A fail-safe non-pressure locking valve, actuated by hydraulic controls responsive to ambient sea pressure, disposed over 1000 feet below the surface on a submerged pipeline controlling the flow of fluids therethrough. The valve includes a housing having a chamber within which a gate, having upper and lower attached stems, reciprocates for opening and closing the valve to fluid flow. A piston, responsive to the hydraulic actuator controls, is attached to the upper stem for urging the gate to the open position upon application of hydraulic actuator fluid pressure. A spring is arranged in the valve housing to assist the internal valve pressure on the stem in urging the gate to its closed position in the event of loss of hydraulic actuator fluid pressure. A lower detached stem is disposed in the valve chamber below the lower attached stem and is responsive to ambient sea pressure. When the ambient sea pressure becomes greater than the internal valve pressure, the lower detached stem engages the lower attached stem. A second spring is disposed below the lower detached stem to overcome frictional forces between the lower detached stem and seals in the valve housing when the lower detached stem moves to its engagement position. A port extends through the valve housing from between the lower attached and detached stems to the side of the valve opposite the side of the valve connected to the short section allowing fluid between the lower attached and detached stems to be displaced as the gate moves downwardly to the open position or as the lower detached stem moves upwardly to engage the lower attached stem. Thus, by venting the internal valve pressure through the port, pressure lock is avoided where internal valve fluids otherwise would be prevented from being displaced from the valve chamber.