The word siphon (also spelled syphon) is sometimes used to refer to a wide variety of devices that allow the flow of liquids through tubes. But in the English language today, a siphon is commonly understood to be a tube, in an inverted U shape, which allows a liquid to flow uphill without a pump, over an obstacle and then discharge at a level lower than the surface of the original reservoir. Practical siphons operate because gravity causes the hydrostatic pressure Fluid statics is the science of fluids at rest, and is a sub-field within fluid mechanics. The term usually refers to the mathematical treatment of the subject. It embraces the study of the conditions under which fluids are at rest in stable equilibrium. The use of fluid to do work is called hydraulics, and the science of fluids in motion is fluid at the entrance to the tube to exceed that at the top of the tube by a sufficient amount to force fluid from the reservoir into the tube and uphill over the obstacle. Gravity causes the hydrostatic pressure at the downstream end of the tube to be significantly higher than the surrounding pressure so fluid flows out of the tube into the atmosphere or into a second reservoir lower than the first.^[1]

Contents 1 History 2 Operation 2.1 Theory 2.2 Analogy 3 Practical requirements 4 Applications 5 Siphon terminology 6 Sample building code regulations regarding back siphonage 7 Self-siphons 8 Siphons in nature 9 Explanation using Bernoulli's equation 9.1 Velocity 9.2 Maximum height 10 Vacuum siphons 11 Oxford English Dictionary 12 See also 13 Notes 14 References 15 External links

History

Egyptian Ancient Egypt was an ancient civilization of eastern North Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. The civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh, and it developed over the next three millennia. Its history reliefs from 1500 BC depict siphons used to extract liquids from large storage jars.^[2]

Hero of Alexandria Hero of Alexandria (Greek: Ἥρων ὁ Ἀλεξανδρεύς) (c. 10–70 AD). was an ancient Greek mathematician who was a resident of a Roman province (Ptolemaic Egypt); he was also an engineer who was active in his native city of Alexandria. He is considered the greatest experimenter of antiquity and his work is representative of the wrote extensively about siphons in the treatise Pneumatica.^[3]

In the 9th century, the Banu Musa brothers invented a double-concentric siphon, which they described in their Book of Ingenious Devices.^[4]

Operation

Theory

A siphon operates to move liquid from an upper reservoir to a lower reservoir because gravity causes the hydrostatic pressure Fluid statics is the science of fluids at rest, and is a sub-field within fluid mechanics. The term usually refers to the mathematical treatment of the subject. It embraces the study of the conditions under which fluids are at rest in stable equilibrium. The use of fluid to do work is called hydraulics, and the science of fluids in motion is fluid of the liquid in the discharge end of the tube to be greater than the surrounding pressure in the lower reservoir. If a siphon operates to move liquid out of a reservoir and into the atmosphere it is because the hydrostatic pressure of the liquid in the discharge end of the tube is greater than atmospheric pressure. Liquid is drawn into a siphon and rises above the surface of the upper reservoir because gravity causes the hydrostatic pressure of liquid near the crest of the siphon to be less than atmospheric pressure.^[1]

When the column of liquid is allowed to fall from C down to D, the reduced pressure at the top (B) will allow atmospheric pressure at the upper reservoir (A) to push the liquid in the upper reservoir up to B and over the top. No liquid tensile strength is needed. Even the falling lighter lower leg from C to D can cause the liquid of the heavier upper leg to flow up and over into the lower reservoir

An occasional misunderstanding of siphons is that they rely on the tensile strength of the liquid to pull the liquid up and over the rise.^[5] While water has been found to have a great deal of tensile strength in some experiments (such as with the z-tube^[6]), and siphons in vacuum rely on such cohesion, common siphons can easily be demonstrated to need no liquid tensile strength at all to function.^[5][7] Furthermore, since common siphons operate at positive pressures throughout the siphon, there is no contribution from liquid tensile strength, because the molecules are actually repelling each other in order to resist the pressure, rather than pulling on each other. To demonstrate, the longer lower leg of a common siphon can be plugged at the bottom and filled almost to the crest with liquid, leaving the top and the shorter upper leg completely dry and containing only air at ambient pressure. When the plug is removed and the liquid in the longer lower leg is allowed to fall, it will cause a reduction of pressure at the top of the siphon, resulting in the liquid in the upper reservoir being pushed up into the reduced pressure area by atmospheric pressure acting on the upper reservoir. The liquid will then typically sweep the air bubble down and out of the tube and continue to operate as a normal siphon. As there is no contact between the liquid on either side of the siphon at the beginning of this experiment, there can be no cohesion between the liquid molecules to pull the liquid over the rise. This demonstration may fail if the air bubble is so long that as it travels down the lower leg of the siphon it displaces so much liquid that the column of liquid on the longer lower leg of the siphon is no longer heavier than the column of liquid being pushed up the shorter leg of the siphon. Another simple demonstration that liquid tensile strength isn't needed in the siphon is to simply introduce a bubble into the siphon during operation. The bubble can be large enough to entirely disconnect the liquids in the tube before and after it, defeating any liquid tensile strength, and yet if the bubble isn't too big, the siphon will continue to operate with little change.

