Butterfly Valve

Abstract

To provide a butterfly valve capable of suppressing cavitation.SOLUTION: A butterfly valve 1 includes a cylindrical valve box 2 having a hollow portion functioning as a flow passage 4 through which water flows, and a valve element 6 which is arranged in the flow passage 4 so as to rotate around a valve rod 5. The valve rod 5 is eccentric to a downstream side with respect to the valve element 6, and is eccentric to an orifice side with respect to a center line P of the flow passage 4. A cavitation suppressing atmosphere inflow port 7 through which the atmosphere flows into the flow passage 4 is provided in each of a nozzle side half circumference 3A and an orifice side half circumference 3B of a peripheral wall 3 of the valve box 2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a butterfly valve used for water such as tap water, sewage, industrial water, hot spring water, and agricultural water.

[0002] Here, in this specification and claims, "downstream side" and "downstream direction" mean the downstream side and downstream direction, respectively, in the direction of water flow, and "upstream side" and "upstream direction" mean the upstream side and upstream direction, respectively, in the direction of water flow.

[0003] Furthermore, the "nozzle side" means the side on which half of the valve disc rotates downstream with the valve stem as a boundary when the valve disc rotates in the opening direction from the fully closed position, and the "orifice side" means the side on which half of the valve disc rotates upstream with the valve stem as a boundary when the valve disc rotates in the opening direction from the fully closed position. [Background technology]

[0004] Generally, when a valve is used to control (adjust) the flow rate of water flowing through a pipe such as a water supply pipe, cavitation can occur due to changes in fluid pressure near the downstream side of the outer periphery of the nozzle half of the valve body. When cavitation occurs, problems arise such as impact noise and vibration, and damage such as erosion to the valve and pipe.

[0005] Among various valves, butterfly valves are particularly susceptible to cavitation. To prevent cavitation in butterfly valves, a method has been proposed in which atmospheric air is introduced into the pressure drop region that causes cavitation. Specifically, Japanese Patent Laid-Open Publication No. 2004-36705 (Patent Document 1) discloses a butterfly valve in which a plurality of atmospheric air inlet holes are arranged circumferentially in at least one of two quarter-circumferential portions located on either side of the nozzle-side half-circumferential portion of the peripheral wall of the valve body, allowing atmospheric air to flow into the pressure drop region. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-36705 Summary of the Invention [Problem to be solved by the invention]

[0007] However, simply providing multiple air inlet holes in at least one of the two quarter-circumferential portions of the nozzle-side semicircular portion, as in the butterfly valve of the above publication, may not be able to suppress the occurrence of cavitation depending on the type of butterfly valve and the opening degree of the valve body.

[0008] The present invention has been made in view of the above-mentioned technical background, and an object of the present invention is to provide a butterfly valve that can reliably suppress the occurrence of cavitation. [Means for solving the problem]

[0009] The present invention provides the following means.

[0010] 1) A valve body is provided with a cylindrical valve body having a hollow portion as a flow path through which water flows, and a valve body is disposed in the flow path so as to be rotatable around a valve stem, The valve stem is disposed eccentrically toward the downstream side with respect to the valve body and toward the orifice side with respect to the center line of the flow path. A butterfly valve in which cavitation-suppressing atmospheric inlet holes for allowing atmospheric air to flow into the flow path are provided through the peripheral wall portion of the valve body in each of the nozzle-side half portion and the orifice-side half portion of the peripheral wall portion.

[0011] 2) A butterfly valve as recited in the preceding paragraph 1, wherein the number of the atmospheric inlet holes provided in the orifice-side semicircular portion is smaller than the number of the atmospheric inlet holes provided in the nozzle-side semicircular portion.

[0012] 3) When the atmosphere inlet hole provided in the nozzle-side semicircular portion is a nozzle-side atmosphere inlet hole, the number of the nozzle-side atmosphere inlet holes is three or more, 3. A butterfly valve as recited in claim 1 or 2, wherein the nozzle-side atmosphere inlet holes are arranged in the nozzle-side semi-circumferential portion at a half-circumferential position of the nozzle-side semi-circumferential portion and at positions diagonally arranged downstream from the half-circumferential position in circumferential directions that are opposite to each other.

