CN210461798U - Pressure-reducing backflow preventer - Google Patents

Abstract

The utility model discloses a pressure-reducing backflow preventer, which comprises a valve body, two check valves with the same structure and a water drain valve, wherein the two check valves are respectively positioned at a water inlet and a water outlet, and the water drain valve is positioned at the water drain port; the check valve comprises a valve seat, a valve clack, a rocker and a rocker torsion spring; one side of the valve clack is hinged at the upper end of the valve seat, and the other side is provided with a roller; the roller wheel slides between the fixed end and the free end; the fixed end of the rocker is also provided with an arc groove, the roller is movably arranged in the arc groove, and when the valve clack is closed, the rocker applies a pre-tightening force with a direction approximately horizontal to the roller through the arc groove; the spring force of the rocker torsion spring acts on the rocker to enable the valve clack to be in a normally closed state, and the roller on the valve clack rolls on the rocker through external force to achieve opening of the valve clack. The check valve can adopt a thinner torsion spring or can reach enough pretightening force, thereby reducing the production and manufacturing cost.

Description

Pressure-reducing backflow preventer

Technical Field

The utility model relates to a pipeline valve technical field, concretely relates to decompression type backflow preventer.

Background

The backflow preventer (backflow preventer) is a device which is composed of non-return parts and can prevent water flow of a water supply pipeline from flowing backwards, and is used for pipelines of sewage treatment and the like to prevent backflow pollution caused by backflow of flowing liquid. The backflow preventer is formed by combining two spaced check valves and a safety drain valve. The check valve is used for limiting fluid to flow only in one direction, and the valve clack is opened under the action of the pressure of the fluid flowing in one direction; when the fluid flows in the opposite direction, the valve flap is closed by the fluid pressure and the self-weight of the valve flap, thereby shutting off the flow. And the effect of the water escape valve lies in that when the pressure is abnormal (the pressure at the outlet end is higher than that of the middle cavity), even if the two check valves can not be sealed reversely, the safe water escape valve can be automatically opened to empty the backflow water, and an air partition is formed, so that the sanitation and safety of upstream water supply are ensured.

The applicant has previously filed a patent application relating to a pressure-reducing type backflow preventer and has obtained a chinese utility model patent grant (application No. CN201710066249.6 entitled-approval grant publication No. CN 106594325B).

The present application is a technical improvement made on the granted patent. Through the verification of production practice and the thought research of the applicant on the technical proficiency, the following defects of the issued patent are found:

1. after the check valve is installed in the valve body, the check nut needs to be screwed down to fix the two check valves in the valve cavity of the valve body. This kind of installation dismantlement mode need place the spanner in the valve pocket in order to carry out the elasticity, if the space of valve pocket is limited, then can restrict the operating space of spanner greatly, is difficult to operate, makes the installation of check valve dismantle very loaded down with trivial details, therefore this kind of structure is not applicable to on the valve of small-scale.

2. Referring to fig. 5, when the valve flap is closed, the rocker needs to apply a pre-tightening force to the valve flap to make the valve flap overcome the impact of the water flow and maintain the sealing state. The pretightening force is provided by the spring force of the double torsion springs, the direction of the spring force is not parallel to the direction of the pretightening force, and the component force of the spring force in the pretightening force direction is equal to the pretightening force, so that the pretightening force needs to be very large to provide enough pretightening force, which means that thicker double torsion springs need to be provided or the installation pretightening angle of the springs needs to be increased, so that the resistance to the water flow of the valve clack is increased, and the valve clack is opened unsmoo.

3. Referring to fig. 8, when the valve flap is in the open state, the roller moves along the guide of the rocker, when the check valve is in the fully open state, the roller moves to the vertex of the rocker, the direction of the spring force is basically parallel to the direction of the valve flap, the check valve and the rocker form a triangle, the valve flap is stable, and the valve flap cannot rebound, so that the check valve cannot return to the closed state.

SUMMERY OF THE UTILITY MODEL

For overcoming prior art's not enough, the utility model aims to provide a novel decompression type backflow preventer, it can make the rocker pass through the approximate level of pretightning force direction that the circular arc recess applyed the valve clack, makes the pretightning force that spring force ability furthest turned into the valve clack.

