JPH10311018A - Counter-flow preventive gate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a counter-flow preventive gate equipped with a tilting door, with which an alarm is issued prior to occurrence of a counter-flow in case the door does not rise because of any failure and thereby counter-flow is prevented in advance. SOLUTION: A counter-flow preventive gate is equipped with a door 12 borne in a passage 11 with possibility of tilting and generating a buoyancy under the water and a shutting means to shut the passage when the door 12 is raised, and the arrangement further includes an angle meter 30 to sense the inclining angle of the door 12, a calculating means to calculate the height H of the upper edge 12a of the door 12 on the basis of the data given by the angle meter 30, and a liquid level meter 32 to sense the level (h) of the understream water surface 23 of the door 12, wherein an alarm lamp 33 emits alarm light when the difference between the height H of the upper edge 12a of the door 12 and level (h) of the downstream water surface 23 has becomes below the set value S. Further an automatic door shutting mechanism is furnished which shuts the passage by raising the door 12 with electric power etc. in synchronization with the turn-on and -off operation of the alarm lamp 33.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backflow prevention gate installed on a gutter or a gutter pipe as a river management facility, and more particularly to a backflow prevention gate having a backflow detection function.

[0002]

2. Description of the Related Art Conventionally, as a river management facility, a backflow prevention gate has been installed at a gutter or a gutter pipe in order to prevent a backflow when a river is flooded due to a torrential rain.
The conventional backflow prevention gate has a structure in which a water passage is opened and closed by a door body that slides in a vertical direction, and the backflow is prevented by moving the door body up and down according to an increase or decrease in the amount of water.

[0003] When a river is flooded due to a typhoon or torrential rain, the manager goes to the site where the backflow prevention gate is installed, day or night, and adjusts the height of the door according to the flooding condition. This prevents backflow from the river side. Further, when a typhoon or the like has passed and the water volume of the river has returned to normal, the manager again goes to the installation site of the backflow prevention gate and adjusts the height of the door body.

[0004] As described above, in the conventional backflow prevention gate, when the amount of water increases or decreases due to the weather or the like, it is necessary for the manager to go to the site and adjust the height of the door each time. A lot of effort is spent on management.

In many cases, it is necessary to prevent a backflow from a river during a typhoon or a torrential downpour, and the manager goes to the site in the severe wind and rain and operates the floodgate. Therefore, the burden is large and the danger is high.

Further, in the case of a typhoon or a torrential downpour, if the timing of opening and closing the floodgate is incorrect, a disaster such as a flood may be caused. In case of heavy rain,
The reality is that it is difficult to respond quickly.

In order to cope with such a situation, the present applicant has developed a backflow prevention gate having a function of automatically operating when a river rises to prevent backflow, and is disclosed in Japanese Patent Application No. 8-310945. Has filed a patent application.

The backflow prevention gate according to Japanese Patent Application No. 8-310945 has a structure as shown in FIG. 6 (a). However, the backflow prevention gate is required to prevent the door 40 from standing up due to a failure or the like. A backflow detection device is provided for notifying the occurrence of backflow in case a situation occurs in which backflow cannot be performed.

The backflow detecting device includes an external water level meter 43 for detecting the upstream water level 41 of the door body 40, an internal water level meter 44 for detecting the downstream water level 42 of the door body 40, and a flow direction meter 45 for detecting the direction of the water flow. , A warning light 46 and the like. And FIG.
As shown in (b), even if the downstream water level 42 rises, the door body 40 does not stand up, and when a backflow occurs, the flow indicator 45 detects it and the warning light 46 emits a warning light. It has become.

On the other hand, as one of the devices for damping a river or the like and maintaining the water level on the upstream side at a predetermined level, there is a device conventionally called a fall gate, for example, Japanese Unexamined Utility Model Publication No. 59-51826. , Tokiko Sho 61-12045
In Japanese Patent Application Laid-Open Publication No. H10-163, a technique relating to a fall gate is disclosed.

[0011]

However, since the backflow detecting device shown in FIG. 6 detects the occurrence of the backflow and the warning light 46 emits a warning light, it is necessary to detect the backflow unless a backflow actually occurs. Can not. Therefore, the warning light 46
Even if the operator rushes to the site where the backflow prevention gate is installed while watching the warning light from the user, countermeasures may be delayed because backflow has already occurred.

