The base has a straight tube structure, the seat has the merits of good strength, hne rigidity, large thrust, high sealing pressure, excellent sealing effect, broad sealing surface and long service life. Both ands of the sealing surface are designed to keep sharp edges. During the opening and closing process ofthe 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, The dirt-proof design can keep away from dirt deposit.