A ball valve has a valve body (10) with a bonnet bore (12) communicating with a fluid through bore (14). A valve seat (16) in the valve body (10) surrounds the fluid bore axis. A bonnet (20), with a stem bore 22 extending therethrough, is received in the bonnet bore (12). An operating stem (28) is journalled for rotation in the stem bore (22). A ball (30) is connected to the operating stem (28), and located in the fluid bore (14). The ball (30) has a through passageway (32). Rotation of the operating stem (28) causes the ball (30) to rotate eccentrically between an open position, in which the ball is spaced from the valve seat (16) with its through passageway (32) aligned with the fluid bore (14), and a closed position, in which the ball blocks the fluid bore by being wedged into sealing engagement with the valve seat. The ball (30) is externally contoured to provide both a clearance from the valve body (10) to accommodate its eccentric rotation, and a stop (54) which is engageable with th the valve body to positively locate the ball in its open position. The ball valve can be assembled in combination with an actuator (64) having a linearly reciprocating piston (80) mechanically connected to the operating stem (28) by means of a rack (82) and a pinion (86). Linear motion of the piston (80) is limited in one direction by the sealing engagement of the ball (30) with the valve seat (16), and in the opposite direction by the engagement of the ball stop (54) with the valve body (10).
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