Sciencey odd question just occured in my daily musings...

[WaterTight]

Is pressure less, by some infinitesimally small amount, at the end of a pipe run, say at a tap, than at the beginning, say at the internal stopcock? Because the pressure available to push water out of the stop-cock is less than the pressure available to push the water out of the tap, because it was finite to begin with so the further away you get from the source of pressure and the greater the amount of water said pressure is trying to shift the less the effect of the pressure and so the less of the residual pressure that is left....?

And if it is - if you ran a pipe, from the stopcock, in a straight line, level for a, for argument's sake, potentially inexhaustible distance in miles - if there was sufficient water to fill this pipe all the way up until the point of exit but the pressure as the stopcock was just normal mains pressure, would you reach a point where nothing would come out the other end? Because the pressure wasn't great enough to move the water through the pipe? And is there a calculation to work out what this would be? It's much easier to think about water being pumped upwards when gravity is fighting you and the limitations there.. Just wondering if it's was in a straight line..

If this effect does exist and doesn't actually require very long distances before it can cause problems I guess it would be part of the calculations used for commercial plumbing. I only thought because there's another thread about running a pipe for an outside tap for 25metres. Made me think how long you'd have to run a pipe on mains before it was too long to work.

 

[TGor]

Lot's of smoke and mirrors on this one guys. I wonder when they stopped teaching the Hydraulic Gradient phenomenon to plumbers?? ; anyhow our plumbing teacher used to have a rig with 1/4" dia horizontal pipe about 2 metres long with a tap on one end. There were vertical branches (open ended) from the pipe at about 200mm intervals in glass pipe about 400mm high. and the end branch away from the tap end had a bit of a reservoir which was filled with coloured water, firstly with the tap closed so that the whole rig was filled and you could see coloured water at equal heights in each vertical branch. When the tap was opened and the water flowed the level in each branch dropped but not equally so that you could actually run a line through from the resevoir to the tap. This was to demonstrate the difference between Static Pressure and Hydraulic pressure .. that is when water flows through a pipe it loses pressure due to friction against the pipe wall.So in this way you would be able to easily find out if the original question is true by setting up a bigger scale rig (but still with 1/4") and experiment with the reservoir height and length of pipe till nothing comes out. Good luck

 

[fuzzy]

that sounds interesting any chance of a skethc or link to it happening on you tube or something?

 

[fuzzy]

Up hill, down or on the level? I'd be gettn' the meter gov checked if I was getting that sort of presure ... imagine the cooker flame!!! lol

imagine how quick youd cook a pizza

 

[WaterTight]

For me, personally, it turns out I had a big enough brain to think up the question but far too small a brain to understand half the answers. But since ignorance is evidently bliss I'm not complaining.

 

[Mrs Tara Plumbi]

I couldn’t let the challenge of this question leave my head
I think the friction is irrelevant and I think the amount of water in the pipe needs to be big enough to be exerting and equal and opposite force to the mains pressure
I may have the answer found in a plumbing book as to when the 3 bar of mains pressure runs out, I could be very wrong.
Please check my maths I may have made massive mistakes.

Townsend Plumbing 1 second edition 1969

Pages 51-3 chapter about water.

If we assume water pressure of 3 bar = 30 m head
And 15mm pipework

Intensity of pressure = head x 9.8 kilo Newton kN/m2
= 294 kN/m2
Total pressure = intensity of pressure x area
Total pressure = 294 kN/m2 x (3.142 x 7.52) m2= 51,961 kN

1 tonne of force = 1000 kg f = 9800 newtons = 1m3 of water

Therefore:
51,961 / 9.8 = 5,302 tonnes = 53,020m3 or 53 million litres of water

I think this means that 3 bar mains water pressure is enough to move 5,302 tonnes of water through a 15mm pipe

A litre is 1cm3 of water and if this pipe hold 0.15 litres per metre then 150 litre per km

At this point I have lost interest and Big Bang has come on TV … come on I’m nearly there.

353,467 kilometres of pipe filled with water.
By the way, circumference of the earth is a little over 40,000. so to all practical terestrial purposes the water will never stop coming.

 

[villa_tom]

I couldn’t let the challenge of this question leave my head
I think the friction is irrelevant and I think the amount of water in the pipe needs to be big enough to be exerting and equal and opposite force to the mains pressure
I may have the answer found in a plumbing book as to when the 3 bar of mains pressure runs out, I could be very wrong.
Please check my maths I may have made massive mistakes.

Townsend Plumbing 1 second edition 1969

Pages 51-3 chapter about water.