The uphill flow of water in a siphon doesn’t violate the principle of continuity A continuity equation in physics is a differential equation that describes the transport of some kind of conserved quantity. Since mass, energy, momentum, electric charge and other natural quantities are conserved, a vast variety of physics may be described with continuity equations because the mass of water entering the tube and flowing upwards is equal to the mass of water flowing downwards and leaving the tube. A siphon doesn't violate the principle of conservation of energy The law of conservation of energy is an empirical law of physics. It states that the total amount of energy in an isolated system remains constant over time . A consequence of this law is that energy can neither be created nor destroyed, it can only be transformed from one state to another. The only thing that can happen to energy in a closed because the loss of gravitational potential energy In physics, Potential energy is energy stored within a physical system as a result of the position or configuration of the different parts of that system. It has the potential to be converted into other forms of energy, such as kinetic energy, and to do work in the process. The SI unit of measure for energy and work is the joule (symbol J) as liquid flows from the upper reservoir to the lower reservoir equals the work In physics, mechanical work is the amount of energy transferred by a force acting through a distance. Like energy, it is a scalar quantity, with SI units of joules. The term work was first coined in 1826 by the French mathematician Gaspard-Gustave Coriolis done in overcoming fluid friction Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. For example, high-viscosity felsic magma will create a tall, steep stratovolcano, because it cannot flow far before it cools, while low-viscosity mafic lava will create a wide, shallow-sloped shield volcano. All real fluids have some as the liquid flows through the tube.^[1] Once started, a siphon requires no additional energy In physics, energy is a quantity that can be assigned to every particle, object, and system of objects as a consequence of the state of that particle, object or system of objects. Different forms of energy include kinetic, potential, thermal, gravitational, sound, elastic, light, and electromagnetic energy. The forms of energy are often named to keep the liquid flowing up and out of the reservoir. The siphon will draw liquid out of the reservoir until the level falls below the intake, allowing air or other surrounding gas to break the siphon, or until the outlet of the siphon equals the level of the reservoir, whichever comes first.

The maximum height of the crest A 'crest' is the point on a wave with the maximum value or upward displacement within a cycle. A trough is the opposite of a crest, so the minimum or lowest point in a cycle is limited by atmospheric pressure Atmospheric pressure is the force per unit area exerted against a surface by the weight of air above that surface in the Earth's atmosphere. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. Low pressure areas have less atmospheric mass above, the density The density of a material is defined as its mass per unit volume. The symbol of density is ρ . In some countries (for instance, in the United States), density is also defined as its weight per unit volume of the liquid, and its vapour pressure Vapour pressure or equilibrium vapour pressure is the pressure of a vapour in thermodynamic equilibrium with its condensed phases in a closed container. All liquids and solids have a tendency to evaporate into a gaseous form, and all gases have a tendency to condense back to their liquid or solid form. When the pressure within the liquid drops to below the liquid's vapor pressure, tiny vapor bubbles can begin to form at the high point and the siphon effect will end. This effect depends on how efficiently the liquid can nucleate Nucleation is the extremely localized budding of a distinct thermodynamic phase. Some examples of phases that may form via nucleation in liquids are gaseous bubbles, crystals or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation . Nucleation of crystalline, amorphous and even vacancy clusters in bubbles; in the absence of impurities or rough surfaces to act as easy nucleation sites for bubbles, siphons can temporarily exceed their standard maximum height during the extended time it takes bubbles to nucleate. For water Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state, water vapor or steam at standard atmospheric pressure, the maximum siphon height is approximately 10 m The metre , symbol m, is the base unit of length in the International System of Units (SI). Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole, its definition has been periodically refined to reflect growing knowledge of metrology. Since 1983, it is defined as the distance travelled by light in a (33 feet A foot is a non-SI unit of length in a number of different systems including English units, Imperial units, and United States customary units. Its size can vary from system to system, but in each is around a quarter to a third of a meter. The most commonly used foot today is the international foot. There are three feet in a yard and 12 inches in a); for mercury Mercury , also quicksilver (/ˈkwɪksɪlvər/) or hydrargyrum (/haɪˈdrɑrdʒɨrəm/ hye-DRAR-ji-rəm), is a chemical element with the symbol Hg (Latinized Greek: hydrargyrum, from "hydr-" meaning watery or runny and "argyros" meaning silver) and atomic number 80. A heavy, silvery d-block metal, mercury is one of six chemical it is 76 cm (30 inches An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot. A corresponding unit of area is the square inch and a corresponding unit of volume is the cubic inch. The inch is usually the universal unit of measurement in).

