Cartesian diver generator

[Reiyuki]

Take the classic 'cartesian diver' experiment:
https://youtu.be/Ypp4A7q0NV4?t=65

Pressure is changed in the system, causing a change the volume of air in the diver, resulting in a constant force up or down (depending on mass vs buoyancy).


I found it interesting because input energy is a single action (that can mostly be recovered), and yet the resulting force is a constant, limited only by the length of the chamber.



In a hypothetical experiment:
* Make a Cartesian diver with a permanent magnet as the weight.
* Seal it inside a long tube (100+ft?) filled with water.
* Add a long string of coils all the way up and down the tube.
* Drive a hydraulic cylinder to change the pressure of the system.


Now, the question is:
  As the diver slides up and down, could the energy generated be potentially recover greater than the energy required to change the buoyancy of this system?


Granted, there are much better ways to implement this in practice, but I was just wondering if this was mathematically viable, or whether I am missing something?

[Reiyuki]

Instead of miles of copper coils, something like this would save on materials.

I'm still trying to find a reason why wouldn't work (given a long enough cylinder).  As far as the hydraulic cylinder is concerned, the tank is effectively a closed system.

[lumen]

Instead of miles of copper coils, something like this would save on materials.

I'm still trying to find a reason why wouldn't work (given a long enough cylinder).  As far as the hydraulic cylinder is concerned, the tank is effectively a closed system.

At some depth at the bottom of a long cylinder, the water pressure itself would prevent the bladder from expanding and even if you tried to reduce the pressure the water will separate and maintain the pressure on the bladder.

At the top the pressure will need to be very high to collapse the bladder. I would bet if someone did the math you would find it's a wash.

Still an interesting concept, may want to do some calculating.