Hydraulic press

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A hydraulic press is a hydraulic mechanism for applying a large lifting or compressive force. It is the hydraulic equivalent of a mechanical lever, and is also known as a Bramah press after the inventor, Joseph Bramah. Hydraulic presses are the most commonly-used and efficient form of modern press.

[edit] How it works

The hydraulic press depends on Pascal's principle: the pressure throughout a closed system is constant. At one end of the system is a piston with a small cross-sectional area driven by a lever to increase the force. Small-diameter tubing leads to the other end of the system; this is a piston of large cross-sectional area. The large piston exerts a force equal to the force exerted on the small piston multiplied by the ratio of the areas of the heads of the pistons.

\frac{F_1}{A_1}= \frac{F_2}{A_2}

A fluid, such as oil, is displaced when either piston is pushed inward. The small piston displaces a smaller amount of volume, which is proportional to the ratio of areas of the heads of the pistons. Therefore, the small piston must be moved a large distance to get the large piston to move significantly. The distance the large piston will move is the distance that the small piston is moved divided by the ratio of the areas of the heads of the pistons.

For example, if the ratio of the areas is 5, a force of 100 newtons on the small piston will produce a force of 500 newtons on the large piston, and the small piston must be pushed 50 cm to get the large piston to rise 10 cm. This is how energy, in the form of work in this case, is conserved. Work is force times distance, and since the force is increased on the larger piston, the distance the force is applied over must be decreased. The work of the small piston, 100 newtons multiplied by 0.5 meter (50 cm) is 50 joules (J}, which is the same as the work of the large piston, 500 newtons multiplied by 0.1 meter (10 cm).

[edit] Applications

Hydraulic presses are capable of pressure at the head of 2,000 tons, and are used in manufacturing processes such as cold-forming metal and the production of complex shapes in the brick and concrete industry. They are also used in a wide variety of application where a large compressive force is needed, or a large load (such as an elevator in a building) must be raised.

Although not all jacks are hydraulic, hydraulic jacks, which are used to lift automobiles so that they can be repaired, are a common application of the hydraulic press. The small piston is moved using electrical power, or human power in the case of small jacks, while the vehicle is lifted by the large piston. Garbage trucks use hydraulic presses to compact waste, and earth-moving machines, such as bulldozers, use hydraulics to push and lift soil and rocks.

[edit] Trivia

  • The hydraulic press is capable of applying enough pressure to crush solid aluminum into paper-thin pieces.
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