JP5478430B2 - Advance standby pump - Google Patents

Description

  The present invention relates to an improvement of a preceding standby pump.

  A preceding standby pump installed in a suction water tank or the like of a drainage station is a pump that can start operation at a stage before the water level of the suction water tank rises, that is, can perform a standby operation. This standby operation eliminates frequent starting and stopping, enables low water level operation by the self-flow adjustment function, and responds quickly to drainage of water that flows suddenly due to guerrilla heavy rain, etc. In recent years, it has been used widely.

  As conventional examples of such a prior standby pump, a prior standby pump having a vertical pump structure disclosed in Patent Document 1, a vertical pump disclosed in Patent Document 2, and the like are known. Each of the pumps has a vent passage (air pipe) that communicates with the pump casing below the impeller and projects upward.

JP-A-9-228980 JP 2004-239215 A

  However, in the case where the other end of the air passage is simply opened in the suction water tank, there is an inconvenience that a hunting phenomenon is likely to occur due to repeated opening and closing of the front end surface of the air passage due to the undulation of the water surface. There was room for improvement.

  An object of the present invention is to provide a preceding standby pump that is improved so that hunting due to fluctuations in the water level is unlikely to occur.

In the first aspect of the invention, the one end 21a is opened on the upstream side in the fluid flow direction with respect to the portion of the pump casing 3 that houses the impeller 11, and the other end 21b is opened in the suction water tank 2. In the preceding standby pump having the mixing air passage 21,
The aeration path 21 has a substantially inverted U-shape as a whole in which a folded portion 21c that is folded back at a position higher than the highest water level HWL set in the suction water tank 2 is formed between the one end 21a and the other end 21b. A U-shape in which one end 23a is connected to the air passage 21 between the upper and lower sides of the folded portion 21c and the other end 21b, and the other end 23b is opened to the atmosphere as the water level fluctuates. The suction structure portion A having the flow path 23 is provided.

  According to a second aspect of the present invention, in the preceding standby pump according to the first aspect, the other end 23b of the suction structure portion A is opened at a position substantially the same as or higher than a water level for introducing air-water mixing air. The other end 21b of the air passage 21 is open at a position below the water level for introducing the air.

  According to a third aspect of the present invention, in the preceding standby pump according to the first or second aspect, the position of the folded portion 21c of the air passage 21 is higher than the suction head due to the maximum negative pressure generated in the pump casing 3. The position is set.

  According to a fourth aspect of the present invention, in the preceding standby pump according to any one of the first to third aspects, the water level of the suction water tank 2 is pumped from the air passage 21 for mixing air and water in the suction water tank 2. When the water level is lower than the water level in which the air-water mixing operation is carried out while introducing the air sucked into the casing 3, the pumping water is blocked by introducing the air into the portion below the impeller 11 of the pump casing 3. An air passage 22 for switching between air and water is provided.

According to a fifth aspect of the present invention, in the preceding standby pump according to the fourth aspect, the air / water switching air passage 22 is folded back at a position higher than the highest water level HWL set in the suction water tank 2. Is formed between the one end 22a of the air / water switching air passage 22 and the other end 22b of the air / water switching air passage 22 as a whole by a substantially inverted U-shaped tube, and One end 30a is connected to the air / water switching air passage 22 between the folded portion 22c and the other end 22b of the air / water switching air passage, and the other end 30b is opened to the atmosphere. The suction structure portion B having the flow passage tube 30 is provided.

  According to the invention of claim 1, although described in detail in the section of the embodiment, by having a suction structure portion having a U-shaped flow path, a water level difference can be made in the opening and closing of the water surface, and for air-water mixing Hunting is difficult in the air passage. As a result, it is possible to provide a preceding standby pump that is improved so that hunting due to fluctuations in the water level is unlikely to occur.

  According to the second aspect of the present invention, the other end of the suction structure portion is opened at a position substantially the same as or higher than the water level for introducing the air / water mixing air, and the other end of the air passage is from the water level for introducing the air. By opening at the lower position, it is possible to provide a preceding standby pump that is improved so that hunting is unlikely to occur at the air introduction water level for mixing air and water.

  According to the invention of claim 3, since the folded portion is set at a position higher than the suction lift by the maximum negative pressure generated in the pump casing, the water passes over the folded portion of the inverted U-shaped air passage. Since it is not sucked up, it is possible to reduce the possibility that the dust sucked from the air passage will clog the folded portion.