If we assume water pressure of 3 bar = 30 m head
And 15mm pipework

Intensity of pressure = head x 9.8 kilo Newton kN/m2
= 294 kN/m2
Total pressure = intensity of pressure x area
Total pressure = 294 kN/m2 x (3.142 x 7.52) m2= 51,961 kN

1 tonne of force = 1000 kg f = 9800 newtons = 1m3 of water

Therefore:
51,961 / 9.8 = 5,302 tonnes = 53,020m3 or 53 million litres of water

I think this means that 3 bar mains water pressure is enough to move 5,302 tonnes of water through a 15mm pipe

A litre is 1cm3 of water and if this pipe hold 0.15 litres per metre then 150 litre per km

At this point I have lost interest and Big Bang has come on TV … come on I’m nearly there.

353,467 kilometres of pipe filled with water.
By the way, circumference of the earth is a little over 40,000. so to all practical terestrial purposes the water will never stop coming.

My brain just burst :willy_nilly:

 

[unguided1]

I couldn’t let the challenge of this question leave my head
I think the friction is irrelevant and I think the amount of water in the pipe needs to be big enough to be exerting and equal and opposite force to the mains pressure
I may have the answer found in a plumbing book as to when the 3 bar of mains pressure runs out, I could be very wrong.
Please check my maths I may have made massive mistakes.

Townsend Plumbing 1 second edition 1969

Pages 51-3 chapter about water.

If we assume water pressure of 3 bar = 30 m head
And 15mm pipework

Intensity of pressure = head x 9.8 kilo Newton kN/m2
= 294 kN/m2
Total pressure = intensity of pressure x area
Total pressure = 294 kN/m2 x (3.142 x 7.52) m2= 51,961 kN

1 tonne of force = 1000 kg f = 9800 newtons = 1m3 of water

Therefore:
51,961 / 9.8 = 5,302 tonnes = 53,020m3 or 53 million litres of water

I think this means that 3 bar mains water pressure is enough to move 5,302 tonnes of water through a 15mm pipe

A litre is 1cm3 of water and if this pipe hold 0.15 litres per metre then 150 litre per km

At this point I have lost interest and Big Bang has come on TV … come on I’m nearly there.

353,467 kilometres of pipe filled with water.
By the way, circumference of the earth is a little over 40,000. so to all practical terestrial purposes the water will never stop coming.

Yeah wot evar but is it enough fer the loveslave ter fill the kettle?????

 

[WaterTight]

I couldn’t let the challenge of this question leave my head
I think the friction is irrelevant and I think the amount of water in the pipe needs to be big enough to be exerting and equal and opposite force to the mains pressure
I may have the answer found in a plumbing book as to when the 3 bar of mains pressure runs out, I could be very wrong.
Please check my maths I may have made massive mistakes.

Townsend Plumbing 1 second edition 1969

Pages 51-3 chapter about water.

If we assume water pressure of 3 bar = 30 m head
And 15mm pipework

Intensity of pressure = head x 9.8 kilo Newton kN/m2
= 294 kN/m2
Total pressure = intensity of pressure x area
Total pressure = 294 kN/m2 x (3.142 x 7.52) m2= 51,961 kN

1 tonne of force = 1000 kg f = 9800 newtons = 1m3 of water

Therefore:
51,961 / 9.8 = 5,302 tonnes = 53,020m3 or 53 million litres of water

I think this means that 3 bar mains water pressure is enough to move 5,302 tonnes of water through a 15mm pipe

A litre is 1cm3 of water and if this pipe hold 0.15 litres per metre then 150 litre per km

At this point I have lost interest and Big Bang has come on TV … come on I’m nearly there.

353,467 kilometres of pipe filled with water.
By the way, circumference of the earth is a little over 40,000. so to all practical terestrial purposes the water will never stop coming.

.....Guh?

 

[fuzzy]

see if i got this, if you have 353,467km of 15mm tube, 3 bar is sufficient?

 

[Mrs Tara Plumbi]

see if i got this, if you have 353,467km of 15mm tube, 3 bar is sufficient?

Fuzzy - exactly the opposit
3 bar will not move this amount of water!

As I said:
1. i may have made a mistake with the maths as this seems a really big number, the the principles were right but my sums wrong OR
2. these formulas might be completely the wrong way of working out the answer

And - as when the computer said the answer is 42 then they set off to fing out the question.
the question i think i have tried to answer is if pipe was laid completely flat, no bends, how much standing water would be in the pipe before you could turn on 3 bars of mains pressure but not move anything?

Me thinks this should be addressed to some maths forum or we should just stick with the experiment as discussed.
What are the chances of winning lottery funding to fund the experiement which will prove my answer correct or incorrect?

