The industry contributes innovations to improve its processes. One of the great improvements was the application of Hydraulics and Pneumatics . In the previous link you can see the definition of pneumatics, but in this case we will talk about hydraulics .

What is Hydraulics?

Hydraulics is the technology that uses a liquid or fluid , either water or oil (usually special oils), as a way of transmitting the energy necessary to move and operate mechanisms .

Basically it consists of increasing the pressure of this fluid by means of elements of the hydraulic circuit, for example with a compressor, to use it as a useful job, normally in an outlet element called a cylinder.

Hydraulics is related to fluid mechanics , which is largely the one that provides its theoretical foundation. In the end we will see some of these foundations and their history, such as Pascal’s Principle that establishes the increase in pressure in fluids, which we discussed earlier.


– What is Hydraulics .
– Hydraulic Force .
– Hydraulic Mechanisms .
– Theoretical Foundations and Hydraulic History .

Hydraulic Force

Hydraulic force is the force exerted by a hydraulic cylinder when pressed by the liquid in the circuit . This force will be the one capable of lifting a weight, opening a door, etc. Let’s see how it is calculated:

Hydraulic Mechanisms

The cylinders only have forward and reverse travel in rectilinear movement, that is why if we want another movement, for example a circular movement, we must attach to the cylinder a mechanism that makes the change of movement.

In a hydraulic system, the oil replaces the compressed air used in pneumatics. Many excavators, garbage truck, cars, etc. They use hydraulic systems to move mechanisms that are attached to an oil-driven hydraulic cylinder.

When it is called hydraulic, it can be thought that it only uses water, which is not true, it is almost never used water, oil is often used more frequently. In theory if oil is used it should be called Oleo hydraulic, but it’s not like that. In practice when we talk about systems by oil, water or any liquid fluid we use the word hydraulic. In the following image you can see a hydraulic cylinder:

If we compare a pneumatic system with a hydraulic one, we can see the following:

– When operating with oil, it admits much more pressure, with which more hydraulic force can also be applied . Therefore when we need a system with a lot of force we will use the hydraulic system and not the tire .

– It is easier to regulate the forward or reverse speed of the cylinders, you can even stop the hydraulic cylinder.

– In hydraulic systems the oil is in a closed circuit.

– One of the most important things about Hydraulics is that it is self-lubricating. The oil it uses is already its own lubrication mechanisms .

– To finish we will say that these systems have the disadvantages that they are dirtier than tires, oil is flammable and explosive, that circuit elements are more expensive than tires, oil is more sensitive to changes in temperature than the air, and that the oil must be changed from time to time with the consequent added expense.

Here we can see the basic parts of a hydraulic circuit , although if you want to know more we recommend that you learn in Pneumatics(click on the underlined link) and you will learn pneumatics easily. The hydraulics are exactly the same, only the fluid that goes inside the elements changes.

Theoretical Foundations and History of Hydraulics

Harnessing the power of moving fluid is nothing new. It has been a powerful source of energy for thousands of years, to this day, and an integral part in the advancement of humanity. Originally, water was used to spin the wheels and push the levers.

Liquids in motion or under pressure did useful work for man for many centuries before the French scientist and philosopher Blaise Pascal and the Swiss physicist Daniel Bernoulliformulate the laws on which modern hydraulic energy technology is based.

Pascal’s Law or Principle , formulated around 1650, establishes that the pressure in a liquid is transmitted equally in all directions; That is, when water is manufactured to fill a closed container, the application of pressure at any point will be transmitted to all sides of the container. In the hydraulic press, Pascal’s Law is used to gain an increase in strength; A small force applied to a small piston in a small cylinder is transmitted through a tube to a large cylinder, where it equally presses against all sides of the cylinder, including the large piston. To know more: Pascal’s Principle .

Bernoulli’s law, formulated about a century later, states that the energy in a fluid is due to elevation, motion, and pressure, and if there are no losses due to friction and work not done, the sum of the energies remains constant. Therefore, velocity energy, derived from motion, can be partially converted to pressure energy by expanding the cross section of a tube, which decreases the velocity of flow but increases the area against which the fluid is pressing.

Until the 19th century it was not possible to develop speeds and pressures much higher than those provided by nature, but the invention of pumps offered great potential for the application of the discoveries of Pascal and Bernoulli.

In 1882, the City of London built a hydraulic system that supplied pressurized water through street pipes to power machinery in factories.

In 1906 an important advance was made in hydraulic techniques when an hydraulic oil system was installed to raise and control hydraulic pistols .

In the 1920s, they developed autonomous hydraulic units consisting of a pump, control units and an engine, paving the way for applications in machine tools, automobiles, agricultural machinery and earth moving, locomotives, ships, aircraft and ships space.

Hydraulics has become one of the main energy transmission technologies used by all phases of industrial, agricultural and defense activity. Modern airplanes and aircraft, for example, use hydraulic systems to activate their controls and to operate landing gears and brakes. Virtually all missiles, as well as their ground support equipment, use hydraulic power. Automobiles use hydraulic power systems in their transmissions, brakes, and steering mechanisms.

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