JP2019183754A - Prior standby operation pump - Google Patents

Abstract

To provide a prior standby operation pump capable of performing air lock more positively.SOLUTION: This invention provides a prior standby operation pump. This prior standby operation pump comprises an impeller, a casing for storing the impeller, a protrusion part arranged at an inner surface of the casing placed upstream of the impeller in an axial direction and a suction port formed at the surface of the protrusion. The casing has a straight pipe portion located downstream of the impeller in the axial direction. The protrusion part has a guiding surface formed in such a way that its protrusion amount from the inner surface of the casing is gradually decreased as it is far from the suction port. When an outer diameter of the straight pipe part is defined as D, a protrusion amount of the protrusion from the inner surface of the casing is 0.05D or more and 0.09D or less.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a preceding standby operation pump.

  In recent years, due to the progress of urbanization, the heat island phenomenon has occurred due to the decrease in green spaces, the road surface becoming concrete and the expansion of asphalt, and so-called guerrilla heavy rains frequently occur in urban areas. A large amount of local rainfall is introduced into the waterway without being absorbed into the ground on concrete and asphalt road surfaces. As a result, a large amount of rainwater flows into the drainage station in a short time.

  In preparation for the rapid drainage of a large amount of rainwater caused by such a heavy rain, a preliminary standby operation is performed at a drainage pump installed at a drainage station. The preceding standby operation is an operation method in which rainwater is started in advance before reaching the drainage station, and the preceding standby operation prevents inundation damage due to the start delay.

  FIG. 1 is a partial schematic view of a conventional vertical shaft pump that performs a prior standby operation. A vertical shaft pump 110 is disposed in the water tank 100 of the drainage station. The vertical shaft pump 110 includes a rotary shaft 112 arranged vertically and an impeller 114 provided at the tip of the rotary shaft 112. The vertical shaft pump 110 is provided with an air inlet 118 on the side surface of the bell mouth 116 on the inlet side of the impeller 114. An air pipe 120 having an opening 120a that is in contact with outside air is attached to the intake port 118. Thereby, in this vertical pump 110, the supply amount of the air supplied into the vertical pump 110 via the intake port 118 is changed according to the water level, and the drainage amount of the vertical pump 110 is controlled below the minimum operating water level LWL.

  FIG. 2 is a diagram for explaining the operating state of the preceding standby operation. As shown in FIG. 2, in the preceding standby operation, the vertical shaft pump is started in advance based on rainfall information or the like regardless of the suction water level (A: air operation). When rainwater reaches the drainage station, as the water level rises from a low water level, the water level reaches the impeller position, and the vertical shaft pump is an operation that stirs water with the impeller from an empty operation (air operation) (B: air water) Move to stirring operation. Further, the vertical shaft pump performs a full-volume operation (D: discharge of water at a rated flow rate) through an operation of gradually increasing the amount of water (C: air-water mixing operation) while sucking in air supplied through the intake port together with water. Transition to steady operation.

  As described above, the vertical pump for the preliminary standby operation is provided with an intake port that naturally inhales air in the atmosphere to the bell mouth in response to a decrease in the static pressure in the bell mouth accompanying a drop in the water level. As a result, when the water level drops from the high water level, the operation is shifted from the steady operation to the operation (C: air-water mixing operation) in which the amount of water is gradually reduced while the air supplied from the intake port is sucked together with the water. When the water level further decreases and reaches a predetermined airlock water level, an air pool is formed below the impeller, and the operation shifts to an operation in which water above the impeller is agitated by the impeller (E: airlock operation). In the airlock operation, the water above the impeller is stirred by the impeller and the weight of the water is supported, so the pump flow rate is zero. When the water level rises again, the operation moves to the air / water mixing operation.

  By the way, in a normal vertical shaft pump, when the water level drops from steady operation and the water level reaches below the bell suction port, a large amount of air enters at once from the bell suction port exposed to the atmosphere, which causes severe vibration and noise. appear. For this reason, in the vertical shaft pump for the standby operation, it is important that when the water level drops from the steady operation, the bell mouth is appropriately sucked into the bell mouth to surely shift to the air lock operation.

