JPH0972431A - Condensation preventive butterfly valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply structure a condensation preventive butterfly valve, to reduce manufacturing costs by simplifying connection among a main body, a valve shaft cylinder and a seat ring which are composed of different material, to increase durability and to prevent floating of the seat ring from a main body inner surface during use. SOLUTION: A main body 11 is composed of aluminum or other casting articles, a valve shaft cylinder 13 connected the upper part thereof is composed of a molding made of a resin material having a low heat conductivity coefficient and high heat insulation property, the main body 11 and the valve shaft cylinder 13 are made integral by means of melting connection and the main body 11 and an elastic seat ring 12 fixed in the inner surface thereof are made integral by means of vulcanizing connection. Plural lines of recessed and projecting parts 15 to be engaged with the inner surface of the main body 11 and the outer surface of the seat ring 12 are formed, step parts 12c for enlarging an inner diameter are provided in both ends of the inner surface of the seat ring 12 and a rotation receiving seat 12b for a valve body 5 surrounding a valve rod through-hole 6 is provided so as to be projected inward.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention integrally molds a main body made of a different material, a valve shaft cylinder and a seat ring.
The present invention relates to a butterfly valve that prevents dew condensation.

[0002]

2. Description of the Related Art Conventionally, in a pipeline in which a low temperature fluid flows, such as a cooling or freezing pipe, moisture in the atmosphere is condensed on the outer peripheral surface of the pipeline due to a temperature difference between the circulating fluid and the atmosphere. Measures are taken to prevent condensation by covering the outer peripheral surface of the pipeline with a heat insulating cover. A butterfly valve connected to a pipe line covered with such a heat insulating cover has also been provided with measures for preventing dew condensation. However, most of the valve shaft cylinder extending from the main body in a state orthogonal to the pipe, the actuator connected to the outer end of the valve shaft, and the like are complicated in shape and directional with the pipe. However, since the thermal insulation coating is difficult, it is the current situation that it is directly exposed to the atmosphere without thermal insulation coating. For this reason, there is a problem that moisture in the atmosphere is condensed on the exposed valve shaft cylinder and the outer surface of the actuator, the condensed water droplets corrode them, and the dropped water droplets contaminate the floor surface.

In order to solve the above problems, Japanese Patent Laid-Open No. Hei 3
As disclosed in Japanese Patent Laid-Open No. 163286, an actuator is attached to an outer end of a valve shaft cylinder via a heat shield plate, and a tubular heat insulating cover formed in conformity with the outer peripheral surface shape of the valve shaft cylinder is attached to the valve. It is proposed that the shaft cover is attached, and one end of the heat insulating cover is in contact with the heat shield plate, and the other end is bonded to a ring-shaped heat insulating cover that heat-insulates the outer peripheral surface of the main body of the butterfly valve. This has a problem that the structure becomes complicated.

In order to omit the heat shield plate and the cylindrical heat insulating cover in the above-mentioned conventional example, as shown in Japanese Patent Laid-Open No. 3-181691, the base portion of the valve stem that contacts the main body is integrated with the main body. The valve shaft cylinder is made of a metal material, and the outer portion of the valve stem is made of a heat insulating non-metal material. The base portion and the outer portion of the valve portion are connected by a spigot structure, and are firmly integrated by bonding with an adhesive or the like. Have been proposed by the applicant.

On the other hand, the conventional elastic seat ring mounted on the inner surface of the butterfly valve body is, as shown in FIG.
Both ends of the inner surface of the cylinder of the elastic seat ring 2 mounted on the inner surface are formed to have the same diameter as the inner diameter of the pipe 3.
Further, such a structure was the same as in the fitting type butterfly valve shown in FIG. In the figure, 4 is a piping flange, 5 is a valve element, 6 is a valve rod, 7a is a tightening bolt, and 7a.
b is a nut.

[0006]

Among the above-mentioned prior arts, the one disclosed in Japanese Patent Application Laid-Open No. H3-181691 proposed by the applicant of the present invention uses a valve shaft cylinder manufactured separately from the main body with an adhesive or the like. Since the assembly process of joining and integrating with the main body using it is required, the manufacturing cost of the butterfly valve cannot be sufficiently reduced, and the problem that the durability strength is limited by adhesion can be avoided. There was a problem that it could not be done.

