Butterfly Valve

Abstract

A butterfly valve provided with: a valve body in which an internal flow passage is formed; a seat ring attached to an inner peripheral surface of the internal flow passage; a valve shaft supported by the valve body so as to be able to rotate around an axis of rotation; and a valve element (19) supported on the valve body via the valve shaft so as to be able to rotate. The valve element (19) has an annular outer circumferential surface (45), and two valve shaft openings for enabling insertion of the valve shaft are formed at opposing positions in the rotation axis direction on the outer circumferential surface. Two annular opening raised parts (47), which extend along the circumferential edge of the respective valve shaft openings, and a circumferential raised portion (49), which extends so as to connect the two opening raised parts, are provided on the outer circumferential surface of the valve element, and the circumferential raised portion has a circumferential seal surface (49a) extending along the apex portion thereof, and chamfered surfaces (49b) extending obliquely on both sides of the circumferential seal surface.

Description

[Technical Field]

[0001] The present invention relates to a butterfly valve suitable for use in piping lines in various industries such as chemical plants, water supply and sewerage systems, agriculture and fisheries, semiconductor manufacturing, and food manufacturing. [Background technology]

[0002] A butterfly valve comprises a valve body having an internal flow passage formed therein, a seat ring attached to the inner circumferential surface of the internal flow passage of the valve body, a valve stem extending through the seat ring and rotatably supported by the valve body, and a valve disc disposed within the seat ring and fixedly attached to the valve stem so as to rotate together with the valve stem. The valve is opened and closed by rotating the valve disc about its axis of rotation within the valve body using the valve stem, and pressing the outer peripheral surface of the valve disc against and separating it from a valve seat provided on the inner circumferential surface of the seat ring.

[0003] The valve body is provided with a pair of bearing holes at radially opposite positions in the internal flow path for inserting and supporting the valve stem. The seat ring includes a generally cylindrical ring body extending in the central axis direction and annular flanges provided at both axial ends of the ring body and extending outward. The seat ring is attached to the inner circumferential surface of the internal flow path of the valve body by fitting the flanges of the seat ring into fitting recesses provided around the openings at both ends of the internal flow path of the valve body. The seat ring is provided with a pair of through holes at radially opposite positions in the ring body for passing the valve stem therethrough.

[0004] In such butterfly valves, the disc is positioned within a seat ring (more specifically, the ring body) attached to the inner periphery of the internal flow passage, and the seat ring forms a seal by tightly contacting the outer periphery of the disc with a valve seat surface formed on the inner periphery of the seat ring. To ensure a reliable seal between the disc's outer periphery and the seat ring's valve seat surface, the pressure pressing the outer periphery against the valve seat surface must be increased. However, increasing the pressure pressing the outer periphery against the valve seat surface increases the resistance when the disc is rotated to close the valve, thereby increasing the torque required to rotate the valve stem. To reduce this torque, a butterfly valve has been proposed, such as that described in Patent Document 1, in which the disc's outer periphery is formed in a spherical shape with a radius slightly larger than the distance from the center of the disc to the valve seat surface, allowing the outer periphery to smoothly contact the valve seat surface.

[0005] Furthermore, in butterfly valves, when the outer peripheral edge of the valve disc is pressed against the valve seat surface of the seat ring to form a seal, the effective surface pressure is low near the through hole through which the valve stem passes. As a result, even with the same compression rate of the seat ring, the sealing performance near the through hole is reduced, making leakage more likely. To address this issue, a butterfly valve has been proposed, such as that described in Patent Document 2, in which the outer periphery of the ring body of the seat ring is formed into an elliptical shape with the valve axis as the major axis and the inner periphery is formed into a circular shape, thereby increasing the crushing allowance around the through hole, thereby increasing the effective surface pressure near the through hole and improving sealing performance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-233294 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-183711 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, small-diameter butterfly valves employ a structure that combines an elliptical seat ring with a spherical outer peripheral surface. However, for large-diameter butterfly valves, machining the outer peripheral surface of the disc to a spherical shape is difficult and costly. Therefore, if the surface pressure of the disc's outer peripheral surface against the seat ring's valve seat is increased to ensure sufficient sealing performance, the resistance of the disc's outer peripheral surface against the seat ring's valve seat increases when the valve is closed, resulting in a problem of increased disc operating torque. Furthermore, when the side (corner) of the disc's outer peripheral surface comes into contact with the seat ring's valve seat when the valve is closed, the disc's operating torque increases.

[0008] Furthermore, if the surface pressure of the outer peripheral edge surface of the valve disc against the valve seat surface of the seat ring is reduced in order to reduce the operating torque, there is a problem in that the sealing performance around the through hole of the seat ring is reduced.

[0009] Therefore, an object of the present invention is to solve the problems present in the prior art and to ensure the necessary sealing performance between the valve disc and the valve seat surface, even in a large-diameter butterfly valve, while suppressing an increase in the operating torque of the valve disc when the valve is closed. [Means for solving the problem]

[0010] In view of the above object, the present invention provides a butterfly valve comprising: a valve body having an internal flow passage formed therein and extending in a flow passage axial direction; a seat ring attached to an inner peripheral surface of the internal flow passage; a valve stem supported by the valve body so as to be rotatable about a rotation axis; and a generally disk-shaped valve element connected to the valve stem, rotatably supported by the valve body, and disposed within the seat ring, the valve element being rotated about the rotation axis to move a peripheral edge portion of the valve element toward and away from the inner peripheral surface of the seat ring, thereby opening and closing the internal flow passage; two stem openings for inserting the stem at positions corresponding to the openings of the valve disc are formed; and the outer peripheral surface of the valve disc is further provided with two annular opening protrusions protruding from the outer peripheral surface and extending along the periphery of each stem opening; and a peripheral protrusion protruding from the outer peripheral surface and extending in the circumferential direction of the valve disc so as to connect the two opening protrusions; and the peripheral protrusions have a peripheral seal surface extending in an arc shape in the circumferential direction along the top thereof and flat in the width direction, and a chamfered surface inclined at a predetermined angle relative to the peripheral seal surface toward the outer peripheral surface of the valve disc and extending along both sides of the peripheral seal surface. the seat ring has an outer peripheral surface and an inner peripheral surface, and an annular protrusion that protrudes from the outer peripheral surface and extends annularly; an annular fitting groove that fits with the annular protrusion of the seat ring is provided on the inner peripheral surface of the internal flow path of the valve body; two bearing holes for inserting and supporting the valve shaft are opened at opposite positions in the rotation axis direction in the annular fitting groove; the annular fitting groove includes two opening groove portions provided on peripheral edges of the openings of the two bearing holes and two peripheral groove portions extending in the circumferential direction to connect the two opening groove portions; one of the two peripheral groove portions has a chamfered portion at an upper edge on the downstream side, and the other of the two peripheral grooves has a chamfered portion at an upper edge on the upstream side. To provide a butterfly valve.

[0011] In the butterfly valve, the peripheral ridge protruding from the outer peripheral surface of the disc has a flat peripheral seal surface extending circumferentially along its apex and chamfered surfaces extending along both sides of the peripheral seal surface and inclined at a predetermined angle relative to the peripheral seal surface toward the outer peripheral surface of the disc. The flat peripheral seal surface formed at the apex of the peripheral ridge of the disc is pressed against the inner peripheral surface of the seat ring, so that pressure from the peripheral ridge of the disc to the inner peripheral surface of the seat ring is concentrated on the peripheral seal surface, thereby increasing the sealing pressure. Furthermore, the formation of chamfered surfaces inclined relative to the peripheral seal surface along both sides of the peripheral seal surface reduces resistance when the valve disc rotates and the peripheral ridge comes into contact with the inner peripheral surface of the seat ring.