On the other hand, the fall gate disclosed in Japanese Utility Model Application Laid-Open No. 59-51826 and Japanese Patent Publication No. 61-12045 has a function of maintaining the water level on the upstream side at a predetermined level. There is no function to prevent the occurrence of backflow or to notify the occurrence of backflow.

An object to be solved by the present invention is to provide a backflow prevention gate having a tiltable door.
An object of the present invention is to prevent backflow by issuing an alarm before backflow occurs when the door does not stand up due to a failure or the like.

[0014]

In order to solve the above problems, the present invention comprises a door body which is tiltably mounted in a flow path in which a fluid flows in a certain direction and generates a levitation force in the fluid,
A backflow prevention gate for closing the flow path by raising the door body due to an increase in the fluid on the downstream side, a door body height detecting means for detecting the height of the overflow portion of the door body, and a downstream side of the door body. A fluid surface height detecting means for detecting a surface height of a certain fluid is provided, and the detection data of the door body height detecting means and the detection data of the fluid surface height detecting means are compared, and the difference is equal to or less than a set value. A warning means for issuing a warning when a warning occurs.

When a door that generates a levitation force in the fluid is tiltably mounted in a flow path in which the fluid flows in a certain direction, the force by the flow of the fluid and the buoyancy by the fluid act on the door. Then, the door body is in a state of standing slightly upward from the vertical. Therefore, the liquid level on the upstream side of the fluid dammed by the door body is higher than the liquid level on the downstream side,
The fluid on the upstream side flows over the overflow portion of the door body and flows to the downstream side.

Here, when the surface of the downstream fluid rises, the buoyancy of the downstream fluid acting on the door body increases, so that the door body automatically rises to the upstream side,
Finally, the flow path is closed by the upright door body and the closing means, and the backflow is prevented.

Further, if the downstream surface descends and becomes lower than the upstream surface after the flow path is closed, the buoyancy of the downstream fluid acting on the door body decreases, and the door body becomes The fluid on the upstream side will automatically fall to the downstream side,
Again, it flows over the upper edge of the door body and flows downstream.

In order to generate a buoyant force on the door body in the fluid, for example, a structure having an airtight space inside the door body to generate a buoyant force based on the same principle as a so-called floating ring, or a door. A structure that generates a buoyancy by forming the body itself from a material having a smaller specific gravity than the fluid can be employed.

Further, as means for closing the flow path when the door body stands up, a sealing member is provided on the outer peripheral portion of the door body, and a door stop member in contact with the sealing member is provided in the flow path. be able to. With this, when the fluid surface on the downstream side rises and the door body stands, the sealing member on the outer periphery of the door body is in close contact with the door stop member in the flow path without any gap, so that the flow path is completely closed. can do. Therefore,
Backflow does not occur even if the downstream fluid surface is raised.

On the other hand, in the backflow prevention gate of the present invention, the height of the overflow portion of the door is detected by the door height detecting means, and the surface level of the fluid downstream of the door is detected by the fluid level detecting means. Alarm means for detecting the height and comparing the detection data of the door height detection means with the detection data of the fluid surface height detection means, and issuing an alarm when the difference becomes equal to or less than a set value.

Therefore, in the situation where the fluid level on the downstream side is rising, when the door body does not stand due to a failure or the like and the liquid level on the downstream side approaches the upper edge of the door body, the difference is set to the set value. In the following cases, an alarm is issued from the alarm means, so that the fluid on the downstream side can get over the overflow section of the door body and be notified before the backflow occurs.

Here, as the door body height detecting means, a goniometer for detecting the inclination angle of the door body and a door body height calculating device for calculating the height of the overflow portion of the door body based on the detection data of the goniometer. Can be provided. The angle of inclination of the door body is detected with a goniometer, and the door body height calculation device calculates the height of the overflow portion of the door body based on the data, so that the door body is at any inclination angle The height of the overflow portion of the door body can be accurately detected.

In this case, as a method of calculating the height of the overflow portion of the door body based on the inclination angle of the door body detected by the goniometer, for example, the dimension from the pivot portion of the door body to the overflow portion is determined. L, where θ is the detection data of the goniometer, L × si
For example, a method of calculating by nθ can be adopted.

