Siphon drainage system

Abstract

To provide a siphon drainage system that can quickly generate siphon force with a small number of parts.SOLUTION: A siphon drainage system 10 includes: a horizontal pipe 46 letting drain water flow from a water-using site 20 and extending in a horizontal direction; a vertical pipe 48 disposed on a downstream side in a water drainage direction of the horizontal pipe 46 and extending downward; and a drop-down pipe 32 disposed between the horizontal pipe 46 and the vertical pipe 48 and formed bending from a horizontal direction to a down direction. The drop-down pipe 32 is set such that, with a central axis 32CL of a flow passage as a boundary, a flow passage section A inside in a radial direction of the bending is smaller than a flow passage section B outside in the radial direction of the bending.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a siphon drainage system.

Background Art

[0002] In recent years, as an alternative to the conventional gradient drainage system, a so-called siphon drainage system has been proposed (see, for example, Patent Document 1). As described in Patent Document 1, the siphon drainage system is a system that improves the drainage efficiency from plumbing fixtures by connecting a siphon drainage pipe to a plumbing fixture and utilizing the siphon force (negative pressure) generated in the vertical pipe portion that forms the lower part of the siphon drainage pipe.

[0003] In this siphon drainage system, the drainage discharged from the plumbing fixture flows into the siphon drainage pipe and fills the horizontal pipe portion that forms the horizontal part of the siphon drainage pipe and the vertical pipe portion that forms the lower part of the siphon drainage pipe. When the vertical pipe portion of the siphon drainage pipe is filled with drainage, the drainage in the vertical pipe portion falls by gravity, and a suction force corresponding to the water head difference in the vertical pipe portion, that is, a siphon force, is generated inside the vertical pipe portion. The drainage in the horizontal pipe portion is sucked toward the vertical pipe portion by the siphon force, and a so-called full-flow flow in which the siphon drainage pipe is filled with drainage is formed and flows down through the siphon drainage pipe.

[0004] Thus, in the siphon drainage system, since the drainage flows into the vertical pipe portion arranged on the downstream side of the horizontal pipe portion and the siphon force is not generated unless the vertical pipe portion is filled with drainage, there is a time lag from when the drainage is discharged from the plumbing fixture until the siphon force is generated, and it is desired to drain the water quickly from the plumbing fixture.

[0005] Here, a siphon drainage system is known in which the time to fill the inside of the vertical pipe portion with full flow is shortened by making the diameter of the vertical pipe side smaller than the diameter of the horizontal pipe side (see Patent Document 1).

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-31670 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] In the above siphon drainage system, a joint whose diameter gradually decreases and a vertical pipe are connected to the downstream side of the horizontal pipe through an L-shaped vent pipe (also called a drop pipe), and a large number of parts are required.

[0008] In consideration of the above facts, an object of the present invention is to provide a siphon drainage system that can generate siphon force quickly with a small number of parts. [Means for Solving the Problems]

[0009] The siphon drainage system according to claim 1 includes a horizontal pipe that flows the drainage from the plumbing fixture and extends in the horizontal direction, a vertical pipe that is provided on the downstream side in the drainage direction of the horizontal pipe portion and extends downward, and a drop pipe that is provided between the horizontal pipe portion and the vertical pipe and is curved from the horizontal direction to the downward direction. The drop pipe has a reduced-diameter portion in which the cross-sectional area of the flow path on the inner side in the radial direction of the curve is set to be smaller than the cross-sectional area of the flow path on the outer side in the radial direction of the curve with respect to the central axis of the flow path.

[0010] In the siphon drainage system according to claim 1, in the curved drop pipe provided between the horizontal pipe portion and the vertical pipe, a reduced-diameter portion is provided in which the cross-sectional area of the flow path on the inner side in the radial direction of the curve is set to be smaller than the cross-sectional area of the flow path on the outer side in the radial direction of the curve with respect to the central axis of the flow path. Therefore, when the drainage water flows from the horizontal pipe into the drop pipe, compared with the drop pipe in which the cross-sectional area of the flow path on the inner side in the radial direction of the bend and the cross-sectional area of the flow path on the outer side in the radial direction of the bend are set to be the same, in other words, compared with the drop pipe having a normal flow path with a true circular cross-section, the water level rises earlier on the inlet side of the drop pipe, that is, the end side on the upstream side in the drainage direction, and the flow path quickly becomes full flow. As a result, the vertical pipe following the drop pipe also quickly becomes full flow, and it becomes possible to shorten the startup time of the siphon.