[0012] In the butterfly valve, the predetermined angle is preferably in the range of 15° to 30°. The width of the peripheral seal surface is preferably in the range of 3 mm to 10 mm. When the angle between the peripheral seal surface and the chamfered surface is in the above range, the operating torque can be particularly reduced. Furthermore, by setting the width of the peripheral seal surface in the above range, it is possible to achieve both the effect of concentrating the surface pressure on the peripheral seal surface and wear resistance in applications where the valve is repeatedly opened and closed.

[0014] In the above butterfly valve, The peripheral groove portion of the annular fitting groove has a rectangular cross section, the chamfered portion is formed by an inclined surface, and the angle formed by the inclined surface and the extension of the side surface of the peripheral groove portion is determined so as to match the rotation angle of the valve body when the peripheral seal surface of the peripheral protrusion of the valve body comes into contact with the inclined surface, when the rotation angle of the valve body when the butterfly valve is in a fully open state is set to 0°. I like I wish.

[0015] The present invention also provides a butterfly valve comprising: a valve body having an internal flow passage formed therein and extending in a flow passage axial direction; a seat ring attached to an inner circumferential surface of the internal flow passage; a valve stem supported by the valve body so as to be rotatable about a rotation axis; and a generally disk-shaped valve element connected to the valve stem, rotatably supported by the valve body, and disposed within the seat ring, the valve element being rotated about the rotation axis to move a peripheral edge of the valve element toward and away from the inner circumferential surface of the seat ring, thereby opening and closing the internal flow passage; the valve element having an annular outer circumferential edge surface extending in a circumferential direction, and two valve stem openings for inserting the valve stem therethrough formed at opposing positions on the outer circumferential edge surface in the rotation axis direction; the valve body further comprises two annular opening protrusions protruding from the peripheral surface and extending along the peripheral edges of the stem openings, and a peripheral protrusion protruding from the outer peripheral surface and extending in the circumferential direction of the valve body so as to connect the two opening protrusions; the peripheral protrusions have a peripheral seal surface extending in an arc shape in the circumferential direction along their tops and flat in the width direction, and chamfered surfaces inclined at a predetermined angle relative to the peripheral seal surface toward the outer peripheral surface of the valve body and extending along both sides of the peripheral seal surface; the seat ring has an outer peripheral surface and an inner peripheral surface, and an annular protrusion protruding from the outer peripheral surface and extending in an annular shape; and the inner peripheral surface of the internal flow path of the valve body is provided with an annular fitting groove that fits with the annular protrusion of the seat ring, The seat ring is formed with two through holes extending from the outer peripheral surface to the inner peripheral surface at positions opposite to each other in the rotation axis direction, for allowing the valve stem to pass therethrough. The inner peripheral surface of the seat ring is formed with two annular through hole seal surfaces extending planarly along the periphery of each through hole, a valve seat surface extending arcuately in the circumferential direction to connect the two through hole seal surfaces, and an inner peripheral transition surface connecting the through hole seal surfaces and the valve seat surface. The outer peripheral surface of the valve body is further formed with an annular opening seal surface extending to the top of the opening raised portion, and an outer peripheral transition surface connecting the opening seal surface and the peripheral seal surface. The inner peripheral transition surface extends arcuately so as to be coaxial with the through hole, and the inner peripheral transition surface comes into contact with the outer peripheral transition surface when the valve is closed. Offer butterfly valves . In the above butterfly valve, The valve seat surface formed on the inner circumferential surface of the seat ring has a concave shape that forms a part of a spherical surface. I like I wish.

[0016] Furthermore, it is preferable that the annular protrusion includes two annular through-hole protrusions provided on the outer peripheral surface of the seat ring at the periphery of each through-hole, and two outer peripheral protrusions extending circumferentially to connect the two through-hole protrusions, and that a protrusion seal surface extending parallel to the through-hole seal surface is formed at the top of each through-hole protrusion, and that the thickness from the through-hole seal surface to the protrusion seal surface is equal to the thickness from the valve seat surface of the seat ring to the top of the outer peripheral protrusion.

[0017] In addition, the seat ring is preferably provided with two through holes extending from the outer peripheral surface to the inner peripheral surface at positions opposite to each other in the direction of the rotation axis to allow the valve stem to pass therethrough, and the inner peripheral surface of the seat ring is preferably provided with two annular through hole sealing surfaces extending flatly on the peripheries of the through holes, and a valve seat surface extending in an arc shape in the circumferential direction to connect the two through hole sealing surfaces, and the width of the annular protrusion is preferably greater than the width of the valve seat surface.

[0018] In one embodiment of the butterfly valve, the valve body has a reduced thickness on its outer periphery, except for an area adjacent to the bearing hole, located on both sides of the rotation axis within a predetermined angle from the rotation axis around the center of the internal flow path, in which case the predetermined angle is preferably 40° to 60°. [Effects of the Invention]

[0019] In the butterfly valve according to the present invention, the flat peripheral seal surface formed on the top of the peripheral ridge of the disc presses against the inner peripheral surface of the seat ring. This concentrates the pressure from the peripheral ridge of the disc on the inner peripheral surface of the seat ring, thereby increasing the sealing pressure. As a result, it is possible to improve the sealing performance between the outer peripheral surface of the disc and the seating surface of the seat ring while minimizing the pressing force of the disc against the seating surface of the seat ring. In addition, by forming chamfers on both sides of the peripheral seal surface that are inclined relative to the peripheral seal surface, it is possible to reduce resistance when the disc rotates and the peripheral ridge contacts the inner peripheral surface of the seat ring. This reduces the operating torque required to rotate the disc by operating the valve stem and press the peripheral ridge of the disc against the inner peripheral surface of the seat ring. In this way, it is possible to ensure the necessary sealing performance between the disc and the seating surface while suppressing an increase in the operating torque of the disc when the valve is closed. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a longitudinal cross-sectional view of a butterfly valve according to an embodiment of the present invention in a closed state, as viewed from the axial direction of a flow channel. FIG. [Figure 2] FIG. 2 is a partially sectional perspective view showing the valve body of the butterfly valve shown in FIG. 1. [Figure 3] 2 is a partially enlarged perspective view showing the structure around the stem hole on the outer peripheral edge surface of the valve disc of the butterfly valve shown in FIG. 1. FIG. [Figure 4] 3 is a cross-sectional view of the valve body shown in FIG. 2 taken along a horizontal cross section passing through the center of the valve body. [Figure 5] FIG. 5 is an enlarged cross-sectional view showing the circled portion of the butterfly valve shown in FIG. 4. [Figure 6] FIG. 2 is a perspective view showing a seat ring of the butterfly valve shown in FIG. 1. [Figure 7] 7 is a partially enlarged perspective view showing the structure of the seat ring shown in FIG. 6 in the vicinity of the through-hole on the upper side in the figure, viewed from the inner peripheral side. FIG. [Figure 8]8 is a cross-sectional view showing the structure in the vicinity of the through-hole of the seat ring shown in FIG. 7. FIG. [Figure 9] 7 is a cross-sectional view showing the seat ring shown in FIG. 6 cut in half vertically. FIG. [Figure 10] 10 is an enlarged cross-sectional view showing the circled portion of the seat ring shown in FIG. 9. FIG. [Figure 11] 1 is an explanatory cross-sectional view showing a state in which the valve disc of the butterfly valve according to the present invention is rotated from an open state and the outer peripheral edge surface of the valve disc comes into contact with the valve seat surface of the seat ring. FIG. [Figure 12] FIG. 2 is a perspective view showing the overall configuration of a valve body of the butterfly valve shown in FIG. 1. [Figure 13] 2 is a cross-sectional view of the valve body of the butterfly valve shown in FIG. 1 taken along a horizontal cross section passing through the center of the internal flow path. [Figure 14] FIG. 14 is an enlarged cross-sectional view showing the circled portion shown in FIG. 13. [Figure 15] 10 is a line graph showing the relationship between the angle of the chamfered surface of the outer peripheral edge surface of the valve disc and the operating torque of the valve stem in a butterfly valve according to the present invention, obtained by simulation while changing the coefficient of friction between the valve disc and the seat ring. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of a butterfly valve 11 according to the present invention will be described with reference to the drawings, but it goes without saying that the present invention is not limited to this embodiment.

