Strainer, steam valve provided with same, and method for manufacturing strainer

Abstract

The present invention comprises: a strainer body having a plurality of steam passage holes; a temporary strainer having a plurality of temporary steam passage holes; and a plurality of screws for attaching the temporary strainer along the body outer peripheral surface of the strainer body. The temporary strainer additionally has screw part insertion holes that pass through the temporary strainer around a temporary hole formation region in which the plurality of temporary steam passage holes are formed, wherein respective male screw parts of the plurality of screws can pass through the screw part insertion holes. The strainer body additionally has screw holes that are recessed from the body outer peripheral surface of the strainer body toward the body inner peripheral surface around a hole formation region in which the plurality of steam passage holes are formed. The screw holes have female screw holes into which the male screw parts that have passed through the screw part insertion holes are screwed.

Description

Strainer, steam valve equipped with same, and method for manufacturing strainer

[0001] The present disclosure relates to a strainer disposed within a valve casing having a steam flow path, a steam valve including the strainer, and a method for manufacturing the strainer. This application claims priority to Japanese Patent Application No. 2024-105953, filed on July 1, 2024, the contents of which are incorporated herein by reference.

[0002] A steam valve that can adjust the flow rate of steam flowing into a steam turbine is provided with a strainer to remove foreign matter contained in the steam.

[0003] The strainer of Patent Document 1 below includes a strainer body and a temporary strainer. The strainer body is cylindrical so as to be able to be housed in a valve casing of a steam valve. This strainer body is formed with a plurality of steam inlet holes that penetrate from the outer peripheral surface to the inner peripheral surface of the strainer body. The temporary strainer is a temporary perforated plate screen. When attaching the temporary strainer to the main strainer, first, the temporary strainer is brought into contact with the outer peripheral surface of the strainer body, and the entire peripheral edge of the temporary strainer is welded to the strainer body. Furthermore, the temporary strainer is connected to the strainer body with a plurality of rivets that penetrate the temporary strainer and the strainer body.

[0004] After installation or repair work on a boiler that generates steam to be supplied to a steam turbine or on a main steam line connecting the boiler and the steam turbine, when steam is flowed from the boiler to the main steam line, there is a possibility that foreign matter resulting from the work may be mixed into the steam. For this reason, the strainer described in Patent Document 1 includes a strainer body and a temporary strainer. When steam is flowed through the main steam line for a predetermined time and the amount of foreign matter in the steam decreases, the temporary strainer is removed from the strainer body, leaving the strainer body inside the valve casing.

[0005] Japanese Utility Model Application Publication No. 62-074102

[0006] In the technology described in Patent Document 1, when removing the temporary strainer from the strainer body, it is necessary to remove the welded portion between the strainer body and the temporary strainer and also to cut off multiple rivets. Therefore, with the technology described in Patent Document 1, the work of removing the temporary strainer from the strainer body is cumbersome.

[0007] Therefore, an object of the present disclosure is to provide a strainer that allows the temporary strainer to be easily removed from the strainer body, a steam valve including the strainer, and a method for manufacturing the strainer.

[0008] According to one aspect of the disclosure for achieving the above object, the strainer is disposed within a valve casing having a steam flow path. The strainer includes: a cylindrical strainer body having a main body outer peripheral surface, a main body inner peripheral surface back-to-back with the main body outer peripheral surface, and a plurality of steam passage holes extending from the main body outer peripheral surface to the main body inner peripheral surface; a temporary strainer disposed along the main body outer peripheral surface of the strainer body and having a temporary inner peripheral surface facing the main body outer peripheral surface, a temporary outer peripheral surface back-to-back with the temporary inner peripheral surface, and a plurality of temporary steam passage holes extending from the temporary outer peripheral surface to the temporary inner peripheral surface and having inner diameters smaller than the respective inner diameters of the plurality of steam passage holes; and a plurality of screws for attaching the temporary strainer along the main body outer peripheral surface of the strainer body. A temporary hole formation region in which the plurality of temporary steam passage holes are formed in the temporary strainer overlaps with a hole formation region in which the plurality of steam passage holes are formed in the strainer body. Each of the plurality of screws has a cylindrical male threaded portion having a male thread formed therein, and a screw head provided at the end of the male threaded portion that is closer to the base end than the tip end and the base end in the extending direction of the male threaded portion. The temporary strainer further has a screw portion insertion hole that penetrates from the temporary outer peripheral surface to the temporary inner peripheral surface of the temporary strainer around the temporary hole formation area, and through which the male threaded portion of each of the plurality of screws can pass but the screw head cannot pass. The strainer body further has a screw hole that is recessed from the outer peripheral surface of the strainer body toward the inner peripheral surface of the strainer body around the hole formation area, and that communicates with the screw portion insertion hole of the temporary strainer. The screw hole of the strainer body has a female screw hole into which the male threaded portion that has passed through the screw portion insertion hole is screwed.

[0009] In this embodiment, the temporary strainer can be easily removed from the strainer body by removing multiple screws from the strainer using a screwdriver or other screwdriver tool.

[0010] According to one aspect of the disclosure for achieving the above object, a steam valve includes the strainer according to the above aspect, the valve casing, a valve disc reciprocating within the valve casing in an axial direction along an axis thereof to open and close the flow passage, and a valve rod extending on the axis in the axial direction and connected to the valve disc. The flow passage includes an axial flow passage portion extending in the axial direction about the axis, an annular flow passage portion formed in a ring shape around an axial inlet-side flow passage portion that is a portion of the axial flow passage portion in the axial direction and that is in communication with the axial inlet-side flow passage portion, an inlet flow passage portion extending from the annular flow passage portion in a first radial direction relative to the axis and opening at an outer surface of the valve casing, and an outlet flow passage portion extending in either direction from an axial outlet-side flow passage portion that is another portion of the axial flow passage portion in the axial direction and opening at the outer surface of the valve casing. The valve disc is arranged to be reciprocally movable within the axial inlet-side flow passage portion. The strainer is disposed at the boundary between the axial inlet side flow path portion and the annular flow path portion so that the strainer body is cylindrical around the axis.

[0011] In this embodiment, foreign matter contained in the steam that has flowed into the valve casing can be captured by the strainer.

[0012] According to one aspect of the disclosure for achieving the above object, a strainer manufacturing method for a strainer to be disposed in a valve casing having a steam flow path is provided. The manufacturing method includes a preparation step of preparing a cylindrical main body material having an outer circumferential surface and an inner circumferential surface and capable of being disposed in the flow path, a temporary material attachable along the outer circumferential surface of the main body material and having a temporary inner circumferential surface facing the outer circumferential surface and a temporary outer circumferential surface back-to-back with the temporary inner circumferential surface, and a plurality of screws, a main body material processing step of processing the main body material to form a strainer body, a temporary material processing step of processing the temporary material to form a temporary strainer, and an assembly step of attaching the temporary strainer to the strainer body using the plurality of screws. Each of the plurality of screws has a cylindrical male thread portion having a male thread and a screw head provided at the proximal end of the male thread portion. The main body material processing process includes a steam passage hole forming process of forming a plurality of steam passage holes that penetrate from the main body outer peripheral surface to the main body inner peripheral surface within a predetermined hole formation region of the main body material, and a screw hole forming process of forming screw holes that are recessed from the main body outer peripheral surface toward the main body inner peripheral surface around the hole formation region of the main body material and into which the male thread portions of each of the plurality of screws can be screwed.The temporary material processing process includes a temporary steam passage hole forming process of forming a plurality of temporary steam passage holes that penetrate from the temporary outer peripheral surface to the temporary inner peripheral surface within a predetermined temporary hole formation region of the temporary material and have inner diameters smaller than the inner diameters of each of the plurality of steam passage holes, and a screw portion insertion hole forming process of forming a screw portion insertion hole that penetrates from the temporary outer peripheral surface to the temporary inner peripheral surface around the temporary hole formation region of the temporary material and through which the male thread portions of each of the plurality of screws can pass but the screw heads cannot pass. In the screw portion insertion hole forming process, the temporary inner surface of the temporary material is brought into contact with the outer main surface of the main material, and when the temporary hole formation area of ​​the temporary material is overlapped with the hole formation area of ​​the main material, the screw portion insertion hole is formed in the temporary material at a position that can communicate with the screw hole of the main material.In the assembly process, the temporary inner peripheral surface is brought into contact with the outer peripheral surface of the main body, the temporary hole formation area is overlapped with the hole formation area, and then the male threaded portion of the screw is inserted into the threaded portion insertion hole of the temporary strainer and then screwed into the screw hole of the strainer main body.

