At least one ball valve segment is located within a partial valve cage mounted within a tank. The cage is integral with a valve housing removably mounted within a tank mounting flange. The housing includes an inclined sealing surface which the ball valve segment engages in closed position. A lading outlet chamber is located below the inclined sealing surface. An operating shaft is inclined with respect to the outlet chamber. Inclined openings are provided in the valve housing and in the outlet chamber through which the operating shaft passes. The operating shaft includes an eccentric head which is located within a non-round slot in the ball valve segment. Rotation of the operating shaft rotates the eccentric head which drives the valve segment between open and closed positions. Preferably a pair of ball valve segments located approximately 180 DEG apart are connected with supports or ribs. The valve segment which closes the opening into the discharge chamber is larger. The contour of the eccentric head is such that the smaller valve segment is located outwardly from the center of the discharge opening in the valve housing when the larger valve segment is in open position to minimize flow restriction. The smaller valve segment is cam shaped to urge the larger portion into closed and sealed position.
