In a steam valve, a seat-side convexly curved surface ( 35 b ) of a valve body ( 30 ) is configured such that the average radius of curvature Rv from a starting end portion ( 35 c ) on the upstream side in a flow direction of steam to a termination end portion ( 35 a ) has a relationship of Rv<Rs with respect to the radius of curvature Rs of a valve-seat-side convexly curved surface ( 26 a ); the seat-side convexly curved surface ( 35 b ) is formed with an upstream-side curved surface ( 36 ) and a downstream-side curved surface ( 37 ); the seat-side convexly curved surface ( 35 b ) has an abutting area ( 35 s ) abutting a valve seat portion ( 26 ); and the radius of curvature R 1 of the downstream-side curved surface ( 37 ) has a relationship of Rs<R 1 with respect to the radius of curvature Rs in the flow direction of the steam.
1. A steam valve comprising:
a casing with a steam flow path formed therein;
a valve body disposed in the steam flow path and provided so as to be capable of moving relative to the steam flow path;
a valve seat portion which is formed in the steam flow path and provided with a valve-seat-side convexly curved surface having a cross-sectional area gradually increasing toward a downstream side in a flow direction of steam in the steam flow path; and
a seat portion which is formed in the valve body and has, at a site facing the valve seat portion, a seat-side convexly curved surface having an outer diameter gradually increasing toward the downstream side from an upstream side in the flow direction of the steam, wherein
in the seat-side convexly curved surface, an average radius of curvature Rv in the flow direction from a starting end portion on the upstream side in the flow direction of the steam to a termination end portion on the downstream side in the flow direction of the steam has a relationship of Rv<Rs with respect to a radius of curvature Rs in the flow direction of the steam of the valve-seat-side convexly curved surface,
the seat-side convexly curved surface is provided with an upstream-side curved surface on the upstream side in the flow direction of the steam, and a downstream-side curved surface on the downstream side in the flow direction of the steam, the upstream-side curved surface and the downstream-side curved surface having radii of curvature different from each other,
the downstream-side curved surface has an abutting area abutting the valve seat portion, and
a radius of curvature R 1 of the downstream-side curved surface that extends in the flow direction of the steam has a relationship of Rs<R 1 with respect to the radius of curvature Rs in the flow direction of the steam.
2. The steam valve according to claim 1 , wherein
the valve body is provided with a tapered portion which is continuously formed from the termination end portion of the seat portion and formed at the downstream side of the seat portion in the flow direction and which has an outer diameter which is gradually reduced.
3. The steam valve according to claim 1 , wherein
a radius of curvature R 2 of the upstream-side curved surface that extends in the flow direction of the steam, the radius of curvature R 1 of the downstream-side curved surface, and the average radius of curvature Rv of the seat portion have a relationship of R 2 <Rv<Rs<R 1 with respect to the radius of curvature Rs of the valve seat portion.
4. The steam valve according to claim 1 , wherein
a diameter Ds of the abutting area of the seat portion with respect to a center of the valve body and a diameter Dout of the termination end portion of the seat portion have a relationship of 1.02≦Dout/Ds≦1.03.
5. The steam valve according to claim 1 , wherein
the diameter Ds of the abutting area of the seat portion and a diameter Din of the starting end portion of the seat portion have a relationship of Din/Ds≦0.75.
6. The steam valve according to claim 1 , wherein
the diameter Ds of the abutting area of the seat portion and an inner diameter Dt of the steam flow path on the upstream side in the flow direction with respect to the valve seat portion have a relationship of 1.15≦Ds/Dt≦1.25.