JP2000320692A - Butterfly valve and its valve seat mounting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a butterfly valve to be low in a rubber use amount and suitable to environment and a valve seat mounting method to easily and reliably and surely mount a valve seat. SOLUTION: In a butterfly valve, a valve seat 13 is inserted into a valve seat mounting groove 14 in a dovetail shape in cross section, and when it is seen in cross section, an outer peripheral part fronting on the bottom 14a of a valve seat mounting groove 14 is divided in a fork-from shape into fork branches 13a and 13b. A wedge member 15 inserted therebetween and forcibly spreading a space therebetween is mounted on the bottom 14a. Further, a valve seat mounting method comprises a wedge member mounting process wherein the wedge member 15 is inserted in the bottom 14a for mounting, an insertion process wherein after the fork branches 13a and 13b are pressed in a manner to approach each other the valve seat 13 is inserted in the valve seat mounting groove 14, and a forced spreading process wherein thereafter, the valve seat 13 is further inserted in the valve seat mounting groove 14 and by forcibly spreading a space between the fork branches 13a and 13b by the wedge member 15 the valve seat is increased in size in the valve seat mounting groove 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a butterfly valve connected to a pipeline such as a water channel for controlling the pressure and flow rate of a fluid.

[0002]

2. Description of the Related Art In various fields, butterfly valves are widely used for controlling the pressure and flow rate of a fluid. The general structure of a conventional butterfly valve of this type will be described below with reference to FIG. The butterfly valve includes a valve box 1 in which a cylindrical flow path through which a fluid flows is formed, a valve stem 2 vertically and rotatably supported in the flow path in the flow path, A valve body 3 fixed to the rod 2 and rotating to open and close a flow path, a valve seat 4 whose peripheral edge is in close contact with the valve body 3 in a closed state, and a rotational drive for rotating the valve rod 2 And a driving force transmission mechanism 5 (reduction gear) for transmitting a force.

The valve seat 4 is formed by processing a rubber material into a thin cylindrical shape, and has the same length as the entire flow path in the valve box 1 so as to cover the entire inner wall surface 1a of the valve box 1. are doing. In addition, the thickness of the valve body 3 is deformed to some extent when the valve body 3 comes into close contact with the valve body 3 to obtain a sealing property, and in consideration of abrasion,
It has a predetermined thickness. When the valve seat 4 is attached to the butterfly valve, the valve seat 4 is attached to the valve box 1 so that there is no gap between the outer peripheral surface 4a of the valve seat 4 and the inner wall surface 1a.
The fixing method includes a method in which an adhesive is applied between the outer peripheral surface 4a and the inner wall surface 1a, and vulcanization is performed with the valve seat 4 inserted.

[0004]

The conventional butterfly valve described above has the following problems. That is, rubber is preferably used as the material of the valve seat 4 and generally used by lining over the entire length of the flow passage in the valve box 1 as described above. If it is necessary to remove the entire valve seat 4 from the valve box 1, the disposal of the removed valve seat 4 is considered. The problem is that it is not preferable. Another problem is that when the process of attaching the valve seat 4 to the butterfly valve is considered, such a long and large valve seat 4 is required.
The operation of correctly inserting into the valve box 1 and fixing it uniformly and securely at all surface contact portions by vulcanization is troublesome, and there is a problem that it is difficult in some cases.

The present invention has been made in view of the above circumstances, and has the following objects. That is, an object of the present invention is to provide an environment-friendly butterfly valve which uses a small amount of rubber. Another object of the present invention is to provide a valve seat mounting method that can easily and reliably mount and fix the valve seat.

[0006]

The butterfly valve and the valve seat mounting method of the present invention employ the following means to solve the above-mentioned problems. In other words, the butterfly valve according to the first aspect is provided with a valve box having a cylindrical flow path through which a fluid flows, and is rotatably supported in the flow path in the direction perpendicular to the inflow direction of the fluid. A butterfly valve, comprising: a valve stem, a valve body fixed to the valve stem, rotating to open and close the flow path, and a valve seat whose peripheral edge is in close contact with the valve body being closed. The seat is an annular elastic body that is inserted into a valve seat mounting groove having a dovetail shape in cross section formed by opening along the inner peripheral surface of the flow path, and the valve when viewed in cross section. An outer peripheral portion facing the bottom surface of the seat mounting groove is bifurcated so as to expand toward the bottom surface, and the bottom surface has an annular shape inserted between the bifurcated branches and pushed apart in a direction to separate them from each other. The wedge member is attached.

