According to the structure of the sealing mechanism, cast steel ball valve is divided into floating ball cast steel ball valve and fixed ball cast steel ball valve. The former mainly through the medium pressure on the end of the ball valve seat, its use of pressure and diameter are subject to certain restrictions. While the latter valve is supported by the upper and lower bearings mounted on the valve body, the position of the ball is fixed and the sealing effect is achieved by pressing the spring and the medium pressure seat against the sphere. So the opening and closing torque is small, suitable for high pressure and large caliber occasions.