JP2013096122A - Flap gate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flap gate that smoothly discharges water when an upstream-side water level is low or when a large amount of water is discharged, and prevents water from flowing back when a river-side water level and a sluice pipe-side water level is substantially as high as each other.SOLUTION: There is provided the flap gate such that a door body 1 to be freely opened and closed is installed at a river-side exit of a sluice pipe provided to a river bank etc., while suspended by an upper hinge mechanism to cutoff water flowing from the river side, and rotates to a river direction to open the sluice pipe for water flowing from the sluice pipe side, the flip gate being characterized in that a float structure part 1e which generates buoyance is formed at a lower part of the door body 1, a balance weight which moves the position W of the center of gravity of the door body in a downstream direction of the flap gate is installed at an upper part of the door body 1, and the position W of the center of gravity of the door body 1 and the position of a suspension core suspending the door body 1 are arranged downstream from a perpendicular line V2 passing the center of buoyance of the float structure part.

Description

  The present invention relates to an upper hinge-type flap gate that is installed in a lock gate or the like for the purpose of preventing a backflow and automatically opens and closes in response to a water level fluctuation on the upstream and downstream sides of the gate.

  An upper hinge flap gate is installed on the river bank of the river bank to prevent backflow of river water.

  In FIG. 14, the door body 11 is installed so as to be opened and closed by a hinge mechanism including an upper support metal 12, a connection metal 12a, and a connection pin 12b. In the figure, 13 is a door metal fitting, 31 is a riverside riverbed, 32 is a riverside riverbed, 33 is a bank, WL1 is an upstream (floorside) water level, and WL2 is a downstream (riverside) water level.

  As shown in FIG. 14 (a), when the upstream water level WL1 and the downstream water level WL2 are at the same level, the door body 11 is fully closed, and the watertight rubber 11d is pressed against the door fitting 13 to stop water. It should be noted that the connecting hardware 12a of the hinge mechanism ensures a good pressure-bonding property between the watertight rubber 11d of the door body 11 and the door metal fitting 13.

  As shown in FIG. 14 (b), when the upstream water level WL1 rises above the downstream water level WL2, the door body 11 opens in a form that opens the lower end of the door body to the downstream side with the hinge mechanism as the rotation center, Drain from the upstream side to the downstream side in the direction of the water flow indicated by the arrow A.

  The flap gate is used as the most common automatic gate facility because it can respond to fluctuations in the water level upstream and downstream of the gate and can open and close the gate with no power and unmanned operation.

However, the conventional flap gate has the following problems and issues.
As shown in FIG. 15 (a), in the conventional flap gate, the suspended door body 11 always closes the tub tube with a constant closing operation force, so that the door body 11 is sufficient when the upstream water level is low. In some cases, the low water level WL3, which is difficult to drain, is generated in the pipe. This also makes it easier for sediment to accumulate and driftwood or the like 34 to stay in the dredger. Further, as shown in FIG. 15 (b), the accumulated driftwood 34 is easily caught between the door body 11 and the door bracket 13, and an incompletely closed state is easily generated. It is hard to come off, and there is a problem that the river water flows back into the pipe when the river increases in this state.

  Furthermore, as shown in FIG. 16, since the closing operation force of the door body 11 increases as the opening angle θ of the door body 11 increases, the door body opens sufficiently even when a large amount of drainage is performed from the tributaries. There is a problem that smooth drainage is hindered, for example, the door body 11 does not operate and the door body 11 blocks the flowing water, and a relatively large upstream / downstream water level difference Δh is generated.

  The cause of the problem shown in FIG. 15 is the closing operation force when the flap gate is fully closed. As shown in FIG. 17, in the conventional flap gate, the door body 11 when fully closed is installed with an inclination of about 5 ° upstream. In FIG. 17, W is the mass of the door body 11, X1 is the center of gravity position, and L9 is the horizontal distance between the center of gravity position and the hinge mechanism suspension core. In this state, the rotational moment M1 (= W × L9) in the closing direction acts as a closing operation force when fully closed, and presses the door body 11 against the door hardware 13. The flap gate enables the door body 11 to be fully closed even in the same upstream / downstream water level state by this fully closed closing operation force. On the other hand, since it acts as a resistance force during the opening operation, if the upstream side is at a low water level, it may cause poor drainage, sedimentation of sediment, driftwood, etc.

