Water and gravity: look at this video

[sm0ky2]

Think of it like this:


When you expand a baloon under water:


Such as is done in emergency life jackets, with a CO2 cartridge


You are providing an inner pressure, forcing against the mass of that volume's
worth of water.


If you sucked all the air out of a military submarine,
while underwater
It would crush like you stepped on an aluminum can.


Your're fighting the entire atmosphere

[sm0ky2]

The Pistol Shrimp uses this to its' advantage,
as does a particular high-efficiency water heater


But its not of a lot of use for direct gravitational harvesting
outside of some nano-tech we haven't invented yet

[sm0ky2]

Its' called a cavitation-gravitation oscillator
Which uses the difference between 0 ATM and
The 0 state of a denser than air medium
The compress an incalculable mass of incomprehensible atoms
Which in turn radiate all sort of grabbables

[Willy]

In such: the decompression energy from one chamber could add to the compression energy of the other, thereby lowering the energy required to compress the air.
The equilibrium state would be approx half-compression in both.
The piston would only have to half-compress either chamber while energy is extracted from both.
Hmm

                             Very cool

[sm0ky2]

In most cases, the height of the water tank is not large enough to make a
substantial change in the pressure of the bobber


When pressure inside the tank is returned to its' rest state,
the air inside the bobber is more than capable of re-expanding itself