Hydraulic fluid is the medium for power transmission in a hydraulic system.The life and performance of the hydraulic components depends on the kind of hydraulic fluid used in the system.The selection of hydraulic fluid is very important in any hydraulic system design.The main purpose of hydraulic fluid in the hydraulic system is transmission of power but along with that it serves many purpose like lubrication,sealing and heat transfer medium.
PURPOSE OF HYDRAULIC FLUID
POWER TRANSMISSION :- As hydraulic fluids are slightly compressible,whenever force is applied the response to the force is instantaneous.For easy transmission fluid must flow easily through the passage.Too much resistance to the flow creates the power loss.
LUBRICATION :- Lubrication to the internal components is provided by the hydraulic fluid.So anti wear additives are added to hydraulic fluids which increases the service life of the components.
SEALING :- Fluid acts as the sealing agent in the high pressure components like pump cylinder etc. because it has a viscous characteristics which creates a film in the leakage area.But high viscosity of the fluid is not recommended.close mechanical fit and viscosity of fluid determines the leakage rate.
COOLING :- Fluid helps in heat transfer as it flows heat through it .
CLEANING :- Hydraulic fluid helps in cleaning the system by flowing the dust and dirt or the system created particles outside the system.When these particles flow in the system either they settle at the bottom of the reservoir by gravity or they get cleaned through the return line filter.
CHARACTERISTICS OF HYDRAULIC FLUIDS
The demands placed on hydraulic systems change as industry requires greater efficiency and speed at higher operating temperatures and pressures.
Selecting the best Hydraulic fluid requires a basic understanding of each particular fluid's characteristics in comparison with an ideal fluid.
An ideal Hydraulic fluid would have these characteristics.
The table below lists
the major functions of a hydraulic fluid and the properties of a fluid
that affect its ability to perform that function
VISCOSITY :-
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity).
TOO HIGH VISCOSITY INCREASES FRICTION RESULTING IN:-
TOO LOW VISCOSITY RESULTS IN :-
PURPOSE OF HYDRAULIC FLUID
POWER TRANSMISSION :- As hydraulic fluids are slightly compressible,whenever force is applied the response to the force is instantaneous.For easy transmission fluid must flow easily through the passage.Too much resistance to the flow creates the power loss.
LUBRICATION :- Lubrication to the internal components is provided by the hydraulic fluid.So anti wear additives are added to hydraulic fluids which increases the service life of the components.
SEALING :- Fluid acts as the sealing agent in the high pressure components like pump cylinder etc. because it has a viscous characteristics which creates a film in the leakage area.But high viscosity of the fluid is not recommended.close mechanical fit and viscosity of fluid determines the leakage rate.
COOLING :- Fluid helps in heat transfer as it flows heat through it .
CLEANING :- Hydraulic fluid helps in cleaning the system by flowing the dust and dirt or the system created particles outside the system.When these particles flow in the system either they settle at the bottom of the reservoir by gravity or they get cleaned through the return line filter.
CHARACTERISTICS OF HYDRAULIC FLUIDS
The demands placed on hydraulic systems change as industry requires greater efficiency and speed at higher operating temperatures and pressures.
Selecting the best Hydraulic fluid requires a basic understanding of each particular fluid's characteristics in comparison with an ideal fluid.
An ideal Hydraulic fluid would have these characteristics.
1.Thermal stability.
2.Hydrological stability.
3.Low chemical corrosiveness.
4.High anti wear characteristics.
5.Low tendency to cavitation.
6.Long life
7.Total water rejection
8.Constant viscosity regardless temperature.
9.low cost.
Although no single fluid has all the characteristics but the selection requires the knowledge of the system in which it will be used.
like.
1. Maximum and minimum operating and ambient temperature.
2. Type of pump used.
3. Operating pressure
4. Operating cycles
5. Loads encountered by various components
6. Types of control and power valves.
| Function | Property |
|---|---|
| Medium for power transfer and control |
|
| Medium for heat transfer |
|
| Sealing Medium |
|
| Lubricant |
|
| Pump efficiency |
|
| Special function |
|
| Environmental impact |
|
| Functioning life |
|
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity).
VISCOSITY IS A COMPROMISE FOR A HYDRAULIC FLUID AS HIGHER VISCOSITY CAUSES THE RESISTANCE TO FLOW AND LOWER VISCOSITY CAUSES THE WEAR AND TEAR TO THE COMPONENTS.
TOO HIGH VISCOSITY INCREASES FRICTION RESULTING IN:-
1.HIGH RESISTANCE TO FLOW.
2.INCREASED POWER CONSUMPTION DUE TO FRICTIONAL LOSS.
3.HIGHER TEMPERATURE CAUSED BY FRICTION
4.HIGHER PRESSURE DROP DUE TO RESISTANCE.
5.SLOW OPERATION.
6.DIFFICULTY IN SEPARATING AIR FROM OIL IN RESERVOIR.
1.INTERNAL LEAKAGE
2.EXCESSIVE WEAR OF INTERNAL COMPONENTS DUE TO BREAKING OF FLUID FILM BETWEEN THE MATING PARTS.
3.PUMP EFFICIENCY MAY DECREASE DUE TO SLOW OPERATION OF ACTUATOR.
4.LEAKAGE LOSSES MAY INCREASE THE TEMPERATURE.
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