[0011] Further, in the siphon drainage system according to claim 1, unlike the conventional siphon drainage system, a joint with a gradually decreasing diameter is not required on the downstream side of the horizontal pipe. Therefore, compared with the conventional siphon drainage system, the number of components of the system can be reduced. Note that the "inner side in the radial direction of the bend" can be rephrased as the "side closer to the center of curvature of the bend", and the "outer side in the radial direction of the bend" can be rephrased as the "side farther from the center of curvature of the bend".

[0012] The invention according to claim 2 is the siphon drainage system according to claim 1, wherein the cross-sectional area of the reduced-diameter portion is set to be smaller than the cross-sectional area of the flow path of the horizontal pipe.

[0013] In the siphon drainage system according to claim 2, by setting the cross-sectional area of the drop pipe to be smaller than the cross-sectional area of the horizontal pipe, it becomes possible to make the drop pipe full flow even earlier.

[0014] The invention according to claim 3 is the siphon drainage system according to claim 1 or claim 2, wherein the reduced-diameter portion, when viewed in a cross-section perpendicular to the flow path, includes a pair of inclined surfaces in which the inner wall of the pipe on the inner side in the radial direction of the bend approaches each other toward the inner side in the radial direction of the bend with the central axis of the flow path as a boundary, and a connecting surface connecting the end of one of the inclined surfaces and the end of the other inclined surface, and the inner wall of the pipe on the outer side in the radial direction of the bend with the central axis of the flow path as a boundary is configured to include an arc surface having the central axis as the center of curvature.

[0015] In the reduced-diameter portion of the downcomer of the siphon drainage system according to claim 3, when viewed in a cross-section perpendicular to the flow path, the inner wall of the pipe on the radially inner side of the bend with respect to the central axis of the flow path includes a pair of inclined surfaces that approach each other toward the radially inner side of the bend and a connecting surface that connects the end of one inclined surface, the end of the other inclined surface, and the end of the other inclined surface. The inner wall of the pipe on the radially outer side of the bend with respect to the central axis of the flow path is configured to include an arc surface with the central axis as the center of curvature. With such a simple configuration, the cross-sectional area of the flow path on the radially inner side of the bend can be made smaller than the cross-sectional area of the flow path on the radially outer side of the bend.

[0016] In addition, when a pair of inclined surfaces that approach each other toward the radially inner side of the bend are provided on the inner wall of the pipe on the radially inner side of the bend of the downcomer, when the end of one inclined surface and the end of the other inclined surface are connected to each other, the connection portion becomes a shape like a V-shaped sharp bottom of a valley, and foreign matter in the drainage is likely to accumulate at the bottom of the valley.

[0017] In the reduced-diameter portion of the downcomer according to claim 3, the end of one inclined surface and the end of the other inclined surface of the pair of inclined surfaces are connected by a connecting surface, and the end of one inclined surface and the end of the other inclined surface are separated. In other words, the bottom of the valley formed by the pair of inclined surfaces is widened without becoming sharp, so it is difficult for foreign matter in the drainage to accumulate at the bottom of the valley. Also, even if foreign matter stays at the bottom of the valley, it is easily washed away and removed by the momentum of the next drainage.

[0018] The invention according to claim 4 is the siphon drainage system according to claim 3, wherein when the reduced-diameter portion is viewed in a cross-section perpendicular to the flow path, each of the pair of inclined surfaces is linear, and the inclined surfaces are inclined at an inclination angle exceeding 30° and equal to or less than 45° with respect to a virtual horizontal line that passes through the middle portion of the pair of inclined surfaces and is orthogonal to a virtual vertical center line that passes through the central axis of the flow path.

[0019] When the shape of the inclined surface when looking at the reduced-diameter part of the downcomer in a cross-section perpendicular to the flow path is linear, and it passes through the middle part of a pair of inclined surfaces and is inclined at an inclination angle exceeding 30° and not exceeding 45° with respect to a virtual horizontal line orthogonal to the virtual vertical center line passing through the central axis of the flow path, it becomes possible to shorten the startup time of the siphon. Note that when the inclination angle of the inclined surface becomes 30° or less, it may become impossible to form a connection surface. Note that "exceeding 30° and not exceeding 45° with respect to the virtual horizontal line orthogonal to the virtual vertical center line passing through the central axis of the flow path" can be rephrased as "45° or more and less than 60° with respect to the virtual vertical center line".

