Dam Solution?

C’mon guys. Syphon is caused by gravity alone. The weight of the column of water below the level in the source will follow the rules of gravity which Newton sorted out for us some 300 years ago.  Atmospheric pressure will only affect the level in the pipe in as far as it will fill to the same level as the surroundings, nothing more! Only that reduced pressure (in a head of less than 9.81m) will be causing the atmospheric pressure to drive the water up the header, until the forces are in equilibrium.  Forces will be in equilibrium when a vacuum space appears above the liquid in the header. Or the level of the source and receiver are equal.

The famous 9.81m is only applicable for standard atmospheric pressure here on Earth, for water of unit density. It would be more or less, dependent on where the syphon was set up - Earth, Moon, Mars for instance. That static height is fixed by atmospheric pressure, gravitational fields and density of the liquid involved.

Think mercury barometer. The instantaneous height of the mercury column depends on the prevailing atmospheric pressure. The general height also depends on the density of the liquid - Mercury is 760mm, and a water barometer would be ~10 m (errors come in due to the difference in gas vapour pressures above the liquid.

One would not even manage to make a sensible barometer with a volatile iquid like ether as it would actually boil at room temperature under any sort of high vacuum.

Gravity and mass create the weight of everything (the force which, for syphoning is an unbalanced force, so Newton’s Laws of linear motion will apply and the unsupported water clumn will accelerate according to those Laws).

Other things to think about when syphoning, is to consider the diameters and fluid mechanics of flow, along with a pipe that will not collapse under the conditions applied 9often happens when syphoning beer or wine from one bucket to another using a plastic pipe!).

One underlying principle is that liquids are incompressible (measured with equipment available to us laypersons). That makes them unexpandable by the same reasoning.

End of tutorial. Sort out the rest yourselves!

Edited By not done it yet on 04/08/2019 12:01:41

Can't resist pedantically pointing out a repeated typo in NDIY's post. 9.81 is the acceleration due to gravity in metres per second, not the maximum lift achievable by a pump using only atmospheric pressure, which is about 10 or 11 metres.

Apart from that, can't disagree with NDIY except to ask:

1. Can a very thin liquid, like a heavier than air gas, be siphoned? My guess is yes.
2. Can a very sticky liquid like glue be siphoned? My guess is no, because the friction on the sides of the pipe may be enough to overcome friction, much as wet paint stays on ceilings.
3. Which spelling do you prefer. I like Syphon but my allegedly British spell-checker insists otherwise.

Meanwhile, 12pm at Whaley Bridge, they've still not drained enough water to make the dam safe and more rain is on the way. Poor people.

Dave

Dave

For a siphon to work the fluid must have an appreciable density. All gasses have densities much lower than liquids so gas siphons are not met in practice. I write this knowing that someone in an obscure university lab has probably made one. As for ordinary viscous Newtonian liquids a siphon will work. However for non-Newtonian liquids such as many paints, cow muck etc all bets are off.

Your earlier point about having an understand of what is actually happening is very pertinent. My college text book of fluid mechanics describes what a fluid is in five or so pages. For the next 695 pages a fluid, liquid or gas, is treated as a continuum (that is "no part of which is perceptibly different from the adjacent parts". This model is very successful until one has large free molecular paths such as in a vacuum or hypersonics.

Siphon, or syphon which I also prefer, does not feature in the index of my text book.

Enough said, this is a long way from a dam in Derbyshire.

JA

Edited By JA on 04/08/2019 13:09:10

Edited By JA on 04/08/2019 13:10:32

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[ pedant alert ]

... acceleration due to gravity in metres per second per second

MichaelG.

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Now: Thanks for remembering what this is all about, Dave and JA 

The A6 remains closed [not that the idiots driving past the signs believe that, until they are turned back by the Police] and they have stopped people nipping back to their houses in Whaley, because of the high level of risk.

... If you know a 'No Rain' dance, please do it.

Edited By Michael Gilligan on 04/08/2019 13:39:12

I wonder if anyone has used the sheet metal piling used in sea defences, river and canal banks and cofferdams to repair dams such as this? It is relatively fast to use if the machinery could reach the water side of the dam. I don't know what the length of the piles could be or if they could be driven through the puddled clay core. I could imagine a complete wall of piles across the dam, with a 50 feet section in the centre a foot lower for the spillway with a thick tarpaulin like cover secured from the spillway down to prevent the erosion.

Indeed they have, but it's behind a paywall:

opscience.iop.org/article/10.1088/0031-9120/46/4/006/pdf

Neil

Not wishing to detract from this discussion can l make a practical observation. This is an emergency situation and the urgent need is to do something with the equipment you have immediately available and you know works. Hence pumps pumping.

Many years ago l was involved in a similar situation with a flooded quarry caused by an overflowing river, the ground was sand and the erosion of the sand threatened the railway embankment (a little south of LBSC for those that know their geography) Working for the DCE we had first 6 then 12 6"" pumps working before the "Consultant" design scheme of 2 x 12" pumps were even installed. Yes once they were working those pumps started to remedy the situation. But the bank of 6" pumps from the local plant hire companies off the shelf with miles of pipes kept the trains running and commuters happy.

In retrospect l don't think Chinnook's would of helped but it would have been fun trying.

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Well, the authors did borrow the use of lab facilities [at Carleton College, Northfield, MN 55057, USA] for the low pressure experiments.

You may find that you can also read/download the article here: **LINK**

https://www.researchgate.net/publication/231125972_Siphonic_concepts_examined_A_carbon_dioxide_gas_siphon_and_siphons_in_vacuum

MichaelG.