  According to the invention of claim 4, it is possible to introduce an air amount sufficient for shutting off the pumping water only when the pumping water is shut off, and to easily optimize the air amount introduced during the steam-water mixing operation. The generation of vortices and vibrations can be suppressed as compared with the case where air is introduced only by the mixing air inlet. As a result, it is not necessary to increase the strength of the pump, it is possible to reduce the weight of the pump, and it may not be necessary to increase the floor strength of the drainage station.

  According to the fifth aspect of the present invention, it is possible to prevent hunting between the pumping state and the standby state due to the water surface fluctuation in the vicinity of the pumping shutoff water level of the air / water switching aeration passage, so that generation of vibrations and the like can be effectively suppressed. It becomes possible.

Sectional drawing which shows the structure of the prior | preceding standby pump by Example 1 Sectional drawing which shows the structure of the prior | preceding standby pump by Example 2

  Hereinafter, embodiments of a preceding standby pump according to the present invention will be described with reference to the drawings. The first embodiment is a preceding standby pump having only an air / water mixing air pipe, and the second embodiment is a preceding standby pump having both an air / water mixing air pipe and an air / water switching air pipe.

[Example 1]
As shown in FIG. 1, the preceding standby pump 1 according to the first embodiment is configured as a vertical shaft pump that drains water such as rainwater flowing into the suction water tank 2 of the drainage station to the downstream side. The pump casing 3 extending in the vertical direction (vertical direction) includes a straight tubular pumping pipe 4, a pump case 5 connected to the lower end of the pumping pipe 4, and a suction pipe (bell mouth) connected to the lower end of the pump case 5. 6 and a discharge elbow 7 that is connected to the upper end of the pumped-up pipe 4 and curves in the horizontal direction from the vertical direction. A suction port 8 is provided at the lower end of the suction pipe 6 (lower end of the pump casing 3), and a discharge pipe (drain pipe) 10 is connected to the discharge port 9 of the discharge elbow 7 (upper end of the pump casing 3).

  An impeller 11 rotatably disposed in the pump case 5 via the main shaft 13 includes a blade base portion 11A that is fitted to the main shaft 13 in an integrally rotated state, and a plurality of blade portions 11B that extend from the blade base portion 11A. It is constituted by. A plurality of guide vanes 12 are arranged in the pump case 5 above the impeller 11 (downstream in the water flow direction). The main shaft 13 extending in the vertical direction is rotatably supported at the center of the pump casing 3 via a plurality of bearings 14, 15, 16, and the impeller 11 is attached to the lower end of the main shaft 13 in an integrally rotated state.

  The outer surfaces of the intermediate bearings 14 and 15 are fixed to the inner surface of the pumped water pipe 4 by support plates 14a and 15a, respectively. The upper end portion of the main shaft 13 is rotatable with respect to the discharge elbow 7 and penetrates in a watertight manner and protrudes to the outside of the pump casing 3, and includes a drive source such as an engine and an electric motor, a speed reduction mechanism, and the like. The rotary drive mechanism 17 is linked and connected.

  A flange 18 for installation is provided in the upper part of the pump casing 3, and the preceding standby pump 1 below the flange 18 can be inserted into the concrete floor 19 of the drainage pump station covering the upper surface of the suction water tank 2. A hole 20 is provided. The preceding standby pump 1 is installed on the annular plate 29 via the flange 18 in a state where the portion below the flange 18 is suspended in the suction water tank 2 via the insertion hole 20.

  The preceding standby pump 1 has a water level WL in the suction water tank 2 that is the lowest water level described later (an example of the lowest water level that can be pumped without vortices, and is also the highest water level for performing the air-water mixing operation). Air-water mixing air pipe (an example of an air-water mixing air passage) 21 for lowering the amount of drainage by pumping water while introducing air into the pump casing 3 below the impeller 11 in a state below LWL 21 It has. The base end (one end) 21 a of the air / water mixing air pipe 21 has an opening 25 attached to a pipe wall below the impeller 11 in the suction pipe 6 and communicating with the inside of the suction pipe 6. Reference numeral 2 a denotes a bottom wall of the suction water tank 2.