According to the butterfly valve of the first aspect, after inserting and mounting a preformed wedge member on the bottom surface in the valve seat mounting groove of the valve box, the valve is brought close to each other between the forked branches. After pressing the outer peripheral portion of the seat, insert it into the valve seat mounting groove, and insert the valve seat toward the bottom of the valve seat mounting groove so that the wedge member in the valve seat mounting groove enters between the two branches. By doing so, the forked branch is pushed open by the wedge member, and the outer peripheral portion of the valve seat is thickened in the thickness direction so as to match the shape in the valve seat mounting groove, so that it is easily and securely fixed in the valve seat mounting groove. Is done. Further, since the valve seat fixed in this manner is a small annular body as compared with the conventional large-sized valve seat, the amount of disposal is small when the valve is disposed of for reasons such as life. I can do it.

[0008] The butterfly valve according to the second aspect is the first aspect.
The butterfly valve according to claim 1, wherein the valve seat has a hardness of 45.
The wedge member is a rubber material having a hardness in the range of 85 to 95 and higher than the hardness of the valve seat.

According to the butterfly valve of the second aspect, the hardness of the valve seat is in the range of 45 to 75, and the hardness of the wedge member is in the range of 85 to 95 and higher than the hardness of the valve seat. Thus, when the valve seat is inserted into the valve seat mounting groove of the valve box, the wedge member loses the hardness of the valve seat and is not deformed, but is surely pushed and widened between the two branches of the valve seat outer peripheral portion. be able to.

According to a third aspect of the present invention, in the butterfly valve according to the first or second aspect, one of the contact surfaces of the wedge member and the valve seat has an engagement projection, and the other has a projection. Is characterized in that an engagement groove with which the engagement protrusion engages is formed.

According to the butterfly valve of the third aspect, an engagement projection is formed on one of the contact surfaces of the wedge member and the valve seat, and the engagement projection is engaged with the other. By forming the groove, when the valve seat is inserted and fixed in the valve seat mounting groove, the engaging projection engages with the engaging groove, so that the valve seat and the wedge member are inseparably coupled. . Accordingly, since the wedge member does not come off from between the two branches of the valve seat outer peripheral portion, the valve seat outer peripheral portion is maintained in a fat state in the valve seat mounting groove.

According to a fourth aspect of the present invention, there is provided a butterfly valve.
4. The butterfly valve according to any one of claims 1 to 3, wherein a fitting projection is formed on one of the contact surface between the bottom surface of the valve seat mounting groove and the wedge member, and the fitting projection is formed on the other. Is formed with a fitting groove for fitting.

According to the fourth aspect of the present invention, the wedge member is attached to the bottom surface of the valve seat mounting groove by attaching the wedge member to the bottom surface so that the fitting protrusion is fitted into the fitting groove. Can be accurately positioned and fixed.

According to a fifth aspect of the present invention, there is provided a butterfly valve.
5. The butterfly valve according to any one of items 4 to 4, wherein the wedge member is divided into a plurality of pieces along a circumferential direction thereof.

According to the butterfly valve of the fifth aspect, by adopting a configuration in which the wedge member is divided into a plurality of pieces along the circumferential direction, the wedge member is bent while being inserted and fixed in the valve seat mounting groove. No need to insert. Therefore, in selecting the material of the wedge member, it is not necessary to reduce the hardness of the wedge member in consideration of bending during the insertion operation.

According to a sixth aspect of the present invention, there is provided a method for mounting a valve seat on a butterfly valve, comprising: a valve box having a cylindrical flow path through which a fluid flows; In a method of attaching a valve seat to a butterfly valve having a valve stem rotatably supported and a valve element fixed to the valve stem and pivoting to open and close the flow passage, an inner periphery of the flow passage is provided. A wedge member mounting step of inserting and inserting a preformed wedge member into the bottom surface of the valve seat mounting groove having a dovetail shape in cross section formed by opening along the surface, and after the wedge member mounting step, The valve seat, which is an elastic body that is bifurcated and branched so that the cross section viewed in a virtual plane passing through the annular axis and the axis thereof expands toward the outer periphery, is pressed so that the bifurcated branches approach each other, and then the valve seat is attached. An insertion step of inserting the groove into the groove, and after the insertion step, further inserting the valve seat into the valve seat mounting groove. And having a press spread step fattening in Ingress to the valve seat mounting groove and spread again between the bifurcated at said wedge member.

