a continuation from:
@Scott Kenny
It's just a little bit wasteful to fill the ballast tanks with 40 bar of air (at 400 m depth). If a water pump would be used, it would be enough to fill the volume with only 1 bar, so that only 2.5 % of the air mass would have been required. Powering an hydraulic pump would also require much less energy than compressing the air.
Of course, this method would have drawbacks, the pump can be clocked by things floating in the water, the time required for emptying the tank will be longer and you need reliable energy supply to drive the pump. Seems like the air tanks as an emergency system would be needed anyway.
It is a good idea to put the air tanks within the water tanks, so when they leak, they will push out the water which is a good safety feature.
@Scott Kenny
It's just a little bit wasteful to fill the ballast tanks with 40 bar of air (at 400 m depth). If a water pump would be used, it would be enough to fill the volume with only 1 bar, so that only 2.5 % of the air mass would have been required. Powering an hydraulic pump would also require much less energy than compressing the air.
Of course, this method would have drawbacks, the pump can be clocked by things floating in the water, the time required for emptying the tank will be longer and you need reliable energy supply to drive the pump. Seems like the air tanks as an emergency system would be needed anyway.
It is a good idea to put the air tanks within the water tanks, so when they leak, they will push out the water which is a good safety feature.