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.

 

[Howsie]

In short, yes. The frictional resistance of the pipe wall and that of the water itself increase over distance. I'm sure if you had the time and inclination it could be worked out.

 

[fuzzy]

standing pressure remains the same

there is a friction loss that will reduce pressure and flow rate

 

[Plumbstar Tom]

I'm pretty sure water can be compressed so it would take the mass of water into consideration in the undefined length of pipe

 

[WaterTight]

That's what I was thinking, the mass of the water surely has an effect on the pressure and so enough water = no workable pressure?

 

[Howsie]

Water is not very compress able at all. Even at the bottom of the deepest ocean(4 kilometres) its volume reduces by approx 1.7%.

 

[leelister6]

Would it be cheaper to use copper or plastic pipe for this experiment?!

 

[fuzzy]

didnt think you could compress a liquid?

 

[diamondgas]

Water is a hydralic fluid and can't be compressed, the pressure will be the same it's full length and will flow at a constant pressure. Factors that'll effect it will be gravity! If you're going vertical then the pressure requires to move the water becomes more of a factor as weight then has to be taken into account! The pressure then will be noticibly different allong it's vertical height! They are my first thoughts anyhoo's .. I'm sure someone will google it! A fluid acts in a totally different way to a gas regards pressure..

 

[diamondgas]

So I googled it and found this Pressure Drop Along Pipe Length - Fluid Flow Hydraulic and Pneumatic, Engineers Edge ....... Now you can calculate the length I think? Good luck! LOL

 

[fuzzy]

well thats cleared it up lol

 

[WaterTight]

See I might be imagining it wrong but it doesn't need to be compressable to still have the effect I'm thinking of. I almost imagine it like a queue of molecules. The force at the start - and the fact it can't be compressed - pushes everything out. But it still has mass and it still has to be pushed by that force which is finite. So in my head it still seems like the mass of water, if substantial enough over a long enough run could theoretically counter the force at the beginning and create a stand-still?

So I googled it and found this Pressure Drop Along Pipe Length - Fluid Flow Hydraulic and Pneumatic, Engineers Edge ....... Now you can calculate the length I think? Good luck! LOL

No. No I can't. I'm nowhere near clever enough. I notice it doesn't list the weight of the water as a factor that can fight the pressure though. So maybe I'm wrong. In my hypothetical experiement it would be best to suppose that the pipe causes no friction.

 

[LegionellaSlave]

Plumbing really is rocket science!
We should all pat ourselves on the back :yesnod:

 

[unguided1]

Stuff the water what about if you use Dyhdrogen Monoxide that stuff can be leathal if compressed to much !!!!!!!!!!!!

 

[WaterTight]

just google that....daaaangerous stuff indeed

 

[fuzzy]

i can see the length of pipe can reduce flow rate due to friction losses but does it reduce pressure? i doesnt when standing as the pressure will be equal on all surfaces presuming it to be horizontal.

but the thing my head struggles with, as well as chinese (the language no the food) is if the pipe was 25 miles long and you put a very small pump on it wouldnt get to the end would it? the weight of water would eventually get to much, so i presume yes length affects pressure???????

 

[unguided1]

i can see the length of pipe can reduce flow rate due to friction losses but does it reduce pressure? i doesnt when standing as the pressure will be equal on all surfaces presuming it to be horizontal.

but the thing my head struggles with, as well as chinese (the language no the food) is if the pipe was 25 miles long and you put a very small pump on it wouldnt get to the end would it? the weight of water would eventually get to much, so i presume yes length affects pressure???????

and dont forget temperature, as water expands and contracts with different temperatures this can also affect standing pressure

 

[WaterTight]

And if that's true then you could theoretically have a pipe where at one point enters mains pressure water and at the other end, because of it's length, no water comes out?

And if that were calculated exactly, if you then took your pipe slice and shaved off an inch, it would start to pour out.

 

[WaterTight]

Temperature, friction, these are all factors. But for my experiment I'm pretending there are no other factors involved. So the pipe is made of an alien substance which is frictionless and the pipe is in a place with no fluctuating weather / temp conditions.