Further, in the elastic seat ring 2 of the conventional butterfly valve shown in FIG. 8, both ends of the inner surface of the cylinder of the seat ring 2 are formed to have the same diameter as the inner diameter of the pipe 3, so that they are sandwiched by the pipe flange 4. At this time, both end portions of the seat ring 2 are compressed and bulge in the inner diameter direction like the portion C, and as a result, the turning torque of the valve body 5 increases or the valve body turning locus is obstructed. There was a problem.

Further, in the conventional fitting type butterfly valve shown in FIG. 9, the body 1 is clamped by the bolt 7a and the nut 7b by the pipe flange 4 in the same manner as described above. It is in a state of floating in the inner diameter direction from the main body 1 like the part. This tendency is especially shown in FIG.
It was remarkable when the corners at both ends shown in Fig. 8 were right angles.

Further, in FIG. 9, the valve body 5 is in the orifice (throttle) b state along the fluid flow direction indicated by the arrow a at a small opening, and as a result, the rear surface (secondary side) of the valve body 5 is In the vacuum state, the valve body 5 tends to rotate in the closing direction, and similarly to the above, the seat ring 2 of the fitting type butterfly valve bulges in the inner diameter direction like E due to the vacuum state. However, depending on the fluid conditions, the end of the seat ring 2 may be pulled in the inner diameter direction and fall off.

The present invention solves the above-mentioned problems of the prior art and, in particular, simplifies the structure of the dew condensation preventing butterfly valve, and at the same time, the body, the valve stem and the seat ring made of different materials are used. The coupling is simplified to reduce the manufacturing cost, the durability is increased, and the seat ring is lifted from the inner surface of the main body when the butterfly valve is sandwiched by the flanges of the two pipes forming the pipeline. It is an object to provide a butterfly valve that is free from dew condensation and has no condensation.

[0011]

In order to solve the above-mentioned problems, the invention of claim 1 is characterized in that a valve shaft cylinder for axially inserting a drive side valve rod is provided on the upper part of an inner cylindrical body, A seat ring made of a cylindrical elastic material that covers the inner surface and both end surfaces of the main body is attached to form a fluid passage inside the seat ring, and a disc-shaped valve element mounted in the fluid passage is formed into a valve rod. In a butterfly valve adapted to be driven through, the main body is made of aluminum or another cast product, and the valve stem is made of a molded product made of a resin material having a low thermal conductivity and high heat insulation, and The main body and the valve stem are integrated by fusion bonding, and the main body and a seat ring made of an elastic material are integrated by vulcanization bonding.

According to the second aspect of the invention, the main body and the valve shaft cylinder have the same width, and the main body and the valve shaft cylinder are configured such that a part of the valve shaft cylinder comes into contact with the flange surface at the same time during piping. It is characterized in that the main body is made of a cast material having a melting point higher than that of the constituent resin material.

According to the third aspect of the present invention, the inner surface of the cylindrical body and the outer cylindrical surface of the seat ring are formed with a plurality of concavo-convex portions that can mesh with each other, and both end portions of the inner cylindrical surface of the seat ring are formed. It is characterized in that a step portion for enlarging the inner diameter is formed, and a rotation receiving seat of the valve element is provided so as to protrude radially inward on the inner surface of the cylinder so as to surround the valve rod insertion hole.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described with reference to an embodiment shown in the drawings. FIG. 1 is a vertical cross-sectional view of a butterfly valve in a fully closed state showing an embodiment of the present invention, in which the same reference numerals as those shown in FIGS. 8 and 9 denote the same or similar parts. To do.

In the figure, reference numeral 11 denotes a main body (valve main body), which is made of a cast product made of aluminum or another casting material, and a seat ring 12 made of an elastic material is vulcanized and bonded to the inner surface of the main body 11. It is installed as a unit,
A disc-shaped valve body 5 for controlling the opening and closing of the fluid passage 9 by pressing and separating the peripheral portion of the seat ring 12 from each other.
Is rotatably housed by the upper valve rod 6 and the lower valve rod 8.

The upper valve rod 6 is supported as a drive shaft by a valve shaft cylinder 13 which is integrally connected to the outer peripheral surface of the main body 11 and projects outward in the diametrical direction through a bearing 10 and extends further outward. An actuator for driving the valve rod 6 (not shown) is connected to the outer end via an implantation key 6a, and the actuator is fixed to a mounting flange 13a integrally provided on the outer end of the valve shaft cylinder 13. It has become. Also,
The lower valve rod 8 is supported by the main body 11 via a bearing 10.

