Steam valve and steam turbine plant

A steam valve comprising:

• 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;
• and
• a valve rod coupled with the auxiliary valve element, and penetrating a valve hole formed in a valve seat,
• the auxiliary valve element comprising:
• 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;
• and
• an auxiliary-valve cap mounted at an end portion on the opening direction side of the auxiliary-valve tubular part,
• the auxiliary valve element being 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, 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, and
• a contact position in which the auxiliary-valve cap and the main valve element are brought into contact with each other being 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, wherein
• in the auxiliary-valve steam introduction hole, a cross-sectional area of an inlet portion into which the steam flows is larger than a cross-sectional area of an outlet portion from which the steam flows out, and
• the auxiliary-valve steam introduction hole comprises:
• a first auxiliary-valve steam introduction hole part 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;
• and
• a second auxiliary-valve steam introduction hole part formed to surround the first auxiliary-valve steam introduction hole part at an inlet into which the steam flows, and 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.