Advantages of the Invention

[0020] As described above, according to the siphon drainage system of the present invention, it has an excellent effect that siphon force can be generated quickly with a small number of parts.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0022] According to FIGS. 1 to 6, a siphon drainage system 10 according to an embodiment of the present invention will be described. In each figure, the directions indicated by arrows X and Y are directions along the horizontal plane and are perpendicular to each other. Further, the direction indicated by arrow Z is a direction along the vertical direction (up and down direction). In each figure, the directions indicated by arrows X, Y, and Z are assumed to coincide with each other.

[0023] <Siphon drainage system> FIG. 1 schematically shows the overall configuration of the siphon drainage system 10 according to the present embodiment. The siphon drainage system 10 according to the present embodiment is a drainage system that efficiently discharges the drainage from the water Revolution drainage appliance 20 by utilizing the siphon force.

[0024] The siphon drainage system 10 is used in an apartment house composed of multiple floors and includes a standpipe 12 for flowing drainage downward. This standpipe 12 extends in the vertical direction (up and down direction) of the apartment house and penetrates the slabs 14 of each floor of the apartment house.

[0025] Note that the standpipe 12 is arranged in a pipe space formed inside the building, penetrating the slab 14 and spanning multiple floors. Alternatively, the standpipe 12 may be arranged outside the outer wall 16 that partitions the inside and outside of the building, for example, in a meter box or the like. The siphon drainage system 10 of the present embodiment is preferably used in an apartment house, but can be used in various buildings such as detached houses, office buildings, commercial buildings, and factories other than apartment houses.

[0026] In each household on each floor of the apartment house, water Revolution drainage appliance 20 is provided. This water RevolutionThe drainage device 20 is, for example, a kitchen sink, and a disposer 22 and a drain trap 24 are connected to the downstream side in the drainage direction. An L-shaped piping member 26 bent in an L-shape is disposed on the downstream side in the drainage direction of the drain trap 24. The L-shaped piping member 26 includes a vertical portion 26A connected to the drain trap 24 and extending in the vertical direction, a horizontal portion 26B disposed horizontally on the slab 14 and extending in the horizontal direction, and a curved portion 26C connecting the vertical portion 26A and the horizontal portion 26B. Note that the water Revolution The drainage device 20 may be other drainage systems such as a bathtub, a washbasin, and a washing machine.

[0027] On the downstream side in the drainage direction of the L-shaped piping member 26, a horizontal draw pipe member 28 disposed on the slab 14 and extending in a direction perpendicular to the vertical direction, in other words, horizontally, is disposed. The L-shaped piping member 26 and the horizontal draw pipe member 28 are connected via a joint 30.

[0028] At the downstream end of the horizontal draw pipe member 28 in the drainage direction, a curved down pipe 32 is connected via a joint 34. On the downstream side of the down pipe 32, a vertical pipe member 36 extending downward is connected via a joint 38. Note that the downstream side of the down pipe 32 is inserted into a through hole 14A formed in the slab 14.

[0029] The downstream end of the vertical pipe member 36 in the drainage direction is connected via a joint 42 to a junction joint 40 attached to an intermediate portion of the riser pipe 12.

[0030] In the present embodiment, the piping portions disposed horizontally on the slab 14, specifically, the horizontal portion 26B of the L-shaped piping member 26 and the horizontal draw pipe member 28 are used as the horizontal draw pipe 46 of the siphon drain pipe 44. Note that, from the viewpoint of ensuring drainage performance, the horizontal draw pipe 46 may be provided with a water gradient that slopes downward from the joint 30 toward the joint 34. In the present embodiment, "horizontal" includes an inclination of the degree of the water gradient. Also, in the present embodiment, the vertical pipe member 36 extending downward is used as the riser 48 of the siphon drain pipe 44.

[0031] <Drop-in tube> As shown in Fig. 2, a drop-in tube 32, which is an example of the drop-in tube of the present invention, is curved in a substantially arc shape in side view. The drop-in tube 32 is formed of a synthetic resin such as rigid PVC, for example.

