[US] advantage of a standard ball. Fluid resistance, its drag coefficient with the same pipe lengths are equal. 2. Simple structure, small size and light weight. 3. Close and reliable valve sealing surface material widely used plastic, sealing, and has also been widely used in the vacuum system. 4. Easy to operate, opening and closing rapidly, from fully open to fully closed as long as the rotation of 90 °, to facilitate remote control. 5. Easy maintenance, simple ball valve, seals are generally activities, the removal replacement is more convenient. 6. When fully open or fully closed, the sealing surface and the dielectric isolation ball and seat, through the media, will not cause erosion of the valve sealing surface. 7. Wide range of applications, from small diameter to a few millimeters to a few meters from high vacuum to high pressure can be applied. 3] [American Standard ball valve classified according to the structure can be divided into: a floating ball valve The ball valve is floating in the medium under pressure, the ball can produce a certain displacement and pressed at the outlet end of the sealing surface, guarantee outlet end seal. Simple floating ball valve structure, good sealing, but the ball all bear the load of the working medium to pass the exit ring, so to consider the ring material can withstand the work load of the media sphere. This structure is widely used in low-pressure valve. Second, the fixed ball valve ball is fixed, no movement after compression. All with a floating ball valve fixed valve seat, by medium pressure, the valve seat to move, so that the ball seals pressed on, in order to ensure the seal. Usually with the ball, the lower shaft with bearings, operating small torque, suitable for high pressure and large diameter ball valves. Third, elastic ball valve ball valve is elastic. Ball and seat ring are made of metal materials, sealing pressure than large, rely on the media itself has reached less pressure sealing requirements, must apply force. This valve is suitable for high temperature and high pressure media sphere.