The utility model discloses a following technical scheme realizes:

a pressure-reducing backflow preventer comprises a valve body, two check valves with the same structure and a drain valve, wherein a cavity is formed inside the valve body, a water inlet, a water outlet and a drain opening are formed in the wall of the valve body, the two check valves are fixedly arranged in the valve body and are respectively positioned at the water inlet and the water outlet, and the drain valve is fixedly arranged outside the valve body and is positioned at the drain opening; the check valve comprises a valve seat, a valve clack, a rocker and a rocker torsion spring; one side of the valve clack is hinged to the upper end of the valve seat, and the other side of the valve clack is provided with a roller; the rocker comprises a fixed end and a free end, the fixed end is connected to the lower end of the valve seat through a rocker pin shaft, a rocker torsional spring is further sleeved on the rocker pin shaft, and the rocker torsional spring is a double torsional spring; the roller is movably abutted against the rocker and slides between the fixed end and the free end; the fixed end of the rocker is also provided with an arc groove for increasing the pretightening force of the valve clack, the roller is movably arranged in the arc groove, and when the valve clack is closed, the rocker applies the pretightening force in the direction approximately horizontal to the roller through the arc groove; the spring force of the rocker torsion spring acts on the rocker to enable the valve clack to be in a normally closed state, and the roller on the valve clack rolls on the rocker through external force to achieve opening of the valve clack.

Furthermore, the rocker is also provided with a back hook part which is suitable for limiting the roller.

Further, the check valve is characterized by further comprising a limiting hook, the limiting hook is arranged at the lower end of the valve seat, and torsion arms extending out of two sides of the rocker torsion spring are limited by the limiting hook.

Furthermore, one side of the valve clack, which is provided with the roller, is provided with a limiting groove for limiting the movement of the back hook part of the rocker.

Further, the valve body comprises a mounting groove suitable for mounting a check valve, and the check valve is sleeved in the mounting groove; concave structures are arranged on the inner side of the mounting groove and the outer side of the valve seat to form a fixed cavity together; the fixed cavity is internally inserted with a fixed pin shaft, and the mounting groove is provided with a notch for inserting the fixed pin shaft, so that the check valve is fixed in the valve body.

Furthermore, the fixed pin shaft comprises a holding part and a fixing part in the shape of a circular arc, the number of the fixed pin shafts is 2, and the fixed pin shafts are respectively fixedly inserted into the fixed cavity through the notches in the mounting grooves.

Further, the check valve still includes valve clack round pin axle and valve clack torsional spring, the valve clack passes through the valve clack round pin axle to be installed on the disk seat, the valve clack torsional spring cover is located outside the valve clack round pin axle, in order to incite somebody to action the valve clack articulates on the disk seat.

Furthermore, two supporting pieces used for fixing the valve clack are arranged on the valve seat, and the valve clack is arranged between the two supporting pieces through the valve clack pin shaft.

Furthermore, the valve seat is a plastic part, the support piece is a metal part, and the support piece and the valve seat are integrally formed by adopting a plastic insert technology.

Furthermore, the inner side of the valve clack is also provided with a rubber sheet and a pressing plate, and the rubber sheet is fixed on the valve clack through a bolt on the pressing plate.

Compared with the prior art, the utility model discloses the beneficial effect that can reach does: the swing structure in the check valve is improved, when the valve clack is in a sealing state, the valve clack needs to provide enough pretightening force to overcome the impulsive force of water flow, the pretightening force applied to the valve clack by the rocker through the arc groove is approximately horizontal, and is approximately parallel to the impulsive force applied to the valve clack by the water flow, so that the spring force of a torsion spring of the rocker can be converted into the pretightening force to the maximum extent, and therefore, the smaller spring force can provide enough pretightening force, which means that the valve body can achieve enough pretightening force by selecting a thinner torsion spring, so that the resistance to the water flow can; when the valve clack is opened, the roller leaves the arc groove, the direction of the spring force is changed, the pretightening force is instantly reduced, the resistance of the valve clack to water flow is reduced along with the increase of the opening degree, and the valve clack is smoothly opened; the utility model discloses guaranteed opening of valve clack smoothly, can adopt littleer rocker torsional spring simultaneously, reduced the cost of manufacturing.