  The air / water mixing air pipe 21 has a folded portion at the upper end and is bent into an inverted U shape. The folded portion at the upper end is disposed above the floor 19 and supported by the annular plate 29. Then, both end portions are extended into the suction water tank 2 through the insertion holes 20, the base end 21a is extended downward and connected to the suction pipe 6 as described above, and the other end is also extended downward. A suction structure A having a lower end (other end) 21b opened at a height slightly lower than the opening 25 and being branched from the middle and having a U shape in a side view is provided. The tip 21b of the air / water mixing air pipe 21 is located below the pumped water cutoff level SWL set below the lowest water level LWL.

  The suction structure part A includes a branch pipe 27 branched from the upper and lower sides of the folded portion 21c and the lower end 21b at the upper end of the air / water mixing air pipe 21, and a U-shaped pipe (U-shaped flow path following the branch pipe 27). Example) 23). The U-shaped tube 23 is such that the start end 23a and the upper end (opening) 23b, which are also the ends of the horizontal (or substantially horizontal) branch tube 27 at both ends (upper end), are at a height slightly above the lowest water level LWL. Is provided. The horizontal (or substantially horizontal) folded portion 23c at the lower end of the U-shaped tube 23 is provided so that its upper surface is along a water level substantially equal to the lowest water level LWL in this embodiment. That is, the air / water mixing air pipe 21 has two air supply ports with different heights, that is, a lower end 21b which is a lower intake port disposed below the lower surface of the folded portion 23c of the U-shaped tube 23, and an upper side. And an upper end 23b which is an intake port.

  By providing the suction structure portion A in the air / water mixing air pipe 21, a water level difference can be made in the opening and closing of the water surface, and the hunting phenomenon of the air / water mixing air pipe 21 due to slight fluctuations in the water level of the suction water tank 2 ( The excellent effect that it becomes difficult to generate a phenomenon in which pumping without air and pumping without air above the lowest water level LWL causes the water level to fall below the lowest water level LWL and alternately repeat the air-water mixing operation). The In the present embodiment, the lower end 21b of the air / water mixing air pipe 21 which is the lower intake port is set below the pumping cutoff water level SWL, so that the lower end 21b is always in a submerged state. However, it is not always necessary to make such a setting, and it is sufficient that it is below the upper end of the folded portion 23c of the U-shaped tube 23.

  With reference to FIG. 1, the relationship between the structure of the preceding standby pump 1 in the height direction and the water level WL will be described. First, the maximum water level HWL peculiar to the suction water tank 2 is set to the suction water tank 2 as the allowable water level. Below the maximum water level HWL, a minimum water level LWL (an example of a first predetermined water level) unique to a pump (here, the pump is a vertical pump that does not include the air-water mixing air pipe 21) is set. ing. Below that, the minimum water level LWL corresponds to the water level WL where vortex, that is, air is sucked from the suction port 8, vibration and noise are generated, and the operation cannot be continued.

  The standby operation pump 1 automatically adjusts the amount of drainage by pumping water while introducing air into the pump casing 3 below the impeller 11 through the air / water mixing air pipe 21 for air / water mixing. It is possible to drive (while reducing). As a result, starting at a water level WL lower than the lowest water level LWL and continuous operation are possible, and at least the water level WL is lower than the lowest water level LWL at the upper end 23b which is an opening as the air / water mixing air pipe 21. It may be provided at a position that is sometimes opened to the atmosphere.

  The air / water mixing air pipe 21 is bent into an inverted U shape having a folded portion at the upper end, and is formed in a folded portion 21 c. The folded portion 21 c is disposed above the floor 19. Then, both end portions are extended into the suction water tank 2 through the insertion hole 20, and one end 21 a is connected to the first opening 25. In addition, if the folding | turning part 21c is set in the position higher than the suction lift by the maximum negative pressure which generate | occur | produces in the 1st opening 25 with pumping, it will go over the folding part 21c of a reverse U-shaped air pipe, and water Therefore, it is possible to reduce the possibility that dust from the air pipe is clogged in the folded portion.

  In the present embodiment, the case where air / water mixing air is introduced between the water level approximately the same as the lowest water level LWL and the pumping cutoff water level SWL has been described. However, the present invention is not limited to this. The air / water mixing air may be set so as to be introduced between the pumping cutoff water level SWL from above.

