STEAM VALVE AND STEAM TURBINE PLANT

There are provided a steam valve and the like capable of preventing breakage of an auxiliary valve element and effectively suppressing the occurrence of a leak of steam in the auxiliary valve element. In the steam valve of an embodiment, the auxiliary valve element is structured to be in an open state in which the valve rod moves in an opening direction to increase a distance between an auxiliary-valve cap and a main valve element, thereby opening an auxiliary-valve steam introduction hole, and to be in a fully-closed state in which the valve rod moves in a closing direction in which the main valve element is closed to bring the auxiliary-valve cap and the main valve element into contact with each other, thereby closing the auxiliary-valve steam introduction holes. A contact position in which the auxiliary-valve cap and the main valve element are brought into contact with each other is located outside in a radial direction of the valve rod from the outer peripheral surface, of the auxiliary-valve tubular part, through which the auxiliary-valve steam introduction holes are formed.

CROSSREFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application (No. 2021-202347), filed on Dec. 14, 2021; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a steam valve and a steam turbine plant.

BACKGROUND

In a steam turbine plant, a main steam stop valve and a steam control valve are installed at an inlet of a steam turbine. In starting the steam turbine, a warm-up operation is performed to prevent high thermal stress from being applied to the steam turbine.

The warm-up operation is performed by controlling a flow rate of steam with the main steam stop valve with the steam control valve in a fully-open state. The main steam stop valve has a main valve element and an auxiliary valve element, for example, and in the warm-up operation, by controlling an opening degree of the auxiliary valve element with the main valve element in a fully-closed state, the flow rate of steam passing through the main steam stop valve is regulated.

[A] Structure of Steam Valve300J

FIG.7andFIG.8are sectional views schematically illustrating a steam valve (main steam stop valve) according to a related art.FIG.7illustrates a part of the cross section on a vertical plane (xz plane), and inFIG.8, an area A inFIG.7is enlarged and illustrated. InFIG.7andFIG.8, a longitudinal direction is a vertical direction z, a lateral direction is a first horizontal direction x, and a direction orthogonal to the paper sheet is a second horizontal direction y.

A steam valve300J according to the related art is a main steam stop valve including a valve seat310, a main valve element320, an auxiliary valve element330, and a valve rod340, as illustrated inFIG.7andFIG.8.

In the steam valve300J according to the related art, the valve rod340moves in an opening direction AX1 in which the main valve element320is opened in an axial direction AX along a center axis CL of the valve rod340, thereby increasing a distance between the main valve element320and the valve seat310. Further, in the steam valve300J, the valve rod340moves in a closing direction AX2 in which the main valve element320is closed in the axial direction AX, thereby reducing the distance between the main valve element320and the valve seat310.

Further, in the related art, when the warm-up operation is performed on a steam turbine (whose illustration is omitted), in the steam valve300J which is the main steam stop valve, by controlling an opening degree of the auxiliary valve element330with the main valve element320in a fully-closed state, a flow rate of steam is regulated.FIG.7illustrates the auxiliary valve element330in a fully-open state, andFIG.8illustrates the auxiliary valve element330in a fully-closed state.

The respective parts constituting the steam valve300J will be described in order.

The valve seat310has, for example, a ring shape, and a valve hole K310is formed therein. Here, the valve seat310is fixed coaxially with the valve rod340in the inside (valve chamber) of a valve casing (whose illustration is omitted).

The main valve element320has, for example, a cylindrical shape, and is provided to be capable of abutting on the valve seat310. Here, the main valve element320is coupled with one end (upper end in the figure) of the valve rod340so as to be coaxial with the valve rod340inside the valve casing (whose illustration is omitted). Further, inside the main valve element320, an accommodation space S320for accommodating the auxiliary valve element330is formed.

The auxiliary valve element330is accommodated to be coaxial with the valve rod340in the accommodation space S320formed inside the main valve element320, and can slide in the axial direction AX. The auxiliary valve element330is structured such that steam is introduced from the outside thereof through an auxiliary-valve steam introduction hole H330to an auxiliary-valve steam flow path F331, and the steam introduced to the auxiliary-valve steam flow path F331flows out to the valve hole K310.