[0013] 4) When the atmosphere inlet hole provided in the nozzle-side semicircular portion is a nozzle-side atmosphere inlet hole, the number of the nozzle-side atmosphere inlet holes is three or more, 4. A butterfly valve as recited in any one of items 1 to 3, wherein the nozzle-side atmosphere inlet holes are arranged in the nozzle-side semi-circular portion so that the downstream positions of the nozzle-side atmosphere inlet holes in the nozzle-side semi-circular portion are all different.

[0014] 5) When the atmosphere inlet hole provided in the orifice-side semicircular portion is an orifice-side atmosphere inlet hole, the number of the orifice-side atmosphere inlet holes is three or more, 5. A butterfly valve as recited in any one of items 1 to 4, wherein the orifice-side atmosphere inlet holes are provided in the orifice-side semi-circumferential portion at a half-circumferential position of the orifice-side semi-circumferential portion and at positions diagonally arranged downstream from the half-circumferential position in circumferential directions that are opposite to each other.

[0015] 6) When the atmosphere inlet hole provided in the orifice-side semicircular portion is an orifice-side atmosphere inlet hole, the number of the orifice-side atmosphere inlet holes is three or more, 6. A butterfly valve as recited in any one of items 1 to 5, wherein the orifice-side atmospheric inlet holes are arranged in the orifice-side semi-circumferential portion so that the downstream positions of the orifice-side atmospheric inlet holes in the orifice-side semi-circumferential portion are all different. [Effects of the Invention]

[0016] The present invention has the following advantages.

[0017] In the previous paragraph 1, the stem of the butterfly valve is eccentrically positioned downstream relative to the disc and eccentrically positioned toward the orifice relative to the centerline of the flow path, making this butterfly valve at least a double-eccentric type. Therefore, compared to concentric butterfly valves and single-eccentric butterfly valves in which the stem is eccentrically positioned downstream relative to the disc, it has lower closing torque, higher sealing performance, and a longer seat life.

[0018] Furthermore, in conventional double eccentric butterfly valves, it was thought that the pressure drop region that would cause cavitation would be formed near the downstream side of the outer periphery of the nozzle half of the valve disc, rather than near the downstream side of the outer periphery of the orifice half of the valve disc, due to the nozzle effect of the valve disc. However, research by the present inventors has revealed that cavitation occurs due to the formation of a pressure drop region not only near the downstream side of the outer periphery of the nozzle half of the valve disc, but also near the downstream side of the outer periphery of the orifice half of the valve disc.

[0019] Therefore, in the butterfly valve of the preceding paragraph 1, an air inlet hole is provided in each of the nozzle-side half and orifice-side half of the peripheral wall of the valve body, which ensures that the occurrence of cavitation can be suppressed even if the butterfly valve is at least a double eccentric type. In other words, this butterfly valve has a high effect of suppressing the occurrence of cavitation.

[0020] The preceding paragraph 2 has the following effects:

[0021] In other words, in a double eccentric butterfly valve like the one described in item 1 above, the pressure drop area that causes cavitation is less likely to form near the downstream side of the outer periphery of the orifice half of the valve disc than near the downstream side of the outer periphery of the nozzle half of the valve disc. Also, if the number of atmosphere inlet holes in the peripheral wall increases, more machining work such as drilling to provide the atmosphere inlet holes in the peripheral wall will be required.

[0022] Therefore, in the previous section 2, the number of atmospheric inlet holes provided in the orifice-side semicircular portion is made fewer than the number of atmospheric inlet holes provided in the nozzle-side semicircular portion. This makes it possible to minimize the amount of processing work, such as drilling, required to provide atmospheric inlet holes in the peripheral wall while maintaining the cavitation suppression effect of the atmospheric inlet holes. This can reduce the manufacturing costs of the butterfly valve.

[0023] In the preceding paragraph 3, by arranging the nozzle-side atmosphere inlet holes in a half-circumferential position on the nozzle-side half, and in positions diagonally aligned downstream in opposite circumferential directions from the half-circumferential position, atmosphere can be reliably introduced into the pressure drop region in the nozzle-side half that moves as the opening of the valve disc increases or decreases. This makes it possible to more reliably suppress cavitation occurring near the downstream side of the outer periphery of the nozzle-side half of the valve disc.

