Working principle of hydraulic system

Working principle of hydraulic system

The working principle of hydraulic system is based on pascal's law. This law states that the pressure applied to an enclosed fluid is transmitted equally in all direc­tions. Small force acting on small area can produce higher force on a surface of larger area


The hydraulic pump draws up oil from the oil reservoir and sends it to the control valve under high pressure. From the control valve, the oil goes to the hydraulic cylinder to operate the piston, which in turn, raises the lifting arms. The lifting arms are attached with implements. The hydraulic pump is operated by suitable gears, connected with engine.
There are two types of arrangements for storing hydraulic oil in the system
  • There is a common oil reservoir for hydraulic system and the transmission system in some tractors,
  • There is a special tank for hydra­ulic oil. It is separate from the transmission chamber.

Basic Components Of Hydraulic System

  • Hydraulic pump
  • Hydraulic cylinder and piston
  • Hydraulic tank
  • Control valve
  • Safety valve
  • Hose pipe and fittings and
  • Lifting arms.

Hydraulic pump

There are several types of hydraulic pump, such as gear pump, plunger pump, vane pump, and screw pump. Gear pump is widely used in tractors. Gear pump can flow a bigger amount of oil, compared to plunger pump. The oil pressure in the pump varies from 150 to 200 kg/cm2.Schema

Hydraulic cylinder

It is a bigger size cylinder, fitted with a piston and a connecting rod. It is also called ram cylinder. The connecting rod transmits power from the piston to the lifting arms. Piston moves in the hydraulic cylinder and causes reciprocating motion in the cylinder. The lifting arms are raised by the hydraulic pressure while raising the implement but it is lowered by its own weight.

Hydraulic tank

Hydraulic tank is used for storing hydraulic oil for the system. In some tractors, transmission chamber itself works as a hydraulic tank and same oil is used for transmission system as well as hydraulic system. In some tractors, separate tank is there for hydraulic oil.

Control valve

Control valve is a type of valve, which controls the movement of hydraulic oil to have desired direction, magnitude and speed of lifting. Thus the control valve is to perform three functions
  • To change the direction of lifting
  • To change the power of lifting and
  • To change the speed of lifting.

Oil filter

It is small filter, located at a convenient position in the passage of the oil.