In the backflow prevention gate of the present invention, a liquid level gauge can be used as the fluid level height detecting means.
By using the liquid level gauge, it is possible to accurately detect the surface height of the fluid on the downstream side of the door, and to quickly respond to a change in the surface height. in this case,
As a type of the liquid level gauge, for example, a float type, a pressure type, an ultrasonic type liquid level meter, or the like can be adopted.

Further, in the backflow prevention gate of the present invention, an alarm lamp that emits an alarm light, an alarm that emits an alarm sound, and the like can be employed as alarm means. In this way, by giving a warning with a warning light and a warning sound, the danger of backflow can be notified even in a situation where the noise due to a typhoon or heavy rain falls is large or at night.

Here, in the backflow prevention gate of the present invention, a door closing mechanism for closing the flow path by raising the door using at least one of a manual force and an electric force can be provided. In the backflow prevention gate of the present invention, the door body is pivotally supported so as to be tiltable and performs a tilting operation automatically by the action of fluid, but if a mechanism for erecting the door body by manual force or electric force is provided. When the alarm means is activated, the door can be forcibly raised by manual or electric power and the flow path can be closed before the backflow occurs, so that a reliable response can be taken.

Further, in this case, in synchronization with the operation of the alarm means, an automatic door closing mechanism for closing the flow path by raising the door by electric power or the like can be provided. If such a door closing mechanism is provided, when the alarm means is activated, the door is automatically erected and the flow path is closed, so that a quick response is possible and the backflow prevention function is further improved.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing a backflow prevention gate according to the first embodiment, FIG. 2 is an explanatory diagram showing an operation state of the backflow prevention gate, and FIG. 3 is a block diagram showing a backflow detection function of the backflow prevention gate.

As shown in FIG. 1, the backflow prevention gate 10 according to the present embodiment includes a door body 12 which is pivotally supported in a water channel 11 to generate a floating force in water, and the door body 12 stands upright. Sometimes, as a closing means for closing the water channel 11, the door 1
A sealing member 17 is attached to the outer peripheral portion of
Door stops 19 and 20 are provided on the ceiling 5 and the ceiling 18 to prevent the passage of water by contacting the sealing member 17 of the door body 12. A flexible sealing member 14 is disposed on the pivot portion 13 of the door body 12 to prevent water from passing therethrough.

Further, the door body 12 is formed of a stainless steel plate, and has a structure in which an airtight space is provided in order to generate a buoyancy in water. That is, the door 1
2 has a box structure with air sealed inside,
A buoyancy is generated in water by the same principle as a so-called floating ring.

The operation of the backflow prevention gate 10 will now be described with reference to FIG. When the door body 12 that generates buoyancy in water is pivotally supported in the water channel 11 in which the water 21 flows in a certain direction, the door body 12 has a force due to the flow of the water 21 and a buoyancy due to the water 24 on the downstream side. As a result, as shown in FIG. 1, the door body 12 stands up slightly inclining from the vertical to the downstream side.

Therefore, the upstream water surface 22 of the water 21 blocked by the door body 12 is higher than the downstream water surface 23, whereby the upstream water 21 passes over the overflow section 12 a of the door body 12 and is downstream. Flows to the side. As long as the upstream water surface 22 is at a position higher than the downstream water surface 23, this state is maintained, so that the water 21 continues to flow toward the downstream.

On the other hand, when the downstream water surface 23 rises, the buoyancy of the downstream water 24 acting on the door body 12 increases, so that the door body 12 automatically rises upstream.
Eventually, the sealing member 17 located above the upright door body 12 abuts on the door stop member 20 and the water passage 11 is closed. At this time, the sealing member 1 located on the side of the door body 12
Since the abutment 7 is in contact with the door stop member 19 without any gap, the water channel 11 is in a completely closed state.
It is possible to prevent the water 24 from flowing backward from the downstream side to the upstream side.

On the other hand, after the water channel 11 is closed, the downstream water surface 23 descends and becomes lower than the upstream water surface 22.
The buoyancy of the downstream water 24 acting on the door body 12 is reduced, and the door body 12 automatically falls to the downstream side. To flow downstream.

As described above, since the backflow prevention gate 10 of the present embodiment is tilted in accordance with an increase or decrease in the amount of water, when the downstream water surface 23 rises, the water passage 11 is automatically closed to prevent backflow. It also has an excellent function of preventing water leakage even when closed.

