Why Do Siphons Have A Maximum Height? Principle, History & Assumptions (All Explained)

Since the ancient Egyptians, we have used siphons to transfer liquid between containers or over barriers. A siphon is a tube which carries liquid with no air and the rule for a successful siphon is that the water level at the outlet side must be lower than the water level at the inlet. What happens in between and specifically how high the tube is raised is not important.
Website (Atlas Copco): bit.ly/2zdstKY
00:11 What is a Siphon?
00:29 Siphon Assumption
00:45 400 Years Ago Engineers Noticed This!
01:00 Why Do Siphons Have A Maximum Height?
01:38 Torricelli's (Galileo's Student) Brainwave
02:12 Torricelli's Did This To Study The Effects & How Mercury Barometer Was Born?
03:07 Pascal Climbed High Altitudes With Torricelli's Barometer To Prove This
03:43 Why Use Mechanical Bordon Gauges?
For a long time, the assumption held that siphons worked because the weight of water on the outlet side of the siphon is higher than the weight of the water on the inlet side, meaning that the heavier side pulled the water like a rope or a chain over the bend.
400 years ago engineers noticed something interesting. They saw that when a siphon was used at just over 10 meters the water would stall and a gap would appear at the top of the tube. The question that no one could answer was - why do siphons have a maximum height?
Galileo, the father of modern physics even got involved. He suggested that the gap was vacuum and that it was caused by the weight of water overcoming the pull of vacuum as if the imaginary rope was stretching under the weight. He reasoned that vacuum had only a limited power to lift and after a certain height it would run out of strength.
One of the Galileo's students named Torricelli agreed that what they saw was vacuum but he couldn't see the logic of vacuum acting as a force of attraction and he tried to explain things differently. His brainwave was that the atmosphere surrounding the basin at the bottom of the tube has weight and that weight pushes down on the liquid exerting pressure on the pool at the lower end of the siphon, in turn, pushing water up the tube. If the height and therefore the weight of the water in the tube becomes large enough, it balances the force of air pressure at the bottom and the water stalls. The gap at the top then is indeed a vacuum but it's not pulling on the liquid. It can't because there is nothing there.
Instead of a siphon Torricelli filled a tube with water, plugged it in one end and inverted it into a basin of water to study the effects. Say we measured a height of 10.32 meters of water with a density of a thousand kilograms per meter cubed under Earth's gravity force of 9.81 Newton's per kilogram, the equation for water pressure gives us 101298 Newton's per meter square or Pascals of pressure at the bottom. That's 1,013 millibars absolute.
Torricelli's realized that by using a heavier liquid like mercury he could achieve the same way with a much shorter column and so the mercury barometer was born. With measurements in lengths of mercury and still today much of the vacuum world measures pressure in millimeters of mercury or as we call it now Torr.
Soon after Blaise Pascal took ideas further by realizing that if atmospheric pressure has weight then the pressure should change according to the altitude. He used Torricelli's barometer to prove that. By climbing to higher altitudes he measured that the atmospheric pressure would reduce. The barometer is still a very important instrument. Not least because the only pressure acting on it is that which is being measured. It measures to a good accuracy the absolute pressure of a gas irrelevant to any other atmospheric conditions. Clearly, a mercury barometer requiring nearly a meter in height has its practical limitations.
So today mechanical Bourdon gauges are the most common inline pressure measuring device that we use in industrial vacuum. The basic principle is something like a party horn or a party blower, that is, a flattened cylinder will tend to straighten if the pressure inside it raises relative to the outside pressure. What that means is Bourdon tubes are always measuring pressure relative to the surroundings.
If well constructed and well-calibrated regularly Bourdon gauges are a compact and cost-effective way to provide clear, accurate and consistent vacuum measurements.
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[@nvigneswaran3699]

Informative! Good work Adrian..

[@durgeshanand992]

The important thing here is that people call it "suction" which is misleading because vaccum has no pulling force. Its actually the atmosphere on the other side "pushing". Just like in a see - saw , the heavier body pushes more and hence the lighter body rises... Here the atmosphere pushes and water rises.

[@michaelohair1062]

Gravity acting on the contents within the long leg of the airtight conduit creates a suction at the short leg which draws liquid from the source over the crest and to the outlet that is positioned sufficiently below the source.

[@Rick-the-Swift]

It's both pressure, gravity, suction, and molecular bonding at play. If you take away any of these components the siphon simply will not work. You need atmospheric (or some other) pressure to push down on the basin of water, suction to pull (or continue pulling) the liquid up the tube, gravity to continue pulling (sucking) the molecularly bonded chain of water molecules over and down the tube spout exit.

