Hydraulic System

Two principles used in hydraulic system:
  • Liquids are incompressible. 
  • In enclosed system, pressure is transmitted equally throughout the liquid.

Example: hydraulic press

Pressure is same at X and Y as pressure transmitted equally throughout the liquid.
i.e. Px = Py

Fx ⁄Ax = Fy ⁄Ay as P = F⁄A

Since Ax < Ay, Fx < Fy to have same pressure.
A hydraulic press uses this idea to multiply a force, which means that a small effort applied on a small piston can lift a larger load on a bigger piston.

Assume there is no friction, by principle of conservation of energy,

Work done by small force Fx = work done by larger force Fy
               Fx X dx = Fy X dy as work done = F X d

Since Fx < Fy, dx > dy to have a same work done.

Distance moved by small piston is longer than the distance moved by bigger piston.
Note:
  • Liquid used in the hydraulic system is usually oil.
  • When there is air bubble in the oil, work is done to compress the air. Pressure transmitted to large piston is smaller, resulting in smaller force to lift the load.
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