 

[fuzzy]

lol, i suppose that is true, if its not, we can connect the mains to a pipe and let it travel the circumference of the world? we could sit a pod or tram on top of it and have free travel

we not only sorted out water pressure but global travel and carbon footprints also

 

[unguided1]

I aint shaving an inch off nafink that releases water, I aint got enough as it is!!!!!!

 

[fuzzy]

Temperature, friction, these are all factors. But for my experiment I'm pretending there are no other factors involved. So the pipe is made of an alien substance which is frictionless and the pipe is in a place with no fluctuating weather / temp conditions.

where is this place water tight, its as if your making it up!!!

 

[fuzzy]

I aint shaving an inch off nafink that releases water, I aint got enough as it is!!!!!!

Look, if he wants to shave an inch off he can shave an inch off ok!

 

[unguided1]

Woops OK fuzzy, as long as it aint Mine!!!!!

 

[fuzzy]

its his inch, give somebody an inch..................................................

 

[ecowarm]

It soooo simple

[h=3]Flow in Pipe[/h]For flow in a pipe or tube, the Reynolds number is generally defined as:[SUP][6[/SUP]

where:

• D[SUB]H[/SUB] is the hydraulic diameter of the pipe (m).
• Q is the volumetric flow rate (m[SUP]3[/SUP]/s)
• A is the pipe cross-sectional area (m²).
• 
  is the mean velocity of the object relative to the fluid (SI units: m/s)
• μ is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/(m·s))
• ν is the kinematic viscosity (ν = μ / ρ) (m²/s)
• 
  is the density of the fluid (kg/m³)

 

[fuzzy]

are you really reynolds ecowarm?

 

[diamondgas]

Are we getting volume mixed up with pressure? It's a common one!!

If you had a 25 mile piece of pipe totally filled with water and you pushed your finger in one end I'd expect the same amount of water to be displaced at the other end! With minimal resistance yeh? It wouldn't be solid, it's a liquid, they act in different ways, it's mass isn't a factor if gravity is equal throughout it's length.... But like a syringe or piston.

A pump works on moving water using centrifugal force, it doesn't 'push' or 'pull' it spins and throws water about, sucks it up the middle and throws it out the ends of the impellar! There's a limit to how much mass it can move yeh?

 

[fuzzy]

Are we getting volume mixed up with pressure? It's a common one!!

If you had a 25 mile piece of pipe totally filled with water and you pushed your finder in one end I'd expect the same amount of water to be displaced at the other end! With minimal resistance yeh? It wouldn't be solid, it's a liquid, they act in different ways, it's mass isn't a factor if gravity is equal throughout it's length.... But like a syringe or piston.

A pump works on moving water using centrifugal force, it doesn't 'push' or 'pull' it spins and throws water about, sucks it up the middle and throws it out the ends of the impellar! There's a limit to how much mass it can move yeh?

that made my laugh very very much, the thought of one of us running 25 miles of pipe, leaving one of us at one end while the other went to the start and push the water with a finger, lol

we will have to do this or this thread will never come to a conclusion!

how much does 25 miles of 22mm water weigh?

 

[diamondgas]

Hey we're all scientists now!! :rofl:

 

[diamondgas]

that made my laugh very very much, the thought of one of us running 25 miles of pipe, leaving one of us at one end while the other went to the start and push the water with a finger, lol

we will have to do this or this thread will never come to a conclusion!

how much does 25 miles of 22mm water weigh?

I'm in Newcastle fuzzy, where you? I think we should use plastic mind, the copper'll be nicked!!

 

[fuzzy]

were do you live, im in merseyside, ill go to my tap now and push the water, let me know if it comes out, give me 1 minute

 

[fuzzy]

did it move lads???? i bet ive created loads of leaks, i gave it a firm push

 

[diamondgas]

:rofl: fuzzy ... I'm up hill so that'll have to make a difference :rofl:

 

[fuzzy]

my neighbors just been round with an unexplained water surge from all outlets, deny everything