[0032] As shown in Figs. 2 to 4, the drop-in tube 32 includes a linear horizontal tube side connection portion 32A for connecting a joint 34 to the horizontal draw tube member 28 side, and a linear vertical tube side connection portion 32B for connecting a joint 38 to the vertical tube member 36 side, and an arc portion 32C is provided between the horizontal tube side connection portion 32A and the vertical tube side connection portion 32B.

[0033] Note that the horizontal tube side connection portion 32A and the joint 34 are detachably connected by screwing, for example. Also, the vertical tube side connection portion 32B and the joint 38 are detachably connected by screwing, for example.

[0034] As shown in Fig. 2, the drop-in tube 32 of the present embodiment is basically a curved circular tube, but as shown in Fig. 5(A), on its inner wall surface, inside the radius of curvature of the curve when viewed from the side (arrow R IN side), a pair of inclined surfaces 50 are formed at intervals in the circumferential direction. As shown in Fig. 2, the pair of inclined surfaces 50 are formed from the end on the horizontal draw tube member 28 side toward the vertical tube member 36 side. In the drop-in tube 32 of the present embodiment, the portion where the inclined surface 50 is formed corresponds to the reduced diameter portion of the present invention.

[0035] Note that in the drop-in tube 32 of the present embodiment, the pair of inclined surfaces 50 are formed on the inner wall surface of the horizontal tube side connection portion 32A and the inner wall surface of the arc portion 32C, and are not formed on the vertical tube side connection portion 32B, but the pair of inclined surfaces 50 may also be formed on the vertical tube side connection portion 32B.

[0036] In the drop pipe 32, a pair of inclined surfaces 50 are formed to protrude radially inward from the inner wall surface of the circular pipe, and a connecting surface 52 is provided between the end of one inclined surface 50 and the end of the other inclined surface 50. Note that, as in the drop pipe 32 shown in FIG. 5(B), the connecting surface 52 may be absent, and the end of one inclined surface 50 and the end of the other inclined surface 50 that are close to each other may be connected.

[0037] As shown in FIG. 5(A), in the drop pipe 32 of the present embodiment, the inner wall surface of the portion where the inclined surface 50 is not formed (the connecting surface 52 and the inner wall surface of the vertical pipe side connection portion 32B) is an arc surface with the central axis 32CL of the drop pipe 32 as the center of curvature when viewed in a cross section perpendicular to the central axis 32CL of the drop pipe 32, and the radius of curvature of the arc surface is 1 / 2 of the inner diameter D of the portion where the inclined surface 50 is not formed in the drop pipe 32.

[0038] Further, in the drop pipe 32 of the present embodiment, the inner diameter D of the portion where the inclined surface 50 is not formed is the same as the inner diameter of the horizontal draw pipe member 28 connected to the upstream side in the drainage direction.

[0039] Since a pair of inclined surfaces 50 protrude from the inner wall surface on the radially inner side of the curved portion with the central axis 32CL of the flow path as the boundary in the drop pipe 32, the flow path cross-sectional area (the diagonally shaded portion in the upper left) A on the radially inner side (arrow R IN ) of the curved portion is smaller than the flow path cross-sectional area (the diagonally shaded portion in the upper right) B on the radially outer side (arrow R OUT ) of the curved portion with the central axis 32CL of the flow path as the boundary. Therefore, the cross-sectional area of the flow path through which the drainage flows decreases when flowing from the horizontal draw pipe member 28 into the drop pipe 32.

[0040] Note that, in the drop pipe 32, it is preferable to set the flow path cross-sectional area (flow path cross-sectional area A + B) of the portion where the inclined surface 50 is formed within the range of 70 to 80% of the flow path cross-sectional area of the horizontal draw pipe member 28 as an example.

[0041] As shown in FIG. 5(A), the inclined surface 50 of the present embodiment is formed linearly when viewed in a cross-section perpendicular to the flow path. The inclined surface 50 is inclined at an inclination angle θ with respect to a virtual horizontal line FHL that passes through the central portion of the pair of inclined surfaces 50 and is perpendicular to a virtual vertical center line FVCL that passes through the central axis 32CL. As an example, when the flow path cross-sectional area (flow path cross-sectional area A + B) of the portion where the inclined surface 50 is formed is set to 75% of the flow path cross-sectional area of the lateral draw pipe member 28, the inclination angle θ is preferably set to be greater than 30° and equal to or less than 45°.

