Abstract: A ball segment valve for controlling fluid flow in a piping, includes a valve housing with a valve seat disposed therein, a tubular bearing body fitted to an upper axial opening of the valve housing, a rotating spindle inserted through the bearing body into the valve housing, a tightening sleeve unit sleeved on the spindle to ensure full engagement of the spindle with the bearing body, a journal member inserted through a lower axial opening into the valve housing, and a valve body having upper and lower lugs coaxially fitted to the spindle and the journal member, and a spherical segment having a convex outer spherical surface and rotated with the spindle between a fully closed position, where the spherical surface is in sealing contact with the valve seat, and a fully opened position to permit a full fluid communication of the valve housing.