[Example 2]
The preceding standby pump 1 of the second embodiment will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same part as the prior | preceding standby pump 1 of 1st Example, and the description shall be made.

  As shown in FIG. 2, the preceding standby pump 1 according to the second embodiment introduces air into the pump casing 3 below the impeller 11 in a state where the water level WL of the suction water tank 2 is equal to or lower than the lowest water level LWL described later. From the impeller 11 when the water level for lowering the amount of discharged water by pumping up and when the water level of the suction water tank 2 is lower than the lowest water level LWL and the pumping water cutoff level SWL (described later) is reached. Two air pipes for shutting off pumped water for shutting off pumped water by introducing air into the lower pump casing 3, that is, an air pipe 21 for mixing air and water, and an air pipe for shutting off pumped water for switching air and water (An example of an air passage for switching between air and water) 22.

  In the pipe wall of the suction pipe 6 below the impeller 11, a first opening (air inlet for air / water mixing; opening in the casing) 25 that penetrates the inner / outer surface serving as a mounting portion of the air / water mixing air pipe 21. And the 2nd opening (pumping air shut-off air inlet; opening in a casing) 26 used as the attachment part of the water shut-off air pipe 22 is provided.

  There are two (a plurality) of first openings 25, which are arranged at equal intervals at the same height position. The number of the second openings 26 is one, and a height difference is provided with respect to the first opening 25 so as to be disposed below the lower end of the impeller 11 and above the first opening 25. The positions in the circumferential direction are also different so as not to overlap with the opening 25 in the vertical direction. In addition, the circumferential position of the second opening 26 is shifted in the circumferential direction with respect to the first opening 25 so as to be positioned at the approximate center between the two adjacent first openings 25. Therefore, in the second embodiment, two (a plurality) air-water mixing air tubes 21 are provided. The number of air-water mixing air pipes 21 is not limited to this.

  The air / water mixing air pipe 21 is bent into an inverted U shape having a folded portion at the upper end, and is formed in a folded portion 21 c. The folded portion 21 c is disposed above the floor 19. Then, both end portions are extended into the suction water tank 2 through the insertion hole 20, and one end 21 a is connected to the first opening 25. In addition, if the folding | turning part 21c is set in the position higher than the suction lift by the maximum negative pressure which generate | occur | produces in the 1st opening 25 with pumping, water will pass over the folding part of an inverted U-shaped air pipe. Since it is not sucked up, it is possible to reduce the possibility that dust from the air pipe is clogged in the folded portion.

  The suction structure part A includes a branch pipe 27 branched from the upper and lower sides of the folded portion 21c and the lower end 21b at the upper end of the air / water mixing air pipe 21, and a U-shaped pipe 23 following the branch pipe 27. Has been. The U-shaped tube 23 has a start end 23a and an upper end (opening) 23b, which are also ends of the horizontal (or substantially horizontal) branch tube 27 at both ends (upper end) thereof, so that the height is equal to the lowest water level LWL. Is provided. The horizontal (or substantially horizontal) folded portion 23c at the lower end of the U-shaped tube 23 is provided such that its upper surface is positioned between the upper and lower sides of the lowest water level LWL and the pumping start water level RWL. That is, the air / water mixing air pipe 21 has two air supply ports with different heights, that is, a lower end 21b which is a lower intake port disposed below the lower surface of the folded portion 23c of the U-shaped tube 23, and an upper side. And an upper end 23b which is an intake port.

  On the other hand, similarly to the air / water mixing air pipe 21, the pumping-off air pipe 22 is bent and formed in an inverted U shape having a folded portion 22 c at the upper end, and the folded portion 22 c is disposed above the floor 19. It is supported by the annular plate 29. Both end portions are extended into the suction water tank 2 through the insertion hole 20, and one end 22 a is connected to the second opening 26. In addition, if the folding | turning part 22c is set in the position higher than the suction lift by the maximum negative pressure which generate | occur | produces in the 2nd opening 26 with pumping, the folding | turning part 22c of the reverse U-shaped pumping-off air pipe 22 The water is not sucked up beyond. Therefore, it is possible to reduce the possibility that dust from the pumping-off air pipe 22 is clogged in the folded portion 22c.