The above-mentioned valve shaft cylinder 13 is formed of a molded product made of a resin material having a low thermal conductivity and a high heat insulating property, such as polyamide, polyphenylene ether, polyphenylene sulfide, etc., and the valve shaft cylinder 13 is made of aluminum. Of the main body 11 composed of a casting made of other casting material,
A base portion 11a provided at a position to be coupled with the valve stem 13
Further, the valve shaft cylinder 13 is coupled to the main body 11 by integrally molding.

To explain the above in more detail, first, the main body 11 having the base portion 11a is cast from a casting material such as aluminum. Next, in manufacturing the valve stem 13 with a resin material having a low thermal conductivity and abundant heat insulation,
The main body 11 manufactured in advance as described above is attached to the valve stem 1
By setting it in the molding die of No. 3, the base portion 11a is projected and held in the molding space of the die. Then, if the resin material is filled into the molding space and solidified by using an injection molding machine or the like, the main body 11 and the valve stem 13 are surely integrated by fusion bonding.

At this time, a base portion 11a provided on the main body 11
1 is a cross-sectional view taken along the line AA in FIG. 1, showing a heat insulating shape in the direction orthogonal to the axial direction of the valve rod 6 in the base portion 11a in order to secure the bonding stability of the valve stem 13 and the joint strength. As shown in FIGS. 2 and 3, a polygonal shape is formed, or as shown in FIG. 4, an outer periphery is formed in an uneven circular shape so as to prevent relative rotation between the main body 11 and the valve shaft cylinder 13. It has become. In addition, the cross-sectional shape of the base portion 11a in the direction parallel to the axial direction of the valve rod 6 has a cross-section diverging shape as shown in FIG. 5 or an inverted L-shaped cross-section as shown in FIG. Although it is desired to enhance the fall-off preventing effect of the cylinder 13, the joint structure of the main body 11 and the valve shaft cylinder 13 due to the shape of the base portion 11a is not limited to the above-described embodiment.

Further, the width of the valve shaft cylinder 13 and the width B of the main body 11 are formed to be the same, so that the main body 11 and a part of the valve shaft cylinder 13 come into contact with the flange 4 at the same time during piping. Has become. Therefore, when piping, the flange 4 is attached to the main body 1.
When tightened to the gasket portion 12B of the seat ring 12 protruding to both end surfaces of 1, the stress due to this tightening is transmitted to the valve shaft cylinder 13 and the tightening stress acting on the main body 11 is reduced. The tightening stress is 1
The deformation of the main body 11 due to the transmission to the valve 1 is prevented, and the holding action of the flange 4 enhances the stability of the valve shaft cylinder 13 and the detent effect. Therefore, the transmission torque associated with the opening and closing of the valve is supported by the flange 4, and the twisting and bending stress acting on the valve stem 13 is relieved.

Incidentally, the melting point of aluminum used as a casting material constituting the main body 11 is 500 ° C. to 600 ° C.
C., the melting point of cast iron is 1300 ° C. to 1400 ° C.
The melting points of polyamide, polyphenylene ether, and polyphenylene sulfide constituting the valve cylinder 13 are about 240 ° C., respectively. Aluminum has a thermal conductivity of about 190 kcal / m · hr · ° C, stainless steel has a thermal conductivity of about 14 kcal / m · hr · ° C, and the above resin has a thermal conductivity of about 0.223 kcal / m · hr · ° C. Is.

Therefore, even if the valve shaft cylinder 13 is integrally molded by fusion bonding with the base 11a of the main body 11 made of a cast product such as aluminum or cast iron with polyamide, polyphenylene ether and polyphenylene sulfide, Since the body 11 has a large heat transfer coefficient due to molding, the body 11 is not deformed. Further, even if the heat insulating cover is attached, the heat transfer coefficient of the valve shaft cylinder 13 that tends to be an exposed portion is made lower than the heat transfer coefficient of the main body 11 so as to be thermally isolated from the main body 11. Thirteen
Also, dew condensation will not occur on the actuator attached to the outer end of the valve shaft cylinder 13. Further, the valve shaft cylinder 13
Since the heat exchange action of the actuator can be suppressed, energy loss is prevented. In addition, the lower end of the valve stem 13 is
As shown in the figure, when the valve rod insertion hole 14 provided in the main body 11 is extended to the inner peripheral surface and the coating 13b is applied, the heat insulating effect between the main body 11 and the valve stem 13 should be further enhanced. You can