[0024] In the preceding paragraph 4, the nozzle-side atmosphere inlet holes are arranged on the nozzle-side semi-circular portion so that the downstream positions of the nozzle-side atmosphere inlet holes on the nozzle-side semi-circular portion are all different, which makes it possible to reduce the amount of machining work required to provide the atmosphere inlet holes in the peripheral wall portion and to more reliably suppress cavitation occurring near the downstream side of the outer periphery of the nozzle-side half of the valve disc.

[0025] In the above item 5, for the same reason as in the above item 3, it is possible to reliably flow air into the pressure drop region that moves in the orifice side half circumference as the opening of the valve disc increases or decreases, thereby reliably suppressing cavitation that occurs near the downstream side of the outer periphery of the orifice side half of the valve disc.

[0026] In the preceding item 6, for the same reason as in the preceding item 4, the machining work required to provide the atmosphere inlet hole in the peripheral wall portion can be reduced, and cavitation occurring near the downstream side of the outer periphery of the orifice side half of the valve disc can be more reliably suppressed. [Brief explanation of the drawings]

[0027] [Figure 1]FIG. 1 is a schematic front view showing a butterfly valve according to one embodiment of the present invention installed in a water supply pipe. [Figure 2] FIG. 2 is a schematic cross-sectional view of FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a schematic perspective view of the inner circumferential surface of the orifice-side semicircular portion of the peripheral wall of the valve body of the butterfly valve, as viewed from the downstream side. [Figure 5] FIG. 5 is a schematic perspective view of the inner circumferential surface of the nozzle-side semicircular portion of the peripheral wall of the valve body of the butterfly valve, as viewed from the downstream side. [Figure 6] FIG. 6 is a top view of the butterfly valve. [Figure 7] FIG. 7 is a bottom view of the butterfly valve. [Figure 8] FIG. 8 is a perspective view of the atmosphere inlet pipe before the end of the pipe on the outlet port side is cut off. [Figure 9] FIG. 9 is a perspective view of the outlet of the atmosphere inlet pipe. DETAILED DESCRIPTION OF THE INVENTION

[0028] An embodiment of the present invention will be described below with reference to the drawings.

[0029] As shown in Figure 1, a butterfly valve 1 according to one embodiment of the present invention is used to control the amount of water supplied to a water tank (not shown), such as a water distribution tank or a pressure-reducing water tank, and is installed, for example, in a water supply pipe 20 to the water tank. Arrow "D" in the figure indicates the direction of water flow in the water supply pipe 20.

[0030] As shown in Figure 2, the butterfly valve 1 comprises a substantially cylindrical valve body 2 having a hollow portion which forms a flow path 4 through which water flows, a valve stem 5 which passes transversely through the flow path 4, and a substantially disc-shaped valve disc 6 which is disposed in the flow path 4. The valve disc 6 is fixedly attached to the valve stem 5 so as to be rotatable around the valve stem 5. In addition, a substantially annular watertight sheet 9 is provided around the entire circumferential direction on the upstream edge of the inner circumferential surface 3b of the peripheral wall portion 3 of the valve body 2.

[0031] The material of the valve body 2 and the valve element 6 is not limited, and may be cast iron, cast steel, copper alloy, aluminum alloy, or the like.

[0032] This butterfly valve 1 is a so-called double eccentric type. That is, the stem 5 of the butterfly valve 1 is disposed eccentrically downstream from the valve disc 6 (more specifically, the sealing position T of the valve disc 6 with the seat 9) and eccentrically toward the orifice from the center line P of the flow path 4. In the figure, the symbol "s1" indicates the amount of eccentricity of the valve stem 5 from the sealing position T of the valve disc 6, and the symbol "s2" indicates the amount of eccentricity of the valve stem 5 from the center line P of the flow path 4.

[0033] Because the butterfly valve 1 is a double eccentric type, it has a lower closing torque and higher sealing performance than a concentric butterfly valve or a single eccentric butterfly valve in which the valve stem is eccentric downstream relative to the valve body, and the life of the seat 9 can be extended.