According to the method for mounting a valve seat on a butterfly valve according to the sixth aspect, a wedge member formed in advance is inserted and mounted on a bottom surface in a valve seat mounting groove of a valve box. Squeezing the outer peripheral portion of the valve seat so as to approach each other and then inserting the valve seat into the valve seat mounting groove, and further pressing the valve seat so that the wedge member in the valve seat mounting groove enters between the two branches. By inserting toward the bottom surface of the valve seat, the forked branch is pushed open by the wedge member, and the outer peripheral portion of the valve seat is thickened in the thickness direction so as to match the shape of the valve seat mounting groove. Easily and securely fixed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, the butterfly valve according to the present embodiment includes a valve box 10 in which a cylindrical flow path through which a fluid flows is formed. Valve stem 11 movably supported
And a valve body 12 fixed to the valve rod 11 and rotating to open and close the flow path, a valve seat 13 whose peripheral edge is in close contact with the valve body 12 in a closed state, and rotating the valve rod 11. And a driving force transmission mechanism 14A (reduction gear) for transmitting the rotational driving force for the rotation. Note that these drawings show a state in which the butterfly valve is closed, and the valve element 12 is opposed to the flow direction of the fluid and is in close contact with the valve seat 13.

As shown in FIG. 3, the valve seat 13 is formed into a ring-shaped valve seat mounting groove 14 having a dovetail cross section formed by opening 10b along the inner peripheral surface 10a of the flow path. In addition to being an elastic body, the outer peripheral portion facing the bottom surface 14a of the valve seat mounting groove 14 is branched into two branches 13a and 13b so as to expand toward the bottom surface 14a when viewed in cross section. The forked branch 13a and 13b are provided on the bottom surface 14a.
An annular wedge member 15 which is inserted between them and pushes them apart in a direction to separate them is attached.

In the line of sight shown in FIG.
A pair of side surfaces 14 approaching each other from the bottom surface 14a toward the opening 10b and being parallel to each other near the opening 10b.
b and 14c. Further, a fitting groove 14d into which the wedge member 15 fits is formed in the bottom surface 14a in an annular shape.

The wedge member 15 is, as shown in FIG.
5 is an annular body that is divided into two parts by a portion through which the part 1 passes. As shown in FIG. 5, the sectional shape of the annular part tapers as the distance from the fitting protrusion 15a fitted in the fitting groove 14d increases. Has a wedge shape as follows. In particular, the tip portion 15b
The portion 15c indicated by oblique lines in FIG.
When the forked branches 13a and 13b are inserted between the forked branches 13a and 13b to expand them, the forked branches 13a and 13b are formed to provide an escape space for causing bending deformation. By providing this escape space, bifurcation 1
Since the 3a and 13b can perform sufficient bending deformation, the valve seat 13 can be smoothly attached. Further, a radius is attached to the tip end portion 15b, and the forked branches 13a and 13b are smoothly divided along the radius. Similarly, as shown in the cross section of FIG.
A pair of engagement grooves 15d with which the pair of engagement protrusions 13c are engaged
Are formed. Although the wedge member 15 of the present invention is formed in advance, as another method, for example, the valve seat 13 is inserted into the valve seat mounting groove 14 without using the same, and thereafter, the valve seat 13 is inserted. A method is also conceivable in which a resin equivalent to the wedge member 15 is attached by injecting a resin into a space formed between the forked branches 13a and 13b and the bottom surface 14a of the valve seat attachment groove 14 and curing the resin. This causes a problem that the injection step is difficult and time-consuming, and that if the injection fails, it is difficult to start over. However, the method using the wedge member 15 does not cause such a problem.

The valve seat 13 is, as shown in FIG.
Is an annular body divided into two parts by a portion through which
As shown in FIG.
A pair of engaging projections 13c that engage with the engaging grooves 15d of the wedge member 15 are formed inside 3b. Bifurcation 1
A gap g is formed between 3a and 13b so that they can be pressed close to and in contact with each other. In the cross section of FIG. 7, the inner peripheral surface 13 d with which the valve element 12 abuts is a surface inclined toward the direction in which the valve element 12 rotates and approaches. The periphery 12a of the body 12 cuts into the body 12 so that the body 12 can be sealed tightly.

