JP7425922B2 - Backflow prevention device - Google Patents

Description

The present invention relates to a backflow prevention device that is used by being attached to an attached part.

BACKGROUND ART Conventionally, a backflow prevention device (a backflow prevention valve for a septic tank) described in, for example, Patent Document 1 below is known.

This conventional backflow prevention device is attached to the inner circumferential side of piping connected to the outlet of a septic tank, and includes a device body that has an inclined valve seat, and a device that is rotatably provided on the device body and has an inclined valve seat. The valve body is provided with a valve body that moves toward and away from the valve seat portion of the valve body.

Registered utility model No. 3195528

However, in the above-mentioned conventional backflow prevention device, during normal use, the valve body contacts the valve seat due to its own weight, and there is no gap between the valve body and the valve seat, so It may interfere with the normal flow of gas.

The present invention has been made in view of the above points, and an object of the present invention is to provide a backflow prevention device that can prevent the normal flow of gas from being obstructed during normal use, and can appropriately prevent the backflow of fluid during backflow. shall be.

The backflow prevention device according to claim 1 is a backflow prevention device that is used by being attached to an attached part, and includes a device body that is attached to the attached part and has a valve seat portion, and a device body that is rotatable to the device body. and a valve body that moves toward and away from the valve seat, the valve body having an elastic member, and in normal use, when the elastic member comes into contact with the valve seat, the valve body moves toward and away from the valve seat. A gap exists between the body and the valve seat, and the gap disappears when backflow occurs.

The backflow prevention device according to claim 2 is a backflow prevention device that is used by being attached to an attached part, and includes a device body that is attached to the attached part and has a valve seat portion, and a device body that is rotatable to the device body. a valve body that is movable toward and away from the valve seat portion; the valve body includes a valve member rotatably provided on the device body; and an elastic member attached to the valve member. The elastic member has an annular contact portion that moves toward and away from the valve seat portion, and an annular attachment portion provided downstream of the contact portion and attached to the valve member. However, during normal use, a portion of the contact portion of the elastic member comes into contact with the valve seat, so that a gap exists between the valve body and the valve seat, and this gap disappears during backflow. be.

In the backflow prevention device according to claim 3, in the backflow prevention device according to claim 2, the contact portion of the elastic member becomes gradually thinner toward the outside in the radial direction, and the contact portion between the contact portion and the mounting portion is There is a space between them that allows elastic deformation of the contact portion.

The backflow prevention device according to claim 4 is the backflow prevention device according to any one of claims 1 to 3, in which the size of the gap during normal use is adjustable.

The backflow prevention device according to claim 5 is the backflow prevention device according to any one of claims 1 to 4, in which the gap during normal use allows ventilation without interfering with the flow of gas from the upstream side. .

The backflow prevention device according to claim 6 is the backflow prevention device according to any one of claims 1 to 5, and includes an annular elastic body for attaching the device main body to the inner circumferential surface of the attached portion.

According to the present invention, the normal flow of gas can be prevented from being obstructed during normal use, and the backflow of fluid can be appropriately prevented during backflow.

FIG. 1 is a perspective view of a backflow prevention device according to an embodiment of the present invention. It is a perspective view of the backflow prevention device same as the above (the maximum lifting state of a valve body). It is a side view of the backflow prevention device same as the above. It is a side view of the backflow prevention device same as the above (the maximum lifting state of a valve body). It is a sectional view of the backflow prevention device same as the above. It is a sectional view of the backflow prevention device same as the above (at the time of maximum lifting of the valve body). It is a top view of the backflow prevention device same as the above in an attached state (during normal use). It is a sectional view of the backflow prevention device same as the above in an attached state (during normal use). It is a sectional view of the backflow prevention device same as the above in an attached state (at the time of forward flow). It is a sectional view of the backflow prevention device same as the above in an attached state (at the time of backflow). It is a sectional view of the backflow prevention device concerning other embodiments of the present invention. It is a sectional view of the backflow prevention device same as the above in an attached state (during normal use). It is a sectional view of the backflow prevention device same as the above in an attached state (at the time of backflow). It is a sectional view of another installation state of the backflow prevention device same as the above.

An embodiment of the present invention will be described with reference to FIGS. 1 to 10.