Drawings

FIG. 1 is a schematic view showing the construction of a backflow preventer;

FIG. 2 is a sectional view of the backflow preventer;

FIG. 3 is an exploded view of the valve body, check valve and retaining latch;

FIG. 4 is a schematic view of a check valve installed in a valve body;

FIG. 5 is a schematic diagram of the force applied to a check valve in a closed state according to the prior art;

FIG. 6 is a schematic view of the check valve of the present invention in a closed state;

FIG. 7 is a schematic view of the check valve of the present invention in an open position;

FIG. 8 is a schematic view of a prior art valve flap opening to a maximum position;

fig. 9 is a first schematic view of the check valve of the present invention opened to a maximum position;

fig. 10 is a second schematic view of the check valve of the present invention when it is opened to its maximum position.

In the figure: 10. a valve body; 11. a water inlet; 12. a water outlet; 13. a water discharge opening; 14. mounting grooves; 15. a first recess structure; 16. a second recessed structure; 17. a fixed cavity; 20. a check valve; 21. a valve seat; 22. a valve flap; 23. a rocker; 231. a circular arc groove; 232. a hook return part; 24. a rocker spring; 25. a rocker pin shaft; 26. a roller; 27. a limiting hook; 28. a limiting groove; 29. fixing the bolt; 210. a valve clack pin shaft; 211. a valve flap torsion spring; 212. supporting a piece; 213. a rubber sheet; 214. pressing a plate; 30. a water escape valve.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and the detailed description, and it should be noted that the embodiments or technical features described below can be arbitrarily combined to form a new embodiment without conflict.

Referring to fig. 1 to 4 and 6 to 7, the present invention discloses a pressure-reducing backflow preventer, which comprises a valve body 10, two check valves 20 having the same structure, and a drain valve 30. The inside of the valve body 10 forms a cavity, a water inlet 11, a water outlet 12 and a water discharge opening 13 are formed on the valve wall of the valve body 10, two check valves 20 are fixedly arranged in the valve body 10 and are respectively positioned at the water inlet 11 and the water outlet 12, and a water discharge valve 30 is fixedly arranged outside the valve body 10 and is positioned at the water discharge opening 13.

The check valve 20 includes a valve seat 21, a flap 22, a rocker 23, and a rocker 23 torsion spring, and water flows through the valve seat 21 to force the flap 22 through the check valve 20. One side of the valve clack 22 is hinged at the upper end of the valve seat 21, and the other side is provided with a roller 26; the rocker 23 comprises a fixed end and a free end, the fixed end is connected to the lower end of the valve seat 21 through a rocker pin shaft 25, a rocker 23 torsion spring is further sleeved on the rocker pin shaft 25 to hinge the rocker 23 on the valve seat 21, the rocker 23 torsion spring enables the rocker 23 to be pressed towards the valve clack 22, and the rocker 23 torsion springs are double torsion springs and are respectively arranged on the two sides of the rocker 23 in a bilateral symmetry manner; the roller 26 is movably abutted against the rocker 23 and slides between the fixed end and the free end;

the fixed end of rocker 23 still is provided with the circular arc recess 231 that is used for increasing valve clack 22 pretightning force, and gyro wheel 26 activity sets up in circular arc recess 231: when the valve clack 22 is closed, the position of the roller 26 is positioned in the arc groove 231, the rocker 23 applies a pre-tightening force in a direction approximately horizontal to the roller 26 through the arc groove 231, and the direction of the pre-tightening force is approximately parallel to the direction of water inlet; when the valve clack 22 is opened, the roller 26 leaves the arc groove 231 and rolls along the guide of the rocker 23;

the spring force of the torsion spring of the rocker 23 acts on the rocker 23, so that the rocker 23 always exerts the spring force on the roller 26, the valve clack 22 is in a normally closed state, and when the roller 26 on the valve clack 22 rolls on the rocker 23 through external force, the valve clack 22 can be opened. Two check valves 20 are provided, the check valve 20 at the water outlet 12 having a greater elastic force of the double torsion spring than the check valve 20 at the water inlet 11.