The dividing surface 13e of the dividing portion of the valve seat 13
8, the valve stem 1 is aligned with the peripheral surface of the valve stem 11 in the line of sight of FIG.
It has a round shape centered on one axis Ax. Further, as shown in FIGS. 8 and 9, an inclined surface 13f is formed on the inner peripheral surface 13d near the dividing surface 13e in a direction opposite to the inclination direction of the inner peripheral surface 13d. The inclined surface 13f is a surface formed after the rotating valve body is removed so that it can rotate smoothly. In addition, valve seat 1
As a material of No. 3, hardness is 45H _{A to} 75H _A (H _A is
Preferably rubber material having a range of rubber standards) for water, the material of the wedge member 15, hardness 85H _A ~95H _A
And a rubber material having a hardness higher than the hardness of the valve seat 13 is preferable. More preferably, a combination of a valve seat 13 having a hardness of 65 _HA and a wedge member 15 having a hardness of 90 _HA is used.

The method of attaching the valve seat 13 to the butterfly valve described above is performed according to the following procedure. That is, in the wedge member mounting step, the wedge member 15 formed in advance is formed on the bottom surface 14a in the valve seat mounting groove 14 having a dovetail shape in cross section formed by opening along the inner peripheral surface 10a of the flow path. It is inserted so that the fitting projection 15a fits into the fitting groove 14d. At this time, if necessary, the fitting projection 1
An adhesive is applied between 5a and the fitting groove 14d, and then the mounting is performed. In the step of inserting the valve seat 13 after the step of attaching the wedge member, the bifurcated branches 13a and 1a are so formed that the cross section as viewed in an imaginary plane passing through the annular axis extends toward the outer periphery.
The valve seat 13 which is the elastic body 3b is pressed so that the forked branches 13a and 13b approach each other, and then inserted into the valve seat mounting groove 14. Note that an adhesive is applied to the valve seat 13 and the like before insertion as necessary. In the step of expanding the valve seat 13 after the insertion step, the valve seat 13 is further inserted into the valve seat mounting groove 14, and the wedge member 15 is used to separate the forked branch 13 a.
3 and 13b are again expanded and fattened in the valve seat mounting groove 14, so that the mounting is completed as shown in FIG. At this time, each engagement projection 13c of the valve seat 13 is
Of the valve seat 13 and the wedge member 15 are inseparably connected.

According to the butterfly valve of the present embodiment, a large valve seat is not attached so as to cover the entire flow path formed in the valve box as in the conventional butterfly valve, but it is necessary for sealing. Since the minimum configuration is such that the annular valve seat 13 is provided only at the portion where the peripheral edge of the valve element 12 contacts, when rubber is used as the material, for example, the amount of rubber used is smaller than in the past. And an environment-friendly butterfly valve can be provided. Further, since the valve seat 13 of the present embodiment can be fixed simply by inserting it into the valve seat mounting groove 14 to which the wedge member 15 is mounted, it is possible to easily and surely mount and fix the valve seat 13 as compared with the related art. .

Further, according to the butterfly valve of the present embodiment, the hardness of the valve seat 13 in a range of 45H _A ~75H _A, and valve seat hardness of the wedge member 15 in a range of 85H _A ~95H _A 1
3, when the valve seat 13 is inserted into the valve seat mounting groove 14 of the valve box 10, the wedge member 15
Can be surely pushed and widened between the forked branches 13a and 13b of the valve seat 13 without being deformed by losing the hardness of the valve seat 13, so that the valve seat 13 can be firmly attached to the valve box 10.
Can be fixed in the valve seat mounting groove 14.

According to the butterfly valve of the present embodiment, the engagement projection 13c is formed on the valve seat 13 and the engagement groove 15d is formed on the wedge member 15 with which the engagement projection 13c is engaged. When the valve seat 13 is inserted and fixed in the valve seat mounting groove 14, the engaging projection 13c and the engaging groove 15d are engaged, and the valve seat 13 and the wedge member 15 are non-separably coupled. Since the outer peripheral portion of the valve seat 13 can be kept thick in the valve seat mounting groove 14, the valve seat 13 can be more securely fixed in the valve seat mounting groove 14.

According to the butterfly valve of this embodiment, the fitting groove 14d is formed on the bottom surface 14a of the valve seat mounting groove 14, and the bottom of the wedge member 15 is fitted into the fitting groove 14d. 15a, and these fitting projections 15a
The wedge member 15 is attached to the bottom surface 14a so that the wedge member 15 is fitted to the fitting groove 14d.
Can be easily and accurately positioned and fixed to the bottom surface 14a.