In FIGS. 7 to 10, reference numeral 1 denotes a public basin which is a drainage basin, and this public basin 1 is made of, for example, synthetic resin, and has a cylindrical inlet part (inflow pipe connection part) 2 and a cylindrical inlet part (inflow pipe connection part) 2. An outflow port (outflow pipe connection port) 3, an invert part 4 located between the inflow port 2 and the outflow port 3, and a cylindrical cleaning port (cleaning pipe) located above the invert part 4. (connection port) 5.

A downstream end of an inflow pipe 7, which is a drain pipe on the inflow side, is connected to the inflow port 2. The upstream end of the inflow pipe 7 is connected to a septic tank 8 that purifies wastewater from drainage equipment (toilet, bath, kitchen, etc.) in the building. The septic tank 8 has an air supply means (aeration means) 9 that supplies air into the waste water, and air, which is a gas generated in the septic tank 8, flows into the inflow pipe 7 (see FIG. 8).

An upstream end of an outflow pipe 11, which is a drain pipe on the outflow side, is connected to the outflow port 3. The downstream end side of the outflow pipe 11 is connected to a sewer main pipe (not shown). A lower end portion of a cleaning pipe 12, which is a riser pipe, is connected to the cleaning port portion 5. Although not shown, a lid receiving frame is attached to the upper end of the cleaning tube 12, and a lid is detachably attached to this lid receiving frame.

In addition, in the public basin 1, there is a backflow prevention device 15 for the public basin that prevents the backflow of fluid (drainage and air pumped by drainage) from the downstream sewer main pipe during heavy rains such as typhoons. It is located. In other words, the backflow prevention device 15 that prevents backflow of fluid from the downstream side is disposed in the middle of the drainage channel through which the wastewater flows.

Specifically, the backflow prevention device 15 is removably attached to an inflow pipe (attached part) 7, which is a drainage basin connection member connected to the inlet portion 2 of the public basin 1, by retrofitting, for example. It is located within 1. The inflow pipe 7, which is a cylindrical attachment part, is slightly inclined at a predetermined inclination angle θ (for example, 1.5°) with respect to the horizontal direction so that the downstream side is lower.

For this reason, the attached backflow prevention device 15 attached to the inflow pipe 7 is also in a slightly inclined position, being inclined by a predetermined angle of inclination θ. Note that when the inflow pipe 7 is not inclined, the backflow prevention device 15 is attached to the horizontal inflow pipe 7 in a horizontal position.

Here, the configuration of the backflow prevention device (retrofitted backflow prevention valve) 15 will be described with reference to FIGS. 1 to 6. Note that the configuration will be described with the directions of the arrows shown in FIG. 1 as the front-rear direction and the left-right direction, and with the horizontal orientation as a reference.

The backflow prevention device 15 is removably attached afterward to the inner circumferential surface of the downstream end of the inflow pipe 7, which is the attached portion, and has a cylindrical device main body (short cylindrical main body member) having a valve seat portion 20. 21, a plate-shaped valve body 22 which is rotatably provided in the device body 21 in the front and back direction and moves toward and away from the valve seat 20, and a plate-shaped valve body 22 that is provided on the inner circumferential surface of the downstream end of the inflow pipe 7. 21, and an annular elastic body (first packing) 23 that is elastically deformable.

The device main body 21 is formed into a relatively short cylindrical shape (including a substantially cylindrical shape) having a front opening (end opening on the downstream side) 26 and a rear opening (end opening on the upstream side) 27. Then, the front opening (portion to be opened and closed) 26 of the device main body 21 is opened and closed by the valve body 22.

The device main body 21 has an annular and planar valve seat portion 20 on the front surface (downstream end surface). The valve seat portion (valve seat surface) 20 is located around the front opening 26 so as to surround the front opening 26, and is located on the same plane as the front opening 26.

As shown in FIG. 5, the valve seat portion (valve seat portion 20 and front opening 26 located on the same plane) 20 is arranged such that the lower end thereof is located on the rear side (upstream side) in side view. It is inclined at a predetermined angle of inclination α with respect to the vertical direction.

In other words, the inclined valve seat portion 20 is inclined at a predetermined angle with respect to the direction perpendicular to the horizontal central axis It is inclined at an angle α. Note that the predetermined inclination angle α is, for example, 1° to 5°, preferably 3°.

The valve seat portion 20 has a pair of left and right linear surface portions 28 that are vertically longitudinal, and a pair of upper and lower curved surface portions 29 that are arcuate. A protruding surface portion 30 that protrudes forward (horizontally or diagonally forward) is connected to the center portion of the upper curved surface portion 29 in the left-right direction.