It should be noted that, when the valve flap 22 maintains the sealing state, the valve flap 22 needs to provide a large enough pre-tightening force to overcome the impulse force of the water flow, and the direction of the pre-tightening force applied to the valve flap 22 by the rocker 23 through the arc groove 231 is approximately horizontal, and is approximately parallel to the impulse force applied to the valve flap 22 by the water flow, so that the spring force of the torsion spring of the rocker 23 can be maximally converted into the pre-tightening force, and therefore, a small spring force can provide a sufficient pre-tightening force, which means that the valve body 10 can be a thinner torsion spring or a smaller spring installation pre-tightening angle to achieve a sufficient pre; when the valve clack 22 is opened, the roller 26 leaves the arc groove 231, the direction of the spring force changes, the pretightening force is instantly reduced, the resistance of the valve clack 22 to water flow is reduced along with the increase of the opening degree, and the opening is smooth.

Preferably, referring to fig. 6, the rocker 23 is further provided with a back hook portion 232 adapted to limit the roller 26, and when the valve flap 22 is opened to the maximum, the back hook portion 232 limits the roller 26 so that the valve flap cannot roll upwards, so as to limit the opening of the valve flap 22.

Preferably, referring to fig. 9, the check valve 20 further includes a limit hook 27, the limit hook 27 is disposed at the lower end of the valve seat 21, the torsion arms extending from the two ends of the torsion spring of the rocker 23 are limited by the limit hook 27, and the rotation degree of the rocker 23 is limited by limiting the positions of the torsion arms. During operation, only the rocker 23 torsion spring is sleeved on the pin shaft, and then the two extending torsion arms at the left and the right of the double torsion springs are pried to the corresponding limit hooks 27 by a screwdriver, so that the hook mode is convenient for mounting and dismounting the spring.

Preferably, referring to fig. 10, the side of the flap 22 where the roller 26 is installed is provided with a limiting groove 28 for limiting the movement of the hooking portion 232 of the rocker 23. When the check valve 20 in the preventer is cleaned and parts are replaced, an operator pries the rocker 23 open, and then clamps the hook returning part 232 of the rocker 23 in the limiting groove 28 of the roller 26 and the valve clack 22, so that the valve clack 22 is in a normally open state, and the parts are conveniently cleaned and replaced.

The utility model discloses a concrete work flow and theory of operation as follows: when the valve clack 22 is in a normally closed state, due to the fact that the pretightening force is applied to the valve clack 22 through the spring force of the double torsion springs, sufficient sealing performance between the valve seat 21 and the valve clack 22 is guaranteed when the valve clack 22 is in the closed state. When the impulsive force of water flow is greater than the pretightening force applied to the valve clack 22 by the rocker 23, the water flow enters from the water inlet 11, the roller 26 leaves the arc groove 231 and rolls along the guide of the rocker 23, the valve clack 22 is opened to enable the water flow to enter, the roller 26 is limited when rolling to the back hook part 232 of the rocker 23, and the opening degree of the valve clack 22 reaches the maximum; when water flows through the inner cavity of the fruit valve body 10 and out of the water outlet 12, the other check valve 20 is opened in the same manner to realize water outlet. The drain valve 30 is provided with a spring which closes the pressure release valve under normal working conditions, and when backflow is generated in the cavity, the drain valve 30 is opened, and liquid flows away from the lower part.

Preferably, referring to fig. 3 to 4, the valve body 10 includes therein a mounting groove 14 for mounting the check valve 20, the mounting groove 14 having a circular arc shape adapted to mount the valve seat 21 of the circular check valve 20 therein. The check valve 20 is sleeved in the mounting groove 14, wherein triangular recessed structures are arranged on the inner side of the mounting groove 14 and the outer side of the valve seat 21, and the two recessed structures jointly form a fixed cavity 17; a fixing pin is inserted into the fixing cavity 17 to fill the fixing cavity 17, so that the position between the installation groove 14 and the check valve 20 is fixed, thereby completing the installation of the check valve 20. The mounting groove 14 is further provided with a notch for facilitating insertion of the fixing pin shaft, so that an operator can conveniently perform insertion.

Specifically, the recessed structure on the mounting groove 14 is a first recessed structure 15, and the recessed structure on the valve seat 21 is a second recessed structure 16.

Further preferably, referring to fig. 3, the fixing pin comprises a holding portion and a fixing portion, wherein the fixing portion is arc-shaped so as to be engaged with the fixing cavity 17. The number of the fixing pins is 2, and the operator can insert the fixing pins from the notches of the mounting groove 14 through the hand-held grip portion to complete the fixing of the check valve 20.