  Moreover, the front end 22b (the other end; an example of the second air supply port) of the pumping-off air pipe 22 has a pumping-off cutoff water level ("water level lower than the water level LWL for performing the air-water mixing operation"). Example) provided below SWL. Accordingly, the tip 22b of the pumping-off air pipe 22 is opened in the atmosphere until the water level WL rises to the pumping-off water level SWL, and the water in the suction water tank 2 when the water level WL rises to the pumping-off water level SWL. Blocked by. That is, the opening / closing means 24 is constituted by the tip 22 b of the pumping-off air pipe 22.

  In the second embodiment, the two air pipes 21 and 22 for air / water mixing and pumping and shutting off are the amount of air introduced from the two air / water mixing air pipes 21 and one pumping and shutting air pipe. It is desirable to use those having a pipe diameter so that the amount of air introduced from 22 is substantially the same. In that case, since there is one pumping cutoff air pipe 22 for the two air / water mixing air pipes 21, the diameter of each air / water mixing air pipe 21 is the same as that of the pumping / water shutting air pipe 22. Is approximately 1 / √2.

  A plurality of (for example, four) support plates 16a of the lower end bearing 16 has an outer end portion of one support plate 16a in the vicinity of the upstream side of the second opening 26 in the impeller rotation direction when viewed from the axial direction. It is connected to the inner surface of the suction pipe 6.

  A vortex generation preventing plate 28 is provided on the outer surface of the suction pipe 6 between the suction port 8 and the first opening 25. The vortex generation preventing plate 28 is constituted by a horizontal plate that is in surface contact with the water surface WL when the water level WL is lowered to the vicinity of the pumping cutoff water level SWL. The horizontal plate is larger than the suction port 8 and smaller than the insertion hole 20 of the floor 19. The vortex generation preventing plate 28 may be composed of a plurality of vertical plates provided radially on the outer surface of the suction pipe 6 below the first opening 25. Further, a horizontal plate or a vertical plate larger than the insertion hole 20 may be used. The vortex generation preventing plate 28 can be omitted depending on operating conditions.

  Now, as shown in FIG. 2, the hunting phenomenon of the pumping-off air pipe 22 [pumping start state (pumping state) above the pumping-off water level SWL due to the rise in the water level and the pumping-off water level SWL by starting pumping. In order to prevent a phenomenon in which the water level is lowered and the pumping shut-off (standby state) is repeated alternately], a suction structure having a U-shaped pipe 30 branched from the upper end turn-up portion of the pumping-off air pipe 22 and the tip 22b. Part B (suction structure part B for air-water switching) is equipped. In the U-shaped tube 30, the upper surface and the distal end (opening) 30 b of substantially horizontal base ends (branch ends) 30 a at both ends (upper ends) are along the closed water level YWL substantially equal to the water level WL at the upper end of the second opening 26. In addition, the upper surface of the substantially horizontal folded portion 30c at the lower end is provided along the open water level XWL substantially equal to the pumped water cutoff water level SWL. Here, the tip 22b of the pumping-off air pipe 22 is disposed below the lower surface of the folded portion 30c of the U-shaped pipe 30, and the pumping-up air pipe 22 has two air supply ports with different heights, that is, The tip 30b of the U-shaped pipe 30 that is the upper air supply port and the tip 22b of the pumping-off air pipe 22 that is the lower air supply port are communicated with the second opening 26.

  When the water level WL rises from the pumping cutoff water level SWL or lower, since there is no water in the pipe, air is sucked from the tip 30b of the U-shaped pipe 30. When the closed water level YWL is reached, the tip 30b of the U-shaped tube 30 is closed by being submerged, so air is not sucked from the second opening 26, and air-water mixing that sucks air only from the first opening 25 is performed. It becomes driving.

  That is, in the rising phase of the water level WL from the pumping shutoff water level SWL or lower, the pumping shutoff air pipe 22 is held open in the atmosphere until the closed water level YWL, and air is passed through the pumping shutoff air pipe 22 from the second opening 26 to the air. When the water level is equal to or higher than the closed water level YWL, the pumping-off air pipe 22 is blocked, and air is not sucked from the second opening 26. Thus, when the water level WL rises, the tip 30b of the U-shaped ring 30 functions as the opening / closing means 24.