In this embodiment, the wedge member 15
Is divided into two parts so as to avoid only the place where the valve stem 11 passes. However, the present invention is not limited to this two-partitioned structure, and adopts a structure in which the part is finely divided into three or more parts along the circumferential direction. Is also good. In this case, by adopting a configuration in which the wedge member 15 is divided into a plurality of pieces along the circumferential direction, it is not necessary to insert the wedge member 15 while bending it when inserting and fixing the wedge member 15 into the valve seat mounting groove 14. In addition to being able to
Since there is no need to reduce the hardness of the wedge member 15 in consideration of bending at the time of insertion work, for example, a metal material is used.
It is also possible to increase the degree of freedom in material selection.

In the present embodiment, the wedge member 15 and the valve seat 13 are made of rubber. However, the material is not limited to this, and the materials may be appropriately changed according to design conditions. In the present embodiment, the engagement projection 13 between the valve seat 13 and the wedge member 15 is provided.
c and the engagement groove 15d are formed one pair at a time, but the invention is not limited to this, and a configuration in which two or more pairs are provided may be adopted. In the present embodiment, the fitting projection 15 is provided on the wedge member 15 side.
a and a fitting groove 14 d is formed in the valve seat mounting groove 14 side.
However, the present invention is not limited to this. Conversely, a configuration may be adopted in which a fitting groove is formed on the wedge member 15 side and a fitting protrusion is formed on the valve seat mounting groove 14 side.

[0031]

According to the butterfly valve of the first aspect of the present invention, a large valve seat is not mounted so as to cover the entire surface of the flow path formed in the valve box unlike the conventional butterfly valve. Since it adopts a configuration in which an annular valve seat is provided only in a portion where the peripheral edge of the valve body is in contact, which is the minimum necessary for performing sealing, for example, when rubber is used as a material, rubber It is possible to provide an environment-friendly butterfly valve that uses a small amount of water. Also,
Since the valve seat of the present invention can be fixed simply by inserting it into the valve seat mounting groove to which the wedge member is mounted, it is possible to easily and surely mount and fix the valve seat as compared with the related art.

According to the butterfly valve of the second aspect, the hardness of the valve seat is in the range of 45 to 75, the hardness of the wedge member is in the range of 85 to 95, and is higher than the hardness of the valve seat. By doing so, when the valve seat is inserted into the valve seat mounting groove of the valve box, the wedge member loses the hardness of the valve seat and is not deformed, but reliably expands the forked branch between the valve seat outer peripheral portions. Since the valve seat can be thickened, the valve seat can be firmly fixed in the valve seat mounting groove of the valve box.

According to the butterfly valve of the third aspect, the engagement projection is formed on one of the contact surfaces of the wedge member and the valve seat, and the engagement projection is engaged with the other. By forming the engaging groove, when the valve seat is inserted and fixed in the valve seat mounting groove, the engaging protrusion engages with the engaging groove, so that the valve seat and the wedge member cannot be separated from each other. Since the outer peripheral portion of the valve seat can be maintained in a fat state in the valve seat mounting groove, the valve seat can be more securely fixed in the valve seat mounting groove.

According to the butterfly valve of the fourth aspect, a fitting projection is formed on one of the bottom surface of the valve seat mounting groove and the contact surface between the wedge member and the fitting projection on the other. By forming a fitting groove for fitting, a wedge member is attached to the bottom surface such that these fitting protrusions and the fitting groove fit,
The wedge member can be easily and accurately positioned and fixed to the bottom surface of the valve seat mounting groove.

According to the butterfly valve of the fifth aspect, by adopting a configuration in which the wedge member is divided into a plurality of pieces along the circumferential direction, when the wedge member is inserted and fixed in the valve seat mounting groove, It is not necessary to insert while bending, so it is possible to insert easily, and it is not necessary to reduce the hardness of the wedge member in consideration of bending at the time of insertion work, for example, using metal as a material In addition, the degree of freedom in material selection can be increased.

According to the method for mounting a valve seat on a butterfly valve according to the sixth aspect, the valve seat can be fixed only by inserting it into the valve seat mounting groove in which the wedge member is mounted. Then, it is possible to easily and reliably mount and fix.

