JP2006342927A - Backflow preventing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back flow preventing device manufactured to be smaller and more inexpensive for preventing the leakage of tight air from a diaphragm. <P>SOLUTION: In the backflow preventing device, the diaphragm 18 and a piston 6 are integrally operated in close contact with no existence of other components such as a bolt and a nut or a retainer therebetween. Thus, the compact backflow preventing device has a less number of components and lower cost along with no existence of other components. No need exists for providing a fixing hole portion for the diaphragm 18, surely preventing the leakage of tight air. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backflow prevention device, and more particularly to backflow prevention that is arranged between a water supply source pipe and a water supply destination pipe and prevents backflow to the water supply source pipe by draining the backflow water flowing through the water supply destination pipe to the outside. Relates to the device.

  Conventionally, in a hot water supply system, a hot water pipe connected to a hot water supply faucet is branched from a hot water supply apparatus so that hot water is supplied to a bathtub. In the middle of the piping, in general, a flow sensor that detects the amount of hot water to the bathtub, a solenoid valve that controls the supply of hot water to the bathtub, a backflow prevention device that discharges sewage flowing back from the bathtub to the atmosphere, and a bathtub And a check valve for preventing the backflow of sewage.

  By the way, not only a high-rise apartment house but also a detached house, the bathtub is often installed at a position higher than the hot water supply device. For this reason, when the water pressure on the water supply side decreases to a negative pressure due to a water supply stoppage or a stoppage of the water supply pressurizing pump due to a power failure, the negative pressure tries to suck water in the pipe to the bathtub. At that time, if the check valve does not function normally due to foreign matter caught in the valve part, the inside of the bathtub that has flowed back through the faulty check valve from the bathtub installed at a high position. The sewage will be sucked. In preparation for such a case, the sewage in the bathtub that has flowed back through the check valve is not sucked into the hot water supply pipe through the solenoid valve and the flow sensor, but is trapped in front of the solenoid valve and the flow sensor to the atmosphere. A backflow prevention device is provided to flow through the water.

  As such a backflow prevention device, when the primary pressure is reduced by receiving the primary pressure on the water supply source side on one side of the pressure receiving part made of a diaphragm and the secondary pressure on the bathtub side on the other side, Some parts have a structure that opens the valve body by driving the valve body, and allows secondary sewage to escape to the atmosphere (see, for example, Patent Document 1).

FIG. 8 is a diagram illustrating a configuration example of such a hot water supply system.
In the hot water supply system, the water supply water supply pipe 101 is connected to the upstream side of the heat exchanger 103 and the water bypass valve 104 via the flow sensor 102, and merges on the downstream side of the heat exchanger 103 and the water bypass valve 104. After that, it is connected to the water proportional valve 105. The downstream side of the water proportional valve 105 is connected to a hot water supply pipe 106 that discharges hot water to a kitchen faucet, for example. The flow sensor 102, the heat exchanger 103, the water bypass valve 104, and the water proportional valve 105 constitute a hot water supply apparatus.

  Further, the downstream side of the water proportional valve 105 is piped to the bath tub 111 via a flow sensor 107, an electromagnetic valve 108, and two check valves 109, 110 arranged in series. A backflow prevention device 112 is arranged in the piping between 110.

  The backflow prevention device 112 has a body 115 integrally including a connection portion 113 connected to a pipe between the check valves 109 and 110 and a drain port 114 opened to the atmosphere. The piston 116 is arranged coaxially with the opening center of the connection portion 113 so as to be able to advance and retreat in the axial direction, and an annular valve packing 117 fitted to the piston 116 by the advance and retreat movement is provided between the space on the connection portion 113 side of the piston 116. The passage between the drain outlet 114 is configured to open and close. On the side opposite to the connection portion 113 side of the piston 116, the central portion of the diaphragm 118 is fixed by a retainer 119 and a screw 120. The outer peripheral portion of the diaphragm 118 is clamped and fixed by the bodies 121 and 122. The body 122 has a connection portion 124 connected to the water supply pipe 101 via the pressure detection pipe 123, and the space formed by the diaphragm 118 and the body 122 is a room for receiving the original pressure of the water supply pipe 101. It is composed. The piston 116 is urged by a spring 125 in a direction to open a passage between the connection portion 113 and the drain port 114, and the stroke in the opening direction is regulated by contact with the intermediate body 121. ing.