In the auxiliary valve element330, the auxiliary-valve main body331includes a first auxiliary-valve main body part3311, a second auxiliary-valve main body part3312, and a third auxiliary-valve main body part3313.

The first auxiliary-valve main body part3311of the auxiliary-valve main body331has, for example, a cylindrical outer shape.

The second auxiliary-valve main body part3312of the auxiliary-valve main body331has, for example, a truncated conical outer shape, and is structured such that its diameter decreases from an outer diameter of the first auxiliary-valve main body part3311as it goes toward the opening direction AX1 in the axial direction AX.

The third auxiliary-valve main body part3313of the auxiliary-valve main body331has, for example, a cylindrical outer shape, and its outer diameter is the same as that of an end portion located on the opening direction AX1 side of the second auxiliary-valve main body part3312.

Through the third auxiliary-valve main body part3313, an auxiliary-valve steam introduction hole H330is formed. The auxiliary-valve steam introduction hole H330is formed through a portion, of the third auxiliary-valve main body part3313, protruding from the main valve element320in the opening direction AX1 (auxiliary-valve tubular part). The auxiliary-valve steam introduction hole H330is along a radial direction of the valve rod340(a direction orthogonal to the axial direction AX) so that the inside and the outside of the third auxiliary-valve main body part3313communicate between each other. That is, the auxiliary-valve steam introduction hole H330is formed to be along the plane orthogonal to the center axis CL of the valve rod340. The auxiliary-valve steam introduction hole H330is two or more, and a plurality of them are spaced side by side in a circumferential direction of the valve rod340, and a plurality of them are arranged side by side in the axial direction AX of the valve rod340, and moreover, each of the auxiliary-valve steam introduction holes H330precisely faces toward the center axis CL in any stage of the axial direction AX.

Further, on an outer peripheral surface of a portion located on the opening direction AX1 side from a portion in which the auxiliary-valve steam introduction holes H330are formed through a portion, of the third auxiliary-valve main body part3313, protruding from the main valve element320, a male screw is formed.

Moreover, in the auxiliary-valve main body331, the auxiliary-valve steam flow path F331is formed. The auxiliary-valve steam flow path F331includes a first auxiliary-valve steam flow path part F3311, a second auxiliary-valve steam flow path part F3312, and a third auxiliary-valve steam flow path part F3313.

In the first auxiliary-valve steam flow path part F3311, an end portion located on the closing direction AX2 side in the axial direction AX (bottom end) communicates with the valve hole K310of the valve seat310, and an end portion located on the opening direction AX1 side in the axial direction AX (top end) communicates with the second auxiliary-valve steam flow path part F3312. The first auxiliary-valve steam flow path part F3311is two or more, and a plurality of the first auxiliary-valve steam flow path parts F3311are spaced to surround the valve rod340.

The second auxiliary-valve steam flow path part F3312has, for example, a truncated conical shape, and is formed such that its diameter decreases as it goes toward the opening direction AX1 in the axial direction AX.

The third auxiliary-valve steam flow path part F3313has, for example, a cylindrical shape, and its diameter is the same as that of an end portion located on the opening direction AX1 side of the second auxiliary-valve steam flow path part F3312. The third auxiliary-valve steam flow path part F3313communicates with the auxiliary-valve steam introduction holes H330.

In the auxiliary-valve steam flow path F331, the steam introduced from the auxiliary-valve steam introduction hole H330flows through the third auxiliary-valve steam flow path part F3313, the second auxiliary-valve steam flow path part F3312, and the first auxiliary-valve steam flow path part F3311in order, to be discharged to the valve hole K310.

The auxiliary-valve cap335is mounted at an end portion located on the opening direction AX1 side of the third auxiliary-valve main body part3313(auxiliary-valve tubular part) constituting the auxiliary-valve main body331(top end). The auxiliary-valve cap335is structured to block the third auxiliary-valve steam flow path part F3313formed inside the third auxiliary-valve main body part3313.