[0034] The water supply pipe 20 is equipped with an inlet pipe 21 and an outlet pipe 22, which are respectively arranged upstream and downstream of the butterfly valve 1. Then, with the butterfly valve 1 sandwiched between the inlet pipe 21 and the outlet pipe 22, a flange portion 21a of the inlet pipe 21 and a flange portion 22a of the outlet pipe 22 are fastened with bolts and nuts (not shown), whereby the inlet pipe 21 and the outlet pipe 22 are respectively connected to the inlet and outlet of the flow path 4 of the butterfly valve 1. Furthermore, the downstream end of the outlet pipe 22 extends toward the water tank, and its outlet is arranged inside the water tank.

[0035] As shown in FIG. 3, one end of the valve stem 5 of the butterfly valve 1 protrudes outside the valve box 2, and a valve body opening / closing operation member (e.g., an operating handle or an operating gear) (not shown) is connected to this end.

[0036] 2 and 3, a plurality of cavitation-suppressing air inlet holes 7 for allowing air to flow into the flow path 4 are drilled through the peripheral wall 3 of the valve box 2. The direction of penetration of each air inlet hole 7 in the peripheral wall 3 is approximately perpendicular to the center line P of the flow path 4.

[0037] The air inlet hole 7 is intended to suppress the occurrence of cavitation by allowing the air present outside the peripheral wall portion 3 to flow into a pressure drop region that causes cavitation in the flow path 4. The cross section of the air inlet hole 7 is circular, and its diameter is constant along the length of the air inlet hole 7. The diameter of the air inlet hole 7 is not limited, and is set, for example, in the range of 1 / 300 to 1 / 30 times the diameter of the flow path 4.

[0038] In this embodiment, each atmosphere inlet hole 7 is connected to an atmosphere inlet pipe 8 for suppressing cavitation, through which atmosphere flows into the flow path 4. The atmosphere inlet pipe 8 penetrates the peripheral wall 3 of the valve box 2 from its outer peripheral surface 3a side toward the flow path 4 in a direction approximately perpendicular to the center line P of the flow path 4, and the outlet port 8c of the atmosphere inlet pipe 8 protrudes from the inner peripheral surface 3b of the peripheral wall 3 toward the flow path 4. In this connected state, the outlet port 8c of the atmosphere inlet pipe 8 is provided on the inner peripheral surface 3b of the peripheral wall 3 so as to protrude toward the flow path 4. Specifically, the atmosphere inlet pipe 8 is inserted into each atmosphere inlet hole 7 in a watertight manner to achieve this connected state.

[0039] The atmospheric air inlet pipe 8 has a circular cross section, and in this embodiment, the atmospheric air inlet pipe 8 (more specifically, its hollow portion) constitutes the atmospheric air inlet hole 7.

[0040] The material of the atmospheric air inlet pipe 8 is not limited, and may be the same as or a different material from the material of the valve box 2. Specifically, a metal pipe (e.g., iron pipe, steel pipe, copper alloy pipe, aluminum alloy pipe), a resin pipe (e.g., fluororesin pipe), etc. may be used as the atmospheric air inlet pipe 8. The resin pipe is preferably pressure-resistant (e.g., pressure-resistant resin pipe).

[0041] 1, the end of the atmosphere inlet pipe 8 on the suction port side extends outside the valve box 2, and a check valve 10 is provided at this suction port in a direction that allows the flow of atmosphere in the suction direction. However, in the present invention, the check valve 10 is not necessarily provided.

[0042] Next, the position of the atmosphere inlet hole 7 (atmosphere inlet pipe 8) in the peripheral wall portion 3 of the valve box 2 will be described in detail below.

[0043] 1 to 3, the peripheral wall 3 of the valve box 2 is composed of a substantially semi-cylindrical nozzle-side semi-circumferential portion 3A and a substantially semi-cylindrical orifice-side semi-circumferential portion 3B. As shown in Fig. 3, the valve stem 5 is arranged horizontally, with the nozzle-side semi-circumferential portion 3A located below the valve stem 5 and the orifice-side semi-circumferential portion 3B located above the valve stem 5. Note that in Fig. 3, the symbol "Ha" indicates the semi-circumferential position of the nozzle-side semi-circumferential portion 3A, and the symbol "Hb" indicates the semi-circumferential position of the orifice-side semi-circumferential portion 3B.