  The problem shown in FIG. 16 is that, as the door body 11 is opened as shown in FIG. 18, the distance L10 between the door body center-of-gravity position X1 and the suspension core becomes larger, and thus the rotational moment in the closing direction due to the door body mass. This is because M1 (= W × L10) increases. In order to solve this problem, as shown in FIG. 19, the lower part of the door body 11 has a floating structure (float) 11e, and a method of improving the opening operability during drainage by buoyancy F generated by the downstream water level WL2. is there. However, in the conventional flap gate installation mode shown in FIG. 19, there is a problem in that when a large buoyancy is generated in the lower part of the door body, the closing operation force when fully closed is reduced. In this embodiment, the rotational moment M2 (= F × L11) around the hinge mechanism due to the buoyancy F acts in the opening operation direction, and acts opposite to the closing operation force due to the door body mass W. Since the buoyancy distance L11 is larger than the center of gravity distance L12, if the buoyancy F is increased, there is a risk that a reliable full closing operation may be hindered.

  With respect to such problems of the conventional flap gate, in Patent Document 1, a balance weight is provided around the support shaft of the upper hinge type door body, and the door body can be opened and closed with a relatively small operating force. In addition, a floating body that rises and falls by its own weight and downstream water pressure is connected by an interlocking arm to form an integrated automatic gate, and the drainage pipe is always fully open for smooth drainage. An automatic gate is disclosed in which a door body is fully closed in conjunction with an upright operation of a type door body.

  However, the gate of Patent Document 1 has a complicated mechanism for connecting the upper and lower door bodies, and there is a problem that it is difficult to maintain and manage the equipment when used on site for a long period of time.

  On the other hand, in Patent Document 2, the door body has a floating structure, and a door body is installed at the tip of the rotating arm with the protruding upper hinge as a fulcrum. When the river water rises, the door body is fully closed by buoyancy. However, there is disclosed a gate that allows smooth drainage by always supporting the door in an open state at a water level below a predetermined level.

  Further, in Patent Document 3, a door body is provided at one end of a rotary arm having an upper hinge as a rotation center, and a balance weight is provided at the other end so that the door body can be rotated with a slight operating force. A gate is disclosed in which a float is provided above the side surface of the tub tube, and the automatic closing operation is performed by a buoyancy generated in the float due to a certain rise in water level, and smooth drainage is performed with the lower part of the gate always open below a predetermined water level. Yes.

  However, in the gate disclosed in Patent Document 2, approximately 50 to 60% or more of the entire door body is submerged and generates buoyancy for closing. In addition, since the gate disclosed in Patent Document 3 has a structure in which a closing operation force is generated by the float installed above the side surface of the side pipe of the door body, the inside of the side pipe is generally kept until buoyancy is generated in the float installed above. It is necessary to raise the water level by more than half of the height. The gates of Patent Documents 2 and 3 are mechanisms that require a rise in the water level above and below the gate to be 1/2 to 2/3 or more of the inner height of the pipe before the door is fully closed. Backflow from the river side to the side of the culvert pipe occurs until the fully closed state due to the structure that cannot stop the water except during times. Accordingly, there is a problem that it is difficult to prevent a back flow at a middle water level or lower.

Japanese Patent No. 3822715 Japanese Patent No. 3350902 Japanese Patent No. 3500388

  The present invention enables the door body to easily open and drain even when the upstream side is at a low water level, and when large capacity drainage, the door body opens and operates to smoothly drain water. When the water level on the side of the soot pipe is about the same level, a flap gate that can prevent the occurrence of back flow by reliably closing the soot pipe and providing a simple structure is provided.

  In the invention of claim 1 of the present application, an openable and closable door body is installed in a suspended state by an upper hinge mechanism at a river side outlet of a dredger pipe provided on a river bank or the like so that water can be stopped against flowing water from the river side, In the flap gate where the door body rotates in the direction of the river against flowing water from the side of the dredging pipe and opens the dredging pipe, the lower part of the door acts as a closing force when the gate is fully closed and the gate opening operation A floating structure that generates buoyancy acting as an opening actuation force is sometimes formed, and a balance weight that moves the center of gravity of the door body in the downstream direction of the flap gate is installed at the top of the door body. The flap gate is characterized in that a gravity center position and a suspension core position for suspending the door body in a suspended state are arranged on a downstream side of a vertical line passing through a buoyancy center of the floating structure portion.

  With this configuration, the buoyancy generated in the lower part of the door body can be used as an opening operation force when the gate is opened to promote drainage, and can be used as a closing operation force when the gate is fully closed.