[0013] In the strainer manufactured in this manner, as with the strainer in the first manner described above, the temporary strainer can be easily removed from the strainer body by using a screwdriver or other screwdriver tool to remove multiple screws from the strainer.

[0014] According to one aspect of the present disclosure, the temporary strainer can be easily removed from the strainer body.

[0015] FIG. 1 is a cross-sectional view of a steam valve in an embodiment according to the present disclosure. FIG. 2 is a cross-sectional view of a strainer in an imaginary plane perpendicular to the axis in an embodiment according to the present disclosure. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 4 is a development view of a strainer body and a temporary strainer developed in a circumferential direction relative to the axis in an embodiment according to the present disclosure. FIG. 5 is a cross-sectional view of a main portion of a strainer body and a temporary strainer around a thread in an embodiment according to the present disclosure. FIG. 6 is a flowchart showing a manufacturing procedure for a strainer in an embodiment according to the present disclosure. FIG. 7 is a cross-sectional view of a main portion of a strainer and a temporary strainer during a countersink hole co-machining step in an embodiment according to the present disclosure. FIG. 8 is a cross-sectional view of a main portion of a strainer and a temporary strainer after a countersink hole co-machining step in an embodiment according to the present disclosure. FIG. 9 is a cross-sectional view of a main portion of a strainer after a screw hole forming step and a temporary strainer after a threaded portion insertion hole forming step in an embodiment according to the present disclosure. FIG. 10 is a cross-sectional view of a main portion of a strainer body and a temporary strainer around a thread in a comparative example. FIG. 11 is a development view of a strainer body and a temporary strainer developed in a circumferential direction Dc relative to the axis in a first modified example of an embodiment according to the present disclosure. FIG. 10 is a cross-sectional view of a strainer taken along a virtual plane perpendicular to an axis in a second modified example of an embodiment according to the present disclosure.

[0016] Hereinafter, embodiments and various modifications of a strainer and a steam valve including the strainer according to the present disclosure will be described with reference to the drawings.

[0017] "Embodiment of Steam Valve" An embodiment of steam according to the present disclosure will be described in detail with reference to Fig. 1. This steam valve is a valve that can adjust the flow rate of steam flowing into a steam turbine.

[0018] The steam valve comprises a valve casing 10, a valve seat 11, a valve body 12 that can move back and forth within the valve casing 10 in an axial direction Da in which the axis A of the valve casing 10 extends, a valve rod 13 to which the valve body 12 is connected, and a strainer 20.

[0019] The valve casing 10 is formed with a flow path 15 through which steam can flow. This flow path 15 has an axial flow path portion 16, an annular flow path portion 17, an inlet flow path portion 18i, and an outlet flow path portion 18o. The axial flow path portion 16 is a cylindrical flow path portion extending in the axial direction Da with the axis A as its center. The inlet flow path portion 18i is a flow path portion formed in an annular shape with the axis A as its center around the axial inlet-side flow path portion 16i, which is a part of the axial flow path portion 16 in the axial direction Da, and is in communication with the axial inlet-side flow path portion 16i. The inlet flow path portion 18i is a flow path portion extending from the annular flow path portion 17 in a first radial direction Dr1 of the radial directions Dr relative to the axis A and opening at the outer surface of the valve casing 10. The outlet flow path section 18o is a flow path section that extends from the axial outlet side flow path section 16o, which is another part of the axial direction Da in the axial flow path section 16, in a second radial direction Dr2 of the radial direction Dr and opens on the outer surface of the valve casing 10.

[0020] The valve seat 11 is annular and centered on the axis A. The valve seat 11 is disposed at the boundary between the axial inlet-side flow passage portion 16i and the axial outlet-side flow passage portion 16o.

[0021] The valve element 12 is disposed in the axial inlet-side flow passage 16i and is capable of reciprocating movement in the axial direction Da between a closed state in which the valve element 12 is in contact with the valve seat 11 and an open state in which the valve element 12 is separated from the valve seat 11.

[0022] The valve stem 13 extends in the axial direction Da and is disposed on the axis A. The valve disc 12 is connected to a first end of the valve stem 13. A drive mechanism (not shown) is provided to a second end of the valve stem 13. The valve stem 13 and the valve disc 12 connected to the valve stem 13 reciprocate in the axial direction Da due to the operation of the drive mechanism.

[0023] The strainer 20 is a device for capturing most of the foreign matter contained in the steam that flows into the valve casing 10 from the inlet flow path 18i. The strainer 20 is arranged at the boundary between the axial inlet flow path 16i ​​and the annular flow path 17 so as to be cylindrical around the axis A, with the axis A as its center.

[0024] "Embodiment of Strainer" An embodiment of a strainer according to the present disclosure will be described in detail with reference to Figures 2 to 10. This strainer is the strainer 20 disposed within the valve casing 10 described above.

[0025] As shown in Figures 2 and 3, the strainer 20 in this embodiment includes a strainer body 21, two temporary strainers 31, and a plurality of screws 41. Figure 2 is a cross-sectional view of the strainer 20 taken along an imaginary plane perpendicular to the axial direction Da. Figure 3 is a cross-sectional view taken along line III-III in Figure 2.

[0026] The strainer body 21 has a cylindrical shape centered on an axis A. This axis A is the axis A of the valve casing 10, but is also the axis A of the strainer 20 in this embodiment. The strainer body 21 has a body outer peripheral surface 24o, a body inner peripheral surface 24i that is back-to-back with the body outer peripheral surface 24o, and a plurality of steam passage holes 25 that penetrate from the body outer peripheral surface 24o to the body inner peripheral surface 24i.

[0027] The two temporary strainers 31 are arranged along the main body outer peripheral surface 24o of the strainer main body 21. Specifically, the first temporary strainer 31a of the two temporary strainers 31 is arranged on the main body outer peripheral surface 24o along a portion closer to the inlet flow path 18i than the axis A. That is, the first temporary strainer 31a is arranged along approximately half the circumference of the portion of the strainer main body 21 closer to the inlet flow path 18i. Furthermore, the second temporary strainer 31b of the two temporary strainers 31 is arranged on the main body outer peripheral surface 24o along a portion closer to the inlet flow path 18i than the axis A. That is, the second temporary strainer 31b is arranged along approximately half the circumference of the portion of the strainer main body 21 opposite to the inlet flow path 18i. Each of the two temporary strainers 31 has a temporary inner peripheral surface 34i facing the main body outer peripheral surface 24o, a temporary outer peripheral surface 34o that is back-to-back with the temporary inner peripheral surface 34i, and a plurality of temporary steam passage holes 35 that penetrate from the temporary outer peripheral surface 34o to the temporary inner peripheral surface 34i. The inner diameter of each steam passage hole 25 is, for example, 3.0 to 5.0 mm. The inner diameter of each temporary steam passage hole 35 is also, for example, 1.0 to 2.5 mm. Therefore, in this embodiment, the inner diameter of each steam passage hole 25 is smaller than the inner diameter of each of the plurality of steam passage holes 25. The spacing between the plurality of temporary steam passage holes 35 is also narrower than the spacing between the plurality of steam passage holes 25.

[0028] As shown in Fig. 4, the plurality of steam passage holes 25 are formed in the two hole formation regions 22 of the strainer body 21. Furthermore, the plurality of temporary steam passage holes 35 are formed in the temporary hole formation regions 32 of each temporary strainer 31. Note that Fig. 4 is a development view of the strainer body 21 and the temporary strainer 31 developed in the circumferential direction Dc with respect to the axis A.

