science help please (water flow)

[ben10]

could you tell me if the rate of water flowing out of:

a) tank a is faster than tank b

b) tank a is equal to tank b

c) tank a is slower than tank b

thanks

[ben10]

sorry, here's a better image.

[beer4life]

C.

[Tiny]

Water has only one flow rule, it will flow to the path of least resistance.

There is also an unwritten rule until now; if you want water to flow somewhere it will block up & flow will stop at some time, if you want to stop, dam or contain water it will find a way to leak just to annoy you.

Assuming a pump is not in the equation!!

Therefore create enough resistance it will not flow.

Create less resistance it will flow faster.

Resistance can be caused by pipe diameter, pipe length & pipe head or fall. Pipe head/fall in this case can also be influenced by the distance from the bottom of the tank & the water level.

Resistance can also be caused by a sealed container. Eg: fill a small pipe with water, put your thumb over one end & the water will stay in the pipe until you release the thumb.

Taking all these criteria into consideration;

If the pipe from tank 'a' & 'b' are the same diameter & length, have the same head (fall downhill the same distance), neither tank is sealed at the top, the water level is the same & the connection of outlet is the same distance from the bottom of the tank, then they should both flow at the same rate.

The vent or opening at the top of outlet pipe on tank 'a' should make no difference.

If both tanks were sealed at the top, then it would make a big difference by allowing air to enter the tank & reduce the resistance of atmospheric pressure. In this scenario, tank 'a' would have the better flow.

If the pipe flow resistance is low enough & pipe length is long enough to cause a siphon effect, then tank 'a' will most likely suck air in thru that opening causing the water to run faster for a moment, then slower as it sucks air instead of water, so tank 'b' would be the fastest flowing scenario over time if full continuous flow was the objective.

There are probably an infinite amount of variables I could add to this so I'll quit on that.

If you have some detailed measurements & site considerations, there would be a greater chance of the right answer.
If it's an exam question then you guess.

If someone else can confirm or contradict my rant, then I'm happy to learn more.

Hope that helps.

[ben10]

It's no exam, it's actually the setup of my fish tanks at home.
(6 all together, 2 on top of each other)

The set up I have is (water tank B) and every time i change water, the tanks would over flow.

I thought if I change it to (water tank A) setup, it would fix the problem. but from what you guys suggested,
I think I will just leave it as it is.

[Tiny]

Sounds interesting can you post a pic of the fish tanks?

[beer4life]

It's no exam, it's actually the setup of my fish tanks at home.
(6 all together, 2 on top of each other)

The set up I have is (water tank B) and every time i change water, the tanks would over flow.

I thought if I change it to (water tank A) setup, it would fix the problem. but from what you guys suggested,
I think I will just leave it as it is.

Cavitation is the reason for C.

This may help with the best way.



Quite a few tips there.

[ben10]

[gordon_s1942]

Oddly enough on a home renovation show I saw recently, they were installing the 'Stack' for the toilets/baths/showers/hand basins in a 3 story house.
My limited knowledge is that to prevent the water being sucked out of each pan or 'S' bend is that it must be ventilated but the construction of the house didnt allow this so without a lot of real explanation, the Plumber said in this case they were using a 'WET' connection between one level and another.
I gather the term 'WET' meant this section of the stack was NOT ventilated to the atmosphere as it usually would be, ie 'DRY'.
Just think of the vertical pipes suddenly receiving a Flush or a Bathtub/hand basin plug pulled or even a shower, how much water is cascading down the pipes and how much a Vacuum or flow that would create if its not correctly designed.
Water assumes mass once it gets moving and a potent one at that.
Maybe 6 tanks stacked is too much to be handled at once in a singe 'Stack' or Cascade but look at a building at the main sewer stack and they seem to take it in sections until finally all connecting into one.
I am presuming that the water from the last tank is waste and is disposed off.
Top tank Fill, Bottom Tank to waste.
An old Picture Theatre/Restaurant was renovated recently and I was taken by what seemed to me a spider web of piping from the facilities (Toilets/kitchens etc) on different levels but now I realise they didnt do it because it looks artistic but to ensure proper drainage and isolation from each one.

