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I Equation Needed for Calculating Fluid Pressure In a Pipe

  1. Jan 1, 2017 #1
    A friend is planning to utilize a local stream to create electric power. The source of the stream is a small pond. He plans to have a 5 inch pipe start at/near the bottom of the pond and this pipe will follow the stream approximately 1056 feet to a culvert where he wants to put the generator. The drop in elevation is about 40 feet. The pipe will obviously be closed and have no air. Towards the end, the pipe diameter will be reduced, and I know that the velocity will increase and I'll need to use bernoulli's equation but before we even get to that point I need to know how much pressure will be coming out at the end of that pipe and I haven't been able to find an appropriate equation or method of getting there.
  2. jcsd
  3. Jan 1, 2017 #2


    Staff: Mentor


    I just googled "40 feet head to psi" and it gave me the answer 17.32 psi.

    That will be the pressure at zero flow. From that you must subtract the pressure drop due to friction. Google "friction loss pipe calculator.

    With such a long pipe, the inertia will be a significant factor. If you shut the valve suddenly at the generator end, the pressure will surge and it could burst the pipe. Shut a valve suddenly at the pond end could implode the pipe.

    The key to all such calculations is the flow rate and the power generation.

    How much water flow is expected?

    How much power do you need to generate to declare it a success?

    Another Google search, "DIY hydro generator" returned 6360 hits. With a little bit of study, you can learn much from those who have gone before.

    Good luck.
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