INTRODUCTION TO FLUID POWER SYSTEM AND HYDRAULIC FLUIDS

1. Introduction to Hydraulics &
Pneumatics

2. Hydraulic Fluids
They have following primary tasks:
 Power transmission ( pressure and motion transmission)
 Signal transmission for control
Secondary tasks:
• Lubrication of rotating and translating components to
avoid friction and wear
• Heat transport, away from the location of heat generation,
usually into reservoir
• Transport of particles to filter
• Protection of surfaces from chemical attack, especially
corrosion

3. Hydraulic fluids-requirement
Functional
 Good lubrication characteristic
 Viscosity should not depend on temperature and
pressure
 Good heat conductivity
 Low heat expansion coefficient
 Large elasticity modulus
Economic
 Low price
 Slow aging and thermal and chemical stability with
long life cycle.

4. Hydraulic fluids- requirement (cont)
Safety
 High flash point
 Chemically neutral
 Low air dissolving capacity, not inclined to foam
formation
Environment Friendliness
 No environment harm
 To toxic effect

5. Hydraulic fluid types
Broadly classified into three categories based on
major constituents:
Petroleum Based Fluids
Synthetic Based Fluids
Water Based Fluids

6. Petroleum Based Fluids
• Most commonly used fluids
• Additives are added, to avoid oxidation and
reduce foaming and to improve viscosity
Additives:-
o Decrease corrosion
o Increase life duration
o Improve temperature dependence of viscosity
o Improve particle transport

7. Petroleum Based Fluids
Advantages:
• Protection against rust
• Better sealing property
• Better heat dissipating effects
• Low density and light weight
Disadvantages:
• High cost
• Low flash point
• Highly inflammable

8. Synthetic Based Fluids
• Do not contain water or volatile material
• Chemical stability is very good and they can be used for
very high temperature and pressure applications.
• Laboratory prepared fluids
Commonly used fluids:-
Phosphate esters, Halogenated hydrocarbons, silicon
synthetic fluids.

9. Synthetic Based Fluids
Advantages:
 Less inflammable compared to petroleum based oils
 Can operate at higher temperatures (1500 C)
 Useful in high pressure system
Disadvantages:
 Performance is poor at low temperatures, hence
external heating has to be done.
 Viscosity index is low.
 Specific gravity is high, requiring high pumping power.

10. Water Based Fluids
• Clear Water
• Water with additives
• Used when there is an explosion or fire danger
or hygiene problem: Food and Pharmaceutical
industry, textile industry, mining.

11. Water Based Fluids
Advantages:
 Low viscosity and it does not change very much
over a large temperature range.
 Abundantly available and cheap
 Highly non-inflammable and cannot catch fire.
 Very good chemical stability over a wide range of
temperature
 Not slippery when leaked

12. Water Based Fluids
Disadvantages:
 Operating temperature range is limited
 Highly corrosive
 Low lubricating properties
 Water in its pure form can never give the
necessary benefit. The advantages can be
employed by making High Water Based Fluids
(HWBF)

13. HWBF
• HWBF is basically water with addition of certain
additives.
• Water (90-95 %) + Additives (5-10 %)
• The development of HWBF is Soluble oil cutting
fluids, High water content oils, Micro Emulsions,
Thickened Micro emulsions.

14. HWBF
Advantages:
 High flash point
 Good cooling
characteristic
 Biodegradable
 Viscosity remains
constant
Disadvantages
 High density.
 Very high corrosion
 Foaming tendencies are
high
 High rate of leakage due
to low viscosity

15. Properties of Hydraulic Fluids
1. Viscosity:
 Viscosity is affected by changes in temperature and
pressure
 For a hydraulic fluid, viscosity must be high but not
high enough to offer too much resistance to flow.
 Leakage loss is more with thinner liquid. Too viscous
liquid causes the system to become more sluggish and
lead to power consumption.

16. Properties
2. Viscosity Index (VI)
 It is a number used to indicate the effect of
temperature on the changes in the viscosity.
 A low viscosity index is not good – it indicates
large change over given temperature range
which means oil is thin at high temperature
and thick at low temperature.

17. Properties
3. Lubricating Power (Lubricity)
 When pressure forces the liquid of hydrodynamic
system between the surface of moving parts, liquid
spreads out in to a thin film which enables their
motion freely.
 The capability of a liquid to resist being wiped or
squeezed out of surface is lubricity.

18. Properties
4. Chemical Stability
• It represent the liquid ability to resist oxidation and its
deterioration for long period of time
• The chemical reaction result into formation of sludge,
gums, carbon or other deposits. It clogs openings and
cause valves and piston to stick or leak and cause
poor lubrication.

19. Properties
5. Flash Point:
High flash point is always desirable as it gives
resistance to combustion.
6. Fire Point:
It is a temperature at which liquid gives off
sufficient vapours to ignite and continue to burn
when exposed to spark or flame.