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Homework Help: Hydraulic Pump Closing a Floodgate

  1. Jun 13, 2012 #1
    1. The problem statement, all variables and given/known data
    -4" hydraulic cylinder/piston
    -closing a floodgate 4" in diameter, must exert force F=30,000lb to do so.
    -Piston stroke is 2'.
    -Hydraulic fluid specific gravity of 0.9.
    -Pump efficiency of 0.8

    Find A) the pressure on the floodgate and B) the horsepower of the pump.

    2. Relevant equations
    Pressure = Force/Area

    3. The attempt at a solution
    A) was trivial; the area of the gate is 4"=0.33ft, so Pi*r^2=0.087ft^2.
    30,000lb/0.087sqft = 343,774 lb/sqft, or equivalent 2287 psi.

    B) is baffling me, though, because the RPM of the pump is not given, and every equation I'm aware of for calculating horsepower requires the speed of the pump.
  2. jcsd
  3. Jun 13, 2012 #2
    I assume that the cylinder is stroking in the direction to extend the rod. If not, then your area is smaller.

    If they don't tell you how fast they want the gate closed, then a pump of any power rating will work. Bigger pumps will close it quicker.
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