[0044] The valve body 6 is composed of a substantially semicircular nozzle half 6A and a substantially semicircular orifice half 6B. The nozzle half 6A is disposed below the valve stem 5, and the orifice half 6B is disposed above the valve stem 5.

[0045] As shown in Figures 3, 5 and 7, three or more atmospheric air inlet holes 7 (atmosphere inlet pipes 8) are provided in the nozzle side semicircular portion 3A of the peripheral wall portion 3 of the valve box 2, and specifically, the number of atmospheric air inlet holes 7 is six. Also, as shown in Figures 3, 4 and 6, three or more atmospheric air inlet holes 7 (atmosphere inlet pipes 8) are provided in the orifice side semicircular portion 3B, and specifically, the number of atmospheric air inlet holes 7 is three.

[0046] In this way, the number of atmosphere inlet holes 7 provided in the orifice-side semi-circular portion 3B is fewer than the number of atmosphere inlet holes 7 provided in the nozzle-side semi-circular portion 3A, which maintains the effect of suppressing the occurrence of cavitation by the atmosphere inlet holes 7 while minimizing the amount of processing work, such as drilling, required to provide the atmosphere inlet holes 7 in the peripheral wall portion 3. This makes it possible to reduce the manufacturing costs of the butterfly valve 1.

[0047] Here, for the sake of convenience of explanation and to make it easier to understand the position of the atmospheric inlet hole 7 (atmospheric inlet pipe 8), the valve body 6 and the seat 9 are omitted from FIGS. 4 and 5, and the atmospheric inlet pipe 8 is omitted from FIGS. 6 and 7.

[0048] Furthermore, in the following, for convenience of explanation, the atmosphere inlet hole 7 (atmosphere inlet pipe 8) provided in the nozzle-side semi-circular portion 3A will be referred to as the nozzle-side atmosphere inlet hole 7A (nozzle-side atmosphere inlet pipe 8A), and the atmosphere inlet hole 7 (atmosphere inlet pipe 8) provided in the orifice-side semi-circular portion 3B will be referred to as the orifice-side atmosphere inlet hole 7B (orifice-side atmosphere inlet pipe 8B). Furthermore, in the following, unless otherwise specified in the text, the term "atmosphere inlet hole 7" is used to include the "atmosphere inlet pipe 8".

[0049] In a double eccentric butterfly valve 1 such as that of this embodiment, the position of the pressure drop region that causes cavitation in the nozzle-side semicircular portion 3A and the orifice-side semicircular portion 3B moves with the increase or decrease in the opening of the valve disc 6 (valve opening). This will be explained below with reference to FIG.

[0050] In the same figure, the valve element 6 shown by the solid line is positioned in the fully closed position, the valve element 6 shown by the two-dot chain line is positioned in a position slightly rotated in the opening direction from the fully closed position, and the valve element 6 shown by the three-dot chain line is positioned in a position rotated further in the opening direction.

[0051] When the valve disc 6, which is in the fully closed position indicated by the solid line, is rotated slightly in the opening direction from the fully closed position, i.e., when the valve disc 6 is in the position indicated by the two-chain line, the pressure drop region that causes cavitation is formed near the downstream side of the tip of the nozzle-side half 6A of the valve disc 6 (i.e., the position corresponding to the half-circumferential position Ha of the nozzle-side half 3A; see Figure 3). Then, as the opening of the valve disc 6 increases, this pressure drop region shifts diagonally downstream from the downstream side of the tip of the nozzle-side half 6A of the valve disc 6 in mutually opposite circumferential directions.