  In the invention of claim 2 of the present application, the mass and buoyancy of the door body act as a closing operation force due to the gravity of the door body, and are small in the fully closed state and increase with the door body opening operation (S1). The absolute value of the rotational moment (S2) acting as the opening actuating force as the door body opens due to the buoyancy acting on the lower floating body structure of the door body is set to be | S1 |> | S2 | The flap gate according to claim 1, wherein the flap gate is provided.

  The invention according to claim 3 of the present application is characterized in that the lower door hardware of the door body is arranged in an inclined form so as to be upstream of the upper door hardware. It is a gate.

  Since the present invention reduces the center of gravity of the door body and the distance between the suspension cores to reduce the closing operation force due to the weight of the door body when fully closed, the door body can be opened even with a small water pressure due to the low water level on the upstream side. The door body can be easily opened and drained smoothly at the upstream low water level.

  In the present invention, since the floating structure is provided at the lower end of the door body, drainage is promoted by utilizing the generated buoyancy as an opening actuation force when the gate is opened, and as a closing actuation force when the gate is fully closed. Is possible.

  According to the present invention, the door acts as a closing operation force due to the gravity of the door body, and is small in the fully closed state and increases with the door body opening operation (S1), and the buoyancy force acting on the lower floating body structure of the door body. Set the mass and buoyancy of the door body so that the absolute value of the rotational moment (S2) acting as the opening actuating force as the body opens becomes | S1 |> | S2 | If the buoyancy acts in the closing operation direction and the downstream water level rises, the downstream water level generates buoyancy in the floating body structure at the lower part of the door body, increasing the closing operation force and ensuring that the door body is fully closed. Can be operated. In the fully closed position, buoyancy acting on the door body acts in the closing operation direction, so that a constant closing operation force is secured in the upstream and downstream equivalent water level states, and reliable water stopping can be achieved.

  In the drainage operation in which the floating structure at the bottom of the door body is submerged, the buoyancy acts as an opening actuation force and the closing actuation force due to the door body mass can be reduced. The door body can be opened largely to allow smooth drainage.

  Furthermore, since the present invention always ensures a stable closing force even in the above-described state, before the river side water level and the side pipe side water level become comparable in all gate operating ranges, Rotate to the fully closed position to prevent backflow.

  Further, the present invention is arranged such that the lower door hardware of the door body is located upstream of the upper door hardware in the field conditions that can allow backflow generation at a low water level of about 1/3 or less of the inner height of the vertical pipe. Accordingly, in a state where the downstream water level is low, the drainage from the upstream side can smoothly flow down by providing a gap between the suspended door body and the door hardware. During normal operation, smooth drainage is performed with the lower part of the door open, causing the buoyancy acting on the door body to act on the closing operation side as the downstream water level rises, causing the door body to automatically close when the water level rises, The gate can be fully closed early at a low water level of about 1/5 to 1/3.

  The present invention does not require a driving means and suspends the door body by a hinge mechanism, so that a flap gate having a simple structure can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is the installation schematic diagram of the flap gate of this invention, (a) is a bird's-eye view from the downstream, (b) is a cross-sectional schematic diagram of a gate installation part. It is a flap gate schematic diagram of the present invention, (a) is a gate opening operation state diagram, (b) is a structural schematic diagram of the hinge part. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic of the door body of the flap gate of this invention, (a) is the schematic diagram seen from the upstream (the side pipe side), (b) is the schematic diagram seen from the downstream (river side). It is a structure schematic diagram of the lower part of a door body in the flap gate of the present invention. It is the installation form figure of the flap gate of Example 1 of this invention, (a) is a sectional side view when a gate is fully closed, (b) is a sectional side view when a gate is fully opened. It is an installation condition figure of the flap gate of Example 1 of the present invention. It is an operation | movement force form figure of the flap gate of Example 1 of this invention, (a) is at the time of the gate full closure of an anhydrous state, (b) is at the time of the opening | release operation of the drainage state from the upstream. FIG. 5 is a diagram showing the operating force of the flap gate according to the first embodiment of the present invention, and shows the gate in a fully closed state at the same upstream and downstream water levels. FIG. 3 is a diagram showing the operating force of the flap gate according to the first embodiment of the present invention, and shows a state of drainage from the upstream at a constant water level. It is a graph which shows the characteristic of the open degree of a flap gate of Example 1 of this invention, and an operating force. The installation condition figure of Example 2 of this invention is shown. It is an operation power form figure of the low water level drainage state from the upper stream of Example 2 of the present invention. It is an operation force form figure of Example 2 of the present invention, (a) at the time of a fully closed operation water level, (b) is a state figure of all submersion of a lower floating body structure part in a fully closed state. In the schematic diagram of the conventional flap gate, (a) shows a fully closed state, (b) shows an open operation state. It is the schematic which shows the problem of the conventional flap gate, (a) is the drainage failure in the vertical pipe and accumulation of driftwood, etc., (b) shows the state where driftwood etc. are sandwiched between the door body and door metal fittings. . It is a schematic diagram which shows the problem at the time of the drain operation of the conventional flap gate. It is a schematic diagram which shows the gravity center position at the time of the full closure of the conventional flap gate. It is a schematic diagram which shows the gravity center position in the door body open state of the conventional flap gate. It is a schematic diagram which shows the gravity center position and buoyancy position in the fully-closed state in the example which made the lower part of the door body the floating body structure in the conventional flap gate.