Further, the device main body 21 has an annular groove 31 on the outer peripheral surface. Fitted into the concave groove 31 is an attachment elastic body 23 that is elastically deformed and comes into close contact (pressure contact) with the inner circumferential surface of the downstream end of the inflow pipe 7 . The device main body 21 is fixedly attached to the inner circumferential surface of the downstream end of the inflow pipe 7 via the elastic body 23 so as to be positioned and fixed at a desired position.

Further, when the apparatus main body 21 is attached to the inner peripheral surface of the downstream end of the inflow pipe 7 via the elastic body 23, the apparatus main body 21 maintains a posture that maintains the attitude of the apparatus main body 21 in this attached state. It has a protrusion (rib) 33 on the outer peripheral surface.

The posture maintaining convex portion 33 is formed at least on the upper and lower sides of the outer peripheral surface of the device main body 21. That is, for example, a longitudinal posture maintaining convex portion 33 (33a) is formed on the upper side of the outer peripheral surface of the device main body 21, and a longitudinal posture maintaining convex portion 33 (33a) is formed on the lower side of the outer peripheral surface of the device main body 21. A maintenance protrusion 33 (33b) is formed.

The lower posture maintaining convex portion 33 (33b) is located forward of the upper posture maintaining convex portion 33 (33a), and the front end surface of the lower posture maintaining convex portion 33 (33b) constitutes a part of the valve seat portion 20. When the device main body 21 is attached to the inner circumferential side of the inflow pipe 7 by the elastic body 23 as shown in FIG. By contacting them, the posture of the device main body 21 is maintained in the desired mounting posture.

Further, the device main body 21 has vertical gripping flat portions 35 formed on both left and right sides of the outer peripheral surface of the device main body 21. The gripping flat portion 35 is formed on the outer circumferential surface of the device main body 21 at a position in front of the elastic body 23. The gripping flat portion 35 is formed in a shape whose vertical dimension increases from the rear end side to the front end side.

When the device main body 21 is attached to the inner circumferential surface of the downstream end of the inflow pipe 7 via the elastic body 23, the gripping flat portions 35 on both left and right sides and the opposing surface portion 36 on the inner surface of the public basin 1 are connected to each other. In between, there is a space 37 into which the operator's (installer's) finger can enter (see FIG. 7).

Further, the device main body 21 has an upwardly projecting protrusion 41 on the upper side of the front end, and this protrusion 41 has a left-right shaft portion 42 that is a rotation fulcrum that rotatably supports the valve body 22. are integrated. Note that the lower surface of the protruding portion 41 constitutes the protruding surface portion 30 having a horizontal surface shape. Furthermore, at least a portion of this shaft portion 42 is located rearward of the upper end of the valve seat portion 20 in side view.

The valve body 22 includes a plate-shaped valve member 51 provided on the shaft portion 42 of the device main body 21 so as to be rotatable (swiveable) in the front and rear directions about the shaft portion 42, and an outer circumferential end of the valve member 51. It has an annular elastic member (second packing) 52 that is attached to the valve seat section and can be elastically deformed toward and away from the valve seat section 20 of the device main body 21.

The valve member 51 includes a plate-shaped main body 53 having a shape corresponding to the front opening 26 of the device main body 21 and capable of covering the front opening 26, and a mounting portion 54 integrally provided on the main body 53. The mounting portion 54 is rotatably attached to the shaft portion 42 of the device main body 21. In this way, the valve member 51 is suspended from the shaft portion 42 of the device main body 21.

The main body portion 53 has a gripping recess 55 that opens toward the front side (downstream side, which is the side opposite to the device main body 21 side). The gripping recess 55 has a flat portion 56 on which the operator (installer) hangs his or her fingers, and this flat portion 56 is located on the upper surface of the space 57 into which the finger is inserted. Further, the gripping recess 55 has a protruding shape toward the device main body 21 so as to be located inside the device main body 21, and the lower part of the portion located inside the device main body 21 is formed into a curved surface shape. ing. Note that the main body portion 53 has an annular protrusion 59 on the outer peripheral side.

The elastic member 52 includes an annular contact portion 61 having an L-shaped cross section that approaches and separates from the valve seat portion 20, and an annular mounting portion 62 having a U-shaped cross section connected to the front side of the contact portion 61. have. The attachment portion 62 of the elastic member 52 is removably fitted into the annular protrusion 59 of the main body portion 53 of the valve member 51.