  In addition, a pump for improving the intake from the intake port is known as a pump for the preliminary standby operation. For example, Patent Document 1 discloses a structure in which an air inlet is formed in a slit shape along the circumferential direction on the inner surface of a bell.

Japanese Patent No. 4463484

  While the vertical pump is in steady operation, the liquid is discharged at the rated flow rate. The liquid flowing in the vertical pump at this time is dominated by the axial flow of the vertical pump. On the other hand, when the flow rate decreases as the water level decreases from steady operation (for example, at a partial flow rate of 30% of the rated flow rate), the liquid flow at the height of the intake port is affected by the rotating impeller. Ingredients become dominant. Therefore, when liquid is discharged at a partial flow rate, a centrifugal field is generated at the height of the intake port in the bell mouth, and a relatively high static pressure is generated radially outside the bell mouth, that is, near the opening of the intake port. Become.

  In this regard, in the intake structure disclosed in Patent Document 1, the intake port is formed on the inner surface of the casing. However, as described above, when liquid is discharged at a partial flow rate, a relatively high static pressure is generated in the vicinity of the intake port. May not be done properly.

  The present invention has been made in view of the above problems. An object of the present invention is to provide a preceding standby operation pump that can perform air lock more reliably.

  According to one embodiment, a pre-standby operation pump is provided. The preceding standby operation pump includes an impeller, a casing that houses the impeller, a convex portion that is provided on the inner surface of the casing on the upstream side in the axial direction from the impeller, and an intake port that is formed on a surface of the convex portion. Have The casing includes a straight pipe portion located on the downstream side in the axial direction from the impeller. The convex portion has a guide surface formed so that the amount of protrusion from the inner surface of the casing gradually decreases as the distance from the intake port increases. When the outer diameter of the straight pipe portion is D, the protruding amount of the convex portion from the inner surface of the casing is 0.05D or more and 0.09D or less.

It is a partial schematic diagram of a conventional vertical shaft pump that performs a prior standby operation. It is a figure for demonstrating the driving | running state of a prior | preceding standby driving | operation. It is a schematic sectional side view of the advance standby operation pump which concerns on this embodiment. FIG. 4 is a schematic enlarged view of the vicinity of a bell mouth of the preceding standby pump shown in FIG. 3. It is the schematic which looked at the inner surface of the lower end part of the bell mouth shown in FIG. 4 from the axial direction downstream side. It is the front view which looked at an example of the convex part from the radial direction inner side of the bellmouth. It is the side view which looked at the convex part shown to FIG. 6A from the circumferential direction. It is the side view which looked at the convex part shown to FIG. 6A from the axial direction downstream. It is a schematic diagram for demonstrating the physical mechanism in which a static pressure falls in the inlet-port vicinity. It is a side view which shows another example of a convex part. It is a graph which shows the simulation result of the static pressure fluctuation | variation in the inlet port of the prior | preceding standby operation pump which has a convex part from which protrusion amounts differ. It is a bar graph which shows the average value of the static pressure shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings described below, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted. In the embodiment described below, a vertical shaft pump is described as an example of the preceding standby operation pump of the present invention.

  FIG. 3 is a schematic sectional side view of the preceding standby operation pump according to the present embodiment. As shown in FIG. 3, the preceding standby operation pump includes an impeller 11, a rotating shaft 18, and a casing 12. The casing 12 has a cylindrical shape as a whole, and includes a discharge elbow 12a, a straight pipe portion 12b, a discharge bowl 12c, and a bell mouth 12d. The discharge elbow 12a is fixed to a pump installation floor (not shown), and one end is connected to a discharge pipe (not shown). The straight pipe portion 12b is connected to the lower end of the discharge elbow 12a. The discharge bowl 12c is connected to the lower end of the straight pipe portion 12b and stores the impeller 11 therein. The bell mouth 12d is connected to the lower end of the discharge bowl 12c and constitutes an inlet for sucking water.

