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Pascals's Law I think

  1. Mar 9, 2012 #1
    I think the solution I need lies within Pascal's Law, but I'm not quite sure I'm doing it right. I'm not looking for the answer to the problem, that's no fun, but I at least need the right series of formulas.

    I have a storage vessel in my basement with water in it. My plan is to basically make a hydraulic ram (in theory), by adding a sealed plate with heavy weights, pressurizing it into a smaller pipe, thus supplying water to the upstairs. How do I go about figuring out what weight it is that I need for this to supply ample pressure? Or is this a completely worthless idea, meaning that it would require the weight a school bus?

    My biggest problems is that all I read about Pascal's Law is the exact opposite of what I want and the formulas never seem quite right... probably because all of science exists in metric, and I learned SAE. Again, not looking for a solution to the problem, but need the way to figure it out.

    Thank you,
  2. jcsd
  3. Mar 10, 2012 #2


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    Homework Helper

    For Pascal's Law, the pressure is transmitted equally throughout a liquid. Take the case here:


    Pressure at 1 = Pressure at 2

    i.e. P1= P2 but you know that P = F/A

    i.e. F1/A1= F2/A2

    Based on your piping you will have the values for A1 and A2. F2 would be the weight of what you want to lift. F1 would be how much force you would need to apply.

    You can simplify the formula to make F1 the subject to get the required force.

    EDIT: I am also not sure if what you are asking is called "Pascal's Law" though.
    Last edited: Mar 10, 2012
  4. Mar 10, 2012 #3
    I need F2 to be @80 psi out of .5" pipe. What formula would I use to figure out how much weight its required for F1? Am I missing a step or am I just dense? LOL
  5. Mar 10, 2012 #4


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    If you have P2 = 80 psi, then you would need to know the inlet pipe size (to get A1).

    Then just F1 = 80A1 which give F1 in lbs.
  6. Mar 10, 2012 #5
    A1=452.16sq" • 80psi = 36,172.8lbs

    Is that right? Seems a little excessive.
  7. Mar 10, 2012 #6
    Your calculation is correct.. You would need 36,173 lbs on a 452 square inch plate to pressurize the fluid to 80 PSI. The reason it seems excessive is you're using Pascal's Law backwards. Usually you use a small force on a small surface area to lift a heavier weight on a large surface area.
  8. Mar 10, 2012 #7
    Looks like I will have to abandon that idea. I really hoped it was going to work. Don't suppose anyone has a better idea to do this without using energy (electricity,etc)?
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