  On the other hand, when the water level WL is lowered from the minimum water level LWL or more, even if the water level WL is lowered to the lowest water level LWL, both the tip 30b of the U-shaped pipe 30 and the tip 22b of the pumping-off air pipe 22 are submerged. Yes. When the closed water level YWL is reached, the tip 30b of the U-shaped tube 30 comes into the atmosphere, but the water accumulated on the tip 30b side of the U-shaped tube 30 cannot be drained, but if the water level is below the pumping cutoff water level SWL, If the water level is further lowered and the water surface is lowered from the upper part of the folded portion 30c of the U-shaped tube 30, air is sucked from the tip 30b of the U-shaped tube 30.

  That is, when the water level WL from the minimum water level LWL or higher is descending, the pumping shut-off air pipe 22 is blocked up to the pumping shut-off water level SWL, and air is not sucked from the second opening 26. Below the pumping-off cutoff level SWL, the pumping-off cutoff air pipe 22 is held open in the atmosphere, and air is sucked from the second opening 26 through the pumping-off cutoff air pipe 22. Thus, when the water level WL decreases, the folded portion 30 c of the U-shaped tube 30 functions as the opening / closing means 24.

  In the preceding standby pump 1 according to the second embodiment, the pumping off air pipe 22 is opened to the atmosphere at different water levels WL when the water level WL rises and falls. That is, when the water level WL is lowered, the pumping cutoff air pipe 22 is opened to the atmosphere at the pumping cutoff water level SWL (open water level XWL). The blocking air tube 22 is opened to the atmosphere. Therefore, even if the water level WL rises to the re-pumping start water level CWL due to a backflow from the pump casing 3 to the suction water tank 2 at the time of pumping off, pumping is not started and the pumping off operation is continued. Accordingly, it is possible to prevent the hunting phenomenon of the pumping-off air pipe 22.

  Here, the U-shaped tube 30 branched from the pumping-off air tube 22 is not essential, and may be omitted depending on operating conditions. Further, in the second embodiment, the example in which the opening 25 of the air / water mixing air pipe 21 is located above the opening 26 of the pumping-off air pipe 22 is shown. Provided) or the same height. Although the example using the U-shaped tube 30 as an example of the U-shaped flow path has been described, a U-shaped flow path may be formed by providing a partition plate inside the hollow container. Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 2 Suction water tank 3 Pump casing 11 Impeller 21 Air flow path for air-water mixing 21a One end 21b Other end 21c Folding part 22 Air flow path for air-water switching 23 U-shaped flow path 23a One end 23b The other end (opening)
A Suction structure HWL Highest water level LWL Low water level (top)

Claims (5)

A preceding standby pump having an air-water mixing air passage whose one end is opened upstream in the fluid flow direction from the portion accommodating the impeller of the pump casing and the other end is opened in the suction water tank. ,
The aeration path is formed by a substantially inverted U-shaped tube as a whole in which a folded portion that is folded back at a position higher than the highest water level set in the suction water tank is formed between the one end and the other end. And a standby structure in which a suction structure portion having a U-shaped flow path having one end connected to the ventilation path between the folded portion and the other end and opened to the atmosphere at the other end is provided. pump.   The other end of the suction structure portion is opened at a position that is substantially the same as or above the water level at which air-to-air mixing air is introduced, and the other end of the air passage is opened at a position below the water level at which the air is introduced. The preceding standby pump according to claim 1.   The preceding standby pump according to claim 1 or 2, wherein a position of the folded portion of the air passage is set to a position higher than a suction head by a maximum negative pressure generated in the pump casing.   When the water level of the suction water tank becomes lower than the water level for performing the air / water mixing operation of pumping water while introducing the air sucked into the pump casing from the air / water mixing vent in the suction water tank, the pump casing The preceding standby pump according to any one of claims 1 to 3, wherein an air passage for air / water switching is provided for shutting off pumping by introducing air into a portion below the impeller. The air / water switching vent has a folded portion that is folded back at a position higher than the highest water level set in the suction water tank, in addition to one end of the air / water switching vent and the air / water switching vent. together they are formed by a substantially inverted U-shaped tube as a whole is formed between the end, ventilation for the steam-water switching between the upper and lower the other end of the vent passage for the steam-water switch and the folded portion 5. The preceding standby pump according to claim 4, wherein a suction structure portion having a U-shaped flow channel pipe having one end connected to the passage and the other end opened to the atmosphere is provided.

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