e of gravity induced vacuum pumping to carry water horizontally from multiple roof drains to a single downpipe and to increase flow velocity. Metal baffles at the roof drain inlets reduce the injection of air which increases the efficiency of the system. One benefit to this drainage technique is reduced capital costs in construction compared to traditional roof drainage. Another benefit is the elimination of pipe pitch or gradient required for conventional roof drainage piping. However this system of gravity pumping is mainly suitable for large buildings and is not usually suitable for residential properties.
The term self-siphon is used in a number of ways. Liquids that are composed of long polymers can "self-siphon" 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.
"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 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". 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.
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).
There has been a debate if whether the siphon mechanism plays a role in blood circulation. However, in the 'closed loop' of circulation this was discounted; 'In contrast, in "closed" systems, like the circulation, gravity does not hinder uphill flow nor does it cause downhill flow, because gravity acts equally on the ascending and descending limbs of the circuit', but for 'historical reasons', the term is used. One hypothesis (in 1989) was that a siphon existed in the circulation of the giraffe. But further research, in 2004 found that, 'There is no hydrostatic gradient and since the "fall" of fluid does not assist the ascending arm, there is no siphon. The giraffe’s high arterial pressure, which is sufficient to raise the blood 2 m from heart to head with sufficient remaining pressure to perfuse the brain, supports this concept.' However, a paper written in 2005 urged more research on the hypothesis;
'The principle of the siphon is not species specific and should be a fundamental principle of closed circulatory systems. Therefore, the controversy surrounding the role of the siphon principle may best be resolved by a comparative approach. Analyses of blood pressure on a variety of long-necked and long-bodied animals, which take into account phylogenetic relatedness, will be important. In addition experimental studies that combined measurements of arterial and venous blood pressures, with cerebral blood flow, under a variety of gravitational stresses (different head positions), will ultimately resolve this controversy.'
Some species are named after siphons because they resemble siphons in whole or in part. Geosiphons are fungi. There are species of alga belonging to the phylum Chlorophyta in the genus Siphonocladaceae which have tube-like structures. Ruellia villosa is a tropical plant in the Acanthaceae family that is also known by the botanical synonym, 'Siphonacanthus villosus Nees'.
In speleology, a siphon or a sump is that part of a cave passage that lies under water and through which cavers have to dive to progress further into the cave system, it is not an actual siphon.
Explanation using Bernoulli's equation
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