4 ms·

How does the air "push the water up"? What mechanism prevents the air from simply bubbling up through the water column? I'm assuming some kind of valve or pisto

How does the air "push the water up"? What mechanism prevents the air from simply bubbling up through the water column? I'm assuming some kind of valve or piston, but would be interested to see what it looks like.

liftm 2y ago
I'll assume the inlet is below water level / at the bottom of the tank…
ulrikrasmussen 2y ago
I wondered the same thing. I guess it would work if the water shaft was actually U-shaped, but that would mean drilling three shafts instead of one.
- ajb 2y ago
  Why three? Their diagram shows two (plus the cavern, which must already exist)
  - ulrikrasmussen 2y ago
    To build a trap, the pipe would have to go almost all the way up to the reservoir, then down, and then up again to connect to the reservoir: https://en.wikipedia.org/wiki/Trap_(plumbing) https://en.wikipedia.org/wiki/Trap_(plumbing) But there might another way to avoid bubbling which I have missed. Maybe the compressed air is under so much pressure that it becomes denser than the water?
    - ajb 2y ago
      It doesn't need to be denser than the water because the incoming air is always above the water. Imagine an cavern shaped like the great pyramid of Giza, full of water. They dig two pipes, an air entry pipe to the point at the top, and a water exit pipe to one of the corners at the base. Air pumped in at the top pipe will almost evacuate the cavern, before the water level drops to the point where air could get to the exit pipe. What this means is that depending on the shape of the cavern, they may not be able to utilise its whole volume. In the worst case, if its roof were entirely flat, they would not be able to use any. They can use the volume of a section, bounded by horizontal planes, from the air entry pipe either down as far as the exit pipe, or (if the roof dips down between the two) down as far as the lowest point on the highest possible path between the two. That's assuming totally vertical pipes. I know they can curve them a bit, but I don't know if they can curve them enough to enter a cavern from below. If they could, then they can utilise the entire volume, as long as they can identify the lowest and highest points
Slartie 2y ago
Put the air inlet/outlet at the top of the cavern, and the water inlet/outlet at the bottom. Then just stop pumping air while the water level in the cavern is still above the water outlet. A little water has to remain in the cavern at all times.
Cthulhu_ 2y ago
As long as the water pipe inlet is below the water level that isn't going to happen. Think of a plant spray or super soaker, same principle. Nothing personal to the commenter I'm replying to, but I love watching HN re-engineer long existing basic systems.

liftm 2y ago

I'll assume the inlet is below water level / at the bottom of the tank…

ulrikrasmussen 2y ago

I wondered the same thing. I guess it would work if the water shaft was actually U-shaped, but that would mean drilling three shafts instead of one.

ajb 2y ago
Why three? Their diagram shows two (plus the cavern, which must already exist)
- ulrikrasmussen 2y ago
  To build a trap, the pipe would have to go almost all the way up to the reservoir, then down, and then up again to connect to the reservoir: https://en.wikipedia.org/wiki/Trap_(plumbing) https://en.wikipedia.org/wiki/Trap_(plumbing) But there might another way to avoid bubbling which I have missed. Maybe the compressed air is under so much pressure that it becomes denser than the water?
  - ajb 2y ago
    It doesn't need to be denser than the water because the incoming air is always above the water. Imagine an cavern shaped like the great pyramid of Giza, full of water. They dig two pipes, an air entry pipe to the point at the top, and a water exit pipe to one of the corners at the base. Air pumped in at the top pipe will almost evacuate the cavern, before the water level drops to the point where air could get to the exit pipe. What this means is that depending on the shape of the cavern, they may not be able to utilise its whole volume. In the worst case, if its roof were entirely flat, they would not be able to use any. They can use the volume of a section, bounded by horizontal planes, from the air entry pipe either down as far as the exit pipe, or (if the roof dips down between the two) down as far as the lowest point on the highest possible path between the two. That's assuming totally vertical pipes. I know they can curve them a bit, but I don't know if they can curve them enough to enter a cavern from below. If they could, then they can utilise the entire volume, as long as they can identify the lowest and highest points

Slartie 2y ago

Put the air inlet/outlet at the top of the cavern, and the water inlet/outlet at the bottom. Then just stop pumping air while the water level in the cavern is still above the water outlet. A little water has to remain in the cavern at all times.

Cthulhu_ 2y ago

As long as the water pipe inlet is below the water level that isn't going to happen. Think of a plant spray or super soaker, same principle. Nothing personal to the commenter I'm replying to, but I love watching HN re-engineer long existing basic systems.