Lifter (device)

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A lifter , suction lifter or angle lifter is a device or device with which a liquid can be transferred from a container over the edge of the container to a lower container or emptied into the open without tipping the container over or needing a hole or an outlet below the liquid level . The hydrostatic pressure is used here .


Use of suction
cups to suck amphora wine out of amphorae , ancient Egyptian representation

Reliefs from ancient Egypt from 1500 BC BC show siphon siphons with which wine from amphorae was filled.

Heron of Alexandria already described a series of siphon applications in his work Pneumatica .


Function of a hydraulic jack, see text for explanations.

The sketch opposite shows two vessels filled with water. The water level of the upper vessel is the height above that of the lower one. The vessels are connected by a filled line that is initially closed by a valve. The heights and indicate the heights of the valve above the water level. The following applies to the pressures on the left and right of the valve

( = Air pressure , = water density , = acceleration due to gravity ).

The water pressure in the pipe decreases with increasing altitude. It decreases compared to the air pressure ( negative pressure ) acting on the water level . According to the smaller height is greater than .

After opening the valve, the liquid in the line is in the direction from higher to lower pressure, i.e. H. towards the lower vessel, set in motion.

The pressure difference is

When the siphon spout is not submerged, the height of the valve is above the lower end of the outlet pipe.

The derived pressure difference is independent of how the siphon line actually runs (with the beginning and end fixed) (e.g. with a slack), and the imaginary valve can be located anywhere in the line. The flow in the pipe, which is completely filled with liquid, occurs due to this pressure difference according to the principle of communicating tubes .

Limit of the inlet height

At the top of the siphon there is a reduced pressure , which, depending on the temperature, is sufficient to boil the liquid from a certain top height and low external air pressure . A vapor-liquid mixture flows through a height corresponding to the difference in level at the apex (“waterfall phenomenon”, steam due to cavitation ) before the flow is interrupted if the air pressure continues to fall or if the apex is raised further.

For large cable diameter is capillary generally negligible. The height is therefore limited by the maximum geodetic suction height . This is proportional to the pressure if it corresponds to the vapor pressure of the liquid. The prerequisite is that there is no delay in boiling ; Under appropriate laboratory conditions that allow delayed boiling (with degassed water), the geodetic suction height can also be exceeded. Above the geodetic suction height, the pressure inside the siphon is so low that gaseous form is actually the stable state (compare the phase diagram of the liquid). Therefore, the fluid in this area is in a metastable state.

With normal air pressure , gravitational acceleration , vapor pressure and density of water at 20 ° C, a maximum peak height of is obtained for large pipe diameters


The smaller the line diameter , the stronger the capillary effect. This is due to the fact that the cohesive forces of the liquid molecules at the phase boundaries, i.e. the surface between gas and liquid as well as liquid and line material, result in a force of adhesion . This means that the liquid can rise to a certain height in the line even without a pressure difference . The capillary forces add to the forces due to the maximum possible pressure difference . With a pipe diameter of , a surface tension and a contact angle , the maximum inlet height is then


Due to the capillary effect, it is 13 millimeters higher than with large pipe diameters. A lifter with a small pipe diameter that uses this effect is called a capillary lifter .


Lifting weir

Siphon weir (animation)

The siphon effect is used on a larger scale in the flood relief of dams . An easily accessible example of a flood relief constructed as a siphon weir can be seen at the outlet structure of the Treysa-Ziegenhain flood retention basin .

Pump replacement after flood disasters

(Self-made) jacks made of water-filled hoses can be used after a flood disaster instead of a pump to empty flooded cellars and areas, provided that the water can be drained into a lower area.

Hydrostatic lifter

Alternatively, pipes are used that can be closed at the inlet and outlet and have a lockable inlet opening at the top of the construction. Through this the pipe construction is filled with muddy water or tap water and then closed at the top. If you then open the inlet and outlet, the flooded area empties. Sometimes a suction pump helps to fill the pipes or hoses used with water, which then continues to flow without a pump.

This happens all the faster, the greater the difference in height between the water surface above and the water level below (or outlet opening below) and (based on the law of Hagen-Poiseuille ) the larger the hose or pipe radius is:

Delivery rate in m 3 / h = approx. 50,000 * (height difference in m * radius in m) 2 .

The dependence of the volume flow on the fourth power of the radius of the pipe is remarkable; for example, reducing the pipe diameter by half would increase the flow resistance by a factor of 16. A fire hose , for example, with a diameter of 10 cm and a height difference of 1 meter, pumps approx. 125 cubic meters of water per hour. With a smaller hose (approx. 1–5 mm) the calculated performance is not achieved because of the hose resistance . With an even smaller tube (<1 mm), the capillary effect is stronger than the pressure difference due to the height difference.

