Hydraulics | Definition, History, Principles + Video

What Is Hydraulic

What is Hydraulic?

The word “hydraulic” originally comes from the Greek word “hydraulikos” and it’s formed by “hydor” meaning water and the word “aulos” meaning pipe. Hydraulic is actually a mechanical function that acts through the force caused by fluid pressure. In hydraulic-based systems, power is usually generated through the mechanical movement of movable pistons in hydraulic cylinders containing liquid or pumped fluid. Due to the property of causing rust and corrosiveness of water on metal materials, it is not used as a fluid in the hydraulic system, and oil is usually used instead of water.

Hydraulic System

In the past, open loop circuit hydraulic systems were widely used, for example, the hydraulic system used in Shushtar city in Iran, is an example of it. Below you can see a picture of this hydraulic system in Shushtar.

Historical Hydraulic System in Shushtar

How did hydraulic create?

It is not possible to make a precise statement about who invented hydraulics, when inventing it, and how it was invented. Nevertheless, the use of hydraulic-based systems can be attributed to the 1st century AD. Blaise Pascal, a French physicist, mathematician, inventor, and philosopher who lived between 1623 and 1662, made significant achievements in the fields of hydrostatics and hydrodynamics. He invented the first hydraulic press, which used hydraulic pressure to multiply forces.

Historical Press Machine

Pascal's Press Machine

In addition, he stated Pascal’s law or Pascal’s principle of hydrostatics.

Pascal’s law

Blaise Pascal

Pascal’s law (Pascal’s principle) is a principle in fluid mechanics and states that in the state of equilibrium, an incompressible fluid in a closed environment transfers the pressure exerted on itself to all other points of the fluid without change (reduction).

Pascal’s Mathematics Relation

Pascal's Mathematics Relation

Where P is the pressure in Pascal

F, force on the surface in Newton

A, is the cross-sectional area in square meters.

Application of Pascal’s law:

To better understand the application of Pascal’s principle in hydraulic systems, consider the figure below, which shows a closed-loop system. Two pistons with different cross sections but at the same height are placed relative to each other (equilibrium state).

Application of Pascal's law

In the figure above, we denote the cross-section of the left piston by A1 and the force applied to it by F1, the cross-section of the right piston by A2, and the force applied to it by F2. If we put the left piston under the force F1, this force causes the piston to move downwards and naturally, the fluid under the piston also moves and causes the force F2 to be applied to the right piston and its upward movement. It is exactly equal to the movement of the left piston. If we consider Pascal’s relationship for each side of the piston as follows. we have:

Application of Pascal's law_1

Since fluids are incompressible, the pressure exerted on the fluid is equal everywhere in the hydraulic system. Therefore, we can make the two sides of the above relationship equal. So we get the following relationship:

Application of Pascal's law_2

As a result, according to the above relationship, to calculate the F2 force, we have:

Application of Pascal's law_3

As can be seen from the above relationship, by applying a smaller force F1 to a smaller area A1, on the left piston, a larger force F2 can be obtained on the right piston side with a larger area A2. This concept is the principle of many existing systems, including hydraulic press machines, press brakes, hydraulic shear machines, hydraulic bending machines, car brake systems, hydraulic jacks, cranes, elevators, etc, which perform tasks such as lifting weights and hitting metal.

In the following, you will see a video of how the hydraulic system works in the hydraulic press machine and car brake system.

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