[0029] The first hole formation region 22a, which is one of the two hole formation regions 22 of the strainer body 21, is defined within the region of the strainer body 21 where the first temporary strainer 31a is disposed. The second hole formation region 22b, which is the other of the two hole formation regions 22, is defined within the region of the strainer body 21 where the second temporary strainer 31b is disposed. The first hole formation region 22a and the second hole formation region 22b are the same size. The dimension of each hole formation region 22 in the axial direction Da is, for example, approximately 80% of the dimension of the strainer body 21 in the axial direction Da. The dimension of each hole formation region 22 in the circumferential direction Dc is approximately 40% of the outer circumferential dimension of the strainer body 21.

[0030] The dimension in the axial direction Da of the temporary hole formation region 32 of each temporary strainer 31 is, for example, about 85% of the dimension in the axial direction Da of the strainer body 21. Furthermore, the dimension in the circumferential direction Dc of the temporary hole formation region 32 of each temporary strainer 31 is, for example, about 45% of the outer circumferential dimension of the strainer body 21. In other words, the size of the temporary hole formation region 32 of each temporary strainer 31 is slightly larger than the size of each hole formation region 22 of the strainer body 21.

[0031] As shown in FIG. 9 , the screw 41 has a male thread portion 42 and a screw head 43. The male thread portion 42 is cylindrical, centered on the screw axis Ag, and has a male thread formed on its outer periphery. The screw head 43 is provided at the end of the proximal end Dgb of the distal end Dgt and proximal end Dgb in the extension direction Dg of the male thread portion 42. Note that this extension direction Dg is the direction in which the screw axis Ag extends. The screw head 43 has a conical portion 44 whose outer diameter gradually decreases toward the distal end Dgt. In other words, the screw 41 is a flat head screw. If a pan head screw is used as the screw 41, for example, the force F pressing the screw head against the temporary strainer 31 will be uneven due to the cylindrical shape of the temporary strainer 31. That is, the pressing force F in the circumferential direction Dc of the temporary strainer 31 is lower than the pressing force F in the axial direction Da of the temporary strainer 31. On the other hand, it was confirmed by calculation that if a flat head screw is used and a countersunk hole is provided to match the shape of the flat head screw, a nearly uniform force F is generated. Therefore, in this embodiment, flat head screws are used as the screws 41.

[0032] The thickness of each temporary strainer 31, in other words, the distance (thickness) t2 between the temporary outer peripheral surface 34o and the temporary inner peripheral surface 34i of each temporary strainer 31, is shorter than the dimension in the extension direction Dg of the conical portion 44 of the screw 41, in other words, the distance t3 between the end of the base end side Dgb and the end of the tip side Dgt of the conical portion 44 of the screw 41. In addition, the thickness of the strainer body 21, in other words, the distance (thickness) t1 between the temporary outer peripheral surface 34o and the temporary inner peripheral surface 34i of the strainer body 21, is longer than the distance t3 between the end of the base end side Dgb and the end of the tip side Dgt of the conical portion 44 of the screw 41.

[0033] 4, the temporary strainer 31 further has a plurality of thread insertion holes 36 that penetrate from the temporary outer peripheral surface 34o to the temporary inner peripheral surface 34i of the temporary strainer 31 around the temporary hole formation region 32, and through which the male thread portions 42 of the screws 41 can pass but the screw heads 43 cannot. The strainer body 21 further has a plurality of screw holes 26 that are recessed from the outer peripheral surface 24o of the strainer body 21 toward the inner peripheral surface 24i of the strainer body 21 around the hole formation region 22, and that communicate with the thread insertion holes 36 of the temporary strainer 31.

[0034] 9, the threaded portion insertion hole 36 of the temporary strainer 31 is a countersunk hole. For this reason, hereinafter, the threaded portion insertion hole 36 may be referred to as a countersunk hole 36. This countersunk hole 36 corresponds to the shape of at least a portion of the base end side Dgb of the conical portion 44 of the screw 41, and is a conical hole whose inner diameter gradually decreases from the temporary outer peripheral surface 34o to the temporary inner peripheral surface 34i of the temporary strainer 31 so that at least a portion of the base end side Dgb of the conical portion 44 can be accommodated.

[0035] The threaded hole 26 of the strainer body 21 does not penetrate from the outer peripheral surface 24o to the inner peripheral surface 24i of the strainer body 21, but has a hole bottom 26b. This threaded hole 26 has a counterbore hole 26c and a female threaded hole 26f. The counterbore hole 26c corresponds to the shape of the tip side Dgt portion of the conical portion 44 of the screw 41, excluding at least a portion of the base end Dgb, and is a hole whose inner diameter gradually decreases from the outer peripheral surface 24o of the strainer body 21 toward the inner peripheral surface 24i of the strainer body 21 so as to accommodate the tip side Dgt portion of the conical portion 44 of the screw 41, excluding at least a portion of the base end Dgb. The female threaded hole 26f is a hole into which the male threaded portion 42 of the screw 41 can be screwed. This female threaded hole 26f is formed on the tip side Dgt of the counterbore hole 26c.

[0036] Next, a method for manufacturing the strainer 20 described above will be described with reference to the flowchart shown in FIG.

[0037] First, a main body material 23, two temporary materials 33, and a plurality of screws 41 are prepared (preparation step S1). The main body material 23 is the material for the strainer main body 21. Therefore, the main body material 23 has a size that allows it to be placed within the axial inlet-side flow path portion 16i of the valve casing 10 described with reference to FIG. 1. This main body material 23 is cylindrical and has a main body outer peripheral surface 24o and a main body inner peripheral surface 24i. The distance (thickness) between the temporary outer peripheral surface 34o and the main body inner peripheral surface 24i of this main body material 23 is the same as the thickness t1 of the strainer main body 21 described above. The two temporary materials 33 are each the material for the temporary strainer 31. The temporary material 33 is a plate having a temporary outer peripheral surface 34o and a temporary inner peripheral surface 34i. The distance (thickness) between the provisional outer peripheral surface 34o and the provisional inner peripheral surface 34i of this provisional material 33 is the same as the distance (thickness) t2 between the provisional outer peripheral surface 34o and the provisional inner peripheral surface 34i of the provisional strainer 31.

[0038] Next, the temporary material 33 is processed to form the temporary strainer 31 (temporary material processing step S2), and the main body material 23 is processed to form the strainer main body 21 (main body material processing step S5).

[0039] The temporary material processing step S2 includes a temporary steam passage hole forming step S3 and a threaded portion insertion hole forming step S4. In the temporary steam passage hole forming step S3, a plurality of temporary steam passage holes 35 are formed in the temporary hole formation areas 32 of each of the two temporary materials 33. In the threaded portion insertion hole forming step S4, a plurality of threaded portion insertion holes 36 are formed around the temporary hole formation areas 32. This threaded portion insertion hole forming step S4 includes a counterbore co-machining step S8, which will be described later.

[0040] The main body material processing step S5 includes a steam passage hole forming step S6 and a screw hole forming step S7. In the steam passage hole forming step S6, a plurality of steam passage holes 25 are formed in the two hole formation regions 22 of the main body material 23. In the screw hole forming step S7, a plurality of screw holes 26 are formed around the hole formation regions 22. This screw hole forming step S7 includes a counterbore co-machining step S8, a female screw pilot hole machining step S9, and a female screw machining step S10, which will be described later.

[0041] The counterbore hole co-machining step S8 is a part of the threaded portion insertion hole forming step S4 and a part of the screw hole forming step S7. In this counterbore hole co-machining step S8, as shown in FIG. 7 , the temporary inner peripheral surface 34i of the temporary workpiece 33 is brought into contact with the outer peripheral surface 24o of the main body material 23, and the temporary hole forming region 32 of the temporary workpiece 33 is overlapped with the hole forming region 22 of the main body material 23 so that the position where the main counterbore hole 26c is to be formed in the main body material 23 overlaps the position where the threaded portion insertion hole 36 is to be formed in the temporary workpiece 33. Then, with the main body material 23 and the temporary workpiece 33 in contact as described above, a counterbore hole as the threaded portion insertion hole 36 is machined in the temporary workpiece 33 using a counterbore tool T such as a counterbore drill, and the main counterbore hole 26c is machined in the main body material 23. The counterbore tool T has a conical apex. The angle θ of this apex coincides with the angle θ (see FIG. 9) of the conical portion 44 of the screw 41. The angle of the conical portion 44 of the screw 41 is the angle formed by a first generatrix of the conical portion 44 and a second generatrix of the conical portion 44 that is symmetrical to the first generatrix with respect to the screw axis Ag.