On the other hand, the seat ring 12 integrated with the inner surface of the cylindrical main body of the main body 11 comprises a cylindrical portion 12A covering the inner peripheral surface of the main body 11 and a gasket portion 12B covering both end surfaces of the main body 11. , EPDM, NBR and C
It is molded from an elastic material mainly composed of synthetic rubber such as R, and is fixed and integrated with the main body 11 by vulcanization joining as described above. The inner surface of the cylindrical portion 12A is substantially formed into a cylindrical surface 12a excluding the insertion portion of the upper valve rod 6 and the insertion portion of the lower valve rod 8, and the insertion of each of the upper valve rod 6 and the lower valve rod 8 is performed. Around the periphery of the portion, a rotary receiving seat 12b is formed which is a flat surface that projects inward in the radial direction from the cylindrical surface 12a and is perpendicular to the valve rods 6 and 8. The rotary receiving seat 12b is a valve which will be described later. It enables the body 5 to rotate smoothly. The rotary seat 12b can be formed in a spherical shape slightly recessed from the flat surface depending on the shape of the valve body 5. Furthermore, the inner cylindrical surface 12a of the cylindrical portion 12A
Slant stepped portions 12c are formed at both end portions of the cylindrical portion 12a in a conical surface shape that extends outward in the axial direction, and the inner diameter D of the gasket portion 12B is larger than the diameter of the cylindrical surface 12a, that is, the inner diameter d of the cylindrical portion 12A. Has become. Further, a step α is formed between the end surfaces of the valve shaft cylinder 13 and the main body 11 and the end surface of the gasket 12B of the seat ring 12.

On the inner surface of the main body 11 joined to the outer peripheral surface of the seat ring 12, there are two dovetail grooves on the left and right with the insertion holes for the valve rods 6 and 8 interposed therebetween, and the cylindrical portion 1 of the seat ring 12.
On the outer surface of 2A, a ridge (ant) that fits in the above dovetail groove.
Reference numerals 15 are provided in the circumferential direction, and the main body 11 and the seat ring 12 are more firmly joined by the engagement of the dovetail groove and the projection, and the vulcanization joining together. The inner surface of the main body 11 and the cylindrical portion 12A of the seat ring 12
Instead of the dovetail groove and the ridge, a large number of square grooves as shown in FIG. 7 and any other irregularities 15A may be provided in mesh with each other on the outer surface of the above. Further, the upper and lower portions of the cylindrical portion 12A of the seat ring 12 are provided with insertion holes 16 for the upper valve rod 6 and the lower valve rod 8 along the center line connecting the upper and lower bearings 10, 10, respectively. Insertion hole 16
Open to the upper and lower rotation receiving seats 12b formed inside the cylindrical portion 12A.

On the other hand, the valve body 5 disposed inside the seat ring 12 is made of a cast product or synthetic resin as in the case of the main body 11 and is formed by the inner diameter d of the cylindrical portion 12A of the seat ring 12.
It is formed in a disk shape having a diameter larger than that of the compression margin by an upper connecting portion 5a for connecting the upper valve rod 6 to its upper end and a lower connecting portion for connecting the lower valve rod 8 to its lower end. The side connection portions 5b are formed respectively. The upper connection part 5
The upper surface of a and the lower surface of the lower connecting portion 5b are respectively formed as flat surfaces corresponding to the upper and lower rotation receiving seats 12b inside the cylindrical portion 12A. In this case, the distance between the upper surface of the upper connecting portion 5a and the lower surface of the lower connecting portion 5b is set to be larger than the distance between the upper and lower rotary receiving seats 12b in the cylindrical portion 12A of the seat ring 12 by the compression margin. The upper and lower connecting portions 5a and 5b are provided with holes into which the upper and lower valve rods 6 and 8 can be inserted, and the square lower end of the upper valve rod 6 is connected to the upper square hole of the upper connecting portion 5a so that torque can be transmitted. Further, the upper round bar portion of the lower valve rod 8 is slidably inserted and connected to the lower surface circular hole of the lower connecting portion 5b. Therefore, by rotating the upper protruding end of the upper valve rod 6 by any means, the valve body 5 rotates and the fluid passage 9 inside the cylindrical portion 12A of the seat ring 12 is opened and closed.

According to the above embodiment, the valve cylinder 13
Is made of a resin material having a low thermal conductivity and abundant heat insulation and is thermally insulated from the main body 11, so that dew condensation does not occur on the valve shaft cylinder 13 and the actuator attached to the outer end thereof. . Further, since the valve shaft cylinder 13 is integrated with the main body 11 made of a cast product such as aluminum by fusion bonding, the coupled state of the valve shaft cylinder 13 and the main body 11 becomes reliable and stable, It is possible to prevent deformation and damage of the valve shaft cylinder due to the operating torque caused by opening and closing the valve.