[0022] First, the overall configuration of a butterfly valve 11 will be described with reference to Figures 1 and 2. Figure 1 is a longitudinal cross-sectional view of the butterfly valve as viewed from the axial direction of the flow path, showing the closed state. Figure 2 is a partially cutaway perspective view of the valve body of the butterfly valve shown in Figure 1.

[0023] The butterfly valve 11 comprises a generally hollow cylindrical valve body 13 having an internal flow passage 13a extending in the axial direction of the flow passage, a valve stem 15 rotatably supported by the valve body 13, an annular seat ring 17 attached to the inner periphery of the internal flow passage 13a, a valve element 19 disposed within the internal flow passage 13a, connected to the valve stem 15, and supported by the valve body 13 so as to be rotatable about the rotation axis R, and a synthetic resin bushing 21 rotatably fitted onto the valve stem 15. The internal flow passage 13a can be opened and closed by moving the inner circumferential surface of the seat ring 17 and the outer circumferential edge of the valve element 19 toward and away from each other.

[0024] In the illustrated embodiment of the butterfly valve 11, the valve shaft 15 is composed of a first valve shaft 15a arranged on the upper side in Fig. 1 and a second valve shaft 15b arranged on the lower side in Fig. 1 along the rotation axis R, and the bushing 21 is also composed of a first bushing 21a rotatably fitted onto the first valve shaft 15a and a second bushing 21b rotatably fitted onto the second valve shaft 15b. The valve element 19 is rotatably supported on the valve body 13 by the first valve shaft 15a and the second valve shaft 15b via the first bushing 21a and the second bushing 21b, respectively. A drive unit (not shown) is connected to the first valve shaft 15a, and by rotating the first valve shaft 15a using the drive unit, the valve element 19 is rotated about the rotation axis R to open and close the valve. In the illustrated embodiment, the valve shaft 15 is composed of two valve shafts, a first valve shaft 15a and a second valve shaft 15b, but the first valve shaft 15a and the second valve shaft 15b may be integrally formed to form a single valve shaft 15. Similarly, the first bushing 21a and the second bushing 21b may be integrally formed to form a single bushing 21. The first valve shaft 15a and the second valve shaft 15b may be formed from a metal material such as cast iron, steel, carbon steel, copper, a copper alloy, brass, stainless steel, aluminum, or titanium, but the material is not particularly limited as long as it does not pose a problem in terms of strength.

[0025] The valve body 13 is made of a synthetic resin material. Examples of synthetic resin materials that can be used include polyvinyl chloride (PVC), polypropylene (PP), polyvinylidene fluoride (PVDF), polyethylene (PE), polyphenylene sulfide (PPS), polydicyclopentadiene (PDCPD), polytetrafluoroethylene (PTFE), acrylonitrile butadiene styrene (ABS resin), chlorinated polyvinyl chloride (PVC-C), perfluoroalkoxylalkane (PFA), polydicyclopentadiene (PDCPD), fiber-reinforced plastic (FRP), and other synthetic resin materials reinforced with glass fiber or the like. A substantially disk-shaped top flange 23 is provided at the top of the valve body 13. The valve body 13 also has a first bearing hole 25 and a second bearing hole 27 that face each other in the radial direction of the internal flow path 13a (the vertical direction in FIG. 1) and extend from the internal flow path 13a to the outside.

[0026] The first bearing hole 25 extends through the top flange 23. The first valve shaft 15a is inserted into the first bearing hole 25 with the first bushing 21a fitted thereon and is rotatably supported in the first bearing hole 25 via the first bushing 21a. The upper end of the first valve shaft 15a inserted into the first bearing hole 25 protrudes from the top flange 23 and can be connected to a drive unit installed on the top flange 23. The drive unit may be, for example, a lever-type drive unit, a gear-type drive unit, or an automatic drive unit. Meanwhile, the lower ends of the first valve shaft 15a and the first bushing 21a inserted into the first bearing hole 25 extend so as to protrude from the first bearing hole 25 toward the internal flow path 13a. Similarly, the second valve stem 15b is inserted into the second bearing hole 27 with the second bush 21b fitted thereon, and is rotatably supported in the second bearing hole 27 via the second bush 21b. The second bearing hole 27 has a lower end closed by a valve stem holder 29, and the lower ends of the second valve stem 15b and the second bush 21b inserted into the second bearing hole 27 abut against the valve stem holder 29. Meanwhile, the upper ends of the second valve stem 15b and the second bush 21b inserted into the second bearing hole 27 extend so as to protrude from the second bearing hole 27 toward the internal flow path 13a.

[0027] A reinforcing metal insert member 31 is included inside the valve body 13, spaced apart from and surrounding the first bearing hole 25 and the second bearing hole 27. The metal material used to form the insert member 31 is stainless steel for casting, but this is not limited thereto. The insert member 31 may be formed from another metal material similar to the valve stem 15, or from a non-metallic material, as long as it has a higher mechanical strength than the valve body 13.

[0028] In the embodiment shown in FIG. 1 , the insert member 31 has a generally cylindrical shape. Specifically, the insert member 31 includes a generally rectangular parallelepiped central portion, a cylindrical portion located farther from the internal flow path 13a than the central portion, and a base portion located closer to the internal flow path 13a than the central portion, larger than the cylindrical portion, and smaller than the central portion. A through-hole having a diameter larger than the first bearing hole 25 and the second bearing hole 27 is formed in the center of the cylindrical portion, the central portion, and the base. A bolt hole is formed in the central portion for threading a bolt when connecting the valve body 13 to a pipe. The insert member 31 having such a shape is disposed radially outward of the first bearing hole 25 and the second bearing hole 27 and spaced apart from each other. The reason the insert member 31 is embedded in the valve body 13 and not exposed in the first bearing hole 25 and the second bearing hole 27 is to prevent the metallic insert member 31 from coming into contact with the liquid even if a corrosive fluid enters the first bearing hole 25 and the second bearing hole 27.

