Backflow suppressing coupling

Abstract

To provide a backflow suppressing coupling that can be retrofitted to an existing inflow port and others (a connected port) of a drainage basin and prevents a gap from occurring between an outer periphery of an insertion port and an inner peripheral surface of the inflow port and others even if the insertion port is inserted and fixed in the inflow port and others.MEANS FOR SOLVING THE PROBLEM: A backflow suppressing coupling comprises: a valve tube having an insertion port to be inserted and connected to a connected port and an outflow port communicated with the insertion port; and a valve body that is rotatably supported by the valve tube to open and close the outflow port. The valve tube comprises: an annular elastic body disposed so as to protrude outward more than the surface of an outer periphery at the outer periphery of the valve tube; and a protrusion that is provided at an upper part of the outer periphery on the upstream side of the elastic body and can be elastically displaced in a radial direction of the valve tube. When the valve tube is inserted in the connected port, the valve tube is disposed so that the protrusion presses the inner peripheral surface of the connected port, causing a tip of the insertion port to abut against a bottom of the connected port using the elastic body as a fulcrum.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a backflow prevention fitting, and in particular to a backflow prevention fitting having an elastic body attached to the outer periphery of the fitting body and a protrusion attached upstream of the elastic body that can be elastically displaced in the radial direction, and in which, when the fitting body is inserted into the connecting port, the elastic body and the protrusion position the insertion port of the fitting body so that it abuts against the inner periphery of the connecting port. [Background technology]

[0002] Generally, wastewater discharged from drainage facilities such as toilets in homes is collected in drainage manholes installed within residential areas via drainage pipes connected to each drainage facility in order to mitigate sudden changes in the amount of wastewater or to allow for the removal and inspection of foreign objects such as garbage.The wastewater collected in the drainage manholes then flows out into the main sewer pipe via public manholes or manholes.

[0003] However, when a large amount of rainwater flows into the main sewer pipe in a short period of time, the drainage capacity of the main sewer pipe is exceeded and the overflowing wastewater flows back through catch basins, etc., causing the problem of backflowing wastewater spouting out of indoor drainage equipment connected to the drain pipe.

[0004] Therefore, in order to prevent wastewater that has backflowed from the sewer main pipe from passing through a drainage inlet or the like and overflowing from indoor drainage equipment, a backflow prevention device has been developed that can be retrofitted by inserting and connecting it to an inlet pipe having an inlet such as a drainage inlet (hereinafter, these will be collectively referred to as "connected port"), as described in, for example, JP 2020-153508 A (Patent Document 1). In particular, the backflow prevention device described in Patent Document 1 can be retrofitted by pressing the inner circumferential surface of the connected port with a packing and a protrusion provided on the outer periphery of the device body, thereby positioning and fixing the device body at a desired position of the connected port. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-153508 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as described in Patent Document 1, in the case of a backflow prevention device that can be retrofitted to an inlet such as a drainage manhole, the outer diameter of the insertion port of the device body must be smaller than the inner diameter of the connected port.As a result, when the insertion port is inserted into the connected port and fixed, a gap is created between the outer circumference of the insertion port and the inner surface of the connected port.Furthermore, since the insertion port also has a certain thickness, a large step is created between the tip of the insertion port and the inner surface (bottom) of the connected port, which can cause clogging with dirt and other substances in the drain.

[0007] Therefore, the present invention aims to provide a backflow prevention fitting that can be retrofitted to an inlet (connected port) of a drainage manhole or the like, which prevents a gap from occurring between the outer periphery of the insertion port and the inner surface of the connected port even when the insertion port of the backflow prevention fitting is inserted into the connected port and fixed. [Means for solving the problem]

[0008] After extensive research into the structure of backflow prevention fittings and the manner in which the backflow prevention fittings are attached to inlets such as drainage manholes, the inventors discovered that providing an elastic body such as a gasket on the outer periphery of the fitting body and a protrusion that can be elastically displaced radially above the elastic body, upstream of the elastic body, is extremely effective in solving the above-mentioned problems, and have thus completed the present invention.