[0042] When the counterbore hole co-machining step S8 is completed and the counterbore tool T is withdrawn from the main body material 23 and the temporary material 33, the counterbore hole 36 formed in the temporary material 33 and the main body counterbore hole 26c formed in the main body material 23 appear, as shown in FIG. 8 . The central axis Ag of the main body counterbore hole 26c formed in the main body material 23 is located on the central axis Ag of the counterbore hole 36 formed in the temporary material 33. This central axis Ag coincides with the screw axis Ag described above. The angle of the apex of the main body counterbore hole 26c formed in the main body material 23 is an angle θ1 that is approximately the same as the angle θ of the apex of the counterbore tool T and the angle θ of the conical portion 44 of the screw 41. Meanwhile, the angle of the apex of the counterbore hole 36 formed in the temporary material 33 is an angle θ2 that is smaller than the angle θ1 of the apex of the main body counterbore hole 26c formed in the main body material 23 and the angle θ of the apex of the counterbore tool T. The angle of the apex of the countersunk hole 36 is the angle formed by a first generatrix on the surface of the countersunk hole 36 and a second generatrix that is symmetrical to the first generatrix with respect to the central axis Ag within the generatrix on the surface of the countersunk hole 36. Furthermore, the inner diameter D2 of the countersunk hole 36 at the provisional inner peripheral surface 34i is smaller than the inner diameter D1 of the main body countersunk hole 26c at the main body outer peripheral surface 24o.

[0043] While the temporary workpiece 33 and the main body workpiece 23 are being machined with the countersinking tool T, the amount of elastic deformation of the temporary workpiece 33 in the radial direction relative to the central axis Ag of the countersinking tool T is greater than the amount of elastic deformation of the main body workpiece 23 in the radial direction relative to the central axis Ag of the countersinking tool T. This is thought to be due to the fact that the thickness t2 of the temporary workpiece 33 is thinner than the thickness t1 of the main body workpiece 23, and furthermore, the deformation restraining force of the temporary workpiece 33 in the radial direction centered on the central axis Ag of the countersinking tool T is small, etc. In this way, due to the difference between the elastic deformation amount of the temporary material 33 and the elastic deformation amount of the main material 23, when the countersinking tool T is pulled out from the main material 23 and the temporary material 33, as described above, the angle of the top of the countersink hole 36 formed in the temporary material 33 becomes an angle θ2 which is smaller than the angle θ1 of the top of the main material countersink hole 26c formed in the main material 23 and the angle θ of the top of the countersinking tool T, and the inner diameter D2 of the countersink hole 36 at the position of the temporary inner surface 34i becomes smaller than the inner diameter D1 of the main material countersink hole 26c at the position of the main material outer surface 24o.

[0044] When the countersink hole machining step S8 is completed, the thread insertion hole forming step S4 and the temporary material machining step S2 are completed, and the temporary strainer 31 is completed.

[0045] In the threaded hole forming step S7 of the main body material processing step S5, once the counterbore hole co-machining step S8 is completed, the aforementioned female thread pilot hole machining step S9 and female thread machining step S10 are carried out. In the female thread pilot hole machining step S9, a female thread pilot hole is machined in the main body material 23, connecting to the main body counterbore hole 26c formed in the counterbore hole co-machining step S8. In the female thread machining step S10, a female thread is formed on the inner surface of the female thread pilot hole. When the female thread machining step S10 is completed, the threaded hole forming step S7 and the main body material processing step S5 are completed, and the strainer main body 21 is completed.

[0046] As described above, once the temporary material processing step S2 and the main body material processing step S5 are completed, the two temporary strainers 31 are attached to the strainer main body 21 using a plurality of screws 41 (assembly step S11). In this assembly step S11, the temporary inner peripheral surfaces 34i of the two temporary strainers 31 are brought into contact with the main body outer peripheral surface 24o of the strainer main body 21. Next, the temporary hole formation region 32 of the first temporary strainer 31a is overlapped on the first hole formation region 22a of the strainer main body 21 so that the central axes Ag of the plurality of screw holes 26 in the strainer main body 21 and the central axes Ag of the plurality of threaded portion insertion holes 36 in the first temporary strainer 31a are aligned. Similarly, the temporary hole formation region 32 of the second temporary strainer 31b is overlapped with the second hole formation region 22b of the strainer body 21 so that the central axes Ag of the multiple screw holes 26 of the strainer body 21 and the central axes Ag of the multiple threaded portion insertion holes 36 of the second temporary strainer 31b are aligned. Then, the male thread portions 42 of the multiple screws 41 are inserted into the multiple threaded portion insertion holes 36 of each temporary strainer 31, and then screwed into the multiple threaded holes 26 of the strainer body 21.

[0047] With the above steps, the strainer 20 is completed.

[0048] 9, after the countersink co-machining step S8 is completed and the countersink tool T is withdrawn from the main body material 23 and the temporary material 33, the inner diameter D2 of the countersink 36 at the provisional inner circumferential surface 34i is smaller than the inner diameter D1 of the main body countersink 26c at the main body outer circumferential surface 24o. Therefore, during the process of threading the screw 41 into the threaded hole 26 of the strainer main body 21, as shown in FIG. 5, the hole end 36e of the countersink 36 of the temporary strainer 31, which is the portion of the countersink 36 on the provisional inner circumferential surface 34i side, is pressed by the conical portion 44 of the screw 41 and comes into close contact with the surface of the main body countersink 26c of the strainer main body 21. Therefore, in this embodiment, the pressing force of the temporary strainer 31 against the strainer main body 21 can be increased.

[0049] 5 , in this embodiment, even after the screw 41 is screwed into the threaded hole 26 of the strainer body 21, the maximum inner diameter D3 of the threaded portion insertion hole 36 of the temporary strainer 31 is smaller than the maximum outer diameter D4 of the conical portion 44 of the screw 41. Therefore, in this embodiment, even after the screw 41 is screwed into the threaded hole 26 of the strainer body 21, a portion of the screw head 43 protrudes from the threaded portion insertion hole 36 of the temporary strainer 31 toward the temporary outer peripheral surface 34o of the temporary strainer 31. In this embodiment, the portion of the screw head 43 protrudes toward the temporary outer peripheral surface 34o of the temporary strainer 31 by, for example, 1 mm.

[0050] 10 , even after the screw 41c is screwed into the threaded hole 26 of the strainer body 21, a portion of the screw head 43 does not protrude toward the temporary outer peripheral surface 34o of the temporary strainer 31. In this case, a force F acts from the conical portion 44 of the screw 41c at a middle position in the thickness direction of the temporary strainer 31 on the surface of the threaded portion insertion hole (countersunk hole) 36. However, the force F does not substantially act from the conical portion 44 of the screw 41c at the position of the temporary outer peripheral surface 34o of the temporary strainer 31 on the surface of the threaded portion insertion hole (countersunk hole) 36.

[0051] On the other hand, if a portion of the screw head 43 protrudes from the threaded portion insertion hole 36 of the temporary strainer 31 toward the temporary outer peripheral surface 34o of the temporary strainer 31 as in this embodiment, a force F in a direction that brings the temporary strainer 31 into tight contact with the strainer body 21 acts from the conical portion 44 of the screw 41 not only at a middle position in the thickness direction of the temporary strainer 31 on the surface of the threaded portion insertion hole (counterbore hole) 36, but also at the position of the temporary outer peripheral surface 34o of the temporary strainer 31 on the surface of the threaded portion insertion hole (counterbore hole) 36. Therefore, in this embodiment, the pressing force of the temporary strainer 31 against the strainer body 21 can be increased from this perspective as well.

[0052] 1, the completed strainer 20 is arranged at the boundary between the axial inlet-side flow path portion 16i and the annular flow path portion 17 so as to be cylindrical about the axis A. In this case, as shown in FIG. 2, the completed strainer 20 is arranged in the valve casing 10 so that both ends of the first temporary strainer 31a in the circumferential direction Dc and both ends of the second temporary strainer 31b in the circumferential direction Dc do not face the inlet flow path portion 18i.