[0052] Therefore, as shown in Figures 3, 5 and 7, in the nozzle-side semi-circumferential portion 3A, the nozzle-side air inlet holes 7A are arranged at a semi-circumferential position Ha of the nozzle-side semi-circumferential portion 3A and at positions diagonally arranged downstream from the semi-circumferential position Ha in the circumferential direction in opposite directions. More specifically, one of the three or more nozzle-side atmosphere inlet holes 7A is provided at a half-circumferential position Ha of the nozzle-side semi-circumferential portion 3A, and all of the remaining nozzle-side atmosphere inlet holes 7A are arranged in a row diagonally downstream in opposite circumferential directions from the position of the one nozzle-side atmosphere inlet hole 7A. By arranging the nozzle-side atmosphere inlet hole 7A in the nozzle-side semi-circumferential portion 3A in this way, it is possible to reliably allow atmosphere to flow into the pressure drop region in the nozzle-side semi-circumferential portion 3A that moves as the opening of the valve body 6 increases or decreases, and therefore it is possible to reliably suppress cavitation that occurs near the downstream side of the outer periphery of the nozzle-side half portion 6A of the valve body 6.

[0053] Furthermore, as shown in FIG. 7, the positions of the nozzle-side atmosphere inlet holes 7A in the nozzle-side semi-circular portion 3A are all shifted downstream; in other words, the nozzle-side atmosphere inlet holes 7A are arranged in the nozzle-side semi-circular portion 3A so that the downstream positions of the nozzle-side atmosphere inlet holes 7A in the nozzle-side semi-circular portion 3A are all different. More specifically, the positions of all the remaining nozzle-side atmospheric air inlet holes 7A are arranged so that they are alternately shifted downstream in opposite circumferential directions relative to the position of the single nozzle-side atmospheric air inlet hole 7A and are all at different positions downstream. This makes it possible to reliably reduce the amount of processing work, such as drilling, required to provide the nozzle-side atmosphere inlet hole 7A in the nozzle-side half periphery 3A, and further reliably suppress cavitation that occurs near the downstream side of the outer periphery of the nozzle-side half 6A of the valve body 6.

[0054] As shown in FIGS. 3, 4, and 6, in the orifice-side semi-circumferential portion 3B, the orifice-side air inlet holes 7B are disposed at a semi-circumferential position Hb of the orifice-side semi-circumferential portion 3B and at positions diagonally arranged downstream from the semi-circumferential position Hb in opposite circumferential directions. More specifically, one of the three or more orifice-side atmospheric inlet holes 7B is provided at a half-circumferential position Hb of the orifice-side semi-circumferential portion 3B, and all of the remaining orifice-side atmospheric inlet holes 7B are arranged in a row diagonally downstream in opposite circumferential directions from the position of the one orifice-side atmospheric inlet hole 7B. By arranging the orifice-side atmosphere inlet hole 7B in the orifice-side semi-circumferential portion 3B in this manner, it is possible to reliably allow atmosphere to flow into the pressure drop region in the orifice-side semi-circumferential portion 3B that moves as the opening of the valve element 6 increases or decreases, thereby reliably suppressing cavitation that occurs near the downstream side of the outer periphery of the orifice-side half portion 6B of the valve element 6.

[0055] Furthermore, as shown in FIG. 6, the positions of the orifice-side atmosphere inlet holes 7B in the orifice-side semi-circular portion 3B are all shifted downstream; in other words, the orifice-side atmosphere inlet holes 7B are arranged in the orifice-side semi-circular portion 3B so that the positions of the orifice-side atmosphere inlet holes 7B in the downstream direction are all different in the orifice-side semi-circular portion 3B. More specifically, the positions of all the remaining orifice-side atmospheric inlet holes 7B are arranged so that they are alternately shifted downstream in opposite circumferential directions relative to the position of the single orifice-side atmospheric inlet hole 7B and are all at different positions downstream. This makes it possible to reliably reduce the amount of machining work, such as drilling, required to provide the orifice-side atmosphere inlet hole 7B in the orifice-side half circumferential portion 3B, and further reliably suppress cavitation occurring near the downstream side of the outer circumferential portion of the orifice-side half 6B of the valve body 6.

[0056] Next, the configuration of the atmosphere inlet pipe 8 will be described below.

[0057] As shown in FIG. 2, each of the air inlet pipes 8 is disposed in a direction substantially perpendicular to the center line P of the flow path 4 as described above.

[0058] Furthermore, the opening shape of the discharge port 8c of each atmosphere inlet pipe 8 is a shape that extends in the downstream direction D when viewed from a direction perpendicular to the discharge port 8c, and specifically, is an ellipse that extends in the downstream direction D. More specifically, the discharge port 8c of the atmosphere inlet pipe 8 is not oriented perpendicular to the center line P of the flow path 4, but is arranged in a direction that is inclined downstream.

