Abstract: Selective retraction of a spring-biased valve seat from slidable sealing engagement with a ball valve member is effected by a threaded retraction tool inserted through a threaded retraction port normally sealed by a removable sealing screw and gasket. The tapered distal end of the tool contacts a radially outward-facing and convex camming surface of the valve seat that tapers toward the forward/sealing end of the seat. Rotation of the tool in a direction to increase insertion causes the distal end of the tool to slide along the camming surface while forcing the valve seat away from the valve ball in opposition to the resilient bias sealing force. The taper in the camming surface may be provided as a smooth generally parabolodial configuration or as discrete surface segments subtending different respective cam angles with a reference plane oriented perpendicular to the direction of the spring bias force.