[@kjellg6532]

@@michaelohair1062 Now what happens if you make the suction pipe 1 m in diameter and the exit side as short as possible with a 1 inch pipe? The siphon still sends water from the higher source to the lower exit, despite much more water at the suction side, ref: en.wikipedia.org/wiki/Siphonen.wikipedia.org/wiki/Siphon

[@laughismedicine9319]

We have also a river about 300mtrs from our house but the problem is I need a 20mtrs suction to lift the water from down. My question is, can I use siphon system if my suction height is 20m and the outlet going to our house is 300meters?

[@Rick-the-Swift]

Hi. Did you try it? What did you learn?

[@kjellg6532]

Sorry, but no siphon can lift any water. Water level of source must be higher than point of exit from the siphon.

[@Rick-the-Swift]

@@kjellg6532 Pardon, but yes, siphons can and do "lift" water all the time. I've seen hundreds, maybe thousands and have yet to see one that doesn't, or at least one that doesn't cause water to "rise' ;)

[@michaelohair1062]

A siphon can indeed lift water above the source level. US Patent 5,358,000 was the first to teach how an inline metering chamber can cyclically be emptied and refilled with a siphon conduit.

[@kjellg6532]

@@michaelohair1062 I do not think so. To lift water to a higher elevation you need to add energy to it, ref laws of thermodynamics. How does this patent add energy to the water? I have briefly looked at the patent. From input 12 via a small closed canister 16 to the lower output at 24 this is a copy of the drum-„pump“. It works fine as a siphon as the system is air tight and the output is lower than the source. Then comes the tricky part. At some point in time the valve 42 is opened and water from the high canister 16 are let out at a high elevation at outlet 42. You primed the system, added energy to the system by manually lifting water into canister 16. Now this energy is lost by expelling the water via output 42. To reenergise the system you now have to manually lift another body of water up into canister 16. I can not see that this system can lift any water, no source of energy input but for your arms. There are some discussion about automatic valves, opening and letting air in to the system etc, but this does not explain any energy source. As I see it, this patent does not work.

[@magicvalleycandelariaquezo8137]

Very impormative,thanks for d creator of this video..can we discuss further?there is a limit of this application with respect to the head of the water source or supply..anybody who have d data of the limitations.lets say I want to use this application to a water source 50m below the ground,will this system work by creating an elevation on top of the ground for a siphon system..just an exaggerated scenario..will d water 50m below the ground still be pumped up by siphon system to flow on d ground?

[@AtlasCopcoVacuumSolutions]

Hi Wilbert and thanks for your interest in our videos! You’ve rightly grasped the important takeaway here that it is the strength of Atmospheric Pressure, not Vacuum, that provides the energy to drive water up the tube - every 0.1bar of pressure is enough to push water 1m high, so If you have 1bar of atmospheric pressure at the bottom, you can push water up 10meters of vertical height by creating a vacuum (removing the atmospheric pressure) at the other end. The peak of Mt Everest is at an altitude of 8Km, at this height there is much lower atmospheric pressure- only about 30% compared to sea level. If you set up a barometer on top of Everest, you would find that atmospheric pressure is only strong enough to push water 3.3meters up the column. The reverse is also true of course - if you could dig an empty canyon 8000m deep, the air pressure at the bottom would probably be around 1.7bar - this higher pressure would allow you to make a siphon or barometer with a 17meter column of water. Does that help to explain?

[@magicvalleycandelariaquezo8137]

@@AtlasCopcoVacuumSolutions thanks for the info,with that,kindly confirm my thought that it is possible to use SIPHON in extracting water from d river to a 50m ground to have a continuous water flow since the river has a continuous water flow.Is that right?

[@magicvalleycandelariaquezo8137]

@@AtlasCopcoVacuumSolutions very helpful,thanks a lot,hope u can guide me further to set up a free flowing water to a level ground extracted from a 50m below river using a 5 stages SIPHON as u said 1bar atmospheric pressure can push water 10m above without using external energy.

[@kjellg6532]

@@magicvalleycandelariaquezo8137 No siphon can lift any water to a higher elevation. Thus using 5 stages is equal to 5*0=0

[@timdunk7278]

Does said disappear, and flow resume once the water level rises above the 10.32meter level?

[@AtlasCopcoVacuumSolutions]

Hi Tim, To help you more effectively, we respectfully ask that you further expand on your inquiry.

[@timdunk7278]

When the water stalls, and the gap is formed, does the flow restart when the water level rises past the 10M level? The reason is, whenever my syphone stalls, it’s necessary to open the venting valve which is positioned at the apex and then fill the void to restart the flow. Also another question: does a syphon create bubbles? My siphoned is 300m long by 4” diam. I’ve pressure tested every mm with 30psi of air, but still have a tiny stream bubbles at the discharge, I can also hear bubbles streaming through the apex with a stethoscope. Can you spell the gauge type you referred to? I can’t quite hear the term clearly. Thank you very much.

[@AtlasCopcoVacuumSolutions]

We would appreciate it if you could provide us with your country of origin so that we can refer you to the appropriate team.