[0059] The discharge port 8c of the atmosphere inlet pipe 8 is formed as follows.

[0060] First, an atmospheric air inlet pipe 8 having a circular cross section as shown in Fig. 8 is prepared. The inner and outer diameters of this atmospheric air inlet pipe 8 are constant along its axis Q, and the end face of the pipe end 8d on the discharge port side of the atmospheric air inlet pipe 8 is formed approximately perpendicular to the axis Q. Next, the pipe end 8d on the discharge port side of the atmospheric air inlet pipe 8 is cut along the planned cutting line C (shown by a two-dot chain line) at an inclination angle θ with respect to the axis Q. As a result, as shown in Fig. 9, the discharge port 8c of the atmospheric air inlet pipe 8 is formed at an inclination with respect to the axis Q, and the opening shape of the discharge port 8c changes from a circular shape to an elliptical shape, and the opening area of ​​the discharge port 8c is increased compared to before the pipe end 8d was cut.

[0061] By cutting the pipe end 8d on the outlet side of the atmospheric air inlet pipe 8 in this way, the outlet port 8c of the atmospheric air inlet pipe 8 can be easily formed in an inclined shape.

[0062] Next, the atmosphere inlet pipe 8 is inserted into the atmosphere inlet hole 7 from the outer peripheral surface 3a side of the peripheral wall portion 3 of the valve box 2 so that its discharge port 8c is inclined downstream, and is fixed to the atmosphere inlet hole 7 in a watertight and removable state. In this way, the atmosphere inlet pipe 8 is connected to the atmosphere inlet hole 7.

[0063] 2, when the valve element 6 rotates in the opening direction from the fully closed position, the tip of the nozzle-side half 6A of the valve element 6 passes near the tip of the discharge port 8c of the nozzle-side atmosphere inlet pipe 8A in the downstream direction D. At this time, a pressure drop (i.e., negative pressure due to the Venturi effect) occurs near the downstream side of the tip of the nozzle-side half 6A of the valve element 6, causing atmosphere to be sucked in through the discharge port 8c of the nozzle-side atmosphere inlet pipe 8A and discharged into the pressure drop area.

[0064] Here, because the opening shape of the discharge port 8c of the nozzle-side atmosphere inlet pipe 8A is a shape that extends in the downstream direction D, the area where the discharge port 8c of the nozzle-side atmosphere inlet pipe 8A can discharge atmosphere from the discharge port 8c toward the pressure drop region is increased. Therefore, atmosphere can be reliably caused to flow into the pressure drop region, and the occurrence of cavitation can be reliably suppressed.

[0065] Furthermore, since the discharge port 8c of the nozzle-side atmosphere inlet pipe 8A is disposed in a direction inclined downstream, it is possible to more reliably cause the atmosphere to flow from the discharge port 8c of the nozzle-side atmosphere inlet pipe 8A toward the pressure drop region. The inclination angle θ of the discharge port 8c (see FIG. 9) is not limited, but it is preferable that θ is in the range of 20° to 70°.

[0066] The discharge port 8c of the orifice side atmosphere inlet pipe 8B also functions in the same manner as the discharge port 8c of the nozzle side atmosphere inlet pipe 8A.

[0067] According to the butterfly valve 1 of this embodiment, the atmospheric inlet hole 7 (atmospheric inlet pipe 8) penetrates the peripheral wall portion 3 of the valve box 2 in a direction approximately perpendicular to the center line P of the flow path 4, so that processing work such as drilling to provide the atmospheric inlet hole 7 in the peripheral wall portion 3 can be performed more easily than in the case where the atmospheric inlet hole 7 penetrates the peripheral wall portion 3 of the valve box 2 in a direction oblique to the center line P of the flow path 4.

[0068] Furthermore, because the outer diameter of the atmospheric inlet pipe 8 is constant in the direction of its axis Q, the atmospheric inlet pipe 8 can be easily inserted into the atmospheric inlet hole 7 from the outer peripheral surface 3a side of the peripheral wall portion 3 of the valve box 2, and when performing maintenance on the butterfly valve 1, the atmospheric inlet pipe 8 can be easily removed from the atmospheric inlet hole 7, making maintenance work easy.