Here, the auxiliary-valve cap335includes a cap tubular body part3351and a cap plate-shaped body part3352.

In the auxiliary-valve cap335, the cap tubular body part3351is, for example, a cylindrical tubular body, and coaxial with the valve rod340. On an inner peripheral surface of the cap tubular body part3351, a female screw coupled with the male screw formed on the outer peripheral surface of the third auxiliary-valve main body part3313is formed.

In the auxiliary-valve cap335, the cap plate-shaped body part3352is, for example, a disk-shaped body, and coaxial with the valve rod340.

An outer peripheral surface of an end portion located on the opening direction AX1 side of the cap tubular body part3351(upper end) is along the center axis CL of the valve rod340. In contrast to this, an outer peripheral surface of an end portion located on the closing direction AX2 side of the cap tubular body part3351(lower end) is an inclined surface inclined to the center axis CL of the valve rod340, and in the inclined surface, the closing direction AX2 side is located further inside than the opening direction AX1 side in the radial direction of the valve rod340.

The valve rod340is, for example, a cylindrical rod-shaped body, and its end portion located on the opening direction AX1 side (top end) is coupled with the auxiliary valve element330to be fixed to the auxiliary valve element330by using a locking pin341. Further, the valve rod340extends in the axial direction AX so as to penetrate the valve hole K310.

[B] Operation of Auxiliary Valve Element330

[B Case Where Auxiliary Valve Element330Is Set to Fully-Open State

When the auxiliary valve element330is set to a fully-open state in the steam valve300J according to the related art, the valve rod340is moved in the opening direction AX1 to increase the distance between the auxiliary-valve cap335and the main valve element320, thereby opening all the auxiliary-valve steam introduction holes H330, as illustrated inFIG.7. This causes steam to be introduced from the auxiliary-valve steam introduction holes H330to the auxiliary-valve steam flow path F331. In the third auxiliary-valve steam flow path part F3313of the auxiliary-valve steam flow path F331, the steam flows from the outside to the inside in the radial direction through the plurality of auxiliary-valve steam introduction holes H330to collide on the center axis CL. At a result, in the warm-up operation, in a state in which a flow speed of steam decreases, the steam is introduced from the auxiliary-valve steam flow path F331to the steam turbine.

[B Case Where Auxiliary Valve Element330Is Set to Fully-Closed State

In contrast to this, when the auxiliary valve element330is set to a fully-closed state in the steam valve300J according to the related art, the valve rod340(refer toFIG.7) is moved in the closing direction AX2 to make the auxiliary-valve cap335and the main valve element320abut on each other, thereby blocking all the auxiliary-valve steam introduction holes H330, as illustrated inFIG.8.

As illustrated inFIG.8, in the steam valve300J according to the related art, an abutting position CP at which the auxiliary-valve cap335and main valve element320abut on each other coincides with an outer peripheral surface of a portion, of the third auxiliary-valve main body part3313(auxiliary-valve tubular part), through which the auxiliary-valve steam introduction holes H330are formed. That is, in the steam valve300J according to the related art, when the auxiliary valve element330is set to the fully-closed state, a sharp tip located on the closing direction AX2 side of the auxiliary-valve cap335collides with a flat surface located on the opening direction AX1 side of the main valve element320.

In the steam valve300J according to the related art, when the collision between the auxiliary-valve cap335and the main valve element320is repeated, the tip located on the closing direction AX2 side of the auxiliary-valve cap335is sometimes broken. As a result, a leak of steam occurs, and the steam valve300J sometimes fails to set the auxiliary valve element330precisely to the fully-closed state.

Therefore, a problem to be solved by the present invention is to provide a steam valve and a steam turbine plant capable of preventing breakage of an auxiliary valve element and effectively suppressing the occurrence of a leak of steam in the auxiliary valve element.

