Hydraulic System – Introduction 

 Hydraulic systems are power-transmitting assemblies employing pressurized liquid as a fluid for transmitting energy from an energy-generating source to an energy-using point to accomplish useful work. The figure shows a simple circuit of a hydraulic system with basic components. Hydraulic systems are used for transmission of power through the medium of hydraulic oil. The hydraulic system works on the principle of Pascal’s law which says that “ the pressure in a fluid at rest is transmitted uniformly in all directions”.
The fluid medium used is hydraulic oil, which may be mineral oil or water or combinations. This area is also known as oil hydraulics. 

components of hydraulic system
components of hydraulic system

For explanation watch video.

Functions of the components

1. The hydraulic actuator

2. The hydraulic  Pump 

Importance of Pump : 

1. They convert mechanical energy into hydraulic energy.
2. The Volumetric efficiency of the pump is relatively high
3.They have high-performance characteristics under varying speed and pressure requirements
4.Pumps used to generate high pressure in the hydraulic system.

3. Valves

Different types of valves and their functions :

  1. Pressure relief valves – Relief valve opens and bypasses fluid when pressure exceeds its setting. These are used mostly in all circuits.

  2. Pressure-Reducing Valve – This type of valve (which is normally open) is used to maintain reduced pressures in specified locations of hydraulic systems.

  3. Unloading Valves – high-low pump circuits where two pumps move an actuator at a high speed and low pressure, punching press.

  4. Counterbalance valves – They are used to prevent a load from accelerating uncontrollably. This situation can occur in vertical cylinders in which the load is a weight. This can damage the load or even the cylinder itself when the load is stopped quickly at the end of the travel.

4. External power supply (motor) is required to drive the pump. 

5. Oil Tank or Reservoir:

6.Pipelines : 

7. Filters

8. Pressure regulator

9. Accumulators

10. Hydraulic Power Pack : 

Diagram of hydraulic power packDiagram of hydraulic power pack

Working of Hydraulic Power Pack : 

Cylinder movement is controlled by a three-position change over a control valve.

1. When the piston of the valve is changed to the upper position, the pipe pressure line is connected to port A and thus the load is raised.
2. When the position of the valve is changed to a lower position, the pipe pressure line is connected to port B and thus the load is lowered.
3. When the valve is at the center position, it locks the fluid into the cylinder(thereby holding it in position) and dead-ends the fluid line (causing all the pump output fluid to return to tank via the pressure relief). 

Some questions related to hydraulic circuit : 

Draw a sketch of a simple oil hydraulic circuit and write down the name and working function of each of the components used in it.

Basic Hydraulic Circuit Diagram : 

basic hydraulic circuit diagrambasic hydraulic circuit diagram

a) Oil Tank or Reservoir: This is an oil storage tank in which hydraulic oil is stored. The oil passes through various pipelines and after doing useful work in actuator; the oil returns back to the oil tank. In the regions of low temperature, oil heaters are attached to air tanks.
b) Filter: This element filters the oil before going to the next element i.e. pump.
c) Pump: Hydraulic pump is the heart of any hydraulic system. Its main function is to create the flow of oil under pressure through the entire hydraulic system and hence to assist the transfer of power and motion (i.e. useful work).
d) Direction control valves/Flow control valves/ Pressure Relief Valves (Fluid Controlling Elements): These valves are fitted in hydraulic system at particular locations. These valves control the flow of oil in the system. They also direct the flow of oil in the system as also they control the speed of the actuator.
e) Actuators: (Fluid Power utilization elements): These elements are known as actuators (either rotary or linear). The pressurized oil acts on actuator elements. The oil gives or transfers its power to the actuator to create useful work or Mechanical Advantage.
f) Pipelines (Fluid Conducting elements): It is the functional connection for oil flow in the hydraulic system. The efficiency of oil flow is greatly influenced by the physical characteristics of piping systems.

There are two pipes:
a) Pipe which carries pressurized oil is called as pressure pipelines
b) Pipes that carry low pressurized oil or used oil (are called as return pipelines). Hoses, pipes, pipe fitting are the parts of the fluid power pipeline.