Further, since the elastic seat ring 12 mounted on the inner surface of the main body 11 is integrated with the main body 11 by vulcanization bonding, the main body 11 can be used as a part of a mold for seat ring molding. Can be easily manufactured,
The body is lighter than the one made of cast iron, is easy to handle, and the cylindrical portion 12A of the seat ring 12 does not lift up from the cylindrical body of the main body 11 during use while being attached to the pipeline. Therefore, excessive stress is not applied to a part of the seat ring, and the durability is improved.

The butterfly valve described above is shown in FIG.
As shown in, the two pipes that make up the pipeline
The pipe 3 is interposed between disc-shaped flanges 4 and 4 which are fitted and fixed to the outer surfaces of the ends of the pipes 3 and 3, and the flanges 4 and 4 on both sides are fastened by a plurality of sets of bolts 7a and nuts 7b. , 3 are sandwiched. In this case, since the end surface of the gasket portion 12B of the seat ring 12 covers the end surface of the cylindrical main body of the main body 11 and projects from the end surfaces of the valve shaft cylinder 13 and the main body 11 by the step α, the step α is Forming a compression margin for clamping by fastening both flanges 4, 4 and compressing at the time of clamping to seal the joint surface,
Moreover, it is possible to prevent excessive tightening exceeding the step α.

Further, the cylindrical portion 12 of the seat ring 12
The inner diameter d of A is limited to a size substantially equal to the inner diameter of the pipe 3, but the inclined step portion 12 is provided at both ends of the cylindrical portion 12A.
Since c is formed and a space is formed between the cylindrical portion 12A of the seat ring 12 and the end surface of the pipe 3, the flange 4 of the pipe 3 is pressure-bonded to the gasket portion 12B of the seat ring 12 to move the gasket portion 12B inward. Even if it tries to swell, an excessive load is not applied to the cylindrical portion 12A of the seat ring 12, and the cylindrical portion 12A does not bulge like the portion C of FIG. 8 (conventional example) described above. There is no abnormality in the opening / closing torque of the valve due to the rotation of 5.

[0030]

As described above, according to the present invention,
According to the invention of claim 1, a seat ring made of a cylindrical elastic material for covering the inner surface and both end surfaces of the main body is provided by connecting a valve shaft cylinder for inserting the drive side valve rod to the upper part of the cylindrical main body. In a butterfly valve, which is attached to form a fluid passage inside the seat ring and drives a disc-shaped valve element mounted in the fluid passage through a valve rod, the main body is made of aluminum or other material. In addition to being formed of a cast product, the valve shaft cylinder is formed of a molded product made of a resin material having a low heat conductivity and having a high heat insulating property, and the main body and the valve shaft cylinder are integrated by fusion bonding and the main body and By integrating the seat ring made of an elastic material by vulcanization joining, the following effects can be obtained.

(I) The valve shaft cylinder, which is apt to be exposed because the heat insulating coating is difficult, is made of a resin material having a low heat conductivity and having a high heat insulating property so as to be thermally insulated from the main body. Therefore, dew condensation does not occur on the valve cylinder and the actuator attached to the outer end of the valve cylinder.

(Ii) Since the valve shaft cylinder is integrally molded by fusion bonding with the main body made of a cast product made of aluminum or other casting material, the valve shaft cylinder is securely and stably connected to the valve shaft cylinder. It is possible to prevent deformation and damage of the valve shaft cylinder due to the operation torque associated with opening and closing.

(Iii) Since the main body and the seat ring are integrated by vulcanization joining, the main body can be easily manufactured by the method used for a part of the mold for forming the seat ring, and the main body is cast iron. It is lighter in weight compared to the one made and it is easy to handle, and the cylindrical part of the seat ring does not float up from the cylindrical main body of the main body when it is attached to the pipeline and in use, so part of the seat ring Excessive stress is not applied to the steel, and the durability is improved.

(Iv) Since the main body is made of a cast product such as aluminum or the like, the shape and dimensions of the inner and outer surfaces can be precisely formed by a die casting method or a precision casting method, and the obtained main body can be obtained. As described above, the seat ring is manufactured by using a part of the mold for molding the seat ring, and at the same time, the seat ring is joined to the inner surface of the cylindrical main body, so that the inner surface of the cylindrical main body of the main body as in the case of separately molding the seat ring There is no need to perform precision finishing by machining beforehand.