Analogy

The chain model is a useful but flawed analogy to the operation of a siphon

A simplified conceptual model of a siphon is that it is like a chain hanging over a pulley with one end of the chain piled on a higher surface than the other. Since the length of chain on the shorter side is lighter than the length of chain on the taller side, the chain will move up around the pulley and down towards the lower surface.^[8]

There are two problems with the chain model of a siphon. The first is that under most practical circumstances, dissolved gases, vapor pressure, and (sometimes) lack of adhesion with tube walls, conspire to render the tensile strength within the liquid, ineffective for siphoning. Thus, unlike a chain which has significant tensile strength, liquids usually have little tensile strength under typical siphon conditions, and therefore the liquid on the rising side cannot be pulled up, in the way the chain is pulled up on the rising side.^[5][7]

The second problem with the chain model of the siphon is that the weight of liquid on the up side of the siphon can be greater than the liquid on the down side, yet the siphon can still function. For example, if the tube from the upper reservoir to the top of the siphon has a much larger diameter than the section of tube from the lower reservoir to the top of the siphon, the shorter upper section of the siphon may have a much larger weight of liquid in it, yet the siphon can function normally.

Practical requirements

A plain tube can be used as a siphon. An external pump A pump displaces a volume by physical or mechanical action. Pumps fall into five major groups: direct lift, displacement, velocity, buoyancy and gravity pumps. Their names describe the method for moving a fluid has to be applied to start the liquid flowing and prime the siphon. This can be a human mouth. This is sometimes done with any leak-free hose to siphon gasoline Gasoline or petrol is a petroleum-derived liquid mixture which is primarily used as a fuel in internal combustion engines. It is also used as a solvent, mainly known for its ability to dilute paints from a motor vehicle's gasoline tank to an external tank. (Siphoning gasoline by mouth often results in the accidental swallowing of gasoline, which is quite poisonous, or aspirating In medicine, aspiration is the entry of secretions or foreign material into the trachea and lungs it into the lungs, which can cause death or lung damage.^[9]) If the tube is flooded with liquid before part of the tube is raised over the intermediate high point and care is taken to keep the tube flooded while it is being raised, no pump is required. Devices sold as siphons come with a siphon pump A pump displaces a volume by physical or mechanical action. Pumps fall into five major groups: direct lift, displacement, velocity, buoyancy and gravity pumps. Their names describe the method for moving a fluid to start the siphon process. When applying a siphon to any application it is important that the piping be as closely sized to the requirement as possible. Using piping of too great a diameter and then throttling the flow using valves or constrictive piping appears to increase the effect of previously cited concerns over gases or vapor collecting in the crest which serve to break the vacuum. Once the vacuum is reduced the siphon effect is lost.

Reducing the size of pipe used closer to requirements appears to reduce this effect and creates a more functional siphon that does not require constant re-priming and restarting. In this respect, where the requirement is to match a flow into a container with a flow out of said container (to maintain a constant level in a pond fed by a stream, for example) it would be preferable to utilize two or three smaller separate parallel pipes that can be started as required rather than attempting to use a single large pipe and attempting to throttle it.

Applications

Siphoning the beer Beer is the world's most widely consumed and probably oldest alcoholic beverage, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from cereal grains—most commonly malted barley, although wheat, maize , and rice are widely used. Most beer is flavored with hops, after a first fermentation

When certain liquids needs to be purified, siphoning can help prevent either the bottom (dregs) or the top (foam A foam is a substance that is formed by trapping many gaseous bubbles in a liquid or solid and floaties) from being transferred out of one container into a new container. Siphoning is thus useful in the fermentation of wine Wine is an alcoholic beverage, typically made of fermented grape juice. The natural chemical balance of grapes is such that they can ferment without the addition of sugars, acids, enzymes or other nutrients. Wine is produced by fermenting crushed grapes using various types of yeast. Yeast consumes the sugars found in the grapes and converts them and beer Beer is the world's most widely consumed and probably oldest alcoholic beverage, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from cereal grains—most commonly malted barley, although wheat, maize , and rice are widely used. Most beer is flavored with hops, for this reason, since it can keep unwanted impurities out of the new container.

Self-constructed siphons, made of pipes or tubes, can be used to evacuate water from cellars after floodings. Between the flooded cellar and a deeper place outside a connection is built, using a tube or some pipes. They are filled with water through an intake valve (at the highest end of the construction). When the ends are opened, the water flows through the pipe into the sewer or the river.

Siphoning is common in irrigated fields to transfer a controlled amount of water from a ditch, over the ditch wall, into furrows.

Large siphons may be used in municipal waterworks Water supply is the process of self-provision or provision by third parties in the water industry, commonly a public utility, of water resources of various qualities to different users. Irrigation is covered separately and industry. Their size requires control via valves at the intake, outlet and crest of the siphon. The siphon may be primed by closing the intake and outlets and filling the siphon at the crest. If intakes and outlets are submerged, a vacuum pump A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The vacuum pump was invented in 1650 by Otto von Guericke may be applied at the crest to prime the siphon. Alternatively the siphon may be primed by a pump at either the intake or outlet.

