Abstract: A subaqueous sequence valve mechanism includes one or more main valves each adapted to be disposed in the water below the surface thereof. A first expansible chamber hydraulic actuator on the main valve operates that valve and also operates a second expansible chamber device against a spring. A hydraulic pressure line or lead from a controlled source above the surface is joined to and controls the submerged actuator. The second expansible chamber is connected in sequence through a throttle valve and a pressure relief valve to one side of a movable barrier in a hydraulic accumulator. On the other side of the movable barrier the accumulator is open to the water. There is also a return, one way flow valve shunting the pressure relief valve. The accumulator is hydraulically protected by a spring loaded check valve discharging into the water.