A valve and actuator assembly having a mechanism adapting such assembly for remote actuation by a pressure medium such as hydraulic or pneumatic fluid and including means for controlling the development of resultant forces acting upon the valve stem of the valve. The valve and actuator assembly includes safety means for rendering the valve safe in response to the development of predetermined unsafe conditions and is adapted with a manual override system allowing the valve to be manually opened or closed regardless of the condition of the safety means. Mechanical or fluid actuated interlock means is provided to render fluid actuating means inoperative and is also provided with means for rendering the mechanical override inoperative. The assembly is adapted to lock out the fluid actuator system to allow the assembly to be serviced without risk of inadvertent actuation by automatic systems. Effluent pressure may be communicated to the outer extremity of the valve stem to balance the force applied to the inner extremity of the valve stem by effluent pressure within the valve.