  Embodiments of the present invention will be described with reference to the drawings.

<Example 1>
In FIG. 1, the door body 1 is in contact with the door-to-door hardware 3 by the hinge 2 of the hinge mechanism in the form of closing the river pipe 31 at the river side outlet of the river pipe 31 provided on the river bank 33, and the river It is suspended and installed in a freely rotating direction. 32 is a river side waterway.

  As shown in FIG. 2A, the door body 1 of the present invention is swingably suspended by a hinge mechanism by a hanging object 2 and can be opened. In the hinge mechanism, as shown in FIG. 2B, the connecting portion 1a of the door body 1 and the hanging object 2 are connected to each other by connecting pins 2b via connecting plates 2a. By this hinge mechanism, the door body 1 can freely rotate, and the watertight rubber 1d of the door body 1 when fully closed is smoothly crimped to the door fitting 3 to stop the water from the river side in the direction of the pipe. . As shown in FIG. 2 (a), in the gate opening operation state, the watertight rubber 1d of the door body 1 is separated from the upper door hardware 3a, the lower door hardware 3b, and the side door hardware 3c. And drain the water from the side of the pipe to the river.

  As shown in FIG. 3, the door body 1 of the present invention has a connecting portion 1 a to a hinge mechanism suspension 2 at the upper end girder, and a balance weight arm 1 b fixedly installed at the upper portion of the door body, at the tip of the balance weight arm 1 b. A balance weight 1c is installed. The balance weight arm 1b and the balance weight 1c allow the center of gravity of the door body 1 to be moved in the downstream direction of the gate.

  In addition, a watertight rubber 1d is installed on the upstream surface portion of the door body 1, and the lower downstream side of the door body is a floating body structure 1e so that buoyancy is generated in the door body by the water level on the downstream side of the gate when the gate is fully closed. Yes. For example, as shown in FIG. 4, the floating structure 1e covers a portion surrounded by a skin plate 1e, a vertical girder 1e, a horizontal girder 1e, and a back plate 1e. It is formed by making it a completely airtight structure. However, the magnitude of the maximum buoyancy to be generated is not more than ½ of the weight of the door body 1, and the closing operation force due to the weight of the door body 1 is not lost in the entire operation range in the fully immersed state of the door body.

  As shown to Fig.5 (a), in this installation form, when the gate is fully closed, the door body 1 suspended by the hinge mechanism is installed so as to be substantially vertical. Further, as shown in FIG. 5B, the balance weight 1c does not interfere with the hinge mechanism, the civil engineering structure, or the like in the state where the gate is fully opened, and the door 1 is installed in a form that can be reliably opened.

  In FIG. 6, the door body 1 is in a fully closed state, X1 is a center of gravity of the total mass W of the door body 1, and V1 is a vertical line passing through X1. X2 is the buoyancy of the total buoyancy F of the lower floating body structure 1e of the door body 1, and V2 is a vertical line passing through X2. The vertical line passing through the suspension center position of the door body 1 is V3, V1 and V3 are on the river side from V2, and V3 is the same as V1 or slightly on the side of the tub.

  With this installation condition, as shown in FIG. 7A, the door body 1 has a rotational moment M1 (= W × L1) due to the distance L1 between V3 and V1 and the mass W, with no water level on the downstream side of the gate. Due to this, an operating force in the closing direction is generated. Since L1 is relatively small, M1 also becomes a small force, and the door body 1 can be opened by a relatively small operating force. As shown in FIG. 7B, even when the upstream water level WL1 is a relatively small water level, the door body 1 can be easily opened and drained smoothly. In FIG. 7 (b), the door body 1 is opened and the rotational moment M1 (= W × L1 ′) of the door body 1 becomes larger than that in FIG. 7 (a), but the door body 1 is opened to a state balanced with the water pressure of WL1. Operate.