[0009] That is, according to the present invention, a backflow prevention joint is provided which comprises a cylindrical valve pipe having an insertion port for insertion and connection to a connected port and an outlet port communicating with the insertion port, and a valve body rotatably supported on the valve pipe for opening and closing the outlet port, wherein the valve pipe has an annular elastic body arranged so as to protrude outward from the surface of the outer periphery on the outer periphery of the valve pipe, and a protrusion provided on the upper part of the outer periphery upstream of the elastic body, protruding outward from the surface of the outer periphery and elastically displaceable in the radial direction of the valve pipe, and when the valve pipe is inserted into the connected port, the protrusion presses against the inner periphery of the connected port, and the valve pipe is arranged so that the tip of the insertion port abuts against the bottom surface of the connected port with the elastic body as a fulcrum.

[0010] In the present invention, it is preferable that the protrusion be configured so as to be cantilevered in the axial direction of the valve pipe, thereby allowing elastic displacement in the radial direction of the valve pipe.

[0011] In addition, in the present invention, in order to minimize the step between the inner surface (bottom surface) of the connected port caused by the thickness of the tip of the insertion port, it is preferable that a tapered portion be provided on the inner surface of the insertion port side of the valve pipe so that the thickness of the valve pipe becomes thinner from the outlet toward the insertion port.

[0012] Thus, according to the backflow prevention coupling of the present invention, an annular elastic body is provided on the outer periphery of the valve pipe of the coupling body, and a radially elastically deformable protrusion is provided above the elastic body, upstream of the elastic body. When the insertion opening of the coupling body is inserted into the connection port, the elastically deformable protrusion presses against the upper part of the inner periphery of the connection port, and the coupling body, receiving the reaction force, is tilted so that the lower part of the tip of the insertion opening is pressed against the inner periphery (bottom) of the connection port, with the lower part of the elastic body as a fulcrum. This prevents a gap from forming between the lower part of the tip of the insertion opening and the inner periphery (bottom) of the connection port. Therefore, only a small step equal to the thickness of the insertion opening is formed between the tip of the insertion opening and the inner periphery (bottom) of the connection port, promoting smooth drainage and preventing clogging with filth, etc.

[0013] Furthermore, according to the backflow prevention fitting of the present invention, the protrusion portion presses strongly against the inner surface of the connection port, so that when the fitting body is inserted into the connection port, the fitting body is securely fixed inside the connection port, preventing it from accidentally falling out of the connection port.

[0014] In the present invention, when the amount of displacement of the protrusion and the amount of displacement of the elastic body are the same, it is preferable that the pressing force of the protrusion be greater than the pressing force of the elastic body.

[0015] If the pressing force of the protrusion is made greater than the pressing force of the elastic body as described above, when the valve tube is inserted into the connection port, the amount of displacement of the protrusion is less than the amount of deformation of the elastic body because the pressing force of the protrusion and the pressing force of the elastic body are balanced, making it difficult for the protrusion to displace. As a result, the tip of the insertion port of the valve tube is reliably pressed downward by approximately the protrusion height of the protrusion that protrudes outward from the outer periphery of the valve tube, so that the lower outer periphery of the valve tube is arranged at an angle so that it approaches the inner periphery (bottom) of the connection port as it moves from the downstream side to the upstream side, and it is possible to reliably eliminate any gap that occurs between the lower part of the tip of the insertion port and the inner periphery (bottom) of the connection port.

[0016] In this specification, "amount of displacement of a protrusion" refers to the amount of deflection of the portion of the valve pipe where the protrusion is provided relative to the outer peripheral surface of the valve pipe before deformation when an external force that pushes the protrusion is applied to the protrusion, i.e., the amount of deflection of the portion of the valve pipe where the protrusion is provided relative to the outer peripheral surface of the valve pipe before deformation in the elastically deformable area where the protrusion is provided on the outer peripheral surface of the valve pipe. Also, "amount of deformation of an elastic body" refers to the amount of deformation of an elastic body (e.g., the amount of deformation in the height of the elastic body) before deformation when an external force that deforms an elastic body made of a packing or the like is applied.

[0017] In the present invention, in order to improve the ease of maintenance, it is preferable that a groove be provided on the outer periphery of the valve pipe for the elastic body such as the packing, and that the elastic body be detachably attached to the valve pipe by fitting into the groove.