[0069] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the present invention.

[0070] For example, in the above embodiment, the butterfly valve is a double eccentric type, but in the present invention, the butterfly valve is not limited to being a double eccentric type, and may be a triple eccentric type, quadruple eccentric type, etc.

[0071] Furthermore, in the present invention, the number of orifice-side atmosphere inlet holes 7B (orifice-side atmosphere inlet pipes 8B) is preferably three or more, but is not limited to this and may be one or more. When the number of orifice-side atmosphere inlet holes 7B (orifice-side atmosphere inlet pipes 8B) is, for example, one, this atmosphere inlet hole 7B (orifice-side atmosphere inlet pipe 8B) is preferably provided at half-circumferential position Hb of the orifice-side semi-circumferential portion 3B of the peripheral wall portion 3 of the valve box 2. [Industrial Applicability]

[0072] The present invention can be used in butterfly valves for water such as tap water, sewage, industrial water, agricultural water, hot spring water, and seawater. [Explanation of symbols]

[0073] 1: Butterfly valve 2: Valve box 3: Peripheral wall portion 3A: Nozzle side semi-peripheral portion 3B: Orifice side semicircular portion 4: Flow path 7: Atmospheric inlet 7A: Nozzle side atmospheric inlet 7B: Orifice side air inlet D: Downstream direction of water flow

Claims

1. The valve body has a hollow portion serving as a flow path for water, and the valve element is disposed in the flow path so as to be rotatable around the valve stem. The valve stem is disposed eccentrically toward the downstream side with respect to the valve body and toward the orifice side with respect to the center line of the flow path, a cavitation-suppressing air inlet hole for allowing air to flow into the flow path is provided in each of a nozzle-side semi-circumferential portion and an orifice-side semi-circumferential portion of the peripheral wall portion of the valve body, the air inlet hole penetrating the peripheral wall portion, When the atmosphere inlet hole provided in the nozzle-side semicircular portion is a nozzle-side atmosphere inlet hole, the number of the nozzle-side atmosphere inlet holes is three or more, in the nozzle-side semi-circumferential portion, one nozzle-side atmospheric air inlet hole of the three or more nozzle-side atmospheric air inlet holes is provided at a position halfway along the circumference of the nozzle-side semi-circumferential portion, and all of the remaining nozzle-side atmospheric air inlet holes are arranged in a row diagonally downstream from the position of the one nozzle-side atmospheric air inlet hole in circumferential directions that are opposite to each other, When the atmosphere inlet hole provided in the orifice-side semicircular portion is defined as an orifice-side atmosphere inlet hole, the number of the orifice-side atmosphere inlet holes is three or more, a butterfly valve in which, in the orifice side semi-circumferential portion, one of the three or more orifice side atmospheric inlet holes is provided at a position along half the circumference of the orifice side semi-circumferential portion, and all of the remaining orifice side atmospheric inlet holes are arranged in a row diagonally downstream from the position of the one orifice side atmospheric inlet hole in circumferential directions that are opposite to each other.

2. A butterfly valve as described in claim 1, wherein the positions of all the remaining nozzle side atmospheric inlet holes are arranged so that they are alternately shifted downstream in opposite circumferential directions relative to the position of the one nozzle side atmospheric inlet hole and are all at different positions downstream.

3. A butterfly valve as described in claim 1 or 2, wherein the positions of all the remaining orifice side atmospheric inlet holes are arranged so that they are alternately shifted downstream in opposite circumferential directions relative to the position of the one orifice side atmospheric inlet hole and are all at different positions downstream.

4. 3. A butterfly valve according to claim 1, wherein the number of the atmospheric inlet holes provided in the orifice-side semicircular portion is smaller than the number of the atmospheric inlet holes provided in the nozzle-side semicircular portion.

5. 4. A butterfly valve according to claim 3, wherein the number of the atmospheric inlet holes provided in the orifice-side semicircular portion is smaller than the number of the atmospheric inlet holes provided in the nozzle-side semicircular portion.

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