[0029] The seat ring 17 is formed from an elastic material such as ethylene propylene rubber (EPDM), chloroprene rubber (CR), isoprene rubber (IR), chlorosulfonated rubber (CSM), nitrile rubber (NBR), styrene butadiene rubber (SBR), chlorinated polyethylene (CM), fluororubber (FKM), hydrogenated acrylonitrile butadiene rubber (HNBR), urethane rubber (U), silicone rubber (VMQ, FVMQ), ethylene propylene rubber (EPM), acrylic rubber (ACM), butyl rubber (IIR), or a material in which such an elastic member is coated with a fluororesin. However, these elastic materials are merely examples, and the material is not particularly limited as long as it does not pose a problem in terms of strength and corrosion resistance in the intended use. The seat ring 17 includes a ring body 17a having a generally cylindrical shape and extending in the central axis direction, and flange portions 17b (see FIG. 3) extending outward from both axial ends of the ring body 17a in opposition to each other, and a pair of through holes 17c, 17c are formed at radially opposing positions in the ring body 17a, through which the first valve shaft 15a and the second valve shaft 15b pass, respectively. Furthermore, the outer peripheral edge of the valve element 19 abuts against the inner peripheral surface of the ring body 17a, thereby sealing the gap between the inner peripheral surface of the seat ring 17 and the outer peripheral edge of the valve element 19, and the valve element 19 can close the internal flow path 13a.

[0030] The valve element 19 is disposed inside a seat ring 17 attached to the inner circumferential surface of the internal flow path 13a of the valve body 13. The valve element 19 is integrally formed from a contour-forming member 33 made of a synthetic resin material and having a generally disk-shaped outer shape, and a core member 35 made of a metal material and surrounded by the contour-forming member 33. The valve element 19 in this embodiment is molded by injecting the synthetic resin material forming the contour-forming member 33 into an injection mold in which the core member 35 is previously installed. In this embodiment, the contour-forming member 33 is formed from PVDF, which has high chemical resistance, but is not limited thereto. Other synthetic resin materials, such as PP, PVC, PE, PFA, and PDCPD, can also be used. In this embodiment, the core member 35 is formed from a casting aluminum alloy, but is not limited thereto. The core member 35 may be formed from a metal material similar to the valve stem, or from a non-metallic material, as long as it has a higher mechanical strength than the contour-forming member 33.

[0031] A first valve stem hole 37 and a second valve stem hole 39 are provided on the outer periphery of the valve body 19 at opposing positions along the rotation axis R, and the first valve stem hole 37 and the second valve stem hole 39 are formed coaxially with the rotation axis R. When the first valve stem 15a and the second valve stem 15b are integrally formed and the valve stem 15 is formed by a single valve stem 15, the first valve stem hole 37 and the second valve stem hole 39 are also formed as a single through-hole.

[0032] The first stem hole 37 includes a first large-diameter hole portion 37a having a relatively large diameter and including an open end (an opening to the internal flow path 13a), and a first small-diameter hole portion 37b having a relatively small diameter and extending further inward in the direction of the rotation axis R from the first large-diameter hole portion 37a. The inner circumferential surface of the first large-diameter hole portion 37a is formed by the contour forming member 33, while the inner circumferential surface of the first small-diameter hole portion 37b is formed by the core material 35. The first stem hole 37 receives the first stem 15a and the first bushing 21a, which protrude from the first bearing hole 25 of the valve body 13 and pass through the through-hole 17c of the seat ring 17. The first large-diameter hole portion 37a of the first stem hole 37 supports the first stem 15a via the first bushing 21a. The first bushing 21a is not inserted into the first small diameter hole 37b, but rather the tip end portion of the first valve shaft 15a (hereinafter referred to as the tip end) is directly inserted into the first small diameter hole 37b, so that the tip end of the first valve shaft 15a is non-rotatably fitted into the first small diameter hole 37b around the rotation axis R. For example, the tip end of the first valve shaft 15a and the first small diameter hole 37b can be non-rotatably fitted into each other by forming them to have complementary polygonal shapes or circular shapes with two chamfered sides. However, the method of fitting the first valve shaft 15a and the first small diameter hole 37b into each other is not limited as long as the tip end of the first valve shaft 15a and the first small diameter hole 37b can be non-rotatably fitted into each other.

[0033] Similar to the first stem hole 37, the second stem hole 39 also includes a second large-diameter hole portion 39a with a relatively large diameter including an open end (an opening to the internal flow path 13a), and a second small-diameter hole portion 39b with a relatively small diameter extending further inward in the direction of the rotation axis R from the second large-diameter hole portion 39a. The inner circumferential surface of the second large-diameter hole portion 39a is formed by the contour forming member 33, while the inner circumferential surface of the second small-diameter hole portion 39b is formed by the core material 35. The second stem hole 39 receives the second stem 15b and the second bushing 21b, which protrude from the second bearing hole 27 of the valve body 13 and pass through the through-hole 17c of the seat ring 17. The second large-diameter hole portion 39a of the second stem hole 39 supports the second stem 15b via the second bushing 21b. The second bushing 21b is not inserted into the second small diameter hole 39b, but rather the tip end portion of the second valve stem 15b (hereinafter referred to as the tip end portion) is directly inserted and fitted into the second small diameter hole 39b. The second small diameter hole 39b has a circular cross-sectional shape because there is no need to transmit rotational torque between the second valve stem 15b and the second small diameter hole 39b, and in this respect it differs from the first small diameter hole 37b of the first valve stem hole 37. However, the second small diameter hole 39b may also have a configuration similar to that of the first small diameter hole 37b.

[0034] In the following description, the contour forming member 33 surrounding the first large diameter hole portion 37a and the second large diameter hole portion 39a, which forms the inner peripheral surfaces of these portions, may be specifically referred to as "axial hole forming portion 41".

[0035] As described above, the first stem hole 37 and the second stem hole 39 have similar configurations except for the different cross-sectional shapes of their first small-diameter hole portion 37b and second small-diameter hole portion 39b. Therefore, in the following explanation, the first stem hole 37 will be mainly used as a representative. The first stem 15a will be used as a representative for the stem, and the first bush 21a will be used as a representative for the bush. However, the explanations regarding the first stem 15a, the first bush 21a, and the first stem hole 37 can be applied to the second stem 15b, the second bush 21b, and the second stem hole 39, respectively. Furthermore, for simplicity, the ordinal number "first" included in the names of each component will be omitted. However, this does not apply when it is necessary to distinguish between "first" and "second."

[0036] In this embodiment, the bushings 21 (first bushing 21a and second bushing 21b) are made of PVDF, which has high resistance to corrosive fluids. A plurality of seal members 43, such as O-rings, are provided on the outer circumferential surface of the bushing 21a to prevent fluid from entering the interior of the valve body 19 and contacting the valve stem 15. In the embodiment shown in Fig. 1, four seal members 43 are arranged in the portion of the bushing 21a that is inserted into the large-diameter hole portion 37a of the valve stem hole 37.

[0037] The core material 35 includes a central portion 35a and roughly lattice-shaped main reinforcing portions 35b symmetrically arranged around the central portion 35a. The upper and lower ends of the central portion 35a are provided with roughly cylindrical shaft hole reinforcing portions 35c, 35c, respectively. In the illustrated embodiment, the shaft hole reinforcing portions 35c, 35c have a shape in which holes with diameters larger than the first and second valve shaft holes 37, 39 are formed in roughly rectangular parallelepiped portions provided at the upper and lower ends of the central portion 35a. Preferably, the shaft hole reinforcing portion 35c and the central portion 35a have the same outer shape. The shaft hole reinforcing portion 35c extends into the shaft hole constituent portion 41 that constitutes the large diameter hole portion 37a and surrounds at least a portion of the radially outer side of the large diameter hole portion 37a in the rotational axis direction, reinforcing the shaft hole constituent portion 41, which is made of a synthetic resin material. When the large-diameter hole portion 37a supports the shear force and bending moment generated on the valve disc 19 due to fluid pressure, the shaft hole reinforcing portion 35c supports the force acting from the valve stem 15 on the large-diameter hole portion 37a and the shaft hole constituent portion 41, thereby suppressing deformation of the shaft hole constituent portion 41. As a result, the seal formed by the seal member 43 between the inner circumferential surface of the large-diameter hole portion 37a and the outer circumferential surface of the bushing 21a can be reliably maintained. As shown in FIGS. 1 and 2, the shaft hole reinforcing portion 35c preferably has multiple through-holes 35d penetrating its inner and outer circumferential surfaces. These through-holes 35d function as passages for the synthetic resin material forming the shaft hole constituent portion 41 when the core 35 is placed in a mold and the profile-forming member 33 is injection-molded, thereby suppressing injection molding defects.