[lsemmens]

Well explaine, Gordon

[Tiny]

Yes, well said Gordon, & from the pic ben10 has posted, #8, of the stack of aquariums, the dry setup may be what he needs to do.

Tank 'a' type setup, vented to above the highest tank.

The question isn't which setup will flow the fastest, it's which setup will stop flowing to prevent the overflow.

ben10, are the tanks connected together & to what appears to be a filtration system at the bottom, or is the connection between tanks, if there is one, separate from the filtration?

Is there a pump for the filtration?

Looks like a nice setup, fish or turtles?

[ben10]

fish.
yeh the pump for the filtration is on the bottom.

[Tiny]

Since you have an open ended system already (tanks not sealed), the only thing that should make a difference is the position of the intakes on each tank.

Is it the top tanks that overflow due water not leaving the tank quick enough in the overflow pipe to the next tank?

If so a larger diameter overflow pipe should fix the problem as it is more than likely that the system cannot keep up with the pump until all tanks and pipes are filled.


Edit: Can't quite see from the photo, however I suspect your outlet/overflow pipes maybe inserted in from the top of the tank, therefore starting off with water flow uphill until the siphon takes affect. If so there lies your problem.





You need to have the pipes as you drew them for the syphon to start quickly, or it will be blocked by the resistance of the first uphill run if they are inserted from the top as I have drawn.

[ben10]

the outlet pipe is not from the top of the tank, it's drilled a hole in the back glass (similar to the first image i posted, water tank B) . so there's no siphoning.

bigger overflow pipe will definitely work, but i was hoping for an easier solution. coz having a bigger pipe meaning i will have to re-drill the hole thru the glass.

[Tiny]

In that case disregard my edit on previous post.

we are back to this,

Water has only one flow rule, it will flow to the path of least resistance.

There is also an unwritten rule until now; if you want water to flow somewhere it will block up & flow will stop at some time, if you want to stop, dam or contain water it will find a way to leak just to annoy you.

[fandtm666]

from what i can see

in a setup like you have there are a few things that have to be observed

1: each over flow must be at the same spot in each tank

2: pipe size from each tank is to be the same size

3; pipe length needs to be the same length


Then what you have to play with is the actual volume of water coming from the filtration tank
back up to the top tank, you may need to increase the volume or restrict the volume for it to
work properly..

IE if the volume is say 200ltr ph but your outlet can only handle 180ltr ph then it will over flow

also the reason for all pipes being the same length and size is so each flow rate is exactly the same

we used that method for manifolds servicing multiple hot water systems and alike.

[ben10]

all over flow are at the exact same spot.

all outlet pipe are exactly the same size and same length.

only tube going out of the filter to the left tank is longer than the tube going to the right tank. but not to worry coz on both of these tubes i have a a flow control fitting.

[allover]

I don't know any thing re above BUT could you not have a pump that over supplies but is operated by a float valve????

[Tiny]

all over flow are at the exact same spot.

all outlet pipe are exactly the same size and same length.

only tube going out of the filter to the left tank is longer than the tube going to the right tank. but not to worry coz on both of these tubes i have a a flow control fitting.

Would it be possible to use your "flow control fitting" on both pump pipes to the top tanks to reduce the flow enough to stop the overflow, then after initial refilling after cleaning, turn them back up to the desired flow for filtration & aeration?

[beer4life]

all over flow are at the exac t same spot.

all outlet pipe are exactly the same size and same length.

only tube going out of the filter to the left tank is longer than the tube going to the right tank. but not to worry co on both of these tubes i have a a flow control fitting.

I've had a few problems and slow to reply.

Many years ago, the Engineer that designed the Perth to Kalgoorlie pipeline committed suicide because the pumps did not work.
It was later found that due to the topography and undulations, many air locks were created.
The solution was to put manual or auto bleeds at all high points in the line.

Your solution may simply be to get rid of any coiled piping or undulations in the various tubing connections.



I've the full reference to this phenomena.