[@timdunk7278]

@@AtlasCopcoVacuumSolutions canada

[@michaelohair1062]

A Siphon Pump Having a Metering Chamber can dispense water 25 feet above the source. The weight of the water within the sufficiently sized long leg is acted on by gravity when the system is closed back airtight and the flow is allowed by opening a control valve after a small portion is withdrawn from an inline metering chamber and a vacuum is created that is enough to draw water from the source to refill the chamber and flush any air from the system at the long leg outlet end making the system ready for another withdrawal.

[@AtlasCopcoVacuumSolutions]

Thanks or sharing your insights.

[@michaelohair1062]

@@AtlasCopcoVacuumSolutions US Patent 5,358,000 has defined a Siphon Pump.

[@kjellg6532]

@@michaelohair1062 From what I see, that patent can not work.No energy input to elevate any water.

[@michaelohair8443]

@@kjellg6532 The siphon pump having a metering chamber does work. The basic concept is pictured in figure #1. The siphon is initially primed and the water is allowed to flow through the short leg and the canister and the outlet long leg. The crest of the siphon conduit can be raised 25 feet above the source and gravity acting on the properly sized long leg that is positioned far enough below the inlet elevation will cause a flow. The flow control valve #28 at the crest works in conjunction with an anti backflow valve # 26 at the lower end of the long leg to leave it full when the flow is stopped by closing the shutoff valve. The canister can then be emptied and put back airtight and the foot valve #12 prevents any water from falling back to the source. The control valve can then be opened and the weight of the water within the long leg will draw water from the source replenishing the canister and the small amount of trapped air will be expelled out the end of the long leg and the system will be ready for another withdrawal at the crown. This is a cycle. No outside source of energy is required because gravity is the only power source.

[@kjellg6532]

@@michaelohair8443 I understand that this is how the patent describes it, but I disagree. At startup all tubes and vessel 16 is filled with air. There is no energy stored in the system. By filling the tubes and 16 with water you add energy to the system as static height energy. By letting out water from 16, you expelled energy from the system. After a few cycles, no energy is left in the system. This „siphon" can not work as there is a leakage at the apex of the system. Flow at the output side will not refill 16 and 16 will be filled with air. That is, if the whole system do not stop before that.

[@lucasbarbeau954]

And so a siphon of a less dense liquid, say oil, will have a higher maximum siphon height than that of water?

[@kjellg6532]

Yes, can pass a higher wall, obstacle, but still the output must be lower than the source level at the input.

[@solank7620]

This video at 6:53 to 7:03: kzbin.info/www/bejne/h2ncgZaKetlla9Esi=29CuTGVEi9RVpQyZ Says that siphons work because of gravity, and the liquid’s cohesive force. And that atmospheric pressure is a proven false theory. So what is going on here then? Is that video wrong, and atmospheric pressure does play a role?

[@InclinedTherapy]

Disproved in 24 metres tube experiments 1994 check height limit of a siphon corrigendum

[@magicvalleycandelariaquezo8137]

Hi Andrew,thanks for your comment.whst do u mean by 24 meters tube,is that d difference in height of the tube from d top level of d siphon tank water source and d outlet point?

[@InclinedTherapy]

@@magicvalleycandelariaquezo8137 I used a single 48 metre nylon tube 6mm internal diameter, type used in beer cellers. The tube was raised by it's centre, with both open ends submerged at bottom of two vessels, all was filled with boiled water to remove any gas.

[@magicvalleycandelariaquezo8137]

@@InclinedTherapy thanks Andrew,I saw videos siphoning water from a lower elevation to a higher elevation,is that really possible?the principle of siphon is the outlet should be lower than the inlet..this system will be very useful if it has capability to transfer water from lower elevation to a higher elevation..if that is possible,do u have idea about the elevation difference that this system will work..you said at 24m this will not work but the video said at 10m it will reach the vacuum.i'm thinking to use this system extracting water from a river and transfer it to a 50m above ground using siphon..do u think it's possible?

[@magicvalleycandelariaquezo8137]

The idea is to set up siphon system in between the river and the 50m elevated ground.i think I need multi stages siphon to do that.is this problem can be solved using Bernoulli's principle only or I need other engineering principles for d calculations?

[@AtlasCopcoVacuumSolutions]

Hi Andrew and thanks for taking an interest in our videos! As Vacuum Specialists, our aim with this video is to describe one of the principles of Vacuum Technology: that vacuum cannot pull, it is simply the absence of a pushing force. This concept helps us to see how atmospheric pressure influences the liquid level in a column and to understand how barometers work. While we wouldn’t dispute that surface tension, momentum and other dynamic liquid flow phenomena might enable an operating syphon to extend above 10 meters - we’re quite certain that you could not prime any such siphon in the traditional manner using vacuum at the exit of the tube - instead either the tube should be filled first as in your experiment, or liquid would have to be pumped up the tube from the water source with positive pressure. Would you agree?