DETAILED DESCRIPTION

A steam valve of an embodiment includes:a main valve element capable of abutting on a valve seat;an auxiliary valve element accommodated inside the main valve element, and inside which an auxiliary-valve steam flow path is formed; anda valve rod coupled with the auxiliary valve element, and penetrating a valve hole formed in a valve seat,the auxiliary valve element includes:an auxiliary-valve tubular part being a part capable of protruding from the main valve element in an opening direction in which the main valve element is opened;an auxiliary-valve steam introduction hole formed through the auxiliary-valve tubular part, and through which steam is introduced to the auxiliary-valve steam flow path; andan auxiliary-valve cap mounted at an end portion on the opening direction side of the auxiliary-valve tubular part,the auxiliary valve element is structured to be in an open state in which the valve rod moves in the opening direction to increase a distance between the auxiliary-valve cap and the main valve element, thereby opening the auxiliary-valve steam introduction hole, andto be in a fully-closed state in which the valve rod moves in a closing direction in which the main valve element is closed to bring the auxiliary-valve cap and the main valve element into contact with each other, thereby closing the auxiliary-valve steam introduction holes, anda contact position in which the auxiliary-valve cap and the main valve element are brought into contact with each other is located outside in a radial direction of the valve rod from the outer peripheral surface, of the auxiliary-valve tubular part, through which the auxiliary-valve steam introduction holes are formed.

First Embodiment

[A] Structure of Steam Turbine Plant

FIG.1schematically illustrates the entire structure of a steam turbine plant according to a first embodiment.

In a steam turbine plant100of this embodiment, as illustrated inFIG.1, the steam heated by a steam generator111is introduced as a working fluid to a high-pressure turbine141via a main steam pipe P10in which a main steam stop valve V10aand a steam control valve V10bare installed, to work in the high-pressure turbine141. Then, the steam discharged from the high-pressure turbine141is supplied to a reheater112via a low-temperature reheat steam pipe P11, to be heated in the reheater112again. The steam heated by the reheater112is introduced as the working fluid to an intermediate-pressure turbine142via a high-temperature reheat steam pipe P12in which a reheat steam stop valve V12aand an intercept valve V12bare installed, to work in the intermediate-pressure turbine142. In the steam turbine plant100, a turbine rotor is connected between the high-pressure turbine141, the intermediate-pressure turbine142, and a low-pressure turbine (whose illustration is omitted), and the turbine rotor is rotated by steam work. Then, the rotation of the turbine rotor drives a generator145to generate electricity.

[B] Structure of Steam Valve300

FIG.2is a sectional view schematically illustrating a steam valve (main steam stop valve) according to the first embodiment. InFIG.2, a part of the cross section on a vertical plane (xz plane) is enlarged and illustrated, as inFIG.8.

A steam valve300of this embodiment corresponds to the main steam stop valve V10aconstituting the steam turbine plant100illustrated inFIG.1. Although illustration of the entire structure of the steam valve300of this embodiment is omitted, the steam valve300of this embodiment is a main steam stop valve including a valve seat310, a main valve element320, an auxiliary valve element330, and a valve rod340, as in the case of the related art. Further, the auxiliary valve element330includes an auxiliary-valve main body331and an auxiliary-valve cap335in the steam valve300of this embodiment, as in the case of the related art (refer toFIG.7).

However, as illustrated inFIG.2, in the steam valve300of this embodiment, an abutting position CP in which the auxiliary-valve cap335and the main valve element320abut on each other is different from that of the related art (refer toFIG.8). Except for this point and points related thereto, this embodiment is the same as the case of the related art (refer toFIG.7,FIG.8). Therefore, descriptions of overlapped matters are appropriately omitted.