[0018] The elastic body may also be arranged so that it slopes downward from the insertion port side to the outlet side on the outer periphery of the valve tube. By arranging the elastic body at an angle on the outer periphery of the valve tube in this way, when the valve tube is inserted into the connecting port, the elastic body is also arranged at an angle with respect to the insertion direction of the valve tube, which reduces the insertion resistance (friction resistance) caused by the elastic body against the inner periphery (bottom surface) of the connecting port, allowing the valve tube to be smoothly attached to the connecting port. [Effects of the Invention]

[0019] According to the backflow prevention coupling of the present invention, an annular elastic body is provided on the outer periphery of the valve pipe of the coupling body, and a radially elastically deformable protrusion is provided above the elastic body upstream. When the insertion opening of the coupling body is inserted into the connection port, the elastically deformable protrusion presses against the upper part of the inner periphery of the connection port, and the coupling body, receiving the reaction force, is tilted with the lower part of the elastic body as a fulcrum so that the lower part of the tip of the insertion opening abuts against the inner periphery (bottom) of the connection port. This prevents a gap from forming between the lower part of the tip of the insertion opening and the inner periphery (bottom) of the connection port. As a result, only a small step equal to the thickness of the insertion opening is formed between the tip of the insertion opening and the inner periphery (bottom) of the connection port, which promotes smooth drainage and prevents clogging with filth and the like.

[0020] Furthermore, according to the backflow prevention fitting of the present invention, the protrusion portion presses strongly against the inner surface of the connection port, so that when the fitting body is inserted into the connection port, the fitting body is securely fixed inside the connection port, preventing it from accidentally falling out of the connection port. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a perspective view showing an overall outline of a backflow prevention joint according to an embodiment of the present invention. [Figure 2] 2 is a plan view of the backflow prevention joint shown in FIG. 1 (however, the valve body and bearing portion are omitted). FIG. [Figure 3] FIG. 2 is a plan view showing the backflow prevention joint shown in FIG. 1 (however, the valve body and bearing portion are omitted) attached to the inlet of a catch basin. [Figure 4] 3 is a cross-sectional view of the backflow prevention joint shown in FIG. 2 taken along the line BB. [Figure 5] 4 is a cross-sectional view of the catch basin shown in FIG. 3 with the backflow prevention fitting attached, taken along line AA. DETAILED DESCRIPTION OF THE INVENTION

[0022] A backflow prevention joint according to one embodiment of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following examples, and various modifications are possible within the scope of the technical concept of the present invention. [Example]

[0023] <Backflow prevention joint> Fig. 1 shows a perspective view illustrating the overall outline of a backflow prevention joint 1 according to one embodiment of the present invention. Fig. 2 shows a plan view of the backflow prevention joint 1 shown in Fig. 1 (however, the valve body 6 and bearing portion 62 are omitted), and Fig. 4 shows a longitudinal cross-sectional view of the backflow prevention joint 1 shown in Fig. 2 taken along cross section BB.

[0024] 1, 2 and 4, the backflow prevention joint 1 of this embodiment comprises a cylindrical valve pipe 2 and a valve element 6 rotatably supported on the outlet 22 side of the valve pipe 2. An annular packing (elastic body) 5 is attached to the outer periphery 20 of the valve pipe 2 so as to protrude outward from the surface of the outer periphery 20, and an elastically deformable protrusion 3 protruding outward from the surface of the outer periphery 20 is provided upstream of the packing (elastic body) 5.

[0025] In this embodiment, the components of the backflow prevention joint 1, other than the packing (elastic body) 5 and the metal insertion pin, are basically made of polyvinyl chloride resin, but there are no particular limitations on the materials used, and known resin materials such as plastics can be used. Furthermore, rubber is typically used as the material for the elastic body. In this embodiment, synthetic rubber is preferably used, and SBR (styrene butadiene rubber), NBR (acrylonitrile butadiene rubber), or EPDM (ethylene propylene diene rubber) is more preferably used.

[0026] <Valve body> 1, in this embodiment, the valve element 6 has a disk-shaped valve body 60, and hinge arms 61 extending outward (radially) are formed on the upper peripheral edge of the valve body 60. The end of the hinge arm 61 opposite to the side to which the valve body 60 is connected is disposed between a pair of bearing towers 620 of a bearing unit 62, and the valve element 6 is rotatably attached to the bearing unit 62 by inserting a pin 63 between the hinge arm 61 and the pair of bearing towers 620.