[0053] The strainer 20 of this embodiment traps most of the foreign matter contained in the steam that has flowed into the valve casing 10. The strainer 20 is provided with a temporary strainer 31. The temporary strainer 31 traps most of the foreign matter contained in the steam that has flowed into the valve casing 10 ...

[0054] As described above, in this embodiment, the strainers 20 are arranged in the valve casing 10 so that both ends of the first temporary strainer 31a in the circumferential direction Dc and both ends of the second temporary strainer 31b in the circumferential direction Dc do not face the inlet flow path portion 18i. For this reason, in this embodiment, steam that has traveled straight through the inlet flow path portion 18i in the valve casing 10 does not directly collide with both ends of each temporary strainer 31 in the circumferential direction Dc. Therefore, in this embodiment, separation of each temporary strainer 31 from the strainer body 21 can be suppressed.

[0055] Steam is allowed to flow through the main steam line for a predetermined time, and when the amount of foreign matter in the steam decreases, the strainer 20 is removed from the valve casing 10, and then the temporary strainer 31 is removed from the strainer body 21. In this embodiment, at this time, the temporary strainer 31 can be easily removed from the strainer body 21 by removing the multiple screws 41 from the strainer 20 using a screwdriver or other screwdriver tool.

[0056] Thereafter, the strainer body 21 from which the strainer 20 has been removed is returned to the valve casing 10. This strainer body 21 captures most of the foreign matter contained in the steam that has flowed into the valve casing 10.

[0057] In this embodiment, the threaded hole 26 of the strainer body 21 does not penetrate from the outer peripheral surface 24o to the inner peripheral surface 24i of the strainer body 21, but has a hole bottom 26b. Therefore, when the temporary strainer 31 is removed from the strainer 20 and only the strainer body 21 is placed inside the valve casing 10, foreign matter in the steam located on the outer peripheral side of the strainer body 21 can be prevented from flowing into the inner peripheral side of the strainer 20 body through the threaded hole 26.

[0058] "Modified strainer example" The thickness of the temporary strainer 31 is thinner than the thickness of the strainer body 21, and therefore the rigidity of the temporary strainer 31 is lower than the rigidity of the strainer body 21. For this reason, while the temporary strainer 31 is capturing foreign matter in the steam, a portion of the temporary strainer 31 may repeatedly come into contact with and separate from the strainer body 21 due to the influence of the steam. If a portion of the temporary strainer 31 repeatedly comes into contact with and separates from the strainer body 21 in this way, the temporary strainer 31 may become fatigued and may be damaged.

[0059] In the above embodiment, only both ends of the temporary strainer 31 in the axial direction Da and both ends of the temporary strainer 31 in the circumferential direction Dc are connected to the strainer body 21 by the screws 41. For this reason, while the temporary strainer 31 is capturing foreign matter in the steam, the middle part of the temporary strainer 31 in the axial direction Da may repeatedly come into contact with and separate from the strainer body 21. Therefore, as shown in Fig. 11 , in addition to both ends of the temporary strainer 31 in the axial direction Da and both ends of the temporary strainer 31 in the circumferential direction Dc, the middle part of the temporary strainer 31 in the axial direction Da may also be connected to the strainer body 21 by the screws 41.

[0060] In this case, the hole formation region 22 of the strainer body 21 has a first side hole formation region 22f and a second side hole formation region 22s. The second side hole formation region 22s is aligned with and spaced apart from the first side hole formation region 22f in the axial direction Da in which the cylindrical strainer body 21 extends. Some of the multiple steam passage holes 25 are formed in the first side hole formation region 22f. Other portions of the multiple steam passage holes 25 are formed in the second side hole formation region 22s. The temporary hole formation region 32 of the temporary strainer 31 has a first side temporary hole formation region 32f that overlaps with the first side hole formation region 22f and a second side temporary hole formation region 32s that overlaps with the second side hole formation region 22s. Some of the multiple temporary steam passage holes 35 are formed in the first side temporary hole formation region 32f. Other portions of the multiple temporary steam passage holes 35 are formed in the second side temporary hole formation region 32s. The temporary strainer 31 has, between the first side temporary hole formation region 32 f and the second side temporary hole formation region 32 s, an inter-region threaded portion insertion hole 36B that is one of the plurality of threaded portion insertion holes 36. The strainer body 21 has, between the first side hole formation region 22 f and the second side hole formation region 22 s, an inter-region threaded hole 26B that is one of the plurality of threaded holes 26 and communicates with the inter-region threaded portion insertion hole 36B.

[0061] The strainer 20 in the above embodiment and the modified example includes two temporary strainers 31. However, as shown in Fig. 12, the strainer 20 may include only one temporary strainer 31. In this case, one temporary strainer 31 is disposed around almost the entire circumference of the strainer body 21. Even in this modified example, it is preferable that the strainer 20 including this temporary strainer 31 is disposed inside the valve casing 10 so that both ends of the temporary strainer 31 in the circumferential direction Dc do not face the inlet flow path portion 18i.

[0062] The screw holes 26 in the above embodiment and each of the above modified examples have hole bottoms 26b and do not penetrate from the outer peripheral surface 24o to the inner peripheral surface 24i of the strainer body 21. However, if the minimum inner diameter of the screw holes 26 is smaller than the minimum inner diameter of the steam passage holes 25 of the strainer body 21, the screw holes 26 may penetrate from the outer peripheral surface 24o to the inner peripheral surface 24i of the strainer body 21.

[0063] The present disclosure is not limited to the embodiments described above, and various additions, modifications, substitutions, partial deletions, etc. are possible within the scope of the conceptual idea and spirit of the present invention as derived from the content defined in the claims and their equivalents.

[0064] "Additional Notes" The strainer 20 in the above-described embodiments and modifications can be understood, for example, as follows: (1) The strainer 20 in a first aspect is a strainer 20 disposed in the valve casing 10 in which the steam flow path 15 is formed. The strainer 20 comprises a strainer body 21 having a cylindrical shape and including a main body outer peripheral surface 24o, a main body inner peripheral surface 24i that is back-to-back with the main body outer peripheral surface 24o, and a plurality of steam passage holes 25 that penetrate from the main body outer peripheral surface 24o to the main body inner peripheral surface 24i; a temporary strainer 31 that is arranged along the main body outer peripheral surface 24o of the strainer body 21 and has a temporary inner peripheral surface 34i that faces the main body outer peripheral surface 24o, a temporary outer peripheral surface 34o that is back-to-back with the temporary inner peripheral surface 34i, and a plurality of temporary steam passage holes 35 that penetrate from the temporary outer peripheral surface 34o to the temporary inner peripheral surface 34i and have inner diameters smaller than the inner diameters of each of the plurality of steam passage holes 25; and a plurality of screws 41 that attach the temporary strainer 31 along the main body outer peripheral surface 24o of the strainer body 21. In the temporary strainer 31, a temporary hole formation region 32 in which the plurality of temporary steam passage holes 35 are formed overlaps with the hole formation region 22 in which the plurality of steam passage holes 25 are formed in the strainer body 21. Each of the plurality of screws 41 has a cylindrical male thread portion 42 in which a male thread is formed, and a screw head 43 provided at the end of the base end side Dgb of the tip end side Dgt and the base end side Dgb in the extension direction Dg of the male thread portion 42. The temporary strainer 31 further has screw portion insertion holes 36 that penetrate from the temporary outer peripheral surface 34o to the temporary inner peripheral surface 34i of the temporary strainer 31 around the temporary hole formation region 32, and through which the male thread portion 42 of each of the plurality of screws 41 can pass but the screw head 43 cannot pass. The strainer body 21 further has a threaded hole 26 recessed from the outer peripheral surface 24o of the strainer body 21 toward the inner peripheral surface 24i of the strainer body 21 around the hole formation region 22 and communicating with the threaded portion insertion hole 36 of the temporary strainer 31. The threaded hole 26 of the strainer body 21 has a female threaded hole 26f into which the male threaded portion 42 passing through the threaded portion insertion hole 36 is screwed.

[0065] In this embodiment, the temporary strainer 31 can be easily removed from the strainer body 21 by removing the multiple screws 41 from the strainer 20 using a screwdriver or other screwdriver tool.