  Moreover, when V3 and V1 shown in FIG. 6 are set on the same line, the door body 1 is in a fully closed state and is in a suspended state, and the initial closing operation force in this case is substantially zero. Therefore, it becomes easier to perform the opening operation with respect to the flowing water from the upstream side.

  As shown in FIG. 8, as the downstream water level rises, buoyancy F is generated to generate a rotational moment M2 (= F × L2) in the gate closing direction. Thereby, even if the upstream and downstream are in the same water level state, the gate closing operation force is ensured by the generated buoyancy M2.

  By the opening operation of the door body 1, the vertical lines V1 and V2 shown in FIG. When the vertical line V2 shown in FIG. 6 moves downstream from V3, the buoyancy F acts on the opening operation side.

  As shown in FIG. 9, when the drainage operation is performed with the floating structure 1e of the door body 1 submerged, the rotational moment M1 (= W × L3) due to the mass W acts in the gate closing operation direction, but the buoyancy F The rotational moment M2 (= F × L4) due to acts on the opening operation direction. As a result, the operating force required to open the gate is reduced by an amount corresponding to M2, and the difference in water level between the upstream water level WL1 and the downstream water level WL2 during drainage is reduced, and smooth drainage can be performed.

  In the automatic operating force graph of the flap gate of the present invention shown in FIG. 10, the horizontal axis indicates the gate opening degree, the origin is the opening degree 0 (= fully closed state), and the gate opens in the right direction. The vertical axis indicates the opening / closing direction operating force, with the center line 0 as a boundary, the positive direction (upward) indicates the gate closing operating force, and the negative direction (downward) indicates the gate opening operating force. S1 is a rotational moment M1 due to the gravity W of the door body 1, and always acts as a closing operation force in the present installation form, and has a characteristic of increasing in the door body opening operation in a fully closed state. S2 is a rotational moment M2 due to the total buoyancy F acting on the lower floating structure 1e of the door body 1 and acts in the closing operation direction in the fully closed state, but decreases as the closing operation force with the opening operation of the door body 1, The vertical line V2 shown in FIG. 6 becomes 0 at an angle where the vertical line V2 is the same line as the same V3, and acts as an opening actuating force with the opening. As a result, under the water level condition where the buoyancy F acts, the door closing force is a rotational moment S3 obtained by adding S1 and S2.

  In the flap gate of the present invention, S1 in this automatic operating force graph is always larger than the absolute value of the opening operating force in S2, that is, | S1 |> | S2 | Is set.

As a result, as shown in FIG. 10, under the water level condition where the buoyancy F acts, the door closing force S3 has a characteristic that becomes a stable value with respect to the increase in the gate opening. This easily opens the gate according to the amount of drainage from the upstream, and improves drainage operability. In addition, since the closing operation force is always secured, the automatic closing operation can be quickly performed when the drain pressure from the upstream side decreases, and the gate can be fully closed before the upstream and downstream water levels are reversed. .

  As described above, the flap gate according to the present invention has a small gate closing operation force when there is no water level on the downstream side of the gate or when the downstream water level is low, and the flap gate easily operates to open the drainage flow from the upstream side. Drain smoothly. When the downstream water level rises, buoyancy F acts from the lower part of the door body in the door body closing operation direction, and the gate is reliably closed to prevent backflow from downstream to upstream. Further, in the state of draining from upstream water at a constant water level to the downstream direction, the buoyancy F acts in the opening operation direction, and it is possible to easily increase the gate opening degree according to the amount of drainage and perform smooth drainage.

<Example 2>
In FIG. 11, a frame-like door metal fitting provided around the opening of the tub tube 31 is arranged in an inclined form so that the lower door hardware 3b is upstream from the upper door hardware 3a. As in the first embodiment, the door body 1 is suspended and installed so as to be substantially vertical by a hinge mechanism. The inclination angle is in the range of about 5 to 10 degrees. FIG. 11 shows an installation state in which the vertical line V1 passing through the center of gravity X1 and the vertical line V2 of the door suspension core are on the same line, and the door 1 is suspended vertically. In this embodiment, V1 is set on the same line as the vertical line V3 passing through the suspension center position of the door body 1.