  In such a hot water supply system, the clean water supplied from the water supply pipe 101 passes through the flow sensor 102, partly heated by the heat exchanger 103 to become hot water, and partly through the water bypass valve 104. It is mixed with hot water coming out of the heat exchanger 103. At this time, by controlling the flow rate of bypassing the heat exchanger 103 by the water bypass valve 104, the mixing ratio of the hot water and the hot water temperature is controlled. The hot water controlled to a desired temperature is further supplied with hot water from the hot water supply pipe 106 with the hot water flow rate controlled by the water proportional valve 105.

  In addition, when filling the bathtub 111 with hot water, the solenoid valve 108 is opened so that the hot water that has flowed out of the water proportional valve 105 flows into the bath bathtub 111 via the flow sensor 107, the solenoid valve 108, and the check valves 109 and 110. Supplied.

  At this time, the original pressure (primary pressure P1) of the water supply is introduced into the backflow prevention device 112 through the pressure detection pipe 123. Since this primary pressure is larger than the water flow pressure (secondary pressure P2) in the pipe passing through the check valves 109 and 110, the piston 116 is pushed and the valve packing 117 closes the connecting portion 113.

  Then, when a negative pressure is generated in the water supply pipe 101 due to a stoppage of a feed water pressurizing pump that is pumping up water due to a power failure or a water cutoff, a diaphragm 118 that senses a decrease in the primary pressure P1. Urges the piston 116 in the valve opening direction to connect the pipe between the check valves 109 and 110 to the drain port 114 and discharges water in the pipe to the atmosphere.

At this time, if the check valve 110 has poor water tightness due to foreign matter or the like, the sewage remaining in the bathtub 111 at a high place flows back through the check valve 110 due to the water head pressure. However, since the sewage is discharged to the atmosphere by the backflow prevention device 112, the sewage in the bathtub 111 does not flow back to the hot water supply pipe 106.
Japanese Patent No. 3408806 (paragraphs [0010] to [0011], FIG. 1)

  As described above, in the conventional backflow prevention device, the retainer and the screw are disposed in the body in order to fix the piston and the diaphragm. Alternatively, as an alternative means, flat washer and fixing with a nut and a screw, caulking joining with a rivet, and the like have been proposed.

  However, such a fixing means increases the number of parts and increases the cost. Moreover, since an installation space is required, it becomes a factor which prevents the backflow prevention apparatus from being made compact. Furthermore, since it is necessary to provide a hole for passing a screw or rivet in the center of the diaphragm, if any mistake or abnormality occurs in the assembly process by the fixing means, there is a possibility that an airtight leak will occur from the hole.

  The present invention has been made in view of these points, and an object of the present invention is to provide a backflow prevention device that can be manufactured in a small size and at a low cost and can prevent airtight leakage from the diaphragm.

  In the present invention, in order to solve the above-mentioned problem, it is arranged between the water supply source pipe and the water supply destination pipe, and receives and opens the primary pressure of the water supply source pipe and the secondary pressure of the water supply destination pipe, A backflow prevention device for preventing backflow to the water supply source pipe by draining backflow water flowing through the water supply destination pipe to the outside, the first connection portion connected to the water supply destination pipe, and the water source pipe A body having a second connection portion connected to the drainage port, a drain port for discharging the backflow water introduced from the first connection portion to the outside, a valve body arranged to be reciprocally movable inside the body, and A valve seat provided in a communication passage that communicates the first connection portion and the drain port, and a valve seat that is provided integrally with the valve body and is in contact with and separated from the valve seat in a space that communicates with the drain port. A valve forming part that opens and closes the communication passage, and an inside of the body. The first connection part and the second connection part are partitioned, and the first connection is arranged in contact with an end of the valve body arranged in the space part on the first connection part side. A backflow prevention device comprising: a diaphragm that receives the secondary pressure on the surface on the side and receives the primary pressure on the surface on the side of the second connection portion and operates integrally with the valve body. Provided.

  In such a backflow prevention device, the diaphragm and the valve body are disposed in contact with each other. This diaphragm is normally biased toward the valve body because it receives the primary pressure on the surface opposite to the valve body. At this time, the valve portion is in a closed state, and the valve forming portion abuts against the valve seat to prevent movement of the valve body, so that the diaphragm and the valve body are substantially in close contact with each other. On the other hand, when the primary pressure is lowered and the backflow water is introduced, the valve portion is opened by the differential pressure between the primary pressure and the secondary pressure, and the backflow water is discharged from the drain outlet to the outside. And since secondary pressure becomes low by discharge | emission of this backflow water, a valve part returns to a valve closing state again by the differential pressure | voltage of a primary pressure and a secondary pressure. That is, even at the time of reverse flow, the valve body and the diaphragm operate in close contact with each other by the differential pressure between the primary pressure and the secondary pressure. For this reason, in this structure, separate parts, such as a volt | bolt, a nut, and a retainer, for fixing a valve body and a diaphragm are not provided, As a result, a number of parts is reduced.