[0066] (2) The strainer 20 in the second aspect is the strainer 20 in the first aspect, wherein the screw hole 26 does not penetrate from the outer peripheral surface 24o of the strainer body 21 to the inner peripheral surface 24i of the body, and has a hole bottom 26b.

[0067] When the temporary strainer 31 is removed from the strainer 20 and only the strainer body 21 is placed inside the valve casing 10, foreign matter in the steam located on the outer periphery of the strainer body 21 can be prevented from flowing into the inner periphery of the body of the strainer 20 through the screw hole 26.

[0068] (3) The strainer 20 in a third aspect is the strainer 20 in the first or second aspect, wherein each of the plurality of screws 41 is a flat head screw having a conical portion 44 whose outer diameter gradually decreases as the screw head 43 approaches the tip side Dgt. The threaded portion insertion hole 36 of the temporary strainer 31 is a conical countersunk hole whose inner diameter gradually decreases from the provisional outer peripheral surface 34o to the provisional inner peripheral surface 34i of the temporary strainer 31, corresponding to the shape of the conical portion 44 and allowing at least a portion of the conical portion 44 to be accommodated.

[0069] By using flat head screws to connect the strainer body 21 and the temporary strainer 31, the pressing force between the strainer body 21 and the temporary strainer 31 can be increased.

[0070] (4) The strainer 20 in a fourth aspect is the strainer 20 in the first or second aspect, wherein the plurality of screws 41 are flat head screws having conical portions 44 whose outer diameters gradually decrease as the screw heads 43 approach the tip side Dgt. The distance between the provisional outer peripheral surface 34o and the provisional inner peripheral surface 34i of the temporary strainer 31 is shorter than the distance between the end of the base side Dgb and the end of the tip side Dgt of the conical portion 44. The threaded portion insertion hole 36 of the temporary strainer 31 is a conical countersunk hole whose inner diameter gradually decreases from the provisional outer peripheral surface 34o to the provisional inner peripheral surface 34i of the temporary strainer 31, corresponding to the shape of at least a portion of the base side Dgb of the conical portion 44 and capable of accommodating at least a portion of the base side Dgb of the conical portion 44. The screw hole 26 of the strainer body 21 corresponds to the shape of the tip side Dgt portion excluding at least a part of the base end side Dgb in the conical portion 44, and has a conical body countersunk hole 26c whose inner diameter gradually decreases from the body outer surface 24o toward the body inner surface 24i of the strainer body 21 so as to be able to accommodate the tip side Dgt portion excluding at least a part of the base end side Dgb in the conical portion 44. The female screw hole 26f of the strainer body 21 extends from the end of the body countersunk hole 26c on the side of the body inner surface 24i to the side of the body inner surface 24i.

[0071] By using flat head screws to connect the strainer body 21 and the temporary strainer 31, the pressing force between the strainer body 21 and the temporary strainer 31 can be increased.

[0072] (5) A strainer 20 in a fifth aspect is the strainer 20 in the third or fourth aspect, wherein the maximum inner diameter of the threaded portion insertion hole 36 of the temporary strainer 31 is smaller than the maximum outer diameter of the conical portion 44. A part of the conical portion 44 protrudes from the threaded portion insertion hole 36 of the temporary strainer 31 toward the temporary outer peripheral surface 34o of the temporary strainer 31.

[0073] In this embodiment, the pressing force between the strainer body 21 and the temporary strainer 31 can be increased.

[0074] (6) A strainer 20 in a sixth aspect is the strainer 20 according to any one of claims 1 to 5 in any one of the first to fifth aspects, wherein the hole formation region 22 of the strainer body 21 has a first side hole formation region 22f and a second side hole formation region 22s. The second side hole formation region 22s is aligned with and spaced apart from the first side hole formation region 22f in the extension direction of the cylindrical strainer body 21. Some of the steam passage holes 25 are formed in the first side hole formation region 22f. Another part of the steam passage holes 25 is formed in the second side hole formation region 22s. The temporary hole formation region 32 of the temporary strainer 31 has a first side temporary hole formation region 32f overlapping with the first side hole formation region 22f and a second side temporary hole formation region 32s overlapping with the second side hole formation region 22s. Some of the plurality of temporary steam passage holes 35 are formed in the first side temporary hole formation region 32f. Other parts of the plurality of temporary steam passage holes 35 are formed in the second side temporary hole formation region 32s. The temporary strainer 31 has an inter-region threaded portion insertion hole 36B, which is part of the plurality of threaded portion insertion holes 36, between the first side temporary hole formation region 32f and the second side temporary hole formation region 32s. The strainer body 21 has an inter-region threaded hole 26B, which is part of the plurality of threaded holes 26 and communicates with the inter-region threaded portion insertion hole 36B, between the first side hole formation region 22f and the second side hole formation region 22s.

[0075] In this embodiment, the pressing force between the strainer body 21 and the portion of the temporary strainer 31 between the first side temporary hole formation area 32f and the second side temporary hole formation area 32s can be increased.

[0076] The steam valves in the above embodiments and modified examples can be understood as follows, for example: (7) A steam valve in a seventh aspect includes the strainer 20 in any one of the first to sixth aspects, the valve casing 10, a valve element 12 that can move back and forth within the valve casing 10 in an axial direction Da in which an axis A extends to open and close the flow path 15, and a valve rod 13 that extends on the axis A in the axial direction Da and to which the valve element 12 is connected. The flow path 15 includes an axial flow path section 16 that extends in the axial direction Da around the axis A, an annular flow path section 17 that is formed annularly around the axis A around an axial inlet-side flow path section 16i that is a part of the axial flow path section 16 in the axial direction Da and that is in communication with the axial inlet-side flow path section 16i, an inlet flow path section 18i that extends from the annular flow path section 17 in a first radial direction Dr1 of radial directions Dr relative to the axis A and opens at the outer surface of the valve casing 10, and an outlet flow path section 18o that extends in either direction from an axial outlet-side flow path section 16o that is another part of the axial flow path section 16 in the axial direction Da and opens at the outer surface of the valve casing 10. The valve element 12 is arranged reciprocally within the axial inlet-side flow path section 16i. The strainer 20 is disposed at the boundary between the axial inlet side flow passage portion 16i and the annular flow passage portion 17 so that the strainer body 21 is cylindrical around the axis A.

[0077] In this embodiment, foreign matter contained in the steam that has flowed into the valve casing 10 can be captured by the strainer 20.

[0078] (8) A steam valve according to an eighth aspect is the steam valve according to the seventh aspect, wherein an end of the temporary strainer 31 in the circumferential direction Dc relative to the axis A does not face the inlet flow path portion 18i.

[0079] In this embodiment, the steam that has traveled straight through the inlet flow path 18i in the valve casing 10 does not directly collide with the end of the temporary strainer 31 in the circumferential direction Dc. Therefore, in this embodiment, separation of the temporary strainer 31 from the strainer body 21 can be suppressed.