  In this state, the door body 1 is separated from the lower door metal fitting 3b, and has a shape in which a gap is provided between the lower end of the door body 1 and the lower door metal fitting 3b, and the iron pipe is opened. When a small amount of the suspension core of the door body 1 is moved to the side of the duct, the lower end of the door body 1 is inclined so as to move in the upstream direction. Also in this case, a gap through which dust or the like can pass is secured between the lower end of the door body and the lower door hardware 3b.

  As shown in FIG. 12, when there is no water level on the downstream side, the door body 1 is suspended in a balanced state, and since the lower end of the door body is open, drainage from the upstream is performed smoothly, and driftwood Dust etc. can flow smoothly.

  As shown in FIG. 13A, when the downstream water level rises, the rotational moment M2 (= F × L7) due to the buoyancy F acts on the lower floating structure 1e of the door 1 in the door closing direction. The automatic closing operation is performed in a state exceeding the rotational moment M1 (= W × L6) to restore to the suspended state due to the mass W of the water, and a predetermined water level (approximately 1/5 to 1/3 of the vertical pipe height) ) Is fully closed.

  As shown in FIG. 13B, when the downstream water level WL2 further rises, the buoyancy F increases, the closing operation force is increased, and the door body 1 is pressed against the lower door fitting 3b to stop the water. Since the automatic closing operation force due to the rise of the downstream water level WL2 is designed to act reliably in the upstream and downstream equivalent water level states, the water level differential water pressure further acts in the closing operation direction when the downstream water level WL2 exceeds the upstream water level WL1. Then, the gate is fully closed early.

  On the contrary, when the upstream water level WL1 rises above the downstream water level WL2, the door body 1 starts an opening operation, and performs smooth drainage with a relatively small water level difference as shown in FIG.

1: Door body 1a: Connecting part 1b: Balance weight arm 1c: Balance weight 1d: Watertight rubber 1e: Floating structure part 1e at the lower part of the door body: Skin plate of the door body 1e I: Door end stringer 1e: Crosspiece 1d of door body: Back plate of door body 2: Hanging hardware (hinge mechanism) 2a: Connection hardware (hinge mechanism)
2b: Hanging pin 3: Towel hardware
3a: Upper door hardware 3b: Lower door hardware 3c: Side door hardware 11: Door 11d: Watertight rubber 11e: Floating structure 12 under the door body 12: Hanging metal 12a: Hanging plate 12b: Hanging pin 13: Door-to-door hardware 31: Pipe side waterway 32: River side waterway 33: Embankment 34: Driftwood, etc. WL1: Gate upstream side (floor pipe side) water level WL2: Gate downstream side (river side) water level WL3: Pipe pipe by closing the door Water level generated on the side that is difficult to drain W: Total mass of door body and balance weight F: Buoyant force generated by the floating structure below the door body in the underwater part X1: W center of gravity position X2: F centering position V1: Passed through X1 Vertical line V2 passing through: Vertical line V3 passing through X2: Vertical lines L1 to L11 passing through the suspension core position of the door body: Horizontal distance from the suspension core of the door body to the center of gravity of the door body or buoyancy. Direction △ h: Difference between upstream and downstream water levels during drainage

Claims (3)

An openable door is installed at the river side exit of the dredging pipe on the river embankment, etc., suspended from the river side by the upper hinge mechanism so that it can be stopped against running water from the river side. On the other hand, in the flap gate where the door body rotates in the direction of the river and opens the pipe.
A floating structure for generating a buoyancy that acts as a closing operation force when the gate is fully closed and as an opening operation force when the gate is opened is formed at a lower portion of the door body, and the door body is formed above the door body. A balance weight is installed to move the center of gravity of the door in the downstream direction of the flap gate, and the center of gravity of the door body and the suspension core position for hanging the door body in a suspended state are from the vertical line passing through the buoyancy center of the floating body structure part. A flap gate, which is arranged on the downstream side.   The mass and buoyancy of the door body act as a closing operation force due to the gravity of the door body and are small in the fully closed state and increase with the door body opening operation (S1), and the lower floating body structure of the door body The absolute value of the rotational moment (S2) acting as an opening actuating force as the door body opens due to the buoyancy acting on the door is set to satisfy | S1 |> | S2 |. 1. The flap gate according to 1.   The flap gate according to claim 1 or 2, wherein the lower door hardware of the door body is disposed in an inclined form so as to be upstream of the upper door hardware.

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