has not been sufficiently considered to simultaneously prevent the development of submerged vortices and avoid the decrease in pump efficiency.

  The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to achieve both prevention of underwater vortex development in the suction casing and reduction in pump efficiency in a pump arranged on a vertical shaft. There is.

  A feature of the present invention that achieves the above object is a concrete suction casing of a vertical shaft pump that is positioned below a pump arranged on a vertical shaft so that a flow flowing in a lateral direction changes in a vertical direction, and a bottom portion is a suction port. A center cone fixed to the bottom surface of the casing and disposed opposite to the suction port of the pump, and a flat plate-shaped peeling prevention in which one end side is connected to one end in the flow direction of the suction casing and the center cone is connected to the center cone The center cone has a conical shape upright from the bottom surface of the suction casing, the radius of the center cone gradually decreases as it goes upward, and the thickness of the peeling prevention plate is swirled on the downstream side of the center cone. The thickness is to suppress the occurrence.

  And in this feature, the thickness of the peeling prevention plate is equal to or less than the diameter of the hub at the suction end of the impeller of the pump provided opposite to the center cone or the diameter of the column provided at the top of the center cone. The hub diameter or the diameter of the cylindrical portion of the center cone should be at least 1/2, and the shape of the peeling prevention plate opposite to the center cone connecting end is a bell mouth shape. desirable. Moreover, you may form the taper surface which reduces the thickness from the right-and-left both sides in the upper end part of the said peeling prevention board as it goes upwards.

  Another feature of the present invention that achieves the above object is that any one of the suction casings and the vertical shaft pump is used in combination.

  According to the present invention, in the concrete suction casing in which the vertical shaft pump is installed, a cone-shaped center cone that faces the vertical shaft pump and stands upright from the bottom surface, and the downstream end in the flow direction of the center cone and the suction casing are provided. Since the anti-separation plate for preventing the swirling flow from being connected is provided, it is possible to satisfy both the prevention of the development of the underwater vortex in the suction casing and the reduction of the efficiency of the pump.

The longitudinal cross-sectional view of one Example of the pump apparatus which concerns on this invention. The AA arrow directional view of FIG. It is a figure explaining underwater vortex, Comprising: The longitudinal cross-sectional view of a pump apparatus. It is a figure explaining a turning flow, Comprising: The cross-sectional view of a pump apparatus. It is a figure explaining the flow in a pump device, Comprising: The cross-sectional view of a pump device. Sectional drawing of the baffle plate used for the other Example of the suction casing which concerns on this invention. The graph explaining the thickness of a peeling prevention plate, the pump efficiency, and the relationship between submerged vortex generation frequency.

  Hereinafter, some embodiments of the pump device 100 according to the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of a pump device 100 according to the present invention. FIG. 2 shows an AA arrow view of FIG. The pump device 100 includes a concrete suction casing 1 that forms a flow path that flows in the lateral direction, and a vertical shaft pump 50 that is disposed above the suction casing 1.

  As shown in FIGS. 1 and 2, water flows from the right side to the left side in the suction casing 1. A further right side of the suction casing 1 is an open channel, and a closed channel having a ceiling 10 from the middle. That is, the ceiling 10 having a parallel portion 10 a substantially parallel to the bottom surface 16 of the suction casing 1 is provided so as to form a suction flow path of the pump 50. The ceiling 10 has an inclined portion 10b that narrows the flow path following the parallel portion 10a, and the inclined portion 10b is continuous with the suction port 2 of the pump 50 having a bell mouth shape.

  The left end side of the suction casing 1 shown in FIGS. 1 and 2 is formed in a shape in which the bell mouth 2 extends downward in a cylindrical shape, and forms a downstream side wall surface 4. A protrusion 12 is formed on the downstream side wall surface 4 in the substantially central portion in the width direction of the suction casing 1. A closed portion 4 a and a transition portion 4 b of the suction casing 1 are formed on both sides in the width direction of the suction casing 1 from the protrusion 12, and are connected to the upstream side wall surface 15 that defines the width of the suction casing 1. The protruding portion 12 has a shape (tapered shape) smoothly connected to the closed portion 4a so that the flow flowing along the left and right wall surfaces 15 of the suction casing 1 can flow into the pump 50 with less flow loss. .

A center cone 5 is disposed at the center of the bell mouth 2. The center cone 5 is disposed in order to suppress the generation of a central vortex when water flows into the vertical shaft pump 50 disposed opposite to the center cone 5. The center cone 5 includes a skirt portion (cone portion) 5b that gradually decreases its radius from the bottom surface 16 of the suction casing to a predetermined height so that the inflow of water into the pump 50 is smooth, and the skirt portion. (Cylindrical part) It is comprised from the column part 5a formed above the skirt part (conical part) 5b following the 5b. The diameter of the cylindrical portion is d _0.