[0080] The manufacturing method of the strainer 20 in the above-described embodiments and modifications can be understood, for example, as follows: (9) A manufacturing method of the strainer 20 in a ninth aspect is a manufacturing method of the strainer 20 to be disposed in the valve casing 10 in which the steam flow path 15 is formed. This manufacturing method includes a preparation process S1 for preparing a cylindrical main body material 23 having a main body outer peripheral surface 24o and a main body inner peripheral surface 24i and capable of being placed within the flow path 15, a temporary material 33 that can be attached along the main body outer peripheral surface 24o of the main body material 23 and has a temporary inner peripheral surface 34i facing the main body outer peripheral surface 24o and a temporary outer peripheral surface 34o that is back-to-back with the temporary inner peripheral surface 34i, and a plurality of screws 41; a main body material processing process S5 for processing the main body material 23 to form a strainer main body 21; a temporary material processing process S2 for processing the temporary material 33 to form a temporary strainer 31; and an assembly process S11 for attaching the temporary strainer 31 to the strainer main body 21 using the plurality of screws 41. Each of the plurality of screws 41 has a cylindrical male thread portion 42 on which a male thread is formed, and a screw head portion 43 provided at an end of the base end side Dgb out of a tip end side Dgt and a base end side Dgb in the extension direction Dg of the male thread portion 42. The body material processing step S5 includes a steam passage hole forming step S6 of forming a plurality of steam passage holes 25 that penetrate from the body outer peripheral surface 24o to the body inner peripheral surface 24i within a predetermined hole formation region 22 of the body material 23, and a screw hole forming step S7 of forming screw holes 26 that are recessed from the body outer peripheral surface 24o toward the body inner peripheral surface 24i around the hole formation region 22 of the body material 23 and into which the male thread portion 42 of each of the plurality of screws 41 can be screwed. The temporary material processing process S2 includes a temporary steam passage hole forming process S3 for forming a plurality of temporary steam passage holes 35 that penetrate from the temporary outer peripheral surface 34o to the temporary inner peripheral surface 34i within a predetermined temporary hole forming area 32 of the temporary material 33 and have an inner diameter smaller than the inner diameter of each of the plurality of steam passage holes 25, and a screw portion insertion hole forming process S4 for forming a screw portion insertion hole 36 that penetrates from the temporary outer peripheral surface 34o to the temporary inner peripheral surface 34i around the temporary hole forming area 32 of the temporary material 33 and through which the male screw portion 42 of each of the plurality of screws 41 can pass but the screw head 43 cannot pass.In the threaded portion insertion hole forming step S4, the temporary inner peripheral surface 34i of the temporary material 33 is brought into contact with the main body outer peripheral surface 24o of the main body material 23, and when the temporary hole formation region 32 of the temporary material 33 is overlapped on the hole formation region 22 of the main body material 23, the threaded portion insertion hole 36 is formed in the temporary material 33 at a position that can communicate with the threaded hole 26 of the main body material 23. In the assembling step S11, after the temporary inner peripheral surface 34i is brought into contact with the main body outer peripheral surface 24o and the temporary hole formation region 32 is overlapped on the hole formation region 22, the male threaded portion 42 of the screw 41 is inserted into the threaded portion insertion hole 36 of the temporary strainer 31 and then screwed into the threaded hole 26 of the strainer main body 21.

[0081] In the strainer 20 manufactured in this manner, as with the strainer 20 in the first manner described above, the temporary strainer 31 can be easily removed from the strainer body 21 by removing multiple screws 41 from the strainer 20 using a screwdriver or other screwdriver tool.

[0082] (10) In the tenth aspect, the manufacturing method of the strainer 20 is the same as in the ninth aspect, in the screw hole forming step S7, the screw hole 26 is formed so as not to penetrate from the outer circumferential surface 24o of the main body material 23 to the inner circumferential surface 24i of the main body.

[0083] In the strainer 20 manufactured in this manner, as in the strainer 20 in the second manner described above, when the temporary strainer 31 is removed from the strainer 20 and only the strainer body 21 is placed inside the valve casing 10, foreign matter in the steam located on the outer periphery of the strainer body 21 can be prevented from flowing into the inner periphery of the body of the strainer 20 through the screw hole 26.

[0084] (11) A manufacturing method of a strainer 20 in an eleventh aspect is the manufacturing method of the strainer 20 in the ninth or tenth aspect, wherein each of the plurality of screws 41 is a flat head screw having a conical portion 44 whose outer diameter gradually decreases toward the tip side Dgt of the screw head 43. The distance between the provisional outer peripheral surface 34o and the provisional inner peripheral surface 34i of the temporary strainer 31 is shorter than the distance between the end of the base side Dgb of the conical portion 44 and the end of the tip side Dgt. The screw portion insertion hole 36 is a conical countersunk hole whose inner diameter gradually decreases from the provisional outer peripheral surface 34o toward the provisional inner peripheral surface 34i, corresponding to the shape of at least a part of the base side Dgb of the conical portion 44, and capable of accommodating at least a part of the base side Dgb of the conical portion 44. The screw hole 26 corresponds to the shape of the portion of the tip side Dgt excluding at least a part of the base end side Dgb in the conical portion 44, and has a conical main body countersunk hole 26c whose inner diameter gradually decreases from the main body outer peripheral surface 24o to the main body inner peripheral surface 24i of the strainer main body 21 so as to be able to accommodate the portion of the tip side Dgt excluding at least a part of the base end side Dgb in the conical portion 44. When forming the countersunk hole 36 in the threaded portion insertion hole forming step S4 and forming the main body countersunk hole 26c in the threaded hole forming step S7, the temporary inner peripheral surface 34i of the temporary workpiece 33 is brought into contact with the main body outer peripheral surface 24o of the main body material 23, and the temporary hole forming area 32 of the temporary workpiece 33 is overlapped on the hole forming area 22 of the main body material 23, and the countersunk hole 36 and the main body countersunk hole 26c are co-machined.

[0085] In the strainer 20 manufactured in this embodiment, the pressing force between the strainer body 21 and the temporary strainer 31 can be increased, similar to the strainer 20 in the fourth embodiment described above.

[0086] According to one aspect of the present disclosure, the temporary strainer can be easily removed from the strainer body.

[0087] 10: Valve casing 11: Valve seat 12: Valve disc 13: Valve stem 15: Flow path 16: Axial flow path section 16i: Axial inlet side flow path section 16o: Axial outlet side flow path section 17: Annular flow path section 18i: Inlet flow path section 18o: Outlet flow path section 20: Strainer 21: Strainer body 22: Hole forming region 22a: First hole forming region 22b: Second hole forming region 22f: First side hole forming region 22s: Second side hole forming region 23: Body material 24o: Body outer peripheral surface 24i: Body inner peripheral surface 25: Steam passage hole 26: Threaded hole 26B: Inter-region threaded hole 26c: Body counterbore hole 26f: Female threaded hole 26b: Hole bottom 31: Temporary strainer 31a: First temporary strainer (or simply temporary strainer) 31b: Second temporary strainer (or simply temporary strainer) 32: Temporary hole formation area 32a: First temporary hole formation area 32b: Second temporary hole formation area 32f: First side temporary hole formation area 32s: Second side temporary hole formation area 33: Temporary material 34o: Temporary outer peripheral surface 34i: Temporary inner peripheral surface 35: Temporary steam passage hole 36: Thread portion insertion hole (counterbore hole) 36e: Hole end 36B: Inter-area thread portion insertion hole 41, 41c: Screw 42: Male thread portion 43: Screw head 44: Conical portion A: Axis Da: Axial direction Dc: Circumferential direction Dr: Radial direction Dr1: First radial direction Dr2: Second radial direction Ag: Screw axis (or central axis) Dg: Extension direction Dgt: Tip side Dgb: Base side F: Force T: Counterbore tool

Claims

1. A strainer to be placed inside a valve casing in which a steam flow path is formed, comprising: a strainer body having a cylindrical shape and a main body outer peripheral surface, a main body inner peripheral surface back-to-back with the main body outer peripheral surface, and a plurality of steam passage holes penetrating from the main body outer peripheral surface to the main body inner peripheral surface; a temporary strainer arranged along the main body outer peripheral surface of the strainer body and having a temporary inner peripheral surface facing the main body outer peripheral surface, a temporary outer peripheral surface back-to-back with the temporary inner peripheral surface, and a plurality of temporary steam passage holes penetrating from the temporary outer peripheral surface to the temporary inner peripheral surface and having inner diameters smaller than the respective inner diameters of the plurality of steam passage holes; and a plurality of screws for attaching the temporary strainer along the main body outer peripheral surface of the strainer body, wherein a temporary hole formation region in which the plurality of temporary steam passage holes are formed in the temporary strainer overlaps with a hole formation region in which the plurality of steam passage holes are formed in the strainer body, each of the plurality of screws has a cylindrical male threaded portion on which a male thread is formed, and a screw head provided at the end of the male threaded portion which is on the base end side of the tip end side and the base end side in the extension direction of the male threaded portion; the temporary strainer further has screw portion insertion holes which penetrate from the temporary outer peripheral surface to the temporary inner peripheral surface of the temporary strainer around the temporary hole formation area, and through which the male threaded portion of each of the plurality of screws can pass but the screw head cannot pass; the strainer body further has screw holes which are recessed from the outer peripheral surface of the strainer body towards the inner peripheral surface of the body around the hole formation area, and which communicate with the screw portion insertion holes of the temporary strainer; and the screw holes of the strainer body have female screw holes into which the male threaded portion which has passed through the screw portion insertion holes is screwed.

