Hydraulic Systems

Car lift

hydralic lift

One simple application is shown in the diagram above, the lifting of a car. If there is a relatively small force $F_{1}$, pushing down on piston $A_{1}$, the pressure on the fluid is $p_{1} = \frac{F_{1}}{A_{1}}$.

The pressure is transmitted via the incompressible fluid to the other piston $A_{2}$: $$\begin{aligned} p_{1} &= p_{2} \\ \frac{F_{1}}{A_{1}} &= \frac{F_{2}}{A_{2}} \\ F_{1} &= \frac{A_{1}}{A_{2}} F_{2} \end{aligned}$$

If the area $A_{2}$ is made much larger than that of $A_{1}$, the force $F_{1}$ is now ‘multiplied’ many folds. This force, $F_{2}$ can be used to lift very heavy objects such as cars.

Hydraulic Press

In the hydraulic press, a small force applied to a small piston in a small cylinder is transmitted through a tube to a large cylinder, where it presses equally against all sides of the cylinder, including the large piston, which, in turn, produces a large compressive force upon a stationary anvil or base-plate. A pump is used to force the liquid into the cylinder.

The hydraulic press is widely used in industry for forming metals and for other tasks where a large force is required. It is manufactured in a wide variety of styles and sizes and in capacities ranging from 10 kN or less to 100 kN or more.

Hydraulic Brakes

Most brakes act on the rotating mechanical elements and absorb kinetic energy either mechanically, hydraulically, or electrically.

Mechanical hydraulic brakes are the most common, like those found in cars. They dissipate kinetic energy in the form of heat generated by the mechanical friction between a rotating metallic drum or disk and a stationary friction element brought into contact with it by hydraulic or pneumatic means.

When the driver depresses the brake pedal, the pedal exerts a pressure on the liquid. This pressure is transmitted via the liquid evenly to the 4 larger pistons at the wheels. The pressure makes the pistons compress the brake discs onto the running wheels. If the ratio of its areas is 10 times, the force exerted at the wheels would be 10 times.

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