  The rotating shaft 18 is disposed so as to extend substantially in the radial center of the straight pipe portion 12b, the discharge bowl 12c, and the bell mouth 12d of the casing 12. The rotating shaft 18 is rotatably supported by a slide bearing (not shown). The impeller 11 is connected to one end side (upstream side) of the rotating shaft 18. The other end side (downstream side) of the rotary shaft 18 extends to the outside of the preceding standby operation pump through a hole provided in the discharge elbow 12a, and is connected to a drive source 19 such as an engine or a motor.

  A shaft seal (not shown) such as a floating seal, a gland packing, or a mechanical seal is provided between the rotary shaft 18 and a hole provided in the discharge elbow 12a. This prevents water handled by the preceding standby operation pump from flowing out of the preceding standby operation pump. The drive source 19 is provided on land so that maintenance and inspection can be easily performed. The driving force of the driving source 19 is transmitted to the rotating shaft 18 and the impeller 11 can be rotated. The water whose pressure is increased by the rotation of the impeller 11 is sucked from the bell mouth 12d, passes through the discharge bowl 12c and the straight pipe portion 12b, and is discharged from the discharge elbow 12a.

  4 is a schematic enlarged view of the vicinity of the bell mouth 12d of the preceding standby pump shown in FIG. FIG. 5 is a schematic view of the inner surface of the lower end portion of the bell mouth 12d shown in FIG. 4 as viewed from the downstream side in the axial direction. As shown in FIG. 4, the discharge bowl 12 c and the bell mouth 12 d of the casing 12 are connected via a flange at a position upstream of the impeller 11. The vicinity of the end of the rotary shaft 18 is rotatably supported by the slide bearing 30. The rotating shaft 18 is inserted into the impeller 11, and is fixed by a key so that the rotating shaft 18 and the impeller 11 do not move relative to each other in the rotation direction. Thereby, the driving force in the rotation direction of the rotating shaft 18 is transmitted to the impeller 11. A cap 31 is attached to the end of the rotating shaft 18. Thereby, the rotating shaft 18 and the impeller 11 are fixed so as not to move relative to each other in the axial direction.

As described above, when the flow rate is reduced from the steady operation in the preceding standby operation pump as the water level is reduced, the circumferential velocity component is dominant in the water flow at the intake port height due to the influence of the rotating impeller 11. become. Here, it is empirically known that the air lock occurs when the flow rate is about 30% of the flow rate (rated flow rate) during steady operation. Therefore, immediately before the air lock occurs, the circumferential velocity component is dominant in the water flow at the height of the intake port of the bell mouth 12d. As a result, immediately before the air lock occurs, a centrifugal field is generated in the vicinity of the intake port, and a relatively high static pressure is generated on the radially outer side in the bell mouth 12d, that is, in the vicinity of the opening of the intake port. The amount of intake air from the intake port into the bell mouth 12d depends on the static pressure near the intake port. That is, the higher the static pressure in the vicinity of the intake port, the more difficult it is to intake air from the intake port, and it becomes difficult to generate an appropriate air lock as the intake port decreases.

  Therefore, in the preceding standby operation pump of the present embodiment, the convex portion 13 is provided on the inner surface of the bell mouth 12d, and the intake port 14 is formed in the convex portion 13. Thereby, compared with the case where the convex part 13 does not exist, the static pressure of the suction inlet 14 vicinity can be lowered | hung. As a result, even when a flow of water in which the circumferential velocity component is dominant occurs in the bell mouth 12d, it is possible to appropriately inhale the air into the bell mouth 12d.

  As shown in FIGS. 4 and 5, a plurality of convex portions 13 are provided at equal intervals in the circumferential direction 22 on the inner surface of the bell mouth 12d. Further, the plurality of convex portions 13 are located on the upstream side of the impeller 11. In the present embodiment, the number of the convex portions 13 is four, but is not limited thereto, and may be any number of 3 or less or 5 or more. Moreover, in this embodiment, although the some convex part 13 is provided in the circumferential direction 22 at equal intervals, it is not restricted to this, You may provide unevenly along the circumferential direction 22. FIG. In the present embodiment, the direction in which the rotary shaft 18 extends is referred to as an axial direction 21, and the rotational direction of the impeller 11 is referred to as a circumferential direction 22.

