# pub question

B

#### breezer

a pint rests on the correct answer to this one

a 400 gallon water tank fitted at say 20 feet up ona a wall has two pipes coming from the bottom. one is 15mm the other is 40mm diameter

the pipes run verticaly down the wall to the floor, at the floor each has 2 90 degree bends (to make a u shape)

the tank then has a plug put in each pipe, plugs are chained together.
tank is the filled with water

when full, chain is pulled (so both plugs are removed at same time)

question.

will the water forom one pipe (at the bottom) go higher up that the other, if so which and why.

i say no because although different diameteres they both have same pressure

can you say that in english breezer.

Lets assume both pipes are connected to the tank at the same level, and there's no draw offs.

Then the smaller pipe will air lock and not fill

bottled it...

Not sure (depending if doital is right about the air-lock), but if not, then I would say: same level because of air-pressure

????

no they will both go up the same level as the head of water determines the pressure, although if one pipe is 3 times bigger than the other it will pass a volume of water three times faster.

I'm assuming the top of the tank is open.
They would both squirt back as high as the level of water in the tank if there were no resistance.
But there is resistance, and it's higher for the thinner pipe (by a factor of 11.61). So the water from the large pipe would go higher.

ollski said:
no they will both go up the same level as the head of water determines the pressure, although if one pipe is 3 times bigger than the other it will pass a volume of water three times faster.

If head of water determines pressure, which I do not disagree with, bore of pipe must also be a factor at the point of delivery, otherwise why have a larger bore of pipe when gravity fed, is that not to ensure a greater amount of pressure, if that`s not the case, why bother having large bore pipework on gravity fed systems when you could easily pipe up in say 10mm or 5mm?? Is it for speed of delivery only??? It is isn`t it.....
I`ll get me coat.......

tgm it's like gas in a pipe, there's a pressure drop when the gas/water is running through the pipe. So if you read the pressure at the outlet end of the pipe, you'd get a lower reading from the smaller pipe.

Volume is the word your looking for trainee

If it takes 3 minutes for a given amont of water to pass through a 10mm pipe, it will take 1 minute for the same amount of water to pass through a 30mm pipe....though the pressure will be virtually the same (very slight difference due to frictional resistances as chrisr mentioned). These examples are in theoretical pipe by the way before anyone asks me where to get it.

Thank you for that... so the correct answer is..????

Not so oilski old fruit. Completely wrong! For a start you shoould be looking at the cross-sectional Area of the pipe not its diameter. WHen you take into account the effects of friction, viscosity, laminar flow and all that you end up with a formula, as I implied above.
The nub of the thing is that the water clings to the sides of the pipe , so with a smaller pipe there's more clinging for the area, than there is for bigger pipe.

I will update you tomorrow....I'm going to make a scaled down version of it. I'm fed up reading about kilonewtons and pascals

`specially Rowntree`s Fruit Pascals. Look forward to hearing the answer.

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