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Syrup or milk flowing down a tube

  1. Mar 7, 2014 #1
    Hello everyone,

    I really feel out of my depth here, especially with this simple question. I'm trying to rig something up and understand why it's not working. With a pipe connected to a wine bottle sized bottle, syrup wont flow into the pipe (1cm diameter, 60cm long, down to a tap). For normal liquids like wine or water, this system seems to work ok:


    However, with thicker liquids (i.e. sugar syrup, (consistency similar to full fat milk, its not flowing). I'm hoping for pointers on how to make the syrup flow down the pipe once the tap at the bottom is opened at the bottom. Right now it's not flowing at all. I've been tinkering with pipes and connections, such as the image below:


    What would I need to do to the first drawing, to make thicker liquids flow easier?

    many thanks / simon
  2. jcsd
  3. Mar 7, 2014 #2
    The viscosity of the problem fluids are much higher than that of milk and wine. So they are going to flow very slowly. DONT PRESSURIZE THE AIR. THIS IS VERY DANGEROUS. Maybe you could heat the more viscous fluids so that their viscosity is lower. Otherwise, use much larger diameter tubing (maybe twice as large or even more).

  4. Mar 7, 2014 #3
    Viscous materials have a *wide* range of viscousities.

    In the worst case you might have to wait a really long time for your
    thick fluid to move.

  5. Mar 7, 2014 #4
    Understand the range of viscousities. Am only concerned with milk + syrups for now and how to increase flow. Heat is not an option, but larger diameter is. Am trying that now. Still open to other ideas (i.e. larger air vent? higher air vent position) - smaller diameter air vents seem to work better than larger diameter ones and I have no clue as to why.
  6. Mar 7, 2014 #5


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    I think, a bit like in Jaws, you're gonna need a fatter tube. (Wider topped bottle etc.)
    The air bleed tube can, of course, be very small diameter to help you there. The air flows so easily that even a finite gap will let enough in. When pouring water or fuel from a large inverted can with a long spout, you only need to loosen the connection a tiny amount for the liquid to gush out and for plenty enough air to gush in and for the 'glooping' to stop.
    Is the top of your air tube above the internal surface of the syrup? That could be important.
  7. Mar 7, 2014 #6
    Thank you. I thought bigger air bleed, more air flow. I was wrong. I will keep it small. The top of the air tube is inline with the spout, such that, the bottom of the bottle is raised higher than the air tube top. Perhaps I need to raise the top of the air tube so that it is much higher than the bottom end raised bottle.....
  8. Mar 7, 2014 #7


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    The air tube can be very long so no syrup can run out of it. Take it right to the 'bottom' of the bottle, above the syrup level.
    The ideal solution, though, would be to decant (at your leisure) into a dispensing bottle with a much bigger neck diameter. A wine bottle(?) has a very narrow neck for that sort of job. The speed of flow will tend to be better than pro rata with the cross sectional area of the tubing.
    Could the syrup not be warmed up whilst decanting? That could speed things up a bit.
  9. Mar 7, 2014 #8
    thank you again.

    heat isn't an option, nor is changing the bottle - unfortunately. I do have a little flow, just need to make improvements to the setup to increase it.

    Air tube to right the bottom of the bottle is a good starting point for tweaking this. I will try making a much larger green part (see 1st image), that should help a bit.

    I will also search for the smallest diameter air bleed tube to reduce obstruction in the spout.

    I will also try connected to the spout via the outside, rather than inside
  10. Mar 7, 2014 #9


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    Good idea, that will give you a significant amount of 'free CSA'. As everything will be happening so slowly, I don't think you need to be to fussy about smooth transitions.
    I bet eBay will have some very narrow plastic tubing available.

    PS Is this brewing or "Breaking Bad" haha
  11. Mar 8, 2014 #10
    Thank you again. What is CSA?

    Secret... ;-) but you are more than welcome to join
  12. Mar 8, 2014 #11


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    Haha, CSA is cross sectional area.
    If it involves eating or drinking I may join!
  13. Mar 8, 2014 #12
    Thank you again.

    Deep beneath the surface of admirable intellect, we are all simple creatures when food or drink is involved ;-)
  14. Mar 8, 2014 #13


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    Not far beneath! :approve:
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