  Above the center cone 5, a vertical shaft pump 50 is disposed concentrically with the center cone 5 at a slight distance. In the vertical shaft pump 50, the mixed flow impeller 3 is attached to the tip portion, and a prime mover such as an electric motor (not shown) rotates the rotary shaft 34 extending in the vertical direction to suck water from the suction casing 1. The water sucked from the impeller 3 is rectified in flow by the guide vanes 32, discharged through the discharge elbow 33, and discharged from the discharge port 35 to the outside of the machine. The distal end side of the rotating shaft 34 is connected to a boss portion 31 that forms the hub surface of the impeller 3. In this embodiment, a mixed flow pump is shown as the vertical pump 50, but the vertical pump 50 is not limited to a mixed flow pump, and may be an axial pump.

  Here, as a characteristic configuration of the present invention, the separation preventing plate 6 closes the gap between the protrusion 12 formed on the most downstream side of the suction casing 1 and the center cone 5. That is, the relatively thick flat plate-shaped anti-separation plate 6 is connected to the protruding portion 12 without a gap at a substantially vertical connection end 6a on the protruding portion 12 side, and has a shape that matches the shape of the bell mouth 2 above it. The connection end 6b is connected to the bell mouth 2 without a gap, and on the center cone 5 side, the bottom end 16 is connected to the center cone 5 without a gap by a connection end 6c having a shape corresponding to the shape of the center cone 5. Therefore, the flow that flows in from the upstream side of the suction casing 1 forms two separate flows at the center cone 5 part partitioned by the separation preventing plate 6.

  In the vertical pump 50 having the suction casing 1 according to the present invention configured as described above, the fluid (water) moves in the suction casing 1 in the lateral direction. The fluid that has flowed into the suction casing 1 changes its direction by approximately 90 degrees, and reaches the suction port (bell mouth) 2 of the vertical shaft pump 50 that is disposed facing the upper side of the suction casing 1. Then, it flows into the impeller 3 provided on the downstream side (upper side) of the suction port 2 of the vertical shaft pump 50.

  Since a center cone 5 having a horizontal cross-sectional area gradually decreasing is installed below the suction port 2 and coaxial with the suction port (bell mouth) 2 of the suction casing 1, the fluid flowing in the suction casing 2 in the lateral direction It can be smoothly changed to an upward flow. The center cone 5 is concentric with the suction port 2 and has an arc shape or a free-curved skirt portion 5b in which the horizontal cross-sectional area decreases smoothly as it goes upward, but the skirt portion 5b approximates a smooth curve. It is good also as the shape which connected the several truncated cone to do.

  By the way, with the request | requirement of size reduction of a pump station, the fluid in the suction casing 1 is high-flowing. As a result, the fluid flow loss that increases in proportion to the square of the flow velocity increases, and the pump efficiency tends to decrease. Moreover, since the speed of the fluid in the suction casing 1 has increased, the risk of generating underwater vortices is increasing.

  3 and 4 schematically show generation patterns of the underwater vortex 8. This is a case where the center cone 5 is arranged in order to prevent the central vortex from being generated at the suction port (bell mouth) 2 of the vertical shaft pump 50. The center cone 5 has a skirt portion 5b on the bottom surface 16 side of the suction casing 1 and a cylindrical portion 5a on the upper side thereof, and is concentric with the pump 50 at a slight distance as in the above embodiment. Has been placed.

  The flow that flows into the suction casing 1 is guided to the impeller 3 side of the pump 50 by the pumping force generated by the electric motor driving the rotating shaft of the vertical shaft pump 50. At that time, part of the flow passes through the center cone 5 and wraps around the back surface side (downstream side wall surface 4 side) of the cylindrical portion 5 a of the center cone 5. Then, the swirl flow 9 is generated by the shear flow of the separation of the flow passing through the center cone 5 and the flow on the back side. When this swirl flow 9 develops, it becomes an underwater vortex 8 and flows into the impeller 3. This underwater vortex not only generates vibration and noise in the pump 50, but also reduces the efficiency of the pump 50 due to flow disturbance.

  Further, as shown in FIG. 5, the flow 20 along the left and right walls along the upstream side wall surface 15 of the suction casing and flowing into the suction port 2 of the pump 50 from a position away from the center cone 5 is on the back side of the center cone 5. Collide and form a turbulent flow. The turbulent flow then flows into the impeller 3 and contributes to the performance degradation of the pump 50.

