Quote:
Originally Posted by ABBAFAN
I know about hot air balloons, I was making the comparison with gas balloons which are rather different.
Do they close the valves at the bottom of the ballast tanks once blowing has been done and the vessel is on the way to the surface?
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My mistake about the balloons. In that case the comparison is even further apart.
Now about your question here, I can only speak to American submarines. The US boats have a vent valve on the top of each ballast tank and flood grates on the bottom. This maintains the water pressure in the ballast tank equal with that of sea pressure on the outside. It is my understanding that Russian boats have valves on the top and bottom of their ballast tanks. They submerge by opening both sets of valves. Once the ballast tanks are full of water both valves are shut. This maintains a constant pressure of the water in the tanks, that which would be nearer to surface water pressure. My conjecture is that you could blow HP air into the tanks and then open the bottom set of valves to force the water out quickly even at great depth. I would imagine that the valves would be closed again once the tanks were blown dry. I either used to have a diagram of this or saw one somewhere but damned if I can find it now.