[0038] The shaft hole reinforcing portion 35c surrounds the radially outer side of the first valve stem hole 37 and the second valve stem hole 39, is disposed at a distance from the inner circumferential surfaces of the first valve stem hole 37 and the second valve stem hole 39, and is configured to be embedded in the shaft hole forming portion 41 so as not to be exposed inside the first valve stem hole 37 and the second valve stem hole 39. This is to prevent the metallic shaft hole reinforcing portions 35c, 35c from coming into contact with the liquid even if a corrosive fluid enters the first large diameter hole portion 37a of the first valve stem hole 37 and the second large diameter hole portion 39a of the second valve stem hole 39.

[0039] The butterfly valve 11 further includes a characteristic structure (hereinafter referred to as the "torque reduction structure") for reducing the operating torque required when rotating the valve element 19 around the rotation axis R to close the internal flow path 13a with the valve element 19, and a structural feature (hereinafter referred to as the "sealability improvement structure") for improving the sealing performance between the inner surface of the seat ring 17 and the outer peripheral edge of the valve element 19 when the valve is closed.

[0040] The torque reduction structure and the sealing performance improvement structure will be described in detail below with reference to Figures 3 to 14. Note that the structure of the inner circumferential surface of internal flow path 13a of valve body 13, the structure of seat ring 17, and the structure of the outer circumferential edge portion of valve element 19 are symmetrical between the upper and lower portions of butterfly valve 11 in Figure 1, so the following description will mainly focus on the upper portion, but the lower portion has a similar structure, and the following description also applies to the structure of the lower portion.

[0041] First, the structure of the valve body 19 related to the torque reduction structure and the sealing performance improvement structure will be described in detail with reference to FIGS.

[0042] The disk-shaped valve disc 19 (more specifically, its profile-forming member 33) has an outer peripheral surface 45 extending in the circumferential direction at its peripheral edge, and a first valve stem hole 37 and a second valve stem hole 39 are provided on the outer peripheral surface 45 at opposite positions in the rotational axis direction. The first valve stem hole 37 and the second valve stem hole 39 open into the outer peripheral surface 45 of the valve disc 19, forming two valve stem openings (only the valve stem hole opening 38 of the first valve stem hole 37 is shown in FIG. 3 ). Furthermore, the outer peripheral surface 45 of the valve disc 19 is provided with a raised portion that protrudes radially outward from the outer peripheral surface 45. The raised portion includes two opening raised portions 47 that extend annularly along the peripheries of the two valve stem openings on the outer peripheral surface 45, and two peripheral raised portions 49 that extend in an arc along the outer peripheral surface 45 of the valve disc to connect the two opening raised portions 47.

[0043] The peripheral raised portion 49 has a peripheral seal surface 49a extending along its top and chamfered surfaces 49b extending along both sides of the peripheral seal surface 49a. As shown in Figures 4 and 5, the peripheral seal surface 49a is formed in an arc shape of the same radius in the circumferential direction of the valve disc 19 and extends flatly in the width direction (the direction of the flow path axis when the valve disc 19 is rotated to the closed state). The chamfered surface 49b is an inclined surface that extends at a predetermined angle relative to the peripheral seal surface 49a toward the outer peripheral surface 45 of the valve disc 19. By providing the chamfered surfaces 49b on both sides of the peripheral seal surface 49a at the top of the peripheral protrusion 49, the torque required to rotate the valve disc 19 can be reduced when the valve disc 19 is rotated around the rotation axis R and the peripheral seal surface 49a of the peripheral protrusion 49 is pressed against a valve seat surface 17d (described later) provided on the seat ring 17 attached to the inner circumferential surface of the internal flow path 13a of the valve body 13. Similarly, the opening protrusion 47 has a planar opening seal surface 47a extending annularly along its top, and chamfered surfaces 47b extending along both sides (inner and outer sides) of the annular opening seal surface 47a. The opening seal surface 47a is formed so that the entire surface lies in the same plane. The chamfered surfaces 47b are inclined at a predetermined angle relative to the opening seal surface 47a toward the outer circumferential surface 45 of the valve disc 19. The flat opening seal surface 47a and the arcuate peripheral seal surface 49a are smoothly connected by an outer peripheral transition surface 51 that is provided therebetween and curved so that the curvature changes with the same width as the peripheral seal surface 49a.

[0044] The angle formed by the chamfered surface 47b with respect to the opening seal surface 47a and the angle formed by the chamfered surface 49b with respect to the peripheral seal surface 49a are preferably selected from the range of 15° to 30°, and more preferably selected from the range of 20° to 25°, because this effectively reduces the operating torque required to rotate the valve element 19 by the valve stem 15. If the angle is less than 15°, friction between the chamfered surface 49b and the valve seat surface 17d increases, resulting in an increase in operating torque. If the angle is greater than 30°, the amount of contact (contact area) between the chamfered surface 49b and the valve seat surface 17d becomes significant, and the corners between the peripheral seal surface 49a and the chamfered surface 49b press into the valve seat surface 17d and bite into it, increasing resistance and resulting in an increase in operating torque. When the angle is between 15° and 30°, the chamfered surface 47b functions as a guide, allowing the peripheral protrusion 49 to smoothly engage with the valve seat surface 17d, thereby reducing operating torque. Furthermore, when the angle is 20° or greater, the surface pressure of the peripheral seal surface 49a increases, improving sealing performance. When the angle is 25° or less, the amount of contact (contact area) between the chamfered surface 49b and the valve seat surface 17d increases, reducing the resistance of the peripheral seal surface 49a to the valve seat surface 17d and suppressing wear of the peripheral seal surface 49a. Furthermore, the opening seal surface 47a and the peripheral seal surface 49a are primarily in contact with the through-hole seal surface 61 and the valve seat surface 17d of the seat ring 17, respectively, as described below. Therefore, as the widths of the opening seal surface 47a and the peripheral seal surface 49a become narrower, the surface pressure between the through-hole seal surface 61 and the valve seat surface 17d and the valve disc 19 increases, improving sealing performance, but reducing wear resistance. Since butterfly valve 11 is expected to be used in applications where it will be opened and closed repeatedly, in order to achieve both sealing performance and wear resistance, it is preferable that the widths of opening seal surface 47a and peripheral seal surface 49a be selected from the range of 3 mm to 10 mm.

[0045] As described above, the seat ring 17 includes a ring body 17a having a generally cylindrical shape extending in the central axis direction, and flange portions 17b extending outward from both axial ends of the ring body 17a in a manner opposing each other. As shown in Fig. 6, the ring body 17a has an outer peripheral surface 53 and an inner peripheral surface 55. Two through holes 17c, 17c extending from the outer peripheral surface 53 to the inner peripheral surface 55 are formed in opposing positions in the direction of the rotation axis R of the ring body 17a to allow the valve shaft 15 to pass therethrough. In addition, an annular protrusion 57 is provided at the center of the outer peripheral surface 53 in the width direction (i.e., the central axis direction) and protrudes from the outer peripheral surface 53 and extends annularly in the circumferential direction of the outer peripheral surface 53.

