What is Hydraulic | Definition, Principle, Properties, Advantages


Hydraulic is the transmission and control of forces and motions through the medium of fluids. Oil hydraulic system operate on the principle of  ‘Pascal Law’ and Pascal law says that –

”  The pressure in a static hydraulic fluid in a closed system is same everywhere.”

Below fig. shows the use of Pascal’s law, which is useful for practical application of hydraulic system.

The Pascal’s  law is very useful in designing of equipment’s and machines involved in hydraulic system. It is used in

  • Hydraulic jack
  • Hydraulic lift
  • Crane

Hydraulic or fluid power system has wide spread applications in industry like

  • Mechanical engineering
  • Aircraft manufacturing
  • Earthmoving equipment’s
  • Agricultural equipment’s

Hydraulics refers to the science and technology of using fluids, typically liquids, to generate, control, and transmit power. It involves the use of pressurized fluid, usually oil or water, to perform various mechanical tasks.

In hydraulic systems, a fluid is used to transmit force or motion from one point to another. The basic components of a hydraulic system include:

Hydraulic fluid: Typically, hydraulic oil is used as the working fluid in hydraulic systems. It is selected for its lubricating properties, resistance to degradation, and ability to handle high pressures.

Hydraulic pump: The hydraulic pump is responsible for generating flow and pressurizing the hydraulic fluid. It converts mechanical power, such as an electric motor or an engine’s rotational motion, into hydraulic power.

Hydraulic cylinder: Hydraulic cylinders, also known as actuators, are devices that convert hydraulic pressure into linear mechanical force. They consist of a cylindrical barrel, a piston, and a rod. When pressurized fluid enters the cylinder, it pushes or pulls the piston, resulting in linear motion.

Control valves: Control valves are used to regulate the flow and pressure of hydraulic fluid in the system. They direct the fluid to specific actuators or control the speed and direction of movement.

Hydraulic lines: Hydraulic lines or hoses carry the pressurized fluid from the pump to the actuators and back to the reservoir. They need to be designed and maintained to withstand high pressure and ensure leak-free operation.

Hydraulic reservoir: The hydraulic reservoir stores the hydraulic fluid and helps dissipate heat generated during operation. It also serves as a filter for contaminants in the fluid.

Type of Fluid Power System

Fluid power system is highly versatile power transmission system which utilizes energy of fluid to perform the task.

  • Oil Hydraulic System

When pressurised oil is used as a working medium to perform the task, it is known as hydraulic system.

  • Pneumatic System

When compressed air is used as a working medium to perform the task, it is known as pneumatic system.

Why are hydraulic systems used?

The main reason for using hydraulics is the high power density and secondly the simplicity coming from using few components to realize complex and fast moving machines with a high degree of safety.

Hydraulic system at main drive?

hydraulic system

It is a transmission technology in which a fluid is used to move energy from pump to hydraulic cylinder. The fluid is incompressible and the fluid path can be flexible in the same way as an electrical cable.

Where it is used for?

They are mainly used when high power density is needed. This is especially the case in all types of mobile equipment such as excavators and in industrial systems such as presses.
It is used in hydraulic jack, crane, lift etc. Hydraulic system has wide spread applications throughout industry for e.g. mechanical engineering, aircraft manufacturing, ship building.

Important properties

The primary function of a hydraulic fluid is to convey power to the desired point of application. The efficient running of hydraulic system depends upon using the correct fluid and keeping the fluid in good condition.

1. Compressibility :- Liquids are incompressible in nature hence they are suitable for precise motion control. Hydraulic oil should have low compressibility for better performance.

2. Viscosity :- Oil with low viscosity flows easily but thick oil flows with some difficulty and results in pressure loss in the pipes and fittings.
3. Corrosion resistance :- The oil should have high corrosion resistance to eliminate the problems related to corrosion.
4. Pour point :- It is important during low temperature applications in cold climates. The oil should have low pour point temperature.
5. Demulsibility :- It means water separation, water that enters a hydraulic system can emulsify and causes collection of dust, grit and dirt and reduces operational efficiency. The resistance of a hydraulic fluid to emulsification or the ability of oil to resist with mixing with water is known as demulsibility.


1. No need of lubrication
2. Smooth working
3. Easy power distribution
4. Accuracy of motion


1. Oil leakages problem
2. High maintenance cost
3. Disposal problem of uses oil
4. Dirty environment

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Hi, I’m Aditya Sharma, a professional blogger from Gurgaon, India and I launched this blog called aadityacademy on July 2021. aadityacademy.com is a mechanical Project-oriented platform run by Aditya sharma and I got the motivation to start aadityacademy blog after seeing less technical education information available on google.

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