[0042] Note that, at the end on the side of the lateral draw pipe member 28 into which the drainage water flows, the inclined surface 50 is preferably formed with a rounded chamfer 50A shown in FIG. 6(A) or a tapered surface 50B shown in FIG. 6(B) so that the drainage water can smoothly flow into the drop pipe 32.

[0043] (Operation and Effect) In the siphon drainage system 10 according to the embodiment of the present invention, when Revolution drainage water is discharged from the water

[0044] appliance 20, the drainage water flows into the drop pipe 32 via the disposer 22, the drain trap 24, the L-shaped pipe member 26, and the lateral draw pipe member 28.

[0045] Here, in the portion where the inclined surface 50 is formed, the drop pipe 32 is set such that the flow path cross-sectional area A on the inner side in the radial direction of the curvature is smaller than the flow path cross-sectional area B on the outer side in the radial direction of the curvature with the central axis 32CL of the flow path as the boundary, and the flow path cross-sectional area (flow path cross-sectional area A + B) of the portion where the inclined surface 50 is formed is set to be smaller than the flow path cross-sectional area of the lateral draw pipe member 28.

[0046] In the siphon drainage system 10 according to this embodiment, with a simple configuration of changing the shape of the inner wall surface of the downcomer 32 as described above, the siphon can be started quickly. Also, unlike the conventional siphon drainage system, a joint with a gradually decreasing diameter on the downstream side of the horizontal pipe is not required, so the number of components can be reduced compared to the conventional siphon drainage system.

[0047] In the downcomer 32, if the difference between the flow channel cross-sectional area (flow channel cross-sectional area A + B) of the portion where the inclined surface 50 is formed and the flow channel cross-sectional area of the horizontal pipe member 28 is too small, the starting time of the siphon cannot be shortened. Therefore, it is preferable that the flow channel cross-sectional area (flow channel cross-sectional area A + B) of the portion where the inclined surface 50 is formed is 80% or less of the flow channel cross-sectional area of the horizontal pipe member 28.

[0048] Also, if the difference between the flow channel cross-sectional area (flow channel cross-sectional area A + B) of the portion where the inclined surface 50 is formed and the flow channel cross-sectional area of the horizontal pipe member 28 is too large, the flow channel area of the downcomer 32 relative to the horizontal pipe member 28 becomes relatively too small. Even if siphon force is generated, the drainage capacity (drainage volume per unit time) will decrease. For this reason, since the starting time of the siphon cannot be shortened, it is preferable that the flow channel cross-sectional area (flow channel cross-sectional area A + B) of the portion where the inclined surface 50 is formed is 70% or more of the flow channel cross-sectional area of the horizontal pipe member 28.

[0049] As shown in FIGS. 3 to 5(A), in the downcomer 32 of this embodiment, a connecting surface 52 is provided between one inclined surface 50 and the other inclined surface 50, and the bottom of the valley is widened, so foreign matter in the drainage is difficult to accumulate at the bottom of the valley. Also, even if foreign matter stays at the bottom of the valley, the foreign matter is easily washed away and removed by the momentum of the next drainage.

[0050] If foreign matter in the drainage does not accumulate at the bottom of the valley between one inclined surface 50 and the other inclined surface 50, as shown in FIG. 5(B), the connecting surface 52 may not be provided between one inclined surface 50 and the other inclined surface 50.

[0051] The inclination angle θ of the inclined surface 50 is preferably set to be greater than 30° and less than or equal to 45° when, for example, the flow path cross-sectional area (flow path cross-sectional area A + B) of the portion where the inclined surface 50 is formed is set to 75% of the flow path cross-sectional area of the horizontal draw pipe member 28. The reason for setting the inclination angle θ of the inclined surface 50 to an angle greater than 30° is that when the inclination angle θ is 30° or less, one inclined surface 50 and the other inclined surface 50 are connected, and the bottom of the valley becomes sharp and narrow. On the other hand, the reason for setting the inclination angle θ to 45° or less is that when the inclination angle θ exceeds 45°, the start-up time of the siphon cannot be shortened.

[0052] (Test Example) Table 1 in FIG. 7 shows the flow path cross-sectional shape of the drop pipe when the flow path cross-sectional area of the portion where the inclined surface of the drop pipe is formed is set to 75% of the flow path cross-sectional area of the horizontal draw pipe member and the inclination angle θ of the inclined surface is changed. As shown in Table 1, it can be seen that when the inclination angle θ of the inclined surface is 31° or more, a connecting surface 52 can be provided between one inclined surface and the other inclined surface. When the inclination angle θ is 30°, one inclined surface and the other inclined surface are connected to each other, and the connecting surface 52 cannot be provided.