As illustrated inFIG.2, the abutting position CP in which the auxiliary-valve cap335and the main valve element320abut on each other in the steam valve300of this embodiment is different from that of the related art (refer toFIG.8), and does not coincide with an outer peripheral surface of a portion, of the third auxiliary-valve main body part3313(auxiliary-valve tubular part), through which the auxiliary-valve steam introduction holes H330are formed. In the steam valve300of this embodiment, the abutting position CP in which the auxiliary-valve cap335and the main valve element320abut on each other is located outside in a radial direction of the valve rod340from the outer peripheral surface of the portion, of the auxiliary-valve tubular part3313, through which the auxiliary-valve steam introduction holes H330are formed.

Concretely, the portion in which auxiliary-valve cap335abuts on the main valve element320(abutting position CP) is located on a curved surface S335based on a sphere with a radius R having the center on the center axis CL of the valve rod340. In the above-described curved surface S335, a portion located inside in the radial direction of the valve rod340is located on the closing direction AX2 side, and a portion located outside in the radial direction of the valve rod340is located on the opening direction AX1 side.

Further, in this embodiment, the portion in which the main valve element320abuts on the auxiliary-valve cap335(abutting position CP) is located on an inclined surface S320inclined at an inclination angle K to a plane orthogonal to the center axis CL of the valve rod340. On the above-described inclined surface S320, a portion located inside in the radial direction of the valve rod340is located on the closing direction AX2 side, and a portion located outside in the radial direction of the valve rod340is located on the opening direction AX1 side.

Hence, in this embodiment, the auxiliary-valve cap335and the main valve element320are brought into line contact with each other in the abutting position CP of a diameter ϕA, which is located outside in the radial direction of the valve rod340from the outer peripheral surface of the portion, of the auxiliary-valve tubular part3313, through which the auxiliary-valve steam introduction holes H330are formed.

As described above, in the steam valve300of this embodiment, the abutting position CP in which the auxiliary-valve cap335and the main valve element320abut on each other is located outside in the radial direction of the valve rod340from the outer peripheral surface of the portion, of the auxiliary-valve tubular part3313, through which the auxiliary-valve steam introduction holes H330are formed. In this embodiment, the portion in which the auxiliary-valve cap335abuts on the main valve element320(abutting position CP) is not a sharp tip.

Therefore, in the steam valve300of this embodiment, when the auxiliary valve element330is set to a fully-closed state, the portion in which the auxiliary-valve cap335abuts on the main valve element320is not a sharp tip, and hence, even though the collision between the auxiliary-valve cap335and the main valve element320is repeated, breakage is less likely to occur in the auxiliary-valve cap335. As a result, in this embodiment, since the auxiliary valve element330can be set precisely to the fully-closed state, it is possible to effectively prevent a leak of steam from occurring.

Further, in this embodiment, the portion in which the auxiliary-valve cap335abuts on the main valve element320(abutting position CP) is the curved surface S335based on the sphere having the center on the center axis CL of the valve rod340. This allows easy processing of the curved surface S335. Moreover, when the auxiliary valve element330is fully closed, the auxiliary valve element330and the auxiliary-valve cap335integrated with the valve rod340slide along the truncated cone-shaped inclined surface S320up to a positional relationship to be concentric with, namely, aligned with the center of the main valve element320so as to go toward a tip of the truncated conical shape (the center axis CL of the valve rod340). This results in that the auxiliary-valve cap335and the main valve element320adhere to (is brought into close contact with) each other securely in the abutting position CP, thereby allowing a remarkable improvement in steam sealing performance.

[D] Modified Example

The above embodiment describes a case where the portion in which the main valve element320abuts on the auxiliary-valve cap335(abutting position CP) is the inclined surface S320inclined to the plane orthogonal to the center axis CL of the valve rod340, but this is not restrictive. The portion in which the main valve element320abuts on the auxiliary-valve cap335(abutting position CP) need not be the flat inclined surface S320, but may be a curved surface facing (opposite to) the curved surface S335.

Second Embodiment

[A] Structure of Steam Valve300b

FIG.3is a sectional view schematically illustrating a steam valve (main steam stop valve) according to a second embodiment. InFIG.3, a part of the cross section on a vertical plane (xz plane) is enlarged and illustrated, as inFIG.2.

