Let's say we would fill a long tube with water. Let's say the tube is 1km in height.
At the bottom of this tube, the pressure should be much higher than the top. Also, the tube would lead into a container at the bottom as shown in the picture.
Using some kind of mechanism, we would be able to seal the water within the tube from the container at the bottom. Could be valves or some other shutter mechanism depicted as the red line in the picture.
Then we would open the yellow valve. The water being at a much higher pressure than the pressure outside, should shoot up and be able to rotate the wheel as drawn in the picture.
The water would be collected and be sent back into the container. Then we open up the red valves/shutter and let it pressurize again to repeat the process.
Now i am not looking for a perpetuum mobile, but i do not see why this wouldn't work either, so i am trying to guess where the energy would come from.
Since energy is extracted from the water, my best guess would be the water is getting colder, but since this isn't a completely closed system, the water should heat up back again(repressurized) from the atmosphere surrounding it.
Of course i could be wrong (probably am) but i cannot see where else the energy would come from. Any ideas?
Ignore the green shutter. It's just for some fine tuning not really adding to the experiment much.