# Water Does Not Leak Back To The Other Side.

1. May 23, 2013

### Dug Fmjamul

I sealed with silicone and partitioned a 10 Gallon Aquarium with an 8 inch by 8 inch double glass plate with about 3 gallons on one side and 7 gallons on the other. The 3 gallon side was to be dry and filled with gravel and rocks, while the 7 gallon side would have a thin bottom layer of gravel and filled with water. After some time the water links over to the 3 gallon side until it is level with the water on the 7 gallon side. But when I drain the 7 gallon side of water the 3 gallon side does not leak over to the 7 gallon side and the water level does not drop.

Any clues as to the 'why'? Because I don't have any and I'm baffled why the water doesn't leak back over to the 7 gallon side.

2. May 23, 2013

### Travis_King

You didn't seal it properly

3. May 23, 2013

### davenn

and the poor seal you did do is acting like a valve

Dave

4. May 23, 2013

### Staff: Mentor

Welcome to the PF. Can you upload a picture of the setup? How did you brace the partition?

5. May 23, 2013

### BobG

To expand on previous posts, the water pressure is higher on the 7 gallon side than the 3 gallon side. Your seal may be good enough to handle the pressure on the 3 gallon side, but not good enough to handle the pressure on the 7 gallon side.

That said, I'm surprised the water would continue to leak until both sides were level.

Once initially broken in the direction from the 7 gallon side to the 3 gallon side, they fail to close up again as long as there is any water between the seal and the wall?

While in the opposite scenario, water on the 3 gallon side and none on the 7 gallon side, the pressure from the 3 gallon side acts to close the seals that were initially broken?

6. May 23, 2013

### Dug Fmjamul

I know that.

7. May 23, 2013

### Dug Fmjamul

That makes sense, but a one-way valve?

8. May 23, 2013

### Dug Fmjamul

Thanks, that sounds plausible. But if I gradually add water to the 7 gallon side would there be a point where the 3 Gallon side would start to release water to the 7 gallon side? I'm going to try that and see what happens.

9. May 23, 2013

### physwizard

It is possible that there may be some small stones or obstacles near where the leak happens but only on one side. So this would allow allow water to flow more easily from one side to the other.
I don't really support the caging of fish or animals/birds. They have the same right to freedom as we do.

10. May 24, 2013

### 256bits

Similar to the valves in your heart.
Or the PCV in your car, a foot valve at the bottom of the pipe in a well, ....

11. May 24, 2013

### Averagesupernova

How do you figure there is a pressure difference from one side to the other?

12. May 24, 2013

### BobG

Because one side is empty and the other is full?

Or are you asking why 7 gallons of water exerts more pressure on the divider than 3 gallons will when one side is full and the other is empty?

As straight forward as the question should seem to be, I'm pretty sure I don't really understand what you're asking.

Last edited: May 24, 2013
13. May 24, 2013

### Staff: Mentor

Bob, you aren't suggesting volume has anything to do with pressure, are you? The only thing that matters is the height of the water. (I got the same impression from reading your first post as well.)

Last edited: May 24, 2013
14. May 25, 2013

### Averagesupernova

Yes russ, I read that post the same way you do.

15. May 26, 2013

### 256bits

i think it can be assumed that with one side full and the other empty the full side exerts more pressure than the empty side.

after all the questioner does state
Since after the water equalizes in height of both sides, there had to be more pressure on the 7 gallon side than the 3 gallon side.
i don't see any reference to pressure being a result of volume.

16. May 26, 2013

### Averagesupernova

I DO see a reference to it and I want to know if I am missing something because I think it is pretty common knowledge that the height of the water is what determines the pressure. Obviously the 7 gallon side will have more pressure than the 3 gallon side when the 3 gallon side is lower than the 7 gallon side. But it seemed to me that it was implied that the 3 gallon side does not develop the same pressure in reverse when the 7 gallon side is lower than the 3 gallon side.
-
This is the statement in question:
-
So what is it? Did I miss something?

17. May 26, 2013

### 256bits

the 7 gallons side leaks to the 3 gallon side ( originally empty) until both are of the same height. Then the 7 gallon side is drained and water does not leak from the 3 gallon side to the 7 gallon side. The original height h of the 7 gallon side would have to have been greater than the starting h of the 3 gallon side. That is how I interpreted the original scenario and carried that along from post to post.

It is cumbersome to be calling the containers the 7 gallon side and 3 gallon side.

I am not saying my interpretation is any more correct than yours - just that I did not notice any problem with the statments. You and Russ did. Now I tend to wonder by polling readers what the percentage of readers would see it either way. I cringe at the possibility of being a lonely minority of 1.

Other than Bob coming in with his explanation.

18. May 26, 2013

### Averagesupernova

Ok 256. I was just wondering if I misunderstood the setup. Yes it is a cumbersome description.

19. May 28, 2013

### BobG

Pressure isn't solely straight down (or you wouldn't need the divider at all). Surely the lateral pressure on the glass (which would actually cause the leaking) would be greater the greater the amount of mass the glass divider is holding back. I'm not actually sure, since that's something that seems so obvious that I really haven't thought about it that much.

Edit: Or, the total amount of mass doesn't matter. That seems very counter-intuitive. Obviously, it couldn't be a straight linear relationship, since inserting a hollow tube into the ocean would be holding back the entire ocean, but I'm surprised it doesn't seem to matter at all (at least in a few minutes of browsing).

Last edited: May 28, 2013
20. May 28, 2013

### physwizard

It may be instructive to try and understand why there should be a sideways force in the first place. For eg., if you try to stack a pile of bricks on the floor one on top of the other they would be in stable equilibrium and not require any sideways force. Now if we try to stack a column of water on the floor, its not going to stay that way. Its going to spill. Now lets try the same thing with marbles. It is theoretically possible to stack the marbles with all their centres in a straight vertical line so that they would be in unstable equilibrium and not require a sideways force to keep them in equilibrium. But in practice for the majority of the number of ways in which the stacking can take place this would not be the case. For any two marbles whose centers are not aligned in the same vertical line there would be a sideways force. If you look at a marble which is in the interior, on an average the horizontal forces from all directions would cancel out. But if you look at one at the side, there would be a net outward horizontal force. This horizontal force would only depend on the weight of the marbles on top of it plus the force transmitted downwards (and sideways) by the ones above those. So it appears that it will depend only on the height and not on the total number of marbles.
Anyways this is just a rough example we don't know how water behaves at the molecular level (at least I don't!) but in practice we find that the pressure depends only on the height(depth) $p = p_0 + \rho gh$ so it appears that water behaves more similarly to marbles than bricks!