  Further, although the diaphragm is in contact with the valve body, since no hole for fixing is provided, the occurrence of airtight leakage from the diaphragm can be prevented.

  According to the backflow prevention device of the present invention, the contact state between the two can be maintained without providing a separate part for fixing the valve body and the diaphragm. For this reason, the number of parts can be reduced and the cost can be reduced because no separate parts are provided, and the entire backflow prevention device can be made compact. Furthermore, since it is not necessary to provide a fixing hole in the diaphragm, airtight leakage can be prevented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]
In this embodiment, the backflow prevention device of the present invention is configured for a hot water supply system for a bath. FIG.1 and FIG.2 is a center longitudinal cross-sectional view showing the structure of the backflow prevention apparatus which concerns on 1st Embodiment. FIG. 1 shows the valve closing state of the backflow prevention device, and FIG. 2 shows the valve opening state of the backflow prevention device. The configuration of the entire hot water supply system is substantially the same as that shown in FIG.

  As shown in FIG. 1, the backflow prevention device includes a first body 1, a second body 2, and a relay body 3 interposed between the two bodies. Each body is joined to each other by press fitting.

  The first body 1 is connected to a pipe (corresponding to a “water supply destination pipe”) between two check valves arranged in front of the bathtub of the hot water supply system, and receives a secondary pressure P2. (Corresponding to “first connecting portion”) and a drain port 5 that is open to the atmosphere. In addition, a piston 6 (corresponding to a “valve element”) is disposed on the same axis as the opening center of the connecting portion 4 so as to be reciprocally movable. The piston 6 has a double structure in which a bottomed cylindrical main body 7 is inserted with a bottomed cylindrical guide member 8. An annular valve packing 9 (corresponding to a “valve forming part”) is fitted to the opening end of the main body 7, and is detachable from the valve seat 11 formed by the inner opening end of the internal passage 10 of the connecting part 4. It has become. By opening and closing the valve portion constituted by the valve packing 9 and the valve seat 11, the communication path connecting the connection portion 4 and the drain port 5 is opened or closed. Further, between the flange portion 12 extending outward from the opening end of the main body 7 and the inner wall of the first body 1, a spring 13 that biases the piston 6 in a direction away from the connection portion 4 (“biasing”). Corresponding to “means”).

  The bottom of the guide member 8 is fixed to the main body 7 with a screw 14. A flange portion 15 that extends slightly outward is provided at the open end of the guide member 8, and the flange portion 15 can prevent the valve packing 9 from falling off. Further, at the opening end of the guide member 8, there are provided three guide portions 16 (only two are shown in the figure) extending along the internal passage 10 of the connection portion 4, and the guide portions 16 are By being guided while sliding along the internal passage 10, the piston 6 can stably reciprocate in the axial direction.

  The second body 2 is integrally provided with a connection portion 17 (corresponding to a “second connection portion”) that receives a primary pressure P1 from a water supply pipe (corresponding to a “water supply source piping”) via a pressure detection tube. ing. A diaphragm 18 is disposed so as to be sandwiched between the second body 2 and the relay body 3, and partitions the space between the connection portion 17 that receives the primary pressure P1 and the connection portion 4 that receives the secondary pressure. . The diaphragm 18 has a main body formed in a cup shape by folding the vicinity of the peripheral end portion, and the end portion on the opposite side to the connection portion 4 of the piston 6 contacts and is accommodated along the shape of the main body. It is configured as follows. The diaphragm 18 is actuated by receiving a secondary pressure on the surface on the side of the connecting portion 4 and receiving a primary pressure on the surface on the side of the connecting portion 17, but has a long stroke while keeping the effective pressure receiving area constant by the deep folded portion. Can be activated.

  The relay body 3 has a stepped cylindrical main body with a short axial length, and abuts against the flange portion 12 of the piston 6 by the end face of the portion inserted into the first body 1 to lock it. A stopper portion 19 is configured. That is, the stroke in the valve opening direction of the piston 6 is regulated by the contact with the relay body 3. Further, an O-ring 20 is disposed between the first body 1 and the relay body 3 in order to prevent an airtight leak while the backflow water is open to the atmosphere.

