Abstract: The shape of a back-up ring is a V-shaped sectional shape. In the back-up ring, an annular concave surface part having a V-shaped sectional shape serving as a valley toward a high-pressure side is formed on a surface part on a side that faces a seal ring, and an annular convex surface part having a V-shaped sectional shape serving as a peak toward a low-pressure side is formed on a surface part opposite to the side that faces the seal ring. When a high pressure is applied from a high-pressure side, the back-up ring is deformed such that V-shaped angles of an annular concave surface part and an annular convex surface part are increased as the annular concave surface part is pressed against the seal ring, and is brought into close contact with a housing and a shaft.

Abstract: The shape of a back-up ring is a V-shaped sectional shape. In the back-up ring, an annular concave surface part having a V-shaped sectional shape serving as a valley toward a high-pressure side is formed on a surface part on a side that faces a seal ring, and an annular convex surface part having a V-shaped sectional shape serving as a peak toward a low-pressure side is formed on a surface part opposite to the side that faces the seal ring. When a high pressure is applied from a high-pressure side, the back-up ring is deformed such that V-shaped angles of an annular concave surface part and an annular convex surface part are increased as the annular concave surface part is pressed against the seal ring, and is brought into close contact with a housing and a shaft.