Further, the contact portion (elastic contact portion) 61 of the elastic member 52 gradually becomes thinner toward the outside in the radial direction. This contact portion 61 has an annular contact surface 63 on the rear surface that comes into close contact with the valve seat portion 20 during backflow. There is a space 64 between the contact portion 61 and the attachment portion 62 that allows the contact portion 61 to be elastically deformed.

As is clear from FIG. 5, the contact surface 63 of the contact portion 61 of the elastic member 52 of the valve body 22 is located along the vertical plane based on the weight of the valve body 22, so the valve seat of the device body 21 is It is far from the 20th division. As a result, a relatively small gap 70 exists between these contact surfaces 63 and the valve seat portion (valve seat surface) 20.

In other words, in the horizontal position shown in FIG. 5, a gap 70 exists over the entire circumference of the valve seat 20 between the contact surface 63 of the elastic member 52 of the valve body 22 and the valve seat 20 of the device main body 21. ing. Similarly, the same (including substantially the same) gap 70 exists even during normal use in the slightly inclined position shown in FIG. However, when the flow is reversed as shown in FIG. 10, the gap 70 disappears.

The gap 70 is a small gap of about several mm (for example, 10 mm or less) through which air, which is gas from the upstream septic tank 8, can flow, and gradually increases from the upper end to the lower end. Note that the shaft portion 42 of the device main body 21 is located above the gap 70 in a side view.

Further, the dimension (maximum dimension) L of the gap 70 at the lower end position of the contact surface 63 of the valve body 22 is, for example, 2 mm to 10 mm, preferably 6 mm (see FIG. 5). Since the backflow prevention device 15 is in a slightly inclined position during normal use as shown in FIG. 8, the dimension L of this gap 70 increases slightly by the amount of the inclination. Note that the dimension L of the gap 70 is smaller than, for example, the axial dimension of the annular elastic member 52.

In the example shown in FIG. 5, an annular gap 70 exists around the entire circumference of the valve seat 20 because the valve body 22 is separated from the entire (entire surface) of the valve seat 20. Only the upper end of the contact portion 61 of the elastic member 52 may contact the valve seat portion 20.

Further, as described above, the backflow prevention device 15 is composed of four members: the device main body (main body member) 21, the elastic body (mounting elastic member) 23, the valve member 51, and the elastic member 52. ing. The device main body 21 and the valve member 51 are made of synthetic resin such as PVC, and the elastic body 23 and the elastic member 52 are made of an elastic material such as synthetic rubber, natural rubber, or elastomer.

Next, the operation of the above-mentioned backflow prevention device 15 will be explained.

As shown in FIG. 8, during normal use, a gap 70 exists between the contact surface 63 of the elastic member 52 of the valve body 22 and the valve seat 20 of the device main body 21, and a gap 70 exists between the front opening of the device main body 21 (downstream The side end face opening) 26 is open.

Therefore, air, which is a gas generated in the upstream septic tank 8 and flowing through the inflow pipe 7, flows into the public basin 1 through the front opening 26 and the gap 70. In this way, a normal flow of air (forward-flowing fluid) from the upstream side is ensured, problems such as double traps do not occur, and air generated in the septic tank 8 does not flow back to the drainage equipment in the building.

In addition, as shown in FIG. 9, during forward flow (drainage outflow), the valve body 22 is pushed by the drainage from the upstream side and rotates forward, so the gap 70 expands and the front surface of the device body 21 The front part of the opening 26 is largely opened to ensure a normal flow of drainage (liquid) from the upstream side.

On the other hand, as shown in Figure 10, in the event of backflow, such as when a large amount of rainwater flows into a sewer main pipe due to a typhoon or torrential rain, and exceeds the drainage capacity of the sewer main pipe, the downstream main sewer pipe The fluid (drainage water and air) flowing backward through the outflow pipe 11 pushes the valve body 22 from the front side, so the valve body 22 receives the fluid pressure and rotates slightly backward against its own weight. The elastic member 52 is elastically deformed, and the contact surface 63 of the contact portion 61 comes into close contact with the valve seat portion 20 of the device main body 21.

As a result, the small gap 70 between the valve body 22 and the valve seat portion 20 disappears instantly, and the front opening 26 of the device body 21 is immediately closed by the valve body 22. Therefore, fluid from the downstream side (fluid flowing backward) does not flow into the device main body 21, and fluid from the sewer main pipe side does not flow back toward the drainage equipment in the building.

