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Pressure drop

  1. Jun 24, 2006 #1
    with indoor plumbing, lets say you have 40psi entering the house. The water has to travel vertically to the sinks and showers. Now I know with a foot of height equals a certain psi downforce. But If the water travels 20 feet or so upward, I'll just throw a number out there 10 psi pressure difference. Would you have 30psi reaching the sinks or showers? And would you have to calculate the amount of flow reaching the destination from the 30psi when its been reduced by the pressure difference?
  2. jcsd
  3. Jun 24, 2006 #2


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    There would be a certain amount of pressure loss (head) due to the height of water which acts downward with gravity (weight). When the water is flowing, there is another loss due to friction in the pipes, and the pressure drop depends on the length of pipe. If the water velocity is low, then the pressure drop is likely not very significant.
  4. Jun 25, 2006 #3
  5. Jun 25, 2006 #4
    So if the velocity is low then with friction loss is not very significant. But the pressure drop from head, Is accounted for and that is just subtracting the pressure head off the initial pressure. But would you calculate the flow from the pressure reduced after the head loss.
  6. Jun 25, 2006 #5
    I would suggest you reword your question, I can't make heads or tails of what you are asking in your last post. :confused:
  7. Jun 25, 2006 #6
    sorry. With head I mean the pressure that is applied to the water by gravitational pull. So basically the water reduced pressure when rising vertically. So the vertical rising water is affected by gravity. I know how to determine the pressure differece when gravity is pulling downward with vertical rising fluids because its the same as water flowing downward by gravity. But the water reaching higher ground to sinks or whatever has lower pressure. Is it the lower pressure value that you use to determine the velocity of the water. For example 40psi cityline then rising 20 or so feet could have around 10psi downward pull. Is 30psi the figure to use to determine flow reaching the sink.
  8. Jun 25, 2006 #7
    As the water rises up the building, it will loose pressure. You are correct that it looses pressure because of the decreasing hydrostatic term.

    Provided that you have a single pipe that does not branch out, the flow will be the same value at any point along the pipe, because mass is conserved.

    Are you familiar with the bernoulli equation for incompressible fluids?
  9. Jun 25, 2006 #8
    Thank you very much. I do understand now. I have heard of the bernoulli equation but have not studied them. I really appreciate your time in helping me. Thanks again.
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