Abstract: The disclosed valve assembly permits the automatic scuttling, or sinking, floatable pressure vessels or other containers, and comprises an extensible, spring-restrained nozzle containing a spring-biased ball seal within a flow passage. Vessel internal pressure extends the nozzle from a retracted position to expose the exterior end of the flow passage. A calibrated restraining spring ring maintains the nozzle retracted and in the extended position during pressure vessel operation. The ball seal is displaced from a nonsealing position against a ball seat to preclude pressure relief through the flow passage. After exhaustion of internal pressure, the bias spring and external water pressure force the ball seal from the ball seat to permit water entry and subsequent sinking of the vessel.