When the backflow of fluid from the downstream side is stopped, the valve body 22 slightly rotates forward under its own weight, and a gap 70 is formed between the valve body 22 and the valve seat 20, as shown in FIG. It returns to the state of normal use.

According to such a backflow prevention device 15, during normal use, it is possible to prevent the normal flow of gaseous air from the upstream side, and at the time of backflow, it is possible to appropriately prevent the backflow of fluid from the downstream side. be able to.

In particular, the gap 70 that exists between the valve body 22 and the valve seat 20 during normal use is a small gap through which air from the septic tank 8 on the upstream side can flow. In addition, in the event of backflow, the front opening 26 of the device body 21 can be immediately closed with only a slight rotation (slight movement) of the valve body 22, preventing backflow of fluid from the downstream side. Can be prevented quickly and appropriately. Furthermore, when the gap 70 exists over the entire circumference of the valve seat portion 20, air from the septic tank 8 can escape more efficiently than when the gap 70 exists partially.

Furthermore, since the device main body 21 has an attitude maintaining convex portion 33 that maintains the attitude of the device main body 21 when it is attached to the inflow pipe 7 via the elastic body 23, the attitude of the device main body 21 in the attached state is maintained. The desired mounting posture can be stably maintained.

Furthermore, since the device main body 21 has gripping flat parts 35 on both left and right sides, and the valve body 22 has gripping recesses 55, an operator can easily hold the backflow prevention device 15 even if it is installed at a difficult-to-see location. Installation work (installation work) can be easily and appropriately performed.

Specifically, the worker first grips the backflow prevention device 15 by hooking his fingers on the flat portion 56 of the gripping recess 55, and then moves the backflow prevention device 15 from the cleaning opening 5 into the public basin 1. Move it downward and insert it. Next, the operator horizontally moves the main body 21 of the backflow prevention device 15 into the inflow pipe 7 while holding the backflow prevention device 15 by placing fingers on the gripping flat parts 35 on both sides. and push it in. At this time, since the space 37 exists, the device main body 21 can be pushed into the inflow pipe 7 while being held between the fingers of the hand without the device main body 21 interfering with the inner surface of the public basin 1. In this manner, the operator can easily and appropriately attach the backflow prevention device 15 to the inflow pipe 7.

In the above-mentioned embodiment, the valve seat portion 20 is inclined at a predetermined inclination angle α with respect to the vertical direction so that the lower end thereof is located on the rear side (upstream side) in side view (in other words, the valve seat portion 20 is inclined at a predetermined inclination angle α with respect to the vertical direction). Although we have described a configuration in which the gap 70 is formed by swinging the valve seat 20 to a negative angle, for example, as shown in FIG. It may also be a configuration in which

That is, the valve seat portion 20 of the device main body 21 shown in FIG. 11 is inclined at a predetermined inclination angle α with respect to the vertical direction so that the lower end is located on the front side (downstream side) when viewed from the side. .

In this configuration, the slight gap 70 that exists between the valve body 22 and the valve seat part 20 during normal use is such that a part (upper end part) of the contact surface 63 of the contact part 61 of the elastic member 52 is connected to the valve seat part. It is formed by abutting (engaging) with a part of 20. In other words, the gap 70 is formed by the engagement of the elastic member 52, which is the gap forming means.

That is, the elastic member 52 of the valve body 22 shown in FIG. The upper end portion of the contact portion 61 has an elastically deformable gap forming portion 71 that forms a gap 70 by restricting rearward rotation of the valve body 22 by contacting the contact portion 61 . Therefore, it is also possible to adjust the dimension L of the gap 70, for example, by changing the amount of engagement of the elastic member 52.

Similarly, the same (including substantially the same) gap 70 exists during normal use in the slightly inclined position shown in FIG. 12, but when the flow is reversed as shown in FIG. 13, the gap 70 disappears.

Furthermore, as is clear from these FIGS. 12 and 13, even when the backflow prevention device 15 is attached to the inclined inflow pipe 7 and is in a slightly inclined position, the valve seat portion 20 of the device main body 21 is located at the lower end. It is inclined with respect to the vertical direction so that it is located on the front side (downstream side). Therefore, during backflow, the valve body 22 slightly rotates rearward due to its own weight and the fluid pressure received from the fluid flowing back from the downstream side, and the contact portion 61 of the elastic member 52 is elastically deformed and the valve seat Closely adheres to the entire circumference of part 20.