[Brief description of the drawings]

FIG. 1 is a front view illustrating a butterfly valve according to an embodiment of the present invention.

FIG. 2 is a diagram showing the butterfly valve,
It is the view seen from the -A line side.

FIG. 3 is a view showing the butterfly valve,
It is a part enlarged view.

FIG. 4 is a front view showing a wedge member which is a component of the butterfly valve.

FIG. 5 is a view showing the wedge member of the butterfly valve, and is an enlarged cross-sectional view taken along line CC of FIG. 4;

FIG. 6 is a front view showing a valve seat as one component of the butterfly valve.

FIG. 7 is a view showing the valve seat of the butterfly valve,
FIG. 7 is an enlarged cross-sectional view taken along line DD of FIG. 6.

FIG. 8 is a view showing a valve seat of the butterfly valve,
FIG. 7 is a view seen from the EE line side of FIG. 6.

FIG. 9 is a view showing the valve seat of the butterfly valve,
FIG. 9 is a view seen from the line FF in FIG. 8.

FIG. 10 is a side view showing a conventional butterfly valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Valve box 10a ... Inner peripheral surface 10b ... Opening 11 ... Valve stem 12 ... Valve element 12a ... Peripheral edge 13 ... Valve seat 13a, 13b ... Bifurcation branch 13c ··· Engagement protrusion 14 ··· Valve seat mounting groove 14a · · · Bottom surface 14d · · · Fitting groove 15 · · · Wedge member 15a · · · Fitting protrusion 15d · Engaging groove

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mikio Araki 1-3-3 Kyobashi, Chuo-ku, Tokyo Inside Maezawa Kogyo Co., Ltd. Maezawa Industry Co., Ltd. F-term (reference) 3H052 AA02 BA02 BA25 BA26 CB02 CB19 CB23 CB34 EA02

Claims (6)

[Claims] 1. A valve box in which a cylindrical flow path through which a fluid flows is formed, a valve stem supported in the flow path perpendicularly and rotatably in a flow direction of the fluid, and the valve. A butterfly valve which is fixed to a rod and rotates to open and close the flow path, and a valve seat having a valve body whose peripheral edge is in close contact with the valve body being closed; The elastic body has a shape inserted into a valve seat mounting groove having a dovetail shape in cross section formed by opening along the inner peripheral surface of the valve seat, and the bottom surface of the valve seat mounting groove when viewed in cross section. A bifurcated branch is formed so that the facing outer peripheral portion expands toward the bottom surface, and a wedge member that is inserted between the bifurcation branches and pushes apart in a direction to separate them from each other is attached to the bottom surface. A butterfly valve. 2. The butterfly valve according to claim 1, wherein the valve seat is a rubber material having a hardness of 45 to 75, and the wedge member has a hardness of 85 to 95 and the valve seat. A butterfly valve characterized by being a rubber material having a hardness higher than that of a butterfly valve. 3. The butterfly valve according to claim 1, wherein one of a contact surface between the wedge member and the valve seat includes:
A butterfly valve, wherein an engagement protrusion is formed, and an engagement groove with which the engagement protrusion engages is formed on the other end. 4. The butterfly valve according to claim 1, wherein a fitting projection is formed on one of the contact surface between the bottom surface of the valve seat mounting groove and the wedge member, The other end is formed with a fitting groove in which the fitting protrusion is fitted. 5. The butterfly valve according to claim 1, wherein the wedge member is divided into a plurality of pieces along a circumferential direction thereof. 6. A valve box in which a cylindrical flow path through which a fluid flows is formed, a valve stem vertically and rotatably supported in the flow direction of the fluid in the flow path, and the valve. A method of attaching a valve seat to a butterfly valve having a valve element fixed to a rod and rotating to open and close the flow path, wherein a cross-sectional dovetail formed by opening along an inner peripheral surface of the flow path. A wedge member mounting step of inserting and inserting a preformed wedge member into the bottom surface of the groove-shaped valve seat mounting groove, and after the wedge member mounting step, a cross section as viewed in a virtual plane passing through the ring and the axis thereof is formed. An insertion step of compressing a valve seat, which is an elastic body bifurcated so as to expand toward the outer periphery, so as to bring the bifurcation branches closer to each other, and then inserting the same into the valve seat mounting groove; After that, further insert the valve seat into the valve seat mounting groove and push the wedge member again between the two branches. A method of expanding the valve seat by expanding the valve seat in the valve seat mounting groove.