[0046] The inner peripheral surface of the through hole 17c of the seat ring 17 shown in FIG. 6 is formed by a flat circumferential surface, but a plurality of annular ribs may be provided on the inner peripheral surface of the through hole 17c to improve the sealing performance between the outer peripheral surface of the valve stem 15 inserted into the through hole 17c and the inner peripheral surface of the through hole 17c.

[0047] The annular protrusion 57 is fitted into an annular fitting groove provided on the inner circumferential surface of the internal flow path 13a of the valve body 13, which will be described later, and functions to prevent the seat ring 17 from moving in the flow path axial direction. The annular protrusion 57 includes two through-hole protrusions 57a, 57a provided on the periphery surrounding each opening of the two through-holes 17c, 17c on the outer circumferential surface 53, and two outer circumferential protrusions 57b, 57b extending in an arc shape in the circumferential direction of the ring body 17a to connect the two through-hole protrusions 57a, 57a. The outer circumferential protrusions 57b have a rectangular cross section, and their top surfaces are flat (i.e., at the same height from the outer circumferential surface 53) in the width direction (the direction of the central axis of the ring body 17a) and extend in an arc shape in the circumferential direction. A flat protrusion seal surface 59 is formed at the top of the through-hole protrusion 57a ​​and is positioned in the same plane, and the protrusion seal surface 59 is connected to the top surface of the outer peripheral protrusion 57b, which is flat in the width direction.

[0048] As shown in FIGS. 7 and 8 , the inner circumferential surface 55 is provided with two annular through-hole seal surfaces 61, 61 extending along the periphery (periphery) surrounding the openings of the two through-holes 17c, 17c (the openings toward the internal flow path 13a). A valve seat surface 17d extends in an arc shape around the circumferential direction of the inner circumferential surface 55 to connect the two through-hole seal surfaces 61, 61. An inner circumferential transition surface 63 connects the through-hole seal surface 61 and the valve seat surface 17d. The annular through-hole seal surface 61 is formed flat so as to lie on the same plane and extends parallel to a protrusion seal surface 59 formed on the outer circumferential surface 53 around the periphery of the opening of the through-hole 17c. The thickness from the through-hole seal surface 61 to the protrusion seal surface 59 is set equal to the thickness from the valve seat surface 17d on the inner circumferential surface 55 of the seat ring 17 to the top surface of the outer circumferential protrusion 57b on the outer circumferential surface 53. The thickness from the through-hole seal surface 61 to the protrusion seal surface 59 is equal to the thickness from the valve seat surface 17d to the top surface of the outer peripheral protrusion 57b to ensure that the protrusion on the outer peripheral edge surface 45 of the valve disc 19 uniformly compresses the seat ring 17 when the valve is closed. The thickness from the valve seat surface 17d to the top surface of the outer peripheral protrusion 57b is measured at the shortest point between the valve seat surface 17d and the outer peripheral protrusion 57b. As shown in Figures 9 and 10, the valve seat surface 17d has a concave shape that forms part of a sphere centered at the center (center in the diameter and width directions) of the ring body 17a. The inner peripheral transition surface 63 is positioned so as to contact the outer peripheral transition surface 51 when the valve is closed, and extends in an arc shape with a predetermined width so as to be coaxial with the through-hole 17c.

[0049] The annular protrusion 57 on the outer surface 53 of the seat ring 17 is positioned radially opposite the valve seat surface 17d provided on the inner surface 55 of the ring body 17a. When the valve is closed, the opening seal surface 47a of the opening raised portion 47 of the valve element 19 and the peripheral seal surface 49a of the peripheral raised portion 49 are pressed against the through-hole seal surface 61 of the seat ring 17 and the valve seat surface 17d, respectively. This causes the areas between the through-hole seal surface 61 of the seat ring 17 and the protrusion seal surface 59, and between the valve seat surface 17d and the top surface of the outer protrusion 57b, to elastically compress, thereby creating a seal between the outer edge of the valve element 19 and the inner surface 55 of the seat ring 17. In conventional butterfly valve seat rings, the through-hole protrusions protrude more from the outer periphery and are thicker than the outer periphery protrusions of the annular protrusions, which causes the seat ring to be crushed differently at the portions with the outer periphery protrusions and the portions with the through-hole protrusions when the valve is closed, resulting in varying crush rates at different circumferential locations on the seat ring and non-uniform sealing performance. However, in the butterfly valve 11, the thickness from the through-hole seal surface 61 to the protrusion seal surface 59 of the through-hole protrusions 57a is the same as the thickness from the valve seat surface 17d of the ring body 17a of the seat ring 17 to the top surface of the outer periphery protrusions 57b. This results in the same crush rate at the portions with the outer periphery protrusions 57b and the through-hole protrusions 57a when the valve is closed, and the crush rate does not vary at different circumferential locations on the seat ring 17. Therefore, the butterfly valve 11 has the effect of ensuring uniform sealing between the outer peripheral edge of the valve body 19 and the inner peripheral surface 55 of the seat ring 17 in the circumferential direction regardless of the location.

[0050] In the butterfly valve 11, the inner peripheral transition surface 63 on the inner peripheral surface 55 of the seat ring 17 is positioned so as to contact the outer peripheral transition surface 51 of the raised portion on the outer peripheral edge surface 45 of the valve disc 19 when the valve is closed. Furthermore, the outer peripheral transition surface 51 has the same width as the peripheral seal surface 49a, so that the contact width with the inner peripheral transition surface 63 is small, and the inner peripheral transition surface 63 extends in an arc shape so as to be coaxial with the through hole 17c. The outer peripheral transition surface 51, which is positioned on the raised portion of the valve disc 19, rotates around the rotation axis R as the valve disc 19 rotates. Therefore, in a conventional butterfly valve in which the outer peripheral transition surface 51 is wide and the valve seat surface 17d is cylindrical rather than concave and partially spherical, the outer peripheral transition surface 51 and the inner peripheral transition surface 63 intersect with each other until just before the valve is closed. As a result, the collapse rate tends to be uneven near the inner transition surface 63 of the seat ring 17 until the valve is closed. Furthermore, even a slight deviation in the rotation angle of the valve element 19 when the valve is closed will cause the collapse rate to be uneven near the inner transition surface 63. However, in the butterfly valve 11, the width of the outer transition surface 51 is narrow, and the inner transition surface 63 extends in an arc shape so as to be coaxial with the through hole 17c. Therefore, as the valve element 19 rotates to the closed state, the outer transition surface 51 moves along the inner transition surface 63, which makes it less likely that the collapse rate will be uneven.