Further, in the invention of claim 2, the main body and the valve shaft cylinder have the same width, and the main body and the valve shaft cylinder are partly brought into contact with the flange surface at the same time during piping.
Since the body is made of a cast material that has a higher melting point than the resin material that forms the valve stem, the tightening stress of the flange that acts on the body during piping can be relieved to prevent deformation of the body and the valve that accompanies opening and closing of the valve. The torsion and bending stress of the barrel can be relieved.

Further, in the invention of claim 3, a plurality of concavo-convex portions capable of meshing with each other are formed on the inner surface of the cylindrical main body and the cylindrical outer surface of the seat ring, and both end portions of the cylindrical inner surface of the seat ring are formed. On the inner surface of the cylindrical main body by forming a step portion for enlarging the inner diameter, and providing a rotation receiving seat of the valve body on the inner surface of the cylinder so as to surround the valve rod insertion hole and project inward in the radial direction. Further, the physical joining that accompanies the concavo-convex portion formed on the outer surface of the cylindrical portion of the seat ring is added to the chemical joining that accompanies the vulcanizing joining, and the joining force between the main body and the seat ring is further improved.

Further, since the stepped portion for enlarging the inner diameter is formed at both ends of the inner surface of the cylindrical portion of the seat ring, when the flange portion of the seat ring is compressed by inserting the butterfly valve through the pipe line, Since the edge of the cylindrical portion of the ring does not bulge inward, and the rotation receiving seat of the valve body is provided inwardly so as to surround the insertion hole of the valve rod on the inner surface of the cylindrical portion, Smooth body rotation.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a butterfly valve according to an embodiment of the present invention when the butterfly valve is closed.

2 is a cross-sectional plan view of the main body base taken along the line AA of FIG.

FIG. 3 is a cross-sectional plan view showing another embodiment of the main body base portion.

FIG. 4 is a cross-sectional plan view showing still another embodiment of the main body base portion.

FIG. 5 is a vertical sectional side view of a main body base portion.

FIG. 6 is a vertical sectional side view showing another embodiment of the main body base portion.

FIG. 7 is a cross-sectional view of essential parts showing another embodiment of the present invention.

FIG. 8 is a sectional view of a main part of a conventional example.

FIG. 9 is a sectional view of a main part of a conventional example.

[Explanation of symbols]

 3 Pipe (pipe) 4 Pipe flange 5 Valve body 5a Upper side connection part 5b Lower side connection part 6,8 Valve rod 9 Fluid passage 10 Bearing 11 Main body 12 Seat ring 12A Cylindrical part 12B Gasket part 12a Cylindrical surface 12b Rotation receiving seat 12c Inclined Step portion 13 Valve shaft cylinder 13a Mounting flange 13b Cover 14 Valve rod insertion hole 15, 15A Concavo-convex portion 16 Valve rod insertion hole

Claims (3)

[Claims] 1. A seat ring made of a cylindrical elastic material for covering an inner surface and both end surfaces of the main body is provided by connecting a valve stem for axially inserting a drive side valve rod to an upper part of the cylindrical main body. Then, in the butterfly valve in which a fluid passage is formed inside the seat ring, and a disc-shaped valve body mounted in the fluid passage is driven via a valve rod, the main body is made of aluminum or another cast product. In addition to the above, the valve stem is formed of a molded product of a resin material having a low thermal conductivity and high heat insulation, and the main body and the valve stem are integrated by fusion bonding, and the main body and the elastic material are used. A butterfly valve that prevents dew condensation, characterized by being integrated with the configured seat ring by vulcanization joining. 2. The main body and the valve shaft cylinder have the same width so that a part of the main body and the valve shaft cylinder come into contact with the flange surface at the same time during piping, and the melting point is higher than that of the resin material forming the valve shaft cylinder. The butterfly valve according to claim 1, wherein the main body is made of a high casting material. 3. A step portion for forming an inner diameter on both ends of the cylindrical inner surface of the seat ring while forming a plurality of concavo-convex portions capable of meshing with each other on the inner surface of the cylindrical main body and the cylindrical outer surface of the seat ring. 3. The dew condensation according to claim 1 or 2, characterized in that a rotation receiving seat of the valve body is provided on the inner surface of the cylinder so as to surround the valve rod insertion hole and project inward in the radial direction. Prevented butterfly valve.