  An intake port 14 is formed near the apex of the convex portion 13. A cylindrical space (intake hole) extending from the intake port 14 is formed so as to penetrate the convex portion 13 and communicates with an annular air chamber 17 provided on the radially outer side of the convex portion 13. An air pipe 16 having one end exposed to the atmosphere is connected to the air chamber 17. Thereby, air in the atmosphere is supplied into the bell mouth 12d through the air pipe 16, the air chamber 17, and the air inlet 14 according to the pressure difference between the pressure near the air inlet 14 and the atmospheric pressure. The shape of the intake hole extending from the intake port 14 is not limited to a cylindrical shape, and any shape can be adopted.

  The convex part 13 can be manufactured by casting integrally with the casing 12, for example. As will be described later, the protruding amount of the convex portion 13 is appropriately set according to the inner diameter of the bell mouth 12d at the position where the convex portion 13 is provided. As shown in FIG. 5, the shape of the inner surface 12e of the bell mouth 12d when viewed from the axial direction 21 is substantially circular.

  Next, the shape of the convex portion 13 shown in FIGS. 3 to 5 will be described in detail. FIG. 6A is a front view of an example of the convex portion 13 as viewed from the inside in the radial direction of the bell mouth 12d. 6B is a side view of the convex portion 13 shown in FIG. FIG. 6C is a side view of the convex portion 13 shown in FIG. 6A as viewed from the downstream side in the axial direction 21.

  As shown to FIG. 6A, the convex part 13 of this embodiment is formed in a substantially circular shape when it sees from a front. Further, in the present embodiment, the intake port 14 is provided at a substantially central portion of the convex portion 13. As shown in FIG. 6B, the convex portion 13 has a guide surface 15 in which the protruding amount from the inner surface 12e of the bell mouth 12d gradually decreases as the distance from the intake port 14 in the axial direction 21 increases. Further, as shown in FIG. 6C, the convex portion 13 has a guide surface 15 in which the amount of protrusion from the inner surface 12e of the bell mouth 12d gradually decreases as the distance from the air inlet 14 in the circumferential direction 22 increases. Specifically, the guide surface 15 of the convex portion 13 has a convex surface 15a located at a substantially central portion of the convex portion 13 and a concave surface 15b located on the outer periphery of the convex surface 15a. The convex surface 15a is a curved surface that forms the top of the convex portion 13 and protrudes in a direction away from the inner surface 12e of the bell mouth 12d. The concave surface 15b is a curved surface connecting the convex surface 15a and the inner surface 12e of the bell mouth 12d, which is recessed so as to approach the inner surface 12e of the bell mouth 12d. The convex surface 15a and the concave surface 15b are formed continuously with each other, and the convex surface 15a and the concave surface 15b constitute the guide surface 15 of the convex portion 13. The protruding amount of the bell mouth 12d from the inner surface 12e gradually decreases as the guide surface 15 of the convex portion 13 moves away from the central portion (intake port 14) in a direction orthogonal to the protruding direction of the convex portion 13. it can.

  As shown in FIGS. 6B and 6C, the convex surface 15a of the convex portion 13 is formed to be substantially flat in a side view when the air inlet 14 is formed. On the other hand, FIG. 6B and FIG. 6C show a virtual line 15d obtained by extending the convex surface 15a along the curvature of the convex surface 15a of the convex portion 13. In the present embodiment, the protruding amount of the convex portion 13 refers to the length from the inner surface of the bell mouth 12d to the top of the virtual line 15d at the position where the convex portion 13 is provided.

  Next, the principle that the static pressure in the vicinity of the intake port 14 is lowered by the convex portion 13 will be described. FIG. 7 is a schematic diagram for explaining a physical mechanism in which the static pressure is reduced in the vicinity of the intake port 14. As shown in FIG. 7, when the convex part 13 exists in a flow path, the fluid which flows through the flow path A near the guide surface 15 of the convex part 13 is along the surface of the convex part 13 by the viscosity of the fluid. Flowing. Here, the fluid flowing along the surface of the convex portion 13 passes between the cross sections S1 and S2 in the flow direction as compared with the fluid flowing through the flow channel B farther from the guide surface 15 of the convex portion 13 than the flow channel A. Since the road to go becomes long, the fluid in the vicinity of the guide surface 15 of the convex portion 13 tends to increase in flow velocity.