[0051] 9 and 10, in the seat ring 17 of the butterfly valve 11, the width of the outer peripheral protrusion 57b of the annular protrusion 57 (the length in the central axis direction of the ring body 17a) is set to be wider than the width of the valve seat surface 17d. If the width of the valve seat surface 17d were wider than the width of the outer peripheral protrusion 57b, when the peripheral seal surface 49a of the peripheral raised portion 49 on the outer peripheral edge surface 45 of the valve disc 19 begins to contact the valve seat surface 17d, the outer peripheral protrusion 57b of the annular protrusion 57 may not be present between the inner circumferential surface of the internal flow path 13a of the valve body 13 and the contact portion between the peripheral seal surface 49a of the valve disc 19 and the valve seat surface 17d of the seat ring 17 attached to the inner circumferential surface of the internal flow path 13a. In this case, when the outer peripheral protrusion 57b of the annular protrusion 57 transitions to a state in which it is between the inner peripheral surface of the internal flow passage 13a of the valve body 13, to which the seat ring 17 is attached, and the contact area between the peripheral seal surface 49a and the valve seat surface 17d, the amount of compression of the seat ring 17 changes discontinuously depending on the rotational position of the valve disc 19, resulting in discontinuous changes in the operating torque and sealing performance of the valve disc 19. However, in the butterfly valve 11, the width of the outer peripheral protrusion 57b is wider than the width of the valve seat surface 17d. As a result, as shown in FIG. 11 , when the peripheral seal surface 49a of the peripheral raised portion 49 on the outer peripheral surface 45 of the valve disc 19 begins to contact the valve seat surface 17d of the seat ring 17, the outer peripheral protrusion 57b of the annular protrusion 57 is always between the inner peripheral surface of the internal flow passage 13a of the valve body 13, to which the seat ring 17 is attached, and the contact area between the peripheral seal surface 49a and the valve seat surface 17d. Therefore, after the peripheral seal surface 49a of the valve element 19 abuts against the valve seat surface 17d of the seat ring 17 when the valve is closed, the amount of compression of the seat ring 17 changes little depending on the rotational position of the valve element 19, and the operating torque and sealing performance of the valve element 19 also change little.

[0052] As shown in Figure 12, the valve body 13 has a generally cylindrical shape with an internal flow path 13a formed in the center. A first bearing hole 25 and a second bearing hole 27 are formed to extend opposite each other in the radial direction of the internal flow path 13a (the up-and-down direction in Figure 12). A top flange 23 is provided at the top of the valve body 13, and the first bearing hole 25 penetrates the top flange 23 and extends to the outside. The lower end of the second bearing hole 27 is closed by a valve stem holder 29.

[0053] An annular fitting groove 65 into which the annular protrusion 57 of the seat ring 17 is fitted is provided on the inner peripheral surface of the internal flow path 13a of the valve body 13. The annular fitting groove 65 has a shape complementary to the annular protrusion 57 of the seat ring 17. More specifically, the annular fitting groove 65 includes an open groove portion 65a having a flat groove bottom surface formed around the openings of the first bearing hole 25 and the second bearing hole 27 to the internal flow path 13a, and peripheral groove portions 65b, 65b having two curved bottom surfaces extending in an arc and complementary to the peripheral protrusion 57b, connecting the two open groove portions 65a, 65a. The peripheral groove portion 65b has a generally rectangular cross section complementary to the peripheral protrusion 57b.

[0054] As shown in Figure 12, the outer periphery of the valve body 13 is recessed to reduce weight. However, certain areas near the first bearing hole 25 and the second bearing hole 27 are not recessed and are made thicker than the remaining parts. This is to suppress deformation of the valve body 13, which tends to expand in the direction of the rotation axis R and contract in the diametric direction of the internal flow path 13a perpendicular to the rotation axis R when the valve disc 19 is pressed into the internal flow path 13a (more specifically, inside the seat ring 17 attached to the inner circumferential surface of the internal flow path 13a). The areas without recessed parts are preferably located on both sides of the rotation axis R within a range of 40° to 60° from the rotation axis R around the center of the internal flow path 13a.

[0055] In the annular fitting groove 65, one of the two peripheral groove portions 65b, 65b is located downstream of the internal flow path 13a, and a chamfered surface 67 is provided at the upper edge of the peripheral groove 65b (an edge adjacent to the peripheral groove 65b on the inner circumferential surface located downstream of the peripheral groove 65b in the internal flow path 13a), and the other of the two peripheral groove portions 65b, 65b is located upstream of the internal flow path 13a, and the provision of such a chamfered surface 67 forms a space between the inner circumferential surface of the internal flow path 13a and the outer circumferential surface of the seat ring 17 when the annular protrusion 57 is fitted into the annular fitting groove 65 and the seat ring 17 is attached to the inner circumferential surface of the internal flow path 13a, thereby providing a clearance for the seat ring 17 to deform. Therefore, by providing the chamfered surface 67 on the side where the outer peripheral edge of the valve disc 19 rotates about the rotation axis R and enters the valve seat surface 17d of the seat ring 17 when the valve disc 19 is switched from the open state to the closed state, a relief space can be provided for deformation of the seat ring 17 when the peripheral seal surface 49a of the peripheral protrusion 49 of the valve disc 19 begins to abut against the valve seat surface 17d (i.e., when seated). As a result, it is possible to suppress the phenomenon in which the operating torque of the valve stem 15 increases suddenly before the valve is fully closed, thereby improving operability. The chamfered surface 67 is preferably formed as an inclined surface. Furthermore, it is more preferable that the angle formed by the inclined surface and the extension of the side surface of the peripheral groove 65b is set so that, when the rotation angle of the valve disc 19 in the fully open state of the butterfly valve is set to 0°, the angle of the valve disc 19 when the peripheral seal surface 49a of the peripheral protrusion 49 of the valve disc 19 comes into contact with the inclined chamfered surface 67 coincides with the rotation angle of the valve disc 19. For example, the angle formed between the inclined surface and the extension of the side surface of the peripheral groove portion 65b may be set to 80° to 85°.

[0056] The chamfered surface 67 may be provided on the upper edge end portion on both sides of the peripheral groove portion 65b of the annular fitting groove 65. However, in order to avoid reducing the effect of preventing the annular protrusion 57 of the seat ring 17 from moving in the axial direction of the flow passage relative to the annular fitting groove 65, it is preferable to provide the chamfered surface 67 on only one upper edge end portion of the peripheral groove portion 65b. [Example]

[0057] 15 is a line graph showing the relationship between the angle of the chamfered surface 49b of the peripheral ridge 49 on the outer peripheral surface 45 of the disc 19 in a butterfly valve 11 according to the present invention and the operating torque of the valve stem 15, as determined by simulation while changing the coefficient of friction between the disc 19 and the seat ring 17. The simulation was performed under the following conditions: the width of the peripheral seal surface 49a of the peripheral ridge 49 was 4 mm, the chamfered surface 49b was positioned 3 mm vertically away from the peripheral seal surface 49a, and the peripheral ridge 49 was pressed against the valve seat surface 17d of the seat ring 17 while compressing it by 3 mm. The operating torque of the disc 19 was determined when the angle of the chamfered surface 49b (the angle that the chamfered surface 49b makes toward the outer peripheral surface 45 relative to the peripheral seal surface 49a) was changed. It was also assumed that the seat ring 17 was made of EPDM, and the disc 19 was made of PP. Furthermore, the simulation was performed when the coefficient of friction between the valve disc 19 and the seat ring 17 was 0.1 and 0.2. When the coefficient of friction was 0.1, the simulation was also performed under the condition that the amount by which the peripheral ridge 49 pressed against the valve seat surface 17d of the seat ring 17 was set to 2.5 mm.

[0058] 15, regardless of the friction coefficient conditions or the amount of compression conditions, it is clear that the operating torque can be kept low when the angle of the chamfered surface 49b is in the range of 15° to 30°. Therefore, in the butterfly valve 11, it is preferable to set the angle of the chamfered surface 49b in the range of 15° to 30°.