  Therefore, in order to prevent a reduction in efficiency of the pump 50, the loss due to the turbulent flow generated between the suction casing 1 and the suction port 2 of the pump 50 is reduced, that is, between the suction casing 1 and the pump suction port 2. It is necessary to guide to the impeller 3 without disturbing the flow of the air as much as possible. Moreover, it is also necessary to reduce the friction loss by reducing the wetted edge area on the downstream side wall surface 4 of the suction casing 1 and the surface of the center cone 5.

  On the other hand, in order to prevent the generation of the underwater vortex 8, it is important to suppress the swirling flow generated on the back surface of the center cone 5, particularly the back surface of the cylindrical portion 5a. As described above, the generation of the swirling flow is caused by the separation of the flow in the center cone 5, so that no separation region is formed on the back side (downstream side wall surface 4 side) of the center cone 5, that is, the center. It is preferable to prevent the flow from flowing into the back side of the cone 5.

Therefore, in the present invention, in order to suppress the occurrence of a swirling flow that is prominent on the back surface side (downstream side wall surface 4 side) of the cylindrical portion 5a of the center cone 1, separation with a thickness similar to that of the cylindrical portion 5a of the center cone 1 is performed. The prevention plate 6 is provided to prevent the separated flow from flowing into the back side of the cylindrical portion 5a. In addition, since the swirl flow is substantially suppressed if the region where the separation flow flows into the back side (downstream side wall surface 4 side) of the center cone 5 is reduced to about ½ of the diameter of the cylindrical portion 5a, the separation flow is substantially suppressed. The thickness θ of the prevention plate 6 is set to θ = ½d ₀ to d ₀ .

Here, the diameter d ₀ of the cylindrical portion 5a of the center cone 5, as disturbances to the impeller 3 of the pump 50 is small and the flow enters, and substantially the same diameter as the hub side diameter d _1h suction mouth of the impeller 3 ing. Therefore, the thickness θ of the rectifying plate may be θ = ½d _{1h to} d _1h .

  In the conventional suction channel, as described in Patent Document 2, paying attention to the smooth flow of the flow, the thickness of the partition plate attached to the center cone 5 is sufficiently thin compared to the diameter of the center cone. . For example, the thickness is 10% or less of the minimum diameter D between the pump suction port 2 and the impeller 3. In this way, when thin partition bodies are installed on the upstream side and the downstream side of the center cone 5, the partition body does not fill the separation region that may be formed on the back surface of the center cone 5. There is concern about the generation of underwater vortices due to the separated flow.

  In the present invention, since the separation preventing plate 6 is provided in the suction casing 1, the flow path between the downstream side wall surface 4 and the center cone 5 of the suction casing 1 is partitioned, and collision of flows along the left and right wall surfaces is prevented. . Further, since the separation preventing plate 6 has a thickness sufficient to prevent the separation of the flow, which is particularly noticeable in the cylindrical portion 5a of the center cone 5, it is possible to suppress the generation of underwater vortices resulting from the swirling flow.

  If the thickness θ of the separation preventing plate 6 is any one of the above thicknesses, the separation region that may be formed on the back side of the center cone 5 can be crushed, and the generation of the underwater vortex 8 can be prevented. Even if the swirling flow 9 is generated depending on the operating conditions of the pump 50, the separation preventing plate 6 has a sufficient thickness, so that the swirling flow 9 interferes with the separation preventing plate 6 and develops into the underwater vortex 8. Can be prevented. Since the swirl flow 9 is suppressed, the flow flowing into the impeller 3 is rectified, and the efficiency reduction of the pump 50 can be suppressed.

  The protrusion 12 formed at the center of the downstream side wall surface 4 of the suction casing 1 in the channel width direction is a trapezoidal cross-sectional shape, and is an inclined surface 12a whose both side portions are inclined upstream. The protrusion 12 is connected to the anti-separation plate 6 and prevents the flow around the back side of the center cone 5 from staying. Thereby, the efficiency fall of the pump 50 is suppressed. In the present embodiment, the protrusion 12 has a trapezoidal shape, but the same effect can be obtained even if the inclined surface 12a has a circular arc shape or a free curve shape.

  FIG. 6 shows another embodiment of the peeling preventing plate 6. In this embodiment, a tapered surface 7 is formed on the upper end portion of the peeling preventing plate 6. If the tapered surface 7 is formed, peeling that may occur at the upper part of the peeling prevention plate 6 due to the upward flow as the suction flow into the pump 50 can be prevented more reliably. Generation | occurrence | production of a submerged vortex and the turbulent flow can flow into an impeller, and can prevent that the efficiency of the pump 50 falls. Thus, since the taper surface 7 was formed in the upper part of the peeling prevention board 6, a fluid flows along the taper surface 7, and peeling is suppressed. In the present embodiment, the tapered surface 7 is formed at the upper end portion of the peeling preventing plate 6, but the same effect can be obtained even when the shape is an arc shape or a free curve.

