The base has a tee-shape structure, which greatly controls the medlum thrust to enable the opening/clasing torque to be less, and the operation is more convenient, Both ends of the sealing surlace are designed to keep sharp edges. During the opening and closing pracess 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, The preloaded spring mounted at the seat head eliminates the dirt deposit and the trouble of spring catching