2. A strainer according to claim 1, wherein the screw hole does not penetrate from the outer peripheral surface of the strainer body to the inner peripheral surface of the body, and has a hole bottom.

3. A strainer as claimed in claim 1, wherein each of the plurality of screws is a flat head screw having a conical portion whose outer diameter gradually decreases as the screw head approaches the tip, and the screw portion insertion hole of the temporary strainer is a conical countersunk hole whose inner diameter gradually decreases from the temporary outer peripheral surface to the temporary inner peripheral surface of the temporary strainer, corresponding to the shape of the conical portion and capable of accommodating at least a portion of the conical portion.

4. A strainer according to claim 1, wherein the plurality of screws are flat head screws having a conical portion whose outer diameter gradually decreases as the screw head approaches the tip end, the distance between the provisional outer peripheral surface and the provisional inner peripheral surface of the temporary strainer is shorter than the distance between the base end end and the tip end end of the conical portion, the threaded portion insertion hole of the temporary strainer is a conical countersunk hole whose inner diameter gradually decreases from the provisional outer peripheral surface to the provisional inner peripheral surface of the temporary strainer, corresponding to the shape of at least a portion of the base end side of the conical portion and capable of accommodating at least a portion of the base end side of the conical portion, and the screw hole of the strainer body is a conical body countersunk hole whose inner diameter gradually decreases from the body outer peripheral surface to the body inner peripheral surface of the strainer body, corresponding to the shape of the tip end side portion of the conical portion excluding at least a portion of the base end side, and capable of accommodating the tip end side portion of the conical portion excluding at least a portion of the base end side, The female screw hole of the strainer body extends from an end of the body countersunk hole on the side of the inner circumferential surface of the body to the side of the inner circumferential surface of the body.

5. A strainer as claimed in claim 3, wherein the maximum inner diameter of the threaded portion insertion hole of the temporary strainer is smaller than the maximum outer diameter of the conical portion, and a part of the conical portion protrudes from the threaded portion insertion hole of the temporary strainer towards the temporary outer peripheral surface of the temporary strainer.

6. A strainer according to claim 1, wherein the hole formation region of the strainer body has a first side hole formation region and a second side hole formation region, the second side hole formation region is aligned with and spaced apart from the first side hole formation region in the direction in which the cylindrical strainer body extends, some of the steam passage holes are formed in the first side hole formation region, and another part of the steam passage holes is formed in the second side hole formation region, the temporary hole formation region of the temporary strainer has a first side temporary hole formation region overlapping with the first side hole formation region and a second side temporary hole formation region overlapping with the second side hole formation region, some of the temporary steam passage holes are formed in the first side temporary hole formation region, and another part of the temporary steam passage holes is formed in the second side temporary hole formation region, and the temporary strainer has an inter-region thread portion insertion hole which is a part of the plurality of thread portion insertion holes between the first side temporary hole formation region and the second side temporary hole formation region, The strainer body has an inter-region threaded hole between the first side hole forming region and the second side hole forming region, the inter-region threaded portion insertion hole being a part of the plurality of threaded holes.

7. A strainer according to any one of claims 1 to 6, comprising: the valve casing; a valve element capable of reciprocating within the valve casing in an axial direction along which an axis extends to open and close the flow path; and a valve rod extending on the axis in the axial direction and to which the valve element is connected, wherein the flow path has: an axial flow path section extending in the axial direction with the axis as its center; an annular flow path section formed in an annular shape around an axial inlet side flow path section that is a part of the axial flow path section in the axial direction and centered on the axis, and communicating with the axial inlet side flow path section; an inlet flow path section extending from the annular flow path section in a first radial direction relative to the axis and opening at the outer surface of the valve casing; and an outlet flow path section extending in any direction from an axial outlet side flow path section that is another part of the axial flow path section in the axial direction, and opening at the outer surface of the valve casing, wherein the valve element is arranged reciprocally within the axial inlet side flow path section, The strainer is disposed at a boundary between the axial inlet side flow path portion and the annular flow path portion so that the strainer body has a cylindrical shape around the axis.

8. A steam valve according to claim 7, wherein an end of the temporary strainer in the circumferential direction relative to the axis does not face the inlet flow path portion.

9. A method for manufacturing a strainer to be placed inside a valve casing in which a steam flow path is formed, the method comprising the steps of: a preparation step of preparing a main body material that is cylindrical, has a main body outer peripheral surface and a main body inner peripheral surface, and can be placed inside the flow path; a temporary material that can be attached along the main body outer peripheral surface of the main body material, and has a temporary inner peripheral surface that faces the main body outer peripheral surface and a temporary outer peripheral surface that is back-to-back with the temporary inner peripheral surface; and a plurality of screws; a main body material processing step of processing the main body material to form a strainer main body; a temporary material processing step of processing the temporary material to form a temporary strainer; and an assembly step of attaching the temporary strainer to the strainer main body using the plurality of screws, wherein each of the plurality of screws has a cylindrical male thread portion on which a male thread is formed, and a screw head provided at the end of the base end out of the tip end and base end in the extension direction of the male thread portion, and the main body material processing step comprises: a steam passage hole forming process for forming a plurality of steam passage holes penetrating from the outer circumferential surface of the main body to the inner circumferential surface of the main body within a predetermined hole formation region of the main body material; and a screw hole forming process for forming screw holes recessed from the outer circumferential surface of the main body toward the inner circumferential surface of the main body around the hole formation region of the main body material, into which the male thread portions of each of the plurality of screws can be screwed; and the temporary material processing process includes a temporary steam passage hole forming process for forming a plurality of temporary steam passage holes penetrating from the temporary outer circumferential surface to the temporary inner circumferential surface within a predetermined temporary hole formation region of the temporary material, and having inner diameters smaller than the inner diameters of each of the plurality of steam passage holes; and a screw portion insertion hole forming process for forming a screw portion insertion hole penetrating from the temporary outer circumferential surface to the temporary inner circumferential surface around the temporary hole formation region of the temporary material, through which the male thread portions of each of the plurality of screws can pass but the screw heads cannot pass, In the threaded portion insertion hole forming step, the temporary inner peripheral surface of the temporary material is brought into contact with the main outer peripheral surface of the main material, and when the temporary hole formation region of the temporary material is superimposed on the hole formation region of the main material, the threaded portion insertion hole is formed in the temporary material at a position that can communicate with the screw hole of the main material,In the assembling step, the temporary inner peripheral surface is brought into contact with the outer peripheral surface of the main body, the temporary hole formation area is overlapped with the hole formation area, and then the male thread portion of the screw is inserted into the thread portion insertion hole of the temporary strainer and then screwed into the screw hole of the strainer body.

10. A strainer manufacturing method according to claim 9, wherein in the screw hole forming step, the screw holes are formed so as not to penetrate from the outer circumferential surface of the main body to the inner circumferential surface of the main body material.

11. A method for manufacturing a strainer as set forth in claim 9 or 10, wherein each of the plurality of screws is a flat head screw having a conical portion whose outer diameter gradually decreases as the screw head approaches the tip end, the distance between the provisional outer peripheral surface and the provisional inner peripheral surface of the provisional strainer is shorter than the distance between the base end end and the tip end end of the conical portion, the screw portion insertion hole is a conical countersunk hole whose inner diameter gradually decreases from the provisional outer peripheral surface to the provisional inner peripheral surface, corresponding to the shape of at least a portion of the base end side of the conical portion and capable of accommodating at least a portion of the base end side of the conical portion, the screw hole is a conical body countersunk hole whose inner diameter gradually decreases from the body outer peripheral surface to the body inner peripheral surface of the strainer body, corresponding to the shape of the tip end portion of the conical portion excluding at least a portion of the base end side, and capable of accommodating the tip end portion of the conical portion excluding at least a portion of the base end side, a manufacturing method for a strainer, wherein when forming the countersunk hole in the threaded portion insertion hole forming step and forming the main body countersunk hole in the screw hole forming step, the temporary inner peripheral surface of the temporary material is brought into contact with the main body outer peripheral surface of the main body material, and the temporary hole forming area of ​​the temporary material is overlapped on the hole forming area of ​​the main body material, and the countersunk hole and the main body countersunk hole are machined together.

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