  FIG. 7 is a graph showing the relationship between the plate thickness θ of the separation preventing plate 6, the efficiency η of the pump 50, and the underwater vortex generation frequency fq. The thickness θ of the separation preventing plate 6 is compared with the minimum diameter D between the pump suction port 2 and the impeller 3. When the thickness θ of the separation preventing plate 6 is 15% or less (θ <0.15D) of the minimum diameter D between the pump suction port 2 and the impeller 3, the swirl flow 9 generated from the back surface portion of the center cone 5. Can not be suppressed, and the frequency of development of underwater vortices increases.

  On the contrary, if the plate thickness θ of the separation preventing plate 6 becomes too thick (θ> 0.3D), the flow width (circumferential width) of the upward flow flowing from the suction casing 1 to the pump suction port 2 is increased. It becomes narrow, the inflow speed to the impeller 3 becomes too large, and the loss in the suction flow path increases. As a result, the efficiency of the pump 50 is reduced. Therefore, the thickness θ of the peeling prevention plate 6 is effectively 15% to 30% of the minimum diameter D between the pump suction port 2 and the impeller 3.

  As described above, the reduction in pump efficiency can be suppressed and the occurrence of the underwater vortex 8 can be prevented only by installing one separation preventing plate 6 according to the present invention. Conventionally, parts and devices have been provided individually to prevent the pump efficiency from decreasing and to prevent the generation of underwater vortices. However, according to the present invention, both problems can be solved by a single peeling prevention plate. Therefore, the number of parts can be reduced. Thereby, cost reduction and downsizing of the suction casing can be realized.

DESCRIPTION OF SYMBOLS 1 ... Suction casing, 2 ... Pump suction port (bell mouth), 3 ... Impeller, 4 ... Suction casing downstream side wall surface, 4a ... Closure part, 4b ... Transition part, 5 ... Center cone, 5a ... Cylindrical part, 5b ... Skirt part (conical part), 6 ... peeling prevention plate, 6a ... connection end (projection part side), 6b ... connection end (bell mouth side), 6c ... connection end (center cone side), 7 ... taper surface, 8 ... underwater vortex, 9 ... swirl flow, 10 ... ceiling wall surface, 10a ... horizontal portion, 10b ... inclined portion, 11 ... collision flow, 12 ... protrusion of suction casing, 12a ... inclined surface, 15 ... upstream side wall surface, 16 ... bottom, 20 ... lateral wall along the flow, 31 ... boss part, 32 ... guide vane, 33 ... discharge elbow, 34 ... rotary shaft, 35 ... discharge port, 50 ... (vertical spindle) pump, 100 ... pumping device, _{d 0} ... The diameter of the cylindrical part of the center cone, D ... the inlet diameter of the impeller.

Claims (7)

In the concrete suction casing of the vertical shaft, which is located below the pump arranged on the vertical shaft and formed so that the flow flowing in the lateral direction changes in the vertical direction,
A flat plate in which the bottom is fixed to the bottom of the suction casing and is disposed opposite to the suction port of the pump, and one end connected to one end in the flow direction of the suction casing is connected to the center cone. The center cone is a conical shape upright from the bottom surface of the suction casing, and its radius gradually decreases as it goes upward, and the thickness of the peel prevention plate is on the downstream side of the center cone. A suction casing having a thickness that suppresses the generation of swirling flow.   The thickness of the peeling prevention plate is equal to or less than a hub diameter at a suction end portion of an impeller included in a pump provided to face the center cone, and is equal to or more than ½ of the hub diameter. The suction casing according to Item 1.   2. The suction casing according to claim 1, wherein a thickness of the peeling prevention plate is equal to or less than a diameter of a columnar portion provided on an upper portion of the center cone and is equal to or greater than ½ of a diameter of the columnar portion.   The suction casing according to claim 1, wherein the thickness of the peeling prevention plate is 15% to 30% of a minimum diameter between the pump suction port and the impeller.   The suction casing according to claim 1, wherein a shape of an end opposite to the center cone connecting end of the peeling preventing plate is a bell mouth shape.   The suction casing according to claim 1, wherein a taper surface is formed on an upper end portion of the peeling prevention plate so as to decrease its thickness from both left and right sides as it goes upward.   A vertical shaft pump used in combination with the suction casing according to any one of claims 1 to 6.

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