Gas in the liquid is a concern in large siphons.^[10] The gas tends to accumulate at the crest and if enough accumulates to break the flow of liquid, the siphon stops working. The siphon itself will exacerbate the problem because as the liquid is raised through the siphon, the pressure drops, causing dissolved gases within the liquid to come out of solution. Higher temperature accelerates the release of gas from liquids so maintaining a constant, low temperature helps. The longer the liquid is in the siphon, the more gas is released, so a shorter siphon overall helps. Local high points will trap gas so the intake and outlet legs should have continuous slopes without intermediate high points. The flow of the liquid moves bubbles thus the intake leg can have a shallow slope as the flow will push the gas bubbles to the crest. Conversely, the outlet leg needs to have a steep slope to allow the bubbles to move against the liquid flow; though other designs call for a shallow slope in the outlet leg as well to allow the bubbles to be carried out of the siphon. At the crest the gas can be trapped in a chamber above the crest. The chamber needs to be occasionally primed again with liquid to remove the gas.

Siphon terminology

Bowl siphon

Bowl siphons are part of flush toilets A flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets , but many squat toilets also are made for automated flushing. Modern toilets incorporate an 'S','U', 'J', or 'P' shaped bend that causes the water in the toilet. Siphon action in the bowl siphon A flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets , but many squat toilets also are made for automated flushing. Modern toilets incorporate an 'S','U', 'J', or 'P' shaped bend that causes the water in the toilet siphons out the contents of the toilet bowl and creates the characteristic toilet "sucking" sound.

Some toilets also use the siphon principle to obtain the actual flush from the cistern A cistern is a waterproof receptacle for holding liquids, usually water. Often cisterns are built to catch and store rainwater. Cisterns are distinguished from wells by their waterproof linings. Modern cisterns range in capacity from a few litres to thousands of cubic metres, effectively forming covered reservoirs. The flush is triggered by a lever or handle that operates a simple diaphragm-like piston pump that lifts enough water to the crest of the siphon to start the flow of water which then completely empties the contents of the cistern into the toilet bowl. The advantage of this system was that no water would leak from the cistern excepting when flushed.

Early urinals A urinal is a specialized toilet for urinating into generally used by males. It has the form of a container or simply a wall, with drainage and automatic or manual flushing incorporated a siphon in the cistern which would flush automatically on a regular cycle because there was a constant trickle of clean water being fed to the cistern by a slightly open valve.

Trap under a sink which functions as an inverted siphon

Inverted siphon

An inverted siphon is not a siphon but a term applied to pipes that must dip below an obstruction to form a "U" shaped flow path. Inverted siphons are commonly called traps for their function in preventing smelly sewer gases from coming back out of drains and sometimes making dense objects like rings and electronic components retrievable after falling into a drain.^{[citation needed]} Liquid flowing in one end simply forces liquid up and out the other end, but solids like sand will accumulate. This is especially important in sewage Sewage is water-carried wastes, in either solution or suspension, that is intended to flow away from a community. Also known as wastewater flows, sewage is the used water supply of the community. It is more than 99.9% pure water and is characterized by its volume or rate of flow, its physical condition, its chemical constituents, and the systems or culverts A culvert is device used to channel water. It may be used to allow water to pass underneath a road, railway, or embankment for example. Culverts can be made of many different materials; steel, polyvinyl chloride and concrete are the most common. Formerly, construction of stone culverts was common which must be routed under rivers or other deep obstructions where the better term is "depressed sewer". Large inverted siphons are used to convey water being carried in canals Smaller transportation canals can carry barges or narrowboats, while ship canals allow seagoing ships to travel to an inland port , or from one sea or ocean to another (e.g.: Caledonian Canal, Panama Canal) or flumes across valleys, for irrigation or gold mining.

Back siphonage

Back siphonage is a plumbing term applied to clean water pipes that connect directly into a reservoir without an air gap. As water is delivered to other areas of the plumbing system at a lower level, the siphon effect will tend to siphon water back out of the reservoir. This may result in contamination of the water in the pipes. Back siphonage is not to be confused with backflow. Back siphonage is a result of liquids at a lower level drawing water from a higher level. Backflow is driven entirely by pressure in the reservoir itself. Backflow cannot occur through an intermediate high-point. Back siphonage can flow through an intermediate high-point and is thus much more difficult to guard against.