  Based on Bernoulli's equation, when the fluid flow rate increases, the fluid static pressure decreases. For this reason, the static pressure of the fluid locally decreases in the vicinity of the guide surface 15 of the convex portion 13, particularly in the vicinity of the intake port 14. 6A to 6C has a curved guide surface 15, the fluid in the vicinity of the intake port 14 can smoothly flow along the guide surface 15, and the fluid peels from the guide surface 15. This can be suppressed.

  As described above, immediately before the air lock occurs, the circumferential velocity component is dominant in the flow of water at the height of the inlet 14 of the bell mouth 12d. As a result, immediately before the occurrence of airlock (at the time of partial flow), a centrifugal field is generated in the vicinity of the intake port 14, and a relatively high static pressure is generated on the radially outer side in the bell mouth 12d, that is, near the opening of the intake port 14. . On the other hand, according to the preceding standby operation pump of the present embodiment, the static pressure in the vicinity of the intake port 14 is locally reduced by the circumferential speed component formed at the partial flow rate because the intake port 14 is formed in the convex portion 13. Therefore, the air can be sucked into the bell mouth 12d, and the success rate of the air lock can be increased.

  In the present embodiment, the guide surface 15 of the convex portion 13 has been described as having the convex surface 15a and the concave surface 15b, but the surface shape of the guide surface 15 is not limited to this. FIG. 8 is a side view showing another example of the convex portion 13. The convex portion 13 in the example shown in FIG. 8 has a convex surface 15a and a concave surface 15b, and further has a transition surface 15c that connects the convex surface 15a and the concave surface 15b. The convex surface 15 a is a curved surface that forms the top of the convex portion 13. The transition surface 15c is a surface parallel to the protruding direction of the convex portion 13, that is, the radial direction of the bell mouth 12d. The concave surface 15b is a curved surface that connects the transition surface 15c and the inner surface 12e of the bell mouth 12d. The guide surface 15 in the convex portion 13 shown in FIG. 8 is a convex surface 15a and a concave surface 15b in which the amount of protrusion from the inner surface 12e of the bell mouth 12d gradually decreases as the distance from the central portion (intake port 14) increases.

  Further, the guide surface 15 may have a curved surface such as a convex surface 15a or a concave surface 15b, or may have an inclined surface having a predetermined angle. For example, the convex portion 13 may have a guide surface 15 whose protrusion amount decreases linearly with distance from the central portion (intake port 14). More specifically, the transition surface 15c shown in FIG. 8 is a surface parallel to the protruding direction of the convex portion 13, but the transition surface 15c may be inclined at a predetermined angle with respect to the protruding direction of the convex portion 13. In this case, the transition surface 15 c can also be a part of the guide surface 15.

Next, an appropriate protrusion amount of the convex portion 13 will be described. In the preceding standby operation pump of the present embodiment, the convex portion 13 is provided on the inner surface of the bell mouth 12 d and the intake port 14 is formed in the convex portion 13. Thereby, compared with the case where the convex part 13 does not exist, the static pressure of the suction inlet 14 vicinity can be lowered | hung. Furthermore, the present inventor has found that the degree of decrease in the static pressure at the air inlet 14 varies greatly depending on the protrusion amount of the convex portion 13, and found a suitable protrusion amount.

FIG. 9 is a graph showing a simulation result of the static pressure fluctuation at the intake port 14 of the preceding standby operation pump having the protrusions 13 having different protrusion amounts. In the graph, the horizontal axis represents elapsed time (seconds), and the vertical axis represents static pressure (Pa). This graph is obtained by analyzing the static pressure fluctuation in the intake port 14 by the finite volume method when the outer diameter of the straight pipe portion 12b is φ600 mm and the rotation speed of the impeller 11 is 960 min ^−1. . The pump flow rate was approximately 19.3 m ³ / min, and approximately 30% of the rated flow rate. Therefore, the pump flow rate at this time is in the vicinity of the flow rate at which the airlock is generated. In this analysis, as shown in FIG. 5, the four convex portions 13 are provided on the inner surface 12 e of the bell mouth 12 d at equal intervals in the circumferential direction 22.

