I had an idea in a dream where a pressure vessel had a buoyancy valve at the lowest point. The idea was that a ball would sit in a hole and water that may condense inside the vessel would lift the ball allowing the water to drain after which the pressure of the vessel would seal the ball back into place. That made me wonder about the possibility of a pressure based buoyancy valve and whether the physics were there.
In order for this to work, force exerted on the ball by the pressure differential between the inside and the outside must not exceed the maximum buoyant force on the ball. If the pressure differential exceeds that value, the ball will stay stuck to the bottom even when completely submerged.