As shown in FIG. 14, the same applies even when the backflow prevention device 15 is attached to the horizontal inflow pipe 7 and is in a horizontal position, and when the backflow occurs, the valve body 22 rotates due to its own weight and fluid pressure. Then, it comes into close contact with the valve seat part 20.

The inflow pipe 7 shown in FIG. 14 is fixed horizontally to the side wall 1a of the public basin 1 made of concrete, for example. The apparatus main body 21 attached to the inflow pipe 7 is stably maintained in its posture by the upper and lower posture maintaining convex portions 33. Although not shown, the same applies when the backflow prevention device 15 shown in FIG. 5 is attached to the horizontal inflow pipe 7.

In the example shown in FIG. 11, the valve seat portion 20 is inclined so that the lower end is located toward the front side (downstream side) when viewed from the side, but the configuration is not limited to this, and for example, the valve seat portion A structure in which the valve seat portion 20 is formed in a reversely inclined shape, a structure in which the valve seat portion 20 is formed in a vertical shape, etc. may also be used.

Furthermore, in any of the above embodiments, the part to which the backflow prevention device is attached is not limited to an inflow pipe connected to a drainage basin such as a public basin; for example, an outflow pipe (piping) connected to a septic tank. ), or a backflow prevention device may be attached to the inner surface of the drainage basin or the inner surface of the septic tank.

Furthermore, for example, the device main body may be fitted and connected to the inner peripheral side of the cylindrical attachment portion without using an elastic body.

Further, the number of posture maintaining protrusions (ribs) on the main body of the apparatus is arbitrary, and may be one or three or more.

Further, the valve body is not limited to a configuration in which an annular elastic member is adhesively fixed to the outer circumferential side of the valve member, but may be, for example, a configuration in which the annular elastic member is detachably attached to the outer circumferential side of the valve member. In the case of this configuration, for example, multiple types of elastic members with different thicknesses, shapes, etc. of the contact parts that come into contact with and separate from the valve seat are prepared in advance, and the desired elastic member is selected according to the site etc. By (exchanging), the dimension L of the gap can be adjusted.

Although several embodiments of the present invention and their modifications have been described, it is also possible to combine the embodiments and modifications as appropriate without departing from the gist of the present invention.

7 Inflow pipe which is the attached part
15 Backflow prevention device
20 Valve seat
21 Device body
22 Valve body
23 Elastic body
33 Convex part for maintaining posture
35 Gripping flat part
42 Shaft that is the pivot point
51 Valve member
52 Elastic member as gap forming means
55 Gripping recess
70 Gap
71 Gap forming part

Claims (6)

A backflow prevention device used by being attached to an attached part,
a device main body that is attached to the attached part and has a valve seat part;
a valve body rotatably provided on the device main body and moving toward and away from the valve seat portion;
The valve body has an elastic member,
A backflow prevention device characterized in that during normal use, the elastic member comes into contact with the valve seat, so that a gap exists between the valve body and the valve seat, and when backflow occurs, the gap disappears. A backflow prevention device used by being attached to an attached part,
a device main body that is attached to the attached part and has a valve seat part;
a valve body rotatably provided on the device main body and moving toward and away from the valve seat portion;
The valve body is
a valve member rotatably provided on the device main body;
an elastic member attached to the valve member;
The elastic member is
an annular contact portion that moves toward and away from the valve seat portion;
an annular attachment portion provided downstream of the contact portion and attached to the valve member;
During normal use, a part of the contact portion of the elastic member comes into contact with the valve seat, so that a gap exists between the valve body and the valve seat, and when reverse flow occurs, the gap disappears. backflow prevention device. The contact portion of the elastic member gradually becomes thinner toward the outside in the radial direction.
The backflow prevention device according to claim 2, wherein a space exists between the contact portion and the mounting portion to allow elastic deformation of the contact portion. The backflow prevention device according to any one of claims 1 to 3, wherein the size of the gap during normal use is adjustable. The backflow prevention device according to any one of claims 1 to 4, wherein the gap during normal use allows ventilation without interfering with the flow of gas from the upstream side. The backflow prevention device according to any one of claims 1 to 5, further comprising an annular elastic body for attaching the device main body to the inner peripheral surface of the attached portion.

Images