An improved plug-type valve of the type having a plug connected to slips wherein opening and closing the valve involves both vertical and rotational motion of the plug, the novel features of the invention residing in geometrical characteristics of plug, slips and valve body to make the vertical motion of the plug, both prior to and subsequent to the rotation of the plug and slips, unidirectional. Thus, unlike prior art plug-type valves wherein opening the valve may require a sequence comprising vertical upward motion, rotation and vertical downward motion, in the present invention the opening sequence comprises vertical upward motion, rotation and vertical upward motion. This unidirectional vertical component of plug motion both before and after plug and slip rotation, significantly reduces the complexity and cost of the operator or actuator to which the plug is connected by the trunnion.

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