 

[fuzzy]

thanks tara, good effort

i love the maths, when i get chance ill work through the sums and tell you how far 3bar can push

 

[TGor]

This is a sketch of the hydraulic gradient rig as I remember it! The difference in head seen at each vertical is caused by the friction loss due to flow in the pipe. This rig demonstrates it in a really practical way .. of course there are many formulae and methods to calculate theoretical friction losses in pipework systems but seeing is believing!!

 

[TGor]

Mrs Tara Plumbing .. friction is not irrelavent ot the question as if there were no friction there would be pressure loss and that is the key to this question.

pressure losses due to friction between th water flowing and the pipe wall are a function of the velocity (and a few other things like pipe roughness etc.) the higher the pressure the higher the velocity the higher the pressure loss .. therefore as the water runs through this imaginary endless pipe the pressure will gradually reduce proportionally to the loss due to friction and thus the velocity will reduce and so the loss will reduce and so on and so and until there will be such little velocity that there is hardly any loss and the pipe will not run full and it will trickle out but never stop fully as the flow and friction will reach equilibrium.

There is a true story about an engineer in Western Australia that ran a 30" water pipe from Perth to Kalgoorlie to the western goldfields a total length of 330 miles and the water took only 2 day to get there. The engineer commited suicide towards the end of the project because everyone was saying it wouldn't work!!

Interesting stuff this thanks all!

 

[dontknowitall]

Hmmm ...

View attachment 3465

 

[Kimou]

Gravity can't be dismissed. It's relative to pressure. It's like doing an experiment on the shadow of a 5p coin but removing the coin.

The moon affects the tides by proxy. It affects airs pressures which in turn compress and releases pressures on the oceans.

This pipe would have to be lined in exact ratio to the sea as no land mass will keep constant levels for the duration of such lengths.But by gradual reduction due to friction it will inevitably reduce to a trickle. This trick will eventually still manage to pass out the other end due to water's property of adhesion so cutting an inch off the terminal will not result in a sudden gush of pressure due to that pressure being exhausted miles ago.

 

[kay-jay]

working on the principle that every action has an equal and opposite re-action is it possible that at one end of this ridiculously long pipe if i insert my finger, it will appear out of the other end of the pipe and poke watertight in the eye for opening this can of worms?????

 

[PlumbBobBob]

A litre is 1cm3 of water.[/QUOTE

i think it is actually 10cm3 not 1cm3

 

[kay-jay]

yep thats right steve, well spotted.

1x1x1 does not equal 1000, 10x10x10 on the other hand...............

 

[Kimou]

A litre is 1cm3 of water.[/QUOTE

i think it is actually 10cm3 not 1cm3

I thought it was just a typo. But it's something every plumber should know about; relative density. Again, this is at atmospheric pressures. If you move the goal posts all sorts can happen. It's how the Triple State of Water exists at the same time. Solid-liquid-gaseous.

@Kay-jay. About Newton's Laws. Action/reaction etc... Did you know that know this has been turned on its head. It has something to do with the race for finding absolute zero-0 degrees Kelvin and reactions found in those experiments. And in turn it's creating havoc with all kinds of accepted philosphies from Decarte to Aristotle. It's fascinating stuff.

 

[quality]

They call them gas laws Boyles, Dalton , Charles etc. but just has be stated a substance can exist as a solid, liquid. vapour or all 3 even plasma.
The good thing about physics is it is they same every time unlike Mrs Smiths cetral heating problem that occured since you fitted thier outside tap

 

[GQuigley67]

now they reckon that nothing is in actual fact a solid, it is just made up of densely packed atoms which makes it seem like it is a solid but in actual fact things can pass through it like other atoms.

Most scientific "Facts" are not actual facts, they are theories, as we evolve we learn more and previous "facts" no longer become facts as they have been proven wrong. Most theories contradict each other aswell so they can not all be laws of physics.

 

[fuzzy]

View attachment 3464

This is a sketch of the hydraulic gradient rig as I remember it! The difference in head seen at each vertical is caused by the friction loss due to flow in the pipe. This rig demonstrates it in a really practical way .. of course there are many formulae and methods to calculate theoretical friction losses in pipework systems but seeing is believing!!

interesting stuff, so if the istern was 10m high ie 1bar pressure, regardless of the length of pipe water would come out, just that te pressure will be minmal once the friction losses have decreased with the reduction in velocity?

so at some point the final pipe would show same pressure

 

[Dan]

Don't mind me while I reply to a few of the threads. We need the new thread pages to be picked up correctly. If this thread isn't current, just visit the plumbing forum and post your own new thread or checkout the other existing threads.