  In the backflow prevention device configured as described above, in a normal use state, as shown in FIG. 1, the connection portion 17 receives the original pressure (primary pressure P1) from the water supply pipe via the pressure detection tube, and the connection portion 4 receives the water pressure (secondary pressure P2) in the pipe passing through the check valve. Since the primary pressure P1 is higher than the secondary pressure P2, the diaphragm 18 senses these differential pressures and drives the piston 6 in the valve closing direction to seat the valve packing 9 on the valve seat 11. Thereby, the communication path which connects the connection part 4 and the drain port 5 is obstruct | occluded.

  Here, when a negative pressure is generated in the water supply pipe due to a stoppage of the feed water pressurizing pump or a water stoppage due to a power failure, the primary pressure P1 becomes lower than the secondary pressure P2. Therefore, as shown in FIG. 18 senses the drop in the primary pressure P1, and allows the piston 6 to move in the valve opening direction. For this reason, the piston 6 moves in the valve opening direction by the differential pressure between the primary pressure P1 and the secondary pressure P2 and the urging force of the spring 13. At this time, the valve packing 9 is lifted from the valve seat 11, but is held in the fully open position when the flange portion 12 contacts the stopper portion 19. Thereby, the communicating path between the connection part 4 and the drain port 5 is open | released, and piping between the two check valves arrange | positioned in series is open | released to air | atmosphere.

  At this time, if the bathtub is installed at a position higher than the hot water supply device and the check valve placed in front of the bathtub has become watertight due to foreign matter biting, the sewage in the bathtub Will flow back to the backflow prevention device via the check valve due to the water head pressure, but since the sewage is released to the atmosphere by the backflow prevention device, the sewage in the bathtub will not flow back to the hot water supply pipe. . Thereby, it is possible to completely prevent the sewage from flowing back to the water supply side by this backflow prevention device.

  As described above, in the backflow prevention device of the present embodiment, the diaphragm 18 and the piston 6 operate integrally with each other without interposing other parts such as bolts, nuts, and retainers. For this reason, the number of parts can be reduced and the cost can be reduced because no separate parts are provided, and the entire backflow prevention device can be made compact. Furthermore, since there is no need to provide a fixing hole in the diaphragm 18, airtight leakage can be reliably prevented.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The backflow prevention device according to the present embodiment is the same as the configuration of the first embodiment except that the structure and assembly structure of the piston and the diaphragm are different. A description thereof will be omitted, for example. 3 and 4 are central longitudinal sectional views showing the configuration of the backflow prevention device according to the second embodiment. FIG. 3 shows the closed state of the backflow prevention device, and FIG. 4 shows the open state of the backflow prevention device.

  As shown in FIG. 3, in this backflow prevention device, the piston 206 (corresponding to “valve element”) has a bottomed cylindrical main body 207, but does not have a double structure. A fitting hole 208 is formed in the bottom center of the main body 207 so as to penetrate the main body 207 in the axial direction.

  On the other hand, the diaphragm 218 is integrally formed with a fitting portion 219 having a T-shaped cross section that protrudes from the surface on the piston 206 side and is inserted into the fitting hole 208. After the head of the fitting portion 219 is inserted into the fitting hole 208, the diaphragm 218 and the piston 206 are fixed by elastically returning and fitting into the fitting hole 208.

  The operation of the backflow prevention device having such a configuration is substantially the same as that of the backflow prevention device according to the first embodiment. Usually, as shown in FIG. 3, the diaphragm is caused by the primary pressure P1 higher than the secondary pressure P2. 218 presses the valve packing 9 against the valve seat 11 to block the communication path between the connecting portion 4 and the drain port 5. And when negative pressure generate | occur | produces in a water supply pipe | tube by a power failure or water stop, etc. and the primary pressure P1 becomes lower than the secondary pressure P2, as shown in FIG. 4, a valve part will fully open and drain the connection part 4 The pipe is connected to the atmosphere via the port 5 and the pipe between the two check valves arranged in series is opened to the atmosphere. At this time, even if the sewage in the bathtub flows back through a check valve that has malfunctioned, the sewage flows back to the atmosphere through the backflow prevention device. Can be completely prevented.

  As described above, also in the backflow prevention device of the present embodiment, the diaphragm 218 and the piston 206 operate integrally with each other without interposing other parts such as bolts, nuts, and retainers. For this reason, the number of parts can be reduced and the cost can be reduced because no separate parts are provided, and the entire backflow prevention device can be made compact.

