If u compress a fluid it creates a higher boyent force to any object in it that compress at a higher pressure. When decompressing the fluid you will get back the energy u put in to compress it(not taken in consideration friction), regardless of any movment by the object. Moving the object higher when the fluid is compressed and let it drop when fluid is decompressed allows for force gain from gravity. The system will be using more then gaining but if u dont look at friction you can see that this is a way to show you could harness energy from gravity. gravity energy generator?