Next, referring to FIGS.
A description will be given of a backflow detecting function of the backflow prevention gate 10 when the door body 12 does not stand up due to a failure or the like in a state where 3 is rising.

The backflow prevention gate 10 includes a goniometer 30 for detecting the inclination angle of the door body 12 and a downstream water surface 23 of the door body 12.
Liquid level gauge 32 for detecting the height h of
And a warning light 33. The detection data of the goniometer 30 and the detection data of the liquid level gauge 32 are transmitted to the backflow detecting device 31. The liquid level gauge 32 uses an ultrasonic type.

The backflow detecting device 31 includes a door height calculating circuit 3.
4. A comparison circuit 35 and an alarm generation circuit 36 are provided. The door body height calculation circuit 34 calculates the height H of the overflow portion 12a of the door body 12 based on the detection data of the goniometer 30. At this time, the dimension from the pivot portion 13 of the door body 12 to the overflow portion 12a is L, and the inclination angle of the door body 12 detected by the goniometer 30 is θ.
Then, the height H of the overflow portion 12a of the door body 12 is H = L
× sin θ.

On the other hand, in the comparison circuit 35, the height H of the overflow portion 12a of the door body 12 calculated by the door body height calculation circuit 34 and the height h of the downstream water surface 23 detected by the liquid level gauge 32 are calculated. Are constantly compared, and when the difference is smaller than a preset value S, a danger signal is sent to the alarm generation circuit 36. Then, the alarm generation circuit 36 turns on the alarm lamp 33 in response to the danger signal from the comparison circuit 35 to notify that a backflow may occur. The comparison between the height H of the overflow portion 12a of the door body 12 and the height h of the downstream water surface 23 in the comparison circuit 35 may be performed intermittently at predetermined time intervals.

Therefore, due to a typhoon or torrential rain,
In a situation where the downstream water surface 23 is rising, the door body 12 does not stand up due to a failure or the like, and the downstream water surface 23 approaches the overflow section 12a of the door body 12 and an alarm is issued when the difference becomes equal to or less than the set value S. Since the lamp 33 is turned on, the downstream water surface 23 is
Before the backflow occurs over the overflow section 12a. In this embodiment, the set value S is set to 5
cm, the downstream side water surface 23 approaches the overflow section 12a of the door body 12, and when the difference becomes 5 cm or less, a danger signal is issued from the comparison circuit 35 and the warning lamp 33 is turned on.

As described above, the backflow prevention gate 10 warns of the danger of backflow when the door 12 does not stand up due to a failure or the like in a situation where the downstream water surface 23 is rising due to a typhoon or heavy rain. Since the backflow detecting function for notifying by the lamp 33 is provided, it is possible to take measures before the backflow occurs, and it is possible to prevent a disaster or the like from occurring.

A goniometer 30 for detecting the inclination angle of the door 12 and a door height calculating circuit 34 for calculating the height of the overflow portion 12a of the door 12 based on the detection data of the goniometer 30 are provided. Thus, the height of the overflow portion 12a can be accurately detected regardless of the inclination angle of the door body 12, so that the presence or absence of backflow can be accurately determined.

Further, the provision of the liquid level gauge 32 allows the height h of the downstream water surface 23 to be accurately detected, and immediately responds to a change in the height of the downstream water surface 23. It is possible to quickly determine the possibility of backflow.

In this embodiment, the alarm lamp 33 that emits an alarm light is employed as the alarm means. However, an alarm 38 that emits an alarm sound may be employed. It can also be attached. When the warning light 33 and the warning device 38 are provided side by side, there is an advantage that the danger of the backflow can be notified even in a situation where the noise is large due to a typhoon or a heavy rainfall or at night.

By the way, the backflow prevention gate 1 of this embodiment
At 0, the door body 12 is pivotally supported so as to be tiltable and operates by the action of water. However, based on a danger signal from the comparison circuit 35, the door body 12 is closed by an electric force or the like. A mechanism 37 can also be provided. If such a mechanism is provided, the door body 12 can be moved by the electric force at the same time that the alarm lamp 33 is turned on, and the water channel 11 can be closed before the backflow occurs. improves.