In a steam valve300bof this embodiment, as illustrated inFIG.3, a structure of an auxiliary-valve steam introduction hole H330is different from that of the first embodiment. Except for this point and points related thereto, this embodiment is the same as the case of the first embodiment (refer toFIG.2). Therefore, descriptions of overlapped matters are appropriately omitted.

As illustrated inFIG.3, in the steam valve300bof this embodiment, the auxiliary-valve steam introduction hole H330is formed to be inclined to a plane orthogonal to a center axis CL of a valve rod340. Here, in the auxiliary-valve steam introduction hole H330, similarly to an inclined surface S320including a portion in which a main valve element320abuts on an auxiliary-valve cap335(abutting position CP), a portion located inside in a radial direction of the valve rod340is located on a closing direction AX2 side, and a portion located outside in the radial direction of the valve rod340is located on an opening direction AX1 side.

Therefore, in the steam valve300bof this embodiment, steam flows along the inclined surface S320, thereafter flowing into the auxiliary-valve steam introduction hole H330smoothly to pass therethrough. As a result, in this embodiment, impurities contained in the steam are less likely to collide with an inlet portion of the auxiliary-valve steam introduction hole H330, which makes it possible to prevent erosion from occurring at the inlet portion of the auxiliary-valve steam introduction hole H330.

Note that in this embodiment, an angle A320at which the inclined surface S320including the portion in which the main valve element320abuts on the auxiliary-valve cap335(abutting position CP) is inclined to the plane orthogonal to the center axis CL is preferably the same as an angle A330at which the auxiliary-valve steam introduction hole H330is inclined to the plane orthogonal to the center axis CL (namely, A320= A330). This causes the steam having flowed along the inclined surface S320to flow into the auxiliary-valve steam introduction hole H330more smoothly to pass therethrough, which makes it possible to achieve more effective prevention of the erosion.

Third Embodiment

[A] Structure of Steam Valve300c

FIG.4is a sectional view schematically illustrating a substantial part of a steam valve (main steam stop valve) according to a third embodiment. InFIG.4, a portion through which auxiliary-valve steam introduction holes H330are formed is enlarged and illustrated. InFIG.4, a part of the cross section on a vertical plane (xz plane) is enlarged and illustrated in the right portion, as inFIG.2, and thick arrows correspond to flow of steam. InFIG.4, the left portion illustrates a state observed when a sight line is along a radial direction of a center axis CL.

In a steam valve300cof this embodiment, as illustrated inFIG.4, a structure of an auxiliary-valve steam introduction hole H330is different from that of the first embodiment. Except for this point and points related thereto, this embodiment is the same as the case of the first embodiment (refer toFIG.2). Therefore, descriptions of overlapped matters are appropriately omitted.

As illustrated inFIG.4, in this embodiment, the auxiliary-valve steam introduction hole H330is formed so that an inlet portion into which the steam flows includes a portion larger in cross-sectional area than an outlet portion from which the steam flows out.

Specifically, the auxiliary-valve steam introduction hole H330of this embodiment has a first auxiliary-valve steam introduction hole part H331and a second auxiliary-valve steam introduction hole part H332.

The first auxiliary-valve steam introduction hole part H331, whose cross section is, for example, circular, is formed with a uniform cross-sectional area across from an inlet side into which the steam flows to an outlet side from which the steam flows out.

The second auxiliary-valve steam introduction hole part H332, whose cross section is, for example, circular, is provided to surround the first auxiliary-valve steam introduction hole part H331at an inlet into which the steam flows, and formed to reduce a cross-sectional area from the inlet side into which the steam flows toward the outlet side from which the steam flows out. Here, the cross-sectional area of the second auxiliary-valve steam introduction hole part H332on the inlet side is larger than the cross-sectional area of the first auxiliary-valve steam introduction hole part H331, and the cross-sectional area of the second auxiliary-valve steam introduction hole part H332on the outlet side is the same as the cross-sectional area of the first auxiliary-valve steam introduction hole part H331.