  This analysis was performed when the protruding amount of the convex portion 13 was 33 mm, 45 mm, 56 mm, and 67 mm. The result shown in FIG. 9 shows the static pressure fluctuation during two revolutions of the impeller 11. As shown in FIG. 9, it can be seen that the static pressure at each protrusion amount varies between approximately −25000 Pa and −40000 Pa.

  FIG. 10 is a bar graph showing the average value of the static pressure shown in FIG. As shown in FIG. 10, the static pressure average value when the protrusion amount is 33 mm is about −30600 Pa, the static pressure average value when it is 45 mm is about −33000 Pa, and the static pressure average value when it is 56 mm is about −29500 Pa and 67 mm. In this case, the static pressure average value was −28400 Pa. Therefore, it has been found that the protrusion amount is preferably 45 mm because the static pressure is the lowest. Also, when the protrusion amount was 33 mm, a better result was obtained as compared with the cases of 56 mm and 67 mm.

  Next, in the preceding standby operation pump having the protruding portion 13 of the protruding amount shown in FIGS. 9 and 10, an experiment was performed to confirm the water level at which the airlock occurred when the water level was gradually lowered from the steady operation. . As described above, when the water level drops from the steady operation and the water level reaches below the bell suction port, a large amount of air enters at a stretch from the bell suction port exposed to the atmosphere, and intense vibration and noise are generated. Since the water level does not necessarily gradually decrease, the airlock needs to occur at the design value water level planned at the time of design. In particular, an air lock at a water level lower than the design value is dangerous and must be avoided. Therefore, in this experiment, when the height of the bell suction port (opening end of the bell mouth 12d) is 0 and the height from the bell suction port to the intake port 14 is H, the water level from 0 to 100 m upwards. The case where an air lock occurred at the time of the test was regarded as acceptable, and the case where the air lock occurred at a water level lower than 0 was regarded as unacceptable. As a result of the experiment, when the protrusion amount was 33 mm and 45 mm, the water level at the time of air lock was within the above acceptable range. On the other hand, when the protrusion amount was 56 mm and 67 mm, the water level at the time of air lock was in the above-mentioned range of rejection.

  In view of the above simulation results and experimental results, under the reference static pressure condition at the time of the simulation conducted this time, if the static pressure average value at the intake port is about −30000 Pa or less, airlock occurs at the water level in the acceptable range. It is guessed. Then, it is estimated that the preferable range of protrusion amount is 0.05D or more and 0.09D or less, where D is the outer diameter of the straight pipe portion 12d. Furthermore, if the convex part 13 is 0.07D or more and 0.08D or less, the fall of a static pressure is anticipated more and the air lock in a still higher position is attained.

As mentioned above, although embodiment of this invention was described, embodiment of the invention mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes the equivalents thereof. In addition, any combination or omission of each component described in the claims and the specification is possible within a range in which at least a part of the above-described problems can be solved or a range in which at least a part of the effect is achieved. is there.

Some of the forms disclosed in this specification will be described below.
According to the first embodiment, a preceding standby operation pump is provided. The preceding standby operation pump includes an impeller, a casing that houses the impeller, a convex portion that is provided on the inner surface of the casing on the upstream side in the axial direction from the impeller, and an intake port that is formed on a surface of the convex portion, Have The casing includes a straight pipe portion located on the downstream side in the axial direction from the impeller. The convex portion has a guide surface formed so that the amount of protrusion from the inner surface of the casing gradually decreases as the distance from the intake port increases, and when the outer diameter of the straight pipe portion is D, The protrusion amount of the convex portion from the inner surface of the casing is 0.05D or more and 0.09D or less.