Anti-siphon valve

Anti-siphon valves^[11] are required in such designs. Building codes A building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of building codes are to protect public health, safety and general welfare as they relate to the construction and occupancy of buildings and structures often contain specific sections on back siphonage and especially for external faucets A tap is a valve controlling release of liquids or gas. In the British Isles and most of the Commonwealth, the word is used for any everyday type of valve, particularly the fittings that control water supply to bathtubs and sinks. In the U.S., the term "tap" is more often used for beer taps, cut-in connections, or wiretapping, with the. (See sample building code below.) The reason is that external faucets may be attached to hoses which may be immersed in an external body of water, such as a garden pond A garden pond is a water feature constructed in a garden, normally either for aesthetic purposes or to provide wildlife habitat. The UK charity Pond Conservation has estimated that there are about two million garden ponds in the UK, swimming pool A swimming pool, swimming bath, wading pool, or simply a pool, is a container filled with water intended for swimming or water-based recreation. There are many standard sizes; the largest and deepest is the Olympic size. A pool can be built either above or in the ground, and from materials such as metal, plastic, fiberglass or concrete, aquarium An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants. The term combines the Latin root aqua, meaning water, with the suffix -arium, meaning "a place for relating to& or washing machine A clothes washer, or washer, is a machine designed to wash laundry, such as clothing, towels and sheets. The term is mostly applied only to machines that use water as the primary cleaning solution, as opposed to dry cleaning or even ultrasonic cleaners. Should the pressure within the water supply system fall, the external water may be siphoned back into the drinking water system through the faucet. Another possible contamination point is the water intake in the toilet tank. An anti-siphon valve is also required here to prevent pressure drops in the water supply line from siphoning water out of the toilet tank (which may contain additives such as "toilet blue") and contaminating the water system. Anti-siphon valves function as a one-direction check valve A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction.

Anti-siphon valves are also used medically. Hydrocephalus Hydrocephalus , also known as "Water on the Brain", is a medical condition. People with hydrocephalus have an abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head, convulsion, and mental, or excess fluid in the brain, may be treated with a shunt In medicine, a shunt is a hole or passage which moves, or allows movement of fluid from one part of the body to another. The term may describe either congenital or acquired shunts; and acquired shunts may be either biological or mechanical which drains cerebrospinal fluid Cerebrospinal fluid , Liquor cerebrospinalis, sometimes called brain juice, is a clear bodily fluid that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord. In essence, the brain "floats" in it from the brain. All shunts have a valve to relieve excess pressure in the brain. The shunt may lead into the abdominal cavity such that the shunt outlet is significantly lower than the shunt intake when the patient is standing. Thus a siphon effect may take place and instead of simply relieving excess pressure, the shunt may act as a siphon, completely draining cerebrospinal fluid from the brain. The valve in the shunt may be designed to prevent this siphon action so that negative pressure on the drain of the shunt does not result in excess drainage. Only excess positive pressure from within the brain should result in drainage.^[12][13][14]

Note that the anti-siphon valve in medical shunts is preventing excess forward flow of liquid. In plumbing systems, the anti-siphon valve is preventing backflow.

Other anti-siphoning devices

Along with anti-siphon valves, anti-siphoning devices also exist. The two are unrelated in application. Siphoning can be used to remove fuel from tanks. With the cost of fuel increasing, it has been linked in several countries globally to the rise in fuel theft. Trucks, with their large fuel tanks, are most vulnerable. The anti-siphon device prevents thieves from inserting a tube into the fuel tank.

Siphon barometer

A siphon barometer is the term sometimes applied to the simplest of mercury barometers A barometer is a scientific instrument used to measure atmospheric pressure. It can measure the pressure exerted by the atmosphere by using water, air, or mercury. Pressure tendency can forecast short term changes in the weather. Numerous measurements of air pressure are used within surface weather analysis to help find surface troughs, high. A continuous U-shaped tube of the same diameter throughout is sealed on one end and filled with mercury. When placed into the upright position, mercury will flow away from the sealed end, forming a partial vacuum, until balanced by atmospheric pressure on the other end. The term "siphon" is used because the same principle of atmospheric pressure acting on a fluid is applied. The difference in height of the fluid between the two arms of the U-shaped tube is the same as the maximum intermediate height of a siphon. When used to measure pressures other than atmospheric pressure, a siphon barometer is sometimes called a siphon gauge and not to be confused with a siphon rain gauge. Siphon pressure gauges are rarely used today.

Siphon bottle

Siphon bottles

A siphon bottle (archaically called a siphoid^[15]) is a pressurized bottle with a vent and a valve. Pressure within the bottle drives the liquid up and out a tube. It is a siphon in the sense that pressure drives the liquid through a tube. A special form was the gasogene.

Siphon cup

A siphon cup is the (hanging) reservoir of paint attached to a spray gun. This is to distinguish it from gravity-fed reservoirs. An archaic use of the term is a cup of oil in which the oil is siphoned out of the cup via a cotton wick or tube to a surface to be lubricated.

Siphon rain gauge

A siphon rain gauge is a rain gauge A rain gauge is a type of instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation (solid precipitation is measured by a snow gauge) over a set period of time that can record rainfall over an extended period. A siphon is used to automatically empty the gauge. It is often simply called a "siphon gauge" and is not to be confused with a siphon pressure gauge.