[0059] Although the butterfly valve 11 according to the present invention has been described above with reference to the illustrated embodiment, the present invention is not limited to the illustrated embodiment. For example, in the illustrated embodiment, the valve element 19 is rotatably supported on the valve body 13 by two valve shafts 15a, 15b, but the valve element 19 may be supported on the valve body 13 by a single valve shaft 15. [Explanation of symbols]

[0060] 11 Butterfly valve 13 Valve body 13a Internal flow path 15 Valve stem 15a First valve stem 15b Second valve stem 19 Valve body 45 Outer peripheral surface 47 Opening ridge 47a Opening seal surface 47b Chamfered surface 49 Peripheral ridge 49a Peripheral sealing surface 49b Chamfered surface 51 Outer transition surface 53 Outer surface 55 Inner surface 57 Annular protrusion 57a Through hole protrusion 57b Outer protrusion 59 Protrusion sealing surface 61 Through-hole sealing surface 63 Inner transition surface 65 Fitting groove 65a Opening groove 65b Peripheral groove 67 Chamfered surface

Claims

1. a valve body having an internal flow passage extending in a flow passage axial direction; a seat ring attached to an inner circumferential surface of the internal flow passage; a valve stem supported by the valve body so as to be rotatable about a rotation axis; and a generally disk-shaped valve element connected to the valve stem, rotatably supported by the valve body, and disposed within the seat ring, wherein the valve element is rotated about the rotation axis to move a peripheral edge of the valve element toward and away from the inner circumferential surface of the seat ring, thereby opening and closing the internal flow passage, the valve disc has an annular outer peripheral surface extending in a circumferential direction, and two stem openings for inserting the valve disc are formed on the outer peripheral surface at opposite positions in the direction of the rotation axis, and the outer peripheral surface of the valve disc is further provided with two annular opening protrusions protruding from the outer peripheral surface and extending along the peripheries of the stem openings, and a peripheral protrusion protruding from the outer peripheral surface and extending in the circumferential direction of the valve disc so as to connect the two opening protrusions, and the peripheral protrusions have a peripheral seal surface that extends in an arc shape in the circumferential direction along its top and flat in the width direction, and a chamfered surface that is inclined at a predetermined angle relative to the peripheral seal surface toward the outer peripheral surface of the valve disc and extends along both sides of the peripheral seal surface, the seat ring has an outer peripheral surface and an inner peripheral surface, and an annular protrusion that protrudes from the outer peripheral surface and extends annularly, and an annular fitting groove that fits with the annular protrusion of the seat ring is provided on an inner peripheral surface of the internal flow path of the valve body, a butterfly valve characterized in that two bearing holes for inserting and supporting the valve stem open at opposing positions in the direction of the rotation axis of the annular fitting groove, the annular fitting groove including two open groove portions provided on peripheral portions of the openings of the two bearing holes and two peripheral groove portions extending in the circumferential direction so as to connect the two open groove portions, one of the two peripheral groove portions having a chamfered portion at an upper edge portion on the downstream side, and the other of the two peripheral groove portions having a chamfered portion at an upper edge portion on the upstream side.

2. 2. The butterfly valve of claim 1, wherein the predetermined angle is in the range of 15 degrees to 30 degrees.

3. 3. A butterfly valve according to claim 1 or claim 2, wherein the width of the peripheral sealing surface is in the range of 3 mm to 10 mm.

4. 2. The butterfly valve according to claim 1, wherein the peripheral groove portion of the annular fitting groove has a rectangular cross section, the chamfered portion is formed by an inclined surface, and the angle formed by the inclined surface and an extension of the side surface of the peripheral groove portion is determined so as to match the rotation angle of the valve disc when the peripheral seal surface of the peripheral ridge of the valve disc comes into contact with the inclined surface, when the rotation angle of the valve disc when the butterfly valve is in a fully open state is set to 0°.

5. A butterfly valve comprising: a valve body in which an internal flow path extending in the flow path axial direction is formed; a seat ring attached to the inner peripheral surface of the internal flow path; a valve stem supported on the valve body so as to be rotatable about a rotation axis; and a roughly disk-shaped valve body connected to the valve stem, rotatably supported on the valve body, and disposed within the seat ring, wherein the valve body is rotated about the rotation axis to move the peripheral portion of the valve body toward and away from the inner peripheral surface of the seat ring, thereby opening and closing the internal flow path, the valve disc has an annular outer peripheral surface extending in a circumferential direction, and two stem openings for inserting the valve disc are formed on the outer peripheral surface at opposite positions in the direction of the rotation axis, and the outer peripheral surface of the valve disc is further provided with two annular opening protrusions protruding from the outer peripheral surface and extending along the peripheries of the stem openings, and a peripheral protrusion protruding from the outer peripheral surface and extending in the circumferential direction of the valve disc so as to connect the two opening protrusions, and the peripheral protrusions have a peripheral seal surface that extends in an arc shape in the circumferential direction along its top and flat in the width direction, and a chamfered surface that is inclined at a predetermined angle relative to the peripheral seal surface toward the outer peripheral surface of the valve disc and extends along both sides of the peripheral seal surface, the seat ring has an outer peripheral surface and an inner peripheral surface, and an annular protrusion that protrudes from the outer peripheral surface and extends annularly, and an annular fitting groove that fits with the annular protrusion of the seat ring is provided on an inner peripheral surface of the internal flow path of the valve body, the seat ring has two through holes extending from the outer peripheral surface to the inner peripheral surface at positions opposite to each other in the rotation axis direction for receiving the valve stem; the inner peripheral surface of the seat ring has two annular through hole seal surfaces extending planarly along the peripheries of the through holes, a valve seat surface extending arcuately in the circumferential direction to connect the two through hole seal surfaces, and an inner peripheral transition surface connecting the through hole seal surfaces and the valve seat surface; the outer peripheral surface of the valve disc further has an annular opening seal surface extending to a top of the opening raised portion, and an outer peripheral transition surface connecting the opening seal surface and the peripheral seal surface, the inner peripheral transition surface extending arcuately to be coaxial with the through holes, and the inner peripheral transition surface contacts the outer peripheral transition surface when the valve is closed.

6. 6. The butterfly valve according to claim 5, wherein the valve seat surface formed on the inner circumferential surface of the seat ring has a concave shape that forms a part of a spherical surface.

7. 6. The butterfly valve according to claim 5, wherein the annular projection includes two annular through-hole projections provided on the outer peripheral surface of the seat ring at peripheries of each through hole, and two outer peripheral projections extending circumferentially to connect the two through-hole projections, each having a projection seal surface formed at its top that extends parallel to the through-hole seal surface, and a thickness from the through-hole seal surface to the projection seal surface is equal to a thickness from the valve seat surface of the seat ring to the top of the outer peripheral projection.

8. 2. The butterfly valve according to claim 1, wherein the seat ring has two through holes extending from the outer peripheral surface to the inner peripheral surface at positions opposing each other in the direction of the rotation axis for receiving the valve stem, the through holes having a width greater than a width of the valve seat surface, and the inner peripheral surface of the seat ring has two annular through hole sealing surfaces extending planarly along peripheral edges of the through holes, and two annular valve seat surfaces extending in an arc shape in the circumferential direction to connect the two through hole sealing surfaces, the annular protrusion having a width greater than a width of the valve seat surface.

9. 5. The butterfly valve according to claim 1, wherein the valve body has a reduced thickness on an outer periphery thereof except for areas adjacent to the bearing hole located on both sides of the rotation axis within a predetermined angular range from the rotation axis around the center of the internal flow path.

10. 10. The butterfly valve according to claim 9, wherein the predetermined angle is equal to or greater than 40 degrees and equal to or less than 60 degrees.

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