A ball valve including a body having two longitudinally aligned fluid passages and a lateral opening communicating with a central space. A rotatable ball, having an opening communicable with the fluid passages, is positioned within the central space. A pair of annular seat rings of wedge shape cross section, fit against and clampingly secure the ball therebetween. A pair of seat ring retainer means, integral with the body, having side walls inclined downwardly and inwardly, wedge the ball and seat rings therebetween. Bonnet means is secured to the body in covering relationship to the seat rings and ball. Piston means extend through the bonnet means for selectively applying pressure to an upper portion of the seat rings to compress the seat rings to the ball and the retainer means side walls. Various means are disclosed for the actuation of the piston means. A rotatable valve stem passes through the lateral opening and the bonnet means, and is connected to the ball to rotate the ball between positions of permitting and preventing the passage of fluid therethrough.