In addition, a mechanism for closing the door 12 by a manual force may be provided.
When 3 is lit, the door body 12 is raised by human power to close the water channel 11, thereby preventing backflow.

In the backflow prevention gate 10 of the present embodiment, the sealing member 17 attached to the door 12 and the door 1
Although the flexible sealing member 14 disposed on the second pivot portion 13 is formed of rubber, rubber has high sealing properties, and has excellent strength and durability in a fluid such as water. Excellent function as a sealing member. In addition, sealing member 1
7. The flexible sealing member 14 can also be formed of a synthetic resin or the like.

Next, another embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a side view showing a backflow prevention gate according to the second embodiment, and FIG. 5 is a side view showing a backflow prevention gate according to the third embodiment.

The backflow prevention gate 50 of the second embodiment includes a goniometer 30 for detecting the inclination angle of the door body 51, a liquid level gauge 32 for detecting the height of the water surface on the downstream side of the door body 51, and a backflow detection device. 31 and a warning light 33, and, like the backflow prevention gate 10 shown in FIG.
The danger of backflow can be indicated by the warning light 33.

Further, in the backflow prevention gate 50,
A door closing mechanism 37 that operates in synchronization with the warning light 33 based on a danger signal from the comparison circuit 35 (see FIG. 3) of the backflow detection device 31 is provided. The door closing mechanism 37 is shown in FIG.
As shown in FIG. 7, a hydraulic cylinder 52 that expands and contracts a rod 55 by electric power, and a tilt arm 54 that is attached to a shaft support portion 53 of the door body 51 and interlocks with the door body 51 are provided.

Therefore, when a danger signal is generated from the comparison circuit 35 of the backflow detecting device 31, the alarm lamp 33 is turned on, and at the same time, the hydraulic cylinder 52 is operated to cause the rod 55 to protrude. The water body 11 is automatically closed by bringing the door body 51 upright by contacting and rotating it.

As described above, the backflow prevention gate 50 is provided with a mechanism for detecting the danger of backflow in advance, turning on the warning lamp 33, and automatically closing the water channel 11 by the door body 51. Therefore, quick response in an emergency is possible, and the backflow prevention function is high.

Next, a backflow prevention gate according to the third embodiment will be described with reference to FIG. The backflow prevention gate 60 shown in FIG.
And a liquid level meter 32 for detecting the height of the water surface on the downstream side of the door body 61.
, A backflow detecting device 31 and a warning light 33, like the backflow prevention gate 10 shown in FIG. .

Further, in the backflow prevention gate 60,
As a door closing mechanism that operates in synchronization with the warning light 33 based on the danger signal from the comparison circuit 35 of the backflow detecting device 31, a weight 62 that pivotally supports the base end of the door 61 in a tiltable manner.
A wire 63 locked to the tip of the weight 62;
3 is provided.

Therefore, when a danger signal is issued from the comparison circuit 35 of the backflow detecting device 31, the alarm lamp 33 is turned on, and at the same time, the hoisting machine 64 is operated to wind up the wire 63, thereby raising the door body 61, and 11 is automatically closed.

As described above, the backflow prevention gate 60 has a mechanism for detecting the danger of backflow in advance and turning on the warning lamp 33, and at the same time, automatically closing the water channel 11 by the door 61. Therefore, quick response in an emergency is possible, and the backflow prevention function is high. In addition, since the door body 61 and the wire 63 are connected via the weight 62, in a situation where the door body 61 is tilting smoothly without operating the hoisting machine 64, the weight 62 moves downward. Tilt always wire 6
Since the tension is applied to the door 3, the wire 63 does not bend when the door 61 stands up, and the door 61 tilts smoothly. On the other hand, when the wire 63 a is directly connected to the door 61, the bent wire 63 a may swing in the water and hinder the tilting of the door 61.

[0057]

According to the present invention, the following effects can be obtained.

(1) In a backflow prevention gate having a levitation door, which is tiltably mounted in a flow path,
An alarm that includes a door body height detecting means and a surface height detecting means, compares the height of the overflow portion of the door body with the surface height of the downstream fluid, and issues an alarm when the difference becomes equal to or less than a set value. By providing the means, when the difference between the surface height of the downstream fluid and the height of the overflow part of the door body becomes equal to or less than the set value, an alarm is issued from the alarm means, and the occurrence of backflow is known in advance. Therefore, even when the door does not stand up due to a failure or the like, backflow can be prevented.