Usually a hose is held like a "U", the hose is filled with water and without air entering the hose or the filled water running out, the hose is first held below the water level of the "upper water" and then the drain hose is laid below. It is also possible to sink a hose into the liquid in the container to be emptied until it is completely filled. Then the end of the hose is closed (possibly by kinking), pulled out of the container and led outside under the liquid level and opened there.

Decanting (in process engineering)

The siphon principle can also be used when withdrawing ( decanting ) wine from a fermentation balloon or to withdraw the supernatant after a sedimentation process .

Hand pump with suction device
Suction lifter with suction tube, also called
poison lifter (drawing from 1872)

Hand pumps

Liquids can be pumped out of barrels, for example, with a hand pump if the outlet opening is lower than the inlet opening. Various methods are used to fill the submerged hose or a pipe with a hose attached to the end:

  • If necessary, suction by sucking with the mouth (at the end of the hose or at an additional pipe opening - "T-piece"),
  • suction with a suction ball
  • by pushing the pipe into the liquid, a non-return valve in the pipe preventing it from flowing back ,
  • by pulling a sponge or ball on a string or a plunger on a rod through the tube
  • By blowing breathing air into the vessel with the help of a second hose (principle as with a glass squirt bottle ) to generate overpressure. The opening of the vessel is sealed airtight with a rag.

Drain siphon

Overflow of a Pythagorean cup

A drain siphon ( English siphon pump ) is a hydraulic component that, using the siphon principle, empties a (water) container at intervals in a surge automatically and without the necessary monitoring. For this purpose, the water must be in a downwardly bent tube or in a bell , which to a water stand pipe upturned is crowded.

The invention of the drain siphon is attributed to the Greek philosopher Pythagoras of Samos (around 570 - 510 BC), who is said to have used the principle in the Pythagorean beaker .

The word siphon is borrowed from the French siphon (for "lifter"), which goes back to the Latin sīpho, which in turn is borrowed from the ancient Greek σίφων (síphōn) (for "(water) pipe"). A common property of all siphons ( e.g. siphons ( caving ) or tube siphons ) is a U-shaped bent pipe that is completely filled with water during operation.

A drain siphon is used in several procedures:

Soxhlet attachment

Animation of the extraction mechanism of a Soxhlet appliance

Franz von Soxhlet (1848–1926) used the principle of the drain siphon (as a capillary siphon ) to automatically derive the desired extract in a chemical extraction device so that the extraction material is always extracted from pure solvent. See Soxhlet essay .

Hotoppscher siphon

Ludwig Hotopp (1854–1934) used a drain siphon to fill and empty lock chambers . So that the jacks “start”, their tops are pumped full of water using negative pressure. The negative pressure is generated with the help of a hydraulic piston through a small amount of water taken from the upper water. A boiler ("suction bell" = piston) initially filled with upper water is connected to the siphon apex. The boiler is emptied through a downpipe that is immersed in the underwater . The resulting negative pressure leads to the lifting of the water in the siphon pipe up to the lower edge of the apex and to the complete filling. The connecting pipes and the necessary operating valves have a relatively small cross-section compared to the jacks. The water consumption is small compared to the filling of a lock chamber (see also the graphic by Friedrich Engelhard: Kanal- und Schleusenbau and the article Communicating tubes ).

Ebb and flow system

Plants on plant tables in nurseries and in hydroponic systems in plant cultivation are often irrigated and drained with an ebb and flow system (English ebb and flow or flood and drain ). The plants are placed in watertight tubs. The irrigation takes place by means of water pumps . The automatic draining of the irrigation water (enriched with fertilizer) means that the plant roots are supplied with oxygen again; otherwise they would rot in the absence of air . In addition, oxygen is necessary for nutrient uptake. The inflowing water dissolves the root respiratory metabolic product carbon dioxide and removes it from the substrate, the sinking water level then sucks in fresh air from above, which means that the plant can again absorb nutrients and it grows faster (than just the usual humidification of the substrate) and making hydroponic growing more efficient.

In some hydroponic ebb and flow systems, the irrigation water is pumped continuously (i.e. without intervals, without an error-prone timer ) from a water reservoir (or, in aquaponics, from a fish tank) into the plant tub ("head water"). After the desired water level has been reached in the plant tub, the water is drained again in a gush through the drain siphon into the water reservoir ("underwater") below, thus emptying the plant tub.

Loop siphon

A variant of a drain siphon with minimal use of material consists of a hose suspended in a circle on the outside of the container (English loop-siphon translates as "loop siphon "). The water leaves the container via a floor drain and rises in the hose until it overflows in the bend in the hose and the siphon starts. By hanging the hose at different heights, the desired maximum water level of the container can be varied very easily. The surface tension of the water forms a water front in narrow hoses, which prevents the water from flowing away from the apex and thus starts the siphon effect. Several variants of "loop siphons" are known, the common feature is that the water flows over only in a curved pipe (in the form of a "U" rotated by 180 °) with a constant diameter.

