The base has a straight tube structure, the seat has the merits of good strength, fine rigidity, large thrust, high sealing pressure,excellent sealing effect, broad sealing surface and long service life. Both ends of the sealing surface are designed to keep sharp edges. During the opening and closing process of the valve,the spherical adhesion dirt can be scraped to reduce the corrosion of the sphere and the damage of the sealing surface of the valve seat. When the valve is fully opened, the spring preloaded force enables the sphere to be positioned in the center of the valve, while the fully closed, the medium thrust pushes the sphere to attain the downstream sealing.