[0053] Also, the inclination angle θ of the inclined surface of the drop pipe was variously changed, and the time from the start of draining until full flow was achieved at each part on the vertical pipe side of the drop pipe was obtained by simulation with respect to the inclination angle θ. The parts where full flow was measured were three locations: a measurement location 63 mm below the central axis of the inlet of the drop pipe, a measurement location 100 mm, and a measurement location 150 mm. As a result of the simulation, it was found that when the inclination angle θ is in the range of 31° to 45°, the time until the vertical pipe becomes full flow is shorter compared to other cases. From this, it can be seen that by setting the inclination angle θ of the inclined surface in the range of 31° to 45°, the start-up of the siphon can be accelerated while suppressing the deposition of foreign substances.

[0054] [Other Embodiments] As described above, an embodiment of the present invention has been explained. However, the present invention is not limited to the above, and it goes without saying that various modifications can be made without departing from the gist of the invention.

[0055] In the downcomer 32 of the above embodiment, the inclined surface 50 was linear in cross section. However, as shown in FIGS. 8(A) and 8(B), the inclined surface 50 may be curved in cross section. Further, in the downcomer 32 of the above embodiment, the inclined surfaces 50 were formed on both sides with the central axis 32CL interposed therebetween in cross section. However, as shown in FIG. 8(C), the inclined surface 50 may be provided only on one side of the central axis 32CL.

[0056] In the downcomer 32 of the above embodiment, the inclined surface 50 was provided from the upstream end to the downstream end of the arc portion 32C (or the downstream end of the vertical pipe side connection portion 32B). However, if it is provided in a part of the downcomer 32 (as an example, from the longitudinal middle part of the arc portion 32C to the downstream side), it is possible to accelerate the start-up of the siphon. That is, if the start-up time of the siphon can be shortened, the inclined surface 50 may be formed anywhere in the downcomer 32.

Explanation of reference numerals

[0057] 10... Siphon drainage system, 20... Water Revolution discharge appliance, 32... Downcomer, 46... Horizontal draw pipe, 48... Vertical pipe, A... Flow path cross-sectional area on the radially inner side of the bend, B... Flow path cross-sectional area on the radially outer side of the bend, 50... Inclined surface (diameter-reducing portion), 52... Connection surface

Claims

1. A horizontal drain pipe that drains water from plumbing fixtures and extends horizontally, a vertical pipe provided on the downstream side in the drainage direction of the horizontal drain pipe portion and extending downward, a drop pipe provided between the horizontal drain pipe portion and the vertical pipe, which is on the downstream side of the horizontal drain pipe portion and the upstream side of the vertical pipe, and is curved from the horizontal direction to the downward direction, comprising: the drop pipe has a reduced-diameter portion in which the cross-sectional area of the flow path on the inner side in the radial direction of the curve is set to be smaller than the cross-sectional area of the flow path on the outer side in the radial direction of the curve, with the central axis of the flow path as the boundary, a siphon drainage system.

2. The cross-sectional area of the reduced-diameter portion is set to be smaller than the cross-sectional area of the horizontal drain pipe. The siphon drainage system according to Claim 1.

3. When viewed in a cross-section perpendicular to the flow path, the reduced-diameter portion is composed of a pair of inclined sides where the inner wall of the pipe on the inner side in the radial direction of the curve approaches each other toward the inner side in the radial direction of the curve with the central axis of the flow path as the boundary, and a connecting side that connects the end of one of the inclined sides and the end of the other inclined side. The inner wall of the pipe on the outer side in the radial direction of the curve with the central axis of the flow path as the boundary is composed of an arc surface with the central axis as the center of curvature. The siphon drainage system according to Claim 1 or Claim 2.

4. When the reduced-diameter portion is viewed in a cross-section perpendicular to the flow path, each of the pair of inclined sides is linear. The inclined sides are inclined at an inclination angle exceeding 30° and not exceeding 45° with respect to a virtual horizontal line that passes through the central portion of the pair of inclined sides and is perpendicular to a virtual vertical center line passing through the central axis of the flow path. The siphon drainage system according to Claim 3.

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