Heron's siphon

Heron's siphon is a siphon that works on positive air pressure and at first glance appears to be a perpetual motion Perpetual motion would occur in a device or system if a motion, once started, were to continue indefinitely. The laws of thermodynamics demonstrate that perpetual motion devices cannot be created machine. In a slightly differently configuration, it is also known as Heron's fountain.^[16]

Venturi Siphon

A venturi siphon, also known as an eductor, is essentially a venturi which is designed to greatly speed up the fluid flowing in a pipe such that an inlet port located at the throat of the venturi can be used to siphon another fluid. See pressure head. The low pressure at the throat of the venturi is called a siphon when a second fluid is introduced, or an aspirator when the fluid is air.

Siphonic roof drainage

Siphonic roof drainage makes use of the siphoning principle to carry water horizontally from multiple roof drains to a single downpipe and to increase flow velocity^[17]. Air baffles at the roof drain inlets reduce the injection of air which causes embolisms in siphons. One benefit to this drainage technique is the reduction in required pipe diameter to drain a given roof surface area, up to half the size. Another benefit is the elimination of pipe pitch or gradient required for conventional roof drainage piping.

Sample building code regulations regarding back siphonage

From Ontario's building code:^[18]

7.6.2.3.Back Siphonage

1. Every potable water system that supplies a fixture or tank that is not subject to pressures above atmospheric shall be protected against back-siphonage by a backflow preventer.
2. Where a potable water supply is connected to a boiler, tank, cooling jacket, lawn sprinkler system or other device where a non-potable fluid may be under pressure that is above atmospheric or the water outlet may be submerged in the non-potable fluid, the water supply shall be protected against backflow by a backflow preventer.
3. Where a hose bibb is installed outside a building, inside a garage, or where there is an identifiable risk of contamination, the potable water system shall be protected against backflow by a backflow preventer.

Self-siphons

The term self-siphon is used in a number of ways. Liquids that are composed of long polymers can "self-siphon"^[19][20] and these liquids do not depend on atmospheric pressure. Self-siphoning polymer liquids work the same as the siphon-chain model where the lower part of the chain pulls the rest of the chain up and over the crest. This phenomenon is also called a tubeless siphon.^[21]

"Self-siphon" is also often used in sales literature by siphon manufacturers to describe portable siphons that contain a pump. With the pump, no external suction (e.g. from a person's mouth/lungs) is required to start the siphon and thus the product is inaccurately described as a "self-siphon".

If the upper reservoir is such that the liquid there can rise above the height of the siphon crest, the rising liquid in the reservoir can "self-prime" the siphon and the whole apparatus be described as a "self-siphon".^[22] Once primed, such a siphon will continue to operate until the level of the upper reservoir falls below the intake of the siphon. Such self-priming siphons are useful in some rain gauges and dams.

Capillary action can be used in self-priming siphons. In these, water soaks upwards (into a cotton-filled hose) and below the crest to begin the siphon gradually, and as weight is added to the down stream, this kind of siphon will speed up, but it will never be as fast as the same diameter of open hose.

Siphons in nature

The term "siphon" is used for a number of structures in human and animal anatomy, either because flowing liquids are involved or because the structure is shaped like a siphon, but in which no actual siphon effect is occurring: see Siphon (biology).

Biologists debate whether the siphon mechanism plays a role in blood circulation.^[23] It is theorized that veins form a continuous loop with arteries such that blood flowing down veins help siphon blood up the arteries, especially in giraffes and snakes.^[24] Some have concluded that the siphon mechanism aids blood circulation in giraffes.^[25] Many others dispute this^[26][27] and experiments show no siphon effects in human circulation.^[28] Some cite negative pressure in the brain as supporting the role of the siphon effect in the brain.^[29]

Explanation using Bernoulli's equation

Bernoulli's equation may be applied to a siphon to derive the flow rate and maximum height of the siphon.

Example of a siphon with annotations to describe Bernoulli's equation

Let the surface of the upper reservoir be the reference elevation.

Let point A be the start point of siphon, immersed within the higher reservoir and at a depth −d below the surface of the upper reservoir.

Let point B be the intermediate high point on the siphon tube at height +h_B above the surface of the upper reservoir.

Let point C be the drain point of the siphon at height −h_C below the surface of the upper reservoir.

Bernoulli's equation:

= fluid velocity along the streamline

= gravitational acceleration downwards

= elevation in gravity field

= pressure along the streamline

= fluid density

Apply Bernoulli's equation to the surface of the upper reservoir. The surface is technically falling as the upper reservoir is being drained. However, for this example we will assume the reservoir to be infinite and the velocity of the surface may be set to zero. Furthermore, the pressure at both the surface and the exit point C is atmospheric pressure. Thus:

(Equation 1.)

Apply Bernoulli's equation to point A at the start of the siphon tube in the upper reservoir where P = P_A, v = v_A and y = −d

(Equation 2.)

Apply Bernoulli's equation to point B at the intermediate high point of the siphon tube where P = P_B, v = v_B and y = h_B

(Equation 3.)

