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Homework Help: Flow Rate and PSI of water exiting a pipe

  1. Jun 28, 2011 #1
    I am trying to figure out the flow rate (gallons per minute) and PSI of the water just as it exits the top of the pipe. Is it possible to figure out these out given the information in the diagram?

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  3. Jun 28, 2011 #2


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    Homework Helper

    If you are ignoring the friction losses, you can use the continuity equation Q=Av= constant to get the flow rate Q and the fact that pressure is transmitted equally through a fluid to get the psi at the end.
  4. Jun 28, 2011 #3
    I don't know the velocity. The piston will only move up as quickly as the water can exit the top. I can't just assign an arbitrary velocity to the piston, can I?

    As for the PSI of the water coming out the top of the pipe... I must admit I have a bit of confusion. 2000 lbs. is being applied to a piston with an area of roughly 452.16 square inches... which I guess means the piston is applying 4.42 PSI. But when the pipe narrows at the top to 1 square inch.... does that mean the water comes out at 4.42 PSI, or does that mean the water comes out at 2000 PSI?

    (yes, I am ignoring the weight of the water and the weight of the piston itself, but I could deduct it and still have the same question with a force a bit lower than 2000 lbs being applied to the water).
  5. Jun 28, 2011 #4


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    Homework Helper

    At the top the water would come out at 4.42 psi.

    I am not sure given the information you can find the flow rate at the top.
  6. Jun 28, 2011 #5


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    Staff: Mentor

    I think you'll want to take a look at Bernoulli's principle.

    You can relate the (unknown) speed of the piston to the (unknown) speed of the water exiting at the top via the areas of the piston and pipe opening. Bernoulli's relationship will provide a relationship between the flow rates, heights, and pressures.
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