1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question about siphons

  1. Jul 28, 2006 #1
    Hello, On a siphon, can the mouth of the outflow be submerged and still flow? If yes, what allows this to happen? Thank you!
  2. jcsd
  3. Jul 28, 2006 #2

    As long as the top of the water column of the output end is below the top of the water column of the supply end it will continue to flow.

    As for the "why" a siphon works because gravity acts on the water in the siphon creating an area of low pressure at one end of the siphon. If a siphon is filled with water and one end is placed below the water surface gravity pulls the water down. This creates vacuum pressure behind the downward moving water. Since nature abhors a vacuum the water in the supply must be drawn along with the downward moving water. When the two water columns are the same height the water in the siphon is pulled down equally on both sides. When this happens the downward movement of the water stops, and once again because nature abhors a vacuum all flow stops.

    You can see these effects more clearly by taking a section of clear tubing and submersing it in water until it is completely filled. Then you can lift the tubing in a manner that leaves both ends submerged but has the middle section above the water column. Even though the water it being pulled down by gravity in two directions the water remains in the elevated section of the tubing do to vacuum pressure. I have seen clear hard plastic tubes situated in this manner on top of fish tanks where the fish will swim up into the tube, and down the other side.
  4. Jul 28, 2006 #3

    Doc Al

    User Avatar

    Staff: Mentor

    Sure, as long as the mouth is not submerged too deep. (The level of fluid in the outflow tank must be below the level of fluid in the intake tank.)
  5. Jul 30, 2006 #4
    Thank you both for your replies. You've answered my question.
  6. Jul 30, 2006 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Is there a peer reviewed (AJP or suchkinds) article on the siphon effect?

    I've read all kinds of articles that talk about cavitation, tensile strength of water and other things which I think are totally irrelevant or at least not important to first order. My self-formulated understanding of the effect is very simple and based on nothing more than hydrostatic forces, but I've not read it anywhere. Moreover, my own explanation easily accounts for the maximum siphoning height found from experiment.

    So, I need a reliable verification. Got one?
  7. Jul 30, 2006 #6

    Doc Al

    User Avatar

    Staff: Mentor

    I think I have the same understanding as you do, Gokul. A simple hydrostatic argument allows you to say whether the siphon will work or not. But once it starts flowing, you need to consider Bernoulli to find the actual pressure at various points in the fluid. (At least to first order.)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook