Some suggest or imply that it is the difference in weight of liquid in the two siphon arms that causes and sustains siphon action. Some suggest that water is lifted pulled up the input tube by some mysterious force. A website asserts that a siphon could not work on the moon or in a vacuum , because the outside pressure is zero.
Which of these are correct and which are not? The "information highway" is a rich source of misinformation on this subject. I'll bet most candidates would get it wrong. It's also interesting to note how many modern textbooks avoid any mention of siphons. The Siphon. From The Wikipedia. What is a siphon? First, let's define "siphon". The siphon is a liquid reservoir with an inverted U-tube. The liquid initially fills the tube. There are several methods to achieve this initial state.
The purpose of the siphon is to drain liquid from the reservoir by liquid flow that passes over a higher level than the liquid surface in the reservoir. The net result is that the liquid passes from the reservoir to a lower level and does so continually and without external energy input until the reservoir level falls below the ouput end of the U-tube.
The practical difference between a siphon and a leaky bucket is the fact that the liquid passes to a higher level before draining out to a lower level. So we have several things to explain. Water rising in the input tube. The liquid barometer is an example of water rising above the level of a reservoir. A tube closed at one end is filled with the liquid, then the closed end is raised up while the lower end is immersed in the liquid reservoir.
The liquid in the tube stays there, until the tube height is greater than a certain height that depends on the density of the liquid and the pressure of the air outside the tube. Then a near-vacuum forms above the water in the tube, and the water level does not rise further. Air pressure is sufficient to sustain a liquid height of about 34 feet for water, only about 32 inches for liquid mercury. Above that height, a near-vacuum forms above the liquid in the closed tube.
Actually, the pressure there is the vapor pressure of the liquid. The vapor pressure of mercury is 0. This tells us that if the height of the U-tube of a siphon were too great, the same thing would happen, and a near-vacuum would be created near the top of the U-tube.
This would interrupt the continuity of liquid in the tube, and siphon action would stop. This is exactly what happens. Ancient Roman engineers who built siphons into their water aqueducts were quite aware of this limitation of siphons. In this case we must be clear about the reason that the siphon would fail if the U-tube were too high. It is simply because air pressure on the input side is insufficient to raise the input liquid column as high as the top of the tube.
If it doesn't get to the top, it won't flow over to fall down the output tube. So air pressure is important to siphons by putting a limitation on how high they can lift water, and without lifting the water to the top of the U-tube, no siphon flow can occur. What sustains the liquid flow? But this isn't the whole story. Is it air pressure that sustains the water flow in a siphon? It is not. If siphon flow is analyzed, with a nearly incompressible liquid like water, the work done at each end of the siphon against air pressure is NET zero, for equal volumes of air are displaced at each end.
The two ends water surface in bucket and at the output end of the tube are both at the same atmospheric pressure, p , so pdV is the same size for equal volumes displaced, but the signs are opposite.
So air pressure does not drive the siphon. Siphoning in a vacuum. If there were no air pressure, could a siphon work? Yes, at least for some liquids, but something else would be required to cause the liquid to form a continuous path through the elevated U-tube.
Very cohesive liquids can do this, the molecules attracting each other so strongly that they can maintain a chain-like continuity up and across a U-tube, yet still maintain liquid properties. This has been demonstrated in the laboratory. Apr 16, Thanks for sharing, Michael T. Michael T Mar 10, The perfect siphon hose would have a control valve at the crest. This is made possible by adding anti-backflow check valves to the inlet and outlet to allow the liquid to flow in the direction to the outlet while preventing air from entering and breaking the siphon when the shutoff valve is closed.
Once the siphon is initially primed, the system will stay primed if air is not allowed to enter at the inlet. Andreas Jan 29, Michael Feb 7, The perfect controllable siphon hose would have a foot check valve at it's inlet and a shutoff valve at it's crest and an anti-backflow valve at it's outlet.
Once this siphon is filled and primed, it would work automatically by opening and closing the shutoff valve. The hose would stay primed as long as air was not allowed to enter the line.
Feb 8, Michael Taylor Aug 8, Siphon's can run perpetually using only their own power. The only true perpetual motion machine that continually causes mechanical motion is a Siphon with a Metering Chamber and US Patent discloses this in figure number four of the art. Timing and the weight of the water allows for a continuous water flow above the source. Aug 13, Thanks for sharing, Michael! This was very interesting! Could you maybe do a wonder about computer code? I would find that even more interesting.
Nov 15, Caleb Jan 5, That experiment is cool, is it safe to do without my parents? Jan 6, Dec 16, Jace Nov 24, Nov 26, Jace Nov 30, Dec 2, Related Wonders for You to Explore Match its definition: a mechanical device that moves fluid or gas by pressure or suction. Word Match Congratulations! Share results. Play Again Quit. Next Question. See your results. Share Results.
Retake The Quiz. Be the first to know! Share with the World Tell everybody about Wonderopolis and its wonders.
Share Wonderopolis. Add widget. You Got It! Once the air is out and the liquid has reached the end of the tube, you must prevent any air from getting back in.
To do this, maintain suction and carefully crimp the hose or use your thumb as a stopper. Now drop the end of the hose into the other container and release.
Liquid should start traveling from the source container to the new one. Be sure to keep an eye on your source liquid and make sure the hose stays fully submerged, otherwise you'll end up with bubbles. When you need to stop, lift the new container and hose higher than your source container.
0コメント