Apply Bernoulli's equation to point C where the siphon empties. Where v = v_C and y = −h_C. Furthermore, the pressure at the exit point is atmospheric pressure. Thus:

(Equation 4.)

Velocity

As the siphon is a single system, the constant in all four equations is the same. Setting equations 1 and 4 equal to each other gives:

Solving for v_C:

Velocity of siphon:

The velocity of the siphon is thus driven solely by the height difference between the surface of the upper reservoir and the drain point. The height of the intermediate high point, h_B, does not affect the velocity of the siphon. However, as the siphon is a single system, v_B = v_C and the intermediate high point does limit the maximum velocity. The drain point cannot be lowered indefinitely to increase the velocity. Equation 3 will limit the velocity to a positive pressure at the intermediate high point to prevent cavitation. The maximum velocity may be calculated by combining equations 1 and 3:

Setting P_B = 0 and solving for v_max:

Maximum velocity of siphon:

The depth, −d, of the initial entry point of the siphon in the upper reservoir, does not affect the velocity of the siphon. No limit to the depth of the siphon start point is implied by Equation 2 as pressure P_A increases with depth d. Both these facts imply the operator of the siphon may bottom skim or top skim the upper reservoir without impacting the siphon's performance.

Note that this equation for the velocity is the same as that of any object falling height h_C. Note also that this equation assumes P_C is atmospheric pressure. If the end of the siphon is below the surface, the height to the end of the siphon cannot be used; rather the height difference between the reservoirs should be used.

Maximum height

Setting equations 1 and 3 equal to each other gives:

Maximum height of the intermediate high point occurs when it is so high that the pressure at the intermediate high point is zero; in typical scenarios this will cause the liquid to form bubbles and if the bubbles enlarge to fill the pipe then the siphon will 'break'. Setting P_B = 0:

Solving for h_B:

General height of siphon:

This means that the height of the intermediate high point is limited by velocity of the siphon. Faster siphons result in lower heights. Height is maximized when the siphon is very slow and v_B = 0:

Maximum height of siphon:

This is the maximum height that a siphon will work. It is simply when the weight of the column of liquid to the intermediate high point equates to atmospheric pressure. Substituting values will give approximately 10 metres for water and 0.76 metres for mercury.

Vacuum siphons

Experiments have shown that siphons can operate in a vacuum, provided that the liquids are pure and degassed and surfaces are very clean.^[30][31]

Oxford English Dictionary

The Oxford English Dictionary (OED) entry on siphon, published in 1911, states that a siphon works by atmospheric pressure. Stephen Hughes of Queensland University of Technology criticised this in a 2010 article^[8] which was widely reported in the media.^{[32][33][34][35]} The OED editors stated, "there is continuing debate among scientists as to which view is correct. ... We would expect to reflect this debate in the fully updated entry for siphon, due to be published later this year."^[36]

See also

• 1992 explosion in Guadalajara for details of an accident involving a siphon.
• Gravity feed