The utility model discloses the installation dismantlement process to check valve 20 as follows: the valve seat 21 of the check valve 20 is partially sleeved in the mounting groove 14 of the valve body 10, the triangular recessed structures of the valve seat 21 and the mounting groove 14 form a fixing cavity 17 together, and then the fixing portion of the fixing pin shaft is inserted into the fixing cavity 17 from the gap of the mounting groove 14, so that the check valve 20 is mounted. When the fixing pin shaft is detached, the holding part of the fixing pin shaft is held by hand, the fixing pin shaft is pulled out from the fixing cavity 17, the check valve 20 is in a loose state, and the fixing pin shaft can be taken out from the mounting groove 14. The advantages of this mounting are: the pin shaft is convenient to disassemble, and can be assembled and disassembled without auxiliary tools such as a spanner; the installation space is small, a large space is not required for operation, a backflow preventer with a small specification can be used, and the working hours are saved.

Preferably, referring to fig. 9, the check valve 20 further includes a flap pin 210 and a flap torsion spring 211. The valve clack 22 is installed on the valve seat 21 through a valve clack pin shaft 210, and a valve clack torsion spring 211 is further sleeved outside the valve clack pin shaft 210 so as to hinge the valve clack 22 on the valve seat 21 to complete opening and closing of the valve clack 22. The spring force of the flap torsion spring 211 is less than the spring force of the rocker spring 24. The valve flap torsion spring 211 is a double torsion spring.

Further preferably, two support pieces 212 for fixing the valve flap 22 are further disposed on the valve seat 21, the valve flap 22 is disposed between the two support pieces 212 through the valve flap pin 210, and the support pieces 212 function to support the valve flap pin 210.

Set up valve clack torsional spring 211's effect on valve clack round pin axle 210 and lie in: referring to fig. 8-9, when the opening of the valve flap 22 reaches the maximum, the valve flap 22, the check valve 20, the valve seat 21 and the rocker 23 form a stable triangle, and the torsion spring of the rocker 23 exerts a spring force on the roller 26 close to being parallel to the valve flap 22 through the rocker 23, so that the valve flap 22 is easily locked and is not easily reset due to self weight. Through setting up valve clack torsional spring 211, make valve clack 22 obtain a power of kick-backing, the valve clack 22 of being convenient for can kick-back and reclose, and this power is less than the spring force of rocker 23, only plays the additional action, and can not produce very big resistance to opening of valve clack 22 to the rivers resistance that produces is not big.

Preferably, the valve seat 21 is a plastic member, the support piece 212 is a metal member, and the support piece 212 is integrally formed with the valve seat 21 by using a plastic insert molding technique. The utility model discloses a plastics inserts technique is known processing technology among the prior art, is applied to the utility model discloses a better effect has been obtained among the check valve 20, has solved check valve 20 and has opened and close the problem that vibrations, parts appear becoming flexible easily between each spare part of in-process and disk seat 21 repeatedly.

Preferably, referring to fig. 10, the inner side of the valve flap 22 is further provided with a rubber sheet 213 and a pressing plate 214, and the rubber sheet 213 is fixed on the valve flap 22 by bolts on the pressing plate 214. Since the valve flap 22 is frequently opened, the rubber sheet 213 is provided to facilitate buffering to protect the check valve 20. The rubber sheet 213 is a member which is easily worn and fixed by bolts, so that an operator can directly turn on the bolts on the pressing plate 214 to replace the rubber sheet 213.

Through the detailed explanation of the above embodiments, the present invention can achieve the following three beneficial effects:

(1) the utility model discloses open structure soon to valve clack 22 improves, through set up circular arc recess 231 on rocker 23, makes valve clack 22 when closing, and the direction of the pretension force that rocker 23 was applyed to valve clack 22 is close to parallel with the direction of rivers, and rocker spring 24's spring force can be close to whole pretightning forces of turning into promptly, compares in prior art, the utility model discloses a littleer spring or littleer spring installation angle can provide sufficient pretightning force, has saved the material cost of production.

(2) The mounting means to check valve 20 has improved, establishes into mounting groove 14 through the manual cover with check valve 20 in, and reuse fixed pin axle pegs graft fixed cavity 17, can realize check valve 20's fixed mounting. Compared with the prior art, complex processes of machining threads, pits, threaded connection, nut looseness prevention and the like are not needed, the installation is fast and time-saving, the required operation space is small, and the backflow preventer is suitable for backflow preventers of large and small specifications.