Bell siphon or (English) bell siphon

A more efficient variant of the drain siphon, which creates a larger throughput of the withdrawn water, is a bell siphon. It consists of a conventional overflow pipe on which a larger pipe (or, in a primitive version, a cut-off water bottle) closed at the top is put over as a bell ( bell English for bell ). If the water level in the plant tub rises, water rises from below in the bell and falls down at the upper edge of the drainage pipe. The air in the bell and in the drain pipe is gradually carried along in small air bubbles until the siphon effect “starts”.

According to a construction manual, the bell should have twice the diameter of the drain pipe:

The inner cross-sectional area of ​​the drain pipe is

The total internal cross-sectional area of ​​the bell would then be .

Thus, the cross-sectional area of ​​the circular ring in the bell that is effective for the water drainage is three times the cross-sectional area of ​​the drain pipe. Due to the narrowing of the effective cross section to one-third arises in the discharge tube (after insertion of the water flow in the entire cross-section) is a Venturi effect , There is static pressure reduced, the occurring water swirls in the flow tube and the venturi effect to suck the remaining air from the bell, which means that the lifter "starts" faster and emptying starts.

The Hotopp system shown above is used in a modified form in order to guarantee "switch off" the lifter when there is a strong inflow or outflow . From the top of the bell a thin tube or capillary tube (English called "snorkel" for snorkel ) leads under the water level of the upper water. Since the plant container is mostly emptied via the deeper suction tube and the capillary tube opening fixed above this suction opening is safely exposed to the air (which is then sucked into the system from there), the siphon effect is guaranteed to stop. Because air sucked in at the suction opening would be carried away with a strong flow of water without filling the bell. With the height of the opening of the capillary tube, the residual water content of the plant tub can be easily adjusted. The drain pipe ends below the water level of the underwater or there in an open water-filled bowl or in a U ( pipe siphon ) so that no air can get into the overflow pipe . At the same time, the water level in this bowl must be kept low, because the air sucked into the drain pipe (when it is “switched off”) has to overcome the hydrostatic pressure there in order to be able to bubble out.

American washdown toilet bowls

Typical American-style washdown toilet with flush valve. In the sump, the water jet opening into the siphon

The flushing process differs between European and North American washdown toilets : While in Europe the water running in during flushing transports away the excrement, in North America part of the flushing water is directed into the pipe siphon ( odor trap ) as a water jet. The function is initially that of a jet pump with water as the driving medium and for flushing with the function of a siphon. The contents of the bowl are thus emptied by suction and then refilled.

Suction from urinals at regular intervals

If a urinal is used, the water can be flushed manually with a flush valve or via automatic sensors and the urine-water mixture flows through a covered pipe siphon ( odor trap ) into the sewer system. If the drains of several urinals are connected by a pipe, constant flow into the pipe can lead to an overflow of a drain siphon and the contents of the pipe are regularly sucked off in a quasi-automated manner.

Toilet flush without seal

Up until 2000, overflow siphons were a legal requirement in Great Britain as leak- free flushing systems in cisterns. In the idle state, no water can run out, when the release lever is actuated the drain siphon is activated and the flushing water pours into the toilet bowl. The refill valve to the pressurized water pipe is of course still necessary and, if defective, fills the cistern up to the safety overflow.

Problems due to the siphon effect

In -ground as a swimming pool or as a mobile makeshift water tank for drinking water disinfection a leaky pump hose can after stopping of the pump due to the siphon effect to the running away of the basin result, even when the tube protrudes from above into the basin.

In aquariums , the pump that blows air into the water is occasionally installed in a noise-insulated cabinet. If the pump stops in the event of a power failure, the water that penetrates with the sudden kickback can fill the hose, ruin the air pump through the siphon effect and also cause the fish tank to drain out. To prevent this, a water check valve is installed in the air supply line as a precaution .

In toilet cisterns, if there is a pressure drop in the supply line, the contents of the cistern could be sucked back into the drinking water line due to the siphon effect (pressure drop, for example when emptying lines or because a valve with a high flow rate was opened on a lower floor , such as the flush valve of a toilet or by drawing off water from a Fire hydrants ). For this reason, technical rules stipulate that the cistern must be filled using a safety fitting in the "free outlet" (by positioning the filling valve above the maximum water level). As a result, air could only be sucked in because there is no siphon effect.

See also

Web links

Commons : Lifter (device)  - collection of images, videos and audio files

Individual evidence

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  2. THE PNEUMATICS OF HERO OF ALEXANDRIA. Retrieved June 1, 2018 .
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