  In addition, since the fitting portion 219 for fixing the diaphragm 218 to the piston 206 is integrally formed, the diaphragm 218 and the piston 206 can stably operate integrally. Also in this case, there is no need to provide a fixing hole in the diaphragm 218, and airtight leakage can be reliably prevented.

[Third Embodiment]
FIG. 5 is a central longitudinal sectional view showing the configuration of the backflow prevention device according to the third embodiment. FIG. 6 is a left side view of the backflow prevention device. FIG. 7 is a bottom view of the backflow prevention device. The configuration of the entire hot water supply system is substantially the same as that shown in FIG.

As shown in FIGS. 5 to 7, the backflow prevention device includes a first body 301 and a second body 302 fitted to the first body 301 by press fitting.
The first body 301 is connected to a pipe (corresponding to a “water supply destination pipe”) between two check valves arranged in front of the bathtub of the hot water supply system, and receives a secondary pressure P2. (Corresponding to a “first connecting portion”) and a drain outlet 304 that is open to the atmosphere are provided integrally. In the space formed by both bodies, a plug 305 (corresponding to a “valve element”) is arranged coaxially with the center of the opening of the connecting portion 303 so as to be reciprocally movable in the axial direction.

  The body 301 is provided with a bearing portion 307 for supporting a shaft portion (described later) of the plug 305 in the internal passage 306 of the connection portion 303. The bearing portion 307 has a bearing hole 308 at the center, and three communication holes 309 arranged concentrically around the hole 308 are provided. In addition, a cylindrical valve seat forming portion 310 extending in a direction away from the connection portion 303 is provided inside the body 301, and a valve seat 311 is formed by the tip end surface thereof.

  The plug 305 has a stepped columnar main body 312 whose diameter is reduced in a plurality of steps toward the connection portion 303 side, and a shaft whose tip is inserted into the hole 308 of the bearing portion 307 and is slidably supported. Part 313. In addition, an annular valve packing 314 (corresponding to a “valve forming portion”) is fitted into a groove provided in the outer peripheral portion near the center of the main body 312, and is detachable from the valve seat 311. By opening and closing the valve portion constituted by the valve packing 314 and the valve seat 311, the communication path connecting the connection portion 303 and the drainage port 304 is opened or closed. A convex engagement portion 315 protrudes from the end surface of the main body 312 opposite to the shaft portion 313. Further, a spring 316 (corresponding to “biasing means”) that biases the plug 305 in a direction away from the connection portion 303 is interposed between the main body 312 and the bearing portion 307.

  The second body 302 is integrally provided with a connection portion 317 (corresponding to the “second connection portion”) that receives the primary pressure P1 from the water supply pipe (corresponding to the “water supply source piping”) via the pressure detection tube. ing. The connecting portion 317 extends in a direction intersecting at an angle of about 90 degrees with respect to the communication path connecting the connecting portion 303 and the drainage port 304. A diaphragm 318 is disposed so as to be sandwiched between the first body 301 and the second body 302, and partitions the space between the connection portion 317 that receives the primary pressure P1 and the connection portion 303 that receives the secondary pressure. ing. The diaphragm 318 is shallower than the diaphragm 18 of the first embodiment and has a shorter operating stroke. A main body 319 of the diaphragm 318 is thick, and an engaging portion 320 formed of a concave portion complementary to the engaging portion 315 of the plug 305 is formed at the center thereof. Accordingly, the plug 305 reciprocates in the axial direction with one end side supported by the bearing portion 307 and the other end side supported by the diaphragm 318.

  The operation of the backflow prevention device having such a configuration is substantially the same as that of the backflow prevention device according to the first embodiment. Normally, the diaphragm 318 causes the valve packing 314 to be moved by the primary pressure P1 higher than the secondary pressure P2. By pressing against the valve seat 311, the communication path between the connection portion 303 and the drain port 5 is blocked. Then, when a negative pressure is generated in the water supply pipe due to a power failure or a water stoppage and the primary pressure P1 becomes lower than the secondary pressure P2, the valve portion is fully opened and the connection portion 303 is brought into the atmosphere via the drainage port 304. The piping between the two check valves arranged in series is opened to the atmosphere. At this time, even if the sewage in the bathtub flows back through a check valve that has malfunctioned, the sewage flows back to the atmosphere through the backflow prevention device. Can be completely prevented.