[0027] In this embodiment, the bearing portion 62 of the valve body 6 is detachably attached to the upper part of the outlet 22 of the valve pipe 2, which will be described later. More specifically, a partition-like stopper 4 and a pair of ribs are formed on both ends of the upper outer periphery 20 of the valve pipe 2 near the outlet 22, and the bearing portion 62 of the valve body 6 is attached to the outer periphery 20 of the valve pipe 2 by being pushed from above toward the valve pipe 2 in an attachment position surrounded by the stopper 4 and the ribs in a U-shape in plan view.

[0028] In this embodiment, the partition-shaped stopper 4 is provided with an engagement hole, and the bearing portion 62 is provided with a claw portion that engages with the engagement hole, so that when the bearing portion 62 is pushed into the above-mentioned mounting position, the claw portion of the bearing portion 62 aligns and engages with the engagement hole of the stopper 4, thereby fixing the bearing portion 62 to the valve pipe 2. Also, in this embodiment, a fixing clamp 64 is attached that clamps the bearing portion 62 and the stopper 4 from the outside so as to tightly contact them, preventing the claw portion of the bearing portion 62 from unintentionally coming off the engagement hole of the stopper 4.

[0029] On the other hand, when removing the bearing portion 62 of the valve body 6 from the valve pipe 2, the fixing clamp 64 is removed from the bearing portion 62 and the stopper 4, and then the claw portion of the bearing portion 62 is pushed in and out from the back surface of the engagement hole to release the engagement between the claw portion and the engagement hole.

[0030] In this embodiment, the valve body 60 has a generally flat plate shape, but the valve body 60 may also have a shape that is concave from the downstream side to the upstream side so that when backflow water occurs, the valve body 6 that is hit by the backflow water receives as much force as possible in the closing direction. In addition, it is preferable to attach a seal ring 65 made of an elastic material such as rubber to the peripheral edge of the valve body 60 at a position where it abuts against the valve seat portion 23 of the valve pipe 2, thereby improving the sealing performance when the valve body 6 is closed.

[0031] <Valve pipe> In this embodiment, the valve pipe 2 has a cylindrical shape with an insertion opening 21 at one end for connection to a connected opening 70 such as a manhole inlet 70 of the catch basin 7 (see FIGS. 3 and 5) or a piping outlet (not shown), and an outlet 22 at the other end on the opposite side that is opened and closed by the valve element 6. Therefore, a valve seat 23 against which the valve element 6 abuts is formed at the open end of the outlet 22 of the valve pipe 2.

[0032] In this embodiment, the valve seat 23 of the outlet 22 is formed in a substantially vertical direction, but it may be formed so as to be inclined from the downstream side to the upstream side as it goes from top to bottom. In this case, the valve element 6, which is normally suspended by its own weight, opens the outlet 22 of the valve pipe 2 and can allow a small amount of forward flow wastewater to flow, thereby effectively preventing clogging due to foreign matter contained in the wastewater.

[0033] In this embodiment, as described above, the valve pipe 2 has an annular packing (elastic body) 5 arranged on its outer periphery 20 so as to protrude outward from the surface of the outer periphery 20. The valve pipe 2 also has a groove 25 on its outer periphery 20 that is recessed below the surface of the outer periphery 20, and the annular packing 5 is fitted into the groove 25 so as to be detachably attached to the valve pipe 2.

[0034] In this embodiment, although not shown, a groove is provided on the outer circumferential portion 20 of the valve pipe 2 so that it slopes from the insertion port 21 side toward the outlet port 22 side as it goes from top to bottom, or from the outlet port 22 side toward the insertion port 21 side as it goes from top to bottom, and by fitting a gasket into the groove, the gasket can also be arranged on the outer circumferential portion 20 of the valve pipe 2 so that it slopes from the insertion port 21 side toward the outlet port 22 side as it goes from top to bottom, or from the outlet port 22 side toward the insertion port 21 side as it goes from top to bottom.

[0035] If the packing 5 is arranged at an angle on the outer periphery 20 of the valve pipe 2 as described above, when the valve pipe 2 is inserted into the connecting port, the packing 5 is also arranged at an angle with respect to the insertion direction of the valve pipe 2, thereby reducing the insertion resistance (frictional resistance) of the packing 5 with the inner surface (bottom surface) of the connecting port, and enabling the valve pipe 2 to be smoothly attached to the connecting port.