(3) The connection mode of the valve clack 22 is improved, and the valve clack torsion spring 211 is additionally arranged at the hinged position of the valve clack 22, so that when the valve clack 22 is opened to the maximum and forms triangular stability with the valve seat 21 and the rocker 23, the spring force of the valve clack torsion spring 211 drives the valve clack 22 to rebound, and the valve clack 22 returns to a closed state in a self-weight matching mode. In addition, the spring force of the valve clack torsion spring 211 is small, only an auxiliary effect is achieved, great resistance cannot be achieved on water flow, great influence is not caused on opening of the valve clack 22, and the problem that the valve clack 22 cannot rebound in certain working conditions and therefore fails is solved.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention cannot be limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are all within the protection scope of the present invention.

Claims (10)

1. A pressure-reducing backflow preventer is characterized by comprising a valve body, two check valves with the same structure and a water drain valve, wherein a cavity is formed inside the valve body, a water inlet, a water outlet and a water drain opening are formed in the valve wall of the valve body, the two check valves are fixedly arranged in the valve body and are respectively positioned at the water inlet and the water outlet, and the water drain valve is fixedly arranged outside the valve body and is positioned at the water drain opening;

the check valve comprises a valve seat, a valve clack, a rocker and a rocker torsion spring; one side of the valve clack is hinged to the upper end of the valve seat, and the other side of the valve clack is provided with a roller; the rocker comprises a fixed end and a free end, the fixed end is connected to the lower end of the valve seat through a rocker pin shaft, a rocker torsional spring is further sleeved on the rocker pin shaft, and the rocker torsional spring is a double torsional spring; the roller is movably abutted against the rocker and slides between the fixed end and the free end;

the fixed end of the rocker is also provided with an arc groove for increasing the pretightening force of the valve clack, the roller is movably arranged in the arc groove, and when the valve clack is closed, the rocker applies the pretightening force in the direction approximately horizontal to the roller through the arc groove;

the spring force of the rocker torsion spring acts on the rocker to enable the valve clack to be in a normally closed state, and the roller on the valve clack rolls on the rocker through external force to achieve opening of the valve clack.

2. The pressure-reducing type backflow preventer according to claim 1, wherein the rocker is further provided with a back hook portion adapted to limit the roller.

3. The pressure-reducing backflow preventer according to claim 1, wherein the check valve further comprises a limiting hook disposed at a lower end of the valve seat, and the torsion arms extending from both sides of the rocker torsion spring are limited by the limiting hook.

4. The pressure-reducing type backflow preventer according to claim 1, wherein a side of the valve flap to which the roller is attached is provided with a limiting groove for limiting movement of the hooking portion of the rocker.

5. The pressure-reducing type backflow preventer according to claim 1, wherein the valve body includes an installation groove adapted for installation of a check valve therein, the check valve being fitted in the installation groove; concave structures are arranged on the inner side of the mounting groove and the outer side of the valve seat to form a fixed cavity together; the fixed cavity is internally inserted with a fixed pin shaft, and the mounting groove is provided with a notch for inserting the fixed pin shaft, so that the check valve is fixed in the valve body.

6. The pressure-reducing backflow preventer according to claim 5, wherein the fixing pins comprise a holding portion and arc-shaped fixing portions, the number of the fixing pins is 2, and the fixing pins are respectively fixedly inserted into the fixing cavities through the notches of the mounting grooves.

7. The pressure-reducing backflow preventer of claim 1, wherein the check valve further comprises a flap pin and a flap torsion spring, the flap being mounted on the valve seat via the flap pin, the flap torsion spring being sleeved outside the flap pin to hinge the flap on the valve seat.

8. The pressure-reducing type backflow preventer according to claim 7, wherein said valve seat is provided with two support pieces for fixing a valve flap, said valve flap being disposed between said two support pieces by said valve flap pin.

9. The pressure-reducing backflow preventer according to claim 8, wherein said valve seat is a plastic member, said stay is a metal member, and said stay is integrally formed with said valve seat by a plastic insert technique.

10. The pressure-reducing type backflow preventer according to claim 1, wherein a rubber sheet and a pressure plate are further provided on an inner side of the valve flap, the rubber sheet being fixed to the valve flap by a bolt provided on the pressure plate.

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