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Understanding head pressure

  1. Apr 12, 2014 #1
    It may be a simple question to you but I need help understanding head pressure and I need to set things up to ask it.

    Assume two 4 ft diameter by 25 ft tall water tanks, both are equally filled to 23 ft. Both tanks have chambers of the same diameter as the tank attached below them. Each chamber has a piston and has 2 ft of water above their pistons. Both chambers have a 4 inch diameter hose going from their chambers and into the tanks. On one of them, the other end of the hose penetrates the tank at 3 feet above the chamber. On the other the hose penetrates the tank at 22 ft above the chamber.

    My question is, which piston will require more force or is there any difference. I would also appreciate any explanation that you want to include.
    Last edited: Apr 12, 2014
  2. jcsd
  3. Apr 12, 2014 #2


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    Ahh.. Can you show a simple diagram? :biggrin:
  4. Apr 12, 2014 #3


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    The pressure head depends on the density and elevation of liquid (or gas) above a given point by virtue of ρgΔh, where ρ is the mean fluid density, g is the acceleration of gravity, and Δh is the height of the fluid above the point of interest. The higher the column of water, the greater the pressure at the base or lowest point.

  5. Apr 14, 2014 #4
    I have added a diagram called Undrstnd hd.png in hopes of clarifying this question.

    Attached Files:

  6. Apr 15, 2014 #5


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    Big fat blank. Please try again. Always use the 'preview' button to check how your material displays before you post.
  7. Apr 16, 2014 #6
    Sorry for the problem with the picture I attached previously. I’m having an issue with the latest update of DraftSight not exporting DWG files. Several of the formerly possible file types (.png, .tif, .wmf, .emf) create the file but they are not visible. So it seems the attached JPEG is visible.


    Attached Files:

  8. Apr 16, 2014 #7
    static pressure head at a point inside a body of liquid is given by ρgh , as Astronuc Stated, where h is the height of the column of water above the point of interest, think of it this way, if you have two paper cups filled to the brim with water, and you put a hole in each cup, one near the top, and one near the bottom, the water will flow out faster from the hole near the bottom , because the h is higher, ie the column of water is higher, hence the static pressure is higher. similarly, your piston with the hose near the base of the tank will experience greater pressure
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