Wikimedia Commons has media related to: Siphons

Notes

1. ^ ^{a b c} Streeter, V.L., Fluid Mechanics, Section 10.2 (4th edition)
2. ^ Usher, Abbott Payson (April 1, 1988). A History of Mechanical Inventions (Revised Edition). Dover Publications. pp. 461. ISBN 978-0486255934. http://print.google.com/print?id=xuDDqqa8FlwC&pg=93&lpg=93&dq=siphon+vacuum&sig=Rv57Nd2RzUgKoz58zrP1BKqpH_I&auth=DQAAAGsAAABhdj2gK7YELIVEZdsG3IH-FT4vEQAnsHKdFbCsD0h61ukaejc3D-jxmBy7UlR0ykMcybLZ01jMj88yM4izr039yiMQbqqw6jIHxekeEm13thfbOsRjpR_s2Xt3lGTIDe0A472OREwbsvVy91tPSjAo.
3. ^ "THE PNEUMATICS OF HERO OF ALEXANDRIA". www.history.rochester.edu. http://www.history.rochester.edu/steam/hero/index.html. Retrieved 2010-05-11.
4. ^ Banu Musa (authors), Donald Routledge Hill (translator) (1979). The book of ingenious devices (Kitāb al-ḥiyal). Springer. p. 21. ISBN 9027708339
5. ^ ^{a b c} "The Great Siphon Definition Debate". http://www.youtube.com/watch?v=T_FJe-HdFPw. Retrieved 2010-05-31.
6. ^ [1]
7. ^ ^{a b} Nokes M C 1948 "Vacuum siphons" School Science Review 29 233
8. ^ ^{a b} Hughes, Stephen W. (2010). "A practical example of a siphon at work". Physics Education 45 (2): 162–166. doi:10.1088/0031-9120/45/2/006. http://eprints.qut.edu.au/31098/8/31098a.pdf.
9. ^ "Material Safety Data Sheet for MidGrade Unleaded Gasoline". 2006/11/28. http://www.marathonpetroleum.com/content/documents/mpc/msds/0125MAR019.pdf
10. ^ "Siphons for Geosiphon Treatment Systems". sti.srs.gov. http://sti.srs.gov/fulltext/tr2000066/tr2000066.html. Retrieved 2010-05-11.
11. ^ "Toiletology ... Anti-siphon needs an explanation". www.toiletology.com. http://www.toiletology.com/anti-sph.shtml. Retrieved 2010-05-11.
12. ^ "Importance of anti-siphon devices in the treatment... [Childs Nerv Syst. 1994 - PubMed result"]. www.ncbi.nlm.nih.gov. http://www.ncbi.nlm.nih.gov/pubmed/7923233?dopt=Abstract. Retrieved 2010-05-11.
13. ^ "Spina Bifida Association - Spina Bifida Association". www.spinabifidaassociation.org. http://www.spinabifidaassociation.org/site/c.liKWL7PLLrF/b.2642297/k.5F7C/Spina_Bifida_Association.htm. Retrieved 2010-05-11.
14. ^ [2]
15. ^ [3]
16. ^ "[physics/0310039 Magic Fountain"]. arxiv.org. http://arxiv.org/abs/physics/0310039. Retrieved 2010-05-11.
17. ^ Arthur, S. & Wright, G. B. (2007), Siphonic roof drainage systems—priming focused design, Building & Environment, Volume 42, Issue 6 , Pages 2421-2431.
18. ^ [4]
19. ^ "Physics Demonstrations - Light". sprott.physics.wisc.edu. http://sprott.physics.wisc.edu/demobook/chapter6.htm. Retrieved 2010-05-11.
20. ^ [5]
21. ^ [6]
22. ^ [7]
23. ^ [8]
24. ^ "Independent effects of heart-head distance and caudal blood pooling on blood pressure regulation in aquatic and terrestrial snakes -- Seymour and Arndt 207 (8): 1305 -- Journal of Experimental Biology". jeb.biologists.org. http://jeb.biologists.org/cgi/content/full/207/8/1305. Retrieved 2010-05-11.
25. ^ "Siphon mechanism in collapsible tubes: application to circulation of the giraffe head -- Hicks and Badeer 256 (2): 567 -- AJP - Regulatory, Integrative and Comparative Physiology". ajpregu.physiology.org. http://ajpregu.physiology.org/cgi/content/abstract/256/2/R567. Retrieved 2010-05-11.
26. ^ "Blood flow uphill and downhill: does a siphon faci... [Comp Biochem Physiol A Comp Physiol. 1987 - PubMed result"]. www.ncbi.nlm.nih.gov. http://www.ncbi.nlm.nih.gov/pubmed/2890463?dopt=Abstract. Retrieved 2010-05-11.
27. ^ "The heart works against gravity -- Seymour et al. 265 (4): 715 -- AJP - Regulatory, Integrative and Comparative Physiology". ajpregu.physiology.org. http://ajpregu.physiology.org/cgi/content/abstract/265/4/R715. Retrieved 2010-05-11.
28. ^ "Standing up to the challenge of standing: a siphon does not support cerebral blood flow in humans -- Dawson et al. 287 (4): R911 -- AJP - Regulatory, Integrative and Comparative Physiology". ajpregu.physiology.org. http://ajpregu.physiology.org/cgi/content/abstract/287/4/R911. Retrieved 2010-05-11.
29. ^ "The siphon controversy counterpoint: the brain need not be "baffling" -- Hicks and Munis 289 (2): R629 -- AJP - Regulatory, Integrative and Comparative Physiology". ajpregu.physiology.org. http://ajpregu.physiology.org/cgi/content/full/289/2/R629. Retrieved 2010-05-11.
30. ^ Ganci, S. et al. (2008). "Historical and pedagogical aspects of a humble instrument". Eur. J. Phys. 29: 421–430. doi:10.1088/0143-0807/29/3/003. http://www.iop.org/EJ/abstract/0143-0807/29/3/003
31. ^ Nokes M. C. (1948). "Vacuum siphons". Am. J. Phys. 16: 254
32. ^ QUT physicist corrects Oxford English Dictionary
33. ^ AOL News, For 99 Years, Oxford English Dictionary Got It Wrong
34. ^ Calligeros, Marissa, Dictionary mistake goes unnoticed for 99 years, Brisbane Times, May 10, 2010
35. ^ Malkin, Bonnie, Physicist spots 99-year-old mistake in Oxford English Dictionary, The Daily Telegraph (London}, 11 May 2010
36. ^ "On The Definition of “Siphon”". OUPblog. Oxford University Press. 21 May 2010. http://blog.oup.com/2010/05/siphon/. Retrieved 23 May 2010.

References

• Streeter, Victor L., Fluid Mechanics, McGraw-Hill, New York, USA. Library of Congress Catalog Card No. 66-15605

External links

• The Straight Dope: How Does A Siphon work?
• Pnematics of Hero of Alexandria - Interesting Applications of Siphons

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