Note that in this embodiment, an inner peripheral surface of the second auxiliary-valve steam introduction hole part H332is a curved surface, or may be a flat surface. That is, the second auxiliary-valve steam introduction hole part H332may have a taper shape.

[B] Regarding Flow of Steam

In the steam valve300cof this embodiment, when an auxiliary valve element330is in an open state, a gap is formed on an opening direction AX1 side between a curved surface S335of an auxiliary-valve cap335and an inclined surface S320of a main valve element320, and steam passes through the gap (refer toFIG.2). Therefore, at the inlet of the auxiliary-valve steam introduction hole H330, the steam having passed through the gap flows thereinto, and then, through the auxiliary-valve steam introduction hole H330, the steam flows along a direction orthogonal to a center axis CL.

The steam contains impurities such as a drain and oxides. Therefore, the impurities contained in the steam collide with the inlet portion of the auxiliary-valve steam introduction hole H330, and erosion sometimes occurs at the inlet portion of the auxiliary-valve steam introduction hole H330.

However, the auxiliary-valve steam introduction hole H330of this embodiment is formed so that the inlet portion is larger in cross-sectional area than the outlet portion. Therefore, in this embodiment, the steam flows into the auxiliary-valve steam introduction hole H330smoothly to pass therethrough. As a result, in this embodiment, it is possible to prevent the erosion from occurring at the inlet portion of the auxiliary-valve steam introduction hole H330.

[D] Modified Example

Modified Examples of This Embodiment Will Be Used and Described

FIG.5andFIG.6are sectional views schematically illustrating substantial parts of the steam valves (main steam stop valves) according to modified examples of the third embodiment. InFIG.5andFIG.6, portions through which auxiliary-valve steam introduction holes H330are formed are enlarged and illustrated, as inFIG.4.

As illustrated in each ofFIG.5andFIG.6, a second auxiliary-valve steam introduction hole part H332of the auxiliary-valve steam introduction hole H330is different from that of the above embodiment (refer toFIG.4), and may be provided on a closing direction AX2 side further than a first auxiliary-valve steam introduction hole part H331at an inlet into which steam flows.

Concretely, as illustrated inFIG.5, the second auxiliary-valve steam introduction hole part H332has a semicircular shape, and may be provided to surround a portion located on the closing direction AX2 side of the first auxiliary-valve steam introduction hole part H331. That is, the second auxiliary-valve steam introduction hole part H332need not be provided in a portion located on an opening direction AX1 side of the first auxiliary-valve steam introduction hole part H331. As can be seen fromFIG.5, the erosion due to steam is likely to occur because the impurities contained in the steam tend to collide with, in particular, the portion located on the closing direction AX2 side at an inlet portion of the auxiliary-valve steam introduction hole H330. However, in this modified example, similarly to the above embodiment, the second auxiliary-valve steam introduction hole part H332is provided at the inlet portion of the auxiliary-valve steam introduction hole H330, which makes it possible to prevent the erosion from occurring. In this modified example, the auxiliary-valve steam introduction hole H330further has a merit of facilitating control of a steam flow rate.

Further, as illustrated inFIG.6, the second auxiliary-valve steam introduction hole part H332may be provided in a portion located on the closing direction AX2 side further than the first auxiliary-valve steam introduction hole part H331. That is, the second auxiliary-valve steam introduction hole part H332need not be provided in a portion other than the portion located on the closing direction AX2 side further than the first auxiliary-valve steam introduction hole part H331. Also in this modified example, in the portion on the closing direction AX2 side in which the erosion is likely to occur at an inlet portion of the auxiliary-valve steam introduction hole H330, the second auxiliary-valve steam introduction hole part H332is provided. Therefore, also in this modified example, it is possible to prevent the erosion from occurring. Further, in this modified example, the second auxiliary-valve steam introduction hole part H332can also be formed with a tool used in forming the first auxiliary-valve steam introduction hole part H331, which allows effective processing operation.

Others

REFERENCE SIGNS LIST