(2) As a door body height detecting means, a goniometer for detecting the inclination angle of the door body, and a door body height calculating device for calculating the height of the overflow portion of the door body based on the detection data of the goniometer. Is provided, the height of the overflow portion can be accurately detected even when the door body is at any inclination angle, so that the presence / absence of backflow can be accurately determined.

(3) Since the liquid level gauge is provided as the surface height detecting means, the surface height of the fluid can be accurately detected, and the fluid immediately responds to a change in the surface height. The presence or absence of occurrence can be quickly determined.

(4) By adopting at least one of a warning light that emits a warning light and a warning device that emits a warning sound as a warning means, a backflow can be generated even in a situation where the noise is large due to a typhoon or a heavy rainfall or at night. The danger can be notified.

(5) By providing a door closing mechanism for closing the flow path by raising the door by at least one of a manual force and an electric force, when the alarm means is activated, it is forcibly operated manually or by an electric force. Since the flow path can be closed before the backflow occurs by moving the door body, it is possible to reliably cope with the danger of the backflow.

(6) By providing an automatic door closing mechanism for raising the door by electric power and closing the flow path in synchronization with the alarm means, the flow path is automatically closed when the alarm means is activated. Therefore, a quick response in an emergency is possible, and the backflow prevention function is further improved.

[Brief description of the drawings]

FIG. 1 is a side view showing a backflow prevention gate according to a first embodiment.

FIG. 2 is an explanatory diagram showing an operation state of a backflow prevention gate of FIG. 1;

FIG. 3 is a block diagram showing a backflow detecting function of the backflow prevention gate of FIG. 1;

FIG. 4 is a side view showing a backflow prevention gate according to a second embodiment.

FIG. 5 is a side view showing a backflow prevention gate according to a third embodiment.

FIG. 6 is an explanatory diagram showing a backflow detection function of a conventional backflow prevention gate.

[Explanation of symbols]

 10, 50, 60 Backflow prevention gate 11 Waterway 12, 51, 61 Door body 12a Overflow portion 13, 53 Shaft support portion 14 Flexible sealing member 15 Side wall 17 Sealing member 18 Ceiling 19, 20 Door stop member 21, 24 Water 22 Upstream Water Surface 23 Downstream Water Surface 30 Angle Meter 31 Backflow Detector 32 Liquid Level Meter 33 Alarm Light 34 Door Height Calculation Circuit 35 Comparison Circuit 36 Alarm Generation Circuit 37 Door Closing Mechanism 38 Alarm 52 Hydraulic Cylinder 54 Tilt Arm 55 Rod 62 Weight 63, 63a Wire 64 Hoist H Height of overflow section of door body h Height of downstream water surface L Dimension of door body in height direction θ Angle of inclination of door body

Claims (6)

[Claims] A door that is pivotally supported in a flow path in which a fluid flows in a certain direction and that generates a levitation force in the fluid;
A backflow prevention gate for closing the flow path by raising the door body by an increase in fluid on the downstream side, a door body height detecting means for detecting a height of an overflow portion of the door body, and the door body Surface height detecting means for detecting the surface height of the fluid on the downstream side of the fluid, comparing the detection data of the door body height detecting means with the detection data of the surface height detecting means, and setting a difference therebetween. A backflow prevention gate, comprising an alarming means for issuing an alarm when the value becomes equal to or less than a value. 2. A goniometer for detecting an inclination angle of the door body as the door body height detecting means, and a door body height for calculating a height of an overflow portion of the door body based on detection data of the goniometer. The backflow prevention gate according to claim 1, further comprising a calculating device. 3. The backflow prevention gate according to claim 1, wherein said surface height detecting means is a liquid level gauge. 4. The backflow prevention gate according to claim 1, wherein said alarm means includes at least one of an alarm light emitting an alarm light and an alarm device emitting an alarm sound. 5. The backflow prevention gate according to claim 1, further comprising a door closing mechanism for closing the flow path by raising the door by at least one of a manual force and an electric force. 6. The backflow prevention gate according to claim 1, further comprising an automatic door closing mechanism for raising the door and closing the flow path in synchronization with the operation of the alarm means.