The four-stroke engine P.28
See also
• Rust and oxidation protection properties;
• Low flash point (the lowest temperature, at
which the oil vapors are ignitable);
• Resistance to cavitation;
• Low foaming;
• Compatibility with sealant materials.
Hydraulic systems are widely used in industrial machinery, construction equipment,
automotive, aircraft and marine applications.
Critical areas of lubrication in a hydraulic
system
Types of hydraulic fluids
Optimal properties of hydraulic oils are
achieved by a combination of a base oil and
additives (Anti-wear additives, detergents,
anti-oxidants, anti-foaming agents, corrosion
inhibitors, etc.).
Critical areas of lubrication in a hydraulic system
Component
Concern
Gear pump
Enmeshed gears
Vane pump
Vanes sliding against the ring
Piston pump
Pistons and shoes run against the cylinder
Valves
Valves can stick
Actuator
Low speed, high loads and corrosion
Filter
Filter blockages
Reservoir
Low temperature operation,
oil conditioning and corrosion
Piping and sealing
Leakages and corrosion
Property of Oil
Viscosity, Anti-wear
(if required), oil condition
Viscosity, Anti-wear,
oil cleanliness
Viscosity, Anti-wear, Metal
compatibility, Oxidation
and hydrolytic stability
Cleanliness, Demulsibility,
thermal stability
Viscosity, Anti-wear
and Anti-rust
Demulsibility, Filterability
Air release, low foaming,
Demulsibility, Anti-rust and
paint compatibility
Compatibility
a) Mineral hydraulic oil
(petroleum base)
Mineral based oils are the most common
and low cost hydraulic fluids. They possess
most of the characteristics important for
hydraulic oils. The disadvantages of mineral (petroleum) based oils are their low fire
resistance (low flash point), toxicity and very
low biodegradability. Petroleum-based oils
contain most of the desired properties of a
hydraulic liquid.
However, they are flammable under
normal conditions and can become explosive when subjected to high pressures and a
source of flame or high temperatures.
Nonflammable synthetic liquids have been
developed for use in hydraulic systems where
fire hazards exist.
b) Phosphate ester based synthetic
hydraulic fluids
Phosphate esters are produced by the reaction
of phosphoric acid with aromatic alcohols.
Phosphate esters based hydraulic fluids possess excellent fire resistance. However, they
are not compatible with paints, adhesives,
some polymers and sealant materials. They
are also toxic.
These fluids will burn if sufficient heat
and flame are applied, but they do not support combustion.
Drawbacks of phosphate ester fluids are
that they will attack and loosen commonly
used paints and adhesives, deteriorate many
types of insulations used in electrical cables,
and deteriorate many gasket and seal materials. Therefore, gaskets and seals for systems
January-March 2012 | Lubezine Magazine
23