  As described above, also in the backflow prevention device of the present embodiment, the diaphragm 318 and the plug 305 operate integrally with each other without interposing other parts such as bolts, nuts, and retainers. For this reason, the number of parts can be reduced and the cost can be reduced because no separate parts are provided, and the entire backflow prevention device can be made compact.

  In addition, since the diaphragm 318 and the plug 305 are configured to engage with each other via the respective engaging portions, the diaphragm 318 and the plug 305 can stably operate integrally. Also in this case, since it is not necessary to provide a fixing hole in the diaphragm 318, airtight leakage can be prevented.

  In each of the above embodiments, the backflow prevention device of the present invention is configured for a hot water supply system for a bath. However, it goes without saying that the present invention is applicable to various systems in which backflow may occur. Nor.

  In each of the above embodiments, the spring is used as the biasing means for biasing the pistons 6, 206 and the plug 305 toward the diaphragms 18, 218 and 318, but rubber or other biasing means is also used. You can also.

It is a central longitudinal cross-sectional view showing the structure of the backflow prevention apparatus which concerns on 1st Embodiment. It is a central longitudinal cross-sectional view showing the structure of the backflow prevention apparatus which concerns on 1st Embodiment. It is a center longitudinal cross-sectional view showing the structure of the backflow prevention apparatus which concerns on 2nd Embodiment. It is a center longitudinal cross-sectional view showing the structure of the backflow prevention apparatus which concerns on 2nd Embodiment. It is a center longitudinal cross-sectional view showing the structure of the backflow prevention apparatus which concerns on 3rd Embodiment. It is a left view of the backflow prevention apparatus which concerns on 3rd Embodiment. It is a bottom view of the backflow prevention apparatus which concerns on 3rd Embodiment. It is a figure which shows the structural example of a hot water supply system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,301 1st body 2,302 2nd body 3 Relay body 4,303 Connection part 5,304 Drain port 6,206 Piston 9,314 Valve packing 11 Valve seat 13,316 Spring 17,317 Connection part 18,218, 318 Diaphragm 19 Stopper part 208 Fitting hole 219 Fitting part 305 Plug 307 Bearing part 311 Valve seat 313 Shaft part 315, 320 Engagement part

Claims (7)

It is arranged between the water supply source pipe and the water supply destination pipe, receives and opens the primary pressure of the water supply source pipe and the secondary pressure of the water supply destination pipe, and externally flows the backflow water flowing through the water supply destination pipe. A backflow prevention device that prevents backflow to the water supply source pipe by draining into
A body having a first connection part connected to the water supply destination pipe, a second connection part connected to the water supply source pipe, and a drain outlet for discharging the backflow water introduced from the first connection part to the outside;
A valve body arranged to be reciprocally movable inside the body;
A valve seat provided in a communication path communicating the first connection portion and the drain port;
A valve forming portion that is provided integrally with the valve body and opens and closes the communication passage by contacting and separating from the valve seat in a space communicating with the drain port;
The space between the first connection portion and the second connection portion inside the body is partitioned, and is disposed in contact with an end portion of the valve body disposed in the space portion on the first connection portion side. A diaphragm that receives the secondary pressure on the surface on the first connection portion side, receives the primary pressure on the surface on the second connection portion side, and operates integrally with the valve body;
A backflow prevention device characterized by comprising:   The diaphragm has a main body formed in a cup shape by folding the vicinity of a peripheral end fixed to the body, and the end of the valve body is partially accommodated in the main body. The backflow prevention device according to claim 1, wherein The valve body has a fitting hole drilled in the bottom of the bottomed cylindrical main body,
The diaphragm has a fitting portion protruding from the surface on the valve body side, and the fitting portion is fixed to the valve body by being inserted and fitted into the fitting hole.
The backflow prevention device according to claim 1.   2. The backflow prevention device according to claim 1, wherein the valve body and the diaphragm are engaged with each other by complementary engaging portions formed on respective opposing surfaces.   2. The backflow prevention device according to claim 1, further comprising an urging unit that applies an urging force to the valve body toward the diaphragm.   The valve body has the end portion supported by the diaphragm, and the shaft portion provided on the opposite side of the end portion is supported by the bearing portion provided on the body so as to be slidable in the axial direction. The backflow prevention device according to claim 1. The body is composed of a first body forming the first connection portion and a second body forming the second connection portion;
The diaphragm is sandwiched between the first body and the second body;
The backflow prevention device according to claim 1.

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