how does a hydraulic system work in a machine such as a backhoe or a crane?

i need to know how a hydraulic system on a backhoe or a crane or other large construction machines. i need a diagram so i can do a science project.

One Response to “how does a hydraulic system work in a machine such as a backhoe or a crane?”

  1. Austin Semiconductor  on June 29th, 2011

    Hydraulic systems apply force over an area to create a mechanical advantage.
    Imagine a container filled with liquid, with two cylinders ( like in a an engine) of different diameters that can act on the liquid.
    Where one cylinder is very small ( 1 square inch of surface area) but has a long cylinder length ( travel), and the other cylinder is much wider, with greater surface area ( ~ 100 square inch of surface area).
    If a small force is applied on the small cylinder, for example ~ 1 lb, this produces one pound per square inch of force on the liquid with in the cylinder. The larger cylinder experiences a force of 1 pound per square inch over its larger area of 100 square inches, and produces 100 lbs of lifting force.
    If the small cylinder is depressed 100 inches ( it is a long cylinder ; . )
    Then the large cylinder can lift a 100 lb weight 1 inch.
    The small cylinder had to move 100 times the distance with 100 times less force than the larger cylinder, which produces the mechanical advantage. This is similar to a long lever requiring a small force, but lifting a very heavy object a small distance.

    See the photo on the second link p2-7 figure 2-11 for a similar setup.

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