The valve core adopts upper and lower stem bearing structure, which has high mechanical stability, small start-up torque, and guarantees excellent sensitivity of the valve. The valve seat adopts spring-loaded movable structure, because the spring elastic restoring force pushes the valve seat to match the ball core optimally and achieves zero leakage. The ball core is designed with V-notch, which has great shearing force and self-cleaning function, and precise control performance and percentage flow characteristics. Ball valves with nominal diameter of 25 mm can provide different small CV values according to user's flow requirements, and can accurately control small flow.