[0036] Furthermore, the valve pipe 2 has a protrusion 3 located upstream of the annular gasket 5 and at the upper part of the outer circumferential portion 20, which protrudes outward from the surface of the outer circumferential portion 20 and is elastically displaceable in the radial direction of the valve pipe 2.

[0037] The shape of the protrusion 3 is not particularly limited as long as it protrudes outward from the surface of the outer circumferential part 20 of the valve pipe 2 and is capable of pressing against the inner circumferential surface of the connection port when the valve pipe 2 is inserted into the connection port. In this embodiment, the shape of the protrusion 3 is a mountain-like shape with a triangular cross section that forms an acutely pointed peak so that it can easily catch on the inner circumferential surface of the connection port and is less likely to slip.

[0038] Furthermore, there are no particular limitations on the configuration that allows the protrusion 3 to be elastically displaced in the radial direction of the valve pipe 2, and for example, the protrusion itself may be formed from an elastic material such as an elastomer. In this embodiment, since it is easy to manufacture the protrusion as a single unit, a slit 30 is provided in the outer periphery 20 of the valve pipe 2 so as to hollow out (partition) the periphery of the protrusion 3 in a U-shape, and the protrusion 3 is supported in a cantilever manner on the outer periphery 20 of the valve pipe 2, thereby allowing it to be elastically displaced in the radial direction of the valve pipe 2.

[0039] In addition, the direction in which the protrusion 3 is cantilevered on the valve pipe 2 is preferably such that two of the three slits 30 arranged in a U-shape that are arranged parallel to each other are parallel to the axis of the valve pipe 2, so that the movement (displacement) of the protrusion 3 does not interfere with the insertion of the valve pipe 2 into the connecting port, and the protrusion 3 is cantilevered in the axis direction of the valve pipe 2.

[0040] Figure 3 shows a plan view of the backflow prevention fitting 1 shown in Figure 1 (however, the valve body 6 and bearing portion 62 are omitted) attached to the manhole inlet 70 of the drainage manhole 7, and Figure 5 shows a longitudinal cross-sectional view of the drainage manhole 7 attached with the backflow prevention fitting 1 shown in Figure 3 taken along the AA section.

[0041] 3 and 5 includes a mass inlet 70, a mass outlet 71 that communicates with the mass inlet 70 via an invert, and an upper connection port 72 that opens upward between the mass inlet 70 and the mass outlet 71. The connection ports of the mass inlet 70 and mass outlet 71 that connect to external connection pipes 73 are receptacle-shaped, and the external connection pipe 73 is connected to the connection port of the mass inlet 70.

[0042] In this embodiment, as shown in Figures 3 and 5, the backflow prevention fitting 1 can be attached to the mass inlet (connected port) 70 of the drainage manhole 7 by inserting the insertion port 21 of the valve pipe 2 of the backflow prevention fitting 1 into the mass inlet (connected port) 70 of the drainage manhole 7 and pushing the valve pipe 2 into the mass inlet 70 until the stopper 4 of the valve pipe 2 abuts the inner wall surface of the drainage manhole 7 that defines the mass inlet 70.

[0043] As described above, the backflow prevention fitting 1 of this embodiment has an annular gasket 5 on the outer periphery 20 of the valve pipe 2 and a protrusion 3 that is elastically displaceable in the radial direction at the upper part upstream of the gasket 5.When the insertion port 21 of the valve pipe 2 is inserted into the mass inlet 70 of the drainage manhole 7, the elastically displaceable protrusion 3 presses against the upper part of the inner periphery of the mass inlet 70, and the valve pipe 2, receiving the reaction force, is positioned at an angle with the lower part of the gasket 5 as a fulcrum, so that the lower part of the tip of the insertion port 21 abuts against the inner periphery (bottom) of the mass inlet 70.

[0044] Therefore, the backflow prevention joint 1 of this embodiment can prevent a gap from occurring between the lower part of the tip of the insertion port 21 and the inner circumferential surface (bottom surface) of the mass inlet 70. Furthermore, with the backflow prevention joint 1 of this embodiment, only a small step equal to the thickness of the insertion port 21 occurs between the tip of the insertion port 21 and the inner circumferential surface (bottom surface) of the mass inlet 70, which promotes smooth flow during drainage and prevents clogging with filth and the like.