I thought it might be interesting to see what is being done regarding the Canal:

**LINK**

https://www.towpathtalk.co.uk/event/peak-forest-canal-macclesfield-canal/

[quote] In the meantime we have taken the decision to close the Marple flight on the Peak Forest canal and the Bosley flight on the Macclesfield canal whilst we manage the potential risks. The emergency services are taking every precaution including evacuating local properties and closing local roads to maintain public safety. If you are boating in this area please take every precaution. [/quote]

MichaelG.

[struggling to comprehend the meaning of that final sentence]

Rod Renshaw, regarding that 32 foot lip ...... correct up to a point, but .....

1 atmosphere will push water 32 feet, and no more, up a longer vertical pipe sealed at the top, and evacuated of all air. Here's the 'but', if a syphon pipe is constructed, exceeding the 32 foot draw pipe length, but with an even longer discharge pipe, then it will syphon, provided the entire pipe is initially filled with water. 32 feet of the discharge pipe cancels out 32 feet of drawpipe and we have a working syphon. Of course we must remember when talking about pipe lengths, we should really be referring to differences in water level on each side of the syphon. For practical reasons the draw pipe would have to extend some distance below the surface to avoid whirlpools admitting air into the flow (killing the syphon dead0 and similarly the discharge pipe should end underwater to avoid sneaky bubbles creeping upward against the flow (similar effect).

Hi there, all,

I recommend this YouTube channel. **LINK**

Juan Brown gave the most objective running account I was able to find throughout the Oroville Dam situation.

Best regards,

Swarf, Mostly!

To All, and Rod Renshaw in particular ... Having thought a little more I'm not sure I can agree with what I wrote just above. My hypothetical syphon pipe starts off closed at each end, and is filled via a port at the top. When the port is closed we have a filled syphon, but, when either end is opened its column of water would fall to a level 32 feet above the adjacent water surface, because that's as much as 1 atmosphere can support, and we would have a vacuum zone, longer on the discharge side than the draw side, and a static situation i.e. no flow and no help to anyone.

This will teach me to do my thinking before I write, and to do it at home and not on the forum. Apologies all round,

(slinks off, stage left)

KKKD Indeed the top of the "hump" in a syphon cannot be higher than the local air pressure can push the fluid for a simple fluid. One other issue is vapour pressure. Not a real issue with water but I once looked at control system for a project that was sucking solvent out of a tank to a higher level (pump at higher level) I said it would not work, they would just boil the solvent, but hey I'm just an electronics engineer so they didn't listen to me. Then the pump supplier came over from North America to discuss details, took one look at what they we doing and said "no we don't do pumps that defy the laws of physics".

Robert G8RPI.

Hi, many people don't understand about pumping water out of a hole or a container of some sort. Where I used to work many years ago, processing water was a main thing and very often pits and clarifiers had to be pumped out before we could do maintenance work on the pipes or equipment within them. One occasion I remember was a new chap (you know the sort, been everywhere, done everything, got the T shirt, but alas knew Jack nothing at all) this particular day he got the job of rigging up a hired Sykes pump like **LINK** in a pit, he had spent about 3 to 4 hours setting it all up and couldn't get it to pump when he came and asked me to advise him what the problem was, so I went along and as soon as I saw the pump on top of the bank, where Sykes had off loaded it, I said to him "you'll never get that to pump in a month of Sundays" to which he asked why and had to explain that it was beyond the vacuum priming at around 45 feet above the water level and he had to move it down much closer to the water, bit of a lazy git he was, because it was a lot more work to do it in the first place and he wasn't all that pleased that he had to redo his work. Of course when he did finally set it up correctly it pumped full bore on the first attempt.

Regards Nick.

Edited By Nicholas Farr on 05/08/2019 13:25:50

Nope, it can - read all about it here. I think we've established that air pressure doesn't push the fluid in a siphon. But the appearance of a vacuum at the top of a siphon would break the column so the 32 ft figure isn't too far off for practical purposes. Bubbles and leaks will break it too.

Another interesting factoid at the end of that link is a figure for the tensile strength of water - about 150Mpa, which I think is amazingly high.

Dave

Firstly, this paper refers to fully degassed water, not a lot of that in Todbrook reservoir. In real life as opposed to some artificial laboratory situation 32 feet is about your lot

Secondly, the definition of tensile strength used by most sensible people refers to a steady uniaxial stress. Not too sure how you apply a uniaxial stress to water as pressure (stress) in a liquid acts in all directions. If they are talking about the stress necessary to rip molecules away from each other the I'll believe them but that bears little relationship to what most people would call strength. Metals fail due to crack propagation, which happens very quickly indeed, but not all bonds broken instantaneously.

Some fascinating links in this thread.. thanks folks, I enjoyed it so far: siphoning gasses, breaking the 32 foot water head and siphoning in a vacuum. I note the degassed water was tap water so still colligative properties from dissolved minerals - makes me wonder whether the column could be higher still with really pure water +/- what effects one might get with different adhesion/friction values between water and tube.

I recall some talk of using high molecular weight polmers to reduce friction on the boundary layer of boats (back in the 60's) to reduce drag.

pgk

Just don't get me on that one. They are used in fuel pipe lines in the States and cause havoc. They block filters and can do other horrible things.

JA

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Just returning to Neil's opening post, for a 'sanity check'

Does anyone actually believe that a "syphon [...] with a bore of about 0.5 metres [...] would shift a lot of water a lot faster." than the pumps ?

Can any of you clever chaps give a realistic estimate of the flow-rate provided by a 0.5m syphon ?

Thanks

MichaelG.

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No offence intended; I'm just an interested neihbour

Here is an example of what I suggest is water in tension, in free space. The front of the raft has just bounced up off a rock. The water is being pulled up, not falling down. For those who like to see the numbers: Canon EOS 30D, f/4.5, 1/1600 sec, ISO-400, focal length 200mm

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