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Theory of water displacement

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  • Theory of water displacement

    Hey all!

    I've been scratching my head for a while on this one...

    Water has a specific weight. Suppose you have a constant pressure inside a given size pipe, water will be able to travel to a certain height. Now you bump the size to that pipe to a larger diameter. Pressure is still the same... will it travel as high as the smaller diameter pipe?

    Say you have 65psi, an infinite length of 1/2 pipe and an infinite length of 3" pipe... which will go the highest?

    Just curious!

    Cheers!

  • #2
    Re: Theory of water displacement

    It may get there faster in a wider pipe but 1/8" or 5' across it will get to the same height with the same pressure. The height in feet is pressure in psi / 0.433
    So at 65 PSI the water will rise to 150.1 feet, diameter of pipe does not matter

    Comment


    • #3
      Re: Theory of water displacement

      err... 5 liters of water is heavier that 1 liter of water. 1 liter of water = 1kg.

      so the content of water of a 3" pipe on say a run of 10' will be greater that the same length but with a 1/2" pipe full of water.

      the power (psi) to move either one will have to be greater with the 3" pipe full of water.

      just blow air into a straw versus blowing air into a 1 1/4" pipe... of try displacing a ping[pong ball by blowing into a 1 1/4" pipe versus a sraw... so i figure that the same principle applies to water... or doesn't it?

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      • #4
        Re: Theory of water displacement

        you get .433 psi per vertical foot of water, regardless of how big a pipe it's in
        No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

        Comment


        • #5
          Re: Theory of water displacement

          gotta break out PSI. Pounds per square inch. water weights the same per square inch no mater the size of the pipe

          Comment


          • #6
            Re: Theory of water displacement

            Originally posted by HornyPotter View Post
            err... 5 liters of water is heavier that 1 liter of water. 1 liter of water = 1kg.

            so the content of water of a 3" pipe on say a run of 10' will be greater that the same length but with a 1/2" pipe full of water.

            the power (psi) to move either one will have to be greater with the 3" pipe full of water.

            just blow air into a straw versus blowing air into a 1 1/4" pipe... of try displacing a ping[pong ball by blowing into a 1 1/4" pipe versus a sraw... so i figure that the same principle applies to water... or doesn't it?
            don't confuse volume with pressure.

            Comment


            • #7
              Re: Theory of water displacement

              The missing element in your story is flow volume. With zero flow, the height is dependent strictly on PSI, not pipe size. This is the principle which makes a water line level work.

              Add any flow to the story, and the situation change big time!


              By the way, displacement is not the term to use in this discussion. Displacement is what happens when an object is placed into the water.

              For example, a 594 class submarine displaces 4500 tons. When it is in a drydock, then the dock is filled, the dock has 4500 tons LESS water in it than if you filled the dock with no submarine in it. Now, the ballast tanks hold 500 tons, so when you open the vents and fill the ballast tanks, the submarine is no longer floating with positive buoyancy. It is bobbing at neutral buoyancy, and displaces only 4000 tons.
              Last edited by lovetheUSA; 07-10-2009, 09:46 AM.

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              • #8
                Re: Theory of water displacement

                typical waste test require a 10' head of water on the waste system. this is accomplished with a 10' piece of pipe sticking up above the rest of the waste system.

                we normally use a piece of 2'' pipe as it's pretty much a standard piece of no hub pipe.

                but in theory, we could get a piece of 1/4'' soft copper like from an ice make hook-up. i'm sure the inspector will challenge it or give me a strange look. pretty difficult for them to verify the line is full.

                but the interesting thing is if we put an accurate pressure gauge at the base of the two lines, both will read the same exact pressure.

                rick..
                phoebe it is

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