[0045] Furthermore, in this embodiment, in order to minimize the step between the inner surface (bottom surface) of the mass inlet 70 caused by the thickness of the tip of the insertion port 21, a tapered portion 24 is provided on the inner surface of the valve pipe 2 on the insertion port 21 side so as to reduce the thickness of the valve pipe 2 from the outlet 22 toward the insertion port 21.

[0046] In addition, in the backflow prevention fitting 1 of this embodiment, the protrusion 3 strongly presses against the inner surface of the mass inlet 70, so that when the valve pipe 2 is inserted into the mass inlet 70, the valve pipe 2 is securely fixed inside the mass inlet 70, effectively preventing it from accidentally falling off from the mass inlet 70.

[0047] In this embodiment, when the amount of displacement of the protrusion 3 and the amount of displacement of the packing 5 are the same, the pressing force of the protrusion 3 is set to be greater than the pressing force of the packing 5 .

[0048] If the pressing force of the protrusion 3 is made greater than the pressing force of the packing 5 in this way, when the valve pipe 2 is inserted into the mass inlet 70, the amount of displacement of the protrusion 3 is less than the amount of deformation of the packing 5 because the pressing forces of the protrusion 3 and the packing 5 are balanced, making it less likely to displace. Therefore, the tip of the insertion port 21 of the valve pipe 2 is reliably pressed downward by approximately the protrusion height of the protrusion 3 protruding outward from the surface of the outer circumferential part 20 of the valve pipe 2, so that the lower outer circumferential part 20 of the valve pipe 2 is arranged at an angle so as to approach the inner circumferential surface (bottom surface) of the mass inlet 70 as it moves from the downstream side to the upstream side, and it is possible to reliably eliminate any gap that occurs between the lower part of the tip of the insertion port 21 and the inner circumferential surface (bottom surface) of the mass inlet 70. [Explanation of symbols]

[0049] 1. Backflow prevention joint 2. Valve pipe 20....Outer periphery 21 Insertion port 22... Outlet 23 Valve seat 24 Tapered section 25 Groove 3...Protrusion 30...slit 4. Stopper 5. Packing (elastic body) 6. Valve body 60 Valve body 61 Hinge arm 62...Bearing section 620···Bearing Tower 63 pins 64····Fixed clamp 65····Seal ring 7. Drainage inlet 70····Mass inlet (connected port) 71. Mass outlet 72····Upper connection port 73 External connection pipe

Claims

1. A backflow prevention joint includes a cylindrical valve pipe having an insertion port for insertion connection to a connected port and an outlet port communicating with the insertion port, and a valve body rotatably supported on the valve pipe for opening and closing the outlet port, wherein the valve pipe is an annular elastic body disposed on the outer periphery of the valve pipe so as to protrude outward from the surface of the outer periphery; a protrusion provided on an upper portion of the outer circumferential portion upstream of the elastic body, protruding outward from the surface of the outer circumferential portion and elastically displaceable in the radial direction of the valve pipe; A backflow prevention fitting characterized in that, when the valve pipe is inserted into the connecting port, the protrusion presses against the inner surface of the connecting port, and the tip of the insertion port abuts against the bottom surface of the connecting port with the elastic body as a fulcrum.

2. A backflow prevention joint as described in claim 1, characterized in that the protrusion is supported cantilevered in the axial direction of the valve pipe by providing slits around the protrusion to define it.

3. 2. The backflow prevention joint according to claim 1, wherein when the displacement amount of the protrusion and the displacement amount of the elastic body are the same, the pressing force of the protrusion is greater than the pressing force of the elastic body.

4. A backflow prevention joint as described in any one of claims 1 to 3, characterized in that the elastic body is arranged so as to incline from the insertion port side to the outlet port side as it moves from top to bottom on the outer periphery of the valve pipe.

5. 4. The backflow prevention joint according to claim 1, wherein the elastic body is a packing.

6. A backflow prevention joint as described in claim 5, characterized in that a groove is provided on the outer periphery of the valve pipe, and the packing is detachably attached to the valve pipe by fitting it into the groove.

7. A backflow prevention joint as described in any one of claims 1 to 3, characterized in that a tapered portion is provided on the inner surface of the valve pipe on the insertion port side so that the thickness of the valve pipe becomes thinner from the outlet toward the insertion port.

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