  According to the first embodiment, since the convex portion has the guide surface, the fluid flowing along the vicinity of the guide surface tends to increase in flow velocity as compared with the fluid flowing in the flow path separated from the guide surface. As a result, the increase in flow velocity is accompanied by a decrease in static pressure according to Bernoulli's equation, so that the static pressure decreases in the vicinity of the guide surface. As a result, the intake air amount supplied from the intake port can be increased in the partial flow rate range where the steady operation changes to the air lock operation, and the success rate of the air lock can be increased. Further, when the protrusion amount of the convex portion is 0.05D or more and 0.09D or less, the height of the bell suction port is set to 0, and the height from the bell suction port to the intake port is set to H. An air lock can be generated when the water level is up to 100 m. As a result, an air lock can be generated at a relatively high position, so that it is possible to prevent the water level from reaching the bell suction port or less and a large amount of air from entering the bell suction port exposed to the atmosphere at once.

  According to the second embodiment, in the preceding standby operation pump of the first embodiment, when the outer diameter of the straight pipe portion is D, the protruding amount of the convex portion from the inner surface of the casing is 0.07D or more and 0. 0.08D or less.

  According to the 2nd form, since the amount of protrusions of a convex part is 0.07D or more and 0.08D or less, an air lock can be made in a higher position, so that the water level reaches below the bell suction port, It is possible to more reliably prevent a large amount of air from entering from the bell suction port exposed to the atmosphere.

  According to the third mode, in the preceding standby operation pump of the first mode or the second mode, the amount of protrusion of the convex portion from the inner surface of the casing gradually increases as the guide surface moves away from the intake port in the axial direction. It is formed to decrease.

  According to the fourth mode, in the preceding standby operation pump of the first mode to the third mode, the amount of protrusion of the convex portion from the inner surface of the casing gradually increases as the guide surface moves away from the intake port in the circumferential direction. It is formed to decrease.

  According to the fifth embodiment, in the preceding standby operation pumps of the first to fourth embodiments, at least a part of the guide surface is a curved surface.

  According to the fifth aspect, the fluid in the vicinity of the inlet near the guide surface can flow smoothly along the guide surface. Thereby, since it can suppress that a fluid peels from a guide surface, the fall of the pump efficiency by the influence of peeling and generation | occurrence | production of a vibration and noise can be reduced.

  According to the sixth embodiment, in the preceding standby operation pumps of the first to fifth embodiments, the intake port is located at the apex of the convex portion.

DESCRIPTION OF SYMBOLS 11 ... Impeller 12 ... Casing 13 ... Convex part 14 ... Inlet port 15 ... Guide surface 12d ... Bell mouth 12e ... Inner surface 15a ... Convex surface 15b ... Concave surface

Claims (6)

Impeller,
A casing for housing the impeller;
A convex portion provided on the inner surface of the casing on the upstream side in the axial direction from the impeller;
An intake port formed on the surface of the convex part,
The casing has a straight pipe portion positioned on the downstream side in the axial direction from the impeller,
The convex portion has a guide surface formed such that the amount of protrusion from the inner surface of the casing gradually decreases as the distance from the intake port increases.
The preceding standby operation pump, wherein when the outer diameter of the straight pipe portion is D, the protruding amount of the convex portion from the inner surface of the casing is 0.05D or more and 0.09D or less. In the preceding standby operation pump according to claim 1,
The preceding standby operation pump, wherein when the outer diameter of the straight pipe portion is D, the protruding amount of the convex portion from the inner surface of the casing is 0.07D or more and 0.08D or less. In the preceding standby operation pump according to claim 1 or 2,
The preceding standby operation pump, wherein the guide surface is formed such that a protruding amount of the convex portion from the inner surface of the casing gradually decreases as the guide surface moves away from the intake port in the axial direction. In the preceding standby operation pump according to any one of claims 1 to 3,
The preceding standby operation pump, wherein the guide surface is formed such that a protruding amount of the convex portion from the inner surface of the casing gradually decreases as the guide surface moves away from the intake port in the circumferential direction. In the preceding standby operation pump according to any one of claims 1 to 4,
The preceding standby operation pump, wherein at least a part of the guide surface is a curved surface. In the preceding standby operation pump according